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Nitrogen Use in Winter Wheat in Response to Systematic Pesticides¹

Various pesticides exhibit plant growth regulating activity and have increased crop yields or altered concentrations of various constituents. Our purpose was to test the effect of commercially available pesticides on winter wheat (Triticum aestivum L.) with regard to N use, protein concentration, and dry matter production. Growth chamber-grown wheat seedlings were supplied 2.5 or 10.0 mM nitrate-N concentrations in nutrient solutions at each of two temperature regimes. Pesticides added to different pots were 0.5 mM concentrations of simazine [2-chloro-4, 6-bis (ethylamino)-S-triazine] or dyrene [2,4-dichloro-6-(0- chloroanilo-s-triazine], and 25 mM concentrations of disulfoton [O, 0-diethyl S-(2-(ethylthio) ethyl) phosphorodithioate] or guthion [O, 0-dimethyl S-(4-oxo-l,2,3-benzotriazin- 3 (4H)-ylmethyl phosphorodithioate]. Simazine increased nitrate reductase activity and nitrate concentration, and decreased glutamine synthetase activity. The same four materials were sprayed on field plots at 0.1 or 1.1 kg/ha at one of four growth stages. No autumn treatment affected yield or protein content of forage. Lower simazine rates applied at anthesis and higher simazine rates applied at all three spring growth stages decreased grain yields. Simazine treatments that decreased grain yields, and guthion applied during autumn increased grain protein concentration. The other treatments had no effect on protein or yield. Simazine applied during anthesis decreased grain test weights significantly. Decreased grain yields and increased grain protein concentrations probably resulted from detrimental effects of simazine on photosynthate accumulation and absence of a direct effect on N assimilation when foliarapplied. Decreased grain test weights apparently resulted from floret sterility and undeveloped grains.

Key Words: Nitrate assimilation • Yield • Protein • Test weight • Simazine • Disulfoton • Dyrene • Guthion

² Former graduate research assistant (now assistant professor, Div. of Plant Science, Univ. of Wyoming, Laramie, WY 82071) and professor, Dep. of Agronomy, Kansas State Univ., Manhattan, KS 6C506.

Received for publication April 24, 1976.