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This article in SSSAJ

  1. Vol. 60 No. 1, p. 183-192
    Received: Aug 23, 1994

    * Corresponding author(s): j.k.ladha@cgnet.com
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Legume Productivity and Soil Nitrogen Dynamics in Lowland Rice-Based Cropping Systems

  1. J. K. Ladha ,
  2. D. K. Kundu,
  3. M. G. Angelo-Van Coppenolle,
  4. V. R. Carangal,
  5. M. B. Peoples and
  6. P. J. Dart
  1. International Rice Research Inst. (IRRI), P.O. Box 933, 1099 Manila, Philippines
    CSIRO Division of Plant Industry, Canberra, ACT 2601, Australia
    Dep. of Agriculture, University of Queensland, Qld 4072, Australia



Rice (Oryza sativa L.) in wet season (WS) preceded by a dry season (DS) fallow, commonly practiced in rainfed lowlands, causes large losses of N through NO3 leaching and denitrification. The green-manure legumes as NO3 catch crops is economically unattractive to farmers. In a 2-yr study, we (i) assessed productivity of one grain and four forage legumes (pigeonpea [Cajanus cajan (L.) Millsp.], crotalaria (Crotalaria juncea L.), clitoria (Clitoria ternatea L.), desmanthus [Desmanthus virgatus (L.) Willd.], and siratro [Macroptilium atropurpureum (Mocino & Sessé ex DC.) Urban]) grown in the DS, (ii) examined NO3-N and NH4-N dynamics in soil (a Typic Tropaquept), and (iii) evaluated legume residues as a N source for succeeding rice. Nitrate-N was dominant in the 30-cm topsoil and was higher under legumes compared with weedy fallow. The legumes produced 4.9 to 9.1 t aboveground biomass ha-1, accumulated 132 to 306 kg N ha-1 of which 67 to 81% was derived from N2 fixation. After harvests, 2.9 to 5.2 t ha-1 of residues containing 81 to 162 kg N ha-1 were returned to soil. By 3 to 4 wk after flooding, legume-treated plots had as much as 33 to 40 kg mineral N ha-1 in topsoil compared with 10 to 13 kg N ha-1 in weedy fallowed plots. Residues significantly increased rice yield and N uptake. Rice recovered 15 to 31% of the residue N. Failow plots required 25 to 50 kg fertilizer N ha-1 to produce comparable plant growth responses to that obtained after the legumes. Belowground residues of the legumes apparently contributed 13 to 37 kg N ha-1 to rice. Such DS legumes that improve farm productivity as well as increase soil fertility might ensure sustainability of production in rainfed lowlands.

This study is part of a collaborative program between IRRI and the Australian Centre for International Agricultural Research (ACIAR) under the project no. 8800 and 8731. The work was partially supported by the Australian International Development Assistance Bureau (AIDAB).

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