Environmental impact of new rice growing technologies: soil microbial biomass in wetland rice soils
1993
Gaunt, J.L. | Neue, H.U. (International Rice Research Inst., Los Banos, Laguna (Philippines))
This study aims to quantify and establish a mechanistic understanding of the role of soil microbial biomass in soil fertility under intensively cultivated wetland rice. The specific objectives were: a) to quantify the relationships between soil microbial biomass and soil organic carbon content; b) to relate the process of reduction upon flooding to soil organic matter content; and c) to investigate the relationship of soil microbial biomass and soil nitrogen (N) under field conditions. Soil microbial biomass of wetland soils under aerobic incubation was linearly related to a labile carbon pool in the plough layer rather than total soil organic carbon. Labile carbon in the Ap horizon reflects organic inputs and part of soil organic matter. The rate of reduction upon flooding was related to the C:N ratio of the enriched organic fraction but not total soil organic carbon. Soil N status was described on a mass basis relative to N uptake by IR72, where the soil N environment was altered by N fertilizer addition. Soil N was measured as exchangeable, soil solution phase and soil microbial biomass N. Soil microbial biomass increased with increasing soil exchangeable and solution phase ammonium resulting in rapid immobilization of large amounts of added fertilizer N by the soil microbial biomass. These results emphasize the importance of soil microbial biomass in the regulation of soil and fertilizer N supply in flooded soils, highlighting the apparent contrasts in the behavior of the soil microbial biomass under aerobic and anaerobic condition
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