Dry Mean Weight Diameter Research Articles

Aggregate stability and carbon and N dymamics in macroaggregate size fractions with different soil texture

Soil nutrient cycling, the distribution of soil aggregates, and their stability are directly influenced by soil texture. Different sizes of soil aggregates provide microhabitats for microorganisms and therefore influence soil carbon (C) and nitrogen (N) mineralization. The purpose of the present study was to assess the aggregate stability and dynamics of carbon and nitrogen in macroaggregate size fractions (1-8 mm) with different clay content from meadow soils. Surface soil samples (0-15 cm) were collected from 4- to 5-year-old forage crops. Four macroaggregate size classes were isolated by dry sieving and analyzed for their mass proportions: fine macroaggregates (FM) (less than 1 mm), medium-fine macroaggregates (MFM) (1-2 mm), medium-coarse macroaggregates (MCM) (2-4 mm), and large-coarse macroaggregates (LCM) (4-8 mm). The dry mean weight diameter (MWD), organic carbon (OC), total nitrogen (TN), carbon and nitrogen of microbial biomass (C-MB, N-MB) were determined. CO2 emission and net nitrogen mineralized (NM) were measured after 14 weeks of incubation. The amounts of FM were significantly lower than those of intermediate macroaggregates (MCM and MFM) and decreased markedly with increasing clay content within soil macroaggregates. In general, the amounts of macroaggregate size fractions were lowest in soils with high clay content. MWD exhibited a significant correlation with particle size distribution, OC, and MB-C. OC, TN, MB-C, and MB-N contents within macroaggregates increased with decreasing macroaggregate size and increasing clay content of macroaggregate fractions. The CO2 emission and NM content increased with increasing macroaggregate size, indicating higher organic C and N mineralization activity in larger macroaggregates. Mineralization of OC was lowest in macroaggregate fractions with the highest clay content. We conclude that clay content can increase the protection of microbial biomass in meadow soils. Small macroaggregates tend to contain more recalcitrant organic matter compared to larger macroaggregates.

Spatial Variability and Mapping of Selected Soil Physical Properties under Continuous Cultivation

Assessments of Soil physical properties and estimation of their associated variability are essential for making site-specific decisions on soil and crop management This study examined the spatial variability of soil hydro-physical properties and variance structure at Sector F1 of the Jibia Irrigation project Katsina State, Nigeria. Grid sampling technique was used to obtain one hundred and forty-four (144) soil samples from 206 ha of land using Google earth. The grids were drawn using Google earth software at intervals of 150 m x 150 m. Surface soil samples (0 - 20 cm) were collected at grid intersection points. The collected soil samples were air-dried and passed through a 2mm sieve, and analyzed using standard laboratory procedures for physical parameters. The ArcGIS software package 10.3 was used to model the variance structure of Sand, Silt, Clay, Bulk density, Particle density, Percent total porosity and Organic Matter (OM). Results obtained revealed that the coefficient of variation (CV) ranged from 5.724% in particle density to 109% in clay. The Semivariogram showed that the range of spatial dependence varied from 0.342m for (Dry mean weight diameter) to 9.3m (Organic matter) for all measured soil properties. High Spatial dependency ratios were observed for Bulk density, Sand, Silt and clay contents. Particle density exhibited moderate spatial dependency (Nugget to sill ratio 0.25 – 0.75%). Wet Mean weight diameter and organic matter content have a weak spatial dependency. The results indicated that sandy textured soils dominated the greater part of the study area with low to moderate organic matter content. The soils being sandy-dominated has a high infiltration rate and low ability to retain moisture and nutrients were observed as the major characteristics of the soil of the study area.

Soil Sensitivity to Wind and Water Erosion as Affected by Land Use in Southern Iran

Land degradation by soil erosion is one of the most severe environmental issues that is greatly dependent on land use management. In this study, the effects of long-term land use management (including annual cultivated field (ACF), fallow field (FF), rangeland (R), and orchard field (OF)), soil depth (0–10 and 10–20 cm), and soil organic matter content (SOM) on wind- and water-erosion indices were investigated in calcareous soils of southern Iran. Soil samples were collected from four above-mentioned land-use types, and some soil properties and erosion indices were measured. Results showed that the most of soil aggregates stability indices in the surface layer (0–10 cm) of OF were higher than those in ACF, FF, and R, respectively, by nearly 39%, 32%, and 47% for dry mean weight diameter of aggregates (MWDdry); 10%, 10%, and 48% for dry geometric mean weight diameter of aggregates (GMDdry); 21%, 17%, and 15% for water-stable aggregates (WSA); and 11%, 16%, and 31% for aggregate stability index (ASI). Moreover, the mean of the soil wind erosion indicators in OF (0–10 cm) were lower than those in ACF, FF, and R, respectively, by nearly 18%, 24%, and 26%, for wind-erodible fraction (EF); 43%, 38%, and 49% for soil erodibility to wind erosion (K); and 36%, 32%, and 41% for wind erosion rate (ER). In ACF, despite the high clay content, some aggregate stability indices such as MWøDdry and WSA were the lowest among studied land-use types which showed the negative effects of conventional tillage practices. Depth factor had only a significant effect on dust emission potential (DEP) in ACF, FF, and OF. In addition, there were significant and strong correlations between SOM and MWDdry (r = 0.79), WSA (r = 0.77), EF (r = −0.85), K (r = 0.74), and ER (r = 0.74) in all datasets.

Long-term soil quality decline due to the conventional tobacco tillage in Southern Brazil

ABSTRACT Since 1970, most of the tobacco has been cultivated using conventional tillage system in Southern Brazil. No long-term soil degradation assessment on tobacco crop has been performed, particularly, on soil erodibility. The objectives of this study were to evaluate the aggregate stability, soil erodibility, and physico-chemical soil changes, as a function of the time of tobacco cultivation i.e. chronosequence (forest, 3, 10, 15, 20, 25, 30, and 40 yr). Several tests for aggregate stability, soil physicochemical, and soil organic matter determination were applied. The dry mean weight diameter of aggregate decreased more than twice from 3.6 mm to 1.6 mm. While the aggregate stability decreased five times from 36.7% to 6.8% following the tobacco chronosequence. The organic matter content decreased abruptly i.e. 57% under tobacco cultivation. Inversely, the pH, cations and particularly, phosphorous concentration, increased three times on older tobacco plots (≥ 25 yr). Surprisingly, an increase of 23% in silt size fraction due to re-organization of particles makes the soil more erodible along the chronosequence. Forty years of soil cultivation with tobacco, using conventional tillage methods caused significant soil physical-chemical degradation. Therefore, a soil conservation policy must be adopted urgently on tobacco crop areas in Southern Brazil.

Soil mechanical properties and wind erosion following conversion of desert to irrigated croplands in central Iran

Conversion of the virgin desert to agricultural lands can obviously alter some soil properties; however, little is known about how this conversion impacts soil mechanical properties and wind erosion. The present study therefore aimed at assessing the impacts of agricultural exploitation on aggregate stability, mechanical properties and wind erosion of desert soils in Abarkooh plain, central Iran. To do so, three land uses were assessed: (1) wheat (Triticum aestivum L.), (2) pistachio (Pistacia vera L.), and (3) the adjacent virgin desert soils. Ten sites including three land uses were selected. At the time of soil sampling, the vane shear test was performed. Then, the composite soil samples (0–20 cm depth) were taken for laboratory analyses. Soil organic carbon, bulk density, mean weight diameter, wind erosion rate, wind erodible fraction, shear strength value, cohesion (c), and angle of internal friction (φ) were measured. The results showed that soil organic carbon content in the croplands was greater than that of desert. Nevertheless, according to findings, soil gravel, electrical conductivity, and bulk density decreased with cultivation. Compared to the desert (0.21 mm), wheat (1.71 mm) and pistachio (1.34 mm) fields had a higher dry mean weight diameter of soil. The wind erosion rate in the desert (1.48 g m−2 s−1) was 16.4 and 13.5 times greater than those of wheat and pistachio fields, respectively. Also, the wind erodible fraction in the desert was significantly higher (85%) compared to the cultivated soils (52–58%). The value of φ was greater in wheat‒cropped soil (41.05°) than in the desert (36.90°). The c values (21.39–22.46 kPa), vane shear strength (14.36–14.78 kPa) and shear strength values (22.14–23.49 kPa) in the croplands were 5.2–5.4, 5.0–5.1, and 4.9–5.2 times greater than those of desert, respectively. These results revealed that sustainable use of irrigated desert lands could be an appropriate method which significantly improves soil mechanical resistance against wind erosion.

Multivariate analysis to model yield variability for defined management zones in a banana agroecosystem

The delineation of management zones is based on the spatial behavior of a few soil variables selected and evaluated previously, and usually not correlated in situ with yield. Since the soil-plant system is multivariate, the analysis of its complexity requires statistical tools of equal size. These tools are convenient in providing an intuitive interpretation of the relationship between variables and the ordering of sampling sites. This study aims at the identification of management zones in a banana agroecosystem, starting from the overall analysis of soil variables with crop performance components, using multivariate statistical tools. Three clusters of sites were identified based on soil variables, dry mean weight diameter, pH, and (Ca+Mg)/K ratio, all correlated with crop yield. The groupings allowed to delineate management zones whose production has a uniform spatial behavior, significantly different between zones (P < 0.01)

The Role of Hydraulic Connectivity and Management on Soil Aggregate Size and Stability in the Clear Creek Watershed, Iowa

The role of tillage practices on soil aggregate properties has been mainly addressed at the pedon scale (i.e., soilscape scale) by treating landscape elements as disconnected. However, there is observed heterogeneity in aggregate properties along flowpaths, suggesting that landscape scale hydraulic processes are also important. This study examines this supposition using field, laboratory and modeling analysis to assess aggregate size and stability along flowpaths under different management conditions: (1) tillage-induced abrasion effects on aggregate size were evaluated with the dry mean weight diameter (DMWD); (2) raindrop impact effects were evaluated with small macroaggregate stability (SMAGGSTAB) using rainfall simulators; and (3) these aggregate proxies were studied in the context of connectivity through the excess bed shear stress (δ), quantified using a physically-based landscape model. DMWD and SMAGGSTAB decreased along the flowpaths for all managements, and a negative correspondence between the proxies and δ was observed. δ captured roughness effects on connectivity along the flowpaths: highest connectivity was noted for parallel-ridge-till flowpaths, where δ ranged from 0–8.2 Pa, and lowest connectivity for contour-ridge-till flowpaths, where δ ranged from 0–1.1 Pa. High tillage intensity likely led to an increase in aggregate susceptibility to hydraulic forcing, reflected in the higher gradients of aggregate size and stability trendlines with respect to δ. Finally, a linear relationship between DMWD and SMAGGSTAB was established.

Impact of land use change on soil aggregate dynamics in the dry tropics

AbstractA 2‐year study was conducted to elucidate land use change (LUC) impact on the distribution of aggregate size fractions and associated carbon (C) concentration involving natural forest (NF), degraded forest (DF), cropland (CL), and biofuel plantation (JP, Jatropha plantation) in the dry tropical region of India across the soil profile (0–10, 10–20, and 20–30 cm). Across the seasons and the land uses, the proportion of macro‐ and microaggregates was maximum at upper and minimum at lower layer whereas mesoaggregates increase with depth. The trend of macro‐ and microaggregate fractions through the soil profile was NF > JP > DF > CL whereas that of mesoaggregates was CL > DF < JP > NF. Dry mean weight diameter was highest at upper layer and decreased down the depth in all the land uses and followed the trend NF > JP > DF > CL. Aggregate associated organic carbon (OC) concentration in all the fractions decreased from NF to DF, CL, or JP indicates that macroaggregate associated OC concentration was more susceptible to loss than that of meso‐ and microaggregate associated OC concentration. LUC induced decline in macroaggregate associated OC stock and increase in meso‐ and microaggregate associated OC stock; indicated redistribution of OC stock among aggregate fractions. It may be concluded that JP in dry tropics can be an efficient strategy for rehabilitation of degraded land as it improves aggregate structure and stability in the whole profile and aggregate associated OC stock in upper layer of soil.

Soil macropore characteristics following conversion of native desert soils to irrigated croplands in a desert-oasis ecotone, Northwest China

Sustainable use of cultivated desert soils is important for agricultural productivity in desert-oasis ecosystems. However, how soil macropore characteristics may change as a result of agricultural exploitation remains unclear. The objective of this study was to quantify and compare soil properties and macropore characteristics in an old oasis field (>50years of cultivation, OOF), young oasis field (20 years, YOF), and adjacent uncultivated sandy land (0year, USL) in Northwest China. Three replicated soil samples were collected from each site to investigate soil properties. Meanwhile, twelve (four replicates by three sites) intact soil core columns, 15cm in diameter and 30cm in height, were taken to analyze soil structure. Each soil column was scanned with a helical medical X-ray computed tomography (CT) at a voxel resolution of 0.469mm×0.469mm×0.600mm. The results indicated that soil properties and macropore features improved after cultivation. Silt and clay content and dry mean weight diameter (DMWD) of aggregates increased with cultivation time, whereas bulk density decreased. Soil organic carbon and total nitrogen were 7.3 times and 6.7 times greater in soils at the OOF site than USL site, respectively. The increase in silt and clay content and aggregates formation likely resulted from irrigation with silt-laden river water, which in turn impacted soil nutrient accumulation. Soils at the OOF and YOF sites had greater macroporosity compared with soil at USL, and macroporosity also increased with cultivation time. X-ray CT revealed that soil macroporosity was 8.7–18.9 times greater in irrigated croplands than native desert. Soil macropores were mainly distributed at soil depths of 0–200mm at the OOF and YOF sites, while smaller and less continuous macropores were randomly distributed across soil depths at the USL site. The larger number of macropores at the cultivated sites can be attributed to greater soil organic carbon, tillage-induced soil horizons, and alternate wetting and drying processes. Few soil macropores at the USL site may be associated with wind erosion and soil fauna burrows. Conversion of native desert soils to irrigated croplands had a positive effect on soil pore development in the desert-oasis ecotone.

Reducing post-fire soil erosion from the air: Performance of heli-mulching in a mountainous area on the coast of NW Spain

Although heli-mulching is frequently used in North America to mitigate post-wildfire soil erosion, its use in other regions, at operational scale, is still very limited and, hence, information of its performance in different environments is lacking. In this study, we compared the effectiveness of straw heli-mulching to reduce soil erosion during the first two years after severe wildfire in Galicia (NW Spain). Seventy experimental plots (each 80m2) were established in five forest areas that were severely burned in the summer of 2013. During the two years of study, the accumulated soil loss in the untreated burned soils ranged from 7.7 to 53.9Mgha−1. Heli-mulching reduced soil loss by on average 90%. The variation in mulch cover in the first and second years after fire was significantly related to mean gust wind velocity. Soil burn severity and the mean dry mean weight diameter of soil aggregates were related to soil loss and modulated the effects of mulching during the study period. Vegetation cover did not protect against soil loss during the first year after fire, highlighting the need for emergency measures to be implemented immediately after fire to protect the soil from erosion.

Stability and heavy metal distribution of soil aggregates affected by application of apatite, lime, and charcoal.

Only a few studies have been reported on the stability and heavy metal distribution of soil aggregates after soil treatments to reduce the availability of heavy metals. In this study, apatite (22.3tha(-1)), lime (4.45tha(-1)), and charcoal (66.8tha(-1)) were applied to a heavy metal-contaminated soil for 4years. The stability and heavy metal distribution of soil aggregates were investigated by dry and wet sieving. No significant change in the dry mean weight diameter was observed in any treatments. Compared with the control, three-amendment treatments significantly increased the wet mean weight diameter, but only charcoal treatment significantly increased the wet aggregate stability. The soil treatments increased the content of soil organic carbon, and the fraction 0.25-2mm contained the highest content of soil organic carbon. Amendments' application slightly increased soil total Cu and Cd, but decreased the concentrations of CaCl2 -extractable Cu and Cd except for the fraction <0.053mm. The fractions >2 and 0.25-2mm contained the highest concentrations of CaCl2-extractable Cu and Cd, accounted for about 74.5-86.8% of CaCl2-extractable Cu and Cd in soil. The results indicated that amendments' application increased the wet soil aggregate stability and decreased the available Cu and Cd. The distribution of available heavy metals in wet soil aggregates was not controlled by soil aggregate stability, but possibly by soil organic carbon.

Physical protection of soil organic matter following mechanized forest operations in Pinus radiata D.Don plantations

Mechanized forest operations have a large impact on soil systems, and may cause disruption of aggregates and exposure of previously protected soil organic matter to microbial attack. In this study, we investigated how C storage, soil structure and unprotected, physically protected and resistant C pools recover 0, 7 and 20 years after mechanical harvesting and site preparation in second rotation Pinus radiata D.Don plantations. We detected differences in dry mean weight diameter (DMWD) of aggregates, with higher DMWD in 0- and 7-year-old pine stands (8.7 and 7.5 mm, respectively) than in 20-year-old stands (4.1 mm). This was attributed to the compaction induced by heavy machinery, as reflected by the positive relationship between DMWD and bulk density ( r = 0.85, P < 0.05). Organic C contents in the top 5 cm were similar 0 and 7 years after disturbance, but were twice as high after 20 years, with mean values of 25, 28 and 52 Mg C ha −1 , respectively. In addition, the resistant C pool was also reduced by up to 7% after clearance. In contrast, unprotected C and physically-protected C were greatest in the youngest stands, indicating that stand establishment and harvesting with heavy machinery may have broken soil aggregates and exposed the previously protected SOM to microbial decomposition and that forest operations may create new mega-aggregates able to protect organic residues. However, the lowest physically-protected C values in 20-year-old pine stands may also be attributed to differences in SOM quality. The alkyl C/O-alkyl C ratios were highest in the oldest stands, indicating that SOM in these stands was more resistant to further decomposition. Mechanized forest operations in radiata pine stands released at least 30 t C ha −1 from the first 5 cm of the soil profile immediately after clearance, caused significant alterations in the soil structure, which lasted for a minimum of seven years, and also reduced the resistant C pool. As the Kyoto Protocol encourages forest management practices that potentially increase carbon sequestration, mechanical harvesting and site preparation in these steep slopes should be reconsidered.

No-tillage improvement of soil physical quality in calcareous, degradation-prone, semiarid soils

Many soils in the semiarid Mediterranean Ebro Valley of Spain are prone to physical and chemical degradation due to their silty texture, low organic matter content, and presence of carbonates, gypsum or other soluble salts. Rainfed agriculture on these soils is also hindered by the scarcity of water. No-tillage can increase plant-available water and soil organic matter, thus helping overcome most factors limiting crop production in this area. Our objective was to determine how conventional- and no-tillage practices affected soil physical quality indicators and water availability in an on-farm study in the Ebro Valley. Soil samples were collected from 0 to 5-, 5 to 15-, and 15 to 30-cm depth increments within adjacent farmer-managed conventional- and no-tillage fields in 2007 and 2008. Both fields were managed for continuous barley (Hordeum vulgare L.) production. The soil at both sites is a silt loam (Haplic Calcisol). Aggregate-size distribution and stability, soil water retention characteristics, organic carbon, and total carbonates were determined in 2007. Pore-size distribution was estimated from the water retention curve. Penetration resistance, soil bulk density and field water content during the entire crop growing season were measured for both fields in 2008. Aggregate dry mean weight diameter and stability in water were 1.2 and 2.2 times greater, respectively, under no-tillage than conventional tillage due to reduced mechanical disturbance and increased soil organic carbon content. Bulk density was 1.12 times greater (P < 0.1) under no-tillage only in the 0–5-cm depth. Two times greater penetration resistance to a depth of 15 cm in this treatment was related to bulk density and aggregates stability. Field water content was greater with no-tillage than conventional tillage during the driest months in 2008. The volume of equivalent diameter pores (0.2–9 μm) was 1.5 times higher under no-tillage. This increased plant-available water content and doubled barley production under no-tillage in 2008, which was a very dry year. We conclude that despite the greater penetration resistance under no-tillage, increased water availability as a result of improved structure characteristics was more important for crop yield. This suggests that producers should seriously consider adopting no-tillage practices for soil conservation in semiarid degraded areas like the one studied.

Aggregate breakdown during tillage in a Mediterranean loamy soil

Long-term tillage negatively affects soil aggregation, but little is known about the short-term effects of tillage. We investigated the effects of intensive tillage (moldboard plowing) and conservation tillage (chisel plowing) on aggregate breakage during tillage in a long-term study located in the semiarid Ebro river valley (NE Spain). The type of tillage resulted in different soil aggregate distributions. In the 0–5-cm and 5–10-cm soil layers, chisel plowing decreased dry mean weight diameter (DMWD) 29% and 35%, respectively, while moldboard plowing decreased DMWD by only 2% and 16%, respectively. The decrease in DMWD was mainly due to breaking of large aggregates ranging (2–8 mm) into small aggregates (<0.5 mm). Tillage method had no effect on water stability of 1–2 mm aggregates. The differences in DMWD demonstrate that the choice of the tillage implement can be a key factor in improving soil management and productivity. The surprising result that aggregate breakdown was greater with chisel than moldboard plowing needs further research to determine the mechanisms controlling aggregate breaking during tillage.

Impact of sugarcane cultivation on soil carbon fractions, consistence limits and aggregate stability of a Yellow Latosol in Northeast Brazil

The effects of continuous sugarcane ( Saccharum officinarum) cropping on the properties of a cohesive Yellow Latosol were studied in the region of the Coastal Tablelands, Northeast Brazil. Four areas were studied at Caeté mill, municipality of São Miguel dos Campos, Alagoas State, involving a native forest (Tn), and sugarcane fields cultivated for periods of 2 years (T2), 18 years (T18) and 25 years (T25). Samples were collected from each area at 0–0.2 and 0.2–0.4 m depth, to determine total organic C, physical fractionation of soil organic matter and consistence limits. Undisturbed samples were collected to determine wet aggregate mean weight–diameter, dry mean weight diameter and aggregate stability. In relation to the soil under native forest, total organic C and particulate organic matter contents were reduced after 2 years of cultivation. Sugarcane cropping for a longer period promoted a recuperation of soil organic matter content. The decrease of total organic C and reduction in aggregate stability and plastic limit after 2 years of sugarcane cultivation rendered the soil more susceptible to compaction.

Management and Soil‐Quality Effects on Fertilizer‐Use Efficiency and Leaching

We tested the hypothesis that particulate organic matter (POM) and aggregate dry mean weight diameter (DMWD) are related to fertilizer‐use efficiency (FUE) and leaching susceptibility. Soil cores (15 cm diam. by 50 cm depth) were collected from 12 farm fields representing three cropping systems: conventional (CT) and no‐tillage (NT) management of corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] rotations, and CT applied to more diversified corn–soybean‐based rotations (R‐CT). Three of the four R‐CT farms were organically managed. In a 95‐d greenhouse trial, cores were seeded with corn, amended with 15N‐labeled urea applied at four rates (0, 75, 150, 225 kg N ha−1), and subjected to a stressful moisture regime. Aggregate DMWD, which serves as a rough index of pore‐size distribution, was greater in NT cores. Although total leached N was similar in all cropping systems, increased macropore flow in NT cores led to greater leaching of fertilizer N and less leaching of soil‐derived N, as well as greater moisture stress and decreased plant N uptake. The R‐CT cores had more POM and organic C in the top 30 cm of soil and higher crop biomass and biomass‐N content. However, FUE in R‐CT cores was relatively low since FUE does not account for contributions of indigenous N. For the same reason, FUE remained relatively high in CT systems despite less labile organic matter. Both FUE and SOM conservation declined with increasing N application rates. Increasing labile sources of N, reflected in POM pools, through crop diversification can substitute for incremental increases in fertilizer N and improve long‐term productivity on Illinois Mollisols.

Influence of land-use on properties of a ferralitic soil under low external input farming in southeastern Swaziland

An assessment of changes in soil properties associated with land-use and management practices is vital for the selection and establishment of appropriate sustainable practices under different agroecosystems. This study compared soil properties between land located on an abandoned kraal site (KS), under fallow (FL) and one that was continuously cropped to maize (CC) for over 12 years. Aggregation and aggregate stability as measured by both dry and wet sieving showed large differences between land-use systems. The soil under CC had a higher proportion (26.4%) of micro aggregates (<0.25 mm) compared with that of FL (10.1%) and KS (6.9%). The dry mean weight diameter (DMWD) was larger in KS (3.03 mm) than in FL (2.17 mm) and CC (1.38 mm). Soil aggregates in CC were the least stable with a wet mean weight diameter (WMWD) of (1.61 mm) compared with those of FL (2.18 mm) and KS (2.89 mm). Reduced stability of aggregates in CC is likely due to the lower organic carbon content of soil in this land-use (1.7%) compared with that of FL (2.5%) and KS (3.2%). The soil under KS had lower bulk density (BD), penetration resistance (PR) and aggregate tensile strength (ATS) than that of FL and CC. Soil moisture content (MC) and available water capacity (AWC) showed an opposite trend. The soil in KS had a higher concentration of total N (TN), available P and exchangeable K, Ca, Mg and Zn. Soil on CC, on the other hand, had a higher concentration of Mn than that from FS and KS possibly because of its acidic nature. There were significant strong correlations between soil organic carbon and BD (−0.86 ∗∗∗), PR (−0.61 ∗), MC (0.82 ∗∗), ATS (−0.62 ∗), WSA (0.79 ∗∗∗), AWC (0.91 ∗∗∗), pH (−0.61 ∗∗) and TN (0.76 ∗∗∗). Grain yields of maize were highest in KS followed by FL and least in CC. The high yields were attributed to improved soil properties in plots of KS compared with both FL and CC. In conclusion, the findings suggested that organic matter had a major influence on soil properties and fertility.

Temporal changes in dry aggregate size and stability: tillage and crop effects on a silty loam Mollisol in Illinois

Soil aggregation is one of the main factors controlling the chemical, physical, and biological processes that contribute to soil productivity and agricultural sustainability. Little is known about the relationship between dry-sieved aggregate size and aggregate stability. Temporal changes in the size and stability of dry-sieved aggregates were studied in a Thorp silt loam (US Taxonomy: fine-silty, mixed, mesic Argiaquic Argialboll; FAO Classification: Orthic Greyzems) in a long-term (1986–present) tillage experiment established in Urbana, IL, US. Tillage treatments included no-tillage (NT), disk/field cultivation (DT), and moldboard/chisel plow (MP) in which corn ( Zea mays L.) and soybeans ( Glycine max L.) were rotated annually. Soil samples were collected in 1995 before and after fall field operations and again before planting in 1996. The dry mean weight diameter (DMWD), wet mean weight diameter (WMWD), and wet aggregate stability (WAS) of surface soil (0–5 cm), and the WAS of dry-aggregate size classes were analyzed. Aggregate DMWD was greater in NT (8.8 mm) than in DT (7.1 mm) or MP (7.2 mm) soils. The DMWD increased regardless of tillage or crop from October (7.3 mm) to December (9.4 mm), and had decreased sharply by April (6.3 mm). Soil water content at the time of sampling did not significantly influence DMWD and WAS. Crop alone had no significant influence on soil aggregation but interacted with sampling time and tillage. Dry aggregate size, WMWD, and WAS were positively correlated. Aggregate size increased with soil organic carbon (SOC) and the large (8–25 mm) dry aggregates, which were most affected by tillage, were the most water stable. These findings suggest that large dry-sieved structural units function like true aggregates and should be studied further.