Demand-Driven Technologies for Sustainable Maize ... - IITA

increased grain yield in the following order: cow dung > M. pruriensvines > L. leucocephala prunings > maize stover.Averaged over years and fertilizer levels (Fig. 3), grain and stoveryields of plots amended with cow dung were similar to those of plotsamended with M. pruriens vines; plots amended with L. leucocephalaprunings had signifi cantly lower yields. Since the N contents of M.pruriens vines and L. leucocephala prunings were almost identical, itmay be concluded that the decomposition and nutrient release of M.pruriens vines was in better synchrony with the demands of the maizecrop than L leucocephala prunings.The release of nutrients such as N, K and S, can lead to formationand accumulation of NO -3 , K + and SO -4 , and the associated cations oranions being leached down the soil profi le, with the wetting front, sothat the crop does not have ready access to the released nutrients (Blairet al. 1997). In soils of low nutrient capacity, such nutrients may beleached below the rooting zone of the crop. A rapid release of nutrientsfrom residues, which was observed with L. leucocephala prunings, maytherefore be inappropriate in tropical systems with such soils. Gillerand Cadish (1995) similarly observed that under fi eld conditions, thecontribution of prunings to crop nutrition is often small. The poor yieldsobtained following application of maize stover could be attributedsolely to the low N content, particularly as the N content was belowthe critical value. This suggests that the maize stover decomposedand released nutrients too slowly to meet crop requirements, due topossible immobilization following the application.Averaged over the three years, grain yield decreased by 54, 76,58, and 70% for the treatments with cow dung, maize stover, M.pruriens vines and L. leucocephala prunings, relative to the recommendedinorganic fertilizer treatment. It is important to note that theorganic materials were added only once before planting and the ureawas applied in two equal split doses. It was, therefore, possible to timethe application of the N fertilizer to the crop, when demand was high.Thus, the inorganic fertilizer had a better synchrony of N release withcrop demand and was thus made more effi cient for grain production.Nutrient release from organic materials is spread over time, and thereis usually no sharp peak in mineralization that can be synchronizedwith plant demand. The application of organic materials at the ratesused in this study would almost always require application of inorganicfertilizer, at least at the initial stages of plant growth.Maize yield was high when organic materials and an optimumquantity of fertilizer were applied together. Signifi cant interactionbetween organic matter type and inorganic fertilizer rate was observedfor grain and stover yields in 1999 and 2000. The interaction showedthat at 0, 25 and 50% of recommended rates of inorganic fertilizer129