Evaluating Effect of Irrigation Regimes and Mulch on Spinach (Spinach Oleraceae) Growth and Development in Naromoru, Kenya

Abstract

Water scarcity is a global concern that has threatened food security. The current study evaluated the growth and development of spinach at varying irrigation levels below field capacity, combined with mulch in Naromoru, Kenya. The study utilized a split-plot arrangement within a Randomized Complete Block Design (RCBD), whereby the main plots consisted of various moisture regimes set at 85%, 70%, and 50% of Field Capacity (FC). Subplots were designated for Irrigation (I), Irrigation combined with mulch (I+M), and sole mulch cover (M). Data on plant height, fresh weight, leaf length and width, and number of leaves was collected on five (5) occasions at two-week intervals, 21 days after transplanting. A neutron Probe Ratescaller Mark 11, installed 100 cm deep was used to monitor soil moisture bi-weekly for a period of eight weeks after transplanting. Irrigation Water Use Efficiency (IWUE) was calculated from the water productivity method using fresh weight (kg) and water used by the spinach crop (mm), equivalent to the spinach actual evapotranspiration (ETspinach). Spinach water requirement was determined as the sum of ETspinach for the entire growing period. Climate, soil and crop data was keyed in the Food and Agriculture Organization (FAO) CROPWAT 8.0 model to determine the irrigation water requirement, and the applicability of deficit irrigation scheduling on spinach (Spinacia oleracea). Spinach subjected to either 85%, 70% or 50% FC soil moisture content had no significant (p ≥0.05) effect on plant height, number of leaves, leaf length and leaf width. Among the treatments, 85% moisture content FC (I+M) increased growth and yield of spinach but was not significant (P ≥ 0.05) in comparison to other treatments. The highest WUE of 35% was recorded at 85% FC (I + M), followed by Mulch (M) and drip (I) at 17% and 5%, respectively. From the CROPWAT model, the spinach water requirement under the prevailing conditions was determined to be 277.7mm, whereas 66.8mm as the demanded/required irrigation water. Owing to an increase in spinach productivity, the use of varying irrigation below the field capacity combined with mulch was found to be ideal in sustainable use of water for irrigation in the research site. Overall, the CROPWAT model was confirmed to be a convenient irrigation management tool that can effectively calculate crop water requirement and schedule for irrigation, thus alternative for reducing water wastage and ensuring effective growth and development of spinach