In the intensive rice ( Oryza sativa L.)‐based cropping systems of the tropics, dry season (DS) nonrice crop‐fallow (dry‐to‐wet [DTW] transition)‐wet season (WS) rice is a common practice. Excessive use of N fertilizer in high‐value crops like vegetables grown in DS is economically motivated. The risk of NO 3 leaching into groundwater during DTW transition is an environmental concern. Experiments were conducted in seven rice‐sweet pepper ( Capsicum annuum L. var. annuum ) farmers' fields to determine (i) the extent of NO 3 ‐N contamination in groundwater, and (ii) the effectiveness of a N‐catch crop to decrease NO 3 leaching. Twelve of twenty water sources had near or above World Health Organization's (WHO) NO 3 ‐N limit for drinking water. Soil mineral N (upper 100 cm) ranged from 111 to 694 kg ha ‐1 was decreased by 10 to 68% in plots with DTW crop. In fallow plots where mineral N was either maintained or increased, there was movement to lower soil profile demonstrating NO 3 leaching without a crop. On average, maize ( Zea mays L.) captured 176 kg N ha ‐1 and indigo ( Indigofera tinctoria L.) 194 kg N ha ‐1 . Indigo acquired <20% N from biological N fixation (BNF); this low contribution was due to inhibition by high soil mineral N. In both fallow and planted plots, mineral N declined to low levels at 100% water‐filled pore spaces (WFPS) before rice transplanting. A suggestion for developing indigo plus maize N‐catch crop rotations is made to decrease NO 3 leaching and maximize N use efficiency in rice‐sweet pepper cropping system.
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Shrestha et al. (1998) studied this question.