Forms of nitrogen in runoff and sediments under a Solanum macrocarpon (L.) Moench farm after urea fertilizer application
2025
Femi Thomas Akinwumi | Durodoluwa Joseph Oyedele | Fatal Oladapo Tijani
Runoff from agricultural fields is major of source nitrogen pollution of surface water resources. The impact of the menace on surface water directly emanating from agricultural fields in different agroecologies has not been fully understood. Applying different urea rates, the runoff and sediments generated from Solanum macrocarpon plots after rainfall and irrigation events were analyzed for nitrite-nitrogen, nitrate-nitrogen and ammonium-nitrogen in a one-year study involving two seasons. Significant nitrite-nitrogen, nitrate-nitrogen and ammonium-nitrogen response to the treatments were observed in 17 – 57% of the runoff events, and nitrate-nitrogen of sediments. Runoff NO2–N concentrations from 80 kg N ha-1 (CA) was in many cases higher than values in plots with lower rates. Commonly, runoff’s NO3–N from plots with urea was higher than controls’ in rainforest but within the urea treated plots, the differences were insignificant. In derived savanna about 67% of significant comparison of runoff NO3–N were between control and plots with urea while about 33% were due to differences noticed between 20 – 60 kg N ha-1 (MD 1 – MD 3) and MD 1 - CA. Moreover, NH4–N in runoff increased with urea in both agroecologies. In conclusion, NH4–N in runoff increased with applied urea while the responses of other nitrogen forms were inconsistent. Based on World Health Organization’s (WHO) standard, runoff‘s NO2–N from CA in derived savanna and all treatments in rainforest tended to be harmful to humans if it enters drinking water. However, NO3–N released from the plots seemed not harmful.
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