Crop Performance and Soil Nutrient Dynamics under Different Organic Based Cropping Systems and Modeling The Effect of Climate Change On Maize (Zea May) Growth In Central Kenya
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A survey and field experiment were done to assess crop productivity under organic based cropping systems and impact of climate change and variability (CCV) on maize growth during the short and long rains seasons of 2012 and 2013 in central Kenya. The survey was carried out to determine the causes of low crop production by looking at the challenges faced by organic based smallholder vegetable farmers and the potential coping strategies employed as well as their experiences, coping and adaptation strategies to climate change and variability (CCV). The survey’s objective was to determine the major crops grown, marketable quality attributes, challenges faced and coping strategies to enhance crop production and understanding of causes, impacts and coping strategies of CCV. The field study examined the impact of the cropping systems and organic inputs on the productivity and quality of maize and tomatoes integrated in chickpea and soil nitrogen, phosphorus and carbon as well as model maize growth using Agricultural Production Systems Simulator (APSIM). The study was conducted both on-farm (farmer’s field in Kajiado County) and on-station at Kabete Campus field station, University of Nairobi, Kenya. The experimental set-up was a randomized complete block design with four replications in a split plot arrangement. The main plots were three cropping systems; monocropping, intercropping and crop rotation and the split plots were farm yard manure (FYM) and Minjingu rock phosphate (MRP) and a control. APSIM model was calibrated using field experimental data collected during 2013 short rain season where coefficient of determination (R2) and mean error (ME) for sites and cropping systems were calculated. The main challenges faced in crop production were unpredictable rains 85%, lack of irrigation equipment 43 %, crop pests and diseases 28 %. The major causes of CCV cited were; emission of green house gases (30 %), deforestation (60 %) and poor agricultural practices (60 %). The main effects of climate change were; reduced crop yields (80%), indicated change in planting time (8%) and increased crop pest and disease attack (6 %). Crop yields and soil; N, P and C increased in the different treatments in the following order; control < MRP < FYM for all cropping systems and seasons at both sites. Maize after a chickpea crop yielded higher dry matter in grain and biomass compared to moncrops. Maize in rotation with chickpea yielded 0.186 t ha-1biomass and 0.249 t ha-1 more than a monocrop in the same season. Tomato performance in rotation with chickpea gave; 0.046 t ha-1 biomass and 0.111 Mg ha-1 fruit yields as compared to monocrop. Chickpea rotations performed better; 0.54 t ha-1 biomass and 1.1 t ha-1 grain yield than in the monocrop. Soil nutrients in maize under rotation with chickpea were; control, 0.08% N, 0.2% C, FYM; 0.1% N, 0.6% C and MRP; 0.2 % N and 0.5% C more than in monocrops. Simulations of crop rotations correlated most (R2=0.48) with observed results at Kabete and Kiserian. Simulations of the intercrops correlated favourable with coefficient of determination (R2) values of >0.4 showing a reasonable relationship between observed and simulated values. However, mono-crop simulation varied highly from observed yields (R2<0.3). The model performed better for Kabete (ME=0.6) and RMSE (2.0) than Kiserian (ME=0.9) and RMSE (2.5). The simulated maize yields (t ha-1)in crop rotations were; control, 3.3 FYM, 5.6 MRP 4.6, intercrop; control, 2.5 FYM, 4.7 MRP 3.6 monocrop; control, 2.4 FYM, 5.5 MRP 4.4 averaged at both sites. The farmers contended that through trainings and exposure, they would be empowered to cope with and reverse the negative impacts of CCV and consequently guarantee food and nutritional security. From the survey, it can be deduced that, more research efforts be directed towards irrigation, soil nutrient analysis and recommendations on site specific input application rates for farmers. The field trials show that, FYM and MRP application and legume integration in cropping systems improves soil fertility resulting in improved crop productivity. The increment in the effects of climate change and variability resulting in reduced rainfall, increasing temperature regimes and declined crop yields, calls for development of appropriate adaptation techniques.