Comparative response of varied irrigated maize to organic and inorganic fertilizer application

Abstract

The response of varied irrigated maize (Zea mays) to organic and inorganic fertilizer N, was evaluated at Kasinthula Agricultural Station (2003–2006), Malawi to determine the optimum nutrient and irrigation frequency combinations for soil–water and nutrient management which will address water stress and low soil fertility problem. Hybrid maize variety (DK 8031) was planted on ridges spaced at 0.75 × 0.25 m in a split-plot design replicated three times, with four irrigation frequencies as main plots and fertilizer sources as subplots. Irrigation frequencies comprised: water balance scheduling at 40% depletion, and irrigating 40 mm every 3–4 days, 7 days and 14 days. The nitrogen sources were compost (C), farmyard manure (FYM), urea (U) and their mixtures [(2U:C); (U:2C); (2U:FYM); and (U:2FYM)]. Organic manure was banded three weeks before planting. Data on grain yield was collected and subjected to ANOVA using the Genstat and LSD 0.05 test separating statistical significant means. There was positive ( P < 0.01) and highly significant interactions between maize grain yield, crop water productivity (CWP) and nitrogen use efficiency (NUE). The water balance scheduling at 40% soil moisture depletion had highest grain yields, CWP and NUE among the four irrigation frequencies that was not significantly different to 40 mm every 3–4 days and every 7 days obtained with nitrogen sourced from sole Urea which were not significantly different to mean grain yields, CWP and NUE from (2U:C) and (2U:FYM). CWP was optimally maximised in sole urea (9.8, 8.8 kg mm −1 ha −1) and mixed treatments of 2U:C (8.2, 7.2 kg mm −1 ha −1) or 2U:FYM (8.2–8.9 kg mm −1 ha −1) for maize irrigated every 7 days and at 40% depletion using soil water balance schedule respectively. The greatest NUE of 53.5 kg kg N −1 under (2U:FYM) treatments was experienced at 40% depletion irrigation schedule and was also not significantly different to sole urea and (2U:FYM) treatments (52.8 and 51.6 kg kg N −1) irrigated at 40% depletion and every 3–4 days irrigation schedule respectively. The minimum NUE 19.8 kg kg N −1was observed in FYM treatments irrigated every 14 days. Generally, yields were optimized in the 40% depletion and 40 mm in 7 days in the 2U:C and 2U:FYM treatment. Maize fertilized with sole organic N sources was lowest in CWP and NUE in all irrigation regimes, and exhibited high water dependencies. An increase in irrigation frequency and urea ratio increased maize yield and NUE, while CWP decreased. It can, therefore, be concluded that with adequate water and high inorganic N ratio, there is great potential to facilitate N release from organic matter. In times of water shortage, sole urea can better or more easily be utilized than organic nitrogen sources.