TILLAGE EFFECTS ON SOIL MICROBIAL AND BIOCHEMICAL CHARACTERISTICS IN A FALLOW-WHEAT ROTATION IN A DARK BROWN SOIL

As the adoption of reduced tillage increases on the prairies, so too d oes the use of herbicides and society's concern regarding their possib le negative impact on the environment. Two experiments were conducted on Regina heavy clay, an Orthic, Dark Brown Chernozem, at Regina, Sask atchewan, for up to 21 yr, to determine the influence of tillage on yi elds of hard red spring wheat (Triticum aestivum L.) in a fallow-wheat (F-W) rotation. The treatments used to control weeds in the fallow ph ase were conventional mechanical tillage (CT) vs. zero tillage (i.e., herbicides only or ZT). In one experiment, glyphosate was the herbicid e used; in the other, paraquat (plus Buctril M) was used. In 1991 (the 21st yr), soil sampled from the 0- to 5-cm depth of each rotation pha se was used to determine the possible long-term effect of these treatm ents on selected soil microbial populations and soil biochemical chara cteristics. The samples were taken in early June (prior to herbicide a pplication), in mid July (3 wk after the 21st herbicide application), and in early September (11 wk after the 21st herbicide application). G enerally, the herbicides had no long-term or short-term (in the 21st y r) deleterious effects on soil microbial populations (bacteria, actimo nycetes, fungi, nitrifiers, denitrifiers), nor on microbial biomass or potential C or N mineralization. Compared with ZT, CT had a negative impact on most soil characteristics. Microbial activity was primarily a function of crop residue inputs and growing season weather condition s near the time of sampling.