Assessing effects of Zai pit with integrated soil fertility management on sorghum yields and soil properties in Kitui county, Kenya

Abstract

Low crop productivity, high evapotranspiration and low, erratic and unreliable rainfall among farms of sub-Saharan Africa (SSA) have necessitated a search for more sustainable production practices with higher efficiency in resource utilization. To ease soil fertility deterioration and reduce runoff and water related stress, integrated soil fertility management (ISFM) coupled with water harvesting technologies such as Zai pit, are alternative options with positive impact on agricultural productivity. The main objective of this study was to assess the effects of Zai pits combined with selected ISFM amendment options on Gadam sorghum (Sorghum bicolor) yields and selected soil properties in Kitui County. The specific objectives were to: 1) assess the effects of Zai pit system combined with ISFM technologies on soil chemical properties and Gadam sorghum yields in Kitui County, 2) evaluate the impact of Zai pit system combined with ISFM technologies on soil aggregate stability and moisture content in Kitui County, 3) determine the effects of Zai pit system in combination with ISFM technologies on soil organic carbon and its labile organic carbon fractions in Kitui County, 4) evaluate the effects of Zai pit system in combination with ISFM technologies on soil microbial biomass (Carbon and Nitrogen) in Kitui County. The experiment was set up in a randomized complete block design (RCBD) with eight treatments replicated three times. Each experimental plot measured 6 by 4.5 m. The field experiment ran for four consecutive cropping seasons; short rains of 2018 (SR2018), long rains of 2019 (LR2019), short rains of 2019 (SR2019) and the long rains of 2020 (LR2020). The treatments comprised of two systems, either Zai pit or convention system (no Zai pits), both with four levels of fertilization (no input - control), sole cattle manure, sole mineral fertilizer and both cattle manure and mineral fertilizer). Soil sampling was done at a soil depth of 0-15cm at the start, during and at the end of the experiment for laboratory analyses of various soil parameters. Data was subjected to Analysis of Variance (ANOVA) and further means separated using the Least Significance Difference (LSD) at p≤0.05. Pairwise comparison of selected soil parameters differences between the start and the end of the experiment were analyzed using t-test at p≤0.05. The results indicated that there was a significant difference (p= 0.01, p= 0.02, p= 0.01 and p= 0.02) in soil pH, EC, % nitrogen and extractable phosphorous, respectively, between treatments at the end of the experiment. Generally, treatments under Zai system recorded significantly (p≤0.05) higher sorghum grain and stover yields during the SR2018, SR2019 and LR2019 seasons as compared to similar treatments under the conventional system. Significantly (p≤0.05) highest grain yields were recorded under Zai system with sole manure and those with manure combined with mineral fertilizers. Generally, aggregate stability of soil particles was significantly higher (p≤0.05) in Zai treatments as opposed to alike treatments in the conventional system. Zai pit with manure combined with inorganic fertilizer recorded the highest significant (p≤0.05) mean weight diameter of 2.06 mm followed by Zai with sole manure (2.01 mm) and this were 35% and 25% higher than the mean weight diameter recorded in similar treatments under conventional system. The determination of Soil moisture content, expressed as volumetric water content, was done at different days (18, 32, 46, 60, 74, 88, 102 and 116) after sowing during the four study seasons. Generally, treatments under Zai pit system recorded significantly (p≤0.05) higher volumetric water content values as opposed to values recorded in similar treatments under conventional system across different days in all the four seasons. Higher values were recorded in treatments with absolute manure and those with organic manure combined with chemical fertilizer under both systems. Significantly (p≤0.05) higher concentrations of total organic carbon, its labile fractions (POC, LFOC, DOC and KMnO4-C) and microbial biomass (carbon and nitrogen) were recorded in treatments under Zai pit technology as compared to the conventional system and in treatments amended with organic manure, either solely or combined with mineral fertilizer as opposed to mineral fertilizer amended treatments and the unfertilized control. Based on the findings, Zai pit technology coupled with integrated organic and inorganic inputs could be a major agricultural intervention for improving soil fertility and enhancing crop productivity in arid and semiarid areas, and therefore, there is need for agricultural policy makers to develop and implement appropriate agricultural guidelines for extension service providers and smallholder farmers on the effectiveness and efficiency of the technologies in the study.