Influence of four pesticide formulations on microbial processes in a New Zealand pasture soil

Abstract

The influence of commercial formulations of four pesticides, applied at a rate of 2.24 kg a.i./ha (about 7.5 ppm), on nitrogen mineralisation and nitrification in a soil under pasture, Motupiko silt loam, in the Nelson area, was investigated. DDT, fenitrothion, and fensulfothion had no effect 49 and 139 days after application, whereas carbofuran may initially have had an indirect, slight stimulatory effect. All formulations influenced these processes when added to soil at the high concentrations of 100 and 500 ppm active ingredient. Three of the formulations, however, contained calcium carbonate which, itself, showed marked effects. At 10000 ppm it stimulated nitrogen mineralisation; at 2000 and 4500 ppm it initially stimulated but then depressed mineralisation. After correction for the calcium carbonate effect, DDT had no influence, but fensulfothion and carbofuran stimulated production of nitrate-Nand mineral-N to some extent. Fenitrothion at 500 ppm initially strongly inhibited the oxidation of ammonium-N to nitrate-N; subsequently. however, it markedly enhanced nitrogen mineralisation. Some possible agronomic implications of these results are briefly discussed.