Phosphates in agriculture

Sauchelli, V. (1955) Phosphates In Agriculture. Reinhold Publishing, New York, 277 pp. 

The formation of many low-soluble compounds with commonly occurring cations in waters causes very low concentrations of phosphates in both natural and wastewaters. The concentration of phosphates in surface waters can be several tenths mg 1. More rich in phosphates are waters from peat moors which can sometimes contain as much as 1 mg 1. Due to detergents and application of phosphates in agriculture their content is continually increasing in natural waters. To prevent further undesirable increase of phosphates in surface waters their application in the production of synthetic detergents is now limited. 

Figure 4.6 Course of the concentration changes of plant available phosphate in agricultural soil as it appeared during the degradation of six biodegradable materials. The values are presented as changes relatively to the control experiments (control = 1). The initial concentration was 262 mg P04 Vkg dry matter. Derived from [67]...

Riparian wetlands are effective though not infinite sinks for nitrate and phosphate from agricultural runoff. Strips of wetland a few tens of metres wide have been shown to remove the bulk of nitrate and phosphate entering in runoff and groundwater, though the limits to this under different circumstances are not well quantified (Baker and Malfby, 1995 Mitsch and Gosselink, 2000). 

Englestad, O.P. Terman, G.L. (1980). Agronomic effectiveness of phosphate fertilizers. In The Role of Phosphorus in Agriculture, ed. F.E. Khasawneh etal., pp. 311-29. Madison, Wl American Society of Agronomy. 

Biocides are known to be tracked into the homes after a certain outdoor application (Lewis and Nishioka, 1999 Nishioka et al., 2001). Furthermore transport routes, that is, transfer from the workplace to the home (para-occupational or take-home exposure) may be relevant. Household dust concentrations of azino-phosmethyl, chlorpyrifos, parathion and phosmet were significantly lower in reference homes when compared with farmer/farmworker homes (Simcox et al., 1995). Dialkyl phosphate metabolites measured in children s urine were elevated for agrarian children compared with children whose parents did not work in agriculture (Fenske et al., 2000). 

Adsorption of nitrate and phosphate, occurring in agricultural effluents, by amino-functionalized materials.118,119... 

Different OP compounds have structural similarities within classes. The phosphorus compounds have the characteristic phosphoryl bond, P=0. Most OP compounds have a phosphoryl bond or a thiophosphoryl bond (P=S). All OP compounds are esters of phosphorus with varying combinations of oxygen, carbon, sulfur, and nitrogen attached. These are classified as (1) phosphates (2) phos-phonates (3) phosphorothioates (4) phosphorodithioates (5) phosphorothiolates and (6) phosphoramidates. Further, the OP compounds are categorized as (1) aliphatic (2) phenyl and (3) heterocyclic derivatives. The aliphatic are carbon chainlike in structure. TEPP, which was used in agriculture for the first time in 1946, is a member of this group. Others include malathion, trichlorfon, monocrotophos, dimethoate, oxydemetonmethyl, dimethoate, dicrotophos, disulfoton, dichlorvos, mevinphos, methamidophos, and acephate. 

It dissolves worse in diethyl ether and carbon tetrachloride. If stored for a long time, its aqueous solutions become acidic. The stability of trichlorfon largely depends on the pH of the medium at pH > 5.5 it slowly transforms into 0,0-dimethyl-0-(2,2-dichlorovinyl)phosphate, which finds an increasing application in agriculture and household. 

Finally, the reaction of calcium phosphate with nitric acid produces two calcium salts that both have value as nutrients in agriculture ... 

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