Many soils of southern Africa are severely deficient in N, but inorganic fertilizers are frequently unaffordable for most farmers. Leguminous fallows or intercrops can alleviate N deficiency, but N use efficiency of organic inputs may be low due to non-synchrony of N release and crop N requirements. We monitored soil inorganic N dynamics for two seasons in a gliricidia [Gliricidia sepium (Jacq.) Walp.]- maize (Zea mays L.) intercrop in the unimodal rainfall area of southern Malawi. Treatments were plus or minus gliricidia, and N at 0, 24 or 48 kg N ha-1 in factorial combination. Application of gliricidia prunings significantly (p < 0.001) increased topsoil (0-20 cm) inorganic N at the end of the dry season. Fertilization alone also increased topsoil N (p < 0.001 ), but accumulated 38 to 41% less N than the tree plots. Differences between tree and fertilized plots became non-significant by 4 weeks after planting. Tree plots accumulated significantly (p < 0.01) more ammonium-N during the dry season. Nitrate-N remained constant during the dry season but rose rapidly in tree plots after the onset of rains. Both tree biomass and inorganic N significantly (p < 0.001) increased maize grain yields. Pre-season inorganic N accounted for 71% of the variation in maize yields for the two seasons data combined. A 2- factor model including pre-season inorganic N and anaerobic N mineralization potential accounted for 84% of the variability in maize yields for the two seasons data combined, Pre-season inorganic N could be used to adjust or eliminate basal applications of N in seasonal rainfall areas, particularly in seasons preceded by a drought year. Delayed timing of biomass additions may increase N use efficiency by the crop.

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0103|AL-Maize Program|AGRIS 0102|AJ

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