A practical means to quantify the response of the rates of net N mineralization and denitrification over a wide range of soil water contents is generally lacking. This study examined the potential to use a nitrification inhibitor (NI) assay system to simultaneously estimate the rates of net N mineralization and denitrification, and applied the NI assay to assess the effect of water content on net N mineralization and denitrification rates in two soils with contrasting soil texture. The compound 3,5-dimethylpyrazole (DMP) applied at a rate of 200 mg kg^-1 was found to provide essentially complete inhibition of nitrification over the duration of the soil incubation for two soils with contrasting soil texture (clay loam vs. sandy loam) and over a range of soil water contents (35%, 55%, and 85% water-filled pore space). This allowed net N mineralization to be estimated as the accumulation of soil ammonium () and of denitrification as the disappearance of added nitrate (). Addition of DMP resulted in a small increase in soil respiration rate but did not appear to influence the rate of net soil N mineralization. The NI assay provides a practical means to quantify the rates of net N mineralization and denitrification simultaneously over a wide range of soil water contents. The assay can be readily scaled up to routinely test multiple soils in an efficient manner, has limited material costs, and is also relatively simple to perform.

We conducted a field experiment with four levels of simulated nitrogen (N) deposition (0, 2.5, 5, and 7.5 g N m^-2 yr^-1, respectively) to investigate the response of litter decomposition of Pinus koraiensis (PK), Tilia amurensis (TA), and their mixture to N deposition during winter and growing seasons. Results showed that N addition significantly increased the mass loss of PK litter and significantly decreased the mass loss of TA litter throughout the 2 yr decomposition processes, which indicated that the different responses in the decomposition of different litters to N addition can be species specific, potentially attributed to different litter chemistry. The faster decomposition of PK litter with N addition occurred mainly in the winter, whereas the slower decomposition of TA litter with N addition occurred during the growing season. Moreover, N addition had a positive effect on the release of phosphorus, magnesium, and manganese for PK litter and had a negative effect on the release of carbon, iron, and lignin for TA litter. Decomposition and nutrient release from mixed litter with N addition showed a non-additive effect. The mass loss from litter in the first winter and over the entire study correlated positively with the initial concentration of cellulose, lignin, and certain nutrients in the litter, demonstrating the potential influence of different tissue chemistries.

This study tested if non-winter cumulative nitrous oxide (N₂O) emissions, emission factors, and yield-scaled N₂O emissions were affected by split application of enhanced efficiency nitrogen fertilizers in a rain-fed winter wheat crop. Based on initial soil tests, fertilizers were applied at 84 kg N ha^-1 in year 1 and 72 kg N ha^-1 in year 2. Two trials were completed each year. Trial 1 applied (1) urea, (2) urea with nitrification inhibitor, (3) nitrification and urease inhibitors, and (4) polymer-coated urea as (1) 100% side-banded at planting, 30% side-banded at planting and (2) 70% surface-applied in late fall, or (3) 70% surface-applied in spring at Feekes growth stage 4 (GS4). Trial 2 applied (1) urea–ammonium nitrate (UAN), (2) UAN treated with nitrification inhibitor, (3) urease inhibitor, (4) a combination of both, (5) granular urea, and (6) polymer-coated urea, all applied 50% side-banded at planting and 50% surface-applied at GS4. Cumulative N₂O emissions from fertilized soils ranged from 0.101 to 0.433 kg N ha^-1. The emission factors for trial 1 were greater in year 1 than year 2 (P ≤ 0.05). There were no treatment differences in cumulative N₂O emissions in trial 2. However, cumulative N₂O emissions, emission factors, and yield-scaled N₂O emissions from trial 1 were higher when fertilizer was split-applied in late fall compared with at GS4 (all P ≤ 0.05). This study demonstrates that under best management practices, it is better to apply the required rate in the form of conventional fertilizer at planting rather than split application.

Residual soil NO₃-N (RSN) is susceptible to loss during the non-growing season. This 5 yr study investigated the effects of three N fertilizer sources [ammonium nitrate (AN), ammonium sulfate (AS), and polymer-coated urea (PCU)] applied at four rates (60, 120, 200, and 280 kg N ha^-1) plus an unfertilized control on RSN following potato production and on overwinter NO₃-N changes in an irrigated sandy soil in Quebec, Canada. Composite soil samples were collected at the 0–15, 15–30, 30–60, and 60–90 cm depths immediately after potato harvest in fall and again in the following spring from 2008 to 2012. Residual soil NO₃-N content within the 0–30 cm depth (RSN_0–30) was highly correlated with the RSN content in the 0–90 cm depth (RSN_0–90), indicating that RSN_0–30 can be used as an indicator of soil profile NO₃-N accumulation. Overall, RSN_0–90 increased with fertilizer N application rate, particularly for above the minimum fertilizer N rate required to maximize yield (N_max), and was generally higher for years with greater pre-plant soil NO₃-N. The split application of AN and AS resulted in lower RSN_0–90 than the single application of PCU at above N_max. Overwinter losses of soil NO₃-N were generally increased with increasing RSN_0–90 in fall. The results suggest that reducing the fertilizer N rate is more important than the choice of N source in managing RSN.

Field experiments were conducted to evaluate the effects of wheat straw return methods, which included the use of surface straw mulch and a buried straw layer, on soil water content, electrical conductivity (EC), and sodium adsorption ratio (SAR) of saline sodic soils in an effort to identify useful ways for reducing soil salt accumulation and enhancing soil water content. The results showed that the straw return treatments were effective for inhibiting salt accumulation and soil water loss, resulting in a reduction of EC and SAR but an enhancement of soil water content. After a year-long experiment, compared with the treatment with no straw return, the straw burial and straw mulching treatments decreased the EC by 10.5% and 3.5%, reduced the SAR by 7.4% and 21.5%, and increased the soil water by 0.9% and 4.4%, respectively. Furthermore, the combined application of straw layer burial and surface straw return had a more significant effect than the individual treatments; the positive effect of straw return occurred mainly focused in the topsoil (0–40 cm) and decreased with increasing soil depth. Our results allowed us to conclude that burial of the straw layer was necessary to enhance the effects of surface mulch, and the combination of surface mulch (3.0 t ha^-1 of wheat straw) and straw layer burial (6.0 t ha^-1 of wheat straw) proved to be a better straw return method than the others.

Two types of organic-matter-rich coversoils are used during reclamation in the oil sands region of Alberta: forest floor material (FFM) salvaged from upland forests, and peat material (PM) salvaged from boreal wetlands. In this study, we tested the hypothesis that carbon (C) and nutrient availability may limit microbial activity in these reclamation materials by measuring their response to either ¹³C-labeled glucose or NPKS addition. Coversoil materials were compared with two natural forest soils corresponding to target sites for reclamation. A shift in microbial community structure (determined using phospholipid fatty acid analysis) was detected after both additions, but it was stronger with glucose than NPKS, especially for the two reclamation materials. For all soils, the increase in microbial respiration was stronger after glucose than after NPKS addition. The majority of CO₂ originated from soil organic matter (SOM) for the natural forest soils but from glucose for the reclamation materials. In PM, glucose addition triggered SOM mineralization, as shown by a positive priming effect. Despite the absence of a priming effect for FFM, microbial communities incorporated higher rates of glucose into their biomass and respired double the amount of glucose compared with the other materials. Furthermore, the overall microbial community structure in the FFM became more similar to that of the natural forest soil materials following glucose addition. These findings indicate that C and NPKS limitations were stronger for the two reclamation materials than for the two natural forest soils. Furthermore, microbial communities in the two reclamation materials responded more readily to labile C than to NPKS addition.

No information exists on the susceptibility of arbuscular mycorrhizal fungal (AMF) communities in Canadian prairie agriculture soils to climate change. An experiment was initiated in mid-May 2011 in which replicated soil cores were transplanted reciprocally from four cultivated prairie sites in Saskatchewan, Canada, representing different regional climatic zones ranging from semiarid to subhumid regional climates, such that replicated (n = 4) soil cores from each site were present at all sites. Field pea was grown in all cores and at harvest in early-September 2011; soil samples were collected to analyze the changes of AMF communities over the cropping season. A total of 82 operational taxonomic units belonging to eight AMF genera were identified using 18S rRNA gene pyrosequencing. When soils were transplanted to new environments, the relative abundance of AMF changed considerably. Typically, Shannon diversity declined when soil cores were transplanted to new environments. We present evidence that with the altered climatic conditions following transplantation of soil cores, the relative abundance of AMF was significantly altered, and some taxa were enhanced, suppressed, or disappeared in the home-away soils compared with home-site soils. This study implies that the future climate change effects on AMF may impact specific phylogenetic taxa differently, such that rare species or those with low abundance may increase or decrease with unknown consequences. Understanding the potential responses of AMF communities to soil–climate interactions is important when considering the impacts of climate change on soil microbial communities.