ASSESSMENT AND EFFECTS OF FERTILIZER AND IRRIGATION LEVEL ON MAIZE (Zea mays L.) PRODUCTIVITY AT BOLOSO SORE DISTRICT, SOUTHERN ETHIOPIA

Abstract

Maize productivity under irrigation is affected by several factors including climate, soil and water management, quality of water and soil, and levels of irrigation and fertilizer application. This study consisted of four objectives to (1) analyze rainfall and temperature variability and change, (2) assess farmers' preferences for soil and water management practices, (3) assess the quality of water and soil, and (4) determine the effects of fertilizer and irrigation levels on maize productivity, for climate change adaptation in Boloso Sore district, southern Ethiopia. Climate variability and change were analyzed using the coefficient of variation, and Mann-Kendall trend test, respectively. The climate was analyzed for the past (1990-2019) and future (2030s, 2050s, and 2070s, under two representative concentration pathways; RCP4.5 and RCP8.5). Farmers' preferences for soil and water management (SWM) practices were analyzed using Multivariate Probit Model. The chemical properties of water and the physicochemical properties of soils were analyzed using standard procedures. Three irrigation levels (70, 85, and 100% crop evapotranspiration; ETc) and four fertilizer rates (0, 50, 100, and 150 kg ha-1) of blended fertilizer (nitrogen, phosphorous, sulfur, and boron; NPSB), were used for field experiments in 2020 and 2021. Randomized complete block design in factorial arrangement with three replications was followed. The impacts of climate variability and change on maize yield were analyzed for 2030, 2050, and 2070 using the AquaCrop model. The results indicate that past rainfall showed medium to very high variability (coefficient of variation; CV ≤ 38.4%), with a non-significantly increasing trend except for Belg. Past maximum temperature (Tmax) and minimum temperature (Tmin) showed low variability, with an increasing trend. Future rainfall has medium to very high variability and deviates from the baseline by up to -1.9% by 2030s, -2.4% by 2050s, and by +2.4 by the 2070s. This trend is confirmed in Belg and Kiermt seasons. A non-significantly decreasing trend of rainfall is expected in the 2030s and 2050s, with an increasing trend by 2070s. From the baseline, Tmax and Tmin would deviate by 0.7-1.2°C by 2030s, 1.3-2.2°C by 2050s, and 1.5-3.2°C by 2070s, under both RCPs. Farmers perceived that irrigation water improved their adaptive capacity to the impacts of climate change by increasing their net income (88%). Their preferences for soil and water management (SWM) practices were xviii significantly positively (p<0.05) related to their education level and perceptions about water availability, distribution, and irrigation roles in climate change adaptation. Water in Soke and Woybo schemes was non-saline (electrical conductivity < 0.2 dS m-1), in the normal pH range (6.5-7.5), and moderate to severe sodicity (sodium adsorption ratio ≤10.9). Surface soils are acidic to neutral (pH: 5-6.5) having a slow infiltration rate (≤ 0.13 cm hour-1), medium total available water (≤ 178 mm m-1), low soil organic carbon (≤ 2.1%), and low total nitrogen (≤ 0.1%), among others. Deficit irrigation with 100 kg ha-1 NPSB accelerated the phenological period. The highest biomass yield was recorded as the main effect of full irrigation (23.27 tons ha-1) and the highest NPSB (24.56 tons ha-1) whereas the highest grain yield (8.8 tons ha-1) was recorded at the interaction of the highest combination. The highest fertilizer use efficiency (51.1 kg kg-1) was recorded at 100% ETc × 50 kg ha-1 NPSB. The maximum water productivity was obtained at the main effect of 30% deficit irrigation (2.71 kg m-3) and 150 kg ha-1 NPSB (3.21 kg m-3). The second-rank maximum net revenue (deviated from the highest treatment level by only 5%) was obtained at the interaction effect of 85% ETc × 100 kg ha-1 NPSB. Maize productivity is projected to decrease by up to 15.11% by 2030, 2050, and 2070, under both RCPs. Finally, it can be concluded that rainfall has medium to very high variability whereas temperature has low variability, in all periods. Farmers' perceptions of irrigation roles in climate change adaptation are positive despite their poor SWM practices. Irrigation water and soils have poor quality for maize production. Maize has an optimum yield at 85% ETc with 100 kg ha-1 NPSB. Improving farmers' awareness of water use, distribution, and regular follow-up and support by Agriculture Offices is suggested. Lime application, organic matter applications, and 85% ETc with 100 kg ha-1 NPSB can be suggested to improve the adaptive capacity of farmers to future impacts of climate change. Further studies with different crops/varieties and locations can also be suggested.