Methods for Soil Phosphorus J Lehmann

Phosphorus availability is a limiting factor for plant production in many agricultural soils (Fairhurst et al., 1999). This is especially true in the highly weathered soils of the humid tropics. At the same time, the global availability of phosphorus fertilizers is limited and known reserves may be exhausted in about 100 years with the current growth of phosphorus usage (Stevenson and Cole, 1999). In regions of the world without a history of use of phosphorus fertilizers, phosphorus deficiency...

Soil organisms and their functional domains

Soil organisms have evolved in an environment that imposes three major requirements (i) to move in a compact environment with a loosely connected porosity (ii) to feed on low-quality resources and (iii) to adapt to the occasional drying or flooding of the porous space (Lavelle, 1997). A continuum of adaptive strategies based on size is observed in soils, from microorganisms to macroinvertebrates (Swift et al., 1979). Soil invertebrates have been divided into micro-, meso- and macrofauna...

Methods for Potassium Calcium and Magnesium in Soil

The cations potassium, calcium and magnesium occur in several forms in the soil that differ in their availability to plants. The most readily plant-available fraction is that in the soil solution, followed by the exchangeable fraction, which replenishes the soil solution if nutrients are removed by either plant uptake or leaching. Potassium fixed in clay interlayers becomes available at a time scale from hours to weeks. The least available forms are various primary and secondary soil minerals,...

Hierarchy of Agricultural Systems as a Background to the Understanding of Farmers Constraints

Figure 2.2 represents a spatial hierarchy of agricultural systems within which farmers' decisions are made. The highest level in the hierarchy, supraregional systems, occupies the largest land area and can transcend national boundaries. Macroeconomic processes, as well as certain geological processes, are best understood at this level. The lowest level (soil systems) covers the smallest spatial unit and is the level at which specific biological processes such as nutrient uptake may be...

Trees and soil fertility

Whatever the reasons farmers have for planting or protecting trees in a specific case, they nearly always fulfil several functions simultaneously. Trees may have been planted on a hillslope to produce timber or fruits, but they may also protect the soil from being eroded. Trees planted or retained for fodder are often nitrogen-fixing and may improve nitrogen availability in the soil. Similarly, trees that have been allowed to regenerate in a riparian zone because of environmental regulation,...

Nutrient capture from the subsoil nutrient pumping

Nutrient capture by trees from the subsoil can include nutrients released by weathering of primary minerals and also nutrients leached from the topsoil that are then recycled by the trees. Capture of newly weathered nutrients is restricted to relatively young soils where weatherable minerals still occur within the reach of tree root systems, including colluvial or alluvial soils with irregular nutrient distribution with soil depth. Despite the prominence of nutrient pumping by trees as a...

Synchrony and synlocation of nutrient release with plant uptake

When biomass decomposes on or in the soil, the nutrients may either remain in the soil in mineral form, be incorporated in the soil biomass and soil organic matter immobilization , be taken up by plants, or be lost from the system through leaching or in gaseous form. The relative importance of these different pathways depends on the respective nutrient, the decomposing material, and the biotic and abiotic conditions under which the decomposition process takes place. It has been hypothesized...