Soil fertility components

Agriculture therefore depends on there being a sufficient supply of inorganic nutrients to plants. Cereals, vegetables, fruit-bearing trees or plants, and animal fodder require bioavailable nutrients, that is, nutrients in forms that they can use. Since intensive agriculture depletes many natural nutrients, synthetic nutrients (fertilizers) must be supplied.1-7 In particular, we need to fix the inert N2 of the atmosphere as soluble, reactive compounds such as nitrates, ammonia, and ammonium salts. Other major fertilizer components are sulfate, potassium, and phosphate ions. It may also be necessary to provide trace nutrients, such as cobalt compounds, or to remove excess soil acidity by treatment with lime (CaO). World fertilizer demand in the year 2001 is expected to be about 1.5 x 10s metric tons N, 7.6 x 107 metric tons P2O5, and 6.7 x 107 metric tons K2O these projections represent an... 

Fertile topsoil is a mixture of at least four components—mineral particles, water, air, and organic matter. The mineral particles are the particles of sand, silt, and clay. Many of the nutrients plants need are released as these particles are formed from the erosion of rock. The size of the particles greatly affects soil fertility. Large particles result in porous soil that has many pockets of space that collect water and air—up to 25 percent of the volume of fertile topsoil consists... 

At any rate, boosting African crop production will require increased use of soil amendments. Natural soil fertility restoration during long fallow periods, as practised in traditional shifting cultivation systems, becomes less and less feasible with rising population pressure. Mineral fertilisers have been key components of strategies to increase crop yields and restore soil fertility (e.g. Quinones et al., 1997), yet their availability and use in SSA remain very low due to lack of production, transport and market infrastructures (Larson and Frisvold, 1996 Dudal, 2002). Nutrient imbalances have resulted in the loss of an estimated 700 kg N, 100 kg P and 450 kg K ha 1 from SSA cropland during the last 30 years, while... 

The examples given above and the work done in the last 10 years on phosphate washing demonstrate that phosphates are very powerful stabilizers of inorganic hazardous contaminants. Phosphate washing is very economical, and once the treated waste is disposed, because phosphates are common fertilizer components, the soil becomes enriched with phosphates. Hence, the entire disposal process is ecologically sound. 

Soil chemistry is closely related to colloid (surface) chemistry, geochemistry, soil fertility, soil mineralogy, and soil microbiology or biochemistry. Soil fertility considers soil as a medium for plant growth. Soil mineralogy examines the structural chemistry of the solid phase. Soil microbiology studies soil biochemical reactions. Such subdivision is necessary to study the soil thoroughly, but these subdivisions sometimes obscure the interaction between soil components, and this interaction is often as important as the properties of the components alone. 

Many agricultural processes such as control of fertilizers and pesticides are influenced by surface and sub-surface movement, percolation and infiltration of water. Stable activateable tracers, such as bromide, analyzed by NAA, have allowed the soil scientist to quantify the distribution of agricultural chemicals under a wide variety of environmental and land use influences. In one of the study on phosphate fertilizers in Egypt using NAA, Abdel-Haleem et al. (2001) have reported the presence of heavy metals Fe, Zn, Co, Cr, and Sc as well as rare earth elements La, Ce, Hf, Eu, Yb and Sm in the samples containing the phosphate fertilizer components (e.g., rock phosphate, limestone, and sulfur) from which fertilizer is produced as final output product. The measurement of Ca/Si concentration ratio in the concrete samples has been carried out using NAA with 5Ci Am-Be neutron source (Khelifi et al. 1999). 

The relationships between bacteria and plants have important economic implications. The activities of the nitrogen-fixing symbiotic bacteria of root nodules are crucial to soil fertility. On the negative side bacterial pathogens are responsible for significant worldwide crop losses. The specificity of bacterial pathogens and symbionts for a particular plant host, the mechanisms involved in the induction of disease symptoms and the triggering of plant host defence mechanisms are all mediated by components of the bacterial cell surface. 

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