Nitrogen (N) plays an important role in agriculture crop production but the increasing application of nitrogen increases the possibilities of groundwater contamination through nitrate leaching. Nitrate leaching is the inevitable part of agriculture production which occurs during nitrogen fertilization. Hence, the quantification of nitrogen fertilizer is required to reduce nitrate leaching. In this study, nitrogen transformation and transport such as ammonium (NH4+) and nitrate (NO3-) at different soil depths and maize crop growth stages were measured during field experiments for two sowing dates (timely and delay) and four N fertilization levels under irrigated (year 2013 and 2014) and rainfed (year 2012 and 2014) conditions for maize crop. NH4+, NO3- and total nitrogen concentrations were measured using spectrophotometer at 410 nm and Kjeldahl method at varying soil depths and maize crop growth stages. Thereafter, nitrogen balance approach was used to estimate the NO3- leaching. Results indicated that NO3- leaching in irrigated condition was higher 109% in N75, 179% in N100, and 292% in N125 level respectively in comparison to the N0 level in timely sowing date, while in delayed sowing date, leaching was higher 54% in N75, 123% in N100, and 184% in N125 level respectively in comparison to N0 level. In rainfed, the NO3- leaching was higher 30% in N60, 59% in N80, and 99% in N100 level respectively in comparison to N0 level for the timely sowing date, while in delayed sowing, leaching was higher 23% in N60, 44% in N80, and 78% in N100 level respectively in comparison to N0 level. The results indicate that leaching losses were less in timely sowing dates for both rainfed and irrigated maize. The study further reveals that sowing dates combination with N levels could be an effective management strategy to reduce NO3- leaching by minimizing the N fertilization.
Keywords: Ammonium; Nitrate; Nitrogen balance; Nitrogen transport; Total nitrogen.
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