Wet Aggregate Stability Research Articles

Multiple soil health indicators are responsive to summer cover crops on an irrigated organic farm

While cover crops (CC) are known to enhance soil health, outcomes are often subtle and confined to a shallow surface soil layer. We assessed 15 soil health indicators over three CC trials with a 15-species Blend polyculture, a Mustard biculture (white ( Sinapsis alba L.) and brown ( Brassica juncea (L.) Czern.) mustards), Buckwheat ( Fagopyrum esculentum Moench), and Faba bean ( Vicia faba L.) monocultures, and a Weedy fallow (no CC, weeds allowed to grow) on an organic farm in southern Alberta. Soil sampling times included (i) summer pretermination; (ii) fall post-termination; and (iii) spring post-termination of CC. Twelve of 15 soil health indicators showed significant effects of CC treatment for at least one sampling time. Soil organic C (SOC) ranked highest with 80% of sampling times showing significant CC effects. N-related indicators (total N (TN), nitrate-N)) were also quite sensitive, being significantly affected by CC treatment at 60% of sampling times. Three soil health indicators (acid phosphomonoesterase (AcP), wet aggregate stability, and free-living nematodes (FLN)) were consistent in their nonresponses to CC treatment at all sampling times. Comparing CC treatments with a Weedy fallow, showed that not all enhancements of soil health were explained by inclusion of a CC, with Weedy fallow as effective for some indicators. A polyculture Blend significantly enhanced soil health over a monoculture CC or Weedy fallow in 46% of instances of soil health indicator improvement. While CC led to enhancement of soil health, results were not always consistent, being contingent on specific indicators.

Nature versus nurture: Quantifying the effects of management, region, and hillslope position on soil health indicators in an on‐farm survey in Minnesota

AbstractA major challenge to implementing effective soil health assessments is how to distinguish the effects of management from underlying soil variability driven by inherent soil properties. This challenge has important consequences for the use of soil health indicators as tools for monitoring and assessment because soil‐forming factors constrain the range of indicator values and the magnitude of management‐induced changes. Here, we present results from a statewide survey of 15 soil health indicators measured on 30 fields on commercial farms across four major land resource areas in Minnesota. Fields included in the study differed in tillage, cover crop implementation, and crop rotation. Within each field, we collected samples from upper and lower hillslope positions to quantify the effect of topography. We consistently detected differences in soil health indicators between regions (13/15 indicators) and hillslope positions (8/15 indicators). However, only wet aggregate stability was sensitive to management across regions and years, highlighting the importance of physical indicators of soil health. This result was surprising in light of existing literature supporting the sensitivity of many soil health indicators to management, but it is consistent with other studies conducted in high organic matter soils in the Upper US Midwest. Our results highlight the need for regionally representative datasets to guide the development of interpretations and benchmarks for soil health indicators. This is particularly important when soil health indicators are applied outside traditional research contexts (such as in commercial soil health testing), where interpretation must take place without the benefit of historical baseline data.

Soil, forage, and weed attributes following tillage in grazed no‐tillage triticale pasture

AbstractGrazing annual forages in dryland cropping systems has been used to integrate crop and livestock systems, rejuvenate soils, enhance in‐field nutrient cycling and soil organic carbon (SOC), and increase net returns by eliminating harvest expenses and feed delivery. However, cattle (Bos taurus) could potentially degrade soil physical properties by increasing compaction and reducing water infiltration in no‐tillage (NT) systems. Minimum tillage (MT) may help correct some of these potential soil quality concerns. The objective of this study was to quantify MT effects on soil properties, forage mass, and weeds compared to NT in a grazed winter triticale [×Triticosecale Wittm. ex A. Camus (Secale × Triticum)] annual forage system from 2020 to 2022 near Jetmore, KS. The experiment had two tillage treatments, NT and MT (sweep plow to a depth of 5–13 cm twice during summer fallow), in a grazed continuous winter triticale cropping system. Bulk density was greater in June, pre‐till (1.31 g cm−3), compared to August, post‐till (1.23 g cm−3), across tillage treatments. The mean weight diameter of dry aggregates decreased, and wind‐erodible fraction increased with MT. Across years, the mean weight diameter of water‐stable aggregates was greater with NT compared to MT. The SOC stocks did not differ between tillage practices near the soil surface, but MT increased SOC at the 5‐ to 15‐cm depth. Nitrate (NO3‐N) concentration was 28% higher with MT compared to NT across depths at the August sampling time. Soil pH was slightly lower in NT (5.81) compared to MT (5.94). Penetration resistance was high due to frequently dry soil conditions, but there were no differences between tillage systems. Early‐season forage biomass was greater in MT compared to NT in one out of two seasons. Our findings suggest that MT could be used to mitigate adverse effects of grazing on soil bulk density in NT systems but could cause short‐term decreases in dry and wet aggregate stability and increased wind‐erodible fraction.

Phacelia and Buckwheat Cover Crops’ Effects on Soil Quality in Organic Vegetable Production in a High Tunnel System

Cover crops (CCs) are regarded as beneficial to agricultural practice as an option for soil quality improvement in field production systems. The main goal of this study was to assess the impact of spring phacelia (Phacelia tanacetifolia Benth.) and buckwheat (Fagopyrum Mill.) in a crop rotation (CC–leek–parsley, 2020–2021) on the physicochemical and biological properties of the soil in an organic high tunnel system. Soil analyses involved measurements of bulk density, water capacity, soil aggregation, soil organic carbon (SOC), available soil nutrients, as well as microbial abundance and diversity. Phacelia generated more aboveground biomass (58.2 t fresh matter ha−1) than buckwheat (33.0 t ha−1), and their biomass contained 161 kg N ha−1 and 67 kg N ha−1, respectively. A large quantity of elements, such as N, Ca, P, S, B, and Cu, were found in phacelia biomass. More Mg and Na were found in buckwheat plants. The results showed that CC biomass significantly improved some of the soil physical and chemical properties, such as soil organic carbon stock and wet aggregate stability, and decreased soil bulk density. Cover crop treatments changed the dynamics of soil bacterial and fungus populations in a high tunnel system. Phacelia increased the quantity of ammonifiers and nitrifiers in the soil substantially. Further research with a long-term focus is needed to assess the impact of cover crops on soil properties, soil quality, and subsequent crop yields in high tunnel crop rotation and management systems.

Temporal changes in soil physical properties following reclamation of underground natural gas pipeline rights-of-way on cropland

Underground oil and natural gas pipeline rights-of-way (ROWs) sometimes traverse croplands, leaving behind tracts of disturbed land characterized by poor productivity even after reclamation. This study investigated temporal post-reclamation changes in soil penetration resistance (PR), field saturated hydraulic conductivity (Kfs), near-saturated hydraulic conductivity (KΨ), soil pore indices, and wet aggregate stability (WAS) on natural gas pipeline ROWs on cropland. These attributes were measured in two fields in late summer of 2021 and 2022. Across the two fields, three ROWs that had been reclaimed four to thirteen years prior (i.e., time since reclamation (TSR) of 4 to 13 yr) were assessed along with adjacent undisturbed (off-ROW) transects located 50 m from the ROWs. Measurement locations on each ROW and on off-ROW were 25 m apart. Samples for WAS were collected from the 0–15 cm layer. The results showed a significant (p < 0.05) TSR by soil depth interaction for PR. Treatments were not significantly different in the 0- to 20-cm and 40- to 60-cm layers, but in the 20- to 40-cm depth interval, PR was 57.7–64.2 % greater on the 4.5-yr ROW than on off-ROW. Saturated hydraulic conductivity was three to four times lower on the 4.5- and 6.5-yr ROWs than on the off-ROW. Near-saturated hydraulic conductivity on the 4.5-yr ROW was 61.6 % lower than that on the off-ROW, while no significant differences were detected between the 6.5-yr and 12.5-yr ROWs and the off-ROW. Effective water conductive macroporosity was 72.5 % lower on the 4.5-yr ROW than on the off-ROW. All measured physical properties improved with increasing TSR. These results indicate a significant but slow recovery in soil physical attributes with increasing TSR of ROWs on cropland. This has implications on the productivity of these ROWs as crop yields, which depend on these soil physical properties, are also expected to recover slowly.

Soil health as a proxy for long-term reclamation success of metal-contaminated mine tailings using lime and biosolids

Mine lands contaminted with heavy metals pose environmental risks, and thus reclamation is paramount for improving soil, plant, animal, and ecosystem health. A metal-contaminated alluvial mine tailing, devoid of vegetation, received 224 ​Mg ​ha−1 of both lime and biosolids in 1998, and long-term reclamation success was quantified in 2019 with respect to soils, plants, and linkages to animals. Reclamation success was quantified using the Soil Management Assessment Framework (SMAF), in conjunction with bioavailable (0.01 ​M CaCl2 extractable) and plant-available (Mehlich-3 extractable) soil metal concentrations, X-ray absorption spectroscopy, plant metal concentrations, and plant quality characteristics. Results showed that all soil indicators were improved in successfully-reclaimed areas as compared to on-site degraded areas, including increases in soil aggregate stability, pH, plant-available P and K, soil organic C, potentially-mineralizable N, microbial biomass C and β-glucosidase activity and decreases in soil bulk density and electrical conductivity. Of indicators, unitless soil health scores were assigned based on the SMAF, with data suggesting that bulk density, wet aggregate stability, potentially- mineralizable N, microbial biomass C, pH, and electrical conductivity should be monitored in the future. The long-term effects of lime and biosolids application have improved soil physical, biological, and overall soil health. Plant metal concentrations have decreased by an order of magnitude since early reclamation, with most plant metal concentrations being tolerable for domestic livestock consumption. From an animal health perspective, feeding grasses from this site during latter parts of a growing season may need supplemental feed to provide greater protein and energy content, and to reduce potentially-harmful Cd concentrations from food chain bioaccumulation. However, a health concern exists based on soil bioavailable Cd and Zn concentrations that exceed ecological soil screening levels. Still, plants have stabilized the soil and acidity remains neutralized, leading to long-term improvements in soil health, with overall improved ecosystem health.

A high throughput approach for measuring soil slaking index

AbstractSoil wet aggregate stability is widely measured for soil health ratings, and two mobile applications have been recently developed that provide simple and fast measurements of wet aggregate stability on three pea‐sized soil aggregates. However, techniques are needed to scale the test to make it practical for studies with large sample numbers. Here, we describe an approach to measure 10‐min slaking index on 20–36 aggregates simultaneously using a multi‐well plate and automated image analysis. We used this approach to measure 160 soil samples (2120 aggregates) from a long‐term tillage and cover crop trial in a corn (Zea mays L.)‐based agroecosystem in central Iowa. We evaluated the statistical power of slaking index, needed replication, sensitivity to cultural practices, and sensitivity to sample collection date to inform future sampling efforts. We found that small numbers of highly unstable aggregates lead to skewed distributions for slaking index. We concluded that at least 20 aggregates per sample were useful to provide confidence in measurement precision, although the experiment had high statistical power with only 10–12 replicates per sample. Slaking index was not sensitive to the initial size of dry aggregates (3‐ to 10‐mm diameter); therefore, pre‐sieving soils was not necessary. Consistent with prior studies, the field trial showed greater aggregate stability under no‐till than chisel plow practice and changing stability over a growing season. This multi‐well method will help researchers measure a useful soil health indicator with greater precision, and more efficiently sample spatial and temporal variation.

SHAPEv1.0 Scoring curves and peer group benchmarks for dynamic soil health indicators

AbstractThe soil health concept has evolved over the past several decades, recognizing that the response of dynamic soil properties to management is dependent on site‐specific factors. The Soil Health Assessment Protocol and Evaluation (SHAPE) tool provides scores and benchmark values by forming soil peer groups based on site‐specific, climate‐edaphic characteristics. Data for model development were compiled from the Cornell Soil Health Laboratory and the Kellogg Soil Survey Laboratory databases. The SHAPEv1.0 interpretation curves produce scores between 0% and 100% for measured laboratory values that reflect the quantile within a population conditional cumulative distribution function along with measures of uncertainty. The original SHAPE tool was developed for soil organic carbon and has been expanded to include two wet aggregate stability methods, permanganate oxidizable organic carbon, autoclaved citrate extractable protein, and 4‐day microbial respiration. In addition, SHAPE provides site‐specific benchmark values at user‐defined percentiles within a given soil peer group. The difference between the actual measured value and the selected benchmark value represents the soil health opportunity gap. Case studies in Missouri and Texas show that the SHAPE scoring curves are sensitive to land‐use and management practices across multiple soil types and provide a regionally relevant interpretation of key soil health indicators.

Pedotransfer Functions for Field Capacity, Permanent Wilting Point, and Available Water Capacity Based on Random Forest Models for Routine Soil Health Analysis

ABSTRACT Available water capacity (AWC), field capacity (θFC), and permanent wilting point (θPWP) are regarded as key physical soil health indicators that directly capture the soil’s capacity to store plant available water but are expensive components of a comprehensive soil health analysis. To reduce costs, pedotransfer functions for θFC, θPWP, and AWC were developed from a dataset of 7,232 soil samples with texture, soil organic matter (SOM), permanganate-oxidizable carbon, soil respiration, AWC, θFC, θPWP, wet aggregate stability, and extractable potassium, magnesium, iron, and manganese. Three functions were developed for each property: a full random forest (RF) model containing all variables, a reduced RF model and a multiple linear regression model containing texture and SOM. Pedotransfer functions were validated with an independent dataset that contained 1,406 samples. The full RF models for θFC, θPWP, and AWC reduced the root mean square error (RMSE) by 16.3, 13.3, and 12.8%, compared to multiple linear regression models, respectively. Furthermore, the full RF models for θFC, θPWP, and AWC reduced RMSE by 11.6, 6.7, and 12.8%, compared to the reduced RF model, respectively. Permanganate-oxidizable carbon, wet aggregate stability, and extractable magnesium, potassium, and iron were useful novel predictor variables for improving prediction of θFC and AWC. AWC was sensitive in 20/57 long-term experiments, and full RF models were able to replicate 5/20 of those significant results. New RF pedotransfer functions for θFC, θPWP, and AWC can enhance prediction compared to traditional modeling techniques, fits into existing interpretative frameworks, and improves cost-effectiveness of comprehensive assessments of soil health.

Soil carbon and aggregate stability are positively related and increased under combined soil amendment, tillage, and cover cropping practices

AbstractAgricultural practices alter the organic carbon dynamics in soil. An experiment was conducted to study the effect of carbon amendments, tillage, and cover cropping on permanganate oxidizable carbon (POXC), total organic carbon (TOC), and wet aggregate stability (WAS) in a 2‐year crop sequence (corn–cover crop–cotton–cover crop) at the Texas A&amp;M Research Farm. Two carbon amendments (biochar and composted biosolid) were applied at the rate of 500 kg C ha−1, along with a control. Two tillage practices were evaluated: conventional tillage (CT) and no‐tillage (No‐Till). A cover crop (CC) mixture of oat, mustard, and pea and no cover crop (No‐CC) were also evaluated. Treatments were arranged in a split‐split plot design with four replications. Amending the soil with carbon as composted biosolid or biochar affected POXC at both the 0‐ to 5‐ and 5‐ to 15‐cm depths. The POXC was significantly higher for the biochar treated plots for corn and CC after corn but significantly lower POXC was observed after cotton with biochar‐treated plots. The POXC increased under No‐Till compared with CT and CC plots relative to No‐CC plots. The TOC was not sensitive to soil management practices. The POXC and TOC both decreased with depth. The WAS greater under No‐Till and CC plots. The POXC and WAS were influenced by soil management practices and can be useful indicators to assess short‐term soil health improvements. The POXC and WAS were positively related, suggesting that one may be used to predict the other.

Identifying the best tillage system to maintain soil properties and crop yields after Conservation Reserve Program grassland conversion

The Conservation Reserve Program (CRP) is a United.States of Americae government program that provides financial incentives to transition marginal croplands to permanent grass cover to conserve soil and water. Few studies have evaluated the best tillage system that maintains soil properties when converting CRP back to cropland. Our objective was to determine how converting CRP to cropland under different tillage practices after three years affects soil C (carbon) stocks, physical and chemical properties, and winter wheat (Triticum aestivium L.) and corn (Zea mays L.) grain yields after 4 yr. We also reviewed literature on the topic to compare previous results against our findings. This experiment was conducted in Sidney, NE, USA on CRP that was converted to production farmland through four tillage practices no-till (NT), disk-sweep (DS), plow-sweep (PS) and deep plow-sweep (DPS) in 2017 and planted to a wheat-corn-fallow rotation. Organic C stock was reduced by 6% in PS and 15% in DPS compared to CRP in the 0–10 cm depth but not in the 0–60 cm. Tillage practice did not affect grain yields in our study but had inconsistent effects according to previous literature. In the upper 10 cm, wet aggregate stability was reduced by 41% in DS, 51% in PS, and 58% in DPS, dry aggregate stability was reduced by 66% in NT, 71% in DS, 74% in PS and 77% in DPS, and plant available water was reduced by 45% in NT, 50% in DS, 39% in PS and 43% in DPS treatment relative to CRP. However, treatments had no effect on cumulative infiltration rate and bulk density. The use of DS or NT when converting CRP to cropland caused the least negative impacts on soil properties when CRP was converted to cropland in our study and in previous studies reported in the literature. Minimizing soil disturbance by reduced or no tillage maintained relevant soil properties 3 yr after CRP conversion to cropland.

Comparing impacts of corn residue removal and amelioration practices on soil properties after 3, 6, and 10 years

AbstractInformation on corn (Zea mays L.) residue removal and organic amendment additions to ameliorate removal effects on soil properties is limited. Thus, we compared impacts of corn residue removal at 59% and organic amendments (winter rye [Secale cereale L.]) cover crop and manure every other year at 24 Mg ha−1 on soil organic carbon (SOC) and physical properties after 10 years under irrigated no‐till continuous corn on a silt loam in the western US Corn Belt. We collected soil property data after 10 years and then compared it with earlier results from this experiment (3 and 6 years). Cover crop and manure amendments maintained SOC concentration, but no amelioration practice reduced SOC concentration (−15%) from 3 to 10 years when residues were annually removed in 0‐ to 5‐cm depth. Under residue retention, SOC concentration increased with time with largest increase (+41%) occurring under manure amelioration practice in the 0‐ to 5‐cm depth. Residue removal reduced soil wet aggregate stability by 34%, soil dry aggregate stability by 73%, bulk density by 6%, water content at −33 kPa matric potential by 14%, and plant available water by 17% after 10 years in the 0‐ to 5‐cm soil depth but did not affect infiltration rate. Cover crops increased wet aggregate stability (32%), but manure and cover crops had limited effects on other soil properties. Residue removal increased the susceptibility of the soil to erosion and reduced water retention and SOC after 3 years, but such effects were not fully offset by amendments.

Impact of no‐till, crop rotation, cover crop, and drainage on soil physical and hydraulic properties

AbstractConservation agriculture and associated soil health practices potentially enhance soil resilience by improving the soil's physical, chemical, and biological properties and processes. This study assessed the impact of tillage (conventional tillage [CT] and no‐till [NT]); crop rotation: 2‐year corn (Zea mays L.)–soybean (Glycine max L.), 3‐year corn–soybean–oat (Avena sativa L.), and 4‐year corn–soybean–oat–wheat (Triticum aestivum L.)]; cover crops (cover crop [CC] and no cover crop [NC]); and drainage (tile drainage [TD] and without drainage [ND]) on soil organic matter (SOM), bulk density, wet aggregate stability (WAS), and field‐saturated hydraulic conductivity (Kfs). Soil samples were collected over 2 years apart from five depths (0–10, 10–20, 20–30, 30–60, and 60–90 cm) and analyzed for SOM, bulk density, and WAS. In‐situ infiltration tests were conducted in each plot to determine field‐saturated hydraulic conductivity. This study showed that NT practice significantly increased SOM by 5.4%, WAS by 7.7%, and bulk density by 6.7% within 0–10 cm soil profile but decreased Kfs by 47.6% compared to CT through increased bulk density in the topsoil. NT increased SOM for every soil depth and, similarly, increased WAS for every depth but only statistically significant increases occurred at 0–10 cm and 60–90 cm. Further, higher crop diversity decreased bulk density and increased WAS. Nine years of CC and six years of tile drainage practices had no significant effect on SOM, bulk density, WAS, and Kfs.

Assessment of Catchment Hydrology and Soil Fertility Under Different Land Use Systems in Fagita Lekuma District, Ethiopia

Acacia decurrens plantations in the Timble-Faguita-Lekma watershed are being actively expanded to accommodate various land uses, mainly to produce charcoal and construction. This study aimed to investigate the effects of various land-use types on the hydrology of a watershed and the physicochemical characteristics of soils. Experiments comprised soil depth (0-15 cm and 15-30 cm) and land cover type (arable land, pasture, 0, 2, and 4-year stand). A 5*2 factorial array of randomized complete block designs (RCBD) with 4 replicates made up the design. The physicochemical parameters of the selected soils were investigated using 40 (5*2*4) composite soil samples. A semi-structured questionnaire and a two-way analysis of variance (ANOVA) were used to investigate selected farmers' perceptions of watershed hydrology. The results revealed that soil particle size (sand, silt, clay) and SOC concentration differed significantly across all land-use types and soil depths studied. Soil pH did not alter with depth (p&lt;0.5605). At 4 years of age, wet aggregate stability (WAS), weight mean diameter (MWD), and geometric mean diameter (GMD) values were significantly different and greater. Two zero-year-old lines from an acacia decurrens plantation (p=0.0264, p&lt;0.0001, and p&lt;0.0161, respectively). Furthermore, WAS, MWD, and GMD scores are highly positively connected with grade (Tone p&lt;0.0096, r=0.83 and SOC p&lt;0.0001, r=0.85). Most households believe that recent land-use adjustments in their acacia decurrens plantations have reduced the severity of soil erosion.

Short-term effects of brassica cover crops on soil quality indicators in organic production in high tunnels

The use of cover crops is aimed at sustaining soil health and productivity in the context of agricultural intensification and accompanying soil degradation. While cover crops have been extensively studied in field production systems, limited research has been conducted concerning their application in high-tunnel vegetable production. This study aimed to assess the effects of turnip (Brassica napus subsp. napobrassica (L.) Jafri) and swede Brassica rapa subsp. Rapifera Metzg) cover crops (CCs) on soil physicochemical and biological properties in an organic high tunnel system in southern Poland in 2017–2019. The planting sequence was as follows: winter cover crops/pumpkin/romaine lettuce/broad bean/chilli pepper. Soil analyses included measurements of bulk density, water capacity, soil aggregation, soil organic carbon (SOC), available soil nutrients, as well as microbial abundance and diversity. Rape crops produced a higher aboveground dry biomass (4.11 t ha−1) than swede (2.85 t ha−1), and the N content in their biomass was 101 kg N ha−1 and 75 kg N ha−1, respectively. The results presented that CC residue significantly contributed to soil organic carbon stock, retention of plant-available nitrogen, and improvement of soil physical properties, especially wet aggregate stability. Soils with the highest SOC concentrations were associated with the highest bacterial and fungal abundance. The most significant number of mesophilic bacteria was detected in the soil where turnip was grown as a cover crop (7.6 × 107 cfu g−1 DM soil). Moreover, a higher abundance of the tested nitrogen cycle bacteria was found in the soils after CC cultivation compared to the control soils, particularly bacteria reducing NH4 +-N and NO₃⁻-N. These findings highlight the importance of cover crop management practices in high tunnels, as they influence the composition of the total bacterial community and the abundance of N-cycling microbial guilds.

Do organic farming practices improve soil physical properties?

AbstractOrganic farming (OF) is a reemerging system that could address food security and adverse environmental footprints of conventional farming (CF). However, how OF affects the soil physical environment, an essential pillar for soil ecosystem service delivery, is not well understood. This paper (1) reviews published global literature up to 13 July 2023 regarding the impacts of OF on soil physical properties compared with CF and (2) underlines research needs. Literature indicates OF improves some soil physical properties relative to CF although studies on some properties were few. Specifically, OF increased wet aggregate stability, saturated hydraulic conductivity, and plant available water in 55% of studies. OF also increased mesoporosity (5–500 μm) and cumulative water infiltration. However, OF had mixed or no effects on soil compaction indicators (i.e. bulk density, penetration resistance). Not all studies reported both soil physical properties and soil organic C to assess how amendment‐induced increase in soil organic C affected physical properties. Based on studies reporting both properties, physical properties such as wet aggregate stability were not significantly correlated (r = 0.12; p &gt; .10) with soil organic C. Variability in data and frequent tillage under OF likely obscured this relationship. Factors tended to affect OF impacts on physical properties in this order: amendment type &gt; duration &gt; others. Most OF studies (1) used animal manure amendments, (2) were long‐term (&gt;10 years), and (3) were conducted in medium textured soils, highlighting the need for more comprehensive assessments of OF and soil physical properties under different management conditions. In general, OF improves some soil physical properties, which can contribute to OF sustainability.

Temporal variability of saturated hydraulic conductivity on a typical black soil slope of northeast China

Saturated hydraulic conductivity (Ks) is highly variable in both space and time. Compared to its spatial variability, however, the temporal Ks variability has rarely been studied or taken into account in the hydrological modelling. The objectives were to characterize the slope-scale temporal variability of Ks and to diagnose the primary factors regulating Ks variation during the growing season. In the black soil region of northeast China, a typical slope farmland dominated by silt loam was selected and divided into five sections with respect to soil erosion. Soil samples were collected in each section at approximately every 3 weeks during the maize growing season, and Ks, bulk density (BD), land surface roughness, wet-aggregate stability (WAS), soil organic carbon content (SOC), clay and sand contents (SAND) were investigated. Mainly owing to root growth, precipitation and agricultural management, strong temporal variability of Ks was observed in each of the five sections, as the corresponding coefficients of variation all exceeded 35 %. Using the redundancy analysis (RDA) and classical correlation analyses, the primary variables controlling Ks distribution varied among sections, i.e., precipitation (P) and SAND in the erosive section and BD in the others. The predominance of BD was also manifested when performing RDA and structural equation modelling (SEM) over the entire slope covering all five sections.The other significant factors included SAND, SOC, P and WAS, in the decreasing order of direct path coefficient. In addition, these factors also indirectly affected Ks through their influence on BD and/or other factors. These findings demonstrate the strong temporal variability of Ks throughout the maize growing season and intricate interactions of Ks with related factors, and have important implications for hydrological modelling and agricultural production in the black soil region of northeast China and other similar regions.

Effect of biochar and hydrochar of pistachio residues on physical quality indicators of a sandy loam soil

The carbonization of agricultural residues into carbon-rich biochars can be considered as one of the practical methods in sustainable management. The objectives of this study were to: (i) investigate and compare the chemical, physical and micromorphological properties of biochar and hydrochar produced from pistachio (Pistacia vera) residues, and (ii) compare the effects of these chars on the physical quality of a sandy loam soil (classified as Typic Haplocalcids) in pistachio orchards. The physical and chemical characteristics of the biochar and hydrochar were determined. Scanning electron microscopy images showed that hydrochar had a spherical pore structure while the biochar had elliptical pores. The chars were different in terms of functional groups, ratio of elemental composition, and electrical conductivity. Both chars were added at the rates of 0, 1 and 2%w/w to the soil and incubated for nine months under wet and dry cycles. Then, soil physical indicators including bulk density (ρb), dry and wet aggregate stability, water retention curve, saturated water content (θs), field capacity (θFC) and plant available water (PAW) were determined. The results showed that the hydrochar and biochar application had no significant effect on the ρb and dry aggregate stability. However, the percentage of water-stable aggregates larger than 0.25 mm increased at the rate of 1%w/w of chars in comparison with the control. The θs, θFC and PAW increased at both rates of chars when compared with the control. The residual water content (θr) increased at the rate of 1%w/w of chars compared to the untreated soil. It can be concluded that chars of pistachio residues can affect soil physical quality indicators and pore size distribution by the means of different mechanisms like the effect of morphological characteristics of chars, forming complexes between the soil particles, and creating hydrophobic coatings on the soil particles and aggregates.

Soil health benefits associated with urban horticulture

As the global population grows and is increasingly concentrated in urban environments, the quality of urban horticultural soils is of mounting importance. Until now, most urban horticultural soil assessments have been applied in nations and continents outside North America, and none have been conducted in Canada—an important agricultural region. Here, we present the first Canadian study to evaluate soil health in urban horticultural soil (gardens producing fruit and vegetables), benchmarked against conventional agricultural soil in surrounding rural areas (producing cereals, oilseeds, and legumes). We assessed a range of soil health indicators (total C, soil organic C [SOC], active C, CO2 evolution, wet aggregate stability [WAS], total N, autoclave citrate extractable [ACE] protein, potentially mineralizable N [PMN], and N2O production), soil fertility indicators (inorganic N, available P, and available K), and inherent soil properties (texture, electrical conductivity [EC], and pH). We found that carbon- and nitrogen-based soil attributes in urban horticultural soils were 200 % that of the agricultural soils, indicating superior soil health—which had significant implications for interpreting soil health scores. As for soil fertility, inorganic N and available K did not differ between the two systems, but available P was 400 % higher in urban horticulture than agriculture soils, indicating that management practices which build soil health might risk also building excessive soil P levels. Our findings suggest that urban horticulture soils may provide superior ecosystem services and function as a reservoir for SOC, likely due to the soil health management practices implemented by gardeners—but care should be taken to manage soil health alongside managing soil fertility. Urban horticulture soil is an ideal platform for expanding research and governance not only for food production but for valuable ecosystem services.

Impact of planting green on soil properties under irrigated no‐till soybean

AbstractPlanting green refers to the practice of planting a row crop into an actively growing cover crop (CC) and terminating it at or after row crop planting. Planting green could have more beneficial impacts on soil properties, erosion control, nutrient cycling, weed suppression, and other soil ecosystem services because it allows greater CC biomass accumulation than early‐terminated CC. The objectives of this 2‐year study were to evaluate the impact of planting green on soil properties (bulk density, wet aggregate stability, sorptivity, particulate organic matter, organic matter, nutrients, and others) and soybean (Glycine max L.) yield in an irrigated no‐till soybean system in south‐central Nebraska. Treatments were cereal rye (Secale cereale L.) CC terminated 2 weeks before planting (2WBP), CC terminated 2 weeks after planting (2WAP) soybean, and no CC. On average, CC produced 2.35 Mg ha−1 of biomass for 2WBP and 12.03 Mg ha−1 for 2WAP. Both 2WBP and 2WAP reduced N concentration by 48% (31.10 vs. 59.70 mg kg−1) but had no effect on other soil properties compared with no CC. Despite the abundant CC biomass production, terminating 2WAP had little to no effect on most soil properties in the short term (2 years). Wet aggregate stability increased as CC biomass production increased, while soil sorptivity (initial water infiltration) increased as wet aggregate stability increased. CC termination timing had inconsistent effects on soybean yield. In general, after 2 years, planting green had no effect on most soil properties or soybean yield, warranting long‐term studies on this topic.