Masters Degrees (Soil, Crop and Climate Sciences)
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Item Open Access Agroclymatic characterization of Lesotho for dryland maize production(University of the Free State, 2004-11) Moeletsi, Mokhele Edmond; Walker, Sue; Barker, Charles H.Agro-climatic characterization of Lesotho for dryland maize farming was performed using temperature and rainfall indices in a GIS environment. The temperature and rainfall meteorological parameters were patched for missing data using the UK method for the maximum and minimum temperatures. Missing daily rainfall data was patched using the inverse distance method. Statistical evaluation of the patching methods showed good performance. The spatial distributions of different temperature variables and indices were mapped. Important meteorological parameters were the frost occurrence (first day, last day and duration) and monthly and seasonal heat units. The onset of frost is early (March) over the highland areas while the low- lying areas onset can be as late as June. The last day of frost over the low- lying areas is mostly in August and on the other hand, the highlands last day of frost is in November/December at some places. Rainfall interpolation was done using the kriging method of the geostatistical analyst. Important aspects mapped include monthly averages, seasonal amounts, annual amounts and number of days of high daily rainfall. Wet season (October to April) rainfall was high (>800mm) over the north to northeastern parts of the country while some areas over the east and southern parts received less than 500mm of seasonal rainfall. Climatic potential of maize under dryland farming in Lesotho was investigated using five climatic suitability indices namely: probability of receiving heat units of greater than 1500GDD, probability of a frost-free growing season, probability of seasonal rainfall of more than 500mm, probability of 15-day dry spells during December to February and the slope of an area. For each of the above parameters a coverage layer was prepared in GIS environment and the layers were overlaid to obtain the agroclimatic suitability map of maize in Lesotho. The districts of Butha Buthe, Leribe and Berea are shown to have areas which are highly favorable for maize cultivation under dryland farming while the unsuitable areas are mostly over the high- lying areas (Mokhotlong, Thaba Tseka and Qacha’s Nek) together with other parts of the southern lowlands.Item Open Access Besproeibaarheid van gestruktureerde gronde(University of the Free State, 1991-11) Nell, Johannes Petrus; Bennie, A. T. P.Afrikaans: Data van 333 profiele se fisiese (breukmodulus, infiltrasie, hidrouliese geleivermoë, lugwaterdeurlatendheidverhouding, waterretensie en Atterberggrense), chemiese (KUK, UNP, NAV, pH, elektriese weerstand, elektriese geleivermoë, Fe-SBD, Al-SBD en organiese koolstof) , morfologiese (grondkleur, struktuur, kleiverhoudings en slik tot kleiverhoudings) en kleimineralogiese eienskappe was gebruik om neokutanies, pedokutanies, prismakutanies, rooi gestruktuurde en vertiese gronde te karakteriseer. Gronde van 15 dreineringstreke is in die ondersoek gebruik. Klem word egter op kalkryke gronde in die Sondagsrivier-, Klein-Visrivier- en Groot-Visrivierdreinerings- gebied geplaas, aangesien heelwat van die gronde deur verdere ontwikkeling van die Oranjerivierprojek geraak word. Daar bestaan regverdiging om verskille tussen diagnostiese horisonte as besproeiingsnorm te gebruik, aangesien duidelike fisiese en chemiese verskille tussen grondvorms, binne dreineringsgebiede voorkom. Daar is 'n afname in die geskiktheid van gronde vir besproeiing met 'n toename in graad van struktuurontwikkeling. Dit kan hoofsaaklik toegeskryf word aan 'n toename in opbou van skadelike soute en 'n verskuiwing van 'n oorwegend illietiese kleimineraalsamestelling na 'n smektietiese samestelling wat tot swelling en/of dispersie aanleiding gee. Laer infiltrasie en hidrouliese geleivermoë waardes, met 'n toename in struktuurontwikkeling, kan grootliks hieraan gewei word. Alhoewel die Na-inhoud ook 'n rol speel by die strukturele eienskappe van vertiese en rooi gestruktuurde gronde, het die tipe en hoeveelheid kleiminerale en seskwioksiedes 'n duideliker invloed by dié gronde se struktuurstabiliteit. Daar bestaan egter nie regverdiging om kleur volgens seriedifferensiasie as besproeiingsnorm by pedokutaniese gronde te gebruik nie. Die stabiliserende effek van die ysteroksiedes wat vir rooi grondkleur verantwoordelik is, word egter in sommige dreinerings- gebiede oorbeklemtoon. Die soort en hoeveelheid soute tesame met die tipe kleiminerale het 'n meer dominante invloed op hierdie gronde se struktuurstabiliteit. Die groot variasie in hidrouliese eienskappe van gestruktuurde gronde kan moontlik beter verstaan word, indien die beskrywing van die graad, tipe en grootte van die struktuureenhede met spesifieke parameters gekwantifiseer kan word. Die oorgang tussen horisonte is ook van belang. By dupleksgronde kom daar in die algemeen 'n drastiese afname in infiltrasie van die A- na die B-horisonte voor. Die lae infiltrasievermoë van die B- horisonte veroorsaak dat horisontale infiltrasie tot 'n groter mate as vertikale infiltrasie plaasvind. Aansienlike interkorrelasie tussen fisiese, chemiese en kleimineralogiese eienskappe kom voor wat tot lae verwantskappe aanleiding gee. Indien gronde egter in pedologiese eenhede gegroepeer word en die korrelasies vergelyk word, kan sommige daarvan verhoog of beter verstaan word.Item Open Access Biokatalitiese komponente in sade van enkele spesies uit die families Fabaceae en Caryophyllaceae(University of the Free State, 2002-11) Du Plessis, Helena Aletta; Pretorius, J. C.; Potgieter, G. P.English: In the south of Germany it was observed that species of the families Fabaceae and Caryophyllaceae survived an unknown environmental catastrophy while this was not the case with plant species from other families (Huster, Personal observation). Seed suspensions of some species belonging to these two families were applied to agricultural crops as foliar sprays, improving both the vegetative growth and yield of the crops. This supplied the rationale to test the seeds of South African species from these two families for its biocatalytic properties. Seeds of two species from each of the mentioned families namely Acacia karroo and Acacia erioloba from the family Fabaceae as well as Pollichia campestris and Dianthus basuticus from the family Caryophyllaceae, were subsequently screened for similar biocatalytic properties. Not much information on the chemical composition of these four plant species and nothing at all about their biocatalytic activity could be found in literature. In the study that followed biocatalytic activity was confirmed in a seed suspension of Acacia erioloba (Fabaceae) as it increased the respiration rate of a mono culture yeast cells as well as root growth of Cress-seedlings markedly. Activity directed liquid-liquid extraction of the A. erioloba seed suspension revealed that most of the biocatalytic activity was present in the ethyl acetate fraction. Further column chromatographic fractionation of the ethyl acetate fraction produced 13 combined column fractions of which two were active. Activity directed preparative thinlayer chromatographic purification of compounds in one of these fractions produced one active compound that was identified as 2-ethylhexylphtalate by means of nuclear magnetic resonans (NMR) spectroscopy. From the second column chromatography fraction six compounds were isolated but in such small amounts that NMR analysis was not possible. By means of colour reagents it was, however, established that three of the six compounds were alkaloids, two were terpenoides and one a coumarin. It is recommended that active components in this group should be identified in a follow-up study by initially extracting much more seed material.Item Open Access Characterization of Yr15 resistance to stripe rust of wheat(University of the Free State, 1999-12) Kotzé, Pieter Malan; Pretorius, Z. A.; Spies, J. J.; Viljoen, C. D.English: Stripe (yellow) rust, caused by Puccinia striiformis Westend f. sp. tritici, is a major disease of bread wheat, Triticum aestivum L., in South Africa. The objective of this study was to evaluate the Yr15 gene as a potential resistance source for breeding purposes. Histological evidence was provided that Yr15 conditions a hypersensitive reaction typical of non-durable resistance. Fluorescence, phase contrast and scanning electron microscopy complemented each other and may be used to quantify various aspects of resistance expression in the wheat stripe rust pathosystem. The frequency of stomatal penetration was extremely low and no meaningful differences in early infection structures were observed between the resistant Yr15 and susceptible Avocet 'S' lines. Papillae were not involved in the resistance response to pathotype 6E16. In studies of defense-related proteins, an induction of β- 1,3-glucanase activity in both resistant and susceptible wheat genotypes was detected within 96 h post-inoculation (hpi). This induction, however, was constitutive and did not depend on the infection process. Likewise, no changes in chitinase activity were observed between resistant and susceptible plants. A pronounced increase of peroxidase activity between 0 and 168 hpi, in both infected and uninfected resistant and susceptible plants was observed, suggesting a constitutive expression of this enzyme. Using AFLP (Amplified Fragment Length Polymorphism) technology to detect possible molecular markers for Yr15, two primer combinations yielded polymorph isms between the bulked susceptible and resistant SST55 x Yr15/6*AvS F2 DNA, as well as between the susceptible and resistant parents. Fragment sizes ranged from 50 to 420 bp. Of these, one 95 bp fragment identified using primers MseCAA + Eco-ACA and one 205 bp fragment identified using primers MseCAA + Eco-AAC were detected in the resistant parent and the resistant F2 group. This indicates that these fragments are closely associated with Yr15 making them ideal candidates for further investigation.Item Open Access Chemical factors influencing dry bean yield(University of the Free State, 2000) Molahlehi, Lebone; Pretorius, J. C.; Ceronio, G. M.English: The abscission of the reproductive organs (flower buds, flowers and pods) of the common bean, Phaseolus vulgaris L., has proved to be a very serious problem affecting bean yields. The yield reductions are mainly significant under conditions of environmental stress, which aggravate production of the abscission causing hormones such as ethylene. The study therefore evaluated the effect of certain nutrients, other chemicals and ethylene (growth regulator) applied as foliar sprays to determine their effect in as far as abscission of the reproductive organs in beans is concerned. Glasshouse trials were carried out during the 1998/99 and 1999/00 seasons to investigate the possible preventative role of some micro and macro-nutrients, abscission inhibitors (e.g. Silver) and growth regulators (e.g. ethylene) all applied as foliar sprays. In another trial, three cultivars were compared where no treatments were applied. Data were collected and the following parameters were measured; number of flowers and pods that abscised, pods formed and abscised, pods that matured and could be harvested, dry pod mass at harvest, seed number per pod, dry seed mass per pod and total yield per hectare. Data were analyzed using a SAS software system and interpreted accordingly. The results of this study indicated that flower and pod formation might not be considered as the major factor affecting bean yields. The reason being that flowering percentage was not very different between the treated and the untreated plants. The abscission of flower buds, flowers and pods, however, was relatively high in general, indicating that this is possibly a primary factor affecting poor yields in beans. Ethrel, an ethylene releasing compound, applied as a foliar spray, aggravated the problem of flower and pod abscission. An ethylene antagonist (silver salt) had a slight alleviating effect on organ abscission but did not improve the final yield significantly. Molybdenum and potassium salts improved flower formation to a certain extent but had no real alleviating effect on organ abscission. This was also revealed in the lack of yield improvement. Foliar application of a copper salt as well as treatment with ComCat®, a natural product with biocatalytic properties, did not influence flower and pod abscission significantly, but increased the final yields to some extend. The latter indicates that other factors besides organ abscission could have had an effect on determining the final yield outcome. In the light of these findings, it is suggested that further studies be undertaken to test a wider range of chemicals for their potential to circumvent flower and pod abscission and improve bean yields. The latter could also include treatment at other growth stages, including post flowering. Other attempts could include an investigation into the effect of other known ethylene antagonists such as AVG (L-a.-(2-arninoethoxyvinyl)-glycinehydrochloride), an inhibitor of ethylene synthesis and NBD (2,S-norbornadiene), an inhibitor of ethylene action, on organ abscission and yield outcome in beans. As the results also showed that other factors besides organ abscission could have played a role in yield improvement, it might be worthwhile to investigate the effect of promising chemicals on physiological processes.Item Open Access The compaction susceptibility of soils in the Free State(University of the Free State, 1998-12) Nhantumbo, Alfredo Bernardino Julio Da Costa; Bennie, A. T. P.Crop production in the Free State is mainly performed on sandy soils. The compaction of these apedal soils can present a management problem which affects crop yields and financial returns. In addition, environmental problems such as soil erosion and siltation of rivers may result. The main objective of the study was to see whether the easily measured soil properties, texture and organic matter, could be used to classify the compact ion degree of soils and to predict their compaction susceptibility. Additional objectives were to define critical densities beyond which crop growth would be impeded, to test the applicability of the relative bulk density concept proposed by Bennie & Van Antwerpen (1988) and to propose a procedure for the prediction and classification of the compactibility of the soils in the Free State. Finally, the results were compared to the data from forestry soils (Smith, 1995) for more humid conditions. Twenty two (22) samples of selected soils covering a large range of soil texture variation were submitted to a determination of the maximum bulk density (using the Proctor test), minimum bulk density, uniaxial compression test and penetrometer resistance measurements. A procedure for the determination of minimum bulk density was developed. Good quadratic relationships were obtained between the maximum bulk density and silt plus clay or organic matter content as loss on ignition. The minimum bulk density can be predicted from the silt plus clay percentage or loss on ignition. When the actual bulk density and the silt plus clay or loss on ignition percentages are available, the relationships allow the estimation of maximum and minimum bulk densities. The measured bulk density can then be used to calculate the relative bulk density of a soil. Threshold relative bulk density classes (5) were derived which can be used to evaluate the degree of denseness or looseness of the soil, and its suitability for different applications. It is proposed that compactibility be regarded as the difference between the maximum and minimum bulk densities, instead of simply the maximum bulk density. Different classes of compactibility were derived. The compression index of all the soils at the critical water content showed good relationships with the silt plus clay, clay or organic matter contents of the soils. Compressibility classes were also established. A combination of the compactibility and compressibility of soils was used to determine its susceptibility to compaction. Compaction susceptibility was classified into five groups varying from very low to very high degrees of susceptibility for apedal soils. The data set from this study when combined with the data reported from the study of forestry soils by Smith (1995), made it possible to derive equations with a more universal applicability for the prediction of the maximum and minimum bulk densities, critical water content as well as compression index. The results from this investigation, when properly transferred in popular terminology set guidelines for the evaluation of the degree of compactness and compaction susceptibility of soils. These guidelines will allow persons responsible for soil evaluation to draw more meaningful conclusions from bulk density measurements.Item Open Access Comparison of field and laboratory measured hydraulic properties of selected diagnostic soil horizons(University of the Free State, 2009-11) Chimungu, Joseph Gregory; Van Rensburg, L. D.; Hensley, M.An adequate characterization of soil hydraulic properties is a necessary solution for agriculturally and environmentally oriented problems such as irrigation, drainage, runoff and pollutants movement. The three approaches to determine hydraulic properties of soils are field measurements, laboratory measurements and mathematical models. In situ measurements, though representative, have the inherent limitation of being costly and time consuming. Laboratory and mathematical techniques are more convenient but require extensive comparison to field results as bench mark for evaluation. The objective of this study was to characterize the hydraulic properties of Bainsvlei and Tukulu form soils utilizing the above mentioned three approaches and to compare the results. The laboratory methods selected were hanging water column and pressure plate apparatus. Undisturbed soil samples were used to determine θ-h relationships at 0-100 kPa suctions and disturbed soil samples up to 1500 kPa. The water retention characteristics for both soils were generally well defined with little variability between replicates. The main variations were due to texture differences between the horizons. The θ-h relationships were used to estimate textural and structural domains using empirical pore class limits and derivative curves. The suction value separating the structural domain from the textural domain varies from horizon to horizon. The boundary between soil pore categories cannot be taken as a fixed value for all soils and all types of soil use. The measured water retention data corresponded well with the fitted curve via the van Genuchten (1980) model, indicating that the model can be successfully used to describe θ-h relationships for Bainsvlei and Tukulu soils. Soil water sensors were calibrated using undisturbed soil samples in climate controlled room for five horizons of a Bainsvlei form soil and three horizons of a Tukulu form soil. Soil water sensors and circuitry show extremely low sensitivity to temperature fluctuations. Horizon specific calibration is essential to get accurate water content estimates from the sensors if used in different soil horizons. Our study demonstrate that horizon specific calibrations of the water sensors improves the accuracy of soil water content monitoring compared with the manufacturer‟s generic calibration equation for the soils tested in this study. Hydraulic conductivity was obtained by measuring the hydraulic head and water content of the Bainsvlei soil form in situ with tensiometers and horizon specific calibrated ECH2O EC-20 probes, respectively. The profile was characterized with several relations of hydraulic conductivity and varied with depth. The reason for this was attributed to heterogeneous nature of the profiles due to variation in particle size distribution. The van Genuchten (1980) model laboratory method was used to predict K-θ relationships utilizing laboratory determined θ-h relationships. The K-θ relationships predicted from the θ-h relationships of the soil cores corresponded well with those determined by the instantaneous profile field method for water contents which they have in common. Thus it appears that this laboratory method is applicable to the soils studied, but the accuracy of the predicted values is quite sensitive to the matching factors. Thus, accurate measurement of these parameters is necessary for its successful use. The instantaneous profile field method is regarded as a reference method to measure in situ unsaturated hydraulic conductivity for both homogenous and layered soils (Hillel et al., 1972). There are, however, several site or profile characteristics that may limit this method (Bouma, 1983). Our studies show that it is not applicable on duplex soils with slow permeable C-horizons i.e. the Tukulu form profile at Paradys, because of negative hydraulic gradients within the profile due to impaired internal drainage. There is a need to adapt this method to duplex soils. Overall results indicate that from a practical perspective, the prediction of K-θ relationship from laboratory determined water retention data can be a viable alternative for determining the hydraulic properties of diagnostic horizons. The prediction of DUL using θ-h relationship has been found to be satisfactory.Item Open Access Conceptual hydrological response models of selected arid soilscapes in the Douglas area, South Africa(University of the Free State, 2016-02) Tinnefeld, Martin; Le Roux, P. A. L.; Van Tol, J. J.The conceptual hydrological response model (CHRM) is a powerful tool, able to transfer hydrological information of hillslopes. Soil, a first order control of partitioning of water flow, is often the only source of information of hillslope water flowpaths and storage mechanisms. Conceptual hydrological models applied at different scales, serve as the framework to understand and structure the hydrological response of sites, hillslopes and catchments. They complement decision making and planning of natural resource allocation and delineation for land-use change in ecology, agriculture, mining and urbanisation. Soil morphology, chemistry and hydrometrics are used singularly and complimented in combination as indicators and controllers of hydrology to construct CHRMs. The more accurate the input parameters of soil morphology, chemistry and hydrometrics, the more accurate the final CHRM. Arid soils of South Africa have been neglected to be investigated for their hydrological properties. This is due to the low rainfall, infrequent hydrological response and resulting low output of data. Where such hydrological studies have been performed under higher rainfall climatic zones, soil has been found to respond as a store and conduit of water. These are referred to as storage mechanisms and flowpaths within the soil and can be determined by studying the soils’ morphology, improved by soil chemistry and are verified by application of hydrometrics. Soil distribution patterns are not random and are influenced by hillslope hydrology. The vastness of the arid regions of South Africa, make it difficult to select singular representative hillslopes. However, by describing the soil distribution patterns of randomly distributed detailed soil maps within different land types, allowed for soil distribution trends to be identified in this study. These soil distribution trends were seen to coincide with terrain morphological units. Representative modal profiles were selected on dominant and representative terrain morphological units of 4 different land types on criteria that they are representative soils of the land type and sites. The soils have well developed horizons resulting in vertical pedological variation including different degrees of carbonate precipitation. Methodology of other research, to interpret morphology in higher rainfall regions of South Africa, was used to construct a conceptual hydrological response model for the arid hillslopes and the region in general. Hydrological properties of modal profiles, were used to confirm the concepts. A class 1 hillslope hydrological response: soil/bedrock interflow to wetland; dominates on all four sites. Individual sites and their respective soil distribution patterns showed fast pedon recharge to the soil/rock interface. Pedon interflow at higher lying topographical positions with associated steeper slope, contributed to carbonate as dominating morphological flowpath indicator lower lying in the landscape. This is primarily driven by a low rainfall/high evapotranspirative demand of arid climates. Topographically lower lying soils showed reduced infiltration due to high alluvial clay and silt deposits and/or soil matrix saturation with carbonate precipitation sufficient to reduce the permeability of the soil.Item 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.Item Open Access Development of an index for wheat stripe rust infection(University of the Free State, 2001-11) De Wet, Linda; Walker, S.; Pretorius, Z. A.English: The main objective of this project was to develop an early warning index for infection of stripe rust (Puccinia striiformis f. sp. tritici) in susceptible cultivars of wheat (Triticum aestivum) for the main wheat growing areas of the R.S.A. Various authors are in agreement that temperature and moisture are the major climatic factors necessary for infection by stripe rust. Temperature limits from the literature vary between -4 and 30°C and no cut-off values were available. It was therefore decided to run an experiment to observe infection of stripe rust under conditions of high relative humidity and a range of temperatures, namely 5°C, 10°C, 15°C and 20°C. Results from the experiment indicated that little or no infection occurred for the 20°C temperature level and for exposure time periods of one hour or less. Exceptions occurred when sudden drops in temperature with removal of plants from growth chambers to the glasshouse took place. For both incidence and severity, it was found that temperatures greater than 22°C inhibited infection. The Pan 3349 cultivar was found to exhibit higher incidence than Karee. The statistical analysis shows significance for severity for Experiment 1 and 2, but not for incidence. Temperatures for Experiment 2 were slightly lower than those in Experiment 1 and could be explained by the presence of the fans in Experiment 2, to allow evaporation of dew from the sensors, allowing the sensors to register correct readings. The resulting higher moisture conditions in the still air In Experiment 1 could have contributed to the higher severity observed in Experiment 1. Conditions in the laboratory are not the same as in the field and possibilities for infections at higher temperatures in the field have been reported by Park (1990). He warned against extrapolation of results from the laboratory to the field, but it was nevertheless decided to use the results from the experiment as a basis for the development of an index for stripe rust infection of susceptible wheat cultivars in South Africa. Values of 14 day total degree days (TDDI4) were calculated from total degree hours (TDH) acquired from the experiment. TDDl4 for the experiment was calculated by summing degree days (DD) from inoculation until 14 days and relating them to average incidence observed on day 14. Two linear regression lines were obtained, one for 5°C 15°C temperature level and the other for the 15 °c - 20°C temperature levels. A cut-off TDDl4 value of 227 where the two lines crossed indicated 67 % cut-off value for incidence. TDDl4 was developed from this information and reads as follows: IfTDDI4> 227, then risk of incidence is low at < 67 %. IfTDDl4 < 227, then risk of incidence is high at > 67 %. TDDl4 was validated by testing on 1996 - 1998 and 1999 - 2000 data. Correct prediction values for highest and average incidence observation were 50 % and 29 % for 1996 - 1998 data (Table 4.7) and 40 % and 33 % for 1999 - 2000 data (Table 4.8). TDDl4 however, was thought to be impractical, so TDD7 was developed by using TDD7 for 7 days from a wet period. TDD7 = 128 was found to be 1.77 times less than the value for TDDl4 = 227 and so this value of 128 was used as the cut-off value. TDD7 thus reads as follows: If TDD7 > 128, then risk of incidence is low at < 67 %. If TDD7 < 128, then risk of incidence is high at > 67 %. TDD7 was validated using the 1999 - 2000 data, with total correct predictions of 53 % and 40 % (Table 4.10). It was therefore decided that TDD7 could be used by the producer as an early warning index, although the index would have to be tested in the field so that necessary improvements could be made. It is recommended that research on stripe rust-environment interaction be continued, also to include other diseases and the recommendations made in Chapter 2. Another possible recommendation would be to plan a refined laboratory experiment with a mechanistic approach to use a constant temperature data determined model in real life situations. Temperature and RH would vary and the results should be useful to producer, as well as the researcher. A model suitable for various other diseases as well, could be of great benefit when the cost of pesticides and fungicides are taken into account. The successful application of such a model would be of great benefit to all. After all, food is our fuel and sustainable production of high quality foodstuffs is essential to our survival.Item Open Access Downscaling of global circulation model predictions to daily rainfall over the upper Olifants River catchment(University of the Free State, 2008) Steyn, Abraham Stephanus; Walker, Sue; Engelbrecht, Francois A.English: Climate change could have far reaching consequences for all spheres of life. Continued greenhouse gas (GHG) emissions at or above current rates will cause further warming and induce further changes in the global climate system. This is particularly true for southern Africa where an ever-increasing population is already causing an increase in the demand for fresh water and much of the agricultural food production depends on rain. Global Circulation Models (GCMs) are the main source of climate projections under varying GHG emission scenarios. The spatial resolution of GCMs is too coarse to resolve sub-grid processes such as convection and precipitation. However, agrohydrological application models often require information at a network of point locations, implying the need to downscale the GCM output. Downscaling approaches have subsequently emerged as a means of employing large-scale atmospheric predictor variables (such as the 500 hPa meridional velocity) to develop station-scale meteorological series. Variables such as daily rainfall, which are not always accurately represented by the GCMs, can be derived using statistical approaches to build relationships between the required forecast parameter and variables that are simulated more accurately. Previous investigators have used the statistical downscaling model (SDSM) to downscale climate projections of daily rainfall over North America and Europe. A similar methodology was adopted to downscale daily rainfall projections under the A2 and B2 emission scenarios at five selected quaternary catchments (QCs) within the Upper Olifants River catchment. The downscaling was performed for the summer months of December, January and February (DJF). The set of generic predictors which were identified across all five QCs included surface airflow strength, vorticity, divergence and specific humidity, 850 hPa wind direction and relative humidity as well as 500 hPa relative humidity and meridional wind velocity. Generally, all the predictors exhibited a reasonably low explanatory power. The considerable variation in the resultant correlations between the large-scale predictors and the observed daily precipitation at the selected QCs may very well have stemmed from the convective nature of the rainfall patterns, being irregularly distributed in space and time. Generally, the downscaling model results were not very encouraging as the model failed to produce satisfactory results for four of the five QCs. For one of the QCs, namely Groblersdal, the projected changes for the future climate were assessed by calculating several delta-statistics. Only a few of the indices revealed a clear change, while most indices exhibited inconsistent changes for DJF across three future periods centred on the 2020s, 2050s and 2080s. Similar changes in the characteristics of the daily rainfall series are projected for the early and mid 21st century under the A2 and B2 scenarios. Differences in the expected GHG forcing under the B2 scenario does not seem to affect any of the rainfall indices differently from the A2 scenario until the late 21st century. It should however be noted that the projected changes are often smaller than the model errors which implies that the downscaling model is simply not sensitive enough for the projected changes to be taken at face value. Therefore the results should only be used with caution. The fact that the downscaling procedure provides similar results for the A2 and B2 scenarios suggests that it is at least to some extent robust and stable.Item Open Access The effect of crop residue cover and soil texture on crusting(University of the Free State, 2002-10) Massingue, Felicidade Isabel; Bennie, A. T. P.Large areas of cultivated soils throughout the world develop rainfall-induced soil crusts. The soil crusts are usually the cause of reduced seedling emergence. To have quantitative information on the factors influencing the development of surface crusts and on the influence of ameliorating treatments on crust strength is valuable. The objectives of this study were firstly, to determine the influence of soil texture on the susceptibility of different soils for crusting; secondly, to quantify the effect of soil crusts on the emergence of wheat, sorghum, soybean and sunflower; and thirdly to determine the optimum level of crop residues that can be used as a mulch to mitigate the effect of soil crust strength. Five soils ranging in texture from sand to loam were sampled from the surface (0 - 200 mm). The soil samples were used in four greenhouse pot experiments that were conducted to examine the effect of crust strength on seedling emergence. Separate pot experiments in the greenhouse were conducted to determine how particle size distribution was related to soil crust strength. Regression analyses showed that silt, silt plus clay and clay contents were related to crust strength as indicated by modulus of rupture, penetration resistance and emergence force. All the relationships were of third order polynomial nature. The crust strength increased initially with increasing silt plus clay contents up to about 35 to 40 %, or clay contents up to about 25 %, then declined as a result of cracking that occurred upon drying. The emergence of wheat, soybean and sunflower was little affected at crust strengths less than 0.7 Mpa or 500 gf when measured as penetration resistance and emergence force respectively. Above these values seedling emergence decreased linearly with increasing crust strength. Large areas of cultivated soils throughout the world develop rainfall-induced soil crusts. The soil crusts are usually the cause of reduced seedling emergence. To have quantitative information on the factors influencing the development of surface crusts and on the influence of ameliorating treatments on crust strength is valuable. The objectives of this study were firstly, to determine the influence of soil texture on the susceptibility of different soils for crusting; secondly, to quantify the effect of soil crusts on the emergence of wheat, sorghum, soybean and sunflower; and thirdly to determine the optimum level of crop residues that can be used as a mulch to mitigate the effect of soil crust strength. Five soils ranging in texture from sand to loam were sampled from the surface (0 - 200 mm). The soil samples were used in four greenhouse pot experiments that were conducted to examine the effect of crust strength on seedling emergence. Separate pot experiments in the greenhouse were conducted to determine how particle size distribution was related to soil crust strength. Regression analyses showed that silt, silt plus clay and clay contents were related to crust strength as indicated by modulus of rupture, penetration resistance and emergence force. All the relationships were of third order polynomial nature. The crust strength increased initially with increasing silt plus clay contents up to about 35 to 40 %, or clay contents up to about 25 %, then declined as a result of cracking that occurred upon drying. The emergence of wheat, soybean and sunflower was little affected at crust strengths less than 0.7 Mpa or 500 gf when measured as penetration resistance and emergence force respectively. Above these values seedling emergence decreased linearly with increasing crust strength.Item Open Access Effect of liquid Maxiflo (Azospirillum SPP) and Trykoside (Trichoderma SPP) cultures on the growth and yield of selected crops(University of the Free State, 2006) Mashamba, Nwagu Rodney; Pretorius, J. C.; Engelbrecht, G. M.English: The challenge for science is to address the need for adequate food provision and a sustainable future for agriculture. The solution for increasing food production can probably only be obtained through expansion of arable land, by increasing irrigation practices or by increasing harvestable yields on available land through the improvement of agricultural technology. With regard to the latter approach, field experiments were conducted at the experimental farm of the University of the Free State, Bloemfontein, during the 2003 and 2004 growing seasons, to determine the effect of Maxiflo and Trykoside (liquid formulations of Azospirillium and Trichoderma based products, respectively) on vegetative growth and yield of two leafy vegetable crops (cabbage and lettuce), a cereal crop (wheat), a fruit crop (tomato), a tuber crop (potato) and a legume crop (peas). A randomized complete block design with six treatments (Control, Maxiflo, Trykoside, Maxiflo + Trykoside, ComCat® and Ke/pak®) was applied in all cases. Maxiflo and Trykoside were applied either separately or together. Two commercially available natural bio stimulants, ComCat® and Ke/pal<®, served as positive controls. Different growth and yield parameters were used to quantify the effect of the test products in the above six economically important crops. In cabbage and lettuce vegetative growth (plant height, plant diameter and stem thickness) were not affected but a significant increase in head mass was observed. Peas were most responsive to treatment with the bio-products in terms of the increase in yield obtained. Treatment with Maxiflo and Trykoside in combination increased the medium/large and large size fruit yield in tomatoes while exactly the same was observed for tuber size in potatoes. However, in both crops the total yield was not significantly affected. In wheat root growth was stimulated significantly by treatment with Trykoside but no significant yield increase was observed at the 5% probability level (P<0.05).Item Open Access The effect of nitrogen fertilisation on the growth, yield and quality of swiss chard (Beta vulgaris var. cicla)(University of the Free State, 2008-05) Motseki, Pontso Christina; Engelbrecht, G. M.; Ceronio, G. M.English: The sustainability of subsistence farming associated with the health of rural communities’ necessitated research on Swiss chard as it forms an integral part of food consumed by the poor in developing countries. Two separate pot experiments were carried out during the 2005/06 and 2006/07 seasons in the glasshouse of the Department of Soil, Crop and Climate Sciences at the University of the Free State. The objective of this study was to determine the effect of nitrogen fertiliser on growth, yield and quality of Swiss chard. The first pot trial was conducted to evaluate the effect of five nitrogen levels (0, 50, 100, 200, 400 kg N ha-1) and four application times on the growth, yield and quality of two Swiss chard cultivars (‘Fordhook Giant’ and ‘Rhubarb’). Two Swiss chard seedlings were planted per pot, filled with topsoil of the fine sandy loam Bainsvlei form. Two weeks after planting plants were thinned to one seedling per pot. Different nitrogen levels were applied to the relevant pots as follows: once every second, fourth, sixth or eighth week. It was only the total dry mass per plant and total nitrogen content per leaf of ‘Rhubarb’ plants that was significant higher than that of ‘Fordhook Giant’. The other parameters measured for the two cultivars did not differ significantly from each other. Nitrogen levels positively influenced the early growth, yield and quality parameters measured. It was the highest nitrogen level (400 kg N ha-1) that resulted in the highest number of leaves harvested, leaf fresh and dry mass, leaf area and leaf nitrogen content. Nitrogen application times significantly influenced only the early growth of Swiss chard plants and the nitrogen content of leaves. Early plant growth reacted better where nitrogen was split into three equal applications (T4). The total nitrogen content of Swiss chard leaves was significantly higher where nitrogen was split into five equal (T2) or three equal (T4) applications. In the second pot trial the effect of different nitrogen sources applied at different levels on the growth, yield and quality of Swiss chard cultivars was determined. The response of Swiss chard plants to nine nitrogen levels (0, 100, 200, 300, 400, 500, 600, 700, 800 kg N ha-1) from six different nitrogen sources (ammonium nitrate, potassium nitrate, calcium nitrate, ammonium sulphate, urea ammonium nitrate and urea) were studied. Based on the findings of this study, nitrogen significantly influenced growth, number of leaves harvested, leaf fresh and dry mass, leaf area and leaf nitrate content of ‘Fordhook Giant’ plants with best results obtained at 800 kg N ha-1. Nitrogen sources did not influence either the total number of leaves harvested nor the fresh mass of harvested Swiss chard leaves. In both cases, ammonium nitrate gave the best results and calcium nitrate the poorest. Urea influenced the leaf area positively followed by urea ammonium nitrate, with calcium nitrate resulting in the smallest leaf area per plant. Dry mass of Swiss chard leaves was also significantly higher where urea was used as nitrogen source compared to where calcium nitrate was used. No significant differences amongst the other nitrogen sources. Ammonium nitrate and potassium nitrate significantly stimulated the accumulation of nitrate in Swiss chard leaves, whereas the other nitrogen sources did not play any role in nitrate accumulation in the leaves of Swiss chard.Item Open Access The effect of plant population and mulching on green pepper (Capsicum annuum L.) production under irrigation(University of the Free State, 2010-11) Hatutale, Gervasius; Engelbrecht, G. M.; Van Rensburg, L. D.English: Green pepper (Capsicum annuum L.) is gaining popularity and the production and consumption thereof is increasing worldwide. Semi-arid regions are characterized by variable and unreliable rainfall which necessitates the use of irrigation for sustainable green pepper production. In this study two field trials were conducted. Objectives of the first trial were to quantify the effect of irrigation and plant population on the growth and yield of green pepper and to optimize its plant population for different water regimes. Four water treatments, full irrigation (781 mm), 70% of full irrigation (627 mm), 40% of full irrigation (497 mm) and dryland (303 mm) and five plant populations (17 689, 23 674, 29 526, 34 979 and 41 496 plants ha-1) were used in this trial. A line source sprinkler irrigation system was used for water application. The trial layout was a split plot design with water applications as main treatments and plant populations as sub-treatments. All treatment combinations were replicated four times. The full irrigation and 40% of full irrigation treatment increased marketable yield with 274% and 162%, respectively. The 70% of full irrigation treatment increased marketable yield with 253%. The marketable yield of all irrigation treatments was significantly higher than that of the dryland treatment. The full irrigation’s marketable yield was however also significantly higher than that of 40% of full irrigation treatment. The optimum plant population for all water treatments, excluding 40% of full irrigation was not reached in this trial because the yield of plant populations (17 689 to 41 496 plants ha-1) used did not reach a turning point, but still increased linearly beyond 41 496 plants ha-1. The objective of the second trial was to quantify the effect irrigation and mulching on yield, water use and water use efficiency. Four water treatments, full irrigation (547 mm), 66% of full irrigation (481 mm), 33% of full irrigation (417 mm) and dryland (303 mm) and two mulching (bare and 9 t ha-1 maize straw) treatments were used. A line source sprinkler irrigation system was also used for this experiment. The trial layout was a split plot design with water treatments as main treatments and mulching rates as sub-treatments. All treatment combinations were replicated four times. Results indicated that green pepper responded well to irrigation. Full irrigation, 66% and 33% of full irrigation treatment produced marketable yield of 37.54, 29.74 and 20.52 t ha-1, respectively. The marketable yield of irrigation treatments was significantly different from each other and they were all significantly higher than that of the dryland treatment which produced a marketable yield of 11.92 t ha-1. As irrigation proceeded over time, the relationship between water use and leaf area index strengthened. The fully irrigated treatment produced the highest water use efficiency. Mulching conserves water by reducing evaporation and mitigates negative effects of water stress on plant growth and yield under semi-arid conditions. At the end of the season, cumulative water use efficiency from the mulched treatment was 6 g m-2 mm-1, significantly higher than that of the bare treatment of 5.3 g m-2 mm-1. Green pepper is very susceptible to water stress and produces poorly under dryland conditions and any irrigation is beneficial to its production. However results also indicated that green pepper has the ability to adapt quite well to high plant populations and has demonstrated its ability to compete for production resources at such populations. The crop also conforms well to the favourable plant growth conditions provided by the mulch. Keywords: marketable yield, water use, water use efficiency, leaf area index, dryland, full irrigationItem 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.Item Open Access Effect of seed size, treatment and sowing depth on quality and yield of Ethiopian wheat (Triticum Spp.), faba bean (Vicia faba L.) and chickpea (Cicer arietinum L.) cultivars(University of the Free State, 2000-11) Mengistie, Demissie Mitiku; Pretorius, J. C.; Van Niekerk, F.English: This study was undertaken in an attempt to obtain information on the quality of seed produced by some of the important crops grown in Ethiopia. Bread and durum wheat was chosen amongst cereals while chickpea and faba bean represented pulses. For all crops two cultivars were included except in the case of durum wheat where a third South African cultivar was additionally investigated. All experiments were carried out at the Small Grain Institute, Bethlehem, South Africa under laboratory and field conditions. The main objectives of this study were 1) to classify seeds of each crop into three different sizes (small, medium and large) and to characterize seeds in terms of kernel mass, hectolitre mass, moisture content and protein content where applicable, 2) to determine the differences in germination potential of untreated seeds and seeds treated with different fungicides under laboratory and field conditions, 3) to evaluate the field performances of different seedlots, including yield components, by means of agronomic parameters, 4) to investigate the effect of two different sowing depths on emergence, seed yield and other yield components and 5) to statistically determine cultivar, seed size, fungicide treatment and sowing depth interactions in a variety of ways. Of the two Ethiopian bread wheat cultivars, Mitikie outperformed Kubsa under laboratory and field conditions for most of the seed quality parameters evaluated. The main reason appeared to be the fact that deeper planted seeds performed well, probably due to longer coleoptile lengths of seedlings, which in turn was positively associated with strong and taller plants. When soil moisture is minimal, as is the case in semi-arid regions, it is possible to plant seeds of this variety deeper than normal in order to utilize soil moisture better. On average, small sized bread wheat seeds performed worst of all and large sized seeds best in terms of most of the measured parameters. Large seeds contributed to a 13.8% increase in seedling emergence and produced plants with a 22.1 % higher yield as well as 11.8% increase in above ground biomass. The effect of fungicides on the field performance of bread wheat seeds was less pronounced as compared to that of seed size. Seedling emergence from shallow planted (5 cm) bread wheat seeds was much better than from deep planted (9 cm) ones. However, although the seed protein content of seeds harvested from plants grown from deep plantedseeds were higher than that from shallow planted ones, shallow planting is still recommended for the Eastern Free State area on grounds of the overall performance of these seeds observed in this study. Durum wheat cultivars performed in a similar fashion as bread wheat. Seedlings of semi-dwarf durum wheat cultivars, as was the case for semi-dwarf bread wheat cultivars, showed longer root lengths than did the tall cultivars. Moreover, seeds from the semi-dwarf cultivar, Gerardo, produced taller plants than Orania and outyielded both other cultivars. Some weevil damage was observed in seeds of Kilinto and therefore its true performance could not be evaluated properly. Large sized durum wheat seeds outperformed the medium and small ones in most respects. Fungicide treatments also had an improving effect on seed performance compared to untreated control seeds. Seedling emergence was also greatly improved by shallow planting and this was reflected in significantly higher yields. The seed protein content, as was the case in bread wheat, were significantly higher in seeds harvested from plants grown from deep-planted seeds except in the case of Gerardo. Seed treatment with Vitavax Plus, together with deep planting, had the most significant increasing effect on the protein content in durum wheat seeds. In comparing the two faba bean cultivars, it was clear that Kuse outperformed Cs 20dk in terms of most of the evaluated parameters under both laboratory and field conditions. Similar to the previous two crops, large sized seeds appeared to outperform the other two seed size groups in most respects. However, surprisingly the small sized seeds produced seedlings with longer epicotyls but this had no real effect on the other quality parameters. Moreover, the fungicide Dividend also had some improving effect on the germination of faba bean seeds. Celest, however, significantly reduced the root length of seedlings compared to the other treatments, and also on grounds of the outcome observed by means of other parameters, Celest is not recommended for treatment of faba bean seeds. Deep planted (10-12 cm) faba bean seeds outperformed the shallow planted ones in many respects and deep planting is therefore recommended. In chickpea, none of the fungicide treatments improved the field performance of seeds. Dividend treatment rather reduced seedling root length. As in the case of bean, deepplanted seeds (10 cm) performed better than shallow planted ones (5 cm). In general, and in most respects, laboratory and field data correlated well. Moreover, recently released cultivars of all crops investigated, outperformed the older ones. This emphasises the need for replacing older cultivars with newer ones on a larger scale in Ethiopia. Large sized seeds are preferred to medium and the medium to small ones for all the crops investigated. Shallow planting for Ethiopian wheat cultivars, but deep planting for pulse cultivars, is recommended. Seed treatment with fungicides is imperative in wheat crops but is not as critical in pulse crops.Item Open Access Effect of spray volume, water quality, adjuvants and ammonium salts on sethoxydim activity(University of the Free State, 1998) Chiconela, Tomás Fernando; Ceronio, G. M.; De Villiers, B. L.The effects of spray carrier, pH, adjuvants and ammonium salts, environmental factors, and spray volume on sethoxydim {2-[ 1-ethoxyirnino-butyl]-5-[2-( etylthio )propyl]-3- hydroxy-2-cyclohexen-1-one} activity in a glasshouse on tomato (Lycopersicum esculentum L cv. Star 9001) and oats (Avena sativa L cv. SSH 241) were studied. Sodium bicarbonate, potassium carbonate and spray solution pH were antagonistic to sethoxydim phytotoxicity. Spray solution pH and ions present were antagonistic to sethoxydim phytotoxicity only when the spray carrier pH exceeded 6.5. Sadol and ammonium salts (ammonium nitrate and ammoruum sulfate) were equally effective in enhancing sethoxydim activity regardless of the presence of antagonistic salts. Bladbuff 5 was moderately effective in the enhancement of sethoxydim phytotoxicity only when sethoxydim was applied at 186.0 g ai.ha¹ and not at 139.5. Addition of Agral 90 and Break- Thru were not beneficial, or were both of little value as adjuvants with sethoxydim. Sethoxydim applications at temperatures ranging between 25 and 35°C were equally more effective as compared to 15°C. However, Sadol, Break- Thru and ammonium salts were most effective in enhancing sethoxydim performance at 25°C than at 15 or 35°C. When averaged across sethoxydim rates and the presence of sodium bicarbonate and in potassium carbonate in the spray solution, oat fresh top mass reduction increased as carrier volume was decreased from 875 to 175 l.ha¹. In all the experiments conducted, tomato plants did not show any injury to negative growth suggesting that sethoxydim may be considered for control of grass weeds in tomatoes.Item Open Access Effect of varying degrees of water saturation on redox conditions in a yellow brown apedal B soil horizon(University of the Free State, 2007) Jennings, Kimberly; Van Huyssteen, C. W.Various studies have been conducted into redox potential (Eh), redox indicators and the measured soil water contents in soil (Franzmeier et al., 1983; Schwertmann & Fanning, 1976; Veneman et al., 1976). Although a measure of success has come from these studies, there are still vast knowledge gaps within this field. The degree of water saturation where reduction in the soil is initiated cannot be determined from literature, although it was approximated that 70% of water saturation (S0.7) was sufficient to initiate reduction (Van Huyssteen et al., 2005). This value will vary for different soil temperatures, varying bulk densities as well as soils with different organic matter contents. This study aimed to determine if it was possible to identify a degree of water saturation at which reduction is initiated for a soil in a closed system. It also aimed to determine the effect of bulk density on reduction. Reduction was defined by a decrease in pe (Eh) of a soil and an increase in the soluble Fe2+ concentration. There were three key aims to the study: to establish the relationship between the degree of water saturation (s) and the onset of reduction; to establish the relationship between the degree of water saturation (s) and the duration of reduction and to establish the effect of bulk density on the above-mentioned processes. A yellow brown apedal B horizon from an Avalon soil form (profile 234) in the Weatherley catchment was used in this study. A soil core experiment was carried out to determine the effect of degree and duration of water saturation on Eh, pH, Fe2+, Mn2+, Ca2+, Mg2+, K+, and Na+. Soil cores were packed to a bulk density of 1.6 Mg m-3 and individually saturated to S0.6 (60% of the pores saturated with water), S0.7 (70% of the pores saturated with water), S0.8 (80% of the pores saturated with water), and S0.9 (90% of the pores saturated with water). Measurements were done in triplicate. The cores were sealed with a double layer of plastic wrap and stored in a laboratory at 23°C until needed. Analysis started three days after initial water saturation. A set of cores (four degrees of saturation with triplicates of each) was analysed every 3.5 days for the first three months after which a set was analysed once a week for the remaining month of analyses. The experiment was terminated after 121 days. The same soil and experimental setup was used for the bulk density experiment. The experiment consisted of a set of three cores packed to an initial bulk density of 1.4, 1.6 and 1.8 Mg m-3. The cores were all saturated to S0.8, each packed in triplicate. The bulk density experiment was terminated after 23 days. There was a good correlation between an increase in degree of water saturation and pe (R2 = 0.95); Mn2+ (R2 = 0.91) and Fe2+ (R2 = 0.92) concentrations. Eh, pH, Fe2+, Mn2+, Ca2+, Mg2+, K+, and Na+ were significantly affected by duration of water saturation and all except Ca2+ and K+ significantly affected by degree of water saturation. Fe2+ and Mn2+ accumulations and depletions (visible segregations or mottles) occurred within 12 months of water saturation in a separate experiment where cores were packed to a bulk density of 1.6 Mg m-3 in a core saturated to S0.9. It was therefore evident that this soil with 0.22% organic carbon and a bulk density of 1.6 Mg m-3 will produce morphological features due to reduction within a year of water saturation at S0.9. An experiment was set up with cores kept at a constant degree of water saturation (S0.8) with varying bulk densities, namely 1.4, 1.6 and 1.8 Mg m-3. All the factors measured (Eh, pH, Fe2+, Mn2+, Mg2+ and K+) except Ca2+ and Na+ were significantly affected by a variation in bulk density. In another part of the experiment two different water temperatures were used to saturated the cores, namely 23°C and 30°C respectively. It was determined that the temperature difference of 7°C caused the cores to react significantly different to each other.. The higher water temperature caused the Eh to decrease more rapidly and therefore a higher Fe2+ concentration occurred in these cores. It was concluded that for this soil at 23°C, Fe3+ and to a certain extent Mn4+ will start to become reduced at a pe of 6 at S0.78. These findings show that the first approximation of Van Huyssteen et al. (2005) where S0.7 was found to be sufficient for reduction is very similar for this soil.Item 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.