No description available.

No description available.

A two year study was initiated in 1999 at the Macdonald Campus Farm, on a 2.4 ha site consisting mainly of St-Amable sand to shallow loamy sand (Typic Endoaquent; Humic Gleysol). The site was planted to alfalfa ( Medicago sativa) prior to the establishment of the experimental design and has been planted to corn (Zea mays L.) since 1991. The experiment was set up as a randomized complete block design and consisted of three tillage levels (NT, no-till; RT, reduced tillage; and CT, conventional tillage) and two residue levels (-R, no residues; +R, with residues). This study was performed in order to ascertain the effect of these management systems on soil organic carbon (SOC), particulate organic matter carbon (POM-C), microbial biomass carbon (MBC) levels and soil physical properties. Soil physical properties measured included bulk density, saturated hydraulic conductivity (Ksat), dry and wet aggregate stability, total porosity, macroporosity at -1 kPa and -6 kPa of matric potential, and moisture content. Crop yield was also measured. Results indicated that lower rates of mineralization of POM-C under NT+R in the surface 0--10 cm led to significantly higher SOC at the same depth. There were no significant differences between treatments at the 10--20 cm depth. The MBC was not a good indicator of the differences in soil organic matter levels between treatments. No-till treatments had higher bulk densities, reduced total porosity and macroporosity, increased moisture content, and increased constant-head measured Ksat. Differences in Ksat as measured with the Guelph permeameter, were not significant between treatments, most likely due to increased earthworm activity in NT. There were no significant differences in crop yield in 1999, but a significantly wetter year in 2000 caused lower grain yields in NT+R compared to NT-R and CT+R.

Corn (Zea mays L.) production under monoculture and conventional tillage systems may land to soil degradation and nitrate (NO$ sb3 sp-$) pollution of surface and groundwater. This study evaluated the impact of no-till and conventional tillage, monoculture corn and soybean, corn-soybean rotations and corn-soybean-alfalfa rotations, and three fertilizer N rates applied to monoculture corn or soybean, and corn in rotation, on soil NO$ sb3$-N and NH$ sb4$-N levels. Experimental sites were a Ste-Rosalie clay (Humic Gleysol) and an Ormstown silty clay loam (Humic Gleysol). Results obtained from fall 1992 to spring 1995 showed that tillage had no effect on soil N levels under corn. Soil N levels under corn showed a linear response to added N, specially in the fall. Soil N levels under corn did not change considerably during the non-growing season. Higher spring NO$ sb3$-N levels, particularly in plots under conventional tillage and alfalfa or soybean, compared to fall values indicated greater nitrification and/or mineralization than denitrification, immobilization or leaching. Low NH$ sb4$-N levels indicated that nitrification processes were active. No consistent estimation could be made of fertilizer N credits for corn from either soybean or alfalfa based on NO$ sb3$-N levels in soil.

No description available.

No description available.

Eutrophication resulting from phosphorus (P) accumulation in water systems has been a worldwide concern for three decades. Agricultural soils are known to be an important non-point source of P in waterways. The objectives of this research are to identify agricultural management practices that reduce the risk of P loss from soils, and to investigate the underlying mechanisms of P retention and loss from soils. In the short term (4 years), dissolved P loads were not affected by tillage and were similar in corn (in a continuous corn rotation) and soybean (in a soybean/corn rotation) production systems. Soils amended with composted cattle manure had a greater P load than chemically fertilized soils. On average, 30% of the total P leached was in organic P forms, indicating that organic P compounds could also be problematic to water systems. Although manure application improved soil aggregation and thus may increase P retention by avoiding soil erosion, P loss through subsurface flow by leaching may be substantial. A simple soil test, either Mehlich-3 P or P saturation ratio can predict the P leaching potential, but water ponding on the surface of agricultural land could significantly affect the accuracy of the prediction. / The P adsorption data was fit with the Langmuir 2-surface model, which predicted that up to 90% of the native adsorbed P was distributed on the high-energy surface. Native adsorbed P in manured soils was weakly retained, as the binding strength coefficient was 50 times less in manured than chemically fertilized soil. This findings was confirmed by measuring P desorption, which showed that P desorption rate was almost 3 times greater from manured soils than from chemically fertilized soils. Manuring alters soil particle surfaces by increasing negative charge. This is the direct reason for less P adsorption and greater P desorption by manured soils. / The Langmuir 2-surface model and the adapted non-ideal competitive adsorption (MICA) model were equally good at modeling P adsorption data. However, the NICA model is more robust and can predict phosphate adsorption with changing soil solution pH. The simultaneously modeling of P adsorption and hydroxyl adsorption with the NICA model makes it a promising tool for analyzing competitive adsorption among anions in soils.

No description available.

Concerns for environmental quality stimulate the development of various management strategies that mitigate nutrient losses to the environment. / Field experiments were conducted at St. Emmanuel, Quebec, from 1998 to 2000 to investigate the combined effects of water table management and N fertilizer application rates on corn yield, concentrations of NO3- -N in the soil profile and tile subsurface drainage water, denitrification and N2O production rates, and N2O:N2O+N 2 production ratios in the soil profile. There were two water table treatments: free drainage (FD) with open drains at a 1.0 m depth from the soil surface and subirrigation (SI) with a water table depth of 0.6 m below the soil surface, and two N fertilization rates: 120 kg N ha-1 (N120) and 200 kg N ha-1 (N 200) arranged in a split-plot design. Compared to FD, subirrigation reduced NO3--N concentration in the soil by up to 50% and in drainage water by 55 to 73%. Water table had little effect on corn yield during the study period. Greater denitrification rates under SI were not accompanied with greater N2O emissions as ratios of N2O:N2O+N2 were lower under SI than in FD plots. Denitrification rate, N2O emissions, and their ratios were unaffected by N rate. / A second field experiment was initiated from 1999 to 2000 to assess impacts of tillage systems on NO3--N, denitrification, N2O, and ratios of denitrification end-products (N2O:N 2O+N2). The experiment was conducted on long-term momocropped corn experimental plots under conventional tillage (CT), reduced tillage (RT), and no-till (NT), located at the Macdonald Research Farm, McGill University. Soil NO3--N concentrations tended to be lower under RT than under NT or CT. Denitrification and N2O were similar among tillage systems. / Approximately 50% of soil denitrification activity was measured within the 0.15--0.45 m soil layer. Consequently, we propose that sampling the 0--0.15 m soil layer alone, as is usually done, may not give an accurate picture of soil denitrification activity. Dissolved organic carbon concentrations remained high in all soil depths sampled, but was not affected by water table, N rate or tillage system.

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.