Soil Organic Matter Content

Acid amide herbicides are nonionic and moderately retained by soils. The sorption of several acid amide herbicides has been investigated (369). Acetochlor [34256-82-1] is sorbed more than either alachlor or metolachlor, which are similarly sorbed by a variety of soils. Sorption of all the herbicides is well correlated to soil organic matter content. In a field lysimeter study, metolachlor has been found to be more mobile and persistent than alachlor (370) diphenamid [957-51-7] and napropamide [15299-99-2] have been found to be more readily leached (356). 

Interrelated with change in particle size and changes in type and kind of soil minerals present, organic matter is formed and accumulates as an integral part of the soil. Organic-matter content varies from practically none in sands to almost 100%, as exemplified by peat formations. The amount of organic matter present thus reflects the interaction of all environmental... 

Application of animal manures to soil serves as an important element of nutrient management. In addition to nutrients and the organic carbon recycled to maintain or increase soil organic matter content, which is a key element... 

This has led to research into identification of labile pools of organic matter (which make up a relatively small proportion of the total pool) that are more sensitive to changes in soil management or environmental conditions than total soil organic matter content. Examples of such pools include C and N held in the microbial biomass and in particulate organic matter and in water-soluble, easily-extractable and potentially mineralizable fractions (Haynes 2005). 

As noted earlier, total soil organic matter content can be considered as a coarse indicator of soil quality. However, changes in the content of organic C and total N occur only slowly and do not provide an adequate indicator... 

Calculation of the microbial quotient can make treatment effects much more obvious. For example, in Fig. 2 the microbial quotient was greater in the row than inter-row and greater under residue return than burning, both to a depth of 30 cm. In addition, values declined with depth as soil organic matter content declined and the proportion of organic C present in labile form declined. 

For these and other reasons, direct oxidation of soil organic matter using high temperature and atmospheric air, although commonly used, is not the best procedure for determining soil organic matter content. 

Titration is a general word used in many different disciplines. Any time a solution of known concentration is used to find the amount of an unknown component in another solution, it can be called a titration. Although this type of analysis is very old, it still finds widespread used in chemical analysis. Titrations are used in soil analysis to measure soil acidity, soil organic matter content, and various constituents isolated from soil, particularly ammonia. 

Sorption. Kqp values have been looked upon as constant for neutral organic chemicals. Independent of soil type (73). The parameter Is valid for comparison of leaching potential of pesticides with widely varying water solubility however. It Is difficult to make quantitative comparisons among polar organics. For example, note the wide range In Kq, for oxamyl described In Table IV. This may be due In part to Interactions with soil mineral fractions which become Important when the soil organic matter content Is low (56,112). Also, use of water solubility... 

Farmers reported that yields following compost application increased up to 4000 kg ha of maize and more importantly, that crops are less prone to damage from dry spells because of higher soil organic matter content. Some farmers even experiment with the combination of compost and fertiliser. They achieve yields of up to 5000 kg ha One particular farmer planted trees around his 8 hectare farm and allowed 2.8 hectares to develop into forest. The leaves of the fence and the... 

The soil organic matter content is mostly determined as the organic carbon content Xsoc. foe is defined as... 

Acidic pesticides such as 2,4-D, 2,4,5-T, picloram, and dinoseb can ionize in aqueous solutions forming anionic species (Saltzman and Yaron, 1986). Sorption of these pesticides on soils has also been correlated with soil organic matter content (Hamaker et al., 1966), and in their anionic form they can be sorbed on soils, clays, and amorphous materials at low pH. The mechanisms of sorption for these compounds are proton association and, for the molecular form, van der Waals sorption (Saltzman and Yaron, 1986). Hydrogen bonding and electrostatic interactions are other possible mechanisms for sorption. 

Spencer et al. (14) reported that the degree of reduction in vapor pressure in soil due to adsorption is dependent mainly upon soil water content, the nature of the pesticide, its concentration and soil properties, particularly soil organic matter content. The concentration of the desorbed pesticide in the soil water dictates the vapor density of the pesticide in the soil air in accordance with Henry s law. Hence, soil water adsorption coefficients can be used to calculate relative vapor densities in the soil atmosphere. 

Estimated t,/2 25 to > 201 d under a variety of agronomic conditions in agriculture soils depending on depth of incorporation, soil moisture, soil temperature, sil air, and soil organic matter content (summary of literature data, Grover et al. 1997)... 

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