Annual removal of tobacco residues and insufficient input of organic materials have exacerbated total organic carbon (TOC) depletion and soil degradation in a tobacco field in the Huanghuai area. Straw residue and biochar application may be effective ways to increase TOC accumulation and improve soil fertility. In this field experiment, wheat straw (WS) and wheat-straw-derived biochar (BC) with mineral fertilizer were compared with mineral fertilizer alone (CK), and we assessed their effects on soil organic carbon fractions, enzyme activities, and nutrients in Shandong Province, China, during 2016 and 2017. At 0–20 cm depth, the WS treatment had a greater overall effect on the measured soil properties. Compared with the control, the WS treatment significantly increased the concentrations of microbial biomass carbon (MBC), hot-water-extractable carbon (HWC), and permanganate-oxidizable carbon concentrations (POXC; by 252.41%, 107.02%, and 65.53%, respectively); the activities of sucrase, urease, and phosphatase (by 112.52%, 7.81%, and 34.33%, respectively); and the contents of alkaline hydrolysable nitrogen, available phosphorus, and available potassium (by 92.22%, 100.78%, and 10.57%, respectively). Compared with the control, the BC treatment significantly increased TOC content, MBC content, light fraction organic carbon (LFOC), and potassium (TK) concentration (by 74.93%, 86.24%, 153.73%, and 21.92%, respectively). Most soil enzyme activity and nutrient parameters were significantly correlated with MBC. Thus, straw application improved soil fertility by increasing the concentrations of high labile organic carbon fractions (HWC, MBC, and POXC), stimulating soil enzyme activities, and releasing more soil available nutrients, and BC addition contributed to the accumulation of TOC, MBC, LFOC, and TK.

Understanding of the risk of phosphorus (P) loss to the environment is crucial to monitor soil P and implement policies for P management. We assessed P sorption characteristics and adapted a P saturation index (PSI) for silage corn and blueberry fields in south coastal British Columbia (BC), Canada. We used 284 composite soil samples with contrasting P levels collected from eight silage corn and 23 blueberry fields across south coastal BC. The P sorption maximum (S_max) varied between 982 and 2532 mg P·kg⁻¹ and was influenced by aluminum concentration and organic matter content. The degree of P saturation was related to water-extractable P (Pw) by a quadratic regression with R² = 0.85. A critical Pw = 3.7 mg·kg⁻¹ was established across the two cropping systems. The silage corn fields with pH > 5.5 had critical PSI value of 10.4%, and blueberry fields with pH < 4.7 had critical PSI value of 18.0%. These results showed that the risk of P loss from soil in the silage corn was high, but it was low for blueberry because the critical PSI for silage corn fields was lower than for blueberry fields, and therefore, saturation would be more easily reached, even though more P is applied to blueberry fields. The combination of a critical PSI and Pw as agri-environmental indicators will help farmers and professionals to identify fields with risk of P loss, to implement a nutrient management plan, and to monitor how this risk changes with time.

Repeated applications of liquid dairy manure (LDM) and perennial crops generally favor nitrogen (N) stocks in soils, but in ways that may differ with soil type and other management practices. The objective of this study was to assess the long-term (21 yr) changes in soil N stocks (0–50 cm) of a silty clay soil, in a cool humid climate, in response to mineral fertilization (MIN) or LDM, combined with two tillage practices [chisel plow (CP), or moldboard plow (MP)], and two crop rotations [cereal monoculture (monoculture) or cereal–perennial forage rotation (forage-based rotation)]. The forage-based rotation favoured a greater accumulation of N in the first 20 cm of soil (+50 kg N·ha⁻¹·yr⁻¹) when compared with the monoculture. Tillage practices did not impact N stocks in the whole soil profile, but influenced its vertical distribution, with greater accumulation at the surface with CP, and at depth with MP. Annual input of LDM increased N stocks at the surface (0–20 cm) compared with MIN, especially when combined with the forage-based rotation. After 21 yr, soil N stocks (0–50 cm) with LDM were 32% (+2 t N·ha⁻¹) higher in the forage-based rotation than in the monoculture, suggesting better retention and more efficient use of manure-N with perennial forages than cereals. Comparisons between the N mass balance computed for each cropping system, and the changes in soil N stocks indicated that accumulation of N under the forage-based rotation was largely due to symbiotic fixation by legumes in the forage mixture.

Predicting the soil-available nitrogen (N) to grain corn over a growing season in humid temperate regions is the key for improving fertilizer N recommendations. The objective of this study was to evaluate a suite of soil-N tests to predict soil N availability to grain corn over two growing seasons at 13 individual sites with long-term history of synthetic N fertilization in Ontario, Canada (13 site-years). At each site, fertilizer N was applied at various rates (0–224 kg N·ha⁻¹) to determine the crop response to N fertilizer, relative yield (RY), and the most economic rate of N (MERN). Across the entire dataset, water-extractable mineral N (WEMN) was the only soil test that strongly correlated to both RY (r = 0.74**) and MERN (r = −0.56*) indicating that in grain corn fields with long-term history of N fertilization, mineral forms of N in soil solution can be used for fertilizer N recommendations in southern and eastern Ontario. We also provide evidence that grouping soils based on clay content could further refine fertilizer-N recommendations for grain corn in Ontario. A multi-year validation of the WEMN test with more field sites and development of a fertilizer recommendation table for this soil test are recommended.

A 2 yr field study was conducted on a coarse-textured soil in Manitoba, Canada, to investigate the effects of liquid hog manure (LHM) and chemical fertilizer application on barley (2005) and red spring wheat (2006) yields, crop nutrient uptake, and nitrogen (N) and phosphorus (P) movement to the environment. The treatments were LHM applied at two rates as 22 000 L·ha⁻¹ (2500 gal·ac⁻¹, abbreviated as M2500) and 43 000 L·ha⁻¹ (5000 gal·ac⁻¹, abbreviated as M5000) and two rates of chemical fertilizer to match total N and P in LHM treatments, F2500 and F5000, along with an unamended control. The M5000 and M2500 treatments showed similar grain yield and N and P uptake. However, M5000 and M2500 significantly increased grain yield by 67% and 78%, respectively, compared with the control in 2005. In 2006, wheat grain yields from M2500 and M5000 were 71% and 86% greater than the control. In 2005, leachate NO₃-N concentrations and leaching loads were higher with chemical fertilizers than M2500. In 2005, the apparent recovery of applied N as leachate was 35% and 23% in F5000 and F2500 treatments, whereas it was 6% and 7% of applied N in M5000 and M2500 plots, respectively. However, the application of M5000 resulted in P accumulation near the surface and may increase the potential risk of P loss with runoff. Our results show that applying LHM at moderate rates (M2500) may ensure desirable crop yields comparable to higher rates of nutrient application with minimal potential losses relative to higher rates.

The depth of mixing layer is one of the important parameters which cannot be assigned a constant value affected by many factors in the slope runoff. The objective of this study was to investigate the effect of slope length and underground biomass on slope runoff, solute transport processes, as well as mixing layer depth. In this study, the experimental plots with the four slope lengths (5, 10, 15, and 20 m) and a width of 2 m were built on the slope with the gradient of 20°. In addition, the plots with the millet or wheat planting were built on the slope. The change of runoff and solute transport was analyzed through simulated rainfall experiments and then to estimate mixing layer depth. The results showed that the runoff rate decreased and more runoff seeped into the slope soil with increasing slope length. Increasing underground biomass also promoted greater rainfall infiltration into the soil. The increase in slope length increased the concentration of solute in runoff, but more underground biomass reduced the nutrients transported with runoff. The effective mixing depth increased with an increase in slope length, but effective mixing depth decreased with increased underground biomass. The modified expression of the equivalent mixing model under different slope lengths and underground biomass could accurately describe the solute transfer process in runoff when compared with complete mixing model and incomplete mixing model based on exponential functions. This research provided a reference for improving the application of mixing layer models in the slope management.

Soil water percolation is an important process required to meet plant water needs, determine soil water storage, and affect soil water quality in riparian buffer strips. However, the effects of plant roots on soil percolation in riparian buffer strips are not totally understood, and contradictory results have been carried out on the effects of the root system on soil percolation rates. This study aimed to investigate soil percolation in natural grasslands and evaluate the relationships between root morphological characteristics and percolation rates. Path analysis was used to provide information on the relative contribution of root characteristics on soil percolation rates. Three mixed grasslands (Imperata cylindrica + Phragmites australis, I. cylindrica + Cynodon dactylon, and I. cylindrica + Juncellus serotinus) were selected in the Yellow River wetland natural reserves of Zhengzhou. Soil percolation rates (initial, average, and steady infiltration rates) were measured by using double-ring methods, and plant root morphological characteristics were analyzed. Soil percolation rates and plant root characteristic parameters of I. cylindrica + P. australis and I. cylindrica + C. dactylon were higher than those of I. cylindrica + J. serotinus. Initial percolation rate of I. cylindrica + P. australis and I. cylindrica + C. dactylon at 0–10 cm depth was 58.06% and 95.55% higher than that of I. cylindrica + J. serotinus, respectively. Percolation rates had a significant positive correlation with root characteristic parameters, and the main factor controlling soil percolation rates was root volume density (RVD). Mixed natural grasslands with more RVD improved soil infiltration and percolation rates.

Continuous or discontinued manure applications to agricultural soils may impact soil organic carbon (SOC) and water balances because of manure carbon inputs and the potential for manure-induced soil hydrophobicity (SH) and soil water repellency (SWR). A laboratory study was conducted using a long-term (44 yr) field experiment on a clay loam soil to determine the effect of application rate of feedlot manure under dryland (0, 30, 60, and 120 Mg·ha⁻¹ wet weight) and irrigation (0, 60, 120, and 180 Mg·ha⁻¹) on SOC, SH, and SWR. In addition, we compared the effect of 44 yr of continuous annual manure applications (C44) to legacy treatments which had discontinued applications for 14 (D14) or 30 yr (D30). Laboratory measurements were conducted on air-dried and sieved (<2 mm) soil to determine SOC, SH using Fourier transform infrared spectroscopy, and SWR using the repellency index (RI) method. Mean RI values for all treatments ranged from 2.20 to 13.0, indicating subcritical (RI > 1.95) SWR. Manure application rate had a significant (P ≤ 0.05) and positive effect on SOC and SH, and both followed an exponential model. In contrast, RI had a negative response to the application rate under dryland and had no response under irrigation. Overall, positive responses of SOC and SH to application rate supported our hypothesis, but it was not supported for RI. The hypothesis of greater SOC, SH, and RI for continuous versus discontinued treatments was also supported for SOC and SH but not for RI.

Appropriate application of corn straw residues increase soil organic carbon (SOC) sequestration. However, sequestration and stabilization of added carbon (C) during corn straw transformation are not fully understood. Here, we present changes in soil humus C and humic acid (HA) molecular structure during corn straw decomposition in an incubation experiment carried out for 270 d at 25 °C. Corn straw was applied at the amount of 74.76 g per 18 kg soil (i.e., 1.57 g C·kg⁻¹), in the soil surface (CS1), incorporated within 0–10 cm (CS2), applied below 10 cm soil depth (CS3), and no corn straw applied. The results showed that after corn straw application (CS1, CS2, and CS3), the accumulation of SOC content was rapid in the first 90 d. The HA spectral results of straw-amended soils showed a slight increase in aliphatic C compounds and amino acids on day 90. On day 180, the degree of condensation was less, and aliphatic C compounds were present in large quantities in soil HA. As decomposition advanced to day 270, the aliphatic character of HA appeared to slightly weaken, and soil HA was enriched with aromatic structures. These results suggest that corn straw application enriches soil HA with more aliphatic C compounds in the early stages of decomposition, and aromatic C structures are formed in the later stage of decomposition. Incorporation of corn straw into the soil (CS2 treatment) is more conducive in increasing SOC and aliphaticity in HA during corn straw decomposition, which can potentially increase C sequestration.

Crops in the northwest arid region of China frequently suffer from low emergence and poor yield due to high water deficit. Mulching is an important approach to reduce irrigation amount while increasing productivity but faces the challenge of ecological adaptability in this region. A field experiment was carried out in the three growing seasons from 2011 to 2013 to study the effects of mulching with crushed wheat straw padding and plastic film on sunflower seed emergence and yield under different irrigation intensities. A two-factor (mulching and irrigation intensity) completely randomized block design was applied, resulting in a total of 12 treatments repeated three times. Mulching treatments include zero mulch (N), straw mulching at the beginning of the experiment (S), plastic film mulching when sowing (F; a commonly used mulching by local farmers), and double mulching with plastic film on the crushed wheat straw layer (SF). Irrigation intensity includes high (H = 900 m³·ha⁻¹), medium (M = 750 m³·ha⁻¹), and low (L = 600 m³·ha⁻¹). Results showed that all mulching treatments promoted the early emergence of seedlings compared with N, with SF and F performing better than the rest. SF was the best-performing mulching approach in this study, and it had significantly improved sunflower yield and yield components compared with other treatments. In SF, medium irrigation level had significantly increased sunflower 100-seed weight. Therefore, SF with M irrigation level showed the most positive effect on sunflower production, and it is now the recommended agronomic solution for sunflower production in the northwest arid regions and, potentially, other irrigated areas with similar ecological conditions.

A plough pan with reduced permeability accumulates infiltrated water along slopes then saturates the cultivated layer under continuous rain. Topsoil saturation is a frequent phenomenon and an important process of the special soil slopes. A methodology and device system was used in this study to keep cultivated purple soil saturated. Strands of scouring tests were developed to quantify the rill erosion and sediment transport processes along a saturated purple soil slope at four experiment slopes (5°, 10°, 15°, and 20°) and three flow discharges (2, 4, and 8 L·min⁻¹). The experimental results indicated that the sediment transport capacity on a saturated purple soil slope ranged from 0.03 to 1.56 kg·s⁻¹·m⁻¹ with the increasing trend along the slope gradient and flow discharge, and the increasing trend could be well matched by a nonlinear multivariable equation. The sediment concentration of the saturated purple soil slope exponentially increased with rill length and decreased with the increment rate, and the maximum sediment concentrations observed in this study in different hydraulic events ranged from 108.13 to 1174.20 kg·m⁻³. Saturated and non-saturated purple soil slopes erode differently with the maximum sediment concentration of saturated purple soil slope recorded at approximately 1.42–2.10 times the values for non-saturated purple soil slope. The findings of this research help illustrate the sediment transportation and erosion behaviors of a saturated purple soil slope and serve as the basis for determining the parameters in the erosion models of the purple soil slope.

Farm soil tests are common decision support tools employed by regulatory agencies and farmers to manage nutrients in an economical and environmentally sustainable way. The complex interplay between the local environment and locally relevant crops makes soil testing, and critically soil-test-based recommendations, site-specific. Newfoundland and Labrador has a relatively small but rapidly growing commercial agriculture industry, mainly on lands converted from the boreal forest over the last 80 yr. A first step towards developing locally calibrated fertilizer recommendations is understanding current practices. For this, we examined regular farm soil test reports and associated recommendations for Newfoundland (Nfld). Following a request distributed to 167 farmers, 1503 soil tests were obtained from 32 farms. Although tests exemplify the gamut of crops in Nfld, more than half were from forage and mixed forage fields in western Nfld, representing dairy farms. Results show that even in the absence of more comprehensive site analyses, an investigative survey of farm tests may be employed to recognize possible environmental and economic inefficiencies of local cropping systems, including regional and crop type-driven differences for both nitrogen (N) and phosphorus (P) fertilizations. Soil-test-based identification of possible N and (or) P inefficiencies and associated crop and regional particularities, including excess fertilization, can be employed to devise targeted research for improved, preventative decision tools to increase the sustainability of Nfld agricultural systems.

In general, anthrosols refer to anthropic soils of high fertility, but the concentration of these nutrients may vary according to the occupation of indigenous people in the past or due to current soil use. This study aimed to evaluate the spatial variability of the chemical attributes of the soil in areas of guandu bean production and pasture and to compare with natural forest systems on anthropogenic dark earth (ADE). For this assessment, 88 sampling points were selected in the area with natural forest vegetation and pasture and 90 sampling points in an area of guandu bean production. Soil samples were collected from layers 0.00–0.05, 0.05–0.10, and 0.10–0.20 m. Chemical analyses of the soil were conducted to determine organic matter, pH, aluminium, soil acidity, phosphorus, potassium, calcium, magnesium, cation-exchange capacity, sum of bases, and base saturation (V%). Data were analyzed using descriptive statistics and geostatistics to sample range, and sample density was estimated for each attribute. Guandu bean showed high content of soil organic matter in relation to pasture in the superficial layer (0.00–0.05 m). Based on sample density, lower variability and higher spatial continuity were observed for guandu bean in relation to pasture and natural forest in the layers of 0.00–0.05 and 0.05–0.10 m. It was found that the use and continuous management of ADE areas alter the content and distribution of soil fertility and, in some cases, may even improve chemical attributes when compared with areas not used with agricultural crops.

Nanoparticles with high reactivity can be applied as amendments to remediate soil metal contaminations by immobilizing toxic elements. Nano-oxides of Fe have been studied but Al and Ti nano-oxides have not been tested for their remediation capacity of toxic metals. The potential of synthesized iron (Fe-O), aluminum (Al-O), and titanium (Ti-O) nano-oxides for stabilizing Cd, Pb, and Zn in mine spoil (Chat) and contaminated soil was compared using adsorption studies and a greenhouse experiment. Chat and soil were amended with nano-oxides at two rates (25 and 50 g·kg⁻¹) and a pot experiment was conducted with sorghum (Sorghum bicolor L. Moench). Leachates were collected twice per week from plant emergence to harvest at maturity and metals were compared against an unamended control. Chat was contaminated with Cd, Pb, and Zn at 84, 1583, and 6154 mg·kg⁻¹, and soil at 15, 1260, and 3082 mg·kg⁻¹, respectively. Adsorption conformed to the Langmuir linear isotherm and adsorption maxima of metals were in the order of Al-O > Ti-O ≥ Fe-O. Nano-oxides reduced Cd concentration by 28% (Fe-O) to 87% (Ti-O) and Zn concentration by 14% (Fe-O) to 85% (Al-O) in plant tissues compared with unamended Chat. Nano-oxides significantly reduced Cd, Pb, and Zn in leachates and available Cd and Zn in Chat/soil relative to the respective unamended controls. Nano-oxides can be used to remediate heavy metal contaminated Chat and soil and facilitate plant growth under proper nutrient supplements. Nano-oxides of Al-O and Ti-O remediated metals more effectively than Fe-O.

Nitrous oxide (N₂O) emissions from soils have been widely studied in the literature — mostly with the chamber method — due to the importance of this gas to climate change. Emissions of N₂O derive from biological reactions and are controlled by soil parameters, which are by nature heterogeneous (i.e., “hot spots” for N₂O emissions) — a source of uncertainty in chamber-based studies. Spatial variation in N₂O fluxes has been assessed in the literature, but the information is still needed for contrasting soil management practices (e.g., tillage) and for specific bioclimatic situations [e.g., non-growing seasons (NGS) under cold weather]. Here, we subsampled daily N₂O data to assess within-plot and between-block spatial variation from an agronomic experiment under conventional tillage (CT) and no-tillage (NT), identifying if patterns differ between growing seasons (GS) and NGS datasets. Within-plot spatial variation in N₂O fluxes was a small source of uncertainties, but half of the comparisons in GS datasets presented a slope different from 1 for the regression of N₂O averages from two vs. one chamber per plot — a source of uncertainty mitigated when within-plot duplication occurred during N₂O “hot moments”. Between-block spatial variation in N₂O emissions was much larger than within-plot errors — an effect more accentuated for NGS and CT than GS and NT datasets. Decreasing the number of sampled blocks resulted in averages that did not represent the N₂O daily average of the whole field, but exceptions occurred. The methodology proposed here may be used in other locations, after appropriate verification, for improved planning and maximization of the resources associated with N₂O measurements.

Recycling phosphorus (P) within the food system is fundamental to long-term sustainability. This greenhouse study compared three sources of recycled P — struvite precipitated from municipal wastewater, black soldier fly frass from food waste, and anaerobic digestate of food waste — to mono-ammonium phosphate (MAP), compost, and a control. Italian ryegrass (Lolium multiflorum) was harvested four times during a 123 d trial from P-depleted soil. In nitrogen (N) sufficient conditions, all amendments significantly increased cumulative ryegrass yields compared with the control and were not significantly different from MAP. Relative P supply was frass = MAP > struvite ≥compost ≥ digestate >> control. The recycled nutrient sources tested show promise as sustainable P sources.