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Nitrate in Groundwater and Integration of Nitrogen-Catch Crop in Rice-Sweet Pepper Cropping System

Soil Microbiology, Soil and Water Sciences Division, International Rice Research Institute (IRRI), P.O. Box 933, Manila, Philippines

*Corresponding author (in%j.k.ladha{at}cgnet.com).

ABSTRACT

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 NO₃ 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 NO₃-N contamination in groundwater, and (ii) the effectiveness of a N-catch crop to decrease NO₃ leaching. Twelve of twenty water sources had near or above World Health Organization's (WHO) NO₃-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 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. 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 NO₃ leaching and maximize N use efficiency in rice-sweet pepper cropping system.

Received for publication September 22, 1997.

This article has been cited by other articles:

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