Effect of Tillage Method, Residue Retention and Nitrogen Fertilizer on Growth and Yield of Snap Bean (Phaseolus Vulgaris L.) in Kenya

Abstract

Snap bean (Phaseolus vulgaris L.) is an export vegetable crop grown by smallholder farmers and large-scale commercial farms in Kenya. The demand and consumption in both local and export market has increased significantly hence need for increased production. This is however limited by erratic rainfall, frequent periods of drought and floods, low soil fertility, and fertilizer nitrogen. Additionally, farmers continuously till their land, which pulverize soil and predispose it to rapid loss of organic matter, moisture and fertility. Two field experiments were conducted at Kenya Agricultural and Livestock Research Organization research station in Thika during 2019 rainfall seasons: (i) evaluate the effects of tillage method, residue retention and nitrogen fertilizer rate on growth, yield, and quality of snap bean; (ii) determine the effects of tillage method, residue retention and nitrogen fertilizer rate on water and nitrogen use efficiency of snap bean. Three tillage method including, conventional tillage, furrow-ridge and zero tillage, two residue applications management comprised of residue addition at 3t/ha and residue removal at 0t/ha and four fertilizer nitrogen rates (0, 40, 80 and 120 kg N/ha) were laid out in a randomized complete block design with split-split plot arrangement and replicated three times. Tillage method formed the main plot; residue management was assigned sub-plot while fertilizer nitrogen rates assumed the sub-sub plots. Data collection was on crop phenology, plant growth traits, yield components, and market quality traits. Results showed that tillage method significantly affected and improved crop phenology with minimal effect on plant height and yield components. Tillage method and residue addition significantly improved recovery efficiency at 57% and 31%. Additionally, nitrogen fertilization had significant effect on crop phenology, plant growth, yield components and market quality traits. Nitrogen fertilization at 120 kg N/ha had maximum effect on growth, yield and quality across the seasons. Additionally, nitrogen fertilization at 120 kg N/ha had significant effect with biomass and grain water use efficiency at 59%, 7% and 3%. Significant and positive relationship was recorded for grain yield with water and nitrogen use efficiency. Grain yield (R2 = 0.997) was positively and significantly (P≤0.001) correlated with water use efficiency (R2 = 0.672). Additionally, grain yield significantly (P≤0.001) and positively affected grain agronomic efficiency during the first rainfall season. The study showed that conservation agriculture in snap bean farming has potential for increasing snap bean yield and quality. The effects of erratic rainfall and rising cost of production, calls for research and integration of improved farming practices. The study was conducted for two seasons and did not capture data for all parameters for analysis. Furthermore, results of study were limited to one study site hence observed results may not reflect the expected yield and quality in snap bean producing regions of Kenya. Further research for comparison of study is recommended in snap bean production regions