Assessment of Optimal Interactions of Water Levels and Nitrogen Fertilizer Rates for Greenhouse Lettuce Performance in Kalro Kabete, Nairobi
Achieving food security globally has been curtailed by several factors including water scarcity, nutrient mining, limiting land resource and climate change. Nevertheless, irrigation under greenhouse farming has been confirmed to have the potential to solve water scarcity and crop nutrition problems thus increasing food production in controlled environments. This study aimed at assessing the optimal interactions of water levels and nitrogen fertilizer rates for greenhouse lettuce performance in the Kenya Agricultural and Livestock Research Organisation (KALRO) at Kabete, Nairobi. The specific objectives were to assess the optimal interactions of nitrogen fertilizer rates and water levels for highest performance of greenhouse lettuce, to determine the effect of N fertilizer dosage on water use efficiency in greenhouse lettuce yield and to investigate the effect of water levels and N-rates on water productivity index for the greenhouse lettuce yield in urban Nairobi. A survey was conducted using questionnaires to establish the amounts of water and N fertilizer rates green-house farmers within the study area were using for their vegetables production. The experiment conducted at the KALRO Kabete entailed use of a split plot randomized complete block design for two seasons between October 2017 and February 2018. The treatments included 3 levels of irrigation (W1-100% W2-70% (and W3-40% to FC) in main plots while 4 nitrogen levels (0, 65, 105, and 145 kgN/ha) were assigned to the subplots, resulting in 12 treatment combinations which were replicated three times. Soil moisture was determined using a neutron probe while water use efficiency (WUE) was calculated by dividing lettuce yield by AETc. A digital calorimeter was used to determine the leaf chlorophyll concentration. All data were subjected to analysis of variance (ANOVA) using Genstat version 15. Separation of means was performed using Turkey’s test at 95% level of confidence. Findings showed significant variations existed due to interaction effect of nitrogen fertilizer rates and water levels on lettuce height and number of leaves at season two. Variations were however insignificant during season one. A significant effect was observed due to the interaction of nitrogen fertilizer rates and water levels on lettuce diameter at season one and season two with 0.004* and 0.008* respectively. There was significant effect (0.005* and 0.003* for S1 and S2) observed due to interaction of nitrogen fertilizer rates and water levels on percentage chlorophyll during both seasons. However, no significant variation was observed due to interaction effect of nitrogen fertilizer rates and water levels on fresh (0.966 and 0.212 for S1 and S2) and dry weight (0.301 and 0.130 for S1 and S2) of lettuce during season one and season two. Findings also showed no significant variation (0.088 and 0.404 for S1 and S2) due to the effect of nitrogen fertilizer application rates on water use efficiency during season one and season two. Findings indicated that water use efficiency was highest at treatment W3N1 with 230.06 kg/Ha/mm and 209.68kg/Ha/mm during season one and season two respectively. Additionally, water productivity index was significant during season one and insignificant during season two with findings indicating that treatment W3N1 was the most water productive treatment during both seasons with 66.29 kg/m3 and 50.46kg/m3 during season one and season two respectively. As such, farmers growing lettuce crop under greenhouse technology should use water applied at 40% field capacity that is 12 minutes and fertilizer rate of 65kg/ha since it showed efficient use of water and high productivity.