Significance of biocatalytic mechanisms in soil nutrient supply for soil fertility improvement indrought-prone, highly degraded rainfed lowland rice soils
2001
Reichardt, W. | Konboon, Y. | Angeles, O. (International Rice Research Inst., Los Banos, Laguna (Philippines)) Meepetch, S.
Rainfed lowland rice farming in northeast Thailand faces the challenge of sustaining and increasing yields on drought-prone, sandy soils with extremely low cation exchange capacity (CEC) and organic matter content. As acidification progresses with continued chemical degradation of once deforested Acrisol-type soils, this steady decline in soil fertility is accelerated by further losses to the organic matter pool. With numerous attempts to restore soil fertility, specific knowledge-based guidance has been lacking due to scarce mechanistic explanation of underlying soil biochemical processes. Field experiments with rice monocropping on acid sandy soil (URRC) were conducted to optimize grain yields through improving the soil organic matter phase. At the same time, biocatalytic parameters which can provide indices for nutrient cycling and supply were identified. These parameters included respiratory electron transport system (ETS) or dehydrogenase activity as a measure of nutrient remobilization from organic pools, and the C and N source utilization on BIOLOG assay plate (% richness) as measure of diversity. Functional diversity related to soil microbial C and N source utilization and total remineralizing capacity (measured as ETS activity) were closely correlated with agronomic parameters of crop growth particularly on the above-ground biomass, tiller density, panicle density, grain yield and grain N uptake. ETS activity and BIOLOG-based diversity of soil microbial functions apparently reflected soil fertility in these cropping systems, hence may be considered as yardsticks for soil fertility improvement in these extremely degraded, drought-prone rice soils
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