Leaching soil property influence

Specific management practices influence triazine runoff and leaching, including fertilizer type, tillage crop residues, and previous crop history, as well as triazine application, formulation, and placement (Baker and Mickelson, 1994). Tillage systems affect various soil properties, such as soil moisture, temperature, pH, organic matter, water flow, and microbial populations, especially at and near the soil surface. These factors can affect transformation, retention, and transport of herbicides in soil. Interactions of and compensations between these processes can influence our prediction of triazine transport in soil. Therefore, triazine movement is usually studied under one management practice at a time. 

Other environmental properties of interest are those that govern movement of chemicals, for these properties can influence not only the possibility of human exposure but also the lifetime and fate of the chemical. Clearly, if a nitrosamine is formed in, or introduced into, the soil and stays there, it presents little threat to man, and its lifetime will depend on the chemical or microbiological properties of the soil. If it should move to the surface and volatilize into the atmosphere, on the other hand, there will exist the possibility of human exposure via inhalation and also the possibility of vapor-phase photodecomposition. If a nitrosamine were to leach from soil into water, it could perhaps be consumed in drinking water alternatively, exposure of the aqueous solution to sunlight could provide another opportunity for photodecomposition. 

The influence of acid rain on the environment is related to the various properties of different ecosystems and varies depending upon physic-chemical characteristics of soil, vegetation type, stemflow and throughfall interactions of rainwater with canopy of different botanic species. For instance, it is well known in Japan that soils close to the stems of Japanese cedar (Cryptomeria japonica) trees are strongly acidic. This is partly due to the leaching of hydrogen ions from the stems. Soil solutions close to a stem (10cm) are markedly acidic (pH 4.5) and contain 47 /zM of total Al in... 

The major emphasis of this discussion centered on the importance of surface and subsurface soil characteristics in influencing deep pesticide leaching. Some factors, such as the depth to groundwater and the amount of incipient rainfall or irrigation, are clearly important factors that do affect the probability of pesticide residues reaching groundwater. Similarly, properties of the pesticide itself (especially its inherent mobility and chemical/biological stability) correlate closely with pollution potential, but their evaluation is outside the scope of this review. 

Critical loads to forest soils have been proposed for the deposition of total nitrogen, total sulfur, and total acidity. Critical loads models assume that indirect effects occur on trees via changes in soil chemistry. However, there exist important direct and indirect impacts of wet and dry deposition on leaves and needles with regard to photosynthesis, nutrient leaching, stomatal function, and leaf surface properties. The values for critical loads are influenced by precipitation, elevation, soil texture, and base cation deposition. 

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