Mean Weight Diameter Of Dry Aggregates Research Articles

Effects of 5 years of corn residue grazing and baling on nitrogen cycling, soil compaction, and wind erosion potential

Corn residue grazing can provide a valuable and cost effective means of feeding cattle and is a common practice in most corn producing states. Mechanical means of residue removal (baling) is also often practiced as a means of harvesting cattle feed. However, there are concerns about the effects of management practices that remove crop residue on soil processes such as compaction, aggregation, and N cycling. To study these concerns, an experiment with four treatments including control, light grazing, heavy grazing, and baling was carried out for 5 years at the University of Nebraska-Lincoln Water Resources Field Laboratory near Brule, NE. Soil penetration resistance was measured after 3, 4, and 5 years of residue removal. Wind erodible fraction, mean weight diameter of dry aggregates, and soil total N were measured after 5 years. Corn yields were determined throughout the study. Results indicate that light grazing showed little or no difference from the no residue removal treatment, but heavy grazing and baled treatments often had higher penetration resistance, indicating that high rates of residue removal may increase risks of soil compaction. However, compaction did not appear to be cumulative over time. No significant differences were observed in wind erodible fraction and dry aggregate mean weight diameter. However, there were trends that suggest heavy grazing and baling may, in the long term, reduce dry aggregate stability, increasing wind erosion potential. Results also show that in the surface 0–2.5 cm grazing animals may increase soil total N and that baling residue may decrease soil N content. There was no impact on corn yields throughout the study. Overall, corn residue grazing and baling appear to have little or no adverse effects on soil compaction, aggregation, or nitrogen cycling after 5 years.

Assessment of Spatial Distribution of Selected Soil Properties using Geospatial Statistical Tools

To gain additional knowledge and better understand forest soil management on a small scale, geostatistical analytical tools were employed to examine the spatial distribution in dry aggregate mean weight diameter (MWD) and other selected soil properties and to assess the possible relationships between MWD and other soil properties. Selected properties of forest soils collected along a 300-m transact in the Nimbia Forest Reserve of Nigeria exhibited moderate to high variability in distribution with sodium ion displaying the greatest variability [coefficient of variation (CV, 91.2%)] and principal component analysis revealed the exchange complex cluster as influencing total variation of field soil properties. The autocorrelation function showed significant spatial correlation from 1 lag in soil organic carbon up to 17 lags (51 m) in soil moisture content (θ). The spherical and Gaussian semivariogram models described the spatial structure of most soil properties; however, for clay, cation exchange capacity (CEC), and soil organic carbon (SOC), an exponential model analyzed their spatial dependence.

Influence of soil aggregation on SOC sequestration: A preliminary model of SOC protection by aggregate dynamics

Aggregation dynamics and soil organic carbon (SOC) fractions collected from long-term tillage trials at two sites in Illinois were used to develop a model to simulate the aggregate dynamics and physical protection of SOC. We used two litter pools which are surface litter and root litter and three SOC pools which are directly measurable from the fractionation: loose particulate organic matter (LPOM), aggregate-occluded particulate organic matter (OPOM), and humified fractions (HF). Decay rates of all of five pools were modified by soil temperature and moisture. In the model, the decay rate of LPOM was not influenced by any type of physical protection and the OPOM decay rate was influenced by dry aggregate mean weight diameter (DMWD) size. The effect of DMWD on OPOM decay rate was expressed as logistic equation based on the threshold value beyond which OPOM decay rate was influenced by the reactive mass concept which is that it is primarily outer layer of aggregates that participates in chemical and biological reactions. The decay of HF was influenced by clay contents. The relative aggregate turnover modified the humification coefficients. The faster aggregate turnover speeded the carbon transfer from LPOM to OPOM by providing more chances for organic matter to be incorporated with macroaggregates and retarded carbon transfer from OPOM to HF due to the fact that there is not enough time for organic mater to be associated with microaggregates and clay particles. Simulated results were compared against actual SOC fraction contents obtained from two long-term tillage trials located in Illinois, DeKalb (silty clay loam) and Monmouth (silt loam). Both actual and simulated data showed that after 10 and 17 years of no tillage (NT) practice adoption, OPOM content was increased at the surface in Monmouth and HF content was increased at the surface in DeKalb. Agreement between the output of aggregate dynamics-based model and actual data suggested that DMWD size, relative aggregate turnover, and their interaction with soil moisture and clay contents can be used to predict the inconsistent effects of tillage practices on SOC sequestration.

Tillage Effects on Aggregate Turnover and Sequestration of Particulate and Humified Soil Organic Carbon

The seasonal dynamics of soil organic carbon (SOC) fractions and dry aggregates were investigated to determine whether aggregate turnover rates explain the variable influence of no‐till (NT) practices on SOC accrual in Illinois. Soils were collected (0–15 cm) of two 17‐yr‐old trials where NT and conventional tillage (CT) practices had variable effects on SOC sequestration in the 0‐ to 30‐cm depth. Soil was fractionated into loose particulate organic matter (LPOM), macroaggregate‐occluded particulate organic matter (OPOM), and humified fractions (HFs) associated with microaggregates and minerals. Dry aggregate mean weight diameter (DMWD) was used to evaluate structure expressed in the field. Within‐season changes in fraction concentrations indicate that C derived from LPOM and plant roots was transferred to OPOM at both sites. At DeKalb (silty clay loam), NT practices had less influence on SOC sequestration than at Monmouth (silt loam). DeKalb HF contents increased under NT while OPOM contents were unchanged. At Monmouth, NT practices increased SOC sequestration by increasing OPOM concentrations. Site‐based differences in SOC accrual were related to aggregate turnover rates, which were increased by NT practices at Monmouth but were unaffected by tillage at DeKalb. Trends in DMWD and aggregate turnover suggest that when aggregate turnover is slow, as at DeKalb, OPOM formation is limited. Slow turnover in the heavier soil permitted accumulation of HF because residues had longer contact times with particle surfaces. When aggregate turnover is faster, as in the Monmouth NT soil, there is greater chance for residue incorporation into aggregates and accumulation of OPOM. Rapid aggregate turnover limits opportunities for mineral affiliation and HF accrual. Aggregate dynamics predicted site‐based differences in the form and rate of SOC accrual caused by the use of NT practices.

Soil Aggregate Characteristics and Organic Carbon Concentration after 45 Annual Applications of Manure and Inorganic Fertilizer

ABSTRACT Soil management practices that increase soil carbon sequestration can improve soil quality and reduce agricultural contribution to carbon dioxide (CO2) emissions. The long-term (45 years) effect of applications of manure (FYM) and inorganic (NPK) fertilizers on soil aggregate characteristics and soil organic carbon (SOC) concentration was studied in surface soil of a Typic Haplustalf sandy loam. Soils from four treatments: inorganic fertilizer in combination with farmyard manure (FYM + NPK), fertilizer only (NPK), farmyard manure only (FYM) and a control receiving neither NPK nor FYM were studied. Results indicate that long-term application of manure with or without NPK improved aggregate stability by increasing mean weight diameter (MWD) of dry aggregate and fraction of dry aggregate > 2.0 mm. Higher values of MWD were also recorded in the water-stable aggregate size distributions for soils amended with either FYM or NPK. Soils amended with FYM + NPK sequestered more SOC than all other treatments. There was a low, but significant positive correlation between MWD of dry aggregates and SOC. Highest values of SOC were recorded in the > 2.0 mm aggregate fractions. This tendency towards greater SOC concentration for > 2.0 mm dry aggregate is suggestive of the effectiveness of this aggregate size range to sequester SOC in savanna Alfisols. These results demonstrate that continuous application of soil amendments like FYM and NPK over a long-term promotes soil aggregate stability and long-term SOC sequestration. Hence, for sustainable production in savanna Alfisols, there is a need to design policies that will promote soil aggregate stability and long-term carbon sequestration under continuous cultivation. Such policies must give attention to soil management practices that maintain higher level of SOC. Here, FYM with or without NPK was essential to increase stability of dry aggregates and SOC sequestration. However, the NPK amended soils possess higher fraction of water-stable aggregates.

Effects of straw, vegetable oil and whey on physical and microbiological properties of a chernozem

A soil microcosm study was carried out to compare the effects of straw, vegetable oil or whey additions on physical and microbiological properties of a chernozem after 18 weeks of incubation. The application rates of the different organic materials were based on the addition of carbon at a concentration equivalent to 1% of soil dry mass. Straw, vegetable oil and whey additions to soil increased dry aggregate size distribution during incubation. All organic treatments had significantly higher mean weight diameter (MWD) of dry aggregates than the untreated control. The ability of whey, straw and oil to increase MWD did not differ significantly. Only straw addition significantly increased soil maximum water-holding capacity after 126 days of incubation. In comparison with the untreated control, straw tended to reduce the resistance of aggregates to abrasion, while addition of whey and vegetable oil seemed to have a positive effect on this property. Aggregates of organic matter amended soil materials had higher resistance to the dispersive action of water than those of the untreated control. Whey and straw additions sustained higher soil biomass-C contents and C mic/ C org ratios than vegetable oil. Biomass development was most favored by whey addition. Fungal contributions to biomass-C dominated over bacterial contributions in whey and straw-amended soil. The opposite was observed for the oil treatment. Increases in MWD of dry aggregates seem to be related to the synthesis of biomass and soil binding metabolites in whey and straw-treated soil. Among the organic treatments, oil-amended soil had the highest respiratory activity and the lowest biomass content. Stabilizing agents derived from the microbial metabolism using oily substrate are discussed.

Monitoring of changes in physical and microbiological properties of a Chernozem amended with different organic substrates

A soil microcosm study was made to monitor changes in soil physical and microbiological properties of a Chernozem during a period of up to 126 or 252 days following the addition of whey, straw or vegetable oil. In the whey treatment soil maximum water-holding capacity (MWHC) had decreased after seven and 28 days of incubation. At both dates, the differences to the untreated control were significant. Straw was able to increase MWHC of soil during incubation and after 42 and 126 days values differed significantly from those of the control. Compared with the control, whey, oil and straw treatments had higher meanweight diameter of dry aggregates. The differences were significant after seven, 28 and 126 days with whey, after 42, 126 and 252 days with oil, and after 126 days with straw. The sensitivity of dry aggregates to abrasion (SAA), representing a negative index of dry aggregate stability, was lower in the whey treatment than in the control after three and seven days incubation. In the later phase of incubation, whey tended to increase SAA. A trend to increase SAA also was observed with straw and after 126 days a significantly higher SAA for the straw than for the oil treatment was determined. This trend still was to observe after 252 days incubation. An increase in SAA observed for the oil treatment after 42 days was followed by a decrease till the end of incubation. Aggregates of organic treatments were more resistant to the dispersive effect of water than those of the control. Microbial biomass-C contents were high in the whey treatment, ranging between 1931 and 754 μg g−1 soil dry mass during incubation. With whey, fungal contributions to biomass-C increased from 40.5% after three to 76.5% after 126 days incubation. Addition of straw or oil stimulated biomass synthesis less than whey. High fungal contributions to biomass-C, approx. 70%, were sustained by straw during incubation. With oil, fungal contributions were 20.5% after three, 76% after 42 and less than 20% after 126 and 252 days incubation. Fungal contributions to biomass-C correlated positively with SAA. High sensitivity of the fungal biomass to mechanical stress is discussed as a cause for the low dry aggregate stability of soils amended with organic substrates encouraging fungal biomass development.

Soil Quality Assessment of Tillage Impacts in Illinois

Successful soil quality assessment strategies are needed to improve our ability to manage soils sustainably. Our objective was to use a multivariate data set to determine whether recent adoption of no‐tillage (NT) practices had altered soil quality in Illinois. In 1995 and 1996, we sampled thirty‐six farm fields under conventional tillage (CT) or NT practices and relatively nondisturbed (ND) areas. Soils were Mollisols or Alfisols. Tillage or region affected 20 of the 23 parameters characterized. Soil chemical parameters were less variable than biological or physical measures. Principal component analysis (PCA) was used to assess soil quality overall. Principal component 1 (PC1) scores, which explained 39% of the total variance of the overall data set, were affected by tillage (ND > NT > CT) and increased with particulate and organic C and total N, biological activity, mineralizable N, and wet aggregate stability, and decreased with bulk density and dry aggregate mean weight diameter. The only significant factor contributing to PC2 was penetration resistance; PC2 explained 13% of the variance and decreased as follows: NT ≥ ND > CT. Multivariate assessment of soil quality indicated use of NT practices improved the biological and physical condition of the soil (0–15 cm) despite increased consolidation. It also showed that those biological and physical aspects of soils influenced by organic matter were the properties most altered by agronomic practices. Particulate organic matter (POM) was identified as a promising soil quality measure. A next step is to determine the biological and environmental relevance of a refined set of soil quality measures in conjunction with soil processes of regional concern.

Microbial Biomass and Soil Structure Associated with Corn, Grasses, and Legumes

AbstractMaintaining long‐term soil productivity requires development of cropping systems that provide maintenance or improvement in soil structure and an understanding of associated rhizosphere microbial populations. The objectives of this study were to determine the effects of several crops on soil biomass C and biomass N contents, their within‐season variability, and the relationships between changes in soil biomass C, biomass N, and soil structure on a Brookston clay loam soil (fine‐loamy, mixed, mesic Typic Argiaquoll). Soil microbial biomass C, biomass N, and soil‐structure parameters (wet aggregate stability [WAS], organic carbon [OC], dry aggregate mean weight diameter [MWD], bulk density, and total and air‐filled porosity) were measured during the third year of corn (Zea mays L.), soybean (Glycine max [L.], Merr.) alfalfa (Medicago sativa L.), red clover (Trifolium pratense L.), reed canarygrass (Phalaris arundinacea L.), orchardgrass (Dactylis glomerata L.), and no‐crop (bare, covered, and shaded) plots at monthly intervals (June, July, August, and September). Reed canarygrass resulted in greater biomass‐C contents than both the corn and soybean at all four sampling dates. Soil biomass C under alfalfa was significantly greater than under corn and soybean for both the first and last sampling dates. Forage species did not affect the soil biomass‐N content. No consistent effects of the no‐crop treatment on biomass C or biomass N were observed between sampling dates. Biomass C was significantly correlated with WAS, OC, and MWD for the cropping treatments. Wet aggregate stability was negatively correlated with soil water content for both the no‐crop and cropping treatments, indicating that improvements in structure were not solely the result of the cropping treatments and associated rhizosphere populations. Reed canarygrass resulted in greater soil biomass C/N than the alfalfa, corn, and orchard grass plots, suggesting that fungal activity, and therefore soil structure, may be preferentially enhanced in the presence of reed canarygrass. This study demonstrated the influence of forage species and seasonal variability on concurrent changes in microbial biomass and soil structural properties.