Partial balance of nitrogen in a maize cropping system in humic nitisol of Central Kenya

Abstract

The application of nitrogen in a soil under agricultural production issubject to several pathways including le-nitrification, leaching andrecovery by an annual crop. This is as well greatly influenced by themanagement practices, nitrogen source and soil conditions. The mainobjective of this study was to investigate the loss of nitrogen (N)through nitrous oxide (N2O) emissions and mineral N leaching and uptakeby Annual crop as influenced by the N source. The study was carried outat Kabete in Central Kenya. Measurements were taken during the secondseason after two seasons of repeated application of N as urea AndTithonia diversifolia (tithonia) leaves. Results obtained indicated thatnitrous oxide (N2O) emissions at 4 weeks after planting were as high as12.3 mu g N m(-2) h(-1) for tithonia treatment and 2.9 mu g N m(-2)h(-1) for area treatment. Tithonia green biomass treatment was found toemit N2O at relatively higher rate compared to urea treatment. This wasonly evident during the fourth week after treatment application. Soilmineral N content at the end of the season increased down the profile.This was evident in the three treatments (urea, tithonia and control)investigated in the study. Urea treatment exhibited significantly highermineral N content down the soil profile (9% of the applied N) comparedto tithonia (0.6% of the applied N). This was attributed to the washingdown of the nitrate-N from the topsoil accumulating in the lower layersof the soil profile. However, there was no significant difference in Ncontent down the soil profile between tithonia treatment and thecontrol. It could be concluded that there was no nitrate leaching in thetithonia treatment. Nitrogen recovery by the maize crop was higher inthe urea treatment (76% of the applied N) as compared to tithoniatreatment (55.5% of the applied N). This was also true for the residualmineral N in the soil at the end of the season which was about 7.8% ofthe applied N in the urea treatment and 5.2% in the tithonia treatment.From this study, it was therefore evident that although there isrelatively lower N recovery by maize supplied with tithonia greenbiomass compared to maize supplied with urea, more nitrogen is beinglost (through leaching) from the soil-plant system in the urea appliedplots than in tithonia applied plots. However, a greater percentage(37.8%) of the tithonia-applied N could not be accounted for and mighthave been entrapped in the soil organic matter unlike urea-applied Nwhose greater percentage (92%) could be accounted for.