دانلود رایگان مقاله انگلیسی پراکندگی گلیفسات در خاک های متفاوت در صورت عدم کاشت و زراعت مرسوم - الزویر 2017

ABSTRACT

Glyphosate is the most used herbicide in Argentina, accounting for 62% of the commercialized pesticides in the market. It is used as a weed controller in no-till systems, and it is also applied in various genetically modified crops (e.g. soybean, corn, cotton). Though it has a high solubility in water, it tends to adsorb and accumulate in agricultural soils. The main objectives of this work were to compare the dissipation of glyphosate and the accumulation of its metabolite aminomethylphosphonic acid (AMPA) over time in three soils from agricultural areas of Argentina, under long-term management of no-till (NT) and conventional tillage (CT) practices. Forty percent of the applied glyphosate was degraded within the first three days in all soils, indicating a fast initial dissipation rate.

However, the dissipation rate considerably decreased over time and the degradation kinetics followed a two-compartment kinetic model. No differences were found between tillage practices. Dissipation was not related to the microbial activity measured as soil respiration. The fast decrease in the concentration of glyphosate at the beginning of the dissipation study was not reflected in an increase on the concentration of AMPA. The estimated half-lives for glyphosate ranged between 9 and 38 days. However, glyphosate bioavailability decreases over time as it is strongly adsorbed to the soil matrix. This increases its residence time which may lead to its accumulation in agricultural soils.

CONCLUSIONS

In all the studied soils the initial dissipation of glyphosate was fast, followed by a decrease in the dissipation rate. Over time, glyphosate becomes less bioavailable, making the remaining fraction more persistent especially in those soils with high adsorption capacity (PAR and PER). In this sense, the partitioning of the herbicide between the aqueous and the solid phase will influence the degradation, as it becomes less available to microorganisms, while it adsorbs to the soil matrix. There were no differences in dissipation between NT and CT, indicating that glyphosate degrading microflora was not modified with the different tillage managements. Also, tillage practices did not alter the general soil properties therefore; glyphosate bio-availability was not affected by NT or CT management.

Glyphosate initial dissipation was fast, whereas the accumulation of its metabolite, AMPA, was scarce. This suggests a fast AMPA degradation or that the preferred degradation pathway in these soils is via sarcosine.

The estimated half-lives for glyphosate in the studied soils under optimal temperature and moisture conditions ranged between 9 and 38 days. However, the less available residues can remain in the soil for almost a year after application. In the field, glyphosate might persist for even longer periods if conditions are temporarily less favorable for degradation (e.g. cold or dry seasons). The implications of this study are that glyphosate residues may accumulate in agricultural soils, especially if it is applied 2 to 3 times per year which is frequently the case. This may lead to negative impacts on the soil biota and furthermore, it increases the risk of polluting surface waters, by soil runoff, and groundwater resources, by vertical transport. It is important that glyphosate applications are kept to the needed minimum, in order to avoid its environmental accumulation and distribution.