Contribution of green and farm yard manure in the nitrogen nutrition of sugarcane

Experiment were conducted to evaluate the amount of nitrogen contributed by various organic fertilisers to the N-nutrition of a growing sugarcane crop, at the sugarcane research farm of National Cereals Research Institute (NCRI) in 1999 and 2000. The objective was to provide alternative source of nutrients in response to the scarcity and high cost of inorganic fertiliser often experienced by local farmers who grow high nutrient requiring crops. Farm Yard Manure (FYM) at (10 tonnes/ha), was applied into soil two weeks before planting, and four leguminous crops; cowpea, soybean, mucuna and sesbania were sown into sugarcane plots and worked into the soil when they were 6 weeks old. There were also control plots with and without inorganic NPK fertilisers. Soil samples carrying each of these treatments were analysed at various stages of the crop's growth to monitor N-levels in soils. Results show that the legumes while still growing, contributed between 1.5 - 1.8 kg/ha and 4.6 to 6.6 kg/ha N to the soil in both years of study, respectively. They also contributed around 20.2 to 30 kg/ha of nitrogen to the soils after incorporation. The FYM contributed the highest amount of 51.0 to 53.1 kg/ha N to the soil within the same period. Periodic N analysis of soil at four weeks intervals showed that the bulk of N in the legumes was released within the first four weeks of incorporation. Data taken at 6 weeks after incorporation showed that N-levels in the soils had declined to between 13.6 to 16.5% of their levels at 4 weeks after incorporation. Cane yields were generally lower under the legume - treated soils (38.7 - 53.4 t/ha) when compared to yields recorded under fym (58.6 - 70.1 t/ha) or even inorganic fertilisers (55.7 - 66.9 t/ha) for the two years of the study.