摘要：

The effectiveness of soil nutrient availability procedures is closely related both to the extent to which the data can be calibrated with field fertilizer trials and to the interpretation of the analysis. Quite often much more is expected from soil testing than the method allows. The chapter discusses the reasons for this discrepancy, with special reference to phosphorus and potassium. Soil analysis mainly provides an indication of the capacity of a soil to supply nutrients to the plants, but does not adequately and in some cases does not at all characterize the mobility of the nutrients in the soil. The chapter discusses these factors, beginning with nutrient availability in relation to mobility in soils and root growth. Although the bioavailability of nutrient concept is focused on aerated soils, its principles may also be applied to submerged soils and plant species such as lowland rice. Three components are considered in the concept: root interception, mass flow, and diffusion. Soil solution mineral nutrient concentration varies widely, depending on such factors as soil moisture, soil depth, pH, cation-exchange capacity, redox potential, quantity of soil organic matter and microbial activity, season of the year, and fertilizer application. Mass flow is the convective transport of nutrients dissolved in the soil solution from the bulk of the soil to the root surface.

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