Showing papers in "Soil & Tillage Research in 2016"

In situ effects of biochar on aggregation, water retention and porosity in light-textured tropical soils

Abstract: Biochar (BC) has been reported to improve soil physical properties mainly in laboratory and greenhouse pot experiments. Here we study, under field conditions, the effect of BC and its particle sizes on soil aggregate stability, bulk density (BD), water retention, and pore size distribution in two experiments in Zambia. A) Farmer practice experiment in sandy loam with maize cob BC in conservation farming planting basins under maize and soybeans crops. B) Maize cob and rice husk BC particle size experiments (≤0.5, 0.5–1 and 1–5 mm particle sizes) in loamy sand and sand. In the farmer practice experiment, BC increased aggregate stability by 7–9% and 17–20% per percent BC added under maize and soybeans crops respectively ( p p p ≤ 0.01). In the maize cob BC particle size experiment after one growing season, dose was a more important factor than particle size across the soils tested. Particle size of BC was more important in loamy sand than in sand, with ≤0.5 and 1–5 mm sizes producing the strongest effects on the measured properties. For example, BD decreased while total porosity increased ( p p

Impacts of rainfall intensity and slope gradient on rill erosion processes at loessial hillslope.

Abstract: Rill erosion constitutes one of the mechanisms of soil loss by water on agricultural land. However, studies on hillslope rill erosion characteristics and its intrinsic mechanisms are still unclear. The objectives of this study were to investigate the impacts of rainfall intensity and slope gradient on hillslope rill erosion processes, rill flow hydraulic characteristics and dynamic mechanisms. A soil pan (10 m long, 1.5 m wide and 0.5 m deep and with an adjustable slope gradient of 0–30°) was subjected to rainfall simulation experiments under three rainfall intensities (50, 75 and 100 mm h −1 ) of representative erosive rainfall and three typical slope gradients (10, 15 and 20°) on the Loess Plateau of China. The results showed that rill erosion exhibited significant contributions to hillslope soil erosion, occupying 62.2–84.8% of hillslope soil loss. The equation between the rill erosion rate with rainfall intensity and slope gradient was generated, which indicated that the impacts of rainfall intensity on hillslope rill erosion were greater than those of slope gradient. For the experimental treatments, the mean headward erosion rates varied between 2.2 and 8.2 cm min −1 , and they increased with an increase in either rainfall intensity or slope gradient. Most rill flow belonged to turbulent and subcritical flow regimes. The critical shear stress, the critical stream power, and the critical unit stream power of rill occurrence were 0.986 Pa, 0.207 N m −1 s −1 , and 0.002 m s −1 , respectively. Additionally, hillslope rill erosion was sensitive to rill flow velocity and stream power. In a word, rainfall intensity and slope gradient exhibited important impacts on rill erosion processes and its hydrodynamic characteristics. Therefore, preventing rainfall erosion and weakening slope gradient effects through conservation tillage are useful for reduction of rill erosion at loessial hillslopes.

Crop yield, plant nutrient uptake and soil physicochemical properties under organic soil amendments and nitrogen fertilization on Nitisols

Abstract: Sustaining soil fertility and enhancing food production on smallholder farms is a great challenge in sub-Saharan Africa. The effects of organic amendments and nitrogen fertilizer on soil physicochemical properties and barley yield were investigated in the central Ethiopian highlands. The treatments were factorial combinations of no organic amendment (control), 10 t ha −1 biochar only (B), 10 t ha −1 compost only (Com), 10 t Com ha −1 + 2 t B ha −1 and 10 t ha −1 co-composted biochar-compost (COMBI) as main plots, and five N fertilizer levels (0, 23, 46, 69 and 92 kg ha −1 ) as sub-plots, with three replicates at two sites (Holetta and Robgebeya) both on Nitisols in the 2014 cropping season. Application of organic amendments and N fertilizer all significantly improved soil fertility and barley yield. The highest yield, chlorophyll content, number of productive tillers and nutrient uptake were obtained from the Com + B soil amendment at Holetta and from Com at Robgebeya. Mean grain yield responses of barley to the organic amendments were 30–49% at Holetta and 51–78% at Robgebeya, compared to the control. Fertilizer N significantly increased grain yield, chlorophyll content and N uptake at both locations. The highest grain yield obtained was at 69 kg N ha −1 at Holetta and at 92 kg ha −1 at Robgebeya. The organic amendment by N fertilizer interaction significantly influenced grain yield at both sites. Com + B and 69 kg N ha −1 addition resulted in the highest grain yield (5381 kg ha −1 ) at Holetta, whereas Com and 92 kg N ha −1 resulted in the highest grain yield (4598 kg ha −1 ) at Robgebeya. Organic amendments significantly improved soil properties through increases in soil water content, soil organic carbon (SOC), cation exchange capacity (CEC) and pH (0–20 cm depth). Addition of B, Com and B + Com increased SOC and CEC by 23–27% and 20–24% at Holetta and 26–34% and 19–23% at Robgebeya compared to their respective initial values. Soil pH increased from the initial value of 5.0 to 5.6 at Holetta and from 4.8 to 5.4 at Robgebeya at harvest due to biochar soil amendment. Grain yield was significantly correlated with total biomass, number of productive tillers, SOC and CEC. We conclude that application of organic amendments optimizes soil physicochemical properties and will help sustain barley yields in the Ethiopian highlands. The use of B, Com or Com + B may substantially reduce the amount of mineral fertilizer required for the sustainable production of barley in the long term.

Estimating the soil clay content and organic matter by means of different calibration methods of vis-NIR diffuse reflectance spectroscopy

Abstract: The selection of calibration method is one of the main factors influencing measurement accuracy of soil properties estimation in visible and near infrared reflectance spectroscopy. In this study, the performance of three regression techniques, namely, partial least-squares regression (PLSR), support vector regression (SVR), and multivariate adaptive regression splines (MARS) were compared to identify the best method to assess organic matter (OM) and clay content in the salt-affected soils. One hundred and two soil samples collected from Northern Sinai, Egypt, were used as the data set for the calibration and validation procedures. The dry samples were scanned using a FieldSpec Pro FR Portable Spectroradiometer (Analytical Spectral Devices, ASD) with a measurement range of 350–2500 nm. The spectra were subjected to seven pre-processed techniques, e.g., Savitzky–Golay (SG) smoothing, first derivative with SG smoothing (FD-SG), second derivative with SG smoothing (SD-SG), continuum removed reflectance (CR), standard normal variate and detrending (SNV-DT), multiplicative scatter correction (MSC) and extended MSC. The results of cross-validation showed that in most cases MARS models performed better than PLSR and SVR models. The best predictions were obtained using MARS calibration methods with CR prep-processing, yielding R2, root mean squared error (RMSE), and ratio of performance to deviation (RPD) values of 0.85, 0.19%, and 2.63, respectively, for OM; and 0.90, 5.32%, and 3.15, respectively, for clay content.

Effects of straw incorporation on the soil nutrient contents, enzyme activities, and crop yield in a semiarid region of China

Abstract: The current cropping system of conventional tillage and stubble removal in the northwestern Loess Plateau of China is known to decrease the water use efficiency and crop yield because of soil infertile and degradation. To determine the effects of straw incorporation on the soil fertility and crop yield, we conducted experiments in semiarid areas of southern Ningxia for 4 years (2007–2010). Four treatments were tested: (i) no straw incorporation (CK); (ii) incorporation of maize straw at a low rate of 4500 kg ha −1 (L); (iii) incorporation of maize straw at a medium rate of 9000 kg ha −1 (M); and (iv) incorporation of maize straw at a high rate of 13500 kg ha −1 (H). After straw incorporation for four years, the results showed that variable straw amounts had different effects on the soil fertility indices, where H treatment had the greatest effect. Compared with CK, the average soil available N, total N, available P, total P, and SOC levels under straw incorporation treatments were 27.5%, 10.8%, 16.6%, 5.2%, and 9.8% higher in 0–40 cm soil layers, especially in 0–20 cm soil layer. The straw incorporation treatments average increased the soil urease, phosphatase, and invertase activities levels by 19.6%, 39.4%, and 44.3% in 0–60 cm soil layers, according to the following order: H > M > L > CK. And higher yields coupled with higher nutrient contents were achieved with H, M and L compared with CK, where these treatments increased the crop yields by 22.5%, 22.8%, and 10.6%, and water use efficiency by 34.6%, 30.7%, and 15.7%, respectively. Our results suggest that straw incorporation (especially in rate of 13500 kg ha −1 ) is an effective practice for improving the soil fertility and increased crop yield in semiarid region of China.

Adsorption and desorption of phosphorus in subtropical soils as affected by management system and mineralogy

Abstract: Phosphorus added to soil is only partly available to crops because it is sorbed to some extent by various soil components. The aim of this study was to assess the influence of mineralogy and soil management (either conventional tillage, CT, or no-tillage, NT) on the maximum P adsorption capacity (P max ), remaining P (P rem ), and maximum desorbable P ( β ) in a Rhodic Paleudult, a Rhodic Hapludox and a Humic Hapludox, all from southern Brazil. P max was estimated from the Langmuir equation describing the sorption curve for soil samples and β from a first-order kinetic equation describing successive P extraction with an anion-exchange resin following incubation of the soils with an amount of P equivalent to 30% of P max (P added ). P max and P rem were significantly correlated with the content of iron oxides (mainly in goethite, Gt). P max was lower under NT than under CT in the Rhodic Paleudult and Rhodic Hapludox. On the other hand, P rem was lower under CT than under NT, and exhibited significant differences between the 0–5 and 5–10 cm layers under NT. Parameter β peaked in the soil with the highest P max but the β /P added ratio was highest in the Rhodic Paleudult, which was the soil with the lowest content in iron oxides. These results suggest that the soil with the highest P max and Gt content (viz., the Humic Hapludox) supplies plants with P at a lower rate than the other two despite its high P desorption potential.

The effects of raindrop impact and runoff detachment on hillslope soil erosion and soil aggregate loss in the Mollisol region of Northeast China

Abstract: Soil aggregates profoundly influence soil fertility and soil erosion. A large number of studies have showed that soil aggregate loss was mainly affected by raindrop impact and runoff detachment during hillslope erosion process; however, few attempts have been made to investigate which one plays the dominant role in soil aggregate loss. Therefore, a laboratory study was conducted to quantify the effects of raindrop impact and runoff detachment on soil erosion and soil aggregate loss during hillslope erosion processes. A soil pan (8 m long, 1.5 m wide, and 0.6 m deep and with an adjustable slope gradient of 0–35°) was subjected to rainfall simulation experiments under two soil surface conditions: with and without raindrop impact through placing nylon net over soil pan. Two rainfall intensities (50 and 100 mm h−1) of representative erosive rainfall and two slope gradients (5 and 10°) in the Mollisol region of Northeast China were subjected to two soil surface conditions. The results showed that raindrop impact played the dominant role in hillslope soil erosion and soil aggregate loss. Soil loss caused by raindrop impact was 3.6–19.8 times higher than that caused by runoff detachment. The contributions of raindrop impact to hillslope soil erosion were 78.3% to 95.2%. As rainfall intensity and slope gradient increased, soil loss caused by raindrop impact and runoff detachment both increased. The loss of each size aggregate was greatly reduced by 46.6–99.4% after eliminating raindrop impact. Meanwhile, the contributions of raindrop impact to the >2, 1–2, 0.5–1, 0.25–0.5 and <0.25 mm soil aggregate loss were 79.1% to 89.7%. Eliminating raindrop impact reduced rainfall intensity effect and increased slope gradient impact on aggregate loss.

Maize yield and soil fertility with combined use of compost and inorganic fertilizers on a calcareous soil on the North China Plain

Abstract: Excessive N fertilization is a problem in the intensive cropping systems on the North China Plain. Proper N management is essential to maximize N efficiency and sustain agricultural production while minimizing negative impacts on the environment. The aim of the present study was to investigate N dynamics, maize yields and soil fertility in response to short term compost application and straw return vs. inorganic fertilization. A field experiment (2012–2014) was conducted for three years on a calcareous soil in Quzhou county, Heibei province, north China. There were four treatments: unfertilized control (T1), inorganic fertilizer (100% NPK, T2), compost (cattle wastes) + 70% NPK (T3), T3 + wheat straw (T4). No significant differences in biomass accumulation or N uptake among the fertilized treatments were observed across the maize growing season. Compost application for three years tended to increase grain yields particularly in the second and third years, and the average yield increase was approximately 7–15% over T2. Residual Nmin down the soil profile (1 m) in the compost treatments (T3 and T4) decreased by 50% deeper in the soil (60–100 cm depth) at the maize harvest in 2014. Compared to T2, the compost treatments significantly increased NUE and soil available P and K contents. Correlation analysis indicates that maize yield in 2014 was significantly correlated with soil available P and K and with soil organic carbon (SOC). Overall, straw return did not have a significant influence on any measured parameters in either soil or plant samples. Our results demonstrate that 30% replacement of N fertilizer by compost is an effective nutrient management strategy to maintain N uptake and yield of maize, reduce N loss and also increase soil fertility. A considerable increase in invertase activity in the compost treatments highlights that the critical importance of integrating the management of carbon and nitrogen for sustainable agricultural production in this region of highly intensive production.

Long term effect of conservation agriculture in maize rotations on total organic carbon, physical and biological properties of a sandy loam soil in north-western Indo-Gangetic Plains

Abstract: Maize-based crop rotations are advocated as alternate to rice-based systems in South Asia due to better suitability for diverse ecologies, higher yields with less water use and more palatable maize fodder compared to rice, and increased demand of maize from piggery and poultry industries. Alternate tillage and crop establishment practices are important management strategies for tackling the issues of soil health deterioration and over exploitation of underground water resources, particularly in rice based intensive crop rotations. The conservation agriculture (CA) based tillage and crop establishment practices such as zero tillage (ZT) and permanent raised beds (PB) hold potential to enhance soil organic carbon (SOC), physical and biological properties for sustainability of soil health. Therefore, a long term study was conducted to evaluate the twelve combinations of tillage practices (03) and irrigated intensive maize based crop rotations (04) on organic carbon, physical properties and microbial biomass and enzymatic activities of a sandy loam (Typic Haplustept) soil in north-western India. The tillage practices consisted of ZT, PB and conventional tillage (CT) in main plots and four diversified intensive maize based crop rotations (MWMb: Maize-Wheat-Mungbean, MCS: Maize-Chickpea- Sesbaina , MMuMb: Maize-Mustard-Mungbean, MMS: Maize-Maize- Sesbania ) in sub plots. In this study we analysed the SOC, physical and biological properties of soil at various depths after 7 years of continuous ZT, PB and CT in diversified maize rotations. Compared to CT plots, the soil physical properties like water stable aggregates (WSA) > 250 μm were 16.1-32.5% higher, and bulk density (BD) and penetration resistance (PR) showed significant (P β Glucosidase and Alkaline phosphatase was also recorded in the CA based treatments. Significant (P Sesbania ) with winter legume/cereal in crop rotations were observed on SOC,WSA, BD, PR and K sat at 0–15 and 15–30 cm depths. Interaction between tillage and crop rotations were significant (P

Long-term monitoring of soil management effects on runoff and soil erosion in sloping vineyards in Alto Monferrato (North–West Italy)

Abstract: Long-term runoff and soil erosion data have been collected from differently managed field-scale vineyard plots within the “Tenuta Cannona Experimental Vine and Wine Center of Regione Piemonte”, located in the Alto Monferrato vine production area (NW Italy) The primary intent of the program was to evaluate the effects of agricultural management practices on the hydrologic, soil erosion, nutrient transport and soil compaction processes in vineyards Field runoff data have been collected for every event since the year 2000 until now Sediment and nutrient concentrations in water have been also monitored Regarding soil properties and initial conditions, surveys have been carried out to investigate spatial and temporal variability of soil bulk density, soil saturated conductivity, soil water content, and penetration resistance The Cannona Data Base (CDB) includes data for more than 300 runoff events and over 90 soil loss events; moreover, periodic measurements for soil physical characteristics are included for the three plots Runoff and sediment yield showed high annual and seasonal variability and were strongly affected by the adoption of different soil management in the vineyard inter-rows, especially after some years of observation Grass cover reduced runoff by at least 37%, in comparison with management by tillage, and average annual sediment yield ranged from 18 Mg ha −1 year −1 to 207 Mg ha −1 year −1 , respectively for the “grass covered” and the “reduced tillage” vineyards Furthermore, results showed the effect of the adopted soil management on soil properties The Cannona Data base (CDB) can be accessed via a website ( http://sustagtocnrit/indexphp/cannona-db ) supported by the IMAMOTER-CNR

Soil physical quality on tillage and cropping systems after two decades in the subtropical region of Brazil

Abstract: Sustainability of crop production systems depends on the preservation of soil physical quality over time. This study aimed to determine long-term effects of soil tillage and cropping systems on physical attributes and hydraulic properties of an Oxisol in Southern Brazil, emphasising management practices to preserve or improve the soil structure quality under no-tillage system. The experiment was conducted in randomized block design, using a 5 × 2 factorial arrangement (tillage × cropping systems), with four replications. The five tillage systems consisted of conventional tillage (CT); minimum tillage, chiselled soil every year (MTC1); minimum tillage, chiselled soil every three years (MTC3); continuous no-tillage for 11 years (NT11); and continuous no-tillage for 24 years (NT24). The two cropping systems consisted of annual crop sequence with wheat in the winter and soybean in the summer, designated as crop succession (CS); and a 4-year crop rotation (CR) with white lupine-maize—black oat-soybean—wheat-soybean—wheat-soybean in winter–summer, respectively. Undisturbed soil cores were collected from 0–0.10; 0.10–0.20 and 0.20–0.30 m of soil depth, to determine the soil bulk density (BD), total porosity, macroporosity, microporosity, pore size distribution and classes, soil water retention curve, infiltration rate and field-saturated hydraulic conductivity. There was no interaction between tillage and cropping systems, and no effects of cropping systems on soil physical and hydraulic properties. Regardless the cropping system, chiselling effects on soil physical properties persisted for less than 22 months, and were restricted to below 0.20 m soil depth. The CT resulted in soil pulverization at 0–0.10 m depth, leading to lower BD and higher macroporosity compared to the other soil tillage systems. At layers below 0.10 m, CT increased the BD and reduced the macroporosity to critical levels for crop growth. Continuous use of no-tillage improved soil physical quality mainly at deeper layers, and provided higher plant available water retention in the soil at matric potentials ranging from −10 to −200 kPa in relation to CT and MTC1. The adoption of NT improves soil physical quality and plant available water over time, and periodic soil chiselling aiming to disrupt compacted layers should be avoided because of its effects on reducing soil compaction level are short-lived.

Conceptual framework for capacity and intensity physical soil properties affected by short and long-term (14 years) continuous no-tillage and controlled traffic

Abstract: Recent studies have shown harmful effects of soil compaction in no-tillage system (NTS), but there are indications that soil structure improves with time of NTS adoption. We formulated the hypothesis that topsoils of NTS initially have worse soil physical conditions than those under conventional systems, but these conditions gradually improve with time also down to deeper depth, even when the soil is wheeled by farm machinery. Our objective was to evaluate the effect of a long-term no-tillage system and machine traffic on soil mechanical and hydraulic properties. The treatments and soil conditions consisted of five periods since the last conventional tillage (or age of NTS) in a Hapludox: 0.2,1.5, 3.5, 5 and 14 years, with and without traffic; named recent tillage, and initial, intermediate, transition and stabilized NTS phases. Soil samples were collected from soil layers 0-7, 7-14 and 14-21 cm depth to determine soil porosity, precompression stress, compressibility coefficient, saturated hydraulic conductivity, air permeability, water retention curve, bulk density and organic carbon. Conventional tillage of soil previously under no tillage significantly affected soil capacity properties, resulting in high macroporosity and deformation susceptibility, low bulk density and precompression stress. Intensity properties were affected initially by an increased soil pore obstruction, negatively affecting air permeability and saturated hydraulic conductivity, from 0 to 21 cm soil depth. However, after five years of no-tillage there was an increase in microporosity and, although small, in soil organic carbon, especially in the 0-7 cm soil layer; thus, soil water retention and soil intensity properties (like soil water and air permeability) were also improved, regardless of farm machinery traffic. Over time, soil reconsolidation occurred, which resulted in reduction of the compressibility coefficient and degree of compactness, mainly in the upper layers (07 and 7-14 cm). However, in the deepest layer with the least disturbance, the degree-of-compactness and bulk density increased. The evolution of physical properties and processes (from recent tillage to stabilized NTS phase) for no-tilled soil is proposed for controlled and uncontrolled traffic systems as a framework based on field data for capacity and intensity soil properties. The process of creating aggregates is represented, at first, by an increased number of contact points before they are re-loosened and strengthened at the same time by a rearrangement of particles, reducing aggregate bulk density but increasing soil strength at the same time. The framework is divided into 4 phases: initial (1.5 years), intermediary (3.5 years), transitional (5 years), and stabilized (14 years) conditions. (C) 2015 Elsevier B.V. All rights reserved.

Changes in microstructural behaviour and hydraulic functions of biochar amended soils

Abstract: Biochar is increasingly used on agricultural soils to enhance productivity and to sequester carbon. However, there is limited research that directly quantifies the underlying mechanisms, particularly those assessing structural changes in amended soils. Also, there is scanty information on the long-term effect of biochar treatment on hydraulic response of soils. Our objective in this study therefore is to determine the effect of biochar treatment on two different soil types and to evaluate the influence on hydrological and mechanical properties that drive aggregate formation and stability. Test substrates were prepared by adding 2, 5 and 10% (by dry mass) of high temperature pyrolysed (HTP) biochar to fine-sand or sandy loamy silt soil material. The repacked cores were exposed to four cycles of wetting and drying in an experiment spanning about 300 days. Changes in the saturated hydraulic conductivity, aggregate sorptivity swelling and shrinkage behaviour, and microstructural stability during desiccation were also investigated. The results indicated that biochar amendment alters the pore structure with the saturated hydraulic conductivity being significantly increased (p < 0.05) in the sandy loamy silt. Repeated wetting and drying significantly increased (p < 0.05) the repellency index of the amended substrates. Moreover micro structural stability was enhanced as the amount of biochar was increased and at lower matric potential. The partial loss of inter-particle cementation at a given pore water pressure due to increasing biochar amount was compensated by the noticeable addition of organic carbon. The combined effects of pore re-arrangement, enhanced particles surface area and improved microstructural stability in the amended soils produces better soil-plant-water environment. These findings proof that the effects of biochar amendment on pore structure, aggregation and stabilization will depend on the amount of biochar, the texture of the original soil material and the number of wetting and drying (WD) cycles. (C) 2015 Elsevier B.V. All rights reserved.

Leaching and fractionation of heavy metals in mining soils amended with biochar

Abstract: Contaminated mining soils might pose risk to the environment due to leaching of heavy metals into ground water, especially under acid conditions. Biochar might be an option for remediation of contaminated mining soils. The aim of this study was to evaluate the effect of soil acidification and biochar (BC) application on Cd, Pb and Zn mobility and chemical fractionation in two mining soils (A and B). Fifteen leaching columns per soil were packed, applying the following treatments: soil + 3% BC; acidified soil; acidified soil + 3% BC and control soil + CaCO 3 . The control treatment was constituted by the original polluted soil (soil A or soil B). BC was produced by slow pyrolysis at 700 °C from sugarcane straw. Ten leaching events were performed and Cd, Pb, Zn and pH were determined for each leaching. A sequential extraction procedure was performed after leaching was finished. The following fractions were evaluated: mobile, exchangeable, bound to Mn oxide, bound to OM, bound to Fe oxide and residual. In the polluted control soil metal mobility was very low. In acidified soils metal mobility increased drastically and BC application reduced the Cd (57–73%), Pb (45–55%) and Zn (46%) concentrations in the leachate. With the sequential extraction it was observed that Cd was mostly bound to the mobile fraction (15–35%) and exchangeable fraction (7–38%), Pb was mainly bound to the Mn oxide fraction (32–70%) and OM (31–43%) and Zn was principally bound to the residual fraction (31–68%). Cadmium presented the highest mobility index (33–53%) and Pb the lowest (1–3%), which is related to the fractions they are bound in the soil. Field studies would be necessary to confirm the effectiveness of BC application on heavy metals’ retention, prior to large scale application.

Effects of cattle manure compost combined with chemical fertilizer on topsoil organic matter, bulk density and earthworm activity in a wheat–maize rotation system in Eastern China

Abstract: Cattle manure compost (CMC) combined with chemical fertilizer (CF) was applied to a wheat–maize rotation field, in Eastern China, to assess soil physical and chemical properties, biological activity and land productivity. Indicators of organic matter, carbon storage and sequestration, bulk density, water content, total N content and earthworm population from topsoil (0–20 cm) were quantified. This consecutive study (2009–2014) was carried out on the base of the same total N, P, K application rate (375.0 kg N ha −1 yr −1 , 92.4 kg P 2 O 5 ha −1 yr −1 and 316.3 kg K 2 O ha −1 yr −1 ) in each treatment that was fertilized. Six treatments were designed as: (1) CK, without any fertilizer; (2) NPK, 100% CF; (3) NPKM1, 25% CMC combined with 75% CF; (4) NPKM2, 50% CMC combined with 50% CF; (5) NPKM3, 75% CMC combined with 25% CF; and (6) CM, 100% CMC. The results demonstrated that organic matter, water content, total N content and earthworm density from topsoil were significantly and positively ( P ≤ 0.01) related to CMC input, with significantly negative correlation being observed between soil bulk density and CMC input. The average annual yield of the wheat–maize rotation system significantly increased ( P ≤ 0.05) in NPK, NPKM1, NPKM2, NPKM3, and CM compared with CK, with the highest yield being obtained from NPKM1. Applying merely CF not only led to the lower SOM, water content and total N content, but also resulted in negative effects on earthworm activity, while CMC alleviated such negative effects. Our finding may help to increase food supply by improving soil conditions with organic fertilizer compost application.

Dynamics of soil labile organic carbon fractions and C-cycle enzyme activities under straw mulch in Chengdu Plain

Abstract: Soil labile organic carbon fractions (LOCF) are valuable indicators of changes in soil quality and soil total organic carbon (TOC), and they are easily influenced by changes in soil management practice. To explore the sensitivity of LOCF and their enzymatic conversion under straw mulch for scientific management of crop straw use on the Chengdu plain, a straw mulch field experiment was conducted to observe the LOCF changes and explore their relationships with C-cycle enzymes during wheat growth. The treatments included no fertilizer or straw (Control), only mineral fertilizer (MF), 10% rice straw nitrogen (N) plus 90% fertilizer N (RS1), 20% rice straw N plus 80% fertilizer N (RS2), 30% rice straw N plus 70% fertilizer N (RS3), 100% rice straw (RS). The water-soluble organic carbon (WSOC) and microbial biomass carbon (MBC) under straw treatments in the 0–20 cm soil layer were significantly higher than those of Control and MF treatments from the seedling stage, and showed significant differences among straw treatments from the tillering stage. Correspondingly, the dissolved organic carbon (DOC) and permanganate oxidized carbon (POXC) showed no obvious differences among straw treatments in most growth stages. Therefore, WSOC and MBC were the most sensitive indicators for assessing soil organic carbon (SOC) change under straw mulch. Moreover, stepwise multiple linear regression revealed that cellulase and β-glucosidase were significantly positive impact factors for LOCF in the two soil layers, while polyphenol oxidase had both positive and negative impacts on WSOC at different soil layers, and peroxidase was a negative factor for LOCF.

Soil physical properties, yield trends and economics after five years of conservation agriculture based rice-maize system in north-western India

Abstract: Rice-maize system (RMS) is emerging as dominant option for diversification of existing rice-wheat systems in Asia due to better suitability and higher yields of maize compared to wheat after long duration rice cultivars, and increasing demand of maize from poultry and fish industries. The conventional practice of cultivation of RMS is input intensive, deteriorates soil health and is less profitable. Conservation agriculture (CA) based management practices such as dry direct-seeded rice (DSR), zero tillage (ZT) and residue retention may hold potential to increase yields, reduce costs and increase farmers' profits in RMS. Therefore, replicated 5-year field study was conducted to evaluate the effects of six combinations of three tillage and crop establishment (TCE) techniques and two residue management options on soil physical properties, system productivity and economics of an irrigated RMS in north-west India. The TCE techniques consisted of transplanted puddled rice (TPR) followed by conventionally tilled maize (CTM); CTDSR followed by CTM; and ZTDSR followed by ZTM in main plots and two residue management options; removal of residues of both the crops (−R) and partial residue (5 t ha −1 ) either retained at soil surface on ZT plots or incorporated into the soil in CT plots (+R) for both rice and maize in sub-plots. Compared with TPR/CTM-R, soil physical parameters such as water-stable aggregates >0.2 mm were 89% higher, and bulk density, penetrometer resistance and infiltration rate showed significant ( P −1 in ZTDSR/ZTM (+R) over conventional practice. Grain yield of TPR was 5 –7% higher compared to CTDSR and ZTDSR, which was attributed to increased number of grains panicle −1 and grain weight. Maize yield under ZTDSR/ZTM was significantly higher by 4.0% and 14.2% compared to CTDSR/CTM and TPR/CTM, respectively, due to increase in number of cobs plant −1 and grain number cob −1 . Gradual improvement in soil physical health in ZTDSR/ZTM +R system resulted in higher and stable crop productivity (17.4–17.6 kg m −3 ) with higher profitability in different years over conventional system. Our study demonstrates that CA based management practices can be adopted for RMS on sandy loam or similar soils for sustaining soil and crop productivity in South Asia.

Buried straw layer plus plastic mulching reduces soil salinity and increases sunflower yield in saline soils

Abstract: Soil salinization is a major limitation to high crop yield in saline soils of the Hetao Irrigation District of Inner Mongolia, China. As such, people are forced to use better and more effective approaches to soil management due to scarcity of freshwater and the adverse effects of climate. A three-year field experiment was conducted to investigate the effects of buried straw layer and plastic film mulch on soil moisture, soil salinity and sunflower ( Helianthus annuus L.) yield in saline soils. Four field management practices were designed: bare ground (BG), plastic mulch (PM), buried maize straw layer (12 t ha −1 ) at a depth of 40 cm (SL), and combined application of plastic mulch and straw layer burial (PM + SL). Soil water at the 0–40 cm layer was higher under SL and PM + SL than under BG and PM within 45 days after sowing (DAS) but the reverse occurred thereafter. Compared to PM and BG, both SL and PM + SL significantly decreased the salt content of the upper 40 cm depth at sowing. Furthermore, PM + SL invariably decreased the salt content throughout the growth period of sunflower. In contrast, SL and PM moderately increased the salt content during the later growth period. Compared with BG, SL significantly decreased salt accumulation in the off season. Over the three years, the highest seed and biomass yield, 100-seed weight and head diameters of sunflower were obtained from the PM + SL plots. The average seed yield (3198 kg ha −1 ) under PM + SL exceeded the yields under BG, PM and SL by 51.9, 5.9 and 35.7% respectively. Therefore, PM + SL may be an efficient practice for reducing soil salinity and increasing sunflower yield in the Hetao Irrigation District and other similar ecological areas.

Effects of long-term (23 years) mineral fertilizer and compost application on physical properties of fluvo-aquic soil in the North China Plain

Abstract: The influence of compost and mineral fertilization on soil organic carbon (SOC) and physical properties varied greatly in previous studies because of differences in site conditions such as climate and soil. This study was conducted as a long-term (1989–2012) field experiment to evaluate the effects of mineral fertilization and compost application on SOC content and some physical properties of an intensively cultivated sandy loam soil in the North China Plain. The experiment consisted of seven treatments: organic compost (OM); half organic compost plus half mineral fertilizer NPK (1/2OM1/2NPK); mineral fertilizer NPK (NPK); mineral fertilizer NP (NP); mineral fertilizer PK (PK); mineral fertilizer NK (NK); and unfertilized control (CK), each with four replicates. Relative to CK, the SOC content was higher in all of the compost and mineral fertilizer treatments, but increments in SOC under the compost application treatments were higher than mineral fertilization application. Compost application (OM, 1/2OM1/2NPK) decreased soil bulk density and increased total porosity significantly in comparison with that in the CK plots. Soil bulk density and total porosity for the mineral fertilization treatments, except NP, did not significantly differ from CK. The lowest penetration resistance at 0–20 cm soil depth was observed in the NK plots, and the highest penetration resistance was found in the CK plots. Compost application increased the total amount of water-stable macro-aggregates (>0.25 mm); however, MWD was not significantly affected by compost application. The MWD in the NK treatment was lower than in CK by 0.2 mm, while its variation among NPK, OM, 1/2OM1/2NPK, NP, PK, and CK was not significant. The compost- and mineral fertilizer-treated soil had 34.6–91.7% higher volume of macropores than the CK soil. The OM and 1/2OM1/2NPK-treated soil had a significantly higher proportion of small pores (

Effects of gasification biochar on plant-available water capacity and plant growth in two contrasting soil types

Abstract: Gasification biochar (GB) contains recalcitrant carbon that can contribute to soil carbon sequestration and soil quality improvement. However, the impact of GB on plant-available water capacity (AWC) and plant growth in diverse soil types still needs to be explored. A pot experiment with spring barley (Hordeum vulgare L.) was conducted to investigate the effect of soil amendment by 1% straw and wood gasification biochar (SGB and WGB), respectively, on AWC and plant growth responses under two levels of water supply in a temperate sandy loam and a coarse sandy subsoil. In the sandy loam, the reduced water regime significantly affected plant growth and water consumption, whereas the effect was less pronounced in the coarse sand. Irrespective of the soil type, both GBs increased AWC by 17–42%, with the highest absolute effect in the coarse sand. The addition of SGB to coarse sand led to a substantial increase in plant biomass under both water regimes: shoot growth by 40–165% and root growth by 50–57%. However, no positive effects were achieved by the addition of WGB. In the sandy loam, soil application of GB had no or negative effects on plant growth. Our results suggest that SGB has considerable potential for enhancing crop productivity in coarse sandy soils by increasing soil water retention and improving root development.

Long-term tillage, rotation and perennialization effects on particulate and aggregate soil organic matter

Abstract: Perennialization and reducing tillage have increased soil organic matter (SOM) in both aggregate and particulate organic matter (POM) in short-term and small scale experiments, but there is a need for investigations into the long-term effects of agroecosystems on these dynamic pools of SOM. The objectives of this study were to investigate how management varying in crop rotation, tillage intensity and organic management from 1990 to 2013 has affected POM and aggregate C and N, and assess the relationship between these SOM fractions and biomass C inputs. We hypothesized that tillage, low biomass inputs, and annual crops in rotation would be associated with decreased POM and aggregate C and N. Soil from six systems from the Wisconsin Integrated Cropping Systems Trial (WICST) on a Phaeozem, or Mollisol, was sampled in 2013: Continuous Maize ( Zea mays L.), Maize–Soybean [ Glycine max (L.) Merr.], Organic Grain (including maize, soybean, and wheat [ Triticum aestivum L.] sequentially seeded with oats [ Avena sativa L.] and berseem clover [ Trifolium alexandrinum L.]), Conventional Forage (three years alfalfa [ Medicago sativa L.] followed by maize), Organic Forage (two years’ alfalfa with oats nurse crop followed by maize), and Pasture (rotationally grazed, seeded to a mixture of red clover [ Trifolium pratense L.], timothy [ Phleum pretense L.], smooth bromegrass [ Bromu sinermis L.] and orchardgrass [ Dactylis glomerata L.]). Among all systems at 0–25 cm depth, we found significantly greater concentrations of POM-C in the Pasture (4.4 g C kg −1 soil) and POM-N in Pasture (0.30 g N kg −1 soil) and Organic Forage (0.25 g N kg −1 soil). The Organic Grain system had lower concentrations of macroaggregates and lower stocks of C and N within macroaggregates. Across all systems, belowground biomass C input was significantly positively correlated with POM-C, POM-N, and aggregate C and N. The data supported our hypothesis in part, as results indicate that frequent cultivation in the form of tine weeding and rotary hoeing for weed control in Organic Grain rotation is likely disrupting formation of aggregates and storage of C and N therein. However, in systems that were chisel plowed every one to three years, high biomass C inputs maintain POM-C and POM-N and soil aggregation equivalent to the fully perennial system.

Soil organic carbon and total nitrogen stocks under different land uses in a hilly ecological restoration area of North China

Abstract: In hilly area of North China, massive deforestation of natural forests and extensive use of agricultural lands have resulted in severe soil degradation. Soil organic carbon (SOC) and total nitrogen (STN) are crucial to soil quality. However, knowledge on the efficiency of changes in SOC under various land uses in these areas is very limited. To address this problem, a study was conducted in Songjiagou Catchment of Mount. Taiyue to evaluate the impact of land use change on SOC sequestration and STN accumulation. The results showed that compared with cropland, the SOC stock of shrub land was 10.8% higher and that of forestland 39.8% higher. Comparative values were 55.9% and 64.7% higher for nitrogen accumulation over the entire soil profile. Among that, the topsoil layer in cropland contained 40.7% of the SOC stock and this layer of the secondary shrub 43.6%. It appears that inappropriate tillage practices and anthropogenic disturbances imply a considerable loss of carbon sequestration. Ground litter biomass and live biomass were considered as the main influence factors of STN and SOC variance in surface soil. As well, soil properties, such as bulk density and pH value, were found to have significant and negative effect on SOC and STN concentrations. Therefore, we conclude that the change of land use from cropland to secondary shrub and restoration of forest plantation can improve SOC and STN concentrations and stocks.

Winter cover crops in soybean monoculture: Effects on soil organic carbon and its fractions

Abstract: Fil: Duval, Matias Ezequiel. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Bahia Blanca. Centro de Recursos Naturales Renovables de la Zona Semiarida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiarida; Argentina

Use of compost as an alternative to conventional inorganic fertilizers in intensive lettuce (Lactuca sativa L.) crops—Effects on soil and plant

Abstract: Intensive crop over-fertilization is causing the diffuse contamination of superficial and ground-waters by nitrates in many Mediterranean areas. At the same time this practice is also damaging the soil in the long-term. In this work the feasibility of using composts as total or partial substitutes for conventional inorganic fertilization (CIF) was evaluated in two successive crops of lettuce (Lactuca sativa L.), one of the most consumed vegetables in Europe. The aim was to offer alternative agricultural practices that are more environmentally friendly. Treatments consisting of various rates of inorganic and organic fertilizers (composts) were assayed in quadruplicate on a sandy loam soil classified as Haplic Calcisol in Southern Spain. Macro- and micronutrients and heavy metal concentrations were analysed in soil and plant leaves. Parameters such as soil basal respiration (BR), microbial biomass C (Cmic) and dehydrogenase (DHA) and hydrolase activities, indicators of soil microbial abundance and activity, were also determined after each crop. After the second lettuce crop, certain physical soil properties such as aggregate stability and soil water holding capacity were also determined. In the first crop lettuce yields in the compost-treated soils did not significantly (p≤ 0.05) differ from the yields of CIF-treated soils. In the second crop, however, lettuce yields were higher in organically treated soils than in soils receiving only inorganic fertilization. Organic fertilizers were able to supply sufficient nutrients to achieve similar yields as those obtained with additional inorganic fertilizer. After the second crop, organically treated soils also showed higher C, N, P concentrations and higher Cmic, BR and DHA than soils receiving conventional inorganic fertilization as well as improved physical conditions (a higher percentage of stable soil aggregates and a greater water holding capacity). Also after the second lettuce crop, compost-treated soils showed significantly higher β-glucosidase and phosphatase activity than CIF-treated soils. Furthermore, lettuces grown in compost-treated soils showed significantly lower leaf nitrate concentration than lettuces grown in soil receiving CIF, thus reducing the potential toxicological risks associated with consuming nitrate-rich foods. Moreover, compost fertilization did not increase the concentration of heavy metals in lettuce leaves. Results confirm that manure and sewage sludge composts can be used as an alternative to inorganic fertilization in lettuce crop cultivation, leading to similar or even higher yields and reducing nutrient-leaching risks, while improving soil chemical, physical and microbiological properties.

Effect of straw management on carbon sequestration and grain production in a maize–wheat cropping system in Anthrosol of the Guanzhong Plain

Abstract: Straw return is a widely recognized strategy for increasing soil organic carbon (SOC) sequestration and improving soil quality and crop productivity. A 4-year-long field experiment established in 2008 was conducted to investigate the effects of the combined return of maize and wheat straw on the SOC stock at a soil depth of 0–20 cm in an intensive summer maize (Zea mays L.)–winter wheat (Triticum aestivum L.) cropping system in the Guanzhong Plain. The study involved four treatments with four replicates: low return of maize and wheat straw (ML–WL), low return of maize straw and high return of wheat straw (ML–WH), high return of maize straw and low return of wheat straw (MH–WL), and high return of maize and wheat straw (MH–WH). Compared with the SOC stock in the pre-experimental soil, the SOC stock in the 0–20 cm soil layer decreased by 2.6% under the ML–WL treatment, and in contrast, increased by 1.9% in ML–WH and 14.4% in MH–WH. Similarly, the stabilization rate gradually increased from 2.4% in ML–WH to 10.0% in MH–WH, though an obvious decrease of 6.8% was found in the ML–WL treatment. A significant linear relationship (P < 0.05) was found between SOC sequestration and the cumulative plant-derived C input to the soil. A minimum C input of 4.07 Mg ha−1 year−1 was required to maintain the initial level of SOC. However, a significant relationship (P < 0.05) also existed between the cumulative plant-derived C input and non-sequestered C. Moreover, the ranking of the treatments with respect to yield and the sustainable yield index (SYI) of maize and wheat was ML–WL < ML–WH < MH–WL < MH–WH. The average SYI of maize and wheat reached a maximum value of 0.651 when the plant-derived C input was 10.51 Mg ha−1 year−1, which was higher than the maximum value (SYI of 0.64, plant-derived C input of 9.76 Mg ha−1 year−1) found in the MH–WH treatment. Although the high return of maize and wheat straw was the best treatment in this research, more suitable practices, such wheat straw return including longer stubble or maize straw return in combination with sub-soiling, might increase yield and soil C sequestration, ultimately achieving sustained agricultural development in this cropping system.

Changes in soil organic carbon fractions under integrated management systems in a low-productivity paddy soil given different organic amendments and chemical fertilizers

Abstract: Labile soil organic carbon fractions are important indicators of soil C dynamics, which is affected by different management practices. However, few studies have reported the short-term effect of a wide range of organic materials mulching on the distribution of soil total organic C (TOC) and its labile C pools in a low-productivity paddy soil. Our objective was quantify TOC and labile organic C fractions down a 0–30 cm soil profile in a 4-year field experiment receiving four organic amendments (spent mushroom compost, green manure, cattle manure and rice straw residues). Soil samples were taken from the 0–5 cm, 5–10 cm, 10–20 cm and 20–30 cm soil depths. Soil total organic carbon (TOC), total nitrogen (TN), microbial biomass C (MBC), particulate organic C (POC), potassium permanganate-oxidizable C (KMnO 4 -C) and dissolved organic C (DOC) were measured. Carbon management index (CMI) was also calculated. Among the four organic amendments, cattle manure showed the most profound effect on TOC, TN and labile organic C fractions and produced the highest 4-year average rice grain yield (9.67 t ha −1 ). The cattle manure combined with NPK resulted in the highest level of TOC (19.2 g kg −1 ) and TN (1.86 g kg −1 ) in the surface soil (0–5 cm). Additionally, KMnO 4 -C and MBC concentrations in the cattle manure plus NPK treatment were 1.3 and 1.5 times higher at the 0–5 cm depth, 1.4 and 1.6 times higher at the 5–10 cm depth, 1.2 and 1.4 times higher at the 10–20 cm depth compared to NPK fertilizer alone, respectively. However, POC was not sensitive to different management practices in the deeper soil layer (10–20 cm). DOC was not significantly affected by fertilization in the 0–20 cm soil layer, suggesting it was unsuitable as an early indicator of soil quality. Overall, the integrated use of cattle manure and NPK fertilizers is the most efficient management practice in improving carbon sequestering under current soil conditions. A long-term assessment is needed to confirm the most effective and sustainable management practice for improving rice grain yield and soil quality.

Modification of chemical and hydrophysical properties of two texturally differentiated soils due to varying magnitudes of added biochar

Abstract: The potential benefit of biochar as a soil conditioner to improve crop yield and simultaneously sequester carbon in the soil, is a subject of intense discourse. Biochar amendment of agricultural soils is presumed to improve water holding capacity of the soil, and enhance nutrient retention within the root zone. However, there are very few investigations which provide quantitative data and qualitative descriptions concerning the specific mechanisms driving these improvements in the properties of biochar-amended soils. In this study, the effect of different rates of biochar amendment on some chemical, physical and hydraulic properties of fine-sand and sandy loamy silt soils was investigated by adding 20, 50 and 100 g biochar kg(-1) (by dry weight). In order to evaluate the additional effects of biochar application, the initial hydrophobicity and rheological properties were also examined. The result showed that biochar amendment improved total carbon and aggregate properties. The available water capacity was significantly higher in the amended substrates, particularly in the amended fine sand. Saturated hydraulic conductivity of the sandy loam silt increased between 25% and 119%, but decreased in the fine sand between 23 and 82%. Moreover, biochar amendment of the sandy loamy silt improved particle to particle bonding and resulted in the development of weaker (compared with the unamended control) but more resilient aggregates which were better structured. With increasing rate of added biochar (>= 50- = 20 g kg(-1)) biochar, to the fine-sand induced particle rearrangements, which in combination with possible surface oxidation at the biochar-soil particles interphase, improved bonding in this originally non-cohesive soil. Beyond an amendment rate of 50 g biochar kg(-1) soil, we observed that most of the positive improvements, associated with the biochar treatment of the soils, were no longer significant and the aggregates became brittle and collapsed more easily. Our results therefore provide more detailed insights into the effect of biochar in agricultural soils depending on texture of the soil and the amount of added biochar. (C) 2016 Elsevier B.V. All rights reserved.

Do we really need large spectral libraries for local scale SOC assessment with NIR spectroscopy

Abstract: Near infrared (NIR) spectroscopy was used to predict the soil organic carbon (SOC) contents at local scale in eleven target sites For that, eight spectral libraries of different sizes (ranging from 3482 to 36 samples) were used to construct national, provincial and local scale models Inaccurate predictions were obtained except when the largest national library was used to construct the model We also obtained SOC predictions once the models were adapted to target sites characteristics For the models’ adaptation, we used a two-step approach consisting on spiking (as first step) and extra-weighting (as second step) The effect of spiking was small in larger-sized models and high in smaller-sized models, whereas the effect of extra-weighting was small in smaller-sized models and large in larger-sized models The very high accuracy obtained after models’ adaptation (R2 > 095; RPIQ > 548), regardless of the size of the spectral library, suggests that large spectral libraries are not needed for local scale SOC assessment These results have important implications regarding the way that NIR spectroscopy can result highly effective for land management and how users can focus and organize the analytical efforts

Effect of ten years of reduced tillage and recycling of organic matter on crop yields, soil organic carbon and its fractions in alfisols of semi arid tropics of southern India.

Abstract: Reducing tillage intensity and retaining residues are important components of conservation agriculture but in small holder systems in developing countries where crop residues have alternate uses such as fodder and fuelwood, recycling or external additions of organic matter may be a possible option. Information on impacts of long term reduced tillage on soil carbon, labile organic carbon fractions and their depth distribution is scant in drylands of semi arid regions. The effect of tillage intensity (CT—conventional tillage; RT—reduced tillage and MT—minimum tillage) and sources of nitrogen (100% OS: 100% of recommended N through organic source; 50% OS +50%IOS: 50% N through organic source and 50% N through inorganic source and 100% IOS: 100% N through inorganic source) on crop yields, soil organic carbon and C fractions in an Alfisol was assessed at the end of a 10 year long term experiment. Finger millet yields decreased significantly with reduction in tillage intensity (29%). Among N sources, highest yields were recorded with substitution of 50% of the N through organic source. After 10 years, the soil organic carbon (SOC) in 0–20 cm soil layer with MT was 11% higher than with CT. The labile fractions of carbon, viz. particulate organic carbon (POC), microbial biomass carbon (MBC) and permanganate oxidizable carbon (KMnO 4 -C) under MT were 47%, 16% and 43% higher, respectively, in comparison to CT in the 0–20 cm soil layer. The total carbon (TC) and total organic carbon (TOC) with MT were higher by 28% and 27% over CT and higher by 20% and 20% with 100%OS over 100% IOS. Labile carbon fractions revealed differential sensitivity and POC, MBC and KMnO 4 -C are sensitive indicators to detect short term management effects. Reducing tillage intensity and applying various N sources enhanced SOC marginally and the C sequestration rate varied from 62 to 186 kg ha −1 yr −1 . Based on the study it can be recommended for substitution of 50% of the recommended N with organic source as it increases crop yields and soil carbon and could be a potential alternative for residue retention for crops which have fodder value. Reducing the tillage intensity can enhance the SOC in semi arid rainfed systems but lower crop yields under MT is a concern which needs to be addressed in order to make these systems acceptable to the farming community.

Carbon and nitrogen mineralization in hierarchically structured aggregates of different size

Abstract: Soil organic matter pools are turned over at different rates, but uncertainty persists regarding how far the hierarchically organized soil structure controls the mineralization dynamics. To better understand carbon and nitrogen mineralization in undisturbed aggregate classes (coarse aggregates: 2–6.3 mm, fine aggregates: