Responses of Maize Growth and Grain Yield to Different Sources and Time of Application of Nitrogen Fertilizer

Soil fertility decline has been identified as one of the major biophysical constraints affecting agriculture in the sub Saharan Africa, including Nigeria. Even though, the use of chemical fertilizer is the most convenient way of improving soil fertility, the high cost and poor distribution of chemical fertilizer have made the commodity inaccessible to resource poor farmers. Consequently, there is a negative balance in nutrient budgets of soils in the country. Ironically large amount of organic wastes abound that can be turned into fertilizers for crop production at possibly low cost. However, the extent to which different type and form of organic sources of N fertilizer could be used for sustainable crop production has not been adequately evaluated in Nigeria. This study was therefore designed to evaluate the responses of maize (Zea mays L) to different types and forms of organic manure as sources of N applied at different periods of crop growth. Field experiments were conducted over two cropping seasons at the National Centre for Agricultural Mechanization Research Farm Ilorin, using a Randomized Complete Block Design arranged as a 7 x 4 factorial combinations with 3 replications. The treatments consisted of 7 sources of N fertilizer combined with 4 different time of application. An improved open- pollinated maize variety (TZEE-SR-Y) was used for the experiment and data were collected on growth and yield parameters, including grain yield. All data collected were analyzed using the analysis of variance (ANOVA) and significant means were separated with the least significant difference (LSD) method at five percent probability level. Results of the study showed that the application of the inorganic source of N (urea) was superior to all types and forms of the organic sources on all growth, yield components and grain yield, suggesting that the application of sole organic sources of N may not be adequate for optimum grain yield. The best grain yield was obtained with the application of fertilizer at 4 WAP, depending on the source, with most sources producing the best yield with application at 4 WAP, while cow dung showed the best yield with application at the planting of maize. The post crop harvest soil properties (Soil pH, total N and organic matter contents) were better with the application of any type and form of organic N sources, indicating probable long term sustainability of crop production. In conclusion, the sole use of organic sources of N in the evaluated rate may not be adequate for optimum crop yield. Nevertheless the long run sustainability of crop production may be better.