The Effect of Repeated Field Applications of Four Herbicides on the Evolution of Carbon Dioxide and Mineralization of Nitrogen in Soil

Abstract

Summary The effect of repeated annual applications over 7‐8 years of MCPA, triallate, simazine and linuron to field plots on the evolution of CO2 and mineralization of nitrogen in soil samples incubated in the laboratory is described. The plots were either cropped and treated with standard doses, or uncropped and sprayed with doses 3‐4 times above the level used in agricultural practice. While the applications of MCPA and tri‐allate did not exert any inhibitory effects in soils from the uncropped plots those of simazine and linuron led to a lowering in CO2 output in several instances and in mineral N on infrequent occasions. These effects are assumed to be the result of a difference in the content of easily‐degradable organic matter between the treated plots and the controls. A direct anti‐microbial action of the two herbicides is not very probable because in laboratory experiments with simazine up to 512 ppm the output of CO2 and the mineralization of N was not affected while linuron at 500 ppm gave only a minor depression in CO2 evolution. Effects on soil fertility are unknown but seem unlikely in view of the small extent and infrequency of the reductions observed. On the cropped plots the MCPA and tri‐allate treatment showed no effects. With linuron and simazine a significant lowering in respiration and mineralization of N occurred on single occasions only, during a 5‐year period.

Impairment of cellulose- and cellobiose-degrading soil Bacteria by two acidic herbicides

“…The findings on the toxic effects of the tested two herbicides agree with observations (1) that MCPA that was applied at the recommended dose did not affect either carbon dioxide production, or oxygen uptake or N‐mineralization in an cropland soil and (2) that aerobic cellulose degradation was only slightly decreased even when MCPA was spread directly on cellulose sheets (Grossbard, ; Schröder, ). Nonetheless, reduction of nitrogen mineralization and soil respiration (i.e.…”

Interactions between herbicides and plant pathogens

“…Since herbicides decrease the population of plants, they may decrease the amount of easily degradable organic matter in the soil. This possibility was suggested by GROSSBARD (1971) to explain the reduction in carbon dioxide output in soil caused by simazine and !inuron.…”

Effects of the Herbicide Barban and its Commercial Formulation Carbyne on Soil Micro‐organisms

“…Manometry. Soil samples (20 g) in modified Warburg flasks (Grossbard 1971) were supplemented with 2 mlO.2% glucose and 0, uptake recorded for 2.5 h at 25 OC using a Gilson dflerential respirometer. Each flask contained 1-5 ml 1 M NaOH in the centre well.…”