The impact of tillage and residue management on soil microorganisms was studied over the maize (Zea mays L.) growing season in southwestern Quebec. Tillage and residue treatments were imposed on a sandy loam to loamy sand soil in fall 1991. Treatments consisted of no till, reduced tillage, and conventional tillage with crop residues either removed from (-R) or retained on (+R) experimental plots, laid out in a randomized complete block design. Soil microbial biomass carbon (SMB-C), soil microbial nitrogen (SMB-N) and phospholipid fatty acid (PLFA) concentrations were measured four times, at two depths (0--10 cm, 10--20 cm), over the 2001 growing season. Sample periods were: May 7th (pre planting), June 25 th, July 16th, and September 29th (prior to corn harvest). The effect of time was of a greater magnitude than those attributed to tillage or residue treatments. While SMB-C showed no seasonal change (160 mug C g-1 soil); SMB-N was responsive to mineral nitrogen fertilizer; and PLFA data showed an increase in fungi and total PLFA throughout the season. PLFA profiles showed better distinction between sampling period, and depth, than treatments. Of the two treatments, the effect of residue was more pronounced than that of tillage, with increased SMB-C and SMB-N (6.1% and 96%) in +R plots compared to -R plots. This study illustrated that measuring soil quality based on soil microbial components must take into account seasonal changes in soil physical, chemical conditions, and nutrient supply.

Due to recent research suggesting that water table management (WTM) can significantly reduce nitrate (NO3") loads in agricultural drainage, a study was carried out in 2001 and 2002 in Coteau-du-Lac, 60 km west of Montreal, to investigate the effect of water table management on the migration of phosphorus (P) via tile drainage and surface runoff. The second main objective was to study the influence of WTM on grain corn yields. Two drainage treatments were compared: conventional free drainage and WTM (combined controlled drainage and subirrigation) with a design water table depth at 0.6 m below the ground surface. Tile drainage and surface runoff were monitored and sampled automatically. Increased outflow volumes and concentrations - and therefore increased P loads - were measured in drainage water from plots under WTM. Plots under WTM also generally exhibited higher P loads in surface runoff. Higher P concentrations in surface runoff from plots under WTM were observed in surface runoff, especially during winter. Phosphorus loads from combined tile drainage and surface runoff were low compared with literature data (<0.4 kg/ha/year). However, the mean P concentrations in tile drainage were above Quebec's surface water quality standard of 0.03 mg total P/L during both growing seasons in plots under WTM, but not in plots with conventional free drainage. Mean P concentrations in surface runoff water routinely exceeded the criteria, except in plots with conventional free drainage in winter 2002. Therefore, P from tile drainage and surface runoff could contribute to the eutrophication of surface water. Based on these results, WTM increases P loads from the field, both in tile drainage and surface runoff. However, the well water used for subirrigation was found to contain P concentrations above Quebec's surface water quality standard, and this could partly explain the higher P concentrations found in water from plots under WTM. Water table management increased grain corn yields by 35% in both years. The growing seasons of 2001 and 2002 were among the driest ever recorded in Canada.

Corn (Zea mays L.) production under monoculture and conventional-tillage management may cause soil degradation and nitrate (NO$ sb3 sp-)$ pollution. This study was conducted from 1991 to 1993 to evaluate the impact of conventional-tillage (CT) and no-tillage (NT) practices under corn-soybean (Glycine max L. Merill) rotations (C-S-C and S-C-S), continuous corn (C-C-C) and continuous soybean (S-S-S) systems on optimum N fertilization rates, yield and soil residual N levels. Field experiments were carried out on a Ste. Rosalie clay (Humic Gleysol) and an Ormstown silty clay loam (Humic Gleysol). Overall, tillage had little effect on soil and crop N levels or grain yields. Residual soil NO$ sb3$-N in the fall was related to fertilizer N rates in C-C-C, but not with S-S-S or soybean in rotation. Residual NO$ sb3$-N values after soybean were high and at zero added N were equivalent to 90 kg N with C-C-C. Consequently, soybean contributed the equivalent of 90 kg N ha$ sp{-1}$ to subsequent corn. Corn yields following soybean were higher than following corn, and less fertilizer N was required following soybean than following corn.

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A study was initiated in 1989 to examine the effects of applying excess liquid hog manure with mineral fertilizers to corn and forage crops. Manure was applied yearly at twice the recommended level either in the spring, fall or a combination of both spring and fall applications. Mineral fertilizers were applied at recommended levels to plots receiving only mineral fertilizers and to manure treatment plots. Two control plots received no fertilizers. / During the summer of 1999, soil samples were taken at a depth of 0--2 cm and analysed using different phosphorus extractants. Six runoff events were sampled and analysed for different phosphorus fractions. / Strong correlations were found in corn plots between average dissolved reactive phosphorus concentrations in runoff and soil test phosphorus concentrations. Timing of manure application had a significant impact on both soil and runoff phosphorus concentrations. Runoff from forage plots had significantly higher concentrations of dissolved phosphorus, but phosphorus loads were greater from corn plots due to higher runoff volumes. Corn plots released significantly higher particulate phosphorus concentrations than forage plots because of higher sediment loads in runoff from corn plots.