Evaluating influence of organic amendments and legume integration on soil chemical properties and crop performance in Central Kenya

Abstract

Demand for organic foods, especially vegetables has increased tremendously due to reasons such as safety, environmental concerns, flavour and freshness, health benefits and nutritional value. In the current agricultural production environment, conventional farming methods pose the greatest risks in terms of reduced crop yields due to soil degradation. In the face of climate change and variability (CCV), field experiments are limited and without appropriate modelling techniques future crop production scenarios can‟t be predicted leading to food insecurity. A survey and field experiment were done to assess crop productivity under organic based cropping systems and impact of CCV on soil nutrients and maize yields 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 smallholder organic farmers and the potential coping strategies employed as well as their knowledge, coping and adaptation strategies to 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 adaptation strategies of CCV. The field study examined the effect of cropping systems and organic inputs on productivity and quality of maize and tomatoes intercropped with chickpea and also examine soil nitrogen, phosphorus and carbon as well as model soil nutrients and maize yields 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. 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), mean error (ME) and root mean square error (RMSE) for sites and cropping systems were calculated. The effect of the changes in rainfall and temperature on maize yields was considered, i.e. current temperature (To), current rainfall (Ro) R1 (R0 -10% rainfall), R2 (R0+10% rainfall), T1 (T0 +2oC), T2 (T0+3oC) and combinations of T1+ R1 and T2+ R1) on maize yields was determined. The main challenges faced in crop production were unpredictable rains 85%, lack of irrigation equipment 43%, crop pests and diseases 28% and inaccessibility to proper soil testing and analysis facilities (37%). The major causes of CCV cited were; deforestation and poor agricultural practices (62%), emission of green house gases (33%). The main effects of climate change were; reduced crop yields (80%), change in planting time (8%) and increased crop pest and disease attack (6%). Crop yields and soil N, P and C on the other hand increased in the different treatments in the following order; control < MRP < FYM for all cropping systems and seasons at both sites. Maize in rotation with chickpea; FYM had, 3.2 t ha-1biomass, 2.15 t ha-1 grain, 0.39% N and 95 ppm P, with white, >500g and 20cm cobs more than control compared to MRP, 1.7042 t ha-1biomass, 1.35 t ha-1 grain, 0.1% N and 350 ppm P. Tomato-chickpea rotation; FYM had, 1.18% N, 64ppm P, 1.8 Mg ha-1 yield, 0.86 t ha-1 biomass, with >170g and 6cm fruit than control while MRP had 0.62% N, 101 ppm P, 0.758 Mg ha-1 yield and 0.336 t ha-1 biomass. 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 good agreement 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. The field trials show that, FYM and MRP application and legume integration in cropping systems improves soil N, P and C resulting in improved maize and tomato 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.