Influence of soil texture and tillage on herbicide transport

Department of Agricultural Engineering, University of Maryland, College Park, MD, USA
Chemosphere (Impact Factor: 3.5). 12/2000; 41(9):1327-1332. DOI: 10.1016/S0045-6535(00)00028-X

ABSTRACT Two long-term no-till corn production studies, representing different soil texture, consistently showed higher leaching of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] to groundwater in a silt loam soil than in a sandy loam soil. A laboratory leaching study was initiated using intact soil cores from the two sites to determine whether the soil texture could account for the observed differences. Six intact soil cores (16 cm dia by 20 cm high) were collected from a four-year old no-till corn plots at each of the two locations (ca. 25 km apart). All cores were mounted in funnels and the saturated hydraulic conductivity (Ksat) was measured. Three cores (from each soil texture) with the lowest Ksat were mixed and repacked. All cores were surface treated with [ring−14C] atrazine, subjected to simulated rainfall at a constant intensity until nearly 3 pore volume of leachate was collected and analyzed for a total of . On an average, nearly 40% more of atrazine was leached through the intact silt loam than the sandy loam soil cores. For both the intact and repacked cores, the initial atrazine leaching rates were higher in the silt loam than the sandy loam soils, indicating that macropore flow was a more prominent mechanism for atrazine leaching in the silt loam soil. A predominance of macropore flow in the silt loam soil, possibly due to greater aggregate stability, may account for the observed leaching patterns for both field and laboratory studies.

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    ABSTRACT: Reducing tillage intensity through the implementation of conservation practices is a way to reach a more sustainable agriculture. Reducing tillage is indeed an efficient way to control soil erosion and to decrease production costs. Nonetheless, the environmental impact of reduced tillage is not well known because conservation techniques may induce strong changes in soil physicochemical properties and biological activity. Knowledge on the fate of applied pesticides under conservation practices is particularly important from this point of view. We review here the advances in the understanding, quantification and prediction of the effects of tillage on pesticide fate in soils. We found the following major points: (1) for most dissipation processes such as retention, degradation and transfer, results of pesticide behaviour studies in soils are highly variable and sometimes contradictory. This variability is partially explained by the multiplicity of processes and contributive factors, by the variety of their interactions, and by their complex temporal and spatial dynamics. In addition, the lack of a thorough description of tillage systems and sampling strategy in most reports hampers any comprehensive interpretation of this variability. (2) Implementation of conservation tillage induces an increase in organic matter content at the soil surface and its gradual decrease with depth. This, in turn, leads to an increase in pesticide retention in the topsoil layer. (3) Increasing retention of pesticides in the topsoil layer under conservation tillage decreases the availability of the pesticides for biological degradation. This competition between retention and degradation leads to a higher persistence of pesticides in soils, though this persistence can be partially compensated for by a more intensive microbial activity under conservation tillage. (4) Despite strong changes in soil physical properties under conservation tillage, pesticide transfer is more influenced by initial soil conditions and climatic conditions than by tillage. Conservation tillage systems such as no-tillage improve macropore connectivity, which in turn increases pesticide leaching. We conclude that more knowledge is needed to fully understand the temporal and spatial dynamics of pesticide in soil, especially preferential flows, in order to improve the assessment of pesticide risks, and their relation to tillage management.
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    Journal of Plant Nutrition 12/2014; DOI:10.1080/01904167.2014.881878 · 0.54 Impact Factor