Soil mineral supply

Calcium. Soil minerals are a main source of calcium for plants, thus nutrient deficiency of this element in plants is rare. Calcium, in the form of pulverized limestone [1317-65-3] or dolomite [17069-72-6] frequendy is appHed to acidic soils to counteract the acidity and thus improve crop growth. Such liming incidentally ensures an adequate supply of available calcium for plant nutrition. Although pH correction is important for agriculture, and liming agents often are sold by fertilizer distributors, this function is not one of fertilizer manufacture. 

Soil minerals play a stabilizing role in organic matter. The Al and Fe that complex and stabilize organic matter against microbial decomposition are released from soil minerals during soil formation. The supply rates apparently control the content of soil organic matter to a great extent. This is demonstrated by the relationship between pyrophosphate-extractable C and pyrophosphate-extractable Al plus Fe (Wada 1995). 

The Ca content of soils varies widely, ordinarily ranging from about 0.07 to 3.60%. Calcium is contained in a number of soil minerals including dolomite, calcite, Ca feldspars, apatite, amphiboles and many others. Coarse-tex-tured soils in humid regions, particularly those formed from rocks low in Ca minerals, are generally low in Ca. In spite of this, Ca deficiencies in crops do not appear to be of widespread occurrence, although a number of other factors affect nutrition in low base status soils. Fertilizers are not generally manufactured specifically to provide Ca as a plant nutrient, since this element is economically supplied by periodic applications of agricultural lime, as discussed subsequently. 

TNT that resides in aerobic environments at the surface of the soil is often degraded by photocatalyzed oxidation of the methyl carbon. This oxidation is probably a multistep process by which the methyl group is initially oxidized to an alcohol, then to an aldehyde, and finally to a carboxylic acid. Decarboxylation of the resultant product yields trinitrobenzene. Evidence for this pathway was supplied by Spanggord et al. [29], who reported formation of trinitrobenzaldehyde and trinitrobenzoic acid during the degradation of TNT to trinitrobenzene. It has been reported that oxidation of the methyl group of TNT is mediated by surface catalysis on soil minerals [30], by ozonation [31], and by the action of sunlight [29], At sites where the TNT contamination is localized to the soil surface, the concentration of trinitrobenzene may often exceed that of TNT [32],... 

The ability of some soils to supply K+ for plants Is remarkable. Tropical soils derived from easily weathered basaltic rocks have supplied up to 250 kg ha-1 yr-1 of K to banana plants for many years without noticeable soil impoverishment. Such rocks typically contain high concentrations of K-containing minerals, which weather rapidly because of their small crystal size and the climate. Soils in temperate regions that supply adequate K for crop needs often contain considerable K-containing mica in their clay fractions. 

At every step in the chain from soils to man, the essential mineral elements interact with other elements, and these Interactions may profoundly affect the availability of essential elements or the amount of the essential element required for normal growth or metabolic function. For example, a high level of sulfate in the soil may depress the uptake of selenium by plants, and cause the people that eat the plants to suffer from selenium deficiency. The availability of zinc may be depressed if the diet is high in calcium. These and other interactions must be considered in assessing whether a given soil will supply plants with needed nutrients, and, in turn, whether plants will supply the people that consume them with needed nutrients. 

Secondary and Micronutrients in Fertilizers The great majority of farm fertilizers are produced, marketed, and appHed with regard only to the primary plant nutrient content. The natural supply of secondary and micronutrients in the majority of soils is usually sufficient for optimum growth of most principal crops. There are, however, many identified geographical areas and crop—soil combinations for which soil appHcation of secondary and/or micronutrient sources is beneficial or even essential. The fertilizer industry accepts the responsibiHty for providing these secondary and micronutrients, most often as an additive or adjunct to primary nutrient fertilizers. However, the source chemicals used to provide the secondary and micronutrient elements are usually procured from outside the fertilizer industry, for example from mineral processors. The responsibiHties of the fertilizer producer include procurement of an acceptable source material and incorporation in a manner that does not decrease the chemical or physical acceptabiHty of the fertilizer product and provides uniform appHcation of the added elements on the field. 

In regions where erosion is transport limited, weathering rates are controlled by the supply of reactive fluids to unstable minerals. This is controlled by soil properties, regional base level, and ultimately, sea level. 

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