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Recycling in situ of Legume‐Fixed and Soil Nitrogen in Tropical Lowland Rice
Author(s) -
George Thomas,
Buresh Roland J.,
Ladha Jagdish K.,
Punzalan Gloria
Publication year - 1998
Publication title -
agronomy journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 131
eISSN - 1435-0645
pISSN - 0002-1962
DOI - 10.2134/agronj1998.00021962009000030018x
Subject(s) - agronomy , weed , legume , dry season , vigna , nitrogen fixation , nitrogen , radiata , biology , chemistry , ecology , organic chemistry
In tropical rice lowlands, vegetation during the dry‐to‐wet season transition (DTW) facilitates in situ recycling of N from soil or legume biological nitrogen fixation (BNF) to wet‐season flooded rice. As little is known, we examined the fates of soil N and BNF N in DTW vegetation in a 2‐yr study on a Philippine Tropudalf using 15 N‐labeled residues produced and soil‐incorporated in situ. During DTW, Sesbania rostrata (Bremek. & Oberm.), mungbean [ Vigna radiata (L.) R. Wilczek var. radiata ], weeds, and a weed‐free fallow were subplots in dry‐season main plots of weedy, weed‐free, and frequently tilled fallows. Rice yield and N uptake were not influenced by dry‐season fallows, which did influence soil N and BNF N in DTW vegetation and, therefore, the amount of soil N lost, removed in a product or recycled. Build‐up and decline of soil NH 4 −N occurred within 5 wk of residue incorporation, before significant N uptake by rice. Rice yield and N uptake responded to greater recycled DTW N; N uptake averaged 103 kg ha −1 with 208 kg S. rostrata N ha −1 , 79 kg ha −1 with 62 kg mungbean N ha −1 , 61 kg ha −1 with 41 kg weed N ha −1 , and 44 kg ha −1 with no residue N. Nitrogen‐15 estimates of N recovery by rice (20% of S. rostrata N, 27% of mungbean N, 16% of weed N) were lower than the actual increase in rice N uptake due to residues. High proportions of residue N remained in soil, but N loss of 32% was estimated for S. rostrata N. As green manure (GM) N is ineffective beyond the first few weeks of incorporation, incorporating much legume N to flooded rice wastes valuable BNF N. Unmet rice N demand beyond early crop stage is better supplied with fertilizer N synchronized with rice N demand. A mixture of native weeds and GM legume is likely to prevent build‐up of soil NO ∐ 3 −N and allow BNF while limiting total N accumulation in the DTW vegetation for use as GM.