No description available.

No description available.

No description available.

Laboratory soil columns, 0.3 m diameter $ times$ 0.7 m long, and two computer simulation models, LEACHM-N and NTRM, were used to investigate nitrate-nitrogen ($ rm NO sb{3 sp{-}}$-N) leaching in a sandy loam soil. The following treatments were studied: no-till (NT), reduced tillage (RT), and conventional tillage (CT) practices, with residue (R) and without residue (NR). Nitrogen fertilizer was applied at a rate of 180 kg/ha in granular form (experiment I), and in solution form a year later (experiment II). In both experiments, water was applied 5 times over 3 to 4 weeks duration, with each application lasting for 30 minutes. Each column received an average of 24 mm water in experiment I and 32 mm in experiment II. Soil moisture contents were measured and water for $ rm NO sb{3 sp{-}}$-N concentration determination sampled at 0.1, 0.2, 0.4, and 0.6 m depths, following each water application. / In each experiment I, higher nitrate-nitrogen concentrations ($ lbrack rm NO sb{3 sp{-}}$-N)), occurred at the 0.1 and 0.2 m soil layers in RT and CT treatments initially, but less leached to lower layers, while more $ rm NO sb{3 sp{-}}$-N leached to lower depths (below 0.4 m) in the NT treatment. In experiment II, more $ rm NO sb{3 sp{-}}$-N leached below 0.4 m in RT and CT than in NT treatments. Conventional tillage exhibited the lowest drainage rates. Tillage and residue effects were significant only at early stages (4 hours or before) at some depths of experiment I ($P<0.05$). Maximum $ lbrack rm NO sb{3 sp{-}}$-N) occurred at 0.4 m depth in all treatments. / LEACHM-N estimated more $ rm NO sb{3 sp{-}}$-N leaching below 0.4 m in RT and CT treatments than in NT treatment. The model performed poorly only immediately after fertilizer application, showing up to 50% deviation from observed data. Although LEACHM-N overpredicted $ lbrack rm NO sb{3 sp{-}}$-N) in the 0.2 m soil layers in all treatments, estimations remained within standard deviations of observed data. NTRM performed well below 0.4 m depths, but often underpredicted $ rm NO sb{3 sp{-}}$-N leaching at shallower depths. / From both the laboratory experiments and mathematical simulations it was concluded that when fertilizer is applied in granular form, no till practice is undesirable because deeper $ rm NO sb{3 sp{-}}$-N leaching (below 0.4 m) occurs. Reduced tillage may be the preferred choice in such a situation. When fertilizer is applied in solution, reduced and conventional tillage practices are undesirable because deeper $ rm NO sb{3 sp{-}}$-N leaching occurred. No till practice may be a better choice in such a case.

Nitrate leaching was studied on a 2.4-ha subsurface-drained corn (Zea mays L.) field in southwestern Quebec. The soil was a sandy loam to loamy sand (mean depth 46 cm) overlying clay. Treatments, begun in fall 1991, consisted of no-till, reduced tillage, and conventional tillage with crop residues either removed or retained at harvest. Drain flow volume and NO$ sb3 sp-$-N concentrations in flow were monitored year-round, and soil NO$ sb3 sp-$-N levels measured in spring and fall. A total of 34 kg NO$ sb3 sp-$-N ha$ sp{-1}$ was recorded in drain flow in 1992 from the site as a whole, equivalent to 20% of applied fertilizer N. In the first 14 months of monitoring, over 70% of water samples had NO$ sb3 sp-$-N levels exceeding Canadian drinking water guidelines (10 mg NO$ sb3 sp-$-N L$ sp{-1}),$ and about 25% had over 40 mg NO$ sb3 sp-$-N L$ sp{-1}.$ Flow-weighted mean concentration for the site as a whole in 1992 was 19 mg NO$ sb3 sp-$-N L$ sp{-1}.$ Unanticipated variations in drain depth significantly affected flow volume and total NO$ sb3 sp-$-N losses, hampering assessment of treatment effects on drain water parameters. In 1992, post-harvest soil NO$ sb3 sp-$-N levels at 0-25 cm were significantly lower in plots with crop residues retained, regardless of tillage system, than in plots with residues removed. In May 1993 (pre-tillage), soil NO$ sb3 sp-$-N levels were similar for all treatments, having dropped in no-residue plots and risen slightly in plots with residues, suggesting immobilization of NO$ sb3 sp-$-N by crop residues in summer-fall and mineralization in spring. The NO$ sb3 sp-$-N measured in drain flow represents a substantial loss of N from the farm system, and has negative implications for water quality. Within the time-frame of the study, crop residues appeared to have a greater effect on soil NO$ sb3 sp-$-N levels, and thus leaching potential, than did tillage system.

A two year study was conducted on the Macdonald Campus Farm on a 2.4 ha site of shallow St. Amble loamy sand cropped to corn (Zea mays L.). Three types of tillage practice (conventional tillage, reduced tillage, and no-till) were combined with 2 residue levels (with and without) in a randomized complete block design. The effect of these practices on NO 3--N distribution at 0--50 cm in the soil profile, and on plant N uptake were studied. Organic matter, pH, bulk density, and soil moisture contents were also monitored. Residues were found to have a greater influence on soil NO3--N transformations (mineralization and immobilization), than tillage. In July 1996 residues suppressed NO3--N levels in reduced tillage (RT), but increased NO3--N levels in conventional tillage (CT). Residues initially increased N03--N levels in no-till (NT), but a few weeks later caused a sharp decline in NO 3--N levels in NT. In August 1996, RT and NT treatments without residue were found to have much greater concentrations of NO 3--N than those with residue. The effect of N suppression caused by residues was observed in Spring 1996, July 1996, August 1996, and August 1997. Reduced tillage demonstrated less NO 3--N fluctuation than the other tillage treatments. Wheel tracked rows had up to 20 times more NO3--N at 0--15 cm than the non wheel tracked rows, caused by the uneven distribution of N fertilizer. However, high NO3--N levels in the wheel tracked rows decreased to levels comparable with those in non fertilized (non wheel track) rows at 50 cm. Corn yields were not affected by tillage or residue treatments, neither were they influenced by the percentage of tissue N content. (Abstract shortened by UMI.)

No description available.

No description available.

A two year study was initiated in 2001 on a 2.4 ha site of mostly St. Amable loamy sand and shallow loamy sand at the Macdonald Campus Research Farm. This study sought to assess the effects of long term tillage and residue practices on soil physical properties and to relate these properties to their influence on total carbon, total nitrogen and soil microbial biomass-carbon. The site was set up as a factorial experiment with three tillage practices (no till---NT; reduced till---RT; and conventional till---CT) and two residue practices (with residue (grain corn), +R; without residue (silage corn), -R). Soil physical properties measured were bulk density, macroporosity at -6 kPa, saturated hydraulic conductivity (Ksat ), dry aggregate distribution, soil moisture and soil temperature. Wheel versus non-wheel track bulk density was also determined in the NT plots. Total porosity, soil water characteristic curves and pore volume distribution were derived from field samples. Crop yield was also assessed. Tillage alone had an effect on total porosity, bulk density, pore diameter and macroporosity. No individual physical property was significantly affected by the residue treatments; however, the tillage and residue interaction was significant for Ksat, soil moisture and soil temperature. Dry aggregate distribution was not affected by either tillage, residue or the combination of the two. Tillage affected total carbon and total nitrogen in the 0--0.10 m depth. Soil microbial biomass-carbon was affected by residue inputs. Total carbon and nitrogen were influenced by the bulk density, but none of the other soil physical properties. Soil microbial biomass-carbon was not influenced by any of the physical properties. Tillage and residue practices had no significant effect on crop yield for either year.

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.