Effect of Applied Pesticide on the Microbial System of Agriculture Soil

Pesticides are widely used to control the pest as well as to improve the yield of agricultural products. Pesticide applied in the soil affects the microorganisms, soil enzymes, and physicochemical parameters in the soil and in turn affect the soil fertility. Understanding the impact of pesticide on the soil both short-term and long-term exposure would provide a set of analytical data for risk assessment and resilience of the soil parameters. This would open up other possible ways given to improve the crop productivity. This review mainly focuses on standard biomarkers such as microbial enzymes, soil enzymes novel proteins, and microbial community other parameters developed as indicators, of pesticide contamination.

Pesticides are anthropogenic products intended to control pest in the agriculture as well in the household maintenance.It been used since the end of the Second World War (EPA 2009) and has been reached to two million tons per year (De et al. 2014).Pesticide usage in India is only 3.75 %, which is comparatively less than any other country in the global scenario.HCH, DDT and Malathion are commonly used pesticides (Brucker et al., 2008).Organophosphates and carbamates are the synthetic pyritheriod used commonly but extremely toxic to living forms (Van Wijngaarden et al. 2005).In India the maximum (44.5%) usage of the pesticide reported from cotton field (Agnihotri 1999).These insecticides effect on beneficial microbial diversity in the soil and decrease in soil fertility (Johnsen et al. 2001).

Fate of Applied Pesticide
Pesticides reach the soil through spray drift, run-off, or wash-off vectors (Racke et al. 1997).Pesticides contaminate water, air, plants, food and ultimately in to human via, runoff and subsurface drainage; interflow and leaching; and the transfer of mineral nutrients and pesticides from soils into the plants and animals that constitute the human food chain (Abrahams 2002).The pesticide that becomes to be as integrated into transport and degradation processes that characterize soi1 ecosystems (Glatfelter et al. 1989).The pesticides in the environment undergo volatilization, leaching, adsorption, photodecomposition, degradation by other nonbiological processes and biodegradation (Sawhney et al. 1989).Biodegradation is the process that involves the use of living microorganisms to detoxify or degrade the pollutants into less toxic forms (Zhang et al. 2011).Several bacteria utilize pesticide as a carbon, energy source and convert into simple harmless forms.

Impact on Soil Enzymes
Extracellular enzymes secreted around the microbial cells (Mayanglambam et al. 2005) influences soil fertility (Antonious 2003;Bucket and Dick 1998).Direct effect on the soil microbial community reflects reduced production of many extracellular enzymes responsible for biogeochemical cycles (Klose et al. 2006).Nevertheless, residual pesticides in the soil alter the functions of hydrolases, oxidoreductases, and dehydrogenase, phosphatase activities (Menon et al. 2005; Monkiedje and Spiteller 2002); (Kucharski et al. 2000;Trasar-Cepeda et al. 2000).Effect of pesticide on the bacteria, fungi and actinobacterial enzymes like dehydrogenase, phosphatase, and to their respiratory activities are detrimental.Pesticide like monocrotophos and quinalphos (organophosphates), and cypermethrin (pyrethroid), tend to increase the activities of cellulase and amylase enzymes.Interestingly, combinations involving monocrotophos with cypermethrin demonstrated synergistic and antagonistic effects on both enzymes in the soils activity of arylsulfatase (Table 1) and β-glycosidase implying that S-mineralization in soils and the total oxidative potential of microorganisms are affected by pesticides (Gundi et al. 2007).

Impact on Soil Microbes
Applied pesticide can change the environment in the size and structure of microbial community.Leads to a shift in the microbial community enhances the growth and establishment of species that are capable to degrade this type of chemical fertilizer, pesticide and change the overall soil quality (Table 2) either short term and long term effects.Residual pesticide in the soil disturbs the physical-chemical properties of soil that leads change in the soil fertility.Ultimately, the bacterial, which has the capacity to transform or degrade the pesticides, surpass the plant growth stimulating bacteria.They can metabolize even the most persistent pesticides either by the utilization of the compounds as sources of energy, or by co-metabolism with other substrates supporting microbial growth Bitmann

Impact on Soil Nutrients
The indiscriminate use of pesticide has found to alter which are that contributing to soil fertility (Tilman et al. 2002).Chemical pesticides are toxic to soil microorganisms; hence, physiology in soil altered when particular populations are altered.Pesticide also affects the size of soil populations (Edwards et al. 1973).Most of the pesticides persist in the soil for such a long period to absorb by plants grown in a field year later (Anonymous 2009).Persistence of pesticide would influence soil population either by increasing the community, which can degrade pesticide.Hence, the loss of the population that is responsible for the release of many of the macro, micro, and trace elements in the soil disrupts the bio-geo cycles.

Soil Enzymes are Indicators of Soil Fertility
Soil Enzymes are biological catabolism of soil organic and mineral components.Soil enzyme activities closely relate to soil organic matter (Table 3), soil physical properties and microbial biomass, changes much faster than other parameters, thus providing early indications of changes in soil fertility, and mostly involve simple procedures (Dick et al. 1996).In addition, the soil enzyme activities are measures for microbial activity, soil productivity, and inhibitor of pollutants (Tate 1995).Well-documented and quick assays are available for a large number of enzyme activities (Dick et al. 1996;Tabatabai 1994).These enzymes include dehydrogenase, glucosidases, urease, amidases, phosphatases, arylsulphatase, cellulases, and phenol oxidases.

CONCLUSION
Impact assessment due to the agricultural usage of pesticide would reveal the many changes taking place in the field.Such chances would be easy tools to evaluate the impact of applied pesticide on all forms, including soil microbes, plant, insects, and human.It will also address many other unresolved questions with regard to soil fertility, emergence of multi drug resistance, taro genic effects in many forms as well as premature puberty in women.Therefore, based on the above discussed data community can develop specific biomarkers for mutual exposure taking advantage of the ongoing characterization of toxicity signaling pathways and cause of many unknown diseases.

Table 1 .
Impact of Different Pesticides on Soil Enzymes

Table 2 .
Impact of different Pesticides on Soil Microflora

Table 3 .
Soil Enzymes influencing mineral cycle