Mean Weight Diameter Of Aggregates Research Articles

Deforestation effects on soil aggregate stability quantified by the high energy moisture characteristic method

Soil aggregate size distribution and structure stability are important soil physical quality indices. The objective of this study was to quantify soil structure stability as a result of land-use conversion from forest to tea farm within Guilan Province of northern Iran over the past 50 years. Soil aggregate or structure stability metrics, along with more common soil chemical and physical properties, were determined on triplicate soil samples (0–30 cm depth), randomly collected from six sites. Dexter's S-index (slope of soil water retention curve at its inflection point), tensile strength (TS), aggregate mean weight diameter (MWD), and water stable aggregate (WSA) were also used to assess stability. Lastly, the high energy moisture characteristic (HEMC) method measured the destructive force used to break the aggregates through controlled wetting. Structure stability using HEMC method and S-index was determined based on the soil water retention curve but using different ranges of matric potentials. The results showed that despite an insignificant decrease in TS, WSA and MWD between land use types there was significant correlation (P < 0.05) between tensile strength with HEMC method's, stability ratio (SR) and Dexter's S-index. The volume of drainable pores after fast wetting of aggregates (fast-VDP) in HEMC method reflected a significant (P < 0.01) decrease in aggregate size between forest and tea farms with means of 0.347 and 0.297 g g−1, respectively. In only one of six locations, the soil water retention curves and the aggregate stability indexes (SI and SR) of HEMC method decreased significantly after land use change. Our results indicated that macro aggregates and structure stability in HEMC method could distinguish differences between two land uses and better than previous methods like MWD, WSA, and TS. The results of S-index and stability ratio of HEMC method were different. This difference can be related to: 1) the soil initial aggregate size that is between 0.5 and 1 mm in HEMC method and about 4 mm in Dexter's S-index and 2) the range of matric potential in each method that is 0 to 50 and 0 to 15,000 hPa in HEMC and S-index, respectively. Although both methods are based on soil water retention curve to estimate soil structure stability and physical quality, but HEMC results show macrostructure stability (macro aggregates) whereas S-index is inflection point of soil water retention curve between textural and structural porosity and estimate microstructure stability.

Interactive effects of raindrop impact and groundwater seepage on soil erosion

Raindrop impact (RI) and groundwater seepage (GWS) play important roles in slope erosion processes. However, reliable quantification of their interactive effects on erosion is still lacking. Therefore, a laboratory study was conducted to reveal the effects of RI and GWS on hillslope erosion. A soil box (5.0 m long, 0.5 m wide, and 0.5 m deep) was subjected to rainfall simulation experiments under free drainage (FD) and GWS conditions. The effect of RI was studied by dissipating raindrop energy, i.e. without raindrop impact (WRI). The results indicated that compared with WRI, RI increased the runoff rate, soil loss and sediment concentration by about 3–14%, 74–696%, and 64–560%, respectively. With a higher runoff rate of 27–54%, GWS increased soil loss and sediment concentration about 70–588% and 27–411% compared with FD, respectively. A power function relation were found between soil losses and runoff rate. The increasing rate of soil loss increased with runoff followed the order: GWS + RI > FD + RI > GWS + WRI > FD + WRI. The erosion and sediment yield seemed to be detachment-limited. As a result of crust formation, RI, compared with WRI, marginally enhanced the average flow velocity and shear stress, and reduced the resistance coefficient. The effects of GWS on flow parameters were more pronounced than RI. The mean weight diameter of aggregates was reduced by about 13–69% because of breakdown by raindrop impact or slaking. The loss of <0.25 mm aggregate accounted for 77–98% of the total aggregate loss in all treatments.

Short-term Conservation Tillage Effects on Corn Silage Yield and Soil Quality in an Irrigated, Arid Agroecosystem

A study was conducted in an irrigated arid agroecosystem in southwestern USA, to compare two conservation tillage systems (strip tillage (ST) and no-tillage (NT)) to conventional, plow-based tillage (PT) system. Corn silage (Zea mays L.) was planted in this trial. Growth parameters (plant population and height) of corn silage were measured during the season and yield was evaluated at harvest. Soil physical measurements assessed included mean weight diameter of dry aggregates, wet aggregate stability, and penetrometer resistance. While soil biological measurements included total microbial biomass, diversity index (DI), total bacteria biomass, total fungi biomass (TFB), arbuscular mycorrhizae fungi (AMF), and total saprophytes. Results showed that plant population and silage yield at 65% moisture content were not significant with tillage during both trial years. Soil physical parameters were mostly not significant with tillage, while three out of the six biological measurements (DI, TF, and AM) were significant with tillage at p ≤ 0.05. No-tillage had higher DI and TFB than the ST, but not different from PT, while AMF was significantly higher in PT than ST, but not different from NT. The study demonstrates that farmers in the study region can adopt conservation tillage without yield losses during the early years of transition.

Soil particle-size distribution and aggregate stability of new reconstructed purple soil affected by soil erosion in overland flow

Artificial soil erosion caused by engineering practices is becoming increasingly severe worldwide. However, little is known about the change of soil structure of new reconstructed purple soil after erosion in the hilly areas of Southwest China. This study aims to analyze the effects of erosion on the soil particle-size distribution (PSD) and aggregate stability of new reconstructed purple soil in the overland flow under different flow discharges, slope lengths, and slope positions. A series of field scouring experiments was conducted. Flow discharges of 5, 15, and 30 L/min were applied in the new reconstructed purple soil plots with different slope lengths (5, 10, 20, 30, 40, and 50 m). Sediment samples were collected in 550-mL bottles. Soil sampling was conducted from the 0–10-cm layers before and after the field scouring experiments. In the laboratory, the pipette method was used to measure the soil PSD and microaggregates. The macroaggregates were determined by the dry and wet sieving method. Silt particles were eroded most at 30 L/min, by 2.11%. The average maximal reduction rate of the mean weight diameter of soil aggregates (MWD) was 20.23% at 15 L/min. Clay loss was maximal at 1.04%, and the average maximal increasing rate of the > 0.25 mm percentage of aggregate disruption (PAD0.25) was 0.86% at 5 L/min. The silt and MWD maximally decreased by 7.72% and 1.86%, and the maximal sand and PAD0.25 increased by 16.70% and 25.18%, which were all observed in the 10-m plot. The percentage of soil aggregates destroyed by the change in the MWD was − 14.32% on the upslope. Silt sediment showed an increasing rate of 6.36% and microaggregate destruction showed a decreasing rate of 13.00% on the middle slope. Microaggregates and clay particles were mainly deposited on the lower slope and the reduction rates of the silt and sand content were smaller than those on the middle slope. The effects of erosion on the soil PSD and aggregate stability of new reconstructed purple soil in the overland flow under different flow discharges, slope lengths, and slope positions were obviously different. Soil and water conservation measures should be effectively implemented on the upper slope and a slope length of 10-m soil. The soil PSD and MWD could be used as parameters for prediction of soil erosion on new reconstructed purple soil.

In situ field measurement of wind erosion and threshold velocity in relation to soil properties in arid and semiarid environments

Field measurement of wind erosion linked to soil properties improves our understanding of erosion processes in arid and semiarid regions to combat this environmental threat. The aim of this study was to investigate wind erosion and threshold velocity (Vt) in relation to soil properties using a portable wind tunnel in 60 sites of Kerman, the largest province of Iran. The result indicated that wind erosion rates ranged from 0.03 g m−2 min−1 to 3.41 g m−2 min−1, indicating a wide variability in the erodibility of soils. Wind erosion was inversely attributed to Vt following a power function. In all cases, the influence of soil properties on wind erosion was supported by their opposite effect on threshold velocity. Clay and silt fractions, mean weight diameter (MWD) of aggregates, dry stable aggregates (DSA), shear strength, surface gravel, the concentrations of K+, Ca2+, and Mg2+, soil organic carbon (SOC) and calcium carbonate equivalent (CCE) were inversely proportional to wind erosion rates following nonlinear functions. Wind erosion was significantly increased as electrical conductivity (EC) and sodium adsorption ratio (SAR) increased. Critical values of 5.7–8.9 m s−1 at 10-m height for Vt, 7% for clay content, .3 mm for MWD, 25% for DSA, and 5% for surface gravel were recognized, approximately. Multiple regression analysis indicated that SAR and MWD were the best predictors of wind erosion rate. Meanwhile, MWD, surface gravel, clay content, and SOC had the best estimation for threshold velocity.

Variation of soil aggregates in response to soil water under short-term natural rainfalls at different land use

The red soils of China, South America, and Africa are highly weathered inherently infertile soils that have high erosion risks and low soil organic carbon levels. In an effort to protect these soils, they are being converted from annual crops to woodlands in China. However, under such a land use change, soil aggregate stability variation (a key factor of soil erosion) to short-term rainfall events is not clear. The objective of this study was to investigate the influence of rainfall type, soil water contents, and vegetation on short-term changes in the aggregate stability of red soils. Surface (0–20 cm) aggregate stability, SWC and dynamics (Δθ) (differences of SWC on the sampling day and prior to the sampling), rainfall, and plant root distribution (0–60 cm) were monitored from 2017 to 2018 under fir (Taxodiaceae), rapeseed (Bassica napus) and Osmanthus fragrans land use. The results demonstrated that the aggregate size distribution and aggregate mean weight diameter were impacted by the soil water content prior to the precipitation and plant species. Plants such as fir, lowered the soil water content which improved short-term aggregate stability. Variation of aggregate under each type of rainfall was attributed to different change of SWC among plants, which was further confirmed by significantly negative relationships between aggregate fractions (< 0.5 mm) and SWC (θ0 and θ0.5, on the sampling time and half day prior to sampling) under all plants. Differences of aggregates as influenced by SWC among plants was also attributed to different plant root distribution and relative root absorption of soil water rate (RASWr) [r between SWC and root percentage (d = 1–3 mm) was 0.99]. The study suggested that plant types should be carefully selected for their ability to protect the soil and the findings will also provide a theoretical basis for land restoration.

Residue retention and minimum tillage improve physical environment of the soil in croplands: A global meta-analysis

Conservation tillage practices, here defined as no-tillage (NT) or reduced tillage (RT) with/without residue retention, have been widely used to alleviate the negative effects caused by intensive tillage practices. Implementing effective and sustainable agriculture requires a deeper understanding of the impacts of conservation tillage practices on soil physical properties. This study examined the effects of conservation tillage practices on soil physical properties, including soil bulk density, aggregate size and stability, hydraulic properties, and soil pH; based on data collected from 264 studies published worldwide since 1980. The results indicated that no-tillage (NT), NT with residue retention (NTS), and reduced tillage (RT) increased bulk density by 1.4, 2.6, and 2.1%, respectively, compared with conventional tillage (CT). Soil bulk density decreased by 2.9% in NTS compared with NT, and 3.9% in RT with residue retention (RTS) compared with RT. The effect size of bulk density significantly decreased with the increasing experimental duration under NT and NTS practices. Compared to CT, conservation tillage practices increased aggregate mean weight diameter (MWD), geometric mean weight diameter and water stable aggregate (WSA) regardless of the residue retention or minimum tillage systems. The largest effect size of MWD (51.9%) and WSA (54.9%) appeared under NTS as compared to the CT. The effect size of MWD and WSA increased under NT with the increasing experimental duration. NT increased saturated hydraulic conductivity by 24.6% compared to CT. All conservation tillage practices increased soil available water capacity (AWC) compared with CT and NTS with a 10.2% increase in AWC compared with NT. The effect size of AWC increased under RT and NT practices with the increasing experimental duration. Soil pH decreased by 1.7 and 1.0% under RTS compared with RT and CT, respectively; and NT led to a 2.8% reduction in soil pH compared with CT. The effect size of soil pH decreased under RT and NT treatments with the increasing experiment duration. Overall, conservation tillage practices positively affected many soil physical properties; and the extent of the effects varied with the duration of the experiment.

Straw Removal Affects Soil Physical Quality and Sugarcane Yield in Brazil

Industrial use of sugarcane straw for bioenergy production represents a promising opportunity for the Brazilian sugarcane sector. Nonetheless, intensified straw removal may aggravate the effects of mechanized harvesting and increase the risks of soil compaction, declining sugarcane yield. An experiment was designed, and four field studies were conducted to evaluate the cumulative effects of straw removal on soil physical attributes (bulk density, BD; soil resistance to penetration, SRP; macroporosity, MaP; microporosity, MiP, and mean weight diameter of soil aggregates, MWD) and their relationship with crop yield under clayey and sandy soils in the Sao Paulo state, Brazil. In each field study, four straw removal rates (no removal, NR; low removal, LR, removal of 5 Mg ha−1; high removal, HR, removal of 10 Mg ha−1; and total removal, TR, removal of 15 Mg ha−1) were arranged in a randomized block design with four replicates. The 4-year intensive management of straw removal (HR and TR) resulted in an increased soil compaction (BD and SRP values) and reduced the MWD in both sandy and clayey soils. Our findings also showed that these effects are more significant in sandy soils, where soil carbon content was substantially reduced in HR and TR treatments. Sites with higher BD and SRP induced by straw removal were strongly associated with lower sugarcane yields, especially in sandy soils. Conversely, our findings indicate that LR was not detrimental to soil physical quality and sugarcane yield. Nevertheless, considering the multifunctionality of straw in sustaining multiple ecosystem services in different soil types, straw management should be defined taking into consideration site-specific conditions. We advocate that recommendations for straw removal should also be combined with other conservationist soil management practices in order to minimize soil compaction and its negative implications on sugarcane yield and other ecosystem services.

Short‐Term Impacts of Conservation Agriculture on Soil Physical Properties and Productivity in the Midhills of Nepal

Core Ideas Aggregation and time‐to‐pond were improved under conservation agriculture.Conventional practice had a higher sorptivity rate than conservation agriculture.Maize yields were similar for conservation agriculture and conventional practice in the first year of production.Maize yields were less in conservation agriculture than in conventional practice in the second year due to patchy plant stands in conservation agriculture.There were no differences in yield between conservation agriculture and conventional practice for rapeseed or wheat. Conservation agriculture (CA) is a management system characterized by zero or minimum tillage, permanent soil cover with crop residue or plant growth, and crop rotation. This study investigated the impact of conservation tillage, crop type, and planting date on crop productivity and the soil physical properties for 2 yr following conversion to CA. After 2 yr, average mean weight diameter of dry aggregates for the 0‐ to 5‐cm and 5‐ to 10‐cm soil depths were 45 and 24% greater in the CA treatment than the conventional practice (CP) treatment, respectively. However, soil sorptivity was about three times slower in CA than in CP for rapeseed (Brassica napus L. toria) rotation treatments, but only 62% slower in CA than CP for wheat (Triticum aestivum L.) rotation treatments. Soil bulk density to a depth of 15 cm was greater in CA (1.30 g cm−3) than CP (1.24 g cm−3), but only for late‐planted treatments. Maize (Zea mays L.) yields for CA were not different from CP in the first year, but were 1.4 Mg ha−1 for CA and 5.0 Mg ha−1 for CP in the second year due to poor stand establishment under CA. There were no effects of CA on dry‐season rapeseed and wheat. Results suggest that during the transition of CP to CA, soil physical properties can be improved but yields may remain constant or decline. Achieving equivalent yield outcomes between CA and CP will largely depend on equivalent stand establishment.

Soil aggregate and intra-aggregate carbon fractions associated with vegetation succession in an alpine wetland of Northwest China

Alpine wetlands can function as carbon sinks because of their high soil organic content and low decomposition rates. However, the effects of alpine wetland succession on soil structure and soil organic carbon (SOC) stability have rarely been reported. The objective of this study was to investigate the effects of vegetation succession on soil aggregate distribution, bulk soil carbon, aggregate-associated C, and intra-aggregate C fraction in the Bayinbuluk alpine wetland. Research sites were selected in adjacent swamp (S), swampy meadow (SM), and meadow (M) locations. Five soil aggregate fractions (>5000, 2000–5000, 250–2000, 53–250 and <53 μm) were separated using a modified Yoder method. The light fraction organic carbon (LFOC), coarse/fine intra-aggregate particulate organic matter carbon (iPOM-C), and mineral-associated organic matter carbon (mSOM-C) were isolated from soil aggregates. In the wetland succession sequence, the mean weight diameter of soil aggregates increased (from 4.16 to 4.63 mm) from S to SM, and then decreased (from 4.63 to 3.23 mm) from SM to M. The bulk soil carbon content initially increased (from 93 to 129 mg kg−1) from S to SM, and then decreased (from 129 to 54 mg kg−1) from SM to M. The same trends were found for the aggregate-associated C in different size aggregates. The coarse iPOM-C content (88–133 mg kg−1) was higher than the fine iPOM-C content (77–118 mg kg−1) in different size aggregates in S samples. In SM and M samples, however, the coarse iPOM-C contents (98–124 mg kg−1 (SM); 60–82 mg kg−1 (M)) were lower than the fine iPOM-C contents (129–151 mg kg−1 (SM); 71–103 mg kg−1 (M)). The ratio of coarse iPOM-C to fine iPOM-C content (ROC/F) exceeded 1 in S but was lower than 1 in SM and M. These results indicate that soil aggregation stability and SOC content increased and then decreased across the wetland succession sequence, and that ROC/F can be used as an indicator of changes in SOC content caused by wetland succession.

Short-term effects of grassland set-asides on soil properties in the Fraser River delta of British Columbia

Grassland set-asides (GLSA) in the Fraser River delta are fields that are taken out of crop production and seeded with a mixture of grasses and legumes for 1–4 yr. During this time, the farmer is compensated with a cost-share payment to recover a portion of the financial returns that could have been earned from cash crops. The objectives of this study were to (i) evaluate the effects of GLSA on soil properties during the initial two seasons of enrollment, (ii) determine how GLSA effects differ between fields that were considered productive and unproductive, and (iii) identify soil baseline indicators and preliminary soil thresholds for predicting GLSA vegetation responses. Out of eight fields entering the program, two were considered to be unproductive and exchangeable sodium had the strongest negative relationship to GLSA aboveground biomass (r = −0.61, P = 0.0002). During the second season of GLSA establishment, the mean weight diameter of water-stable soil aggregates was consistently higher in productive GLSAs than paired annual crop rotation (ACR) fields, being 21% higher in April, 14% in July, and 19% in September after crop harvest. After two seasons of GLSA enrollment, both aeration porosity and bulk density were improved by GLSA relative to ACR fields with aeration porosity being 24% greater and bulk density 7% lower in GLSA. The results suggest that GLSA rotations in productive agricultural fields within the Fraser River delta provide an alternative to continued ACR that can improve soil structure and reduce compaction after only two seasons of establishment.

Relationship between drylands development and some soil properties

Land degradation and changing rangeland to dryland has important effects on ecosystems and soil properties. This process decline soil structure and increases runoff and erosion. Because of increasing manipulation in Iran rangelands, this research was conducted to study the effects of land use change from rangeland to dryland and abandoned dryland, on the basis of some soil factors including clay, silt and sand percent and mean weight diameter (MWD) of soil aggregates in western Iran, Zagros rangelands. Soil samples were collected in August 2016 from two depths of 0–20 and 20–50 cm in three land uses. Findings showed that this land use change affected soil properties significantly as in dryland clay, silt percent and mean weight diameter of soil aggregates were reduced and sand percent was increased. In abandoned drylands soil properties will improve gradually. Finally according to our results land use changes affected soil characteristics and this can be used in ecosystem management.

Variability of physical attributes in tropical weathered soil cultivated with irrigated beans (Phaseolus vulgaris L.)

Soil physical attributes are affected by several events. The ability to identify the variation of those attributes can be used to decide the best crop management. Although it is known that smaller grids are more representative, predicting the least number of points while maintaining accuracy is a tool that might reflect a gain in yield and time. The aims of this study were to evaluate the spatial physical variability and to define the minimum sampling density in a tropical Typic Haplustults soil using a scaled semivariogram in a central pivot area with pinto bean (Phaseolus vulgaris L.) after the eighth bean harvest in Cristalina, Goias State. Soil samples were collected at a regular grid of 10-m intervals, totaling 180 points, and at depths of 0.00–0.10 m, 0.10–0.20 m, and 0.20–0.30 m to determine total sand content (TS), silt (SIL), clay (CL), water-dispersed clay (WDC), mean weight diameter of soil aggregates (MWD), soil penetration resistance (PR), soil macroporosity (Ma), soil microporosity (Mi), and soil bulk density (BD). The results demonstrated that management promoted superficial soil compaction with increasing BD and Mi and decreasing Ma and TP. The scaled semivariogram demonstrated similarity between attributes in the three studied soil layers, evidencing strong spatial dependency. The sample density showed a strong influence of WDC in the irrigated soil properties. Adoption of a scaled semivariogram is a strategy that can be used to determine a minimum number of points that represents the spatial variability of soil physical attributes and to assist the best management in irrigated soils.

Dynamic study of infiltration rate for soils with varying degrees of degradation by water erosion

Ultisols, widely distributed in tropical and subtropical areas of south China, are suffering from serious water erosion, however, slope hydrological process for Ultisols under different erosional degradation levels in field condition has been scarcely investigated. Field rainfall simulation at two rainfall intensities (120 and 60 mm/h) were performed on pre-wetted Ultisols with four erosion degrees (non, moderate, severe and very-severe), and the hydrological processes of these soils were determined. The variation of soil infiltration was contributed by the interaction of erosion degree and rainfall intensity (p < 0.05). In most cases, time to incipient runoff, the decay coefficient, steady state infiltration rate, and their variability were larger at the high rainfall intensity, accelerating by the increasing erosion severity. Despite rainfall intensity, the infiltration process of Ultisols was also significantly influenced by mean weight diameter of aggregates at the field moisture content, soil organic carbon and particle size distribution (R2 > 30%, p < 0.05). The temporal erodibility of surface soil and soil detachment rate were significantly and negatively correlated with infiltration rate (r < -0.32, p < 0.05), but less significant correlation was observed between sediment concentration and infiltration rate for most soils, especially at the high rainfall intensity. The variation of surface texture and soil compactness generated by erosion degradation was the intrinsic predominant factors for the change of infiltration process of Ultisols. The obtained results will facilitate the understanding of hydrological process for degraded lands, and provide useful knowledge in managing crop irrigation and soil erosion.

Freeze–thaw cycles effects on soil physical properties under different degraded conditions in Northeast China

Freeze–thaw cycles alter soil properties markedly and cause a subsequent change in soil erosion, however previous studies about freeze–thaw cycles’ influence on soil physical properties were restricted to simulating runoff and soil loss on cropping slopes in cold regions and failed to invoke responses of soils under different degraded conditions to freeze–thaw cycles. This study was designed to compare and quantify the responses of different degraded soils to freeze–thaw cycles in laboratory setting. The soil conditions were divided into five types: original profile, degraded profile, parent profile, deposited profile and compacted surface. Samples were collected from the black soil region in Northeast China and were frozen (− 12 °C for 12 h) and then thawed (8 °C for 12 h) for certain times. Samples without freeze–thaw cycles were treated as control group. Porosity, aggregate mean weight diameter, saturated hydraulic conductivity and water retention curves were tested for control and experimental samples. Results showed that porosity and saturated hydraulic conductivity significantly increased (maximum for degraded profile), while mean weight diameter decreased (maximum for compacted surface) compared with control group. After 30 freeze–thaw cycles, remaining water contents increased in deposited and original profiles, while decreased in compacted surface. Generally, well-structured soils are more difficult to be broken by repeated FTCs. The first freeze–thaw cycle displayed evident influence on soil physical properties under original profile, and at least one threshold of cycle time (between 5 and 20) existed. These findings may help improve understanding the functional mechanism of freeze–thaw cycles on soil erosion processes.

Long-Term Effects of Different Passages of Vehicular Traffic on Soil Properties and Carbon Storage of a Crosby Silt Loam in USA

The passage of vehicles with heavy axle loads causes soil compaction, and this adversely affects soil properties and crop yield. The adverse effects can persist for several years due to significant changes in key soil properties. However, the mechanisms of the aforementioned effects are not well understood for conservation agriculture (CA) (e.g., no-till (NT)) wherein the use of heavy machinery is considerably common. Therefore, known compaction forces (0 Mg load for compaction (NT-0, control), two passages of 2.5 Mg water wagon axle load (NT-2), and four passages of 2.5 Mg water wagon axle load (NT-4)) were applied to all the plots annually for 20 consecutive years. The experiment was established in 1997 at the Waterman Agricultural and Natural Resources Laboratory (WANRL), Ohio State University, Columbus, Ohio. Each treatment was replicated thrice. Soil samples were obtained in November 2016 to determine the effects of variations in the axle load and vehicular passages on carbon (C) and nitrogen (N) storage and selected soil properties of a Crosby silt loam soil under NT-based corn-soybean rotation with residue retention in Central Ohio, USA. Three locations were also randomly selected in an adjoining natural woodlot (WL) soil plot and sampled (30 m away from the compaction field) to compare the effects of vehicular traffic on soil under NT with WL soil. Results revealed that soil bulk density (ρb) and total porosity at 0–10 and 10–20 cm depths were not affected by the passages of vehicular traffic for 20 years under the NT system. The penetration resistance (PR) (1.86 and 2.03 MPa at 0–10 and 10–20 cm soil depths, respectively) was significantly higher under NT-4 compared with that under other treatments. Saturated hydraulic conductivity at 0–10 and 10–20 cm soil depths ranged from 19.7 to 31.4 and 18.5 to 29.5 mm d−1, respectively, across all the treatments. The proportion of macroaggregates (> 0.25 mm) and microaggregates (< 0.25 mm), mean weight diameter and geometric mean diameter of aggregates, pH, electrical conductivity, and C and N contents and storage did not differ significantly between the treatments at either of the sampling soil depths. The data indicated that 2 to 4 passages of vehicles with 2.5 Mg of axle load did not cause significant compaction of the Crosby silt loam under NT compared with that under natural WL. Therefore, the continuous cultivation of row crops with NT and residue retention is feasible with passages of vehicular traffic for well-drained soils in Central Ohio.

Gypsum amendment effects on micromorphology and aggregation in no-till Mollisols and Alfisols from western Ohio, USA

Synthetic gypsum, a by-product of electricity generation, is used as a soil amendment to overcome water ponding, improve soil and water quality, improve field conditions to support farm equipment, and reduce the variability of crop yield in no-till fields by improving hydrology. Gypsum is a source of soluble calcium (Ca) that improves physical properties of the soil by promoting clay aggregation, thereby increasing water infiltration rates and movement through the soil profile. Undisturbed soil samples from Brookston and Celina soils in Ohio, USA were collected to a depth of 75 cm in agricultural fields treated with gypsum for 0, 4, and 12 years to determine changes in chemical and physical properties. Gypsum applications increased exchangeable Ca and Ca: Mg ratios, and promoted clay flocculation and improved soil structure. Mean weight diameter of aggregates increased with gypsum treatment at most depths in both soils. Micromorphological analysis showed variations in porosity (ɸ), pore size distribution, pore shape and aggregate size related to gypsum treatment, soil, and soil depth. There were no consistent responses to years of gypsum application. Gypsum treated soils had higher porosity than untreated soils in all depths <75 cm and a higher percentage of micropores and mesopores compared to the control. Also, gypsum treated soils had larger aggregates than the control for all soil depths examined. Aggregates <100 μm predominated in the Brookston control soils, and < 200 μm aggregates dominated the Celina control soils. However, there was no prevailing aggregate size for gypsum treated soils. In conclusion, our study found positive effects of gypsum on most properties measured; although, not consistently related to years of gypsum applications to both soils.

Changes on soil structural stability after in natura and composted chicken manure application

PurposeMany studies evaluate the effect of successive applications of chicken manure on soil attributes. In Brazil, the commercialization of this waste is common, implying on its sporadic use instead of many applications at the same area. The short-term effects of a single application of chicken manure and the role of its composting on soil structural stability are not fully understood. This study investigated application of in natura (uncomposted) and composted chicken manure on the structural stability of a Rhodic Ferralsol after a short period following single application.MethodsThe experiment was performed in a Rhodic Ferralsol in Londrina, Paraná. Brazil. We applied in natura and composted chicken manure at doses of 4.5, 9.0, 13.5, and 18.0 Mg ha−1 plus a control without application. Soil samples were collected after 185 days at the 0.0–20.0 cm layer for laboratorial analysis.ResultsThe composting of chicken manure did not affect soil structural stability. Chicken manure did not alter water-dispersible clay (bar{x}=21.7%), but increased the mean weight diameter of water-stable aggregates (MWD = 5.43 + 0.068 × dose) through the agglomeration of aggregates with 0.5–4 mm into 8–19 mm.ConclusionEven after a short period of 185 days, the application of chicken manure increases the structural stability of Rhodic Ferralsols and its composting, in the way performed by many farmers, is not associated with the improvement of soil structural stability in short-term. However, other advantages arise from the composting of the manure and need to be considered prior its use.

Effects of maize straw and its biochar application on organic and humic carbon in water-stable aggregates of a Mollisol in Northeast China: A five-year field experiment

In agricultural ecosystems, one optimized crop residue management practice, i.e., incorporating biochar produced from crop residues via pyrolysis to the soil, is considered a promising technology for mitigating climate change and improving soil quality. However, the potential mechanisms are still not well known. In this study, a five-year (2011–2015) field experiment in a Mollisol of Northeast China that included four treatments, i.e., CK (no fertilizer), NPK (mineral nitrogen, phosphorus and potassium fertilizers), NPKS (NPK plus maize straw) and NPKB (NPK plus maize straw-derived biochar), was conducted to evaluate the effects of maize straw and its derived biochar application on the following: 1) the size distribution and water stability of soil aggregates; 2) the concentrations of organic and humic carbon (C) in bulk soil and water-stable aggregate fractions; and 3) the chemical compositions of organic and humic C in water-stable aggregate fractions. Compared with the CK and NPK treatments, the proportion of macroaggregates (>0.25 mm) [mainly large macroaggregates (>2 mm)] increased whereas the proportions of microaggregates (0.25–0.053 mm) and silt + clay fractions (<0.053 mm) decreased in NPKS and NPKB treatments, resulting in the mean weight diameter (MWD) of soil aggregates being higher under NPKS and NPKB treatments than under CK and NPK treatments. The concentrations of organic and humic C in bulk soil and aggregate fractions were also generally higher under NPKS and NPKB treatments than under CK and NPK treatments. The treatment effects were more apparent for NPKB than for NPKS. With respect to other treatments, the NPKB treatment significantly increased the ratios of macroaggregate- to microaggregate-associated organic C as well as humin C. The solid-state 13C cross-polarization magic-angle-spinning (CPMAS) NMR spectra of small macroaggregates (2–0.25 mm) and its humic acid fraction showed that the NPKS treatment did not alter the proportions of the C functional groups. In contrast, the NPKB treatment clearly decreased the proportions of alkyl C and O-alkyl C but increased the proportion of aromatic C, resulting in the alkyl C/O-alkyl C and hydrophobic C/hydrophilic C ratios being higher whereas the aliphatic C/aromatic C ratio was lower under NPKB than under other treatments. These findings indicate that the application of maize straw biochar enhanced soil aggregate stability and aggregate-associated organic and humic C concentrations. Biochar C was preferentially incorporated into macroaggregates and its humin fraction with respect to microaggregates. Moreover, the molecular structure of small macroaggregates and its HA fraction became more stable, hydrophobic and aromatic. Therefore, physical protection through organic C in aggregate fractions, physical-chemical protection through the encapsulation of humic C within aggregate fractions, and physical-biochemical protection through recalcitrant alkyl C and aromatic C within aggregate fractions may be the primary mechanisms for C preservation in biochar-amended soil. Our results suggested that maize straw biochar application was an effective strategy based on the comprehensive goal of mitigating climate change and improving soil quality in Mollisols of Northeast China.

How relationships between soil organic matter parameters and soil structure characteristics are affected by the long-term fertilization of a sandy soil

Refining our understanding of how soil structure develops is important because soil structure has a major influence on plant growth. Recent studies show positive correlations between soil organic matter and soil structure. However, the question remains: how are the relationships between soil organic matter (SOM) parameters and soil structure characteristics affected by the long-term fertilization of a sandy soil? In contrast to most other studies on SOM vs. soil structure, the present study is composed of long-term field experiments (a total of 3 experiments) with durations of 25, 41 and 94 years. In this paper, the impact of the long-term application of mineral fertilizers and manure on the SOM and soil structure of a sandy soil is quantified, and the relationships between the SOM and soil structure of a sandy soil with a dependence on the length of fertilizer application are determined. Soil samples were collected from all three long-term field experiments in central Poland, which were located at Skierniewice experimental station including a 94-year-old experiment with mineral fertilization, a 41-year-old experiment with mineral fertilization and a 25-year-old experiment with mineral fertilization + farmyard manure (FYM) in a 4-year cycle. In the spring of 2017, soil samples were collected (Co – no fertilizers, NPK – NPK fertilizers, CaNPK – CaNPK fertilizers). In the 94-year-old experiment, the content of soil organic carbon (SOC) in Co, NPK and CaNPK was 4.07, 5.89 and 5.99 g kg−1, respectively. An increase in the SOC content under fertilization was also found in the other two experiments. In the 25-year-old experiment, the SOC contents in FYM, FYM + NPK and FYM + CaNPK were 6.07, 8.36 and 7.63 g kg−1, respectively, and in the 41-year-old experiment, the SOC contents in Co, NPK and CaNPK were 6.38, 10.1 and 7.80 g kg−1, respectively. The content of labile carbon (CL) increased significantly in the fertilized treatments only in the 94-year-old experiment. The contents of humic substances significantly increased in the soil of fertilized treatments in the 25- and 41-year-old experiments. In all fertilized treatments, the humus quality significantly decreased. After 94 years of mineral fertilization, the content of water-stable macroaggregates (WSAma) in size fractions > 5 and 5–2 mm was significantly higher in the NPK than in the Co and CaNPK treatments. After 94 years of mineral fertilization, the mean weight diameter of aggregates for dry sieving (MWDd) differed between Co (0.41) and both treatments of mineral fertilization (NPK: 0.88; CaNPK: 1.70). The application of FYM with CaNPK resulted in a statistically significant decrease in aggregate stability (Sw) in the 25-year-old experiment. For Co and NPK treatments in the 41-year-old experiment, the contents of WSAma > 5 mm were 41% and 51% lower, respectively, whereas the content of WSAma 5–3 mm was lower by 40% and 50%, respectively, which was higher than that for the CaNPK treatment. The aggregate stability significantly decreased due to NPK application in the soil of the 41-year-old experiment. The number of correlations between SOM parameters and the soil structure decreased in the following order: 94-year-old experiment with mineral fertilization > 41-year-old experiment with mineral fertilization > 25-year-old experiment with mineral fertilization + FYM.