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Nitrate Dynamics during the Aerobic Soil Phase in Lowland Rice‐Based Cropping Systems
Author(s) -
George T.,
Ladha J. K.,
Buresh R. J.,
Garrity D. P.
Publication year - 1993
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1993.03615995005700060022x
Subject(s) - agronomy , weed , tillage , vigna , alfisol , mulch , sesbania , biology , radiata , soil water , ecology
In tropical rice ( Oryza sativa L.) lowlands, soil NO 3 is lost during the transition from the dry to the wet season. To understand how soil and crop management influences NO 3 loss, we examined NO 3 dynamics during a 2‐yr period in an Alfisol in the Philippines: weedy, weed‐free, and frequently tilled main plots during the February to May dry season (DS), and Sesbania rostrata (Brem. & Oberm), mungbean [ Vigna radiata (L.) R. Wilczek var. radiata ], weedy, and weed‐free subplots during the May to July dry‐to‐wet transition (DWT). Weed‐free plots were maintained by removing weeds as they emerged. Soil NH 4 (0–60 cm), which was not affected by management, averaged only 9 kg N ha −1 . While soil NO 3 increased under frequent tillage and weed‐free fallowing, it decreased rapidly under weedy fallowing. On most sampling dates, NO 3 was the highest in DS tilled main plots. The widest range of NO 3 during the DS or DWT was 14 to 110 kg N ha −1 in the first year, and 12 to 155 kg N ha −1 in the second. During the second half of the DWT, NO 3 declined in all plots, but more markedly when plants were present than when not, indicating plant N uptake. Above‐ground plant N prior to permanent flooding ranged widely from 31 kg N ha −1 in weeds to 222 kg N ha −1 in N 2 ‐fixing S. rostrata plants in the first year, and 37 to 193 kg N ha −1 in the second. The data also indicate NO 3 leaching following heavy rains. Further, the high water‐filled pore space, exceeding 0.7 L L −1 in the second half of the DWT and approaching 1 L L −1 with permanent flooding, is presumed to have favored denitrification. Regardless of DS management or DWT plant N accumulation, the soil was virtually depleted of NO 3 soon after permanent flooding; NO 3 rarely exceeded 10 kg N ha −1 when measured after 9 d (first year) and 11 d (second year) of permanent flooding. Our data indicate the immense capacity of this lowland soil to accumulate NO 3 and the marked effect of DS and DWT management on the amount of NO 3 that actually accumulates. In tropical rice lowlands, soil and crop management during the DS should be designed to limit NO 3 buildup so as to reduce NO 3 that is prone to loss during the DWT.