Doctoral Degrees (Soil, Crop and Climate Sciences)
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Browsing Doctoral Degrees (Soil, Crop and Climate Sciences) by Author "Buitendag, Roelof Adriaan"
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Item Open Access 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.