Effects of Flooding on Dinitroaniline Persistence in Soybean (Glycine max) – Rice (Oryza sativa) Rotations

Abstract

A field study was conducted with fluchloralin [N-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)aniline], profluralin [N-(cyclopropylmethyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine], and trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) at 1× and 2× rates in soybeans [Glycine max (L.) Merr.] for 2 consecutive yr to evaluate their persistence in soil and to determine their residual effect on rice (Oryza sativa L.). In another field study that was conducted to evaluate the effect of winter flooding on the persistence of 4× rates of the same herbicides, gas chromatographic analysis and bioassay procedures both revealed increased dissipation of these herbicides because of winter flooding. Flooding rice for 2 or 4 months during winter reduced the adverse effect from herbicidal residues. Laboratory studies evaluated the persistence and volatility of these herbicides at 4 and 25 C in two soils at three moisture contents (air-dried, field capacity, and flooded). The persistence of the three herbicides was similar in the field and in the laboratory and usually followed the order fluchloralin > profluralin = trifluralin. Volatility was most rapid with moisture at field capacity, but overall dissipation was most rapid in flooded soil. Significant dissipation and volatility losses of all three herbicides occurred at 4 C in flooded soil and in soil at field capacity. These studies indicated that winter flooding is effective in reducing the concentration of dinitroaniline herbicides in soil.