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Release Rate and Leaching of Starch‐Encapsulated Atrazine in a Calcareous Soil
Author(s) -
Williams C. F.,
Nelson S. D.,
Gish T. J.
Publication year - 1999
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1999.03615995006300030001x
Subject(s) - atrazine , granule (geology) , leaching (pedology) , chemistry , calcareous , bromide , starch , environmental chemistry , agronomy , soil water , soil science , pesticide , botany , environmental science , materials science , inorganic chemistry , biochemistry , biology , composite material
Starch encapsulation (SE) has been proposed as a mechanism for minimizing the impact of atrazine [6‐chloro‐ N ‐ethyl‐ N′ ‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine] on the environment. A two‐part study was conducted to evaluate: (i) atrazine release rate as a function of starch granule size, temperature, and water potential; and (ii) to compare the leaching of SE atrazine with the leaching of a commercial formulation in a calcareous soil. Atrazine release‐rates from the starch granules were determined as a function of three granule sizes (1.40‐0.85, 0.85‐0.43, and <0.43 mm) at five temperatures (4, 10, 20, 25, and 35°C), and five matric potentials (0, −0.1, −0.5, −1.0, and −1.5 MPa). Atrazine release‐rates from the starch granules increased with decreasing granule size, increasing temperature, and increasing water potential. To evaluate leaching as a function of atrazine formulation, each starch‐encapsulated granule size, commercial formulation, and control treatment was replicated six times in irrigated soil columns (0.188 m 2 × 0.25 m). A pulse of bromide (10.7 kg Br ‐ ha ‐1 ) and atrazine (1.7 kg ha ‐1 ) were coapplied to the soil columns and effluent concentrations monitored. Irrigation events of 55 mm in 5 h were applied through drip emitters at 10‐d intervals for 120 d for a total application of 11.5 pore volumes. Averaged bromide breakthrough curves for each soil column treatment were similar, which indicated that differences in the averaged atrazine mobilities were a result of formulation and not of heterogeneity in the soil matrix. Starch‐encapsulated atrazine leaching decreased with increasing granule size; however, all SE formulations were less mobile than the commercial formulation. After 11.5 pore volumes and 120 d, >52% of the commercial atrazine had leached through the soil columns, compared with <38% for the smallest starch granule size and 11% for the largest granule. Starch‐encapsulated formulations may be an effective tool for reducing pesticide leaching in calcareous soils.