Effect of tree foliage of locust bean (Parkia biglobosa) and neem (Azadirachta indica) on soil fertility and productivity of maize in a savanna alfisol

Organic matter (OM) management is key to sustainable fertility and productivity of tropical soil systems. Short-term evaluation of the potentials of foliage of neem and locust bean in soil fertility improvement, as measured by the productivity of maize, was carried out on a savanna Alfisol from 1995 to 1997. The trees are indigenous to the savanna, and common in farms and homesteads in the region. The objective was to determine the effects of these easily renewable and cheap OM sources on maize response to applied inorganic fertilizer and soil chemical properties. Treatments consisted of three sources of organic matter: no-OM, neem and locust bean, and three rates of inorganic fertilizer, applied at 0, 1/4 and 1/2 of the recommended rate of 120-27-50 NPK for maize, which in addition served as check. Results obtained over the three seasons were consistent, and revealed that neem was superior to locust bean by a factor of 2 and also to no-OM treatments, but were all inferior to the recommended fertilizer rate (with a maximum yield of 3.75 t/ha). Isolated relative effects for neem and locust bean only in the third year were 138% and 86% respectively, and declined progressively with increasing levels of applied inorganic fertilizer. This trend was consistent for the three years, during which soil productivity (relativity index) clearly appreciated. Results also revealed that P and organic C accumulation was greater with locust bean, but neem decomposed faster and depressed pH less, a clear indication that indices of soil productivity may not always be tied to OM or absolute values of soil properties alone in savanna soil systems. The study also revealed that the effects of the tree foliages, the inorganic fertilizer rates and the interactions were significant at various levels of probability for grain, stover, plant height, available P, OM and pH. There was the possibility of better crop performance with combinations of OM and inorganic fertilizer levels for the soils. Integrated fertility management systems using 3 tons of neem foliage and 1/2 recommended inorganic fertilizer rate produced a good maize crop, and offers an economically viable option for the resource poor maize farmers of the Nigerian savanna.