caa a22 4500 477112145 CHVBK 20180405111612.0 cr unu---uuuuu 170330e19960501xx s 000 0 eng 10.1007/BF00029058 doi (NATIONALLICENCE)springer-10.1007/BF00029058 Soil organic matter and the indigenous nitrogen supply of intensive irrigated rice systems in the tropics [Elektronische Daten] [K. Cassman, A. Dobermann, P. Cruz, G. Gines, M. Samson, J. Descalsota, J. Alcantara, M. Dizon, D. Olk] Soil organic matter (SOM) has been proposed as an index of N supply in paddy soils although field validations are few. We evaluated the relationship between the indigenous N supply (N i ) of the soil-floodwater system and soil organic carbon (SOC) or total N (N t ) in surface soil of long-term fertility experiments (LTFEs) at 11 sites, in 42 farmer's fiels with similar soil type, and in the same field in ten consecutive rice (Oryza sativa L.) crops. The N i was estimated by crop N uptake from plots without applied N (N o plots) under otherwise favorable growth conditions. There was a tight linear correlation between yields and N uptake in N o plots and tremendous variation in both parameters among LTFE sites, farmer's fields, and in the same field over time. Correlation between N i and SOC or N t explained little of this variation. Factors likely to contribute to the poor correlation were: (1) inputs of N from sources other than N mineralization of SOM in surface soil, (2) degree of congruence between soil N supply and crop demand, which is sensitive to soil drying, length of fallow, crop rotation, and residue management, and (3) differences in SOM quality related to intensive cropping in submerged soil. Better understanding of the processes governing the N i of tropical lowland rice systems would contribute to the development of crop management practices that optimize utilization of indigenous N resources. Kluwer Academic Publishers, 1996 anaerobic soil nationallicence flooded soils nationallicence intensive cropping nationallicence long term experiments nationallicence lowland rice nationallicence nitrogen mineralization nationallicence nitrogen uptake nationallicence on-farm research nationallicence organic carbon nationallicence organic matter nationallicence Oryza sativa nationallicence plant nitrogen nationallicence soil nitrogen nationallicence Cassman K. International Rice Research Institute, P.O. Box 933, 1099, Manila, Philippines aut Dobermann A. International Rice Research Institute, P.O. Box 933, 1099, Manila, Philippines aut Cruz P. International Rice Research Institute, P.O. Box 933, 1099, Manila, Philippines aut Gines G. International Rice Research Institute, P.O. Box 933, 1099, Manila, Philippines aut Samson M. International Rice Research Institute, P.O. Box 933, 1099, Manila, Philippines aut Descalsota J. International Rice Research Institute, P.O. Box 933, 1099, Manila, Philippines aut Alcantara J. International Rice Research Institute, P.O. Box 933, 1099, Manila, Philippines aut Dizon M. International Rice Research Institute, P.O. Box 933, 1099, Manila, Philippines aut Olk D. International Rice Research Institute, P.O. Box 933, 1099, Manila, Philippines aut Plant and Soil Kluwer Academic Publishers; gopher://gopher.wkap.nl 182/2(1996-05-01), 267-278 0032-079X 182:2<267 1996 182 11104 https://doi.org/10.1007/BF00029058 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/BF00029058 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Cassman K. International Rice Research Institute, P.O. Box 933, 1099, Manila, Philippines aut NATIONALLICENCE 700 1- Dobermann A. International Rice Research Institute, P.O. Box 933, 1099, Manila, Philippines aut NATIONALLICENCE 700 1- Cruz P. International Rice Research Institute, P.O. Box 933, 1099, Manila, Philippines aut NATIONALLICENCE 700 1- Gines G. International Rice Research Institute, P.O. Box 933, 1099, Manila, Philippines aut NATIONALLICENCE 700 1- Samson M. International Rice Research Institute, P.O. Box 933, 1099, Manila, Philippines aut NATIONALLICENCE 700 1- Descalsota J. International Rice Research Institute, P.O. Box 933, 1099, Manila, Philippines aut NATIONALLICENCE 700 1- Alcantara J. International Rice Research Institute, P.O. Box 933, 1099, Manila, Philippines aut NATIONALLICENCE 700 1- Dizon M. International Rice Research Institute, P.O. Box 933, 1099, Manila, Philippines aut NATIONALLICENCE 700 1- Olk D. International Rice Research Institute, P.O. Box 933, 1099, Manila, Philippines aut NATIONALLICENCE 773 0- Plant and Soil Kluwer Academic Publishers; gopher://gopher.wkap.nl/ 182/2(1996-05-01), 267-278 0032-079X 182:2<267 1996 182 11104 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer