Doctoral Degrees (Soil, Crop and Climate Sciences)

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Browsing Doctoral Degrees (Soil, Crop and Climate Sciences) by Author "Allemann, J."

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    The growth, yield and physiological response of rain fed maize to foliar applied fertilizer
    (University of the Free State, 2012-01) Buitendag, Roelof Adriaan; Pretorius, J. C.; Grobbelaar, J. U.; Allemann, J.
    English: Regardless of past research, great uncertainty still exists amongst the research community, fertilizer agents and farmers alike with regard to the benefits of foliar inorganic fertilizer application for crop production. This supplied a rationale for investigating foliar nutrition as an agricultural practice, with the main aim of increasing maize kernel yield, under standard farm management practices. Fertilizer salts used in this study included potassium nitrate (KNO3), mono potassium phosphate (MKP) and mono ammonium phosphate (MAP). Three objectives were set in order to obtain information about i) the optimal application growth stage (2004/05 season), ii) the optimum concentration rate (2005/06 season) and iii) the contribution of either the P or K moiety (or both) contained in foliar applied salts towards growth, physiological and yield responses measured in maize (2006/07 season). During the 2004/05 season a 4% solution of MKP and a 3% solution of KNO3 were applied at growth stages V3 and V8. MKP applied at V8 was the best treatment as it increased plant height significantly (11%) as well as plant fresh and dry mass markedly, compared to the control, when measured at the end of the vegetative growth period at V19. The higher yield (+23%) obtained with MKP applied at V8 during season one, compared to treatment at V3, corresponded with an increase in grain filling of the second ear (+16%), total ear mass (+20%), kernel mass (+20%) and number of kernels (+16%) as well as higher total sugar and starch that accumulated in kernels. During the 2005/06 season, vegetative growth and yield parameters showed no significant differences between the single and double rates for both salts applied at V8. However, MKP applied at both the single and double rates contributed to marked yield increases of 12% and 14% respectively. Although neither KNO3 nor MKP significantly influenced chlorophyll content or photosynthesis efficacy (chlorophyll a fluorescence), higher sugar levels were detected in kernels at the milk and soft dough stages as well as starch at harvest of plants treated with both salts and at two different concentrations. This strongly indicated that improvement of sucrose translocation from the leaves to kernels was rather causative of higher carbohydrate content measured in harvestable parts than sugar production per se. During the 2006/07 season MAP had either no significant effect or suppressed both growth and yield eliminating its purpose to verify P or K involvement. Further, the third season was significantly drier compared to the first two seasons further complicating the use of third season data to distinguish between P and K in terms of its involvement in causing the vegetative and yield responses measured in maize. Overall, it was only MKP applied at 4% and at V8 that tended to increase kernel yield over the first two seasons.
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    Yield and quality response of hydroponically grown rose geranium (Pelargonium SP.) to changes in the nutrient solution and shading
    (University of the Free State, 2012) Sedibe, Moosa Mahmood; Allemann, J.; Engelbrecht, G. M.
    This study was undertaken to determine the effect of different concentrations of phosphate, ammonium, nitrate, and sulphate as well as that of shading and moisture stress on oil yield and quality of hydroponically grown rose geranium. Five separate trials were conducted during the 2009 and 2010 growing seasons. Different concentrations of phosphate, ammonium, nitrate and sulphate were used in the first four trials, while the last study focused on the effects of shading and moisture stress on rose geranium. The phosphate, nitrate, ammonium and sulphate trials were conducted in a greenhouse at the west campus of the University of the Free State in Bloemfontein, South Africa. Plants were grown for four months using a randomized complete block experimental design. The concentrations of phosphorus evaluated were 0.10, 0.80, 1.50 and 2.20 meq L-1. Ammonium concentrations were 0.00, 0.50, 1.00 and 1.50, nitrate concentrations were 8, 10, 12 and 14 and sulphate concentrations were 0.36, 1.90, 3.44 and 4.98 meq L-1. Foliar drymass and oil yields increased as P concentrations were increased to 2.20 meq L-1. Both, the guaia-6,9-diene content and the citronellol:geraniol (C:G) ratio were better at the high level of phosphate indicating that the best quality oil, as required by the perfume industry is obtained with relatively high phosphate concentrations. Plant growth as measured by the number of branches and biomass production, peaked at 10 to 12 meq L-1 nitrate concentrations. The highest chlorophyll content in the foliage was found at the nitrate concentrations of 10 and 12 meq L-1, where the best oil yield was also produced. At this nitrate level the citronellol:geraniol (C:G) ratio was slightly higher than the upper limit required for good oil quality but the geraniol and citronellylformate contents were within range for top quality oil. Height, biomass, oil yield and chlorophyll content of the leaves were not affected by ammonium, but the concentrations of plant tissue sulphur and nitrogen increased linearly with increasing concentrations of applied ammonium. Rose geranium needs to be grown at a relatively high nitrate concentration (10 to12 meq L-1) to ensure high oil yield. This application falls within the range that is used for most vegetable and ornamental crops under soilless conditions. Ammonium concentrations of up to 1.00 meq L-1 can be used without affecting yield or oil quality of rose geranium. A significant effect of sulphate on branches, height and branch:height (B:H) ratio and foliar dry mass (DM) was observed. The four sulphate concentrations showed a statistically non significant trend on yield. Based on the standards used by the perfume industry the oil of rose geranium was not of a good quality in this trial probably due to the autumn planting time. Shading and moisture stress were used as treatments in a study conducted at the University of the Free State experimental farm during spring and summer. A split plot experimental layout was assigned using 0%, 20%, 40%, 60% and 80% shade treatments allocated to the main plots. The subplots were exposed to moisture stress levels at 0 and -0.15 MPa of osmotic pressure. Rose geranium grew well under a shading of 40%, where plant growth parameters such as foliar fresh mass (FM), foliar dry mass (DM) and the branch:height ratio were increased. Subsequently the best oil yield was obtained at this level. Proline content was high due to excessive solar radiation at 0% shade as well as where moisture stress was induced, however, oil quality was not affected. The number of oil glands cm-2 of leaf area was not significantly affected by shading, but tended to be lower at shading levels higher than 60%. Fresh mass, DM, the ratio of branches to height and oil yield were affected by shading. Proline content gave a clear indication of stress conditions of plants at full radiation as well as moisture stress. Growers are advised to use 40% shading to grow geraniums in summer at radiation levels similar to those found in this study.