Understanding the spatial variability of soil mineral nitrogen (SMN) and crop growth is an important step for implementing precision nitrogen (N) management technologies for canola production. A 3 yr field experiment in Ontario investigated the within-field spatial variability of SMN in relation to growth parameters and yield. Each year, large strips in a commercial field were randomly assigned a preplant N treatment (0, 50, 100, and 150 kg ha^-1), with three replicates of each. Our data showed that SMN varied widely among field-strips receiving different treatments and also within strips receiving the same N rate, indicating significant spatial variability in N availability at the field- and strip-scale. Some crop measurements exhibited wide variations in parallel with the SMN dynamics. At the early flowering stage, SMN contents displayed a strong relationship with plant height and branch numbers. Although grain yield showed a positive response to N, the inconsistent yield increase with increasing N supply was likely due to the inherent variations in soil N supply among years and fields, indicating an inefficient use of the uniformly applied preplant fertilizer N by the crop. The strong associations between SMN and crop parameters or yield provided a substantial evidence for implementing in-season variable rate N application.

Enhancement of inorganic phosphorus (Pi) release by low molecular weight organic acids (LMWOA) increases soil phosphorus (P) availability to plant, but the release of organic phosphorus (Po) and the associated kinetics of both Pi and Po release by LMWOA have not been well considered. The aim of this study was therefore to investigate the impacts of three common LMWOA (citric acid, oxalic acid, and malic acid) on the kinetic release of Pi and Po in a black clay soil in northeast China. All kinetic data were well described by the Elovich and power functions models (P < 0.01). The LMWOA at 10 mmol kg^-1 soil increased the rate of the kinetic release of both Pi and Po. Organic phosphorus released by LMWOA derived from the soil-labile Po (NaHCO₃-Po) fraction in the order of oxalic acid (3.58 mg kg^-1) > citric acid (2.67 mg kg^-1) > malic acid (1.76 mg kg^-1). In contrast, Pi release by LMWOA resulted from mobilization of the moderately labile NaOH-Pi (Fe/Al-P) and HCl-Pi (Ca-Pi) fractions in the order of citric acid (4.83 mg kg^-1) > oxalic acid (2.40 mg kg^-1) > malic acid (2.04 mg kg^-1). Therefore, the release of Po by LMWOA is mainly via the dissolution of soil-labile Po (NaHCO₃-Po) rather than via chelation of organic acid ligands.

The use of construction and demolition waste (CDW) and peat moss as bedding in beef cattle feedlots may affect the amount of plant-available nitrogen (N) in manure. Such an effect, however, may differ between manure from cattle fed a regular grain diet (RM) and those fed dried distiller grains with solubles (DGM). We used five 40 d crop cycles in a greenhouse bioassay to determine the effects of RM and DGM manure containing CDW or peat moss on canola (Brassica napus L.) growth and N uptake in a Black Chernozem (loam, Typic Hapocryoll) and a Brown Chernozem (sandy clay loam, Aridic Haploboroll) with or without the addition of a nitrification inhibitor (nitrapyrin) in each cycle to minimize nitrate (NO₃) leaching. Our results showed that the presence of CDW in DGM and RM manure depressed (P < 0.05) cumulative dry matter yield (CDMY) and N uptake in canola relative to manure without CDW, whereas the presence of peat increased (P < 0.05) CDMY and N uptake. Results suggest that it may be necessary to supplement CDW-amended DGM and RM manure with synthetic N fertilizer to supply adequate available N for plant uptake because the addition of CDW decreases organic N mineralization.

Introducing boundary-layer (BL) theory to solve problems of solute transport provides a simple and accurate alternative method to estimate transport parameters. Most BL solutions to the convection–dispersion equation (CDE) are derived from the hypothesis of a zero concentration gradient at the position of solute front, which is inconsistent with the actual situation. This study assumes a logarithmic concentration profile and presents a novel analytical solution to the equilibrium CDE. The concentration gradient at solute front for the logarithmic model is not regarded as zero. A range of parameter values was used to evaluate the accuracy of the logarithmic model based on the relative error between the logarithmic and the corresponding exact profiles, and soil-column experiments were used to examine the reliability of the model for parameter estimation. The accuracy of the new BL solution was greatly influenced by the values of the transport parameters. The logarithmic profile matched the exact profile well when the rate of change of concentration was large in shallow porous media. These findings will integrate the methodology of using BL theory to solve problems of solute transport and provide a more accurate method for some cases of solute transport.

Identifying the predominant sources of sediment is a key requirement for soil erosion control within watersheds. A 4 yr study from 2009 to 2012 was conducted to apportion sediment sources in a subcatchment of the Lower Little Bow River watershed, AB, Canada. This study catchment lies along a 6 km reach of the river, having an upstream inlet and downstream outlet; as such, it represents the first application of the sediment fingerprinting technique in a reach setting. Six monitoring stations were established along this reach of river to collect sediments using passive time-integrated sediment samplers. Source material samples were collected throughout the study catchment. Reflectance spectra of source and sediment samples were determined using a diffuse reflectance spectrometer. Source materials were classified into five sources using canonical discriminant analysis. Following the normality test, analysis of variance and stepwise discriminant function analysis, four colour coefficients were selected and fitted to the Bayesian mixing model of stable isotope analysis in R. The results indicated that the unknown upstream sediment source was the single largest (37.4%) contributor of sediments, suggesting that there is sediment coming from a significant source or sources not represented within the study catchment. Irrigation return flow channels were the second largest contributor (25.6%), while the third largest contributor, agricultural land, had a minimal contribution (9.2%). Source contribution had a small spatial but large temporal variation. The results indicated that identifying the origin of secondary sediment sources of upstream and irrigation flow channels is a critical step for soil erosion control in the study subwatershed.

Understanding the temperature sensitivity of soil respiration is very important to quantify the climate–carbon cycle feedback. Most existing studies have only focused on responses of growing-season respiration to warming. Soil respiration of non-growing season may be more sensitive to warming. However, to our knowledge, this hypothesis remains poorly understood. An experiment was conducted in a mountain pine forest of southwestern China to compare the sensitivity of soil respiration to warming ( 5 °C) between growing and non-growing seasons. Experimental warming decreased soil moisture but increased soil respiration on most of the measuring dates. Warming-caused increase in soil respiration and Q₁₀ value was greater during the growing season than during the non-growing season. Q₁₀ values decreased linearly with warming-induced changes in soil moisture. This study provides preliminary evidence that soil respiration of non-growing season is less sensitive to warming compared with that of growing season in the mountain forests experiencing monsoon climate.

Infrared spectroscopy has the capacity to predict soil organic carbon (SOC) and total nitrogen (TN) at local/regional scales, but no studies have been conducted to evaluate this technique at a large (cross-regional) scale in Canada. In this paper, mid-infrared (MIR) and near-infrared (NIR) spectroscopies in combination with partial least-squares regression (PLSr) were used to predict SOC and TN in whole soil and in particulate organic matter (POM) fractions on cross-regional, regional, and local scales. Both MIR- and NIR-PLSr models have well estimated SOC [coefficient of determination (R²) = 0.79–0.92, residual prediction deviation/ratio of prediction to deviation (RPD) = 2.19–3.47], TN (R² = 0.70–0.92; RPD = 1.83–3.50), POM-C (R² = 0.76–0.96; RPD = 2.04–5.25), and POM-N (R² = 0.70–0.97; RPD = 1.83–5.78). The prediction efficiency of cross-regional models (R² = 0.90–0.96; RPD = 3.13–5.49) was similar to or better than the prediction of regional (R² = 0.70–0.97; RPD = 1.83–5.78) and local models (R² = 0.70–0.96; RPD = 1.83–5.33) and overall MIR-PLSr models (R² = 0.90–0.96; RPD = 1.98–3.47) yielded similar predictions for SOC and TN relative to NIR-PLSr models (R² = 0.70–0.92; RPD = 1.83–3.50) at cross-regional scale. Hence, it may be possible to develop MIR and (or) NIR spectral models to estimate and monitor SOC, TN, POM-C, and POM-N, and therefore, soil quality, in a rapid and cost-efficient manner across regions with diverse soil types, climate, and cropping history.

Transition from conventional tillage to no-tillage may alter the depth distribution of soil organic carbon (SOC) and its chemical composition. The effects of 15 yr contrasting tillage systems on soil aggregation and the concentration and chemical composition of SOC were investigated in a semi-arid and semi-humid area of North China. Three treatments were established in 1996, including conventional tillage with (CTS) and without (CT) straw incorporation, and no-tillage with straw mulching (NTS). ¹³C nuclear magnetic resonance (NMR) spectroscopy was used to quantify the chemical characteristics of SOC in the 0–10 and 10–20 cm layers. NTS had a higher SOC stratification ratio than the CTS and CT. Aggregate stability, as indicated with the mean weight diameter, was higher for NTS and CTS than that for CT. SOC occluded in the >1 mm fraction was higher under NTS and CTS than under CT. Both NTS and CTS had more aliphatic carbon than CT did, and CT contained more aromatic carbon in the 0–20 cm layer. We concluded that NTS increased aggregate stability, enhanced SOC stratification, and altered the chemical composition of SOC in the plow layer, and could be a viable option for improving soil quality in the study area.

Enhanced mobilization of potentially toxic trace elements (PTTE) is well documented for contaminated floodplains, wetlands, and rice paddies. Limited information is available on flooding-induced PTTE release from uncontaminated agricultural soils from temperate regions. We conducted an incubation study with simulated flooding using calcareous, uncontaminated agricultural soils to assess the release dynamics of a few PTTE and to identify the controlling factors. Packed soils were flooded, and soil redox potential (Eh), pH, total dissolved metals, and sulfur (S) concentrations in pore water and floodwater were measured for 8 wk. Pore water arsenic (As) and nickel (Ni) concentrations were initially low, but significantly increased with flooding by 12- and 6-fold, respectively. Copper (Cu) concentration declined with flooding, whereas zinc (Zn) showed no consistent trend. Arsenic and Ni concentrations correlated negatively with Eh, and positively with other redox-sensitive elements, whereas Cu behaved in a manner opposite to that of As and Ni, however, correlating positively with S. Pore water Zn correlated negatively with pH and Ca, and positively with Al. Principal component analysis confirmed the role of Eh on As, Ni, and Cu release from flooded soils and the pH dependency on Zn release. Prolonged flooding released environmentally significant quantities of some PTTE from uncontaminated agricultural soils.

Over a period of 2 yr, the effects of dehydrated septic tank sludge application on the chemical properties of a severely disturbed forest clayey soil were assessed and compared with application of native forest floor (i.e., from neighboring forest). Six treatments [fresh and mature sludges × two depths (15 and 25 cm), forest floor, and a control] were replicated three times according to a complete random design. Total organic C and N concentrations of amendments and their chemical structure, based on ¹³C nuclear magnetic resonance (NMR) spectroscopy, were determined. Mineral soil C and N concentrations and C mineralization rates were monitored as well as nutrient supply rates using Plant Root Simulator^™ probes. White spruce [Picea glauca (Moench) Voss] seedling foliar nutrition and growth were also monitored. NMR spectroscopy revealed differences among amendments, with the forest floor spectra displaying lower O-alkyl C and higher alkyl C and carbonyl C proportions relative to sludge. Neither soil C concentrations nor mineralization were significantly improved in the mineral soil under any treatment, even at application rates exceeding 700 t sludge ha^-1 (dry mass). The sludges supplied more NO₃ and P, and less NH₄ and K to the mineral soil than the forest floor and control. Increased nutrient availability under sludge and forest floor generally resulted in improved foliar nutrition and growth of white spruce seedlings. Despite differences in organic matter quality and mineral N form supplied by sludge and forest floor, sludge application is a valid restoration approach.

Bioavailability of phosphorus (P) in soils is controlled by, inter alia, the presence of iron (Fe) and aluminum (Al) oxides, which readily bind with P. Biochar has been suggested for minimizing P sorption to oxides and, therefore, improving P availability to plants. However, the kinetics and temperature dependence of biochar influence on P sorption are poorly understood. The objective of this study was, therefore, to determine the kinetics and thermodynamics of P sorption by goethite as affected by biochar application at 0 and 40 g kg^-1 oxide. Batch equilibration tests were run at 15, 25, and 35 °C, and solution P concentrations were measured 0.5, 1, 3, 6, 9, 12, and 24 h after the start of incubation. Sorption of P by the oxides followed pseudo-first-order kinetics. Biochar application enhanced cumulative P sorption by both oxides, and the increase was greater for Al-goethite. Phosphorus sorption increased as temperature increased from 15 to 25 °C but declined at 35 °C. Phosphorus sorption on biochar-amended oxides was associated with low activation energy (E_a) values, indicating that the sorbed P in soils containing goethite and Al-goethite could still be plant available. This information will contribute towards a better understanding of processes affecting biochar effects on P fate in soils.

How soil carbon dioxide (CO₂) and methane (CH₄) fluxes and above- and belowground C respond to grazing management across a grassland landscape is poorly understood. Thus, we quantified soil CO₂ and CH₄ fluxes, and above- and belowground C, for sandy loam and loamy sand soils within a dry mixed-grass prairie subjected to annual rotational cattle grazing (grazed) since 1970 or grazing exclusion for 4 yr (rested). Gas samples were collected weekly (May to October). The CO₂ flux was 24% greater from the rested than grazed sandy loam. Higher CO₂ fluxes from the rested than grazed sandy loam were associated with 49% and 68% greater water-extractable organic C concentrations in May and July, respectively, a 34% greater soil organic C concentration, and 88% greater peak aboveground vegetation C. In contrast, the rested and grazed loamy sand had similar CO₂ flux and above- and belowground C, but 16% more CH₄ uptake occurred in the grazed than rested. Across soil textures, water-filled pore space (WFPS) explained 59% of early-season CH₄ flux variability and 37% overall. Soil respiration and above- and belowground C appeared most responsive to grazing in the soil with finer particle texture, whereas WFPS most strongly controlled early-season CH₄ fluxes across soils.

Large volumes of generated animal manures necessitate knowledge of how its production and storage affects composition, losses, and utilization potential. Stratification of liquid dairy manure was the main source of observed variability within outdoor uncovered manure storage, during a yearlong monitoring of 24 physicochemical manure parameters. Coefficient of variation (CV) ranged from 4% to 24% for plant nutrients and 33% to 89% for biogas feedstock parameters. Nitrogen (N) volatilization losses during storage between manure additions were ?10% mo^-1 of total Kjeldahl nitrogen (TKN). Acetic acid was up to 100% of total volatile fatty acid concentration. Bioavailability and solubility of manure parameters, reflected in ratios of volatile solids to total solids (VS:TS), total ammoniacal nitrogen to total Kjeldahl nitrogen (TAN:TKN), and dissolved phosphorus to total phosphorus (O-PO₄:TP) ratios, was high. There was substantial pathogen survival during the study, with an increased count with added manure. Manure temperature changes and precipitation levels likely played a major role in mineralization and volatilization rates of nutrients and reduction of solids, especially in surface levels of manure in storage. Study results underline the importance of sampling method, timing, and location within stored manure to obtain representative samples unless thorough mixing is previously applied.

The spatiotemporal characteristics of soil water content (SWC) have a significant influence on vegetation degradation and growth in alpine meadow ecosystems. The spatiotemporal variability and temporal stability (TS) of SWC, however, have rarely been studied on the northern Tibetan Plateau owing to the rugged and hostile sampling environment. The objective of this study was to analyze the spatiotemporal variability and the TS of SWC in various layers of the soil, to a depth of 50 cm in a 33.5 hm² plot, with the data obtained from 113 measuring locations collected on 22 sampling occasions during the growing seasons of 2015 and 2016. The SWC was moderately variable both in time (two consecutive growing seasons) and horizontal space (plot). The variabilities, however, did not vary consistently with increasing depth for the various dominant influencing factors. The SWC in the undeveloped, shallow, and stony alpine meadow soil was temporally stable; TS did not depend on depth due to disturbances by grass roots and stones. The best representative location of TS at each depth could be determined, and all accurately estimated the field mean SWC. Vegetation coverage, soil organic carbon, gravel and stone contents, and saturated hydraulic conductivity were the main factors influencing TS. This study provides useful information for the management of alpine meadows and provides an effective method for studying SWC at a hectometre scale on the Tibetan Plateau.

We used visible near-infrared reflectance spectroscopy (VNIRS) to characterize a set of organic materials (n = 75). Good predictions for total carbon, excellent predictions for total nitrogen, but poor predictions for pH were found. This preliminary study showed that VNIRS could rapidly characterize organic materials before soil application.