Effect of Induced Soil Compaction on Changes in Soil Properties and Wheat Productivity under Sandy Loam and Sandy Clay Loam Soils: A Greenhouse Experiment

The continuous use of heavy machinery and vehicular traffic on agricultural land led to an increase in soil compaction, which reduces crop yield and deteriorates the physical conditions of the soil. A pot experiment was conducted under greenhouse conditions to study the effects of induced soil compaction on growth and yield of two wheat (Triticum aestivum) varieties grown under two different soil textures, sandy loam and sandy clay loam. Three compaction levels [C₀, C₁, and C₂ (0, 10 and 20 beatings)], two textural classes (sandy loam and sandy clay loam), and two genotypes of wheat were selected for the experiment. Results indicated that induced soil compaction adversely affected the bulk density (BD) and total porosity of soil in both sandy loam and sandy clay loam soils. Compaction progressively increased soil BD from 1.19 Mg m^?3 in the control to 1.27 Mg m^?3 in C₁ and 1.40 Mg m^?3 in C₂ in sandy loam soil while the corresponding increase in BD in sandy clay loam was 1.56 Mg m^?3 in C₁ and 1.73 Mg m^?3 in C₂ compared to 1.24 Mg m^?3 in the control. On the other hand, compaction tended to decrease total porosity of soil. In case of sandy loam, porosity declined by 5% and 17% in C₁ and C₂, respectively, and declined in sandy clay loam by 29% and 54%, respectively. Averaged over genotypes and textures, shoot length decreased by 15% and 26% at C₁ and C₂, respectively, and straw yield decreased by 21% and 61%, respectively. The compaction levels C₁ and C₂ significantly decreased grain yield by 12% and 41%, respectively, over the control. The deleterious effect of compaction was more pronounced on root elongation and root mass, and compaction levels C₁ and C₂ decreased root length by 47% and 95% and root mass by 41% and 114%, respectively, over the control. Response of soil texture to compaction was significant for almost all the parameters, and the detrimental effects of soil compaction were greater in sandy clay loam compared to sandy loam soil. The results from the experiment revealed that soil compaction adversely affected soil physical conditions, thereby restricting the root growth, which in turn may affect the whole plant growth and grain yield. Therefore, appropriate measures to avoid damaging effects of compaction on soil physical conditions should be practiced. These measures may include soil management by periodic chiseling, controlled traffic, conservation tillage, addition of organic manures, and incorporating crops with deep tap root systems in a rotation cycle.     

土壤紧实度对伴矿景天生长及镉锌吸收性的影响研究

采集黏土、壤黏土和砂质壤土,分别设置无压实、低紧实度及高紧实度3种处理,通过盆栽试验研究了土壤紧实度对Cd、Zn超积累植物伴矿景天生长和Cd、Zn吸收性的影响。结果表明,与无压实处理比较,砂质壤土、壤黏土和黏土中伴矿景天地上部生物量在低紧实度下显著下降66.8%~83.5%、59.9%~60.4%和57.9%~71.4%;高紧实度处理却显著提高了伴矿景天的根系活力(142%~241%)。高紧实度处理显著降低了壤黏土上伴矿景天地上部Cd和Zn含量,但低紧实度对砂质壤土和黏土上伴矿景天地上部Cd和Zn含量无显著影响。与无压实处理比较,低紧实度显著降低了砂质壤土、壤黏土和黏土上伴矿景天的Cd吸取量,分别下降50.4%~73.8%、61.4%~74.9%和43.4%~63.3%,Zn吸取量下降48.7%~79.5%、73.6%~79.0%和46.1%~63.5%;土壤紧实度对壤黏土上伴矿景天的镉锌吸取效率影响最明显。     

Directional strength in aggregates as affected by aggregate volume and by a wet/dry cycle

Reduction of aggregate size in the upper, tilled soil layer as a result of one wet/dry cycle was observed for sandy soil and clay soils. Bulk density of aggregates tended to increase as their size diminished for the clay after the wet/dry cycle, whereas similar changes in bulk density for the loam were observed only for aggregates smaller than 5.6 cm. Slaking and water-drop impact seem to be the major factors in reducing the aggregate size of the sandy loam, while swelling and shrinkage affect clay aggregates of all size groups, but only aggregates smaller than 4.0 mm for the sandy loam. Tensile strength of the sandy loam aggregates was related to the axis along which the stresses were applied. A definite directional dependence of tensile strength was observed, e.g. the shorter the axis, the larger the tensile strength. The directional strength dependence was apparently not affected by one wet/dry cycle.     

A study of some tillage practices for sustainable crop production in India

Soil tilth has been defined in terms of a ‘Physical Index’ based on the product of the ratings of eight physical properties — soil depth, bulk density, available water storage capacity, cumulative infiltration or apparent hydraulic conductivity, aggregation or organic matter, non-capillary pore space, water table depth and slope. The Physical Index and a tillage guide were used to identify the tillage requirements of different soils varying in texture from loamy sand to clay in the semi-arid tropics. The physical index was 0.389 for a loamy sand, 0.518 for a black clay loam and 0.540 for a red sandy loam soil and the cumulative rating indices in summer and winter seasons were 45 and 44 for loamy sand, 52 and 51 for red sandy loam and 54 and 52 for black clay loam soils, respectively. The compaction of the loamy sand by eight passes of a 490 kg tractor-driven roller (0.75 m diameter and 1.00 m length) increased the physical index to 0.658 and chiselling of the red sandy loam and black clay loam increased the physical indices to 0.686 and 0.729, respectively. The grain yields of rainfed pearl millet and guar and irrigated pearl millet, wheat and barley increased significantly over the control (no compaction) yields by compaction.

The chiselling of the soils varying in texture from loamy sand to clay at 50 to 120-cm intervals up to 30–40 cm depth, depending upon the row spacing of seedlines and depth of the high mechanical impedance layer, increased the grain yields of rainfed and irrigated maize on alluvial loamy sand, rainfed maize on alluvial sandy loam and red sandy loam, rainfed sorghum on red sandy loam and black clay loam, irrigated sorghum on black clay loam and rainfed black gram on red sandy loam, pod yield of rainfed groundnut, tuber yield of irrigated tapioca and fresh fruit yield of rainfed tomato on red sandy loam and sugarcane yield on black clay soil, significantly over the yields of no-chiselling systems of tillage such as disc harrow and country plough.     

Pot study on wheat growth in saline and waterlogged compacted soil: I. Grain yield and yield components

The information of soil compaction effects on growth and yield of crops for saline and waterlogged soils is scanty. A pot experiment was conducted on a sandy clay loam soil during 2001–2002 to study the interactive effects of soil compaction, salinity and waterlogging on grain yield and yield components of two wheat (Triticum aestivum) genotypes (Aqaab and MH-97). Compaction was achieved at 10% moisture level by dropping 5 kg weight, controlled by a tripod stand for 20 times from 0.6 m height on a wooden block placed inside the soil filled pots. Soil bulk density of non-compact and compact treatments was measured as 1.21 and 1.65 Mg m⁻³, respectively. The desired salinity level (15 dS m⁻¹) was developed by mixing the required amount of NaCl in soil before filling the pots. Waterlogging was developed by flooding the pots for 21 days both at tillering and booting stages. Compaction aggravated the adverse effect of salinity on grain yield and different yield components of both the wheat genotypes. Average reduction in grain yield was 44% under non-compact saline conditions against 76% under compact saline conditions. Similarly, the reduction was about 20% more for 100 grain weight and shoot length, 30% more for number of spikelets per spike, 37% more for number of tillers per plant, and 32% more for straw weight in compact saline treatment than in non-compact saline treatment. Compaction alone caused a reduction of 36% in grain yield. The effect of waterlogging on grain yield and yield components was mostly not changed significantly due to compaction. Rather waterlogging mitigated the effect of compaction for most of the yield components except for number of spikes per plant. Therefore, as for normal soils, the cultivation of salt-affected soils should employ implements and techniques which minimize compaction of root zone soil. The effect of soil compaction can also be minimized by light irrigations with short intervals and by using a stress tolerant crop genotype.     

Physico-mechanical properties and yield of silage corn as affected by soil compaction and tillage methods

Experimental investigations were conducted over three years to test the hypothesis that soil compaction affects the physical and mechanical properties of corn ears and corn cobs. Field experiments were made on sub-drained clay and sandy loam soils at Macdonald College Farm in Quebec Province of Canada. The mechanical properties of corn ears and corn cobs were determined from quasi-static force-deformation analysis performed with a universal Instron testing machine.

The results showed that soil compaction treatments did not significantly influence corn cob elastic modulus and strength in simple bending nor in radial compression. Cob moisture content did not significantly change as a result of the application of various traffic treatments. However, corn cob diameter and pith diameter were both significantly affected by soil compaction.

Corn ear moisture content and bending strength were not significantly affected by soil compaction. However, corn ear yield in all three years was found to be dependent on the amount of soil compaction applied.

Also studied were the effects of various tillage methods in ameliorating the deleterious effects of soil compaction on crop yield and crop quality. It is concluded that a judicious choice of tillage machinery system can minimize the reductions in ear yield due to soil compaction.     

Soil and residue management effects on arable cropping conditions and nitrous oxide fluxes under controlled traffic in Scotland 1. Soil and crop responses

Soil compaction can affect crop growth and greenhouse gas emission and information is required of how both these aspects are affected by compaction intensity and weather. In this paper we describe treatments of compaction intensity and their effects on soil physical conditions and crop growth in loam to sandy loam cambisol soils. Soil conditions and crop performance were measured over three seasons in a field experiment on soil compacted by wheels on freshly ploughed seedbeds. Ploughing buried the chopped residues of the previous crop. After ploughing, traffic was controlled such that the experimental plots received wheel traffic only as treatments. The overall objective was to discover how the intensity and distribution of soil compaction just before sowing influenced crop performance, soil conditions and emissions of nitrous oxide. Compaction treatments were zero, light compaction by roller (up to 1 Mg m⁻¹) and heavy compaction by loaded tractor, (up to 4.2 Mg). The experiment was located at Boghall, near Edinburgh (860 mm average annual rainfall) for the first two seasons under spring and winter barley (Hordeum vulgare L.) and in a drier area at North Berwick (610 mm average annual rainfall) for the third season under winter oil-seed rape (Brassica napus L.). Heavy compaction in dry soil conditions had little effect on crop growth. However, in wet conditions heavy compaction reduced air porosity, air permeability and gas diffusivity, increased cone resistance and limited winter barley growth and grain yield. Heavy compaction in wet conditions reduced winter barley yields to 7.1 Mg ha⁻¹, in comparison to 8.8 Mg ha⁻¹ in the zero compaction treatment. The compaction status of the top 15 cm of soil seemed to be particularly important. Loosening of the top 10 cm of soil immediately after heavy compaction restored soil conditions for crop growth. However, zero seed bed compaction gave patchy and uneven crop emergence in dry conditions. Both zero and light compaction to a target depth of 10 cm gave similar crop productivity. Maintenance of a correct compaction level near the soil surface is particularly important for establishment and overwintering of barley and oil seed rape.     

Nitrogen availability to grain sorghum from organic and inorganic sources on sandy and clayey soil surfaces in a greenhouse pot study

In a greenhouse pot study, we examined the availability of N to grain sorghum from organic and inorganic N sources. The treatments were¹⁵N-labeled clover residues, wheat residues, and fertilizer placed on a sandy clay loam and loamy sand soil surface for an 8-week period. Soil aggregates formed under each soil texture were measured after 8 weeks for each treatment. Significantly greater ¹⁵N was taken up and recovered by grain sorghum in sandy clay loam pots compared with loamy sand pots. Greater ¹⁵N recovery was consistently observed with the inorganic source than the organic sources regardless of soil texture or time. Microbial biomass C and N were significantly greater for sandy clay loam soil compared with the loamy sand. Microbial biomass ¹⁵N was also significantly greater in the sandy clay loam treatment compared to the loamy sand. The fertilizer treatment initially had the greatest pool of microbial biomass ¹⁵N but decreased with time. The crop residue treatments generally had less microbial biomass ¹⁵N with time. The crop residues and soil texture had a significant effect on the water-stable aggregates formed after 8 weeks of treatments. Significantly greater water-stable aggregates were formed in the sandy clay loam than the loamy sand. Approximately 20% greater water-stable aggregates were formed under the crop residue treatments compared to the fertilizer only treatment. Soil texture seemed to be one of the most important factors affecting the availability of N from organic or inorganic N sources in these soils.Contribution from the MissouriAgricultural Experiment Station, Journal Series No.12131     

Guidelines for safe trafficking and cultivation, and resistance–density–moisture relations of three disturbed soils from Alberta

The Atterberg limits and the Proctor compaction test are used by engineers for classifying soils and for predicting stability of building foundations. Field capacity and wilting point (agronomic limits) are used to indicate available water for plant uptake. Few studies have related the engineering criteria to the agronomic ones with regard to compaction hazard for soils. This study investigated the relationships between Atterberg limits, agronomic limits and the critical moisture content (moisture content at Proctor maximum density) for three disturbed soils (sandy loam and clay loam soils from a reclaimed Highvale mine site, and a silt loam soil from a grazing site at Lacombe) of different textures. Relationships between bulk density, moisture content and penetration resistance for these soils were also investigated. For the sandy loam and loam soils, the field capacity was close to the critical moisture content but lower than the plastic limit. Therefore, cultivation of these two soils at moisture contents close to field capacity should be avoided since maximum densification occurs at these moisture contents. Overall, the critical moisture content or field capacity would be a better guide for trafficking of sandy loam and loam textured soils than the Atterberg limits. For the clay loam, field capacity was within the plastic range. Thus trafficking this soil at field capacity would cause severe compaction. In conclusion, either field capacity or plastic limit, whichever is less, can be used as a guide to avoid trafficking at this moisture content and beyond. For the sandy loam and loam soils penetration resistance significantly increased only with increased bulk density (P≤0.05). For the clay loam soil, penetration resistance was positively related to bulk density and negatively related to moisture content.     

Critical limits of the degree of compactness and soil penetration resistance for the soybean crop in N Brazil

In agricultural fields soil compaction is a major cause of physical degradation. Degree of compactness (DC) is a useful parameter for characterizing compaction and the response of crops for different soils. The objectives of this study were: (1) to identify the critical DC and PR values for soybean [Glycine max (L.) Merrill] using plant growth variables and (2) to verify the relationship between DC and PR, and assess which parameter is recommended for the evaluation of soil compaction. The study was conducted in a greenhouse in a completely randomized factorial design of 4 textures × 5 compaction levels for sandy loam and sandy clay loam soils, and 3 compaction levels for the clayey and very clayey soils. Soil samples were collected from the surface of a Xantic Kandiudox from the NE region of the State of Pará, Brazil. The DC was calculated from the maximum bulk density obtained by the Proctor test, and the PR curve was determined in undisturbed samples equilibrated in different matric potentials. The growth and development of the soybean was favored in the DC range of 80 to 85%, regardless of soil texture. The critical degree of compactness for the growth of soybean was around 98% regardless of soil texture, while the critical values for penetration resistance at field capacity varied according to soil texture and bulk density and were 28.2, 5.6, 3.5, and 5.2 MPa for the sandy loam, sand clay loam, clayey and very clayey soils, respectively. The root length was the plant growth variable most susceptible to soil compaction. Change in soil penetration resistance was poorly related with change in degree of compactness showing that one parameter cannot be replaced by the other. Because PR is quickly determined in field and have a direct relationship with plant growth, for the soils evaluated in this study we recommend the use of soil PR to assess the state of soil compaction.     

Soil and residue management effects on cropping conditions and nitrous oxide fluxes under controlled traffic in Scotland2. Nitrous oxide, soil N status and weather

Nitrogen from fertilisers and crop residues can be lost as nitrous oxide (N₂O), a greenhouse gas that causes an increase in global warming and also depletes stratospheric ozone. Nitrous oxide emissions, soil chemical status, temperature and N₂O concentration in the soil atmosphere were measured in a field experiment on soil compaction in loam and sandy loam (cambisols) soils in south-east Scotland. The overall objective was to discover how the intensity and distribution of soil compaction by tractor wheels or by roller just before sowing influenced crop performance, soil conditions and production and emissions of N₂O under controlled traffic conditions. Compaction treatments were zero, light compaction by roller (up to 1 Mg per metre of length) and heavy compaction by loaded tractor (up to 4.2 Mg). In this paper we report the effects on production and emissions of N₂O and relate them to soil and crop conditions. Nitrous oxide fluxes were substantial only when the soil water content was high (>27 g per 100 g). Fertiliser application stimulated emissions in the spring whereas crop residues stimulated emissions in autumn and winter. Heavy compaction increased N₂O emissions after fertiliser application or residue incorporation more than light or zero compaction. The bulk densities of the heavily and lightly compacted soils were up to 89% and 82% of the theoretical (Proctor) maxima. Higher soil cone resistances, temperatures and nitrogen availability and lower gas diffusivities and air-filled porosities combined to make the heavily compacted soil more anaerobic and likely to denitrify than the zero or lightly compacted soil. Compaction sufficient to increase N₂O emissions significantly corresponded with adverse soil conditions for winter barley (Hordeum vulgare L.) growth. Soil tillage, which ensures that soil compaction is no greater than in our light treatment and is confined to near the soil surface, may help to mitigate both surface fluxes of N₂O and losses to the subsoil.     

Physical treatment and reinoculation of soil: Effects on microorganisms and enzyme activities

Three soils, sandy loam, clay loam, and muck were subjected to different physical treatments, reinoculated with fresh soil and the effect of these treatments on the numbers of microorganisms and soil enzyme activities was studied. Soils were subjected to air-drying, freeze-drying, freezing, dry ice-freezing, autoclaving and oven drying. The results indicated that the microbial populations increased with some of the physical treatments after 2 or 7 days incubation, while, some of the treatments decreased the populations. Air-drying the clay loam inhibited urease and phosphatase activities. None of the treatments inhibited dehydrogenase activity in either the clay loam or the muck. However, a stimulatory effect after 4 days was evident in the muck with heat treatments. Heat treatments inhibited phosphatase activity in all soils and urease activity throughout the experiment in loams, whereas after 14 days, there was a rapid recovery of urease activity in the muck soil. Autoclaving resulted in a pronounced increase in C₂H₂ reduction in the three types of soils. Heating appears to have an effect in an organic soil where the formation of 2,3,5-triphenyltetrazolium formazan (formazan) and C₂H₄ were significantly increased.     

Soil carbon responses to past and future CO2 in three Texas prairie soils

Changes in soil carbon storage could affect and be affected by rising atmospheric CO₂. However, it is unlikely that soils will respond uniformly, as some soils are more sensitive to changes in the amount and chemistry of plant tissue inputs whereas others are less sensitive because of mineralogical, textural, or microbial processes. We studied soil carbon and microbial responses to a preindustrial-to-future CO₂ gradient (250–500 ppm) in a grassland ecosystem in the field. The ecosystem contains three soil types with clay fractions of 15%–55%: a sandy loam Alfisol, a silty clay Mollisol, and a black clay Vertisol. Soil and microbial responses to atmospheric CO₂ are plant-mediated; and aboveground plant productivity in this ecosystem increased linearly with CO₂ in the sandy loam and silty clay. Although total soil organic carbon (SOC) did not change with CO₂ treatment after four growing seasons, fast-cycling SOC pools increased with CO₂ in the two clay soils. Microbial biomass increased 18% and microbial activity increased 30% across the CO₂ gradient in the black clay (55% clay), but neither factor changed with CO₂ in the sandy loam (15% clay). Similarly, size fractionation of SOC showed that coarse POM-C, the youngest and most labile fraction, increased four-fold across the CO₂ gradient in the black clay, but increased by only 50% across the gradient in the sandy loam. Interestingly, mineral-associated C, the oldest and most recalcitrant fraction, declined 23% across the gradient in the third soil type, a silty clay (45% clay). Our results provide evidence for priming in this soil type, as labile C availability and decomposition rate (measured as soil respiration and soil C mineralization) also increased across the CO₂ gradient in the silty clay soil. In summary, CO₂ enrichment in this grassland increased the fast-cycling SOC pool as in other CO₂ studies, but only in the two high-clay soils. Priming in the silty clay could limit SOC accumulation after prolonged CO₂ exposure. Because soil texture varies geographically, including data on soil types could enhance predictions of soil carbon and microbial responses to future CO₂ levels.     

Quantification of the effects of soil compaction on water flow using dye tracers and image analysis

Abstract. Soil compaction has long been considered to be a problem in arable land, primarily because it causes damage to soil structure, which can lead to serious reduction in crop yields. However, few studies have sought to investigate the effects of soil compaction on the water transport regime of modified soil pore systems. We attempted to quantify the effects of soil compaction on the initiation of preferential flow by using dye tracers and image analysis. A laboratory methodology involving rainfall simulation enabled us to quantitatively evaluate differences in the mechanisms of water flow between two soil types at several degrees of compaction. The results suggested significant differences in the types of water flow pathways between clay loams and sandy loams at different extents of compaction. In the sandy loam, it was concluded that a high degree of compaction led to an increased likelihood of preferential flow, whereas a more uniform movement of soil water occurred at less compaction. By contrast, preferential routing of soil water was recorded in the clay loam, except at the highest measured compaction. The results indicate that the visual techniques of dye tracing and image analysis could enable improved understanding of flow pathways of soil water associated with soil compaction.     

Effect of Continuous Rice–Wheat Rotation on Soil Properties from Four Agro‐ecosystems of Indian Punjab

In Indian Punjab, rice–wheat is a dominant cropping system in four agro‐ecosystems, namely undulating subregion (zone 1), Piedmont alluvial plains (zone 2), central alluvial plains (zone 3), and southwestern alluvial plains (zone 4), varying in rainfall and temperature. Static and temporal variabilities in soil physical and chemical properties prevail because of alluvial parent material, management/tillage operations, and duration of rice–wheat rotation. A detailed survey was undertaken to study the long‐term effect of rice–wheat rotation on soil physical (soil separates, bulk density, modulus of rupture, saturated and unsaturated hydraulic conductivities, soil water content, and suction relations) and chemical (organic carbon, pH, electrical conductivity) properties of different textured soils (sandy clay loam, loam, clay loam, and silty clay loam) in these four zones of Punjab. Soil samples (of 0‐ to 30‐cm depth) from 45 sites were collected during 2006 and were analyzed for physical and chemical properties. The results showed that sand content and pH increased whereas silt and organic carbon decreased significantly from zones 1 to 4. Compared to other textures, significantly greater organic carbon, modulus of rupture, and pH in silty clay loam; greater bulk density in clay loam, and greater saturated hydraulic conductivity in sandy clay loam were observed. Irrespective of zone and soil texture, in the subsurface soil, there was a hard pan at 15–22.5 cm deep, which had high soil bulk density, modulus of rupture, more silt and clay contents (by 3–5%) and less organic carbon and hydraulic conductivity than the surface (0–15 cm) layer. These properties deteriorated with fineness of the soil texture and less organic carbon content. Continuous rice–wheat cropping had a deleterious effect on many soil properties. Many of these soils would benefit from the addition of organic matter, and crop yields may also be affected by the distinct hardpan that exists between 15 and 22.5 cm deep.     

Alleviation of Soil Acidity and Aluminium Phytotoxicity in Acid Soils by Using Alkaline-Stabilised Biosolids

A pot experiment was carried out to study alleviation of soil acidity and Al toxicity by applying an alkaline-stabilised sewage sludge product (biosolids) to an acid clay sandy loam (pH 5.7) and a strongly acid sandy loam (pH 4.5). Barley (Hordeum vulgare L. cv. Forrester) was used as a test crop and was grown in the sewage sludge-amended (33.5 t sludge DM ha-1) and unamended soils. The results showed that the alkaline biosloids increased soil pH from 5.7 to 6.9 for the clay sandy loam and from 4.5 to 6.0 for the sandy loam. The sludge product decreased KCl-extractable Al from 0.1 to 0.0 cmol kg-1 for the former soil and from 4.0 to 0.1 cmol kg-1 for the latter soil. As a result, barley plants grew much better and grain yield increased greatly in the amended treatments compared with the unamended controls. These observations indicate that alkaline-stabilised biosolids can be used as a liming material for remedying Al phytotoxicity in strongly acid soils by increasing soil pH and lowering Al bioavailability.     

Enzyme activities and microbial community structure in semiarid agricultural soils

This study investigated the effect of management on -glucosidase, -glucosaminidase, alkaline phosphatase, and arylsulfatase activities and the microbial community structure in semiarid soils from West Texas, USA. Surface samples (0–5 cm) were taken from a fine sandy loam, sandy clay loam, and loam that were under continuous cotton ( Gossypium hirsutum L.) or in cotton rotated with peanut ( Arachis hypogaea L.), sorghum ( Sorghum bicolor L.), rye ( Secale cereale) or wheat ( Triticum aestivum L.), and had different water management (irrigated or dryland), and tillage (conservation or conventional). The enzyme activities were higher in the loam and sandy clay loam than in the fine sandy loam. Soil pH was not affected by management, but the soil organic C and total N contents were generally affected by the different crop rotations and tillage practices studied. The trends of the enzyme activities as affected by management depended on the soil, but in general crop rotations and conservation tillage increased the enzyme activities in comparison to continuous cotton and conventional tillage. The soil enzyme activities were significantly correlated with the soil organic C ( r -values up to 0.90, P< 0.001), and were correlated among each other ( r -values up to 0.90, P <0.001). There were differences in the fatty acid methyl ester profiles between the fine sandy loam and the sandy clay loam and loam, and they reflected the differences in the enzyme activities found among the soils. For example, a 15:0 ranged from 1.61±0.25% in cotton-peanut/irrigated/no-till in the fine sandy loam to 3.86±0.48% in cotton-sorghum/dryland/conservation tillage in the sandy clay loam. There were no differences due to management within the same soil.Trade names and company names are included for the benefit of the reader and do not infer any endorsement or preferential treatment of the product by USDA-ARS     

Critical state parameters from intact samples of two agricultural topsoils

The critical state parameters of intact samples of a sandy loam (Eutric Cambisol) and a clay loam (Gleysol) were estimated in a constant cell volume triaxial apparatus. Samples were taken under wet and dry conditions. The parameters describing the clay loam were the more variable. This was true of both its initial condition and its response to deformation. Under dry conditions, the sandy loam was less sensitive to increasing stress but compacted more at low stress than the clay loam. Isotropic stress compacted the wet soils until the percentage saturation reached about 85–95% and axial loading caused little further compaction. The difference in strength between soils was greater for the wet samples, whereas the corresponding compactibility differences were greater under dry conditions. The sandy loam was stiffer than the clay loam and the shear modulus decreased exponentially with increasing specific volume before deformation. The rebound slope was about one-twentieth of the compression index for the dry soils and about one-third of the compression index for the wet soils. A simple model of recompression accounted for plastic deformation below the virgin compression line, where the critical state model usually assumes elasticity. The proposed model reproduced the main observed features of repeated isotropic loading.     

Crop yield and SOC responses to biochar application were dependent on soil texture and crop type in southern Quebec,Canada

Changes to soil nutrient availability and increases for crop yield and soil organic C (SOC) concentration on biochar‐amended soil under temperate climate conditions have only been reported in a few publications. The objective of this work was to determine if biochar application rates up to 20 Mg ha^?1 affect nutrient availability in soil, SOC stocks and yield of corn (Zea mays L.), soybean (Glycine max L.), and switchgrass (Panicum virgatum L.) on two coarse‐textured soils (loamy sand, sandy clay loam) in S Quebec, Canada. Data were collected from field experiments for a 3‐y period following application of pine wood biochar at rates of 0, 10, and 20 Mg ha^?1. For corn plots, at harvest 3 y after biochar application, 20 Mg biochar ha^?1 resulted in 41.2% lower soil NH on the loamy sand; the same effect was not present on the sandy clay loam soil. On the loamy sand, 20 Mg biochar ha^?1 increased corn yields by 14.2% compared to the control 3 y after application; the same effect was not present on the sandy clay loam soil. Biochar did not alter yield or nutrient availability in soil on soybean or switchgrass plots on either soil type. After 3 y, SOC concentration was 83 and 258% greater after 10 and 20 Mg ha^?1 biochar applications, respectively, than the control in sandy clay loam soil under switchgrass production. The same effect was not present on the sandy clay loam soil. A 67% higher SOC concentration was noted with biochar application at 20 Mg ha^?1 to sandy clay loam soil under corn.     

A decision support system for compaction assessment in agricultural soils

Research was conducted to develop a knowledge-based decision support system to assess the degree of compaction in agricultural soils. The experiments were conducted in a laboratory soil bin at the Asian Institute of Technology in three soils, namely, clay, silty clay loam, and silty loam. The research was likewise aimed to quantify the effect of tire variables (section width, diameter, inflation pressure); soil variables (soil moisture content, initial cone index, initial bulk density); and external variables (travel speed, axle load, number of tire passes) on soil compaction and to develop compaction models for soil compaction assessment. Dimensional analysis technique was used in the development of the compaction models.

The soil compaction models were found to provide good predictions of the bulk density and cone index. Using the compaction models and other secondary data, the decision support system was developed to assess the compaction status of the soil in relation to crop yield. The predictions by the decision support system were validated with actual field data from earlier studies and high correlation was observed. Thus, the output of the decision support system may be able to provide useful recommendations for appropriate soil management practices and solutions to site-specific soil compaction problems.