PHYTOTOXICITY OF ATRAZINE AND ALACHLOR IN SOIL AMENDED WITH SLUDGE, MANURE AND ACTIVATED CARBON

Greenhouse studies were conducted to determine the influence of waste-activated carbon (WAC), digested municipal sewage sludge (DMS), and animal manure on herbicidal activity of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-trazine] and alachlor [2-chloro-2',6'-diethyl-N-(methoxymethyl)acetanilide] in a Plainfield sandy soil. Amendments generally reduced bioactivity against oat (Avena sativa L.) and Japanese millet (E. crus-galli frumentacea). The extent to which herbicide phytotoxicity was inhibited depended upon the application rate and the kind of soil amendment. WAC, applied at the loading rate of 2.1 mt C/ha, showed a significant inhibitory effect on both herbicides. In DMS- and manure-amended soil, the reduction of atrazine activity was not significant at the rate of 8.4 mt C/ha, but reduction of alachlor activity was significant at the rate of 4.2 mt C/ha. Despite inhibition of herbicidal activity, the ED50 of atrazine and alachlor was below 2 ppm in most of the amendment treatments. Before adopting carbon-rich waste amendments as management practices for controlling pesticide leaching in coarse-textured soils, further studies are needed to characterize how alterations in sorption, leaching and degradation may affect herbicidal activity.