Large inputs of nitrogen (N) are required to optimize yield and quality of potato (Solanum tuberosum L.), and it may result in a high potential for N losses including denitrification. This 5 yr study compared the effect of three N fertilizer sources [ammonium nitrate (AN), ammonium sulfate (AS), and polymer-coated urea (PCU)] at 200 kg N ha^-1 (N200) and an unfertilized control (N0) on denitrification rate (DR) from irrigated potato production on a coarse-textured soil in eastern Canada. Fertilizer was banded all at-planting (PCU) or split 40% at-planting and 60% at-hilling (AN and AS). The DR was measured biweekly from planting to harvest at two locations (ridge and furrow) using the acetylene blockage technique. The mean annual DR, averaged across N treatments, ranged from 0.8 to 8.0 μg N₂O-N kg dry soil^-1 d^-1, and it was most closely related to the water inputs in the 72 h before DR measurements. Mean DR averaged across year was greater for N200 than for N0 (4.2 vs. 3.4 μg N₂O-N kg dry soil^-1 d^-1) but did not differ among N sources. Our results suggest that choice of N fertilizer source in sandy soils is more important in controlling losses of N by leaching than by denitrification.

In cold agricultural regions, animal manure and synthetic fertilizers may be applied in the fall for convenience. However, the fate of applied nitrogen (N) is unclear and may differ depending on N source and interannual and regional variations in winter conditions. A multi-region study using ¹⁵N-labelled reactive N (NH₄-¹⁵N) applied in the fall with pig slurry, dairy cattle slurry, and ammonium sulfate was carried out under a range of climatic conditions. Nitrification and immobilization of applied NH₄-N occurred throughout the winter period at all sites. Transformation and losses were slower and less at the sites where significant soil freezing occurred than at the site where soil rarely froze, highlighting the repressive effect of frost. Nevertheless, losses were similar among sites with significant freezing despite marked differences in duration and extent of freezing. This suggests that soil microbes were adapted to prevailing winter conditions at each site and able to use and transform fall-applied N throughout the winter period. Overall, 47%–94% of fall-applied NH₄-N was lost from the top 30 cm of soil before seeding in the next spring. Losses were generally greater with synthetic fertilizer than manures, likely because fresh carbon added with manures stimulated immobilization of NH₄-N. This multi-region assessment indicates that reactive N applied in the fall has high vulnerability to loss in cold and frozen soils, and strategies for improving N retention over the winter are required even in areas where prolonged freezing occurs.

Grassland set-asides (GLSA) in the Fraser River delta are fields that are taken out of crop production and seeded with a mixture of grasses and legumes for 1–4 yr. During this time, the farmer is compensated with a cost-share payment to recover a portion of the financial returns that could have been earned from cash crops. The objectives of this study were to (i) evaluate the effects of GLSA on soil properties during the initial two seasons of enrollment, (ii) determine how GLSA effects differ between fields that were considered productive and unproductive, and (iii) identify soil baseline indicators and preliminary soil thresholds for predicting GLSA vegetation responses. Out of eight fields entering the program, two were considered to be unproductive and exchangeable sodium had the strongest negative relationship to GLSA aboveground biomass (r = -0.61, P = 0.0002). During the second season of GLSA establishment, the mean weight diameter of water-stable soil aggregates was consistently higher in productive GLSAs than paired annual crop rotation (ACR) fields, being 21% higher in April, 14% in July, and 19% in September after crop harvest. After two seasons of GLSA enrollment, both aeration porosity and bulk density were improved by GLSA relative to ACR fields with aeration porosity being 24% greater and bulk density 7% lower in GLSA. The results suggest that GLSA rotations in productive agricultural fields within the Fraser River delta provide an alternative to continued ACR that can improve soil structure and reduce compaction after only two seasons of establishment.

Soil samples were collected from commercial agriculture sites within western Canada that were subjected to compaction from farm equipment in both conventional (imposed) traffic and controlled traffic regimes. Soil characteristics such as bulk density, pore volume fractions, and unsaturated hydraulic conductivity were compared with soil physical quality parameters, such as S-index and mass fractal aggregation between trafficked and untrafficked field areas. Our results showed that untrafficked soil characteristics displayed substantial improvements over those exposed to equipment compaction. Untrafficked soils in the controlled traffic regime exhibited total porosity improvements up to 15% in more than half of the study sites. In addition, spatial reductions of equipment compaction increased the volume of soil pore diameters associated with preferential water transmission from 40% to 180%. Changes in these soil characteristics within untrafficked soils correlated well with enhancements in the soil structure metrics, as improvements to the S-index were coupled with evidence of hierarchical aggregation. Irrespective of the positive changes to soil structure, significant increases in crop yield were rarely observed in favor of a controlled traffic regime. Our results suggest that the integration of controlled traffic farming into management systems may take several years for the benefits to soil physical quality to translate into observable improvements in crop yield.

Phosphorus (P) fertilization can increase grassland production, but will also alter P forms, changing their cycling and potential for loss in runoff. We assessed the effects of mineral P fertilization on soil P forms in timothy swards at two sites in Quebec, Canada. Soil samples (10 cm depth) were collected in autumn 2013 from replicate plots at Lévis on a Kamouraska clay and at Normandin on a Labarre clay loam, each having received three rates of triple superphosphate (0, 20, and 40 kg P ha^-1) for 4 yr. These were analyzed for pH, total carbon (TC), total nitrogen (TN), and total phosphorus (TP); Mehlich-3-extractable aluminium (AlM3), iron (FeM3), calcium (CaM3), and P (PM3); and ³¹P nuclear magnetic resonance spectroscopy (³¹P-NMR) following sodium hydroxide–ethylenediaminetetraacetic acid (NaOH–EDTA) extraction. Phosphorus fertilization had no significant effects on soil TC, TN, AlM3, FeM3, CaM3, and pH, but significantly increased TP, NaOH–EDTA-extractable total P and total inorganic P, PM3, orthophosphate, and glucose 6-phosphate at both sites. In contrast, NaOH–EDTA-extractable total organic P, total orthophosphate diesters, and scyllo-inositol hexaphosphate decreased with P fertilization. Phosphorus fertilization over 4 yr increased soluble inorganic P and decreased organic P at both grassland sites.

The co-product of anaerobic digestion, digestate, is nitrogen (N) rich; however, the forms and accessibility of this N by the crops have not been fully explored. This study aimed to determine the mineralization parameters of digestate N and to assess its availability for annual ryegrass (Lolium multiflorum Lam.). Four digestate rates of 0 (control), 38, 75, and 150 mg N kg^-1 soil (equal to 0, 90, 180, and 360 kg total N ha^-1) were applied to a silty clay loam soil in a completely randomized block design with four replications in a greenhouse study. A 100 d aerobic incubation experiment was also conducted with 0 and 150 mg digestate N kg^-1 rates at 25 °C. Digestate feedstock included cattle manure (28%), hay (15%), and silage corn (Zea mays L.; 57%). Total plant biomass and N uptake increased linearly with digestate application rate with average apparent N recovery of 37%. Potentially mineralizable N (N₀) and mineralizable N rate constant (k) were not significantly different in digestate and control treatments; however, a flush of digestate organic N (30 mg N kg^-1) released right after mixing the digestate with soil. Evidences of N immobilization with digestate application were observed in greenhouse study. Majority of plant-available digestate N was in form of NH₄⁺-N; therefore, NH₄⁺-N can be used for estimation of available digestate N for crops. Results need to be validated for specific feedstock and soil properties under field conditions. Further research is needed to assess how long-term build-up of digestate organic N may impact the N availability for crops.

Combined applications of mixed biomaterial amendments and polyacrylamide (MBAP) to maize in semiarid areas have the potential to improve soil physical properties such that improved crop performance may be obtained under deficient irrigation management. In this study, three MBAP applications were C0 (conventional N fertilization application) and C2 and C4 (MBAP applied at rates of 2 and 4 t ha^-1, respectively); three irrigation levels were W3 (nearly full irrigation, 85%–100% of field capacity), W2 (light deficit irrigation, 65%–75% of field capacity), and W1 (medium deficit irrigation, 55%–65% of field capacity). Under the same irrigation level, the MBAP significantly decreased soil bulk densities and increased soil hydraulic conductivities and soil water contents. The effects of irrigation levels on soil bulk densities and soil saturated hydraulic conductivities were not significant. Consequently, MBAP improved soil conditions for maize growth and increased grain and biomass yields, especially at the two deficit irrigation levels. Compared with that of C0, grain yields for C2 and C4 were increased by 52.8% and 39.3% under W2, and by 23.5% and 13.7% under W1, respectively. The MBAP and irrigation had significant interaction effects on evapotranspiration during sowing to jointing and on plant heights at 32 d after sowing. The incorporation of MBAP (2 t ha^-1) and chemical fertilizer (111.8 kg N ha^-1) resulted in the greatest yields under light deficit irrigation and seemed the best approach to improve soil physical properties and sustain maize productivity using limited water resources in dryland regions.

The formation of soil organic matter via humification of plant litter is important for long-term carbon sequestration in forests; however, whether soil fauna affects litter humification is unclear. In this study, we quantified the effects of soil fauna on the optical properties (i.e., ΔlogK and E4/E6) of the alkaline-extracted humic acid-like solutions of four foliar litters by removing soil fauna via litterbags with different mesh sizes in two subtropical evergreen broad-leaved forests. Litterbags were collected at the leaf falling, budding, expanding, maturation, and senescence stages from November 2013 to October 2015 to assess whether the effects of soil fauna on litter humification vary in different plant phenology periods. The results showed that soil fauna significantly reduced the ΔlogK and E4/E6 values in the leaf expanding stage of oak litter and in the leaf falling stage of camphor and fir litters. The richness index of soil fauna explained 21%, 55%, 19%, and 45% of the variations in the E4/E6 values for oak, fir, camphor, and pine litters, respectively. The effects of litter water content on these optical properties were greater than that of temperature. These results indicated that soil fauna plays a key role in litter humification in the leaf expanding and falling stages and are potentially involved in soil carbon sequestration in these subtropical forests.

This study explored the mineral contribution of lignin to humus (HS) formation through the change of HS composition in microbial–mineral residue (MMR). The liquid shake flask culture method was adopted to collect the MMR formed through the microbial utilization of lignin in the presence of goethite, bayerite, δ-MnO₂, kaolinite, and montmorillonite. The carbon (C) contents of humic-like acid (HLA), fulvic-like acid (FLA), and humin-like (HLu) in MMR, represented as C_HLA, C_FLA, and C_HLu, respectively, coupled with the ΔlogK of the HLA alkali-soluble extract and C_HLA/C_FLA ratio were analyzed at 10, 30, 60, and 110 d. In terms of improving HLA aggregated on minerals, the following rule was observed: goethite > bayerite > montmorillonite > kaolinite ≈δ-MnO₂. Goethite was most likely to adsorb organic molecules with a high degree of polymerization. Compared with kaolinite and montmorillonite, goethite, bayerite, and δ-MnO₂ were more helpful for decreasing the molecular weight and the degree of HLA condensation. Goethite, δ-MnO₂, and montmorillonite presented the greatest advantages in enhancing the relative proportions of C_HLA, C_FLA, and C_HLu, respectively, in MMR. In MMR formed in the presence of kaolinite, goethite, and bayerite, C_HLA was decreased by 14.8%, 12.0%, and 5.8%, respectively, at the end of culture, whereas the C_HLA associated with δ-MnO₂ was increased by 12.0%. δ-MnO₂ contributed the most to the conversion of C_FLA to C_HLA. Due to expandability and a much greater adsorption capacity, montmorillonite was most beneficial to the accumulation of C_HLu.

The soil carbon (C) accumulation rate was determined for switchgrass, as compared with selected C₃ species in Nova Scotia, Canada. There was no significant effect of crops on total soil C retention, whereas soil ¹³C signature (δ¹³C) was enriched by 0.4‰ in switchgrass relative to other C₃ species, and C accumulation rate was 0.06 Mg ha^-1 yr^-1 in the top 30 cm of soil.

The lower Fraser Valley is one of the most intensively cropped regions in Canada. Yet, how soil health indicators respond to long-term intensive agricultural management is poorly documented in this region. Thus, we evaluated a suite of soil health indicators in response to 21 growing seasons of continuous silage corn (Zea mays L.) under conventional tillage or no-tillage (0–20 cm soil layer). Wet aggregate stability, available water capacity, active carbon (permanganate oxidizable, POXC), and extractable potassium and extractable magnesium were significantly greater with no-till than conventional tillage, whereas 8 of 13 indicators were similar. Soil health indicators responded more favourably to no-till than conventional tillage.