The nitrogen (N) index for humid temperate southern Ontario, Canada (Ontario N index) incorporates previous and current crop type, fertilizer and (or) manure management, and hydrologic soil group (HSG) to estimate risk for contamination of tile drainage water and groundwater by nitrate leached below the primary crop root zone (top 60 cm of soil). The Ontario N index has received limited ground-truthing, and the leaching component was assessed using chloride tracer (Cl_TR) on five soils (one sandy loam, two loams, and two clay loams) representing four HSG-based risk levels (HSG-A, high risk; HSG-B, medium risk; HSG-C, low risk; HSG-D, very low risk). A square-wave pulse of Cl_TR was applied to the soil surfaces in fall 2007 as KCl, and movement and loss of Cl_TR was tracked over 1-1.2 years using monthly soil core samples collected from the top 60-80 cm. For all five soils, 60-96% of Cl_TR was leached out of the primary crop root zone (below 60 cm depth) during the noncropping period (October 2007 to March 2008 inclusive), and >80% was leached out of the root zone within 1 year. The percentage of Cl_TR that leached did not correlate with precipitation or HSG designation, but produced significant (P < 0.05) power function regressions with minimum and harmonic mean saturated soil hydraulic conductivity (K_sat) measured in the top 50-60 cm. Cl_TR leaching rate appeared to be controlled primarily by K_sat in a manner consistent with infiltration and solute transport theory. It was consequently proposed that solute leaching loss versus K_sat relationships may improve N index risk estimates for both southern Ontario and other humid temperate regions.

Nitrogen (N) leaching from soil into surface and ground waters is a concern in humid areas of Canada. As a result, N management protocols, including the Ontario N Index, are widely used to identify N leaching risk, although field assessment remains limited. Nitrogen fertilizer and chloride (Cl) tracer were fall-applied to five agricultural soils in Ontario with different textures and hydrologic soil groups (HSG) to assess the Ontario N Index and characterize inorganic N movement over 1 yr. The treatments included three N rates (0, 100, and 200 kg N ha^-1) plus Cl tracer and 200 kg N ha^-1 rate without Cl. After spring thaw, N loss from the crop root zone (top 60 cm) ranged from 68% for Brookston clay loam to 99% for Harrow sandy loam. A strong linear relationship between apparent N recovery and apparent Cl recovery indicated that N loss from the root zone occurred primarily by downward leaching. Leaching was controlled by the minimum measured saturated hydraulic conductivity (K_sat), and good estimates of N leaching were obtained using a quasi-theoretical relationship between N loss and K_sat. We concluded that Ontario N Index estimates of N leaching risk might be improved by including site-specific measurements of K_sat.

Determining how agricultural management practices affect changes in soil nitrogen (N) and phosphorus (P) could further our understanding of soil N and P cycle. The main objective of this study was to assess in situ nongrowing season soil nitrate and phosphate dynamics as adsorbed on anionic exchange membranes (AEM-N and AEM-P, respectively). The membranes were buried in the surface horizon (5 cm below the soil surface) over the nongrowing season (mid-November to mid-April) in five consecutive years (2009-2010 to 2013-2014) in a long-term corn-soybean rotation experiment established in 1992 in eastern Canada. The treatments consisted of two tillage systems, namely moldboard plow (MP) and no-till (NT), and nine combinations of fertilizer applications, namely three N rates (0, 80, and 160 kg N ha^-1) and three P rates (0, 17.5, and 35 kg P ha^-1) in a split-plot design with four replications. The results showed that AEM-N and AEM-P averaged 1.8 µg cm^-2 d^-1 and 7.4 ng cm^-2 d^-1 under MP, respectively, and 2.8 µg cm^-2 d^-1 and 67.8 ng cm^-2 d^-1 under NT, respectively. Nitrogen application increased AEM-N in 2010-2011, 2011-2012, and 2012-2013, but decreased AEM-P mainly under NT. Phosphorus fertilization had no effect on AEM-N, but increased AEM-P under both MP and NT. We conclude that AEM can be used as a technique to study N and P dynamics under cold winters of eastern Canada.

Pig (Sus scrofa) manure is added to the soil to supply nutrients and improve soil properties. To our knowledge, no direct comparison has been made on the effect of liquid pig manure (LPM) and solid pig manure (SPM) on the physical properties of a prairie soil. This study was established in 2009 at the University of Manitoba's Ian Morrison Research Station in Carman, Manitoba. The treatment design was a split-plot structure with cropping system as the main plot and manure treatments as subplots. Five years after the study was initiated, soil samples were collected from the 0-10 cm and 10-20 cm depth intervals for determination of bulk density, saturated hydraulic conductivity (K_sat), and water retention at field capacity and permanent wilting point (PWP). For wet aggregate stability, samples were collected from the 0-5 cm layer. Land application of SPM significantly decreased bulk density by 14%, significantly increased K_sat by 110% in the 0-10 cm layer, and resulted in a 30% increase in wet aggregate stability (P < 0.05). In perennial plots, SPM increased water retention at field capacity, PWP, and available water in the 0-10 cm compared with annual plots. This was not the case for LPM-amended soils. We conclude that SPM has the potential as an organic amendment to improve the physical properties of the topsoil.

Little research has evaluated naturally vegetated buffers to retain pollutants in soil from concentrated runoff through deep (2-14 m) gullies. Soil enrichment in the flow path of 11 naturally vegetated gullies in southern Alberta, Canada, was used as a long-term signature of filtering during concentrated flow. Soil was sampled at three depth intervals (0-2.5, 2.5-5, and 5-10 cm) along two 50-m transects inside and outside the flow path of the vegetated gullies in each of 3 yr (2011-2013). The influence of soil type, flow path (inside vs. outside), distance into vegetated flow path, depth, and their interactions on enrichment of nutrients (NH₄-N, NO₃-N, soil test P (STP), total P) and particle size fractions (clay, silt, and sand) was determined. Significantly (P ≤ 0.05) greater enrichment of nutrients and specific particle size fractions inside than outside the flow path of the vegetated gully suggested that greater deposition occurred inside the concentrated flow path. In contrast, there was little evidence for enrichment of nutrients and sediment at the front or inlet of the buffer (except STP), or for infiltration of more soluble nutrients into the subsoil. Soil enrichment in buffers may reveal long-term filtering processes that may not be shown with short-term runoff experiments.

Experiments were conducted to evaluate the effect of rhizobial inoculums and inorganic fertilizers on NP availability, soil microbial activity, wheat NPK concentration and uptake. These experiments were consisted of two factors, four inoculums (no, lentil, peas, and chickpeas) and two NPK doses (120:90:60 and 96:72:48 kg ha^-1). Inoculums significantly increased plant total NPK concentration by 39, 57, and 37%, and their uptake by 66, 86, and 56%, respectively. Peas inoculum was most efficient in wheat NPK concentration and uptake. The interactive effect of inoculums and NPK demonstrated that peas and lentil inoculums with 20% less NPK had statistically better role than full NPK without inoculation. AB-DTPA extractible P and mineral N were progressively increased with incubation periods and exhibited significant differences between inoculated and uninoculated treatments during all incubation intervals for NP except at day 7 for N. Peas inoculum showed maximum mean net NP availability of 131.5 and 3.48 mg kg^-1 over 56 d of incubation, respectively. Significantly higher cumulative CO₂ of 1429 mg kg^-1 with a net increase of 866 mg kg^-1 was recorded for pea's inoculums during 12 d of incubation interval. It is concluded that peas rhizobium could be used as a plant-growth-promoting rhizobacteria for wheat and other cereal crops.

Inter-relationships among soil erosion, soil quality, soil resilience, and legacy effects of organic amendments have not been adequately quantified. Topsoil was mechanically removed (cuts) to simulate erosion in semiarid southern Alberta in 1990. Three cuts (0, 10, and 20 cm) superimposed with three one-time (1990 only) amendment treatments (check, N P fertilizer, and manure) were chosen for this study. In the absence of amendments, light fraction C (C_LF) and mineralizable C (C_min) recovered sufficiently by 2004 to render the cut effect nonsignificant. Organic C (C_org) responded more slowly with the 10-cm cut recovering to the 0-cm cut concentration by 2004, and the 20-cm cut (13.9 g kg^-1) remaining significantly lower than the 0-cm cut concentration (16.3 g kg^-1) through to 2012. Nitrogen fractions behaved similarly. Among cuts and years (2004 and 2012), C fraction values were 19-27% greater on the manure versus check treatment (17.5 vs. 14.7 g kg^-1 for C_org, 1.38 vs. 1.09 g kg^-1 for C_LF, and 650 vs. 531 mg kg^-1 for C_min) demonstrating a strong legacy effect of manure. Water-stable aggregation exhibited a 22-yr legacy effect of manure. Our findings help quantify soil resilience following major disturbance and legacy effects of one-time manure application under semiarid conditions.

Environmental indices for soil P limit P applications when soil tests and risk of P losses exceed a given threshold. Producers' reluctance to reduce P inputs often stem from concerns regarding reduced crop production and soil fertility. Our objectives were to identify changes in soil P fractions after 4 yr of repeated manure or fertilizer P applications at rates ≤ crop removal by corn (Zea mays L.), and the impact of these applications on yields. Olsen P and soil P fractions extracted using a modified Hedley P fractionation procedure were measured. Corn yields were nonresponsive to P applications. After 4 yr, Olsen P was 16.6 and 24.6 mg kg^-1 at the application rates of 0 and 33 kg P ha^-1 yr^-1, respectively, for the inorganic fertilizer treatment indicating that soil P drawdown was occurring. Only the most labile forms of Pi (resin and bicarbonate extractable) were affected by treatment, with greater values at higher P application rates. Adherence to Ontario's P index recommendations for P applications at or below crop removal should not be a crop production concern. Furthermore, given the rate of soil labile P drawdown, routine soil testing (every 3-5 yr) would identify agronomically significant changes in soil test P before the crop yield is impacted.

Soils in plantations of Cryptomeria japonica in Japan have ~threefold more exchangeable Ca compared with soils in other types of forest vegetation even in a Ca-poor environment. To explain mechanisms underlying this phenomenon, we determined the effect of root exudation rate of low-molecular-mass organic acids (LMMOAs) on exchangeable cations in soil. We conducted a pot experiment using C. japonica and five dominant tree species in Japan, and measured the root exudation rates of LMMOAs and exchangeable nutrient concentrations in the soils. To estimate whether the root exudation rate of LMMOAs is elevated in response to Ca deficiency, we created variation in Ca availability by adding different amounts of crushed oyster shells. The root exudation rates of LMMOAs were two to five times higher for C. japonica than for other tree species, but did not differ significantly among the different quantities of oyster shell. Exchangeable Ca and Mg were significantly higher in the soils with C. japonica and significantly correlated with the root exudation rate of LMMOAs (R² > 0.24) at high and moderate quantities of oyster shell. Therefore, variation among species, in terms of root exudation of organic acids, might be one important factor affecting the cation dynamics in soil.

Concerns about climate change have increased interest in ways to maximize carbon (C) storage in forests through the use of alternative forest management strategies. However, the influence of these strategies on soil C pools is unclear. The primary objective of this study was to test for differences in mineral soil C stocks among various silvicultural and harvesting treatments that were initiated in the 1950s and have been maintained since on the Penobscot Experimental Forest in central Maine, USA. Five mineral soil cores below the surface organic horizon to a depth of 1 m were collected from each replicate (n = 2) of selection, shelterwood, and commercial clearcut treatments. For these treatments, the mean mineral soil C stock was 47.7 ± 16.4 Mg ha^-1 (mean ± SD). We found no significant differences in average mineral soil C stocks among treatments. However, a post hoc power analysis indicated that the probability of detecting a significant treatment effect was only 6%. We determined that 98 stands per treatment would be required to be 80% certain that the F test would detect a difference in average mineral soil C stocks whenever any pair of treatments had C stocks differing by more than 5 Mg ha^-1.

Improvement in use efficiency of N fertilizers can potentially better sustain agriculture by reducing N₂O emissions from soils, but little is known about its impact on soil CO₂ emissions. A study, involving both a field experiment and a laboratory incubation, was conducted in eastern Canada to determine the N fertilization effect on soil CO₂ emissions. In laboratory, we incubated nine different types of soil with and without 150 kg N ha^-1 as KNO₃ or (NH₄)₂SO₄. The N-fertilized soils had lower CO₂ emissions compared with the no-N control soils for six of them. Among fertilizer sources, emissions of CO₂ were on average 22% lower with KNO₃ than with (NH₄)₂SO₄. The field experiment conducted on a clay soil included three sources of N (urea-NH₄NO₃, CaNH₄NO₃, and aqua NH₃) at 0-200 kg N ha^-1 band-incorporated at the six-leaf corn stage. Under field conditions, most CO₂ was emitted between N application and grain maturity with cumulative seasonal soil emissions greater in the control (4.9 Mg C ha^-1) than in the N treatments (average of 4.0 ± 0.3 Mg C ha^-1). Evidence suggested that both heterotrophic and autotrophic respiration seemed affected, whereas the NO₃-based source had a more depressing effect on CO₂ emissions than did the NH₄ source.

Soil salinity caused by oil-production-water (brine) contamination is a major issue in regions of oil and gas development. However, rapid site assessment tools such as soil-to-water suspension electrical conductivity (EC) methods and conversion equations have not been previously calibrated and validated for brine-contaminated soils. Our objective was to compare three soil EC methods and derive conversion equations for EC values commonly observed at brine-spill sites. Brine-contaminated soils from western North Dakota were assessed for salinity. Electrical conductivity was determined using 1:1 and 1:5 soil-to-water suspensions (EC_1:1, EC_1:5) and saturated paste extracts (EC_e). Soil EC equilibration times for soil-to-water suspensions were also assessed. Significant relationships (r² = 0.91 to 0.97, P < 0.0001) existed among all methods for EC values ranging between 0 and 126 dS m^-1. Conversion equations were developed based on these relationships and then validated with an independent data set. These new equations reduced EC_e prediction errors by 2 to 4.5 times when compare with 14 predictive equations reported in the literature. The conversion equations developed here are recommended for use in remediation efforts when converting EC_1:1 and EC_1:5 data to EC_e on brine-contaminated and noncontaminated soils where EC_e is highly correlated to Na concentrations.

Inadequate and (or) inconsistent soil sample preparation techniques (SPT) contribute to excessive variance, difficulties in soil test interpretation, and incorrect lime and fertilizer recommendations. The objective of this study was to evaluate the effect of SPT of five laboratories in Quebec (Canada) on chemical parameters measurement reliability. Samples of fine (G1), medium (G2), and coarse (G3) textured soils were collected from the surface layer. Three 500 g portions of each soil were sent to each laboratory for preparation. In addition, all samples were analyzed by the same laboratory for routine analyses. Nested ANOVA in a hierarchical model were performed with components of SPT interlaboratory reproducibility, SPT intralaboratory replicability, and intralaboratory soil analysis repeatability. Before samples were analyzed, we observed an important interlaboratory heterogeneity of particle size distributions for the same samples; due to sample preparation techniques, this can affect results of the analyses. Of all variables analyzed, the only significant, outside acceptable variations due to SPT were (1) pH_water in G1; (2) P_M-III, Al_M-III, and (P/Al)_M-III in G1 and G2; (3) K_M-III, Ca_M-III, Mg_M-III and organic matter in G3; and (4) Mn_M-III and Cu_M-III in G1, G2, and G3. The steps in SPT, mostly drying and crushing, require standardization to reduce the variance of the entire soil testing process.

The land suitability rating system (LSRS) is a spatial modeling tool that generates a class rating for parcels of land for specific agricultural crops based on a soil-climate-landscape potential. We applied the LSRS module for corn suitability to the agricultural portion of the lower Fraser Valley of British Columbia (BC). We used data from six UN-IPCC AR4 projections covering a range of cold to hot and wet to dry scenarios for the time periods 2010-2039, 2040-2069, and 2070-2099 to assess the impacts of climate change on corn production. To obtain satisfactory spatial results, we linked high-resolution (400 m grid) monthly temperature and precipitation values to the individual polygons of a detailed (1 : 25 000 scale) soil map available for the study area. Of the six future climate scenarios evaluated, the Goddard Institute for Space Studies (GISS_EH-A1B/3) yielded the most favourable results whereby land suitability for corn without irrigation remained relatively stable through the 21st century. Conversely, the Hadley Centre Global Environmental Model (HadGEM-A1B/1) projected a large drop in land suitabililty for corn due to increased climatic and soil moisture deficits. The wide range of climate scenario inputs generated a similarly wide range of LSRS ratings. Most scenarios generated positive impacts for land suitability up to mid-century but negative impacts by late century. Overall, increased heat and aridity will produce earlier harvest dates for corn and likely mean significant changes to the types and timing of crop management practices in the region.