Effects of Conservation Agriculture on Soil Physico-Chemical Properties and Soil Microbial Biomass under a Rain-Fed Maize Production System in Laikipia East, Kenya

Abstract

There is reduced crop yield due to soil degradation and climate change. Conservation agriculture (CA) is being advocated to address land degradation and low productivity among small-scale farmers. However, contrasting results on the effects of the CA practices such as tillage, mulching and herbicide application on yield and soil properties have been reported. Thus, the need to carry out more research to appropriately describe the effects of CA components on soil physicochemical properties, soil microbial biomass and crop yield. The study was conducted for three years using split plot experimental design. The main treatments were tillage management (conventional tillage: CT, no tillage: NT and no tillage herbicide: NTH) and four sub-treatments. The sub-treatments were maize intercropped with (a) common beans (MB), (b) dolichos beans (MD), (c) common beans and 1.5 Mg ha-1 of mulch and (d) common beans and leucaena. The rainfall for 1st, 2nd and 3rd seasons was 685, 538 and 270 mm, respectively. The 1st and 2nd years growing seasons were wet while the 3rd year was a dry season. The tillage, mulching and herbicide application only significantly affected a selected physical property; namely saturated hydraulic conductivity and bulk density and had no significant effect on Ca, Mg, Fe, Cu, Mn and Zn. Tillage significantly affected yield, soil moisture and water use efficiency during the dry year, with CT showing significantly lower 33.9% and 33% maize yield and rain water use efficiency (RWUE) respectively than NT. Similarly, mulching significantly affected soil macronutrients, soil microbial biomass carbon (SMBC), soil hydraulic conductivity and increased maize yield and RWUE but had no significant effect on micronutrients and soil physical properties. Maize yield, soil moisture and RWUE were significantly increased in agroforestry treatments. The study found that NT and mulch are critical aspects of CA in that they avoid drought stress of maize during dry seasons while enhancing maize yield. Agroforestry showed potential to further improve CA in semi-arid zones resulting in higher yield in dry years. Even though the dry growing season under study corresponded with a meteorological drought, practicing two or three CA practices avoided agricultural drought due to conservation of soil moisture which became available to the crops during dry periods. The ‘best’ practice (no till with maize, beans and mulch), resulted in up to 74% higher yield in the dry year and still up to 24% higher yield in the wet growing season compared to the conventional practice. The study concluded that NT, mulching and agroforestry had a significant effect on soil moisture, macro nutrients, SMBC, maize yield and RWUE especially in season with rainfall below normal average and mulching is a critical component of CA. There was no significant effect of NT, mulching and agroforestry on soil physical properties. The application of CA practices is recommended to improve the soil physico chemical and microbial properties, improve maize yield and enhance rain water use efficiency.