MINERALIZATION OF STRAW AND FORMATION OF SOIL MICROBIAL BIOMASS IN A SOIL TREATED WITH SIMAZINE AND DINOTERB

Three weeks after treatment with simazine and dinoterb, C-14-labelled straw (2 mg g-1 soil) was added to an arable soil and incubated for a further 66 days. Straw mineralization was not affected by the two herbicides. In the two herbicide treatments, the soil microbial biomass measured by the fumigation-extraction method remained unchanged after the initial 20-day incubation period without straw addition. Also, the initial formation of microbial biomass was not apparently altered by simazine and dinoterb at day 5 after straw addition. However, the two herbicide treatments significantly accelerated the subsequent decline so that significantly lower microbial biomass contents were measured from day 33 after straw addition. Increased values for the metabolic coefficient (qCO2)-C-14 indicate a less efficient use of the added substrate for microbial growth in the soil treated with simazine and dinoterb.