A better understanding of the depth distribution of soil mineralizable nitrogen (N) pools is important to improve prediction of net soil N mineralization. However, our understanding of the depth distribution of these N pools under the semi-arid conditions of western Canada is limited. This study examined the depth distribution of soil mineralizable N pools (k_S, the rate constant of a nondepleting zero-order stable N pool, and N_L, the size of a depleting first-order labile N pool) of six sites in western Canada chosen to vary with respect to soil zone, soil texture, and cropping system. The depth distribution of mineralizable N pools varied substantially among sites, indicating that this distribution needs to be considered in making predictions of net soil N mineralization. A single regression equation including soil total nitrogen (STN), Pool I (a labile mineralizable N pool determined through a 14-day aerobic incubation), and soil pH explained 67% of the variation in k_S across sites and soil depths. In addition, 95% of the variation in N_L was explained by a regression model with Pool I. Thus, although the depth distribution of soil mineralizable N pools can vary substantially among sites, the mineralizable N parameters can be adequately predicted across sites and soil depths from simple soil properties. Comparison with a study using surface soils under humid conditions in New Brunswick suggests that the relationship between N_L and Pool I is applicable across a wide range of soils, climatic zones, and cropping systems, whereas the regression model to predict k_S varied with climatic zone, perhaps reflecting different pedogenic processes stabilizing the organic matter in these climatic zones.

Little is known about nitrous oxide (N₂O) emission from silage corn (Zea mays L.). Studies have shown that controlled-release N fertilizers have the potential to reduce N₂O emissions, compared with conventional N fertilizers. This 2-year field study compared N₂O emissions from urea fertilizer and a slow-release polymer-coated urea (CRU) applied to silage corn on soils managed with conventional tillage (CT) and zero tillage (ZT). The study was conducted on a silty loam soil in the cool, moist climate of south coastal British Columbia, Canada, taking year-around measurements from static chambers. Over 2 study years there was a significant interaction between N sources and tillage methods; under CT there was no significant difference between CRU and urea (557 vs. 447 g N₂O-N ha^-1 year^-1, respectively), but under ZT, emissions from CRU were significantly higher than from urea (968 vs. 381 g N₂O-N ha^-1 year^-1, respectively). Annual emissions of N₂O-N ranged from 0.09 to 0.65% of applied N fertilizer. The CRU also had significantly greater emissions than urea per unit N uptake and plant yield under ZT, while there was no significant difference between N sources under CT. The results do not indicate that NO₃^- release from broadcast CRU matches corn growth or reduces emission of N₂O.

There is growing interest among commercial wine grape (Vitis vinifera L.) growers in reducing water and fertilizer consumption, but little information exists on how best to combine conservative irrigation and soil management practices in the vineyard. In a 3-year-old Merlot vineyard in the semi-arid Okanagan Valley, British Columbia, the interactive effects of resource-conserving micro-irrigation (drippers or microsprinkers), nutrient applications (fertigation or compost), and surface mulching (wood and bark chips) on nitrogen (N) and phosphorus (P) dynamics in the wetted zone of surface soils were examined throughout the growing season using ion-exchange resins. Treatment differences in soil carbon and major nutrient pools, temperature, and moisture were also measured. Higher NO₃-N was adsorbed by resins buried under drippers than under microsprinklers except in mulched plots, where NO₃-N was uniformly low. By enhancing soil carbon availability and moderating soil microclimate, surface mulches may have promoted microbial immobilisation of N. Compost applications increased soil ortho-P levels, especially on mulched plots, suggesting that both P inputs (from compost) and enhanced microbial biomass (from mulch) promoted soil P cycling. Future work will examine the interactive effects of these resource-efficient practices on leaching losses, greenhouse gas emissions, crop productivity, and fruit quality.

Cranberry production requires accurate irrigation management to optimize crop yield and reduce water use. However, irrigation guidelines for that crop are scarce and empirical. The objective of this study was to identify appropriate soil matric potential (ψ) irrigation set points for cranberry production. A three-step process was used to evaluate the set points. Crop water requirements were first evaluated in the field and, second, combined to soil physical properties with a hydrological model to estimate irrigation set points. Third, experimental measurements were carried out in a growth cabinet and in the field to validate the set point estimates from independent observations. Irrigation set point estimates obtained from yield response curves, photosynthesis and transpiration measurements, and soil physical properties were all consistent and suggest that soil matric potential be maintained between -4.0 and -7.0 kPa to ensure an adequate water supply to the crop and optimal fruit yield. Yield responses suggest that cranberries are highly sensitive to small changes in soil matric potential, showing differences of about 20 000 kg ha^-1 when outside of the -4.0 to -7.0 range, with a maximum yield between 35 000 and 40 000 kg ha^-1, depending on the site.

Despite all efforts, agricultural contaminants remain at alarming concentrations in Quebec surface waters. Preferential flow (PF) of soluble contaminants has been suggested as a contributing factor but has not been specifically studied in the humid climate of eastern Canadian soils. Three tracers were surface applied on plots along a catena on a loamy sand under intensive agricultural production in Beauce, Quebec. Tracer distribution in soil profiles was monitored three times over a 12-month period. At the summit, finger flow rapidly transported tracers into the subsurface. The subsurface preferential lateral flow rapidly brought the tracers downslope. Narrow points of preferential seepage and discharge and underground lateral PF were observed at the footslope. The summit and the backslope of the catena showed strong vertical and lateral subsurface PF, which made their contribution to subsurface tracer movement toward surface water equal to or greater than that of the footslope, in part because of the hydrological connectivity between summit, backslope, and surface water. PF and matrix flow were both significant in all parts of the catena. Therefore, all parts of a catena, even those far from surface water, should be considered when evaluating potential belowground contaminant transport toward surface water.

Little is known about the influence of soil pedogenesis and reclamation practices on the chemical composition of soil organic matter (SOM) in eroded Oxisol. We examined the long-term influence of pedogenesis and 8 years of a reclamation practice on SOM in the top 5 cm of an artificially eroded Oxisol of Brazil. The experimental site involved replicated treatments established under native vegetation, and an adjacent site whose top 8.6 m had been removed mechanically (eroded reference). The eroded Oxisol was under reclamation with native tree and grass species, and addition of sewage sludge. Pyrolysis field ionization mass spectrometry was used to characterize SOM. The abundance of most classes of SOM and soil carbon decreased in the following order: native > reclaimed >> eroded soil. Relative to the eroded reference, SOM in the native soil was highly humified and stabilized by inorganic colloids of iron, aluminum, and silicon. Humified and thermally stable SOM in the native and reference eroded soils involved mostly alkylaromatics, lipids, phenols lignin monomers, lignin dimers, and N-heterocyclics. The reclaimed soil SOM was less humified and less stable than the native Oxisol, showing significant contributions of carbohydrates, amino acids, and sterols derived from sewage sludge and plant residues.

Denitrification losses from agricultural land have been identified as a significant nitrogen (N) loss pathway that contributes to poor utilization of applied N. Higher losses have been reported when inorganic fertilizer N is substituted with an organic N source such as livestock manure. This research examines the relationships between denitrification rates, land management practices and soil processes when using spring applied liquid dairy manure (LDM) as principal N source. Mean daily denitrification rates (DDRs) in a perennial hayfield (PH) rotation and a corn-soybean-wheat (CSW) rotation with or without tillage (T and NT respectively) ranged between 0.9 and 27.0 g N ha^-1 day^-1. Mean, seasonal DDRs in the PH rotation were significantly lower in three out of six seasons when compared with the CSW-T and (or) CSW-NT rotation. When averaged across the six season study period, the mean DDR in PH of 4.4 g N ha^-1 day^-1 was also significantly lower than CSW-T and NT (7.6 and 8.1 g N ha^-1 day^-1, respectively). There were no significant effects of tillage in the CSW rotations in any of the six growing seasons. When treatment and growing season data were combined, a positive relationship between water-filled pore space (WFPS) and DDR indicated a threshold of approximately 40% WFPS for onset of significant denitrification. Similarly, the relationship between soil nitrate levels and denitrification rates in the population data set demonstrated that NO₃^- began to limit DDR below 2-5 mg N kg^-1. This 6-year study of denitrification losses suggests a primary effect of WFPS, a secondary effect of O₂ consumption as reflected by soil respiration, and nitrate limiting only at relatively low concentrations. Environmental variables were more consistent drivers of denitrification in three manure-fed crop rotations typical of Atlantic Canada dairy operations than were land management decisions and practices.