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

132Yield increase and relative yieldsTables 4 and 5 show maize and stover yields resulting from theapplication of the different organic materials on maize grain and stoveryields at various inorganic fertilizer rates. Relative yield response to theorganic material at zero and low fertilizer rates were greater in thesecond and third years, probably due to residual effects of the organicmaterials (Jokela 1992). The results indicated that the relative yieldsof sole applications of the leguminous residues and cow dung wereconsistently lower for stover than for grain. This suggests that, with theapplication of these organic materials, nutrients had a greater relativeeffect during the reproductive period than during the vegetative stage.This occurred, perhaps, because the nutrients mineralised from organicmaterials were becoming increasingly available, while the unfertilisedplots were becoming increasingly defi cient in nutrients as the seasonprogressed. The relative effects of the treatments on grain and stoveryields were consistent, and the magnitude varied with the type oforganic material in the following order: cow dung > M. pruriens vines> L. leucocephala prunings > maize stover.Relative yields of treatments with organic materials withoutinorganic fertilizers and at low inorganic fertilizer rates were higherat the end of the study. Kang (1993) similarly reported that maizeyield appeared to be sustainable at low fertilizer rates in combinationwith L. leucocephala prunings. This indicated an improvement in soilfertility conditions due to the capacity of the organic materials to arrestdegradation and maintain the productivity of the soils. Relative yieldsof plots amended with maize stover and varying rates of inorganicfertilizers were generally lower than for the other organic materials.This was true even at the recommended optimum rate of inorganicfertilizer application, indicating the negative effects of maize stoveron soil productivity. This is probably due to the low nutrient contents,relatively slower rate of decomposition and, hence, little nutrient releasefrom the maize stover.The results showed that, with the exception of maize stover, theaddition of the organic materials with and without fertilizer led toincreases in yield. Possible explanations for this response pattern mayinclude more favourable physical, inorganic and biological conditionsof the soil amended with green manure. The application of inorganicfertilizer had a greater effect when combined with M. pruriens vinesthan with any of the other organic materials. The relative effects of theorganic materials on grain yield decreased as inorganic fertilizer ratesincreased. This is expected since the base yield increased with eachincrement of inorganic fertilizer. Earlier studies led to similar conclusions(Uyovbisere and Elemo 2000). The results revealed a wide range ofincreases in maize grain yield with the application of different organic