School of Agriculture, Food and Ecosystem Sciences - Theses

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    Evaluation of the concepts and methods of response farming using crop growth simulation models
    Wafula, Benson Mututa ( 1989)
    This thesis considers aspects of the application of the CERES-Maize simulation model of the growth and yield of the maize crop to the analysis of "response farming" in the semi-arid region of East Kenya. Response farming comprises a set of management tactics by which sowing density and nitrogen application can be targeted to the yield potential of the season based upon the timing and nature of the opening rains. Sowing density and nitrogen application are set by the timing of the opening rains and then further adjustments are made four to five weeks after sowing. The in-season adjustments involve additional nitrogen fertilizer in seasons that promise high yield potential and crop thinning when yield promises to be low. These combinations have the purpose of maximizing yield in seasons of high potential and minimizing fertilizer and seed input in seasons in which the rainfall is too low for it to have any advantage. The scheme is possible, it is proposed, because the timing and nature of the opening rains are closely correlated with total seasonal rainfall and hence yield potential. The thesis discusses the potential that simulation models hold in the analysis of alternative cropping strategies (Chapter 2). It presents a validation study of the model with experimental data collected in the region (Chapter 3) and discusses the relationships between maize agronomy in the region and the components of response farming (Chapter 4). The tuned model is shown to provide a good explanation of the response of the common cultivar of maize to a range of combinations of water and nitrogen supply and a reasonable capacity to describe the response of the crop to thinning (Chapter 5). The model is then used (Chapter 6) to compare response farming with conventional practices at various levels of inputs. It shows that the common practice of the region by which-crops are sown at low density without fertilizer has the least risk of failure but low expected yields. Fertilizer is required to increase yields, but its use incurs a greater chance of crop failure. Compared to alternative strategies using fixed or variable sowing dates at comparable levels of crop density and nitrogen fertilizer, it is shown that response farming does provide higher mean yield with less chance of failure. It is proposed that continuing experimentation with the current and improved versions of the model have an important role to play in the identification of better management strategies for East Kenyan farmers.