Biological activity in soils

By sharply decreasing biodiversity in the soil ecosystem, pesticides negatively affect all soil organisms on which soil productivity depends. Pesticides affect the biological activity in soil, especially through long-term use and accumulation (or accumulation of their residues). 

In this chapter the roles of various physico-chemical parameters in the interaction between globular proteins, e.g. enzymes, and soil minerals have been discussed semi-quantitatively. Knowledge of the mechanism of that interaction provides a basis to manipulate biological activity in soils. 

Diazinon (phosphorothioic acid 0,0-diethyl 0-(6-mcthyl-2-(l-mcthylcthyl)-4-pyrimidinyl) ester) is an organophosphorus compound with an anticholinesterase mode of action. It is used extensively to control hies, lice, insect pests of ornamental plants and food crops, as well as nematodes and soil insects in lawns and croplands. Diazinon degrades rapidly in the environment, with half-time persistence usually less than 14 days. But under conditions of low temperature, low moisture, high alkalinity, and lack of suitable microbial degraders, diazinon may remain biologically active in soils for 6 months or longer. 

Nannipieri P, Grego S, Ceccanti B (1990) Ecological significance of the biological activity in soil. In Bollag J-M, Stotzky G (eds) Soil Biochemistry, Vol 6. Marcel Dekker, New York, pp 293-355... 

Values of pH ranging from 6.5 to 8 are generally within the optimal range for normal biological activity in soils. Extreme pH values (<5 or >10) are unfavorable for remediation purposes. These ranges are typical, however, since indigenous microbes are adapted to their site-specific environment and some sites do maintain healthy microculture in the extreme ranges. 

Stotzky, G. (2000). Persistence and biological activity in soil of insecticidal proteins from Bacillus thuringiensis and of bacterial DNA bound on clays and humic acids. Journal of Environmental Quality, 29, 691-705. 

For much of the history of the Earth, biological activity in soil and natural waters was the primary global source of atmospheric ammonia (Dawson 1977 Dawson and Farmer 1984 National Science Foimdation... 

Chemistry of the soil solution provides useful information on soil processes that are important to both agricultural and environmental sciences. Data on the concentrations of trace elements in a real soil solution are valuable for predicting the availability of those elements, as well as any toxic effects that they might have on crops and on their biological activities in soils. 

Because of the structure-function relationship for (globular) proteins, adsorption-induced changes in the molecular structure are likely to affect the biological activity of the protein, e.g., the enzymatic activity. In soils, as well as in a wide variety of other systems, the impact on biological... 

The enzymatic activity in soil is mainly of microbial origin, being derived from intracellular, cell-associated or free enzymes. Only enzymatic activity of ecto-enzymes and free enzymes is used for determination of the diversity of enzyme patterns in soil extracts. Enzymes are the direct mediators for biological catabolism of soil organic and mineral components. Thus, these catalysts provide a meaningful assessment of reaction rates for important soil processes. Enzyme activities can be measured as in situ substrate transformation rates or as potential rates if the focus is more qualitative. Enzyme activities are usually determined by a dye reaction followed by a spectrophotometric measurement. 

Biotic and abiotic degradation of 1,2-dibromoethane in surface waters is slow relative to volatilization of the compound to the atmosphere (ERA 1987b). 1,2- Dibromoethane is resistant to hydrolysis (Jaber et al. 1984) the hydrolytic half-life of the compound has been reported to range from 2.5 years (Vogel and Reinhard 1982) to 13.2 years (HSDB 1989). As a result of its hydrolytic stability and the limited biological activity in subsurface soils, 1,2- dibromoethane leached to groundwater is expected to persist for years. 

Figure 12.8 shows an example of parathion distribution in sterilized and natural, biologically active Gilat soil columns. We see that, at relatively early times, when the effect of decomposition is minimal, the parathion distribution is similar to that in the sterile soil. After four days, the effect of microbial activity on decomposition is evident, and the distribution pattern is significantly different. After seven days, the parathion is almost completely decomposed. This example emphasizes the necessity to consider additional processes, snch as degradation, in analyses of pollutant transport. 

Fig. 12.8 Distributions of parathion in (A) biologically-inert (sterile) Gilat soil (20% moisture content, 1.4 g cm bulk density) after 3.03 days, and (B) biologically-active Gilat soil (34% soil moisture content, 1.4 g cm bulk density) after 2, 4 and 7 days. The solid curves were calculated using D= 1.67x 10 cm s the points represent experimental measurements (Gerstl et al. 1979a)...

Reeves, J.B. Ill, McCarty, G.W. and Meisinger, J.J. (2000) Near infrared reflectance spectroscopy for the determination of biological activity in agricultural soils. Journal of Near Infrared Spectroscopy 8, 161-1 70. 

Burns, R. G. 1982. Enzyme activity in soil Location and a possible role in microbial ecology. Soil Biology and Biochemistry 14 423—427. 

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