Affiliations: State Key Laboratory of Soil and Sustainable
Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing
210008, China | Graduate School of Chinese Academy of Sciences,
Beijing 100039, China
Abstract: Glyphosate (GPS) is a non-selective, post-mergence herbicide that is
widely used throughout the world. Due to the similar molecular structures of
glyphosate and phosphate, adsorption of glyphosate on soil is easily affected
by coexisting phosphate, especially when phosphate is applied at a significant
rate in farmland. This paper studied the effects of phosphate on the adsorption
of glyphosate on three different types of Chinese soils including two variable
charge soils and one permanent charge soil. The results indicated that
Freundlich equations used to simulate glyphosate adsorption isotherms gave high
correlation coefficients (0.990–0.998) with K values of 2751, 2451 and
166 for the zhuanhong soil (ZH soil, Laterite), red soil (RS, Udic Ferrisol) and
Wushan paddy soil (WS soil, Anthrosol), respectively. The more the soil iron and
aluminum oxides and clay contained, the more glyphosate adsorbed. The presence
of phosphate significantly decreased the adsorption of glyphosate to the soils
by competing with glyphosate for adsorption sites of soils. Meanwhile, the
effects of phosphate on adsorption of glyphosate on the two variable charge
soils were more significant than that on the permanent charge soil. When
phosphate and glyphosate were added in the soils in different orders, the
adsorption quantities of glyphosate on the soils were different, which followed
GPS-soil>GPS-P-soil = GPS-soil-P > P-soil-GPS, meaning a complex
interaction occurred among glyphosate, phosphate and the soils.
