Decomposition, nutrient loss and microarthropod densities in herbicide-treated grass litter in a Georgia piedmont agroecosystem

Abstract

A litterbag experiment was made to investigate the influence of the herbicides atrazine, paraquat and glyphosate on several aspects of the decomposition of grass litter in a fallow field. Litter-bags containing dried Johnson grass ( Sorghum halepense) leaves were dipped in herbicide solutions at recommended and 10 × recommended field application rates, placed in the field, and randomly collected every 3 weeks from July to November 1982. At the highest treatment levels of paraquat and glyphosate, the leaves showed slower weight loss, faster losses of P, Ca and Mg, and higher densities of microfloral-grazing microarthropods than untreated controls. Using a conceptual model of the decomposition subsystem, it is hypothesized that herbicide treatment altered the system by (1) promoting microbial utilization of the herbicide or additive as a carbon source; (2) increasing the importance of microarthropod grazing relative to comminution; (3) eliminating or reducing the importance of the predatory microarthropods; and (4) increasing the rate of nutrient loss from the litter via microbial and microarthropod activity. The system thus became simplified with fewer recycling loops, accelerated soluble nutrient loss, and slower decay of carbon from the leaf tissue.