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Soil‐Applied Atrazine Alters Blue Grama Physiology and Indirectly Influences Soil Nitrogen
Author(s) -
Knight W. G.,
Morgan J. A.,
Guenzi W. D.,
Shoop M. C.
Publication year - 1993
Publication title -
agronomy journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 131
eISSN - 1435-0645
pISSN - 0002-1962
DOI - 10.2134/agronj1993.00021962008500050014x
Subject(s) - atrazine , agronomy , bouteloua gracilis , photosynthesis , chemistry , rangeland , soil respiration , ammonium , biology , botany , respiration , pesticide , grassland , organic chemistry
Atrazine [2‐chloro‐4‐(ethylamino)‐6‐(isopropylamino)‐s‐triazine] applied at sublethal concentrations to rangelands, has resulted in herbage production and/or enhanced plant N concentration of desirable warm‐season grasses beyond that expected from weed control alone. This investigation was conducted to determine whether this is a metabolically regulated plant response, the result of enhanced soil N availability via microbially mediated processes, or both. Aerobic and anaerobic laboratory incubation studies with an atrazine‐amended, rangeland soil indicated no direct effect of atrazine on soil‐mediated N transformations. Applications of atrazine to the same soil type in column‐lysimeters containing blue grama [ Bouteloua gracilis (H.B.K.) Lag. ex Steud.] plants resulted in temporarily elevated soil NO 3 concentrations and reduced NH 4 concentrations in proportion to the different rates of atrazine applied (0, 0.5, 1.0, and 2.0 mg column −1 ). Applications of atrazine to soil containing blue grama plants initially inhibited photosynthesis and plant growth, and resulted in temporarily elevated soil NO 5 concentrations and reduced NH4 concentrations. A strong inverse relationship was observed across the four atrazine treatments between soil available N and shoot N content, strongly suggesting that the dominant plant‐mediated effect of atrazine on soil N pools was elicited through atrazine's initial inhibitory effect on plant growth. A strong negative correlation between leaf photosynthesis rate and tissue NO 3 levels across all four atrazine rates suggests that in addition to its negative effects on blue grama photosynthesis and growth, atrazine also impairs blue grama's ability to reduce NO 3 , enhancing the accumulation of plant tissue NO 5 levels. We conclude that temporary changes in soil NO 3 and NH 4 concentrations from atrazine resulted indirectly from changes in plant growth and metabolism, and not from alterations in soil microbiological processes.