Document Type

Dissertation - Open Access

Award Date

1986

Degree Name

Doctor of Philosophy (PhD)

Department

Plant Science

First Advisor

W.E. Arnold

Abstract

The effect of several variables on herbicide interception and retention by crop residue was investigated. Variables considered include residue type and amount, amount of rain, time of rainfall occurrence, and herbicide formulation. Experiments were conducted in the greenhouse using corn (Zea mays), soybean (glycine max), and wheat (Triticum aestivum) residue. Simulated rainfall was applied using a modified potsprayer. Herbicide concentration in washoff water was determined using the pyridine-alkali colorimeteric technique for chloro-s-triazine herbicides. As the percent ground cover increased, the amount of herbicide reaching the soil surface at application decreased. With normal residue levels attained in South Dakota, 60% or more of the applied herbicide may be intercepted. Generally, cyanazine {2-[ [4-chloro-6- (ethylamino),1,3,5-triazin-2-yl]amino]-2- methylpropanenitrile} was more easily removed from residue with rainfall than was atrazine [6-chloro-N-ethyl-N'- (l-methylethyl)-1,3,5-triazine-2,4-diamine]. The wettable powder formulation of atrazine and the dry flowable formulation of cyanazine were most easily removed. Of the total applied herbicide, 50% of the atrazine and 75% of the cyanazine was removed with 25 mm of rainfall. With a 25 mm rainfall, atrazine removal decreased by 25% and cyanazine removal decreased by 8% fourteen days after application. Both cyanazine and atrazine were most easily removed from corn residue. compared to soybean or wheat residue. A theoretical model was developed f or each herbicide and formulation tested. These models can be used to predict the level of herbicide reaching the soil surface under wheat residue with various rainfall conditions.

Library of Congress Subject Headings

Herbicides -- Biodegradation
Crop residues

Format

application/pdf

Publisher

South Dakota State University

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