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This article in AJ

  1. Vol. 86 No. 2, p. 267-273
    Received: Jan 11, 1993

    * Corresponding author(s): t.george@cgnet.com
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Legumes as Nitrate Catch Crops During the Dry-to-Wet Transition in Lowland Rice Cropping Systems

  1. Thomas George ,
  2. J. K. Ladha,
  3. Dennis P. Garrity and
  4. Roland J. Buresh
  1. ( IRRI-NifTAL Collaborative Program), P.O. Box 933, Manila, Philippines.
    ( IRRI), P.O. Box 933, Manila, Philippines;
    I CRAF Southeast Asia Regional Programme, Jalan Gunung Batu 5, P.O. Box 161, Bogor 16001, Indonesia;
    I CRAF, P.O. Box 30677, Nairobi, Kenya.



In tropical rice (Oryza sativa L.) lowlands, NO3 assimilation by plants during the transition from the dry to the wet season can preclude NO3 loss upon soil flooding and permit recycling of this N. In a 2-yr field study in an Alfisol in the Philippines, we examined the role of legume crops and weeds during the dry-to-wet (DTW) transition in conserving and/or recycling soil NO3 that accumulated under varied dry-season fallow management. During the May-to-July DTW transition, Sesbania rostrata (Bremek. & Oberm.), mungbean [Vigna radiata (L.) Wilczek], weedy, and weed-free treatments were subplots in the February-to-May dry-season mainplots of weedy, weed-free, and frequently tilled fallows. Legume biological N2 fixation (BNF) was measured by 15N dilution. Depending on dry-season management, the maximum extracted N (top 60-cm layer) in the DTW transition ranged from 38 to 164 kg ha−1; this N was 62 to 96% NO3. Soil N uptake by weeds ranged from 31 to 46 kg N ha−1, that by mungbean from 29 to 80, and by S. rostrata from 46 to 125. The minimum estimates of DTW transition NO3 loss varied from none when plants were present to 107 kg N ha−1 in weed-free fallows. Legume BNF partially offset NO3 loss, although increased soil NO3 decreased BNF-N. Nitrogen fixed ranged from 37 to 63 kg N ha−1 by mungbean and 68 to 154 by S. rostrata. Harvest of mungbean caused negative BNF-N contribution to the succeeding rice crop in a few cases. In lowland rice-based cropping systems, weeds are effective in conserving soil N during the DTW transition, but legumes are more suitable nitrate catch crops because they allow the harvest of an economic product or the recycling of more N to a subsequent flooded rice crop.

Joint contribution from the Int. Rice Res. Inst. (IRRI), the Nitrogen Fixation by Tropical Agric. Legumes (NifTAL) Ctr. (Univ. of Hawaii, 1000 Holomua Ave., Paia, HI 96779), and the International Fertilizer Development Ctr., (P.O. Box 2040, Muscle Shoals, AL 35662).

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