Irrigation practices change the soil moisture in agricultural fields and influence emissions of greenhouse gases (GHG). A 2 yr field study was conducted to assess carbon dioxide (CO₂) and nitrous oxide (N₂O) emissions from surface and subsurface drip irrigated tomato (Solanum lycopersicum L.) fields on a loamy sand in southern Ontario. Surface and subsurface drip irrigation are common irrigation practices used by tomato growers in southern Ontario. The N₂O fluxes were generally ≤50 μg N₂O-N m^-2 h^-1, with mean cumulative emissions ranging between 352 ± 83 and 486 ± 138 mg N₂O-N m^-2. No significant difference in N₂O emissions between the two drip irrigation practices was found in either study year. Mean CO₂ fluxes ranged from 22 to 160 mg CO₂-C m² h^-1 with cumulative fluxes between 188 ± 42 and 306 ± 31 g CO₂-C m^-2. Seasonal CO₂ emissions from surface drip irrigation were significantly greater than subsurface drip irrigation in both years, likely attributed to sampling time temperature differences. We conclude that these irrigation methods did not have a direct effect on the GHG emissions from tomato fields in this study. Therefore, both irrigation methods are expected to have similar environmental impacts and are recommended to growers.

Feldspathic sandstone could be used as an effective conditioner to improve the physical quality of sandy soil, and increase the crop yield there. To determine the effects of feldspathic sandstone content on soil hydraulic properties in a sandy soil, the present study added 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100% (no sandy soil) of feldspathic sandstone to sandy soil. Changes in hydraulic parameters were investigated and the results showed addition of feldspathic sandstone increased saturated water content by 37%–61% and field capacity by 29%–44%, and decreased saturated hydraulic conductivity from 10.19 to 0.58 cm h^-1 of the sandy soil. Further data analysis demonstrated that with increasing content of feldspathic sandstone, the parameter n of soil water retention curve in Van Genuchten model dropped from 1.807 to 1.333. The same decreasing trend is detected in parameter a of infiltration rate (3.841–0.703) in Kostiakov formula (i = at^-b) and parameter a₁ of wetting front (6.901–1.174) in the empirical equation (X = a₁t^b1). In terms of hydraulic parameters, 40% feldspathic sandstone and 60% sandy soil, optimally matching indices of loess soil, were the best mixing ratio for sandy land restoration.

Soil water repellency affects soil water movement during infiltration significantly. The HYDRUS software has been popularly applied in soil water dynamics simulation for many years, but its performance in water-repellent (WR) soils has not been assessed thoroughly. Our objectives are to assess the performance of HYDRYUS-1D for cumulative infiltration (CI), wetting front (Z_f), and volumetric soil water content (θ_v) during horizontal imbibition and vertical infiltration in wettable, slightly WR, and strongly WR soils. The key parameters of α and n in water retention curves were inversely estimated by RETension Curve software. The α and n were calibrated inversely until the observed data fitted the simulated values well enough. The α and n were then used for validation using three statistical parameters including relative root-mean-square error, R², and Nash–Sutcliffe efficiency coefficient. The performances of calibration and validation for wettable, slightly, and strongly WR soils were good enough to be used for further simulations (RRMSE ≤20.2% for calibration and ≤21.1% for validation). Soil water movements for strongly WR soils of variable ponded depth during vertical infiltration were simulated. For Lou soil, as the ponded depth increased from 4 to 10 cm, the CI and Z_f increased 2.08 and 5.5 cm, respectively. The simulations for the other three soils also showed gradually increased CI and Z_f values. In conclusion, the performances of HYDRUS-1D in four different soil types with changing WR levels were good, which confirmed the application of HYDRUS-1D in WR soils.

Long-term application of feedlot manure to cropland may change the physical properties of soils. We measured selected soil (surface) physical properties of a Dark Brown Chernozemic clay loam where different amendments were annually applied for 15 (2013), 16 (2014), and 17 (2015) yr. The treatments were stockpiled (SM) or composted (CM) manure with either straw (ST) or wood-chip (WD) bedding applied at three rates (13, 39, and 77 Mg ha^-1) and an unamended control. The effect of selected or all treatments on selected properties was determined in 2013–2015. These properties included field-saturated (K_fs) and near-saturated hydraulic conductivity or K(ψ), bulk density (BD), volumetric water content, soil temperature, soil thermal properties, and wet aggregate stability. The hypotheses that selected soil physical properties would improve more for treatments with greater total carbon in the amendments (SM > CM, WD > ST) was rejected. The exceptions were significantly (P ≤ 0.05) lower soil BD for SM than CM and WD than ST for certain dates, and lower soil thermal conductivity for WD than ST. Most soil physical properties generally had no response to 15–17 yr of annual applications of these feedlot amendments, but a few showed a positive response.

Climate change in northeastern North America is resulting in warmer winters with reduced snow accumulation. Soils under a thin snowpack are more likely to experience freeze–thaw cycles, disrupting carbon (C) and nitrogen (N) transformations. We conducted a 2 year snow removal experiment in Maine to study the effects of soil freezing on soil C and N processes. O horizon soils were sampled during winter and spring of 2015 and 2016, and they were analyzed for labile inorganic N and water-extractable organic carbon (WEOC) concentrations, specific ultraviolet absorbance (SUVA₂₅₄), and potential net N mineralization. The winter of 2015 was cold and snowy, whereas 2016 was warm with a shallow, short-term snowpack. Snow removal caused the soils to freeze, but winter rain-on-soil events in 2015 resulted in the formation of concrete frost, as opposed to granular frost in 2016. Concrete frost increased soil ammonium (NH₄ -N) and WEOC concentrations and decreased SUVA₂₅₄, which we attribute to microbial cell lysis. In contrast, granular frost did not alter soil nutrient concentrations, reflecting limited microbial distress. Our study demonstrates that moisture content influences the intensity of soil freezing, highlighting the importance of snowpack depth and winter rain events in regulating winter and spring biogeochemical processes and nutrient availability.

This research aimed to classify 16 horticultural composts collected across Canada into management group according to their phosphorus (P) fractions and carbon (C) content using isometric log ratio (ilr) and to interpret the clusters against the total P content and C-to-P ratio indices. The ilr approach was found to be more discriminant for grouping the composts compared with the conventional statistical analysis. The C-to-P ratio index was representative of cluster 1 only. This cluster included organic amendments with C-to-P ratios higher than 100 and high capacity to increase soil organic matter content without excessive P dosage. Total P separated clusters 2 and 3 despite the amalgamation of P forms into total P. Cluster 2 showed high total P (>10 g P kg^-1) and low C-to-P ratios (24–38), whereas cluster 3 showed variable C-to-P ratios (18–78) and total P <9 g kg^-1 after excluding one compost close to cluster 2. Clusters 2 and 3 were considered as potential sources of plant-available P. The ilr approach suggests that composts made of municipal biosolids and poultry manures in cluster 2 have the highest potential as plant-available P source compared with those made of other livestock manures or food processing wastes.

We studied mature and adjacent open lichen–spruce woodlands (LWs) and closed-canopy spruce–feathermoss stands (FMs) growing under similar edaphic conditions in the continuous boreal forest zone in Quebec (Canada). A total of six pairs of stands were investigated by profile sampling. Stem density, basal area, and biomass were about four times greater in FMs than in LWs on an area basis. In the humus layer, total stocks of C and N and of exchangeable K, Ca, Mg, Al, and Na were 1.4–2.3 times larger in FM than in LW soils. The first 30 cm and the first metre of mineral soils in LWs and FMs displayed similar available nutrient pools except for total C stocks, which were more than twice as large in FM as in LW soils in these soil layers. For the whole profile, total stocks of C and N and stocks of exchangeable Ca and Mg were 1.3–2.6 times larger in FM than in LW soils. These results highlight the low intrinsic fertility of LW soils, primarily due to the humus layer, but also the importance of the biological control of C, N, and mineral nutrients in these boreal soils.

We grew rice in phosphorus (P) deficient subtropical paddy soil in a field study and used ¹³CO₂ continuous labelling to investigate photosynthetic carbon (C) partitioning and allocation under FLOOD versus WET/DRY conditions, with and without P fertilization (80 mg P kg^-1). The plants and soil were sampled after each of three WET/DRY cycles to determine ¹³C allocation in above- and belowground plant biomass, microbial biomass, the rhizosphere, and bulk soil. Irrespective of water management, P-fertilized plants had higher biomass and P content and more total ¹³C in the rice-soil system, especially the ¹³C incorporation into the shoots (51%–96%), than samples without P fertilization. Root and bulk-soil ¹³C were largely independent of both P fertilization and water management. However, by the third sampling, P fertilization had increased the amount of ¹³C and microbial biomass ¹³C in the rhizosphere soil (RS) by 28% (WET/DRY) and 95% (FLOOD), and by 47% (WET/DRY) and 50% (FLOOD), respectively. The WET/DRY condition had significantly higher microbial biomass and ¹³C contents than FLOOD condition only in the RS. These results indicate that a well-established aboveground plant biomass following P fertilization is required to increase belowground C allocation. Thus, WET/DRY conditions, like FLOOD conditions, can provide moisture sufficient for unhindered P availability in rice-paddy system.

Infrared spectroscopy has the potential to rapidly analyse soil water-dissolved carbon and amino sugars. In this study, mid-infrared (MIR) and near-infrared (NIR) spectra collected from soil water extracts or from bulk soils were analysed with partial least squares regression (PLSr) to estimate the concentrations of water-dissolved carbon and amino sugars in diverse agricultural soils collected from five field sites in two western and two eastern Canadian provinces. The MIR-PLSr models developed from soil water extract spectra estimated hot-water (100 °C) dissolved carbon (HWDC) [R² = 0.97–0.70, ratio of prediction to deviation (RPDp) = 6.13–1.83] well, but the MIR-PLSr models did not estimate cold-water (21 °C) dissolved carbon (CWDC) well (R² = 0.82–0.50, RPDp = 2.35–1.42). The model estimates of HWDC at the multisite scale (all samples together) and for the two western Canada sites (R² = 0.97–0.93, RPDp = 6.13–3.68) surpass the modal estimates for the three eastern Canadian sites (R² = 0.81–0.70, RPDp = 2.28–1.83). The MIR- and NIR-PLSr models derived from bulk soil spectra both estimated HWDC well at the multisite scale (R² = 0.91–0.88, RPDp = 3.32–2.90) and for the western Canada sites (R² = 0.90–0.87, RPDp = 3.18–2.96). Models developed from hot-water extract spectra and bulk soil spectra resulted in poor estimates of soil amino sugars (R² = 0.74–0.21, RPDp = 1.99–1.12), except for the approximate quantitative estimation of muramic acid by models based on soil spectra at the western and the multisite scale (R² = 0.82–0.80, RPDp = 2.33–2.21). We concluded that MIR and NIR models at regional and multisite scales can be used as a tool to monitor HWDC but that additional research is required for estimating soil amino sugars.

To understand the chemical behavior of potassium (K) in soil, rhizobox experiments were conducted to study the effects of K uptake by cultivated rice and soil type on K migration and transformation in soils. The aim of this study was to guide reasonable application of K fertilizer in different soil types. The results showed that at the maximum tillering stage, the migration distances of water-soluble K (Sol-K) were 6 and 5 cm, the depletion of exchangeable K (Ex-K) was 7 and 4 cm, and depletion of nonexchangeable K (Nonex-K) was 1 and 5 cm, respectively, in yellow cinnamon soil (YCS) and fluvo-aquic soil (FS). With the growth of rice, the migration distances of Sol-K showed little difference between YCS and FS. Throughout the season, the contributions of Sol-K, Ex-K, and Nonex-K to K uptake in YCS were 12.0%, 40.0%, and 48.0%, respectively, whereas their contributions in FS were 25.7%, 25.8%, and 48.5%, respectively. K uptake by rice was linearly related to the concentration of different forms of K in soils (R² = 0.687*). In conclusion, soil type significantly affected K mobilization and transformation behavior. This indicated that the location of K fertilizer addition in the root zone should differ with soil type.

Crop rotations on the Canadian prairies commonly include sequences of pulses, oilseeds, and cereals; however, limited information is available regarding the influence that different crop types and sequences may have on direct nitrous oxide (N₂O) emissions. A 3 yr field study was conducted on a site near Scott, SK, to compare N₂O emissions from selected crop phases of rotations containing pea (Pisum sativum L.), wheat (Triticum aestivum L.), and canola (Brassica napus L.) and to examine the potential influence of these residues on N₂O emissions during the subsequent crop phase. Nitrous oxide losses from N-fertilized canola or wheat crops were generally higher than losses from pea or the control treatments. Nitrous oxide losses from N-fertilized wheat or canola crops grown on pea residue were comparable or lower than losses from N-fertilized wheat or canola crops grown on wheat residues. Cumulative N₂O loss over the 3 yr was significantly higher from N-fertilized wheat grown on canola compared with pea or wheat residues. Losses from wheat grown on canola residue were 67% and 56% higher than from wheat grown on pea or wheat residue, respectively. This indicates that the emission factors used to estimate direct N₂O loss may need to be adjusted upwards for N-fertilized crops grown on canola compared with wheat or pea residues.

Restoring ecosystem function after oil sands surface mining involves reestablishing the biotic and abiotic ecosystem components that affect biogeochemical cycles and fluxes. In boreal forest ecosystems, pyrogenic carbon is a native soil component that affects a variety of biogeochemical parameters and biochar is its human-made analog. To evaluate the benefits of biochar amendment to reclamation cover soils, we compared characteristics and function of peat–mineral mix (PM) and forest floor–mineral mix (FFM) with and without biochar in an 18 wk greenhouse study. We assessed nutrient bioavailability (NO₃, NH₄, P, K, S, Mg, and Ca), foliar nutrient concentrations (N, P, K, S, Mg, Ca, Na, and Mo), soil respiration, rhizosphere polysaccharide concentration, soil organic matter stability, and Populus tremuloides Michx. seedling growth. Seedling growth increased significantly on PM cover soil with biochar. Biochar improved K nutritional status and potentially interacted with Na bioavailability in PM, affecting growth. Soil respiration significantly decreased in PM with biochar and increased in FFM. Soil organic matter stability was positively correlated with seedling growth and increased with biochar. Our findings suggest that biochar may have a significant positive effect on upland forest reclamation in the Athabasca oil sands region, especially on sites that are reclaimed with PM.

Change in land use causes changes in soil properties and soil fertility, with long-term effects on ecosystem and crop productivity. This study determined soil fertility along sequential conversion of cropland to grassland in China’s Loess Plateau. Soil samples were collected in 2015 at two sites in the semiarid region, following the conversion of cropland to grassland. Soil particle-size distribution, bulk density, pH, organic carbon (OC), total nitrogen (TN), total phosphorus (TP), available potassium, and available phosphorus were measured in this study. In addition, we analysed the changes of soil OC, TN, and TP, and evaluated soil fertility after the conversion from cropland to grassland. The establishment of grassland significantly increased soil OC, N, and P content, especially in the 0–10 cm soil layer. The highest change in soil OC, N, and P content occurred 6–10 yr after land conversion. The measured soil variables did not change significantly after 10 yr of land conversion. The overall increase in soil fertility after the land conversion was 13% at one site and 26% at the other site. The results suggested that establishing grassland could enhance soil fertility in the semiarid Loess Plateau region of China, and this enhancement is optimal 6–10 yr after the establishment of grassland.

Soil enzymes play a key role in many soil processes that affect soil health and which may be adversely affected under a changing climate. We investigated the short- and long-term effects of bentonite amendments on soil catalase, invertase, urease, and alkaline phosphatase activity in a field experiment in a semi-arid region in northern China. Treatments included six rates of bentonite amendments (0, 6, 12, 18, 24, and 30 Mg ha^-1) applied only once in 2011. Addition of bentonite had a significant (P < 0.01) effect on the activity of each enzyme at different layers and days after millet sowing. Observed increases in catalase, invertase, urease, and alkaline phosphatase activities were up to 42%, 46%, 58%, and 50%, respectively, and they were approximately linear with increasing bentonite rate up to 24 Mg ha^-1 over the 5 yr experimental period. Averaged over 5 yr, the 24 Mg ha^-1 rate of bentonite amendment led to the largest effect on soil enzyme activity in all soil layers at five growth stages over the growing season. The observed increased enzyme activity suggests that bentonite can help maintain and improve soil health to support plant growth and contribute to sustainable agriculture production in a semi-arid environment.

To determine how soil physical and chemical characteristics affect NH₃ volatilization, we measured NH₃ losses from eight different eastern Canadian soils with various soil clay contents and cation exchange capacities (CEC). Losses were measured from soil mesocosms banded (0.05 m depth) with urea (equivalent of 140 kg N ha^-1) in a dynamic chamber system fitted with an acid trap; with soil properties measured in parallel mesocosms. Regression analysis indicated a negative relationship between 28 d of NH₃ volatilization losses and soil clay content (P < 0.001; R² = 0.978), CEC (P < 0.001; R² = 0.941), and buffer capacity (P = 0.006; R² = 0.772), and positive relations with maximum change in soil pH (P = 0.015; R² = 0.670) and maximum water-extractable NH₄ (P = 0.010; R² = 0.721). A 90% reduction in NH₃ losses occurred when clay content increased from 10% to 20%. Also, the correlation between water-extractable NH₄ and NH₃ loss and a lack of correlation between salt-extractable (1 mol L^-1 KCl) NH₄ and NH₃ loss indicate that NH₄ bound to cation exchange sites does not contribute to the rapid NH₃ volatilization. However, more research on soils of different mineralogy is required to ascertain whether this holds in other regions as well.

We planted continuous wheat, with and without nitrogen fertilizer, onto a preceding long-term (44 yr) experiment with contrasting cropping systems, and measured soil organic carbon (SOC) after 6 yr. Changes in SOC were driven mostly by cumulative plant C inputs, as influenced by yield response to added nitrogen.

We examined soluble organic nitrogen (SON) leached from long-term, sequentially leached, aerobic incubations. Leached SON, present in all depths (0–60 cm), ranged from 35% to 56% of total nitrogen (N). This unaccounted-for SON may have important implications in the estimation of plant available N and the potential for environmental N losses.

To improve the estimates of C and N inputs to soil, we developed new estimates of partitioning between the harvested portion, aboveground residue, and belowground residue for 11 major crops based on depth-adjusted root/shoot ratios and grain yield-adjusted harvest indices. We updated the mean N concentration of each partition.

Soil organic carbon (SOC) changes slowly, and final management influences can be measured only after decades. Analysis of archived samples from a site established on grassland in 1911 showed that SOC, under wheat systems, approached steady state after several decades, and that its amount reflected the inputs of residue C.

Researchers may consider the soil effects for one phase representative for the entire long-term rotation. We showed that soil carbon can differ between rotation phases. We recommend sampling all phases for determining the tillage effect across the rotation and, otherwise, to interpret considering potential impacts of sampling one rotation phase.