Nitrate in groundwater and integration of nitrogen-catch crop in rice-sweet pepper cropping system

In the intensive rice (Oryza sativa L,)-based cropping systems of the tropi cs, dry season (DS) nonrice crop-fallow (dry-to-wet [DTW] transition)-wet s eason (WS) rice is a common practice. Excessive use of N fertilizer in high -value crops like vegetables grown in DS is economically motivated, The ris k of NO3 leaching into groundwater during DTW transition is an environmenta l concern, Experiments were conducted in seven rice-sw eet pepper (Capsicum annuum L, var. annuum) farmers' fields to determine (i) the extent of NO3- N contamination in groundwater, and (ii) the effectiveness of a N-catch cro p to decrease NO3 leaching, Twelve of twenty water sources had near or abov e World Health Organization's (WHO) NO3-N limit for drinking water. Soil mi neral N (upper 100 cm) ranged from 111 to 694 kg ha(-1) was decreased by 10 to 68% in plots with DTW crop. In fellow plots where mineral N was either maintained or increased, ;there was movement to lower soil profile demonstr ating NO3 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). Indi go 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 pl ots, mineral N declined to low le,els at 100% water-filled pore spaces (WFP S) before rice transplanting. A suggestion for developing indigo plus maize N-catch crop rotations is made to decrease NO3 leaching and maximize N use efficiency in rice-sweet pepper cropping system.