Masters Degrees (Soil, Crop and Climate Sciences)

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Open Access
Correlation between argronomic and environmental phoshorus analyses of selected soils
(University of the Free State, 2012-06) Nthejane, 'Mabatho Margaret; Du Preez, C. C.; Van Huyssteen, C. W.
English: In crop production phosphorus (P) is an essential nutrient for crop growth, and hence P fertilization is necessary to achieve optimum yields. However, this can induces in soil a P concentration which may contributes to eutrophication of fresh water bodies. Soil P tests are therefore considered very useful in setting threshold values important for both agronomic and environmental management purposes. Soil P tests developed from a water pollution protection point unlike agronomic P tests are not easily adapted for use on a routine basis because they are not considered, for this purpose, and this could make agronomic P tests more practical for routine environmental P assessment also. Determination of appropriate agronomic P tests for this purpose however, involves evaluating the potential use of the tests for environmental purposes. Hence, the objective of this study was to review the current methods used to determine the agronomic and environmental P status of soils, and to establish whether P extracted from a range of soils by various agronomic and/or environmental P determination methods are related or not. Soil samples from the orthic A horison were collected in three cropping areas in the Free State province, namely Jacobsdal, Bloemfontein, and Ficksburg. These samples were treated with K2HPO4 to induce different phosphorus concentration levels and then incubated at room temperature for three months. During incubation the samples were subjected to several wetting and drying cycles to ensure that the applied phosphorus equilibrated. The samples were then analysed for P using the extractants of Olsen, Bray 1, Truog, ISFEI and citric acid commonly employed for routine analysis to establish the agronomic P status of soils. In order to establish the environmental P status of the soils, the samples were analysed for using the extractants calcium chloride (CaCl2) and ammonium oxalate [(NH4)2C2O4.H2O]. The latter was used to calculate the degree of phosphorus saturation (DPSox). The results showed significant relationships among agronomic P tests when data of individual soils were analysed separately (r2=0.65-0.99) and, when data of all soils from a sampling area were pooled (r2=0.52-0.87). All the relationships were significant for the Ficksburg soils (r2≥0.55) and for the Bloemfontein soils (r2≥0.82) but not for the Jacobsdal soils. For the latter soils the Truog-P correlations with Olsen-P (r2=0.44), Bray 1-P (r2=0.42) and ISFEI-P (r2=0.35) were not significant, probably due to that they are calcareous. Significant relationships were also obtained for P extracted by the environmental P tests when regression analysis was done for each individual soil (r2≥0.80). However, when data of soils from a sampling area were pooled significant relationships were obtained for Bloemfontein soils (r2=0.92) and Ficksburg soils (r2=0.56) while Jacbosdal soils (r2=0.33) showed an insignificant relationship. Pooling data of all soils from the three sampling areas also resulted with a lower correlation coefficient (r2=0.40) implying a poor relationship between the environmental P tests. The correlation between P extracted by the agronomic tests and CaCl2-P showed positive relationships (r2 ≥0.57) except in a few instances. Truog-P and citric acid-P showed a poor correlation with CaCl2-P when the Jacobsdal soils’ data were pooled (r2=0.22 and 0.35 respectively). Pooling of all soils’ data resulted also in a poor correlation between CaCl2-P and Truog –P (r2= 0.28). The DPSox correlated significantly with the extractable P of all agronomic tests when the individual soil’s data were analysed separately (r2 ≥0.73). However, when data of all soils from a sampling areas were pooled for regression analysis, all relationships were significant for the Bloemfontein soils (r2 ≥0.70), but not for the Jacobsdal soils, and Ficksburg soils. Pooling data of all soils from the three sites resulted with a positive relationship between DPSox and the extractable P of all agronomic tests (r2 ≥0.50), except ISFEI (r2 ≥0.45). The threshold values estimated for agronomic tests with regression equations from CaCl2-P DPSox threshold values varied greatly between individual soils and even the soils groups of a sampling area. The threshold values for all soils when based on CaCl2 implied that if the extractable P status of cropped soils are maintained at optimum levels for Bray 1, Truog, ISFEI and citric acid the soils may be a threat to water pollution. The opposite is true with the estimated threshold values when based on DPSox. The results therefore showed that agronomic tests can be used also for environmental management of P although only the Olsen test showed the potential for developing a single threshold value for all soils.
Open Access
Effect of potassium humate on soil properties and growth of wheat
(University of the Free State, 2008) Van Tonder, Johan Tobias; Ceronio, G. M.; Du Preez, C. C.
English: Soil properties (biological and chemical) and crop response are dependent on the inherent soil organic matter content. Since South African soils are naturally low in organic matter content commercial humates serve as attractive soil amendments in improving soil quality. This is the result of commercialisation giving the impression that humates have biological and chemical properties similar to those in soil humus. In an attempt to substantiate these claims three separate experiments were conducted at the University of the Free State to examine the effect of K-humate on soil properties and wheat response during the 2006 growing season. The biological (bacterial and fungal count) response was evaluated in growth chambers by applying three different K-humate products at rates of 0, 3 and 5 L ha-1 in a band on a red loamy sand topsoil. Soil cores were sampled on a weekly basis for six weeks and microscopically analysed. Bacterial and fungal count differed significantly as a result of the product by application rate interaction but no consistency was found. Over time both the bacterial and fungal activity increased rapidly for week 2 and 3 but decreased at week 3 for the bacteria. Both the organisms’ reactions stabilised from week 3 to 6. The chemical soil properties were also tested in growth chambers but only K-humate (single product) was applied as a coating on granular 2:3:2 (22) fertiliser at 0 and 3 L ha-1 in a band 50 mm below the soil surface. The chemical soil properties showed no response after 5 months to the application of K-humate. A glasshouse experiment was also conducted to evaluate the growth and yield response of wheat on three textural class topsoil’s (8, 22 and 37% clay) and four K-humate applications (0 L ha-1, 3 L ha-1 single application, and 3 and 6 L ha-1 split application – 50% at planting and 50% at tillering). K-humate as a coating on 2:3:2 (22) granular fertiliser was banded and Greensulph (27) topdressed at the required fertiliser rate for a yield potential of 8 t ha-1. Plant growth parameters were analysed at tillering, stem elongation and maturity, both above- and below-ground. Virtually no significant influences were found with the K-humate application rate and soil texture interaction on the measured parameters. Notwithstanding this, positive effects were noticed and a split application whereof half of the K-humate was applied at planting and the other half at tillering showed the best results. A field experiment was also conducted to examine K-humates influence on wheat growth and yield. Two experiments was conducted, one under full irrigation (700 mm) with a yield potential of 8 t ha-1 and the other supplementary irrigation (350 mm) with a yield potential of 4 t ha-1. K-humate was applied as a coating on granular 2:3:2 (22) fertiliser and bandplaced either as a single application (0, 1.5, 3, 5 and 6 L ha-1) or a split application (5 and 6 L ha-1) 50% at planting and 50% (K-humate as a coating on Greensulph (27)) at tillering. Irrigation was applied using a line source irrigation system. The field experiment confirmed the results obtained in the glasshouse with virtually no significant effects as a result of the applied K-humate on the measured plant parameters.
Open Access
Effect of water application and plant density on canola (Brassica napus L.) in the Free State
(University of the Free State, 2008-11) Seetseng, Keletso Angelique; Van Rensburg, L. D.; Du Preez, C. C.
Canola serves as a very favorable crop to produce oil world wide. Canola production in South Africa is mainly restricted to the Western Cape Province under winter rainfall conditions. The Protein Research Foundation propagated the production expansion to the central part of South Africa. The semi arid area (Central part of South Africa) is characterized by variable and unreliable summer rainfall. Irrigation is therefore vital for sustainable production of a winter crop like canola. The aim of this study was to establish the crop’s plasticity ability, water use, water use efficiency and transpiration coefficient under a range of water application and plant density treatments combinations for the central South Africa. An experiment with a line source sprinkler irrigation system was conducted near Bloemfontein in the Free State Province. Water applications, excluding 57 mm rain were: W1 = 118 mm, W2 = 176 mm, W3 = 238 mm, W4 = 274 mm and W5 = 363 mm. These water applications were combined with the following planting densities: PD25 = 25plants m-2, PD50 = 50 plants m-2, PD75 = 75 plants m-2, PD100 = 100 plants m-2, PD125 = 125 plants m-2. Seeds (1564 - 4653 kg ha-1) and biomass (3150 - 6733 kg ha-1) yields induced by the treatments proved that canola has a high plasticity. This is because over the full range of water application treatments optimized yields were realized at only one plant density though different for seed (25 plant m-2) and biomass (75 plants m-2) yields. Compensation of yields at lower plant densities resulted from branches and hence pods per plant. Total evapotranspiration increased linear (r2 = 0.97) from 245 mm with 118 mm water application (W1) to 421 mm with 363 mm water application (W5) but was not influenced by plant density at all. Water use efficiency confirmed the optimum plant density for fodder production is 75 plants m-2 and for seed production is 25 plants m-2. The water use efficiency at these two plant densities were 12.9 kg ha-1 mm-1 and 9.6 kg ha-1 mm-1, respectively. The β coefficient of canola was constant (2.26) for the full to moderate irrigation regimes (W5 - W3), but not for the low irrigation regimes (W2 - W1). The β coefficient of 2.26 was used to separate the evapotranspiration of the W3 - W5 treatments into evaporation (56%) and transpiration (44%). This method was not suitable to establish the influence of plant density on the two components of evapotranspiration. A transpiration coefficient of 0.0045 was calculated for canola when planted for fodder at an optimum plant density of 75 plants m-2 under moderate (W3) to full (W5) irrigation.
Open Access
Effect of water application and plant density on canola (Brassica napus L.) in the Free State
(University of the Free State, 2008-11) Seetseng, Keletso Angelique; Van Rensburg, L. D.; Du Preez, C. C.
English: Canola serves as a very favorable crop to produce oil world wide. Canola production in South Africa is mainly restricted to the Western Cape Province under winter rainfall conditions. The Protein Research Foundation propagated the production expansion to the central part of South Africa. The semi arid area (Central part of South Africa) is characterized by variable and unreliable summer rainfall. Irrigation is therefore vital for sustainable production of a winter crop like canola. The aim of this study was to establish the crop's plasticity ability, water use, water use efficiency and transpiration coefficient under a range of water application and plant density treatments combinations for the central South Africa. An experiment with a line source sprinkler irrigation system was conducted near Bloemfontein in the Free State Province. Water applications, excluding 57 mm rain were: WI = 118 mm, W2 = 176 mm, W3 = 238 mm, W4 = 274 mm and W5 = 363 mm. These water applications were combined with the following planting densities: PD25 = 25plants m², PD50 = 50 plants m², PD75 = 75 plants m², PD100 = 100 plants m², PD125 = 125 plants m². Seeds (558 - 4653 kg ha-¹) and biomass (1983 - 6733 kg ha-¹) yields induced by the treatments proved that canola has a high plasticity. This is because over the full range of water application treatments optimized yields were realized at only one plant density though different for seed (25 plant m-² ) and biomass (75 plants m-²) yields. Compensation of yields at lower plant densities resulted from branches and hence pods per plant. Total evapotranspiration increased linear (r² = 0.97) from 245 mm with 118 mm water application (W1) to 421 mm with 363 mm water application (W5) but was not influenced by plant density at all. Water use efficiency confirmed the optimum plant density for fodder production is 75 plants m-² and for seed production is 25-² plants m-². The water use efficiency at these two plant densities were 12.9 kg ha-¹ mm-¹ and 9.6 kg ha-¹ mm-¹, respectively. The β coefficient of canola was constant (2.26) for the full to moderate irrigation regimes(W5 - W3), but not for the low irrigation regimes (W2 - Wl). The β coefficient of 2.26 was used to separate the evapotranspiration of the W3 - W5 treatments into evaporation (56%) and transpiration (44%). This method was not suitable to establish the influence of plant density on the two components of evapotranspiration. A transpiration coefficient of 0.0045 was calculated for canola when planted for fodder at an optimum plant density of 75 plants m-² under moderate (W3) to full (W5) irrigation.
Open Access
Estimating organic carbon stocks in South African soils
(University of the Free State, 2009) Rantoa, Nthatuoa Ruth; Du Preez, C. C.; Van Huyssteen, C. W.
The organic carbon stock in South African soils was estimated using existing data with reference to master horizons, diagnostic horizons, soil forms, and land cover classes. The data used for this study was taken from the land type survey which started in 1970 covering the whole of South Africa. Approximately 2 200 modal profiles representing were analysed for physical and chemical properties including organic carbon. The results showed that the organic carbon content in the master horizons ranged on average from 16% in the O horizon to 0.3% in the C horizons. In the diagnostic horizons, the highest organic carbon was recorded in the topsoils and ranged on average from 21% in the organic O to 1.4% in the orthic A horizons. However, the organic carbon content in the diagnostic subsoil horizons ranged from 1.2% in the podzol B to 0.2% in the dorbank B horizons. The organic carbon content was related to the soil forming factors namely climate (rainfall, evaporation, and aridity index), topography (terrain morphological units, slope percentage, slope type, and slope aspect) and soil texture (clay). Organic carbon related poorly with climate and topography in both the master and diagnostic horizons, with low correlations. Organic carbon content was positively correlated with rainfall and aridity index in the A, E, B, G, C, and R master horizons and inversely correlated with evaporation in those horizons. Climate had an opposite effect on organic carbon in the O master horizons. A positive relationship between organic carbon and rainfall was found in the pedocutanic B, prismacutanic B, soft plinthic B, red apedal B, yellow-brown apedal B, red structured B, G, unspecified material with signs of wetness, E, neocarbonate B, neocutanic B, regic sand, stratified alluvium, lithocutanic B, hard rock, unconsolidated material without signs of wetness, unspecified dry material, and saprolite. The relationship between organic carbon and evaporation was negative in those diagnostic horizons. Rainfall and aridity index related negatively with organic carbon content and positively with evaporation in the following diagnostic horizons: soft carbonate B, podzol B, hard plinthic B, saprolite, and the unconsolidated material with signs of wetness. The relationship between organic carbon and topography was not very clear in both the master and diagnostic horizons. However, topography seemed to influence the formation of some horizons by restricting their formation to certain slope percentages. The influence of topography on organic carbon content depends on the morphology of the master and diagnostic horizon and underlying material. A regression was done to study the correlation of organic carbon and the independent variables namely: rainfall, evaporation, slope aspect, aridity index, and clay per master and diagnostic horizon. Unfortunately most of the correlation coefficients were too low for the equations to be used to estimate organic carbon content in South African soils. Organic carbon in the soil forms behaved as their diagnostic topsoils. The environmental conditions such as water content and temperature that influenced the amount of organic carbon in the topsoils also determined the amount of organic carbon in the diagnostic subsoil horizons of that specific soil form. Organic carbon stocks were then estimated using three soil bulk density values namely: low = 1.30 g cm-3, average = 1.50 g cm-3, and high 1.70 g cm-3. The results revealed that the organic carbon stocks of South African soils increased from the warmer, drier western to the cooler, wetter eastern parts of the country. The average soil organic carbon stocks is 73 726 kg ha-1 when calculated using a soil bulk density of 1.50 g cm-3. Most soils had an organic carbon content between 30 000 kg ha-1 and 50 000 kg ha-1. The total organic carbon of the soils of South Africa is estimated to be 8.99 ± 0.10 Pg calculated to a depth of 0.30 m which is 0.57% of the world’s carbon stocks. Since the world’s carbon stocks were calculated to 1 m depth this is not a true representative value for the carbon stocks of South Africa in relation to the worlds. Therefore a lower value will be expected if carbon stocks are estimated to a depth of 1 m in South Africa. The organic carbon stocks in the 27 land cover classes ranged from 9 Mg ha-1 in barren rock to 120.2 Mg ha-1 in forest plantations. The highest accumulation of organic carbon per unit area in South African soils was found in the forests plantations > forests > wetlands. However the biggest contribution to the total organic carbon stocks, was reported in the unimproved grassland> thicket and bushland > shrubland and low Fynbos > forests.
Open Access
Evaluation of the phosphorus status of sugarcane soils in Mauritius using agronomic and environmental criteria
(University of the Free State, 2009-10) Mardamootoo, Tesha; Du Preez, C. C.; Ng Kee Kwong, K.F.
Phosphorus input is vital to the maintenance of profitable sugarcane crop production in Mauritius. The intensive use of some 5,000 tonnes of P annually during the past 50 years is believed to have built up the P status of the sugarcane soils, perhaps even to excessive levels. While this accumulation of P is desirable from an agronomic perspective, there is growing concern in Mauritius about its possible effect on surface water quality. In response to that concern, a study was initiated with the following specific objectives: i. To review the usage of P fertilisers in sugarcane production in Mauritius and assess their resulting impact on the P status of the main soil groups under sugarcane. ii. To enlarge the scope of the current method used (0.1M H2SO4 extraction) for agronomic P testing so that it also indicates environmental status of sugarcane soils in Mauritius. iii. To determine the environmental threshold P in soils above which the P will represent a hazard to surface waters. The five yearly averages of fertiliser P usage by the Mauritian sugarcane industry showed that from the 790 tonnes of P2O5 (mainly as rock/guano phosphates) consumed at the beginning of the 20th century, P usage attained a peak of 5,675 tonnes in the 1970s before declining thereafter as a result of a decreasing land area under sugarcane. During the period 2005 to 2008, an average of 3,350 tonnes of P2O5 mainly as ammonium phosphates were applied annually to sugarcane which is cultivated in Mauritius mainly on five soil groups, namely the Low Humic Latosol (Humic Nitosol)*, the Humic Latosol (Humic Nitosol)*, the Humic Ferruginuous Latosol (Humic Acrisol)*, the Latosolic Reddish Prairie (Eutric Cambisol)* and the Latosolic Brown Forest (Dystric Cambisol)*. A method based on 0.1M H2SO4 as extractant is currently used as a routine soil test to assess P available to sugarcane in the soils of Mauritius. On the basis of soil P test values, four soil P fertility classes could be discerned, namely: Examination of the soil test P data obtained in 1997/1998 showed that 48% of the land still required P fertilisation while approximately 40% had an excess of P (P ≥ 100 mg kg-1). Less than 10% of the soils had an optimum soil P (80 ≤ P < 100 mg kg-1). Moreover, soils with a highly excessive soil P status (P ≥ 150 mg kg-1) rose from 23% in 1997/1998 to 34% in 2005/2006 indicating that with the current P management practice in sugarcane, the P status of soils in Mauritius will shift more and more towards an excess of P. In spite of the extensive information available on the soil P status, its significance from the freshwater protection angle was, prior to this study unknown due mainly to a lack of a suitable environmental soil P test method. From this perspective, as a laboratory extraction of soil with 0.01M CaCl2 gives a very reliable representation of the P in runoff, the P extractable in a 0.01M CaCl2 (0.01M CaCl2-P) solution was determined in 112 soil samples representing the five main soil groups under sugarcane. The soil samples whose characteristics of pH, organic matter content, exchangeable bases and cation exchange capacity were also determined, were selected to cover a range of 10 to 250 mg kg-1 P extractable by the 0.1M H2SO4 used for agronomic soil P testing in Mauritius. As the environmental soil test P must be independent of soil properties and the concept of degree of P saturation (DPS) meets that criteria, the ammonium oxalate DPS (DPSox) was determined in the 112 soil samples to provide a reliable pointer of P susceptibility to loss from soils. Since it is very unlikely that ammonium oxalate extraction would be used as a routine soil test, the relationship between DPSox and 0.1M H2SO4-P was established by conventional statistical regression techniques. The results obtained indicate that no single soil characteristic could be said to have a distinct influence on the amount of P extracted by either the 0.1M H2SO4 or the 0.01M CaCl2 or by the DPSox. Indeed the correlation (r2) between the 0.1M H2SO4-P, 0.01M CaCl2- P, DPSox with the individual measured soil characteristics was low and never exceeded 0.28 in the case of 0.1M H2SO4-P and 0.52 with 0.01M CaCl2-P. The DPSox exhibited the poorest relationship with the soil properties with none of the r2 values being above 0.16. Instead the low r2 values observed indicated as confirmed by multiple regression analysis that the amount of P extracted by each reagent would be the result of the combined effects of certain soil characteristics. The results moreover showed that for soil P not to constitute a hazard to the freshwaters in Mauritius, the DPSox should not exceed 3.10±0.10% and the 0.01M CaCl2-P must lie below 18±1µg L-1. Moreover the linear fit regression equation 0.1M H2SO4-P = 17.3 + 23.2 DPSox with r2 = 0.54 was found to most appropriately describe the relationship between 0.1M H2SO4-P and DPSox. From that equation the threshold DPSox of 3.10±0.10% would correspond to a range of 85 to 95 mg kg-1 of 0.1M H2SO4-P which is henceforth considered as the threshold range of P in sugarcane soils in Mauritius above which the soil P would become a hazard to freshwater sources. Using this environmental threshold range of soil P values as basis, the soils can be divided into the following four environmental classes namely: [table]. Application of the above criteria showed that in 1997/1998, 58% of the soils did not represent any hazard to freshwater quality in Mauritius. As much as 42% of the sugarcane fields in 1997/1998 had from the environmental viewpoint unacceptably high levels of P (P ≥ 95 mg kg-1) in the soils. After one crop cycle in 2005/2006, the number of fields with unacceptably high levels of P (P ≥ 95 mg kg-1) had risen to 53%. The majority (74%) of the sugarcane fields with an environmentally unacceptable P status were located in the Latosolic Reddish Prairie and Latosolic Brown Forest soils. In extending the scope of the current agronomic soil test P using 0.1M H2SO4 as an extractant into an agro-environmental soil P test, this study demonstrated clearly that the agronomic objectives in P management for sugarcane production in Mauritius are incompatible with the environmental aims of protecting the freshwater resources in Mauritius. With the agronomic threshold range of 80 to 100 mg kg-1 P overlapping the environmental range of 85 to 95 mg kg-1 P, soils in Mauritius that are agronomically suitable for sugarcane cultivation are on contrary unsafe from the environment protection viewpoint and vice versa.
Open Access
Grondversuring en bekalking van Oos-Vrystaatse gronde onder droëlandkoring
(University of the Free State, 2003-04) Van Zyl, Hendrik Johannnes Jakobus; Du Preez, C. C.; Kilian, W. H.
English: The value of liming of agricultural land has been demonstrated all over the world during the past century. Therefore liming as an agro-economical practice has been adopted widely by farmers with a beneficial impact on sustainable crop production for future generations. However, soil acidity is still a common yield limiting factor for a variety of crops in the Free State, Mpumalanga, KwaZulu-Natal and parts of the Western Cape. Due to above mentioned reasons incubation and field experiments were conducted over several years to quantify the following after liming of various Eastern Free State soils. Firstly, the changes in soil acidity parameters and secondly, the growth and development of wheat cultivars that differ in tolerance to aluminium (AI). Over time liming increased the pH(KCI) and decreased the percentage acid saturation (%AS) significantly in the top- (0-200mm) and subsoil (200-400mm) of all the localities. In the topsoils a good correlation was obtained between pH(KCI) and %AS. An increase in pH(KCI) of 0.1 will more or less be concomitant with a decrease of 5.5 in %AS. The amount of lime needed to raise the pH(KCI) or to lower the %AS up to a specific level, differed between the localities because of buffer capacity. Since pH(KCI) showed a better correlation with lime than %AS, it was decide to use pH(KCI) as parameter to develop a model with which the lime requirement of a soil can be calculated: Y=8.3240X1-O.0459X2-1.0370, where Y=lime requirement (ton ha"), X1=~pH(KCI and X2=clay content (%) At all localities the good AI-tolerant cultivar gave significant higher yields than the medium and poor AI-tolerant cultivars. When no lime was applied on the unlimed soils the good AI-tolerant cultivar produced economical yields, which was not the case with the medium and paar AI-tolerant cultivars. The medium and poor Al-tolerant cultivars responded therefore very well to liming with yield increases up to 90%. The good, medium and poor Al-tolerant cultivars showed a yield decrease of 15% at an %AS of 30, 10 and 8, respectively. Considering that %AS correlated better with yield than pH(KCI), liming to the required %AS of a cultivar is a possibility. Differences in AI-tolerance between cultivars resulted in that the optimum economic lime levels differ between cultivars. The optimum lime level of the cultivar with good AI-tolerance was the lowest, followed by the medium and paar AI-tolerant cultivars. Liming of acid soil has become an expensive practice for farmers, which led to the adoption of planting AI-tolerant cultivars to bridge the soil acidity problem. During this process soils has slowly started to deteriorate with an accompanying lost of yield and income per hectare. The results of this study clearly indicate the economical value of liming acid soils for wheat production.
Open Access
Improvement of the nitrogen content of grape must with fertilisation
(University of the Free State, 2002-11) Jordaan, Jacques; Engelbrecht, G. M.; Du Preez, C. C.
English: Stuck fermentation is currently a serious production associated problem in the South-African wine industry. This can mainly be attributed to insufficient levels of nitrogen in grape must, thus are not being able to supply in yeast demands. This study was undertaken to investigate whether the nitrogen content of grape must can be improved by fertilisation. In order to achieve this three nitrogen application treatments (N1C = 20 kg N/ha-¹ post-harvest; N2F = 20 kg N/ha-¹ post-harvest, followed with 20 kg N/ha-¹ after budbreak and fruitset respectively; and N2V = 20 kg N/ha-¹ post-harvest, followed with 20 kg N/ha-¹ after budbreak and veraison respectively), were applied to six grape cultivars (Cabernet Sauvignon, Chenin blanc, Pinot noir, Weisser Riesling, Chardonnayand Pinotage) for two seasons (1999/2000 = 1st season and 2000/2001 = 2nd season). The vineyard is situated on a high potential loam soil, classified as a red-brown Oakleaf, with a mean organic matter content of 1.4%. The effect of these nitrogen application treatments on the growth characteristics, grape must composition, leaf nitrogen content, as well as the soil nitrate content, were measured. Nitrogen applications during the vegetative phase had a positive effect on the shoot length and shoot elongation during both seasons, although more so during the 1st season. The pruning mass was significantly affected by cultivar during both seasons. Treatments receiving no nitrogen fertilisation during the vegetative phase (N1C) resulted in higher free amino nitrogen (FAN) and FAN/oB ratio in grape must, indicating a negative reaction to nitrogen fertilisation for soils having a high organic matter content. No nitrogen fertilisation during the vegetative season resulted in significantly lower bunch and berry mass values than those receiving fertilisation. This might indicate a negative relationship between bunch and berry mass and the FAN content of grape must. The nitrate content of the soil differed for the different soil depths and was affected by sampling date and N treatments. Results indicated that 70% of the nitrate was available in the top 30 cm of soil. Nitrogen fertilisation during the vegetative season on soils with an organic matter content of 1.4% should be strongly discouraged. This study therefore indicates that although high organic matter content and inorganic fertiliser applications may increase the nitrate content of the soil, this might not have the same effect on the nitrogen status of the vine.
Open Access
Influence of cropping sequence on wheat production under conservation agriculture in the Eastern Free State
(University of the Free State, 2014-01) Visser, Magdalena Hendrika; Du Preez, C. C.; Barnard, A.
English: Crop rotation is one of the pillars of conservation agriculture (CA). It has been adopted moderately in the summer rainfall area of South Africa, but the adoption of conservation tillage has been very slow. It has been observed that research information on crop rotation helped with the adoption of the CA concept in the Western Cape. Limited research has been done on crop rotation in the Eastern Free State. This study used the crop matrix trial design to evaluate the impact of different cropping sequences in a CA system on the growth, development, yield and quality of wheat as target crop. The profitability and production risk of the different crop rotations were also determined. Only preceding summer crop sequences had a significant (P≤0.1) influence on the yield parameters of the final wheat crop. For the final wheat crop three preceding sequences, namely sorghum × soybean, maize × sunflower and soybean × maize, led to a lower (P≤0.1) number of plants and ears, with a lower biomass and residue yield unit area. Although the poorest response was always recorded on the preceding sorghum × soybean sequence plots, it did not differ significantly from those of the other two crop sequences. The final wheat crop also had a significantly higher TKM and harvest index on preceding sorghum × soybean sequence plots. It was concluded that the lower number of plants on these plots could be attributed to lesser in-row competition for water and nutrients, which resulted in bigger and heavier wheat kernels with a higher TKM. The study confirmed previous research, namely that the final wheat crop planted on second season sunflower plots had a significantly (P≤0.1) higher number of ears m-2, with a better N(grain) use efficiency. That resulted in a significantly higher grain protein content. However, the yield of the final wheat crop did not differ between plantings on second season summer crop plots. Rotation with oats is often recommended to reduce Take-all, a soil-borne disease of wheat. It was found that the final wheat crop planted on second season oats plots had a significantly lower seedling number, with fewer ears and a lower grain yield per unit area. The wheat plants also had a lower (P≤0.1) precipitation use efficiency and grain nitrogen use efficiency, which led to a lower accumulation of grain protein. It was concluded that oats has a negative influence on wheat yield in a rotation system and that the crop should only be used as a break crop against Take-all. Thirty two of the 50 crop rotations had a total profit margin above the chosen target income of R1,000 ha-1. The soybean × maize × wheat rotation gave the highest total profit of R7,549.76 ha-1, while the sorghum × dry bean × wheat rotation realised the highest total loss of R1,903.93. Maize had a stable yield over two seasons, while the yield of the other four preceding summer crops posed a higher production risk under rainy conditions (pod shattering in dry bean and soybean crops), or potential bird damage situations (sunflower and sorghum). The crop matrix technique proved to be a reliable method to generate more information on cropping sequence in the same trial over a much shorter period. A multi-disciplinary approach in future cropping sequence research will help to provide producers with reliable information. If crop sequences can be proven to be effective at research level, clear guidelines and recommendations can be developed to help producers in implementing conservation tillage more successfully in the Eastern Free State.
Open Access
The influence of land use on humic substances in three semi-arid agro-ecosystems in the Free State
(University of the Free State, 2009-05) Akhosi-Setaka, Makuena Cynthia; Du Preez, C. C.; Kotze, E.
English: This study was initiated to complement earlier investigations into soil organic matter degradation and restoration on account of agricultural land use in the Free State Province of South Africa. In these studies no attention was given to the response of humic substances which represent the most active fraction of organic matter. The aim with this study was therefore to quantify the influence of agricultural land use on humic substances in soils of semi-arid regions. Topsoil (0-200 mm) samples from distinctive agro-ecosystems at Harrismith (Mean annual rainfall, MAR = 624 mm and Mean annual temperature, Ta = 13.8°C), Tweespruit (MAR = 544 mm and Ta = 14.8°C) and Kroonstad (MAR = 566 mm and Ta = 16.6°C) were selected for use in this study. An agroecosystem implies a region where the three environmental factors affecting yield, namely climate, slope and soil are for practical purposes homogeneous. The selected samples represent a virgin (grassland soil never cultivated before), cultivated (formerly grassland soil cultivated for at least 20 years) and restored (formerly cultivated soil converted to perennial pasture for at least 15 years) Plinthustalfs (10.6 to 13.5% clay) at every agro-ecosystem. Parameters quantified comprise crude soil, extractable soil, humic acid and fulvic acid C contents, N contents and C/N ratios. Concerning these parameters, cultivated soil was compared with virgin soil and restored soil with cultivated soil. The crude soil C content of the virgin soils varied from 7.3 g C kg-1 soil in the warmer, drier Kroonstad agro-ecosystem to 21.6 g C kg-1 soil in the cooler, wetter Harrismith agro-ecosystem. Across agro-ecosystems the contribution of extractable to crude soil C was almost constant, namely 47.1 to 48.4%. The contribution of humic acid C to extractable soil C decreased and that of fulvic acid C to extractable soil C increased from the Kroonstad to Harrismith agroecosystem. Cultivation reduced crude soil C in the three agro-ecosystems with 50.2 to 51.8%. This is equivalent to absolute losses of 3.8, 8.2 and 10.8 g C kg-1 soil at Kroonstad, Tweespruit and Harrismith agro-ecosystems respectively. Loss of extractable soil C was more variable ranging from 36.7% or 1.3 g C kg-1 soil in the warmer, drier Kroonstad agro-ecosystem to 48.2% or 5.1 g C kg-1 soil in the cooler, wetter Harrismith agro-ecosystem. Trends of this nature were nonexistent for either humic or fulvic acid C losses. Gains of crude soil C ranged from 5.4 g C kg-1 soil in the warmer, drier Kroonstad agro-ecosystem to 8.0 g C kg-1 soil in the cooler, wetter Harrismith agroecosystem. This trend manifested also in extractable soil C gains which were lowest at Kroonstad (1.5 g C kg-1 soil) and highest at Harrismith (2.8 g C kg-1 soil). Neither humic acid C nor fulvic acid C showed trends of this nature. The N contents although more variable than the C contents are to a large extent supportive concerning organic matter in the virgin, cultivated and restored soils of the three agro-ecosystems. Further elaboration on the N contents is therefore not justified here. Based on both C and N indices, it can be stated that humic substances did not show explicit trends on account of land use as was the case with organic matter per se. This phenomenon warrants further investigation since humic substances are regarded as the most reactive fraction of organic matter.
Open Access
Influence of long-term wheat residue management on some fertility indicators of an avalon soil at Bethlehem
(University of the Free State, 2004) Kotzé, Elmarie; Du Preez, C. C.
Awareness of the environmental aspects of soil quality and crop production has been increasing in recent years, which has led to renewed interest in crop residues as a source of soil organic matter and nutrients for crops. Crop residue management is known to both directly or indirectly affect soil quality and therefore soil fertility. Some residue management practices have been tested since 1979 in a long-term wheat trial at the ARC-Small Grain Institute near Bethlehem in the Eastern Free State on an Avalon soil. This trial offered an opportunity to study the influences of wheat residue management practices on some soil fertility indicators and to establish whether differences in wheat grain yield could be attributed to changes in the soil fertility indicators. The treatments that were applied are two methods of straw disposal (burned and unburned) x three methods of tillage (ploughing, stubble mulch and no tillage) x two methods of weed control (mechanical and chemical). Soil samples were collected in 1999 at depth intervals of 0-50, 50-100, 100-150, 150-250, 250-350 and 350-450 mm and analyzed for various soil fertility indicators, viz. organic C and total N as indices of organic matter. In addition the pH, P, K, Ca, Mg, Na, Cu, Fe, Mn and Zn were also determined. The different tillage practices had a larger effect on organic matter than either straw burning or weeding method, especially in the upper 100 mm soil. No tillage and to a lesser extent mulch tillage, especially when combined with chemical weeding were more beneficial to soil organic matter than when ploughing was combined with mechanical weeding. Soil acidification seems to be retarded by mulch or no tillage when combined with chemical weeding. The burning of wheat residues increased pH significantly compared to no burning. It was found that the content of P, K, Cu, Fe, Mn and Zn were increased with straw burning when compared to no burning. No tillage and to a lesser extent also mulch tillage resulted in an accumulation of P, K, Ca, Mg, Cu, Fe, Mn and Zn in the upper 150 mm soil compared to mouldboard ploughing. Grain yield does not coincide with the higher organic matter and lower acidity resulting from mulch and no tillage. A reason for this may be that the nutrients accumulated in the upper 150 mm soil with these two tillage practices, are not always available for plant uptake. This aspect warrants further investigation.
Open Access
Influence of nitrogen and potassium applications on the early growth and development of maize (Zea mays L.)
(University of the Free State, 2000) Emmanuel, Willie President; Ceronio, G. M.; Du Preez, C. C.
English: It is well known that appropriate band applications of N and/or K can result in optimum early growth and development of maize. Two pot experiments were conducted in a glasshouse at the University of the Orange Free State, Bloemfontein to determine the application levels at which the above mentioned phenomena occur. The first experiment was conducted to determine the influence of band placed N and/or K on the early growth and development of maize, while the second experiment was set up to determine the influence of K placement through banding, topdressing and a combination of banding and topdressing on the early growth and development of maize. The first experiment was conducted from January to March 1999 with the cultivar PAN 6479. Two types of soil were used in the experiment, viz. a sandy loam soil collected from Ficksburg and a sandy soil collected from Boshof The plant density was maintained at three plants per pot and the experiment was terminated four weeks after seedling emergence. A complete randomized design with a factorial combination consisting of two main factors, viz. four N and/or K band application levels which were replicated thrice, was used in this experiment. The application rates were the equivalent of 0, 20, 40 and 60 kg N or K.ha-¹ for a row spacing of 1.5 m. The aerial and subsoil plant parameters, as well as, the nutrient uptake by maize were measured to determine the influence of different N and/or K applications on the early growth and development of maize. All the plant parameters measured showed that the interaction of N and K applications had no significant influence on the early growth and development of maize. The best results were obtained with an application of 20 to 40 kg N.ha-¹• An application of 20 kg K.ha-¹ provided the best results. The second experiment was conducted from October to November 1999. With the exception of the fertilization procedure, all other aspects pertaining to the execution of this experiment were the same as those used in the first experiment. This experiment was terminated six weeks after seedling emergence. The experiment consisted of two main factors, viz. four levels and three methods of K application, arranged in a factorial combination in a complete randomized design with four replications. The application rates were the equivalent of 0, 20, 40 and 60 kg K.ha-¹ placed through banding, topdressing and a combination of banding and topdressing for a row spacing of 1.5 m. With regards to the combination application, half of K was banded and another half topdressed. The aerial and subsoil plant parameters, as well as, the nutrient uptake by maize were studied to determine the effect of different levels of banded, top dressed and a combination of banded and topdressed K on the early growth and development of maize. All the plant parameters studied showed that the interaction of K application levels and methods had no significant influence on the early growth and development of maize. It seems the best results were attained with °to 20 kg K.ha-¹ The second experiment was conducted from October to November 1999. With the exception of the fertilization procedure, all other aspects pertaining to the execution of this experiment were the same as those used in the first experiment. This experiment was terminated six weeks after seedling emergence. The experiment consisted of two main factors, viz. four levels and three methods of K application, arranged in a factorial combination in a complete randornized design with four replications. The application rates were the equivalent of 0, 20, 40 and 60 kg K.ha-¹ placed through banding, topdressing and a combination of banding and topdressing for a row spacing of 1.5 m. With regards to the combination application, half of K was banded and another half topdressed. The aerial and subsoil plant parameters, as well as, the nutrient uptake by maize were studied to determine the effect of different levels of banded, top dressed and a combination of banded and topdressed K on the early growth and development of maize. All the plant parameters studied showed that the interaction of K application levels and methods had no significant influence on the early growth and development of maize. It seems the best results were attained with °to 20 kg K.ha-¹. A combination of banding and topdressing in the sandy loam soil and topdressing alone in the sandy soil provided the best results. Finally, it is recommended that field trials should be conducted in order to verify these glasshouse results under field conditions.The second experiment was conducted from October to November 1999. With the exception of the fertilization procedure, all other aspects pertaining to the execution of this experiment were the same as those used in the first experiment. This experiment was terminated six weeks after seedling emergence. The experiment consisted of two main factors, viz. four levels and three methods of K application, arranged in a factorial combination in a complete randornized design with four replications. The application rates were the equivalent of 0, 20, 40 and 60 kg K.ha-¹ placed through banding, topdressing and a combination of banding and topdressing for a row spacing of 1.5 m. With regards to the combination application, half of K was banded and another half topdressed. The aerial and subsoil plant parameters, as well as, the nutrient uptake by maize were studied to determine the effect of different levels of banded, top dressed and a combination of banded and topdressed K on the early growth and development of maize. All the plant parameters studied showed that the interaction of K application levels and methods had no significant influence on the early growth and development of maize. It seems the best results were attained with °to 20 kg K.ha-¹. A combination of banding and topdressing in the sandy loam soil and topdressing alone in the sandy soil provided the best results. Finally, it is recommended that field trials should be conducted in order to verify these glasshouse results under field conditions.. A combination of banding and topdressing in the sandy loam soil and topdressing alone in the sandy soil provided the best results. Finally, it is recommended that field trials should be conducted in order to verify these glasshouse results under field conditions.
Open Access
Long-term effects of residue management on soil fertility indicators, nutrient uptake and wheat grain yield
(University of the Free State, 2012-01) Loke, Palo Francis; Kotzé, E.; Du Preez, C. C.
English: Farmers have largely depended on intensive soil cultivation to reduce nutrient stratification and therefore distribute nutrients homogeneously across the root zone for optimum crop productivity. This attempt however, has led to serious soil organic matter degradation and nutrient outflows. Consequently, food production for the increasingly growing world population was severely threatened. Crop residues as a source of organic matter and nutrients, when properly managed, can restore or improve soil fertility, and hence crop yields. The different residue management practices on some soil fertility indicators have been examined since 1979 in a long-term wheat trial at the ARC-Small Grain Institute near Bethlehem in the Eastern Free State on an Avalon soil. The observations established in 1999 indicated that soil nutrient and organic matter stratification still continues, therefore it was found necessary to further investigate the effects of these residue management practices on some soil fertility indicators, nutrient uptake and wheat grain yield. The applied field treatments include two methods of straw disposal (unburned and burned), three methods of tillage (no-tillage, stubble mulch and ploughing) and two methods of weeding (chemical and mechanical). Soil samples were collected in 2010 at various depths viz. 0-50, 50-100, 100-150, 150-250, 250-350 and 350-450 mm and analyzed for organic C, total N and total S as organic matter indices, pH, some macronutrients (P, K, Ca, Mg and Na) and CEC, as well as some micronutrients (Cu, Fe, Mn and Zn). At mid-shooting stage, plants were sampled in each treatment plot, oven-dried at 68 ºC, weighed, milled and analyzed for N, S, P, K, Ca, Mg, Na, Cu, Fe, Mn, and Zn. The grain yield data of wheat for the 26 years were supplied by the ARC-Small Grain Institute for use as a supplement to the soil data. The methods of straw disposal and tillage had variable influences on soil organic matter indices. Unburned straw increased total N and S, but reduced organic C when compared to the burned straw. No-tillage increased organic C only in the 0-50 mm soil depth when compared to stubble mulch and ploughing. No-tillage and stubble mulch resulted in a higher total N to a soil depth of 450 mm relative to mouldboard ploughing. Ploughing on the other hand, and to some extent stubble mulch, increased total S more than no-tillage in the upper 250 mm soil depth. Mechanical weeding enhanced these indices to 450 mm soil depth as opposed to chemical weeding. No-tillage and to some extent stubble mulch suppressed acidification in the upper 100 mm and lower 350-450 mm soil depths. Mechanical weeding also increased soil pH when compared to chemical weeding. No-tillage combined with either chemical weeding or straw burning suppressed acidification in the surface soil, whereas mechanical weeding combined with either no-tillage or mouldboard ploughing retarded acidification in the subsoil. The concentrations of P, K, Mg, Mn and Zn were higher in the burned treatments than in the unburned plots. The reverse was observed with Ca, Na and Cu. In contrast, mouldboard ploughing, and to some extent stubble mulch, resulted in an accumulation of Cu in the upper 100 mm soil depth when no-tillage served as a reference. Chemical weeding enhanced P, K, Mg, Na and CEC, but resulted in lower Ca, Cu, Fe, Mn and Zn contents when compared to mechanical weeding. The applied management practices were also tested on nutrient uptake and grain yield. Although not always significant, the burned straw increased nutrient uptake, but resulted in a lower wheat grain yield when compared to unburned straw. Despite the beneficial effects of no-tillage and stubble mulch on the fertility status of this Avalon soil, higher nutrient uptake and grain yield were perceived under mouldboard ploughing. Mechanical weeding also enhanced the uptake of most of the studied nutrients relative to chemical weeding. Mouldboard ploughing combined with either unburned straw or chemical weeding increased nutrient uptake and wheat grain yield. However, irrespective of the applied field treatments, nutrient concentrations in oat straw were below optimum levels, and possibly plants were already suffering acute nutrient deficiencies.
Open Access
Long-term effects of tillage practices on biological indicators of a soil cropped annually to wheat
(University of the Free State, 2012-07) Clayton, Hannah Gudrun; Du Preez, C. C.; Kotzé, E.; Rhode, O. H. J.
Soil sustainability is a long-term goal. Although physical and chemical properties of soil have been utilized extensively to evaluate soil quality, the application of biological indicators is becoming more important. In order to assess soil quality, soil enzymes and other biological parameters need to be considered. In semi-arid Bethlehem, South Africa, samples were taken at a wheat (Triticum aestivum L.) monoculture trial which was established in 1979 by the Agricultural Research Council-Small Grain Institute. The treatments were: no-tillage (NT), stubble-mulch (SM), and conventional tillage (CT); all paired with chemical weed control, the absence of burning residues, and 40 kg nitrogen ha-1 as limestone ammonium nitrate with single superphosphate as the fertilizer sources. The study period lasted from October 2010 to October 2011 with eight sampling times conducted over this year and two depths sampled (0-5 cm, 5-10 cm). Oat (Avena sativa L.) was growing in the plots from the start of the study until December 2010 when it was harvested. A fallow period then lasted until the planting of wheat in August 2011 which was harvested after the end of the study period. Potential enzyme activities were assayed for β-glucosidase, urease, acid- and alkalinephosphatase, and dehydrogenase at all eight sampling times, along with soil texture, total carbon, total nitrogen, Olsen-extractable phosphorus, and pH. Whole microbial community profiling using BIOLOG EcoPlatesTM was employed at the first sampling time and phospholipid fatty acid (PLFA) analysis for the first, third, and fifth sampling times. It was found that NT and SM had higher values than CT across all enzymes except alkaline phosphatase, which ranked NT higher than both SM and CT. BIOLOG EcoPlatesTM and PLFA showed similar results across tillage treatments. Microbial biomass, estimated from both potential dehydrogenase activities and PLFA values, was higher in NT and SM than in CT. Over the study period the values for all parameters varied but the average ranking of tillage treatments stayed consistent. In comparing the two soil depths, soil quality was easily shown to be higher in NT and SM in the 0-5 cm depth, but often in the 5-10 cm depth the differences faded. Potential acid phosphatase activity was the only measured parameter which was consistently higher in the 5-10 cm depth. If the parameters can be used as an index of soil quality, then it can be accepted that NT has higher quality than CT and often SM has higher quality than CT, but is not at the same level as NT; it can then be recommended that in semi-arid South Africa, NT will enhance soil quality under a monoculture cropping practice.
Open Access
Organic matter restoration by conversion of cultivated land to perennial pasture on three agro-ecosystems in the Free State
(University of the Free State, 2002-01) Birru, Tilahun Chibsa; Du Preez, C. C.; Hensley, M.
English: Understanding the process of organic matter degradation and restoration is important with regard to sustainable agricultural production on any agro-ecosystem, and of particular importance where degradation is relatively rapid, such as in the coarse textured savannah soils of the South African highveld. Organic matter degradation studies on such soils in three agro-ecosystems, Harrismith, Tweespruit and Kroonstad, have been undertaken by Du Toit et al. (1994), and Lobe et al. (2001). This study is concerned with organic matter restoration on the same agro-ecosystems, and is therefore complementary to the two earlier studies. The objective was to investigate organic matter restoration at three depths, 0-50, 50-100 and 100- 200 mm, on perennial pastures of different ages that had been established on lands which had been cultivated continuously for more than 20 years. Representative C and N values for degraded lands and virgin grasslands for the three agro-ecosystems were obtained from the studies of Du Toit et al. (1994) and Lobe et al. (2001), and used as reference values. To reduce within-site error samples were collected at six places, separated from each other by a few meters, at each site. At each of these places six subsamples of each layer were taken to make up the final sample. There were therefore 18 soil samples per site. A total of 28 sites, ranging in ages from 4 to 25 years, were identified and sampled on the three agro-ecosystems, All the samples were analyzed for C and N, and selected samples were analyzed to characterize the soil fertility levels and particle size distribution at each site. Results showed a wide variation in the rate of organic matter restoration between sites in each of the agro-eco systems , due mainly to differences in natural resource factors and management techniques. Most important of the latter was the application of N fertilizer. Where this was inadequate or absent, very low organic matter restoration rates were generally measured. An approximate threshold value of available N below which organic matter restoration is severely impaired appears to be about 15 mg kg". On pastures up to the age of25 years most of the C and N storage has been in the 0-50 mm layer, a little in the 50-100 mm layer, and very little in the 100-200 mm layer. This observation accentuates the importance of the sampling depth in such studies. These results are in accordance with those of Potter ef al. (1999). The mean C gains over all the sites in the three agroecosystems, excluding those with a Nfertility level considered too low to initiate efficient C sequestration, is 0.56 Mg ha-I yr' as compared to 0.8 Mg ha" yr" suggested by Bruce el al. (1999) for the United States of America and Canada. The relatively coarse texture of the Free State soils, and the lower aridity indices, may account for the difference. An attempt was made by pooling the data for the three agro-ecosystems, and adopting a normalization procedure, to identify common C and Nrestoration curves with time. Although a definite upward trend is visible, large inter-site variation and the shortage of data points above 20 years results in relatively low correlation coefficients and the curves being unreliable at their top end. Further research to obtain data from very old pastures is recommended, as well as ecotope specific research on benchmark ecotopes to define in a reliable way the shape of the organic matter restoration curve.
Open Access
Response of a sandy soil and maize plants to zinc fertilizers
(University of the Free State, 2014) Wessels, C. F.; Du Preez, C. C.; Ceronio, G. M.
English: Maize in Southern Africa is the most important crop for animal and human nutrition. Soil fertility, its management and understanding have an unmistakable role to play in modern agriculture. Maize is prone to zinc deficiency and is known to decrease yield as well as lowering nutritional value. Zinc is reported to be one of the most important micronutrients for the growth and development of maize. An incubation and glasshouse experiment was conducted to evaluate the response of plant available zinc in sandy soil when fertilized with ZnSO4, ZnO and ZnEDTA at different rates. For this purpose a range of extractants were used: HCl, Mehlich I, DTPA, EDTA and Ambic II. In the incubation experiment, two almost similar sandy soils differing only in acidity were treated with the three zinc fertilizers to increase the zinc content with 0 mg kg-1, 1 mg kg-1, 2 mg kg-1, 3 mg kg-1 and 4 mg kg-1. Each treatment was repeated five times. Fertilizers were applied as a solution, and after application soil went through three wetting and drying cycles before plant available zinc was determined in them. In the mentioned glasshouse experiment maize was planted in 40.5 L pots using a complete randomized block design. The same zinc fertilizers were used as for the incubation experiment but application rates differed. One of the soils used for the incubation experiment was selected and treated to increase its zinc content with 0 mg kg-1, 0.5 mg kg-1, 1 mg kg-1, 2 mg kg-1 and 4 mg kg-1. Phosphorus and nitrogen were added to the soil at a constant rate. Fertilizers were dissolved in water and applied as a solution on soil before thoroughly mixed. Maize were planted 50 mm deep and soil was maintained at drained upper limit during the growing period. During the five week growing period stem thickness, plant height and number of leaves were measured weekly while leaf area, root length, root mass and plant available zinc were measured at the end of the growing period. The experiment was repeated at two planting dates. After the growing period soil was sampled for zinc and phosphorus analysis. Concerning zinc source used, ZnSO4 was superior followed by ZnEDTA and ZnO in most of the measured plant parameters as well as plant available zinc content. Plant available zinc content at the end of the incubation experiment differed between the two soils. Extraction methods used to determine plant available zinc content led to different values. For both soils used in the incubation experiment Ambic II, DTPA and EDTA tend to extract more zinc than HCl and Mehlich I. Zinc fertilizers and application rates had a significant effect on plant parameters in the glasshouse experiment. The two plantings differed from each other. The effect of ZnO and ZnEDTA on aerial and subsoil growth parameters was not consistent throughout the glasshouse experiment. Most of the plant parameters showed an impaired development at increasing application rates. This phenomenon however did not occur in the plant available zinc content at the end of the growing period. Extraction method used to determine plant available zinc content at the end of the glasshouse experiment differed. However, the order differs from the results obtained in the incubation experiment. For both experiments the Ambic II and EDTA methods tend to extract the highest amount of zinc from the soil. Zinc source and application rate had a significant effect on both the concentration and uptake of zinc in/by maize. Again ZnSO4 was superior in increasing uptake and concentration of zinc by/in maize, with ZnO and ZnEDTA being inconsistent. Considering the reasons for this study it is clear that ZnSO4 was superior over ZnO and ZnEDTA. This could be attributed that with ZnEDTA and ZnO there were no compensation for the S in ZnSO4. Furthermore the ZnEDTA used was synthetically prepared and may be less effective than natural products. Zinc fertilizer and application rate also proved to have an effect on plant available zinc content and maize growth response.
Open Access
Response of maize to phosphorus and nitrogen fertilizers on a soil with low phosphorus status
(University of the Free State, 2013) Coetzee, Pieter-Ernst; Ceronio, G. M.; Du Preez, C. C.
Maize (Zea mays L.) is an important cereal crop not only in the world but more specifically in South Africa. Therefore, understanding maize’s nutrient requirement becomes an importance factor especially during the vegetative growth period. Nitrogen (N) and phosphorus (P) are reported to be two essential nutrients for both accelerated vegetative growth and maximum yield. Addition of these two plant nutrients should include consideration of both form and total nutrient concentration, since these two factors determine availability and accessibility. In order to evaluate the response of maize to P sources and P application rates as well as N sources a glasshouse experiment was conducted in 40.5 L pots filled with a dark brown sandy-loam topsoil pertaining a medium soil pH of 5.5. Treatments consisted of three main factor treatments viz. N source (urea and limestone ammonium nitrate - LAN), P source (monoammonium phosphate - MAP, nitrophosphate - NP and ammonium polyphosphate - APP) and P application rate (0, 10, 20, 30 and 40 kg P ha-1). Treatments combinations were replicated three times and independently subjected to a randomized complete block design with a factorial combination. The experiment was repeated on two planting dates. Treatments and treatment combinations were band applied to dry soil in a single 0.34 m line, 50 mm below and 50 mm away from the maize seeds; which were planted with a between row spacing of 0.91 m, 50 mm below the soil surface. After planting the soil was watered and maintained at field capacity for a duration of five weeks after emergence. The aerial parameters of three plants per pot were measured on a weekly basis following emergence while the subsoil parameters were taken at the end of the five week vegetative growing period. Both aerial and subsoil parameters showed responses to nitrogen source; which was strongly reflected during both plantings. Plants treated with LAN yielded both greater aerial and subsoil measurements compared to urea, primarily ascribed to immediate availability after application in addition to ease in uptake. Both aerial and subsoil parameter response to phosphorus source and P application rate, though apparent throughout both plantings, was more prominent during the first planting. Monoammonium phosphate and NP (orthophosphate sources) yielded greater aerial measurements compared to that of the APP (polyphosphate source). Subsoil parameter results comparing phosphorus sources were inconsistent. Subsoil parameters of the fertilized zone were significantly greater with the use of MAP (orthophosphate), while APP (polyphosphate) yielded significant greater subsoil parameters within the unfertilized zone. Both aerial and subsoil parameter measurements taken either throughout or at the end of the vegetative growth period were overall significantly greater when P was applied at 40 kg P ha-1. Subsoil parameter response in and away from the fertilizer band was however inconsistent. The aerial dry plant material was analyzed (Omnia Nutriology®) to evaluate the effect of the three main treatments on the quantitative nutrient concentration as well as the uptake thereof. Nutrient concentration and uptake was used to determine the synergistic or antagonistic effect of treatments or treatment combinations. Nutrient concentration measurements were inconsistent for N source, however total uptake proved to be more efficient with the application of LAN compared to urea. Both nutrient concentration and uptake was greater with the application of both the orthophosphate sources (MAP and NP) compared to the polyphosphate source (APP). The 40 kg P ha-1 application yielded a synergistic response to the total uptake of S, N, P, Ca and B, while a synergistic nutrient concentration response was found with the control treatment for N, Mg, Cu and Zn nutrients. Nutrient uptake was also stimulated by an increasing rate of P.
Open Access
The role of ferrolysis in the genesis of selected soils of the Eastern Free State
(University of the Free State, 2007-11) Macheli, Malerata Suzan; Le Roux, P. A. L.; Du Preez, C. C.
English: Plinthic and duplex soil forms make up a substantial part of the soils under cultivation in South Africa. The tendency of these soils to occur either in isolation, or in association with one another, leaves the impression that ideal conditions for the formation of each occur independently but are closely related. This implies that ideal conditions for the development of each vary over short distances. Little research has been done on the duplex-plinthic soil association but a relationship between the two soil groups is implied in literature. A proper understanding of soil genesis may therefore contribute to the better classification, interpretation and evaluation of these soils for sustainable land-use purposes. The hypothesis is that the redistribution of Fe-Mn and degradation of silicate clays are important processes involved in the formation of soils with either a duplex or plinthic character. The objective of the study was to establish the role of ferrolysis and redistribution of Fe-Mn in the genesis of the duplex-plinthic soil association. The catena concept; which describes a sequence of soils of about the same age, occurring under similar macroclimatic conditions and derived from the same parent material; but with different characteristics due to variation in topography and drainage; was adopted. A toposequence of 10 representative profiles was selected in the Eastern Free State. The soils were described, sampled and photographed. Representative composite and undisturbed samples were analysed for several chemical, physical and morphological soil properties. The selected toposequence commences at the crest with a profile of the Hutton soil form. Soils of the Westleigh, Longlands, Avalon (3), Kroonstad (3) and Estcourt forms follow down slope. The characteristic red colour grades to yellow-brown in the soft plinthic soils on the mid slope and grey duplex soils in the valley bottom. The change in colour dominates morphology in the midslope but changes to be dominated by texture differentiation in the valley bottom. Signs of redox activity prevail across the toposequence and its prominence increases drastically with depth in the profiles and down slope in the catena. Subsoil acidification indicates the presence of an early stage of redox activity. Fe-Mn redistribution, present as mottles and concretions, and colour changes are indications of intermediate redox activity. The texture differentiation present indicates an environment supporting ferrolysis to the full.
Open Access
Sampling and extraction methods for soil inorganic N determination to calibrate the EM38 in irrigated fields
(University of the Free State, 2019-06) Steenekamp, Diandra; Van Rensburg, L. D.; Du Preez, C. C.; Barnard, J. H.
Precise management of N variability in crop fields are required to increase yields and ensure sustainable and economic crop production, whilst not having a negative impact on the environment. A popular type of sensor for characterizing soil variability is the EM38-MK2 that measures apparent electrical conductivity (ECa), operating on the principle of electromagnetic induction (EMI). After analysis, inorganic N results can be calibrated to ECa measurements. It has been established that NH4+-N and NO3ˉ-N can be predicted from ECa. This study presented three main research aims to: i) compare single and composite samples for the determination of NH4ˉ-N, NO3ˉ-N, and total inorganic N (TIN), ii) determine if the saturated paste extract (SATe) could replace the standard 2.0 M KCl extraction for determination of NH4ˉ-N and NO3ˉ-N, and iii) determine what combination of single or composite ECa measurements and inorganic N at different sampling depths would produce the most statistically significant inorganic N prediction model. EMI surveys were conducted on four study sites under centre pivots, located on commercial irrigation farms in the districts of Douglas, Luckhoff, Hofmeyr and Empangeni. Using ECa data with the “Electrical Conductivity Sampling Assessment and Prediction” (ESAP) software and it‟s featured “Response Surface Sampling Design” (RSSD) sampling methodology, soil sampling points were identified based on the degree of ECa variability. Before sample collection, additional ECa readings were taken at each sampling point, one in the centre and one on each corner of a 1 m2 area. Afterwards soil samples were collected in the same manner in 300 mm depth increments up to 1500 mm. Samples collected in the centre were considered single, while those from the corners were composited. Concentrations of NH4+-N and NO3ˉ-N in KCl and SATe soil extracts were simultaneously determined colorimetrically. For the first aim, inorganic N concentrations in KCl extracts was loge transformed and pooled to compare sampling methods irrespective of study site, sampling point, and depth. For the second aim, data of inorganic N concentrations determined in KCl and SATe extracts were transformed and pooled for comparison, irrespective of site, sampling point, sampling method, and depth. The third aim was divided into three parts, determining agreement between single and composite ECa measurements, determining what inorganic N values to use, i.e. what sampling method and extract, and finally model calibration. Statistical analysis focused on assessing agreement using the Bland-Altman method for assessing agreement on a 95% confidence interval and multiple-linear regression calibration models were developed in Microsoft Excel. Results revealed poor agreement between single and composite samples for NO3ˉ-N and TIN. A composite sample taken in a 1 m2 area was more suitable when investigating NO3ˉ-N or TIN. Good agreement was found for NH4ˉ-N and a single sample proved sufficient. Agreement between the two extracts was poor for both NH4+-N and NO3ˉ-N and it was concluded that SATe cannot replace KCl for inorganic N determination. Agreement between single and composite ECa measurements was good and one ECa measurement was sufficient per 1 m2 sampling location. Based on the conclusions from the previous research questions, inorganic N results used for model development were those from composite samples extracted using KCl and an average between the single and composite ECa measurements was used. Values of inorganic N, ECa and elevation were loge transformed. Results showed that the majority of the calibration models were statistically insignificant except for one sampling depth (900 to 1200 mm) at Douglas (ECa 0 to 750 mm; R2=0.54 and ECa 0 to 1500 mm; R2=0.57). It was concluded that for the sites investigated, inorganic N was not the dominant soil property influencing ECa.
Open Access
A small lysimeter system to investigate oxygen and carbon dioxide profiles in soils with water tables
(University of the Free State, 2015-01) Schoonwinkel, Benjamin Christiaan; Van Rensburg, L. D.; Du Preez, C. C.
In South Africa a huge amount of time and energy has been spent on evapotranspiration research over the past 30 years, mainly to predict the amount of plant available water needed to prevent crop stress. In the quest to conserve water losses due to transpiration, researchers tended to neglect the importance of soil-air concentrations in relation with soil water. Rising water tables caused by recharged groundwater through irrigation is one of the most important factors that change soil-air concentrations. For measurements, researchers found lysimeters more convenient due to the fact that they can simulate transient or constant water table conditions, which is otherwise very difficult to study in agricultural fields. The dissertation focuses mainly on the development of a monolith-lysimeter to measure soil water and soil-air regimes under rising water table conditions for different soils. The research was conducted on five soils (sandy Hutton, loamy-sand Hutton, Bainsvlei, Sepane and Valsrivier) sampled in small (200 kg) lysimeters. A disturbed and undisturbed Bainsvlei soil was sampled at the experimental farm of the Department of Soil, Crop and Climate Science (University of the Free State) at Kenilworth in the Bloemfontein district while the remaining four undisturbed soils were sampled at the Orange-Riet River Irrigation Scheme. A total of 6 lysimeters was arranged in the glasshouse of the University of the Free State located on the main campus in Bloemfontein, South Africa. The aim was firstly to develop and test a small weighing-lysimeter system for measuring soil temperature, soil water and soil air (oxygen and carbon dioxide) responses under water table conditions in a disturbed and undisturbed Bainsvlei soil monolith. These monolith lysimeters were used to characterize the influence of the lysimeter compared to in situ data that determined the accuracy of the method. After saturation of the soils with de-aired water from the bottom, drainage curves were determined by measuring weight-loss with both a weighing bridge and a capacitance DFM probe. Results showed that the shapes of the drainage curves for both the disturbed and undisturbed soils were similar due to the similarity of the easily drainable pores. However, the water retention was significantly lower in the undisturbed soil compared to the disturbed soil. Furthermore, a water-table height control system was used for both raising, and to keep the water table steady at three heights while soil air measurements took place. According to the results it was found that an undisturbed soil is better to use for studying O2 and CO2 concentrations in soils. This conclusion is supported by the results which showed the sampling method with disturbed soil induced significantly higher O2 and lower CO2 concentrations, respectively compared to that of the undisturbed soil. Overall, the results indicated that the proposed small weighing-lysimeter system contribute towards the understanding of a very important subject, namely soil aeration. Secondly, the monolith-lysimeter technique developed was used to evaluate five undisturbed soils in their O2 and CO2 response to a rising water-table over a period of 6 days. The water table was set at each height for six consecutive days for measurements where after it was raised to the next height. It was found that the O2 and CO2 concentration profiles were significantly influenced by the rise in water-table heights for the five soils under investigation. However, there were some distinct differences in the gas profiles observed between the sandy soils (sandy Hutton, loamy-sand Hutton and Bainsvlei) compared to the clay soils (Sepane and Valsrivier) due to differences in physical composition. The results further showed that time had significantly influenced O2 and CO2 concentrations over the 6-day period. As O2 concentrations gradually decreased, CO2 concentration gradually increased for all five soils. The only difference between the two soil groups was the intensity of respiration that resulted in lower O2 and higher CO2 concentrations for the clay soil group than for the sandy soil group over the 6 day period.