Mean Weight Diameter Of Water-stable Aggregates Research Articles

High-quality fine particulate organic matter drives SOM stocks: Insights from Mollisols in Northeast China

How the quantity and quality of particulate organic matter (POM) affect the mineral-associated organic matter (MAOM) accumulation and the aggregate stability has not been systematically studied, which limits the in-depth understanding of the relationship between POM and SOM stocks. This study investigated the changes in the biomass and C:N ratio of fine roots, the C contribution of POM to SOM and the C:N ratio of POM within different particle sizes in native grassland, plantations and croplands in the Mollisols region of Northeast China. Then, the influence of fine roots and POM characteristics on MAOM accumulation and aggregate stability was analyzed. The results showed that (1) the C contribution of fine POM (fPOM, 0.053–0.25 mm) to SOM and the C:N ratio of fPOM in the native grassland was significantly higher and lower than that in the other sites (P < 0.05), respectively. (2) The C contribution of MAOM to SOM and the mean weight diameter (MWD) of water-stable aggregates were significantly positively correlated with the C contribution of fPOM to SOM (P < 0.01), and negatively correlated with the fPOM C:N ratio (P < 0.01). (3) The effect of fPOM C:N ratio on MWD of water-stable aggregates was stronger compared to the C contribution of fPOM to SOM. (4) The fine roots biomass showed a significant indirect effect on the C contribution of MAOM to SOM and the MWD of water-stable aggregates by influencing the C contribution of fPOM to SOM (P < 0.05). In general, both the quantity and quality (C:N ratio) of fPOM were lower in other land use types than that in native grassland, which significantly affected the SOM stocks. At the same time, the fPOM was also a medium for the fine roots to affect the soil characteristics. Promoting the accumulation of fine POM and focusing on improving the quality of fine POM could be a promising measure to ensure food production and increase soil carbon stocks. Conservation tillage practices such as no-till may be effective.

Management practices differently affect particulate and mineral-associated organic matter and their precursors in arable soils

Our understanding of soil organic matter (SOM) formation and stabilization mechanisms has evolved recently. The SOM is considered as a continuum from coarse fresh and decomposing plant residues (particulate organic matter, >53 μm; POM) to fine and presumably more stable mineral-associated organic matter (fine organic matter, <53 μm; FOM), which represents the major portion of total SOM. Current theoretical models call for a prominent role of microbial by-products in FOM formation. However, there is still relatively little field-based evidence to support these theoretical models, especially in arable soils. We examined surface (0–10 cm) soil quality indicators over 7 years in two Brunisols with contrasting textures (silty clay and sandy loam) under twenty different management systems, combining two tillage regimes (minimum tillage vs inversion tillage), two crop residue management (residue retained vs harvested) and five different fertilizer sources (no-N control, complete mineral fertilization, liquid dairy manure, liquid swine manure, solid poultry manure). Surface soil quality indicators included soil organic carbon (SOC), POM-C, FOM-C, microbial biomass-C (MBC), plant- and microbe-derived carbohydrates, and mean-weight diameter of water-stable aggregates (MWD). An univariate statistical analysis of these indicators was combined with a principal component analysis (PCA) to explore the relationships among soil quality indicators and SOC dynamics. In both soil types, POM-C was closely related to MWD and plant-derived carbohydrates, whereas FOM-C was closely related to microbial amino-sugars. These results support the recent conceptual models mainly attributing the formation of FOM-C to microbial by-products. We found that management practices that favored POM-C formation, such as reduced tillage and residue retention, were particularly efficient to increase surface SOC content, irrespective of soil texture. By contrast, manuring had a pronounced effect on microbial biomass, which resulted in the accumulation of microbial amino sugar and SOC, in the silty clay soil only. Use of N-rich organic amendments with low lignin content, such as manures, could therefore be an efficient way to foster the formation of stable SOC through the accumulation of microbe-derived FOM precursors in arable soils where clay content is sufficient to allow for the stabilization of microbial by-products.

Effect of Distillery Effluent (Spent Wash) Application on Aggregate Size Distribution and Stability in Sodic Soils

Sodic soils of sandy loam, silt loam and clay loam textures having exchangeable sodium percentage (ESP) classes of 20, 40, 60 and 80 were reclaimed with 0, 10, 20, 30 and 40 % solutions of distillery effluent (DE) and gypsum in columns. Soil texture, types of amendment and initial ESP had a larger impact on chemical properties, aggregate stability and size distribution. With increase in concentration of DE, a significant reduction in ESP, pH and insignificant increase in electrical conductivity (EC) of soil was observed for all three textures. Organic carbon (OC) content was also increased significantly in soils amended with DE. Size distribution of water-stable aggregates (WSA) of soils reclaimed using 40 % solution of DE and gypsum were found at par. Depending upon initial ESP and type of amendments used, mean weight diameter (MWD) of WSA varied from 0.51 to 1.14, 0.61 to 1.37 and 0.54 to 1.63 mm for sandy loam, silt loam and clay loam soils respectively. The percentage of water-stable macro-aggregates (WSMA) (>2 mm diameter) ranged from 2.2 to 18.2 in sandy loam, from 2.2 to 19.5 in silt loam and from 4.6 to 28.5 in clay loam soils. Combined as well as individual effects of initial ESP, EC, pH, and OC were found highly significant on WSMA and MWD of WSA in distillery effluent amended soils.

Does inorganic nitrogen fertilization improve soil aggregation? Insights from two long-term tillage experiments.

The relationship between inorganic fertilization and soil aggregation is not well understood. We studied cumulative nitrogen (N) fertilization impacts on aggregation, soil organic C (SOC), pH, and their relationships under irrigated and rainfed experiments in Nebraska after 27 and 28 yr, respectively. The dominant soil series were Crete silt loam at the irrigated site, and Coleridge silty clay loam at the rainfed site. We studied irrigated continuous corn ( L.) in chisel plow (CP) and ridge till (RidgeT) receiving 0, 75, 150, and 300 kg N ha yr and rainfed continuous corn and corn-soybean [ (L.) Merr.] in moldboard plow (MP), reduced till (RT), and no-till (NT) with corn receiving 0, 80, and 160 kg N ha yr. Fertilization altered soil aggregation in all tillage systems under continuous corn. Mean weight diameter of water-stable aggregates (MWDA) increased in the upper 7.5-cm depth in NT but decreased in the 7.5- to 60-cm depth by 1.5 times with N application. Fertilization reduced pH but had little or no effect on SOC. Both MWDA and pH ( = 0.47***) decreased under irrigated corn, particularly in the 7.5- to 30-cm depth. No-till and RT had two to five times greater near-surface MWDA than MP. Continuous corn had greater MWDA than corn-soybean in the upper 30-cm depth except in MP. Long-term N fertilization improves near-surface soil aggregation in NT continuous corn but reduces aggregation in the subsoil. Results also suggest that, if fertilizers are applied at rates of about 80 kg N ha, deterioration of soil aggregation would be minimal.

Tillage and Crop Rotation Phase Effects on Soil Physical Properties in the West‐Central Great Plains

Efficient water use is the primary determinant of profitability in dryland crop production of the western Great Plains. For a sustainable increase in precipitation use efficiency (PUE) from that typical of the traditional winter wheat (Triticum aestivum L.)–fallow rotation with conventional stubble‐mulch (sweep) tillage (CT) to occur, decreased use of fallow and tillage is required. Our objective was to quantify the effect of tillage intensity (no‐till [NT], reduced tillage [RT], and CT) and phase of the winter wheat–grain sorghum [Sorghum bicolor (L.) Moench]–fallow rotation on selected soil properties that influence PUE, with emphasis on infiltration and the association between water‐stable aggregates (WSA) and infiltration rate. Soil water content at −1.5 MPa matric potential, concentration of WSA ≥0.5 mm, mean weight diameter of WSA, and ponded steady‐state infiltration rate were significantly greater with NT than RT or CT (infiltration rates: NT, 30.6; RT, 15.3; and CT, 11.4 mm h−1). Infiltration rate was significantly greater in the wheat phase (25.8 mm h−1) than in the sorghum (15.4 mm h−1) or fallow (16.2 mm h−1) phases. The significantly better conditions of aggregate stability and water infiltration with NT management and the lack of development of poor infiltration properties during the wheat season that would need to be alleviated by tillage after harvest reinforce the appropriateness of NT management in crop production systems of the region.

Surface-soil structural properties under grass and cereal production on a Mollic Cyroboralf in Canada

Conservation tillage has become a major soil management strategy to reduce soil erosion and improve soil quality, yet the impacts of crop rotation on soil responses to conservation tillage remain poorly described. We investigated the effects of (i) perennial grass cover versus annual cropping and (ii) type of break crop in a wheat ( Triticum aestivum L.)-based crop rotation system on surface-soil (0–10 cm) structural and organic matter properties towards the end of a decade of continuous management on an Albic Luvisol in the cold, semiarid region of northwestern Canada. Soil aggregation was at state to resist water erosion more under perennial grass (i.e. bromegrass ( Bromus inermis Leyss.) and red fescue ( Festuca rubra L.)) than under annual cropping systems (mean-weight diameter of 2.1 and 1.6 mm under perennial and annual systems, respectively). Soil organic C was higher (44 g C kg −1 soil versus 38 g C kg −1 soil), but total soil N was lower (3.5 g N kg −1 soil versus 3.9 g N kg −1 soil) under perennial compared with annual cropping systems. There were few significant differences in soil-structural properties among the various annual cropping systems. The largest effect was greater light-fraction C and N under continuous wheat (4.0 g C kg −1 soil and 0.27 g N kg −1 soil) compared with other rotations, especially wheat–wheat–fallow (2.4 g C kg −1 soil and 0.16 g N kg −1 soil), as a result of higher residue inputs. Relationships between mean-weight diameter of water-stable aggregates and biochemical properties were strongest for soil microbial biomass C and soil organic C. Perennial grass cover exhibited greater potential to preserve soil-structural properties than no-tillage annual cropping.

Effect of Forty-Four Years of Grazing on Fescue Grassland Soils

A grazing study was initiated in the foothills of southwestern Alberta on the rough fescue grasslands (Festuca campestris (Rydb.) in 1949 comparing various grazing intensities. In 1992, soil samples were obtained from the Ah horizon of paddocks grazed at 1.2 (light), 2.4 (heavy), and 4.8 (very heavy) animal unit month ha-1 and from an ungrazed exclosure (control). The thickness of the Ah horizon of the control averaged 22 cm while that of the lightly, heavily and very heavily grazed paddocks averaged 18, 12, and 8 cm, respectively. Soil color changed from 10YR 2/1 (black) to 10YR 4/3 (dark brown to brown) in response to very heavy grazing. Grazing pressures decreased the mean-weight diameter of water-stable aggregates, total C and P, monosaccharide content and the galactose + mannose/xylose + arabinose ratio, while it increased bulk density, pH-CaCl2, and total N. The loss of P must be viewed with concern. Treatment effects on most soil parameters were most pronounced at the two heavier grazing pressures. Particularly, the heavy grazing pressure jeopardized the sustainability of the ecosystem by reducing fertility and water-holding capacity.

Effect of freezing and thawing on the stability of soil aggregates treated with organic wastes

The susceptibility of three highly aggregated, texturally contrasting, agricultural soils (in north-central Italy) to frost action and the role of organic matter in moderating the adverse effect of cyclic freezing and thawing on soil aggregate stability were investigated in the laboratory using soils from Lamporecchio (Sandy Loam), Cremona (Sandy Clay Loam) and Vicarello (Clay Loam) and five rates of organic matter (OM): 0, 18, 36, 54 and 90 t/ha. Results indicated that in the samples that were not treated with OM (controls) aggregate stability as evaluated by the mean-weight diameter of water-stable aggregates (MWD) technique differed significantly among the soils, showing an increase with increasing OM level, clay and iron contents and decreasing silica/alumina ratio. This order was Vicarello > Cremona > Lamporecchio. However, the susceptibility of these soils to frost action, defined in terms of a frost-susceptibility factor, showed an order of Lamporecchio ⩽ Cremona < Vicarello, reflecting decreasing clay contents. In the sandy Lamporecchio and Cremona soils, the rate of 36 t/ha OM prior to cyclic freezing and thawing maintained MWD at levels similar to the control pre-freeze stage. With the clayey Vicarello soil, no OM rate was able to maintain the MWD of the frost-treated samples at the pre-freeze levels.

Effect of antecedent matric potential on the stability of soil aggregates subjected to cyclic freezing and thawing as evaluated by three structural indices

Summary Using three texturally-contrasting soils from Modena, Vicarello and Cremona in North-central Italy, the extent to which the antecedent contents of soils predispose them to frost-induced alterations in aggregate stability were studied using three procedures for evaluation of structural stability. Antecedent moisture content was expressed in terms of matric potentials. The three indices, mean-weight diameter of water-stable aggregates (MWD), specific dispersion energy of soil clods (D) and clay dispersion index (CDI) were consistent in placing these soils in the following order of structural stability: Modena (clay) > Vicarello (clay loam) > Cremona (sandy clay loam). This reflected increasing CaCO 3 content and decreasing sand content and SiO 2 /Al 2 O 3 ratio. However, the sensitivity of these soils to cyclic freezing and thawing, expressed in terms of a frost-susceptibility factor (Fi) decreased with decreasing silt + clay content and varied in the order, Cremona (5.7%) With cyclic freezing and thawing treatments, moisture contents between saturation (0.0 MPa) and the −0.033 MPa matric potential reduced substantially MWD and D. At the −1.5 MPa and airdry conditions, little changes in these two indices were observed. The microaggregation index, CDI, did not reflect the effect of moisture content on structural stability.