Cyanazine Losses in Runoff from No‐Tillage Corn in “Living” and Dead Mulches vs. Unmulched, Conventional Tillage

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Abstract
Losses of cyanazine (2‐[[4‐chloro‐6‐(ethylamino)‐s‐triazin‐2‐yl]amino]‐2‐methylpropionitrile) in runoff from untilled soil planted to corn (Zea mays L.) were compared with losses from conventionally planted corn on a 14% slope in the growing seasons of 1977 through 1979. The no‐tillage systems consisted of corn planted into corn stover residue and into “living mulches” of birdsfoot trefoil (Lotus corniculatus) and crownvetch (Coronilla varia L.). The no‐tillage systems reduced runoff, erosion, and herbicide movement. For example, runoff from conventional tillage ranged from 5.5 to 22% of the runoff‐producing rainfall. Soil loss from the same system ranged from 4.4 to 32.2 Mg/ha. On the other hand, runoff from the no‐tillage systems ranged from 0.07 to 2.5% of the runoff‐producing rainfall, while soil losses ranged from 0 to 1.1 Mg/ha.Transport of cyanazine in water runoff and entrained sediment from tilled areas totaled 257.0, 16.0, and 32.7 g/ha for the respective growing seasons, which represented 5.71, 0.73, and 1.48% of the amount applied yearly [4.5 kg active ingredient (ai)/ha—1977; 2.2 kg ai/ha—1978, 1979]. In the same years, cyanazine losses from no‐tillage areas were 6.5–33.7 g/ha, 0.1–1.8 g/ha, and 1.6–3.3 g/ha at similarly applied rates. Collectively, these represented losses ranging from < 0.01 to 0.75% of sprayed levels. Using conventional tillage as a reference treatment, untilled surfaces reduced runoff from 86.3 to 98.7%, soil losses from 96.7 to 100%, and cyanazine losses from 84.9 to 99.4% over the three growing seasons. In general, the “living mulch” surfaces were more effective in retarding erosion than the corn stover residue surfaces. Corn grain yields were not significantly reduced by “living mulches” when adequate legume suppression was obtained with herbicide treatments.