Influence of Amount and Method of Irrigation Water Application on Leaching of Atrazine

Abstract

A study was conducted to relate leaching of a herbicide, atrazine [6‐chloro‐N‐ethyl‐N′‐(1‐methylethyl)‐1,3,5‐triazine‐2,4,‐diamine], and inorganic water tracers, Br− and Cl−, to the amount of deep‐percolating water produced from irrigation. Soil at the site was classified as a Dehli Loamy Sand (Mixed, Thermic, Tepic Xeropsamment) which was an unstructured sandy soil that was low in organic C content, conditions conducive to solute leaching. The relationship between depth of solute movement and amount of deep‐percolating water was measured in sprinkler, basin, and furrow irrigation methods. Soil distribution of inorganic tracers indicated that graded levels of added water treatments, which were based on reference evapotranspiration, produced corresponding increases in the depth of percolated water. Atrazine's soil distribution indicated greater downward movement in response to increases in amount of deep‐percolating water. Magnitude of leaching differed between irrigation methods and increased in the order: sprinkler < basin < furrow. Simulations using the LEACHM model provided a physically based explanation for the differences in water movement between sprinkler and basin methods. The total amount of applied water was similar at each level of percolation but sprinkler irrigations were more frequent, resulting in more evaporation and, consequently, less water available for deep percolation. Both amount and method of water application are important factors that determine pesticide movement and that, in irrigated agriculture, must be considered as integral components of pesticide management.

Modeling Herbicide Movement to Ground Water in Irrigated Sandy Soils of the San Joaquin Valley, California

“…Flood irrigation scenarios yielded higher predicted simazine detection frequencies and ground water concentrations than sprinkler scenarios (Table IV). Irrigation efficiency and frequency both influence rates of leaching (Miller et al, 1965;Oster et al, 1972;Troiano et al, 1993), so both effects are responsible for the differences observed here. An effect of crop type is also evident, potentially attributable to both application timing (early Note Detection frequency based on analytical reporting limit of 0.05 ug L −1 .…”

“…Soil data for the coarse Fresno County Delhi loamy sand used as the representative root zone soil profile are reported elsewhere (Troiano et al, 1993). Summarizing, sand content varied from 84 to 91 percent through the profile, with soil mass fraction organic carbon (OC) steadily decreasing from 0.0071 in the 0-15 cm depth to <0.0001 at the bottom of the profile.…”

“…Estimates of a, b, and λ were obtained by calibrating the model to Br concentration vs. depth data from a 42-d bare-ground leaching study conducted in a Fresno County coarse Delhi loamy sand (Troiano et al, 1993). That study included six irrigation treatments: sprinkler low, medium, and high water applications, and flood low, medium, and high water applications.…”

“…The dominant source of deep percolation in nearly all of California's agricultural regions is irrigation. The qualitative effect of quantity and frequency of irrigation water applications on leaching of both salt and pesticides has long been recognized (Miller et al, 1965;Oster et al, 1972;Troiano et al, 1993). However, estimating irrigation effects on pesticide concentration in ground water is difficult.…”

Furrow Irrigation Management and Design Criteria Using Efficiency Parameters and Simulation Models

“…In addition, pesticides and other chemicals are incorporated in the irrigation; the leaching of pesticides and their breakdown products increases in direct relation with an increase in the amount of percolating water produced by irrigation (Asare et al, 2001). The close association between leaching and amount of deep-percolating water produced by irrigation is expected because leaching occurs through dissolution of solute in soil solution and subsequent movement with soil water (Troiano et al, 1993). Pesticides in California ground water have been found in a variety of diverse climatic and soil conditions, including semiarid, intensively-irrigated, and coarse soil areas with shallow depth to ground-water (Spurlock, 2000).…”