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Natural & Applied Sciences Journal Vol. 3 (2) 2020 50 in these thousand chemical components by means of the food, water and ground are alarming. The sustainable agriculture involves optimizing agricultural resources and at the same time maintaining the quality of environment and sustaining natural resources. In achieving this optimization, the soil microbial community composition is of great importance, because they play a crucial role in carbon flow, nutrient cycling and litter decomposition, which in turn affect soil fertility and plant growth (Chauhan et al., 2006; Tripathi et al., 2006), and hence occupy a unique position in biological cycles in terrestrial habitat. The soil microbial biomass is considered as active nutrient pool to plants and plays an important role in nutrient cycling and decomposition in ecosystem (De-Lorenzo et al., 2001). Herbicides are applied to control weeds in the crop field have direct (or) indirect consequences on non-targeted organisms including soil microflora. After application of herbicides, microorganisms are able to degrade and utilize them as energy source for their metabolic activities and also for physiological processes. While processing these activities there may be a chance of change in soil physicochemical characteristics. Diversified effect of both toxic and as well as beneficial effect of herbicides on soil microorganisms and soil characteristics were studied in different ways in the recent past (Trimurtulu et al., 2015). The continuous use of environmentally persistent herbicides and other synthetic agricultural chemicals posed great risks to soil and water contamination. A viable alternative pesticide that is equally effective and less harmful to the environment is in demand (Souza et al., 2012). The persistence of a pesticide in the soil is defined as the period or extension of time in which it remains active. There is serious concern about the increased use of herbicides, which may cause (i) environmental hazards such as water table and water body contamination, (ii) biological disruption in crop field populations, and (iii) reduced efficiency as a result of increased population of soil microorganisms more efficient in herbicide degradation. The herbicide that are used frequently eventually reach the soil from the crop plants and accumulates in top 0-15 cm layer of soil, where the activities of microbes are found to be maximum. Herbicides in the soil affect the non-target and beneficial microorganisms and their activities which are essential for maintaining soil fertility (Sethi et al., 2015). Atrazine is a selective preand postemergence herbicide providing knockdown and residual action. It has low rate of volatilization from soil and is moderately persistent (half-life of ~60 days). It is more persistent in neutral and alkaline soils than in soils with low pH. It is moderately mobile and able to be leached through soils into groundwater (Kruger et al., 1996). Metolachlor is a selective herbicide used in the control of grassy weeds in the cultivation of corn, soybeans, peanuts, cotton and other crops. Metolachlor is often used in combination with other broadleaved herbicides (e.g. atrazine, metobromuron and propazine) to extend the spectrum of activity (Ayansina and Oso, 2006). Glyphosate is a broad-spectrum systemic herbicide. It is nonvolatile, it is strongly adsorbed by soil particles and is essentially immobile in soil (AATSE, 2002). Paraquat is a broad-spectrum herbicide that destroys plant tissue by contact action. It is highly soluble in water and because of its ionic properties is strongly adsorbed by soil particles and is essentially immobile in soil. The strong binding of paraquat to clay minerals is the factor most likely associated with its long half-life in soils (Clive, 2006). Fertilizers, pesticides, herbicides, and some other materials applied to soil often contribute to water and air pollution. Therefore, soil is a key component of environment chemical cycles. Dissolved mineral matter in soil is largely present as ions. Prominent among the cations are H+, Ca2+, Mg2+, K+, Na+ and usually very low levels of Fe2+, Mn2+ and Al3+. Multivalent cations and anions form ion pairs with each other in soil, solutions (Maynard, 2000). Hence this study determined the effect of selected herbicides (Atrazine, Xtravest, Gramoxone and Glyphosate) on exchangeable cations and also analysed the in-vitro biodegradation of this herbicides as well as assayed for their residual concentration in soils after treatment. Natural & Applied Sciences Journal Vol. 3 (2) 2020 51

natural and applied sciences journal

Determination of exchangeable cations and residual concentration of herbicide treated soils and analysis of the in-vitro biodegradation of the herbicides