Effect of the number of tractor passes on soil rut depth and compaction in two tillage regimes

The initially high level of soil compaction in some direct sowing systems might suggest that the impact of subsequent traffic would be minimal, but data have not been consistent. In the other hand on freshly tilled soils, traffic causes significant increments in soil compaction. The aim of this paper was to quantify the interaction of the soil cone index and rut depth induced by traffic of two different weight tractors in two tillage regimes: (a) soil with 10 years under direct sowing system and (b) soil historically worked in conventional tillage system. Treatments included five different traffic frequencies (0, 1, 3, 5 and 10 passes repeatedly on the same track). The work was performed in the South of the Rolling Pampa region, Buenos Aires State, Argentina at 34°55′S, 57°57′W. Variables measured were (1) cone index in the 0–600 mm depth profile and (2) rut depth. Tyre sizes and rut depth/tyre width ratio are particularly important respect to compaction produced in the soil for different number of passes. Until five passes of tractor (2WD), ground pressure is responsible of the topsoil compaction. Until five passes the tyre with low rut depth/tyre width ratio reduced topsoil compaction. Finally, the farmer should pay attention to the axle load, the tyre size and the soil water content at the traffic moment.     

Seedbed compaction produced by traffic on four tillage regimes in the rolling Pampas of Argentina

The main function of primary tillage is to increase the soil's structural macro-porosity, but during secondary tillage operations over these freshly tilled soils, traffic causes significant soil compaction. In terms of soil conservation however, there is evidence that direct sowing is a more sustainable system, even though there is still insufficient information about the rheology of a non-tilled soil under traffic. The objective of this study was to compare the traffic intensity and soil compaction caused by four different tillage regimes currently used by Argentinean farmers (1 direct sowing with a tractor and planter weighing 127 kN and 3 conventional tillage systems with equipment weighing 55.2 kN). The work was performed in the east of the Rolling Pampa region, Buenos Aires State, Argentina at 34°25′S, 59°15′W. Variables measured were: (1) cone index in the 0–450 mm depth profile; (2) bulk density; (3) total soil porosity; and (4) rut depth. (a) Results indicated that in the depth range 0–150 mm with all tillage treatments, bulk density and cone index values generated by tractor traffic were greater than the 1.3 Mg m⁻³ and 1400 kPa respectively. Similarly in deeper layers these parameters were greater than 1.45 Mg m⁻³ and 2000 kPa respectively. Measurements revealed that traffic reduced topsoil porosity under direct sowing by an average of 7% and under conventional tillage by 7.6–14.8% confirming that both systems cause both topsoil and subsoil compaction.     

Mechanical weeding effects on soil structure under field carrots (Daucus carota L.) and beans (Vicia faba L.)

The successful production of organic vegetables relies heavily on mechanical weeding, flame weeding and stale seedbeds. These operations involve repeated passes by tractors. Mechanical weeding also involves regular tillage. This combination of repeated tillage and compaction changes soil structure. We studied these structural changes in two fields of organic carrots and one field of beans in eastern Scotland. Structure was described by measuring soil strength with a vane shear tester and a cone penetrometer, by measuring bulk density and by visual assessment. Under beans, vane shear strength below the growing root zone was highly variable and in some areas was high enough to restrict root growth (>50 kPa). The carrots were grown in beds containing crop rows separated by bare soil. The bare soil was regularly weeded mechanically. The structure of this weeded soil in the top 10 cm layer of a loam eventually became disrupted and compacted enough to deter root growth (vane shear strength of 70 kPa). In addition the topsoil and subsoil in the wheel-tracks between the beds became very compact with little distinguishable structure. This compaction extended to the subsoil and persisted into the next cropping season (cone resistance >3 MPa at 35–50 cm depth). Reduced tillage by discing without ploughing was used to incorporate the straw used to protect the carrots overwinter and prepare the soil for the next crop. The resulting topsoil quality was poor leading to anaerobic growing conditions which restricted growth of the following crop and led to losses of the greenhouse gas nitrous oxide. The greatest threat to soil quality posed by mechanical weeding was subsoil compaction by tractor wheeling.     

Scale- and location-dependent correlations of soil strength and the yield of wheat

The relationship between soil strength and crop yield may be summarized by a linear correlation coefficient (usually negative). It is likely, however, that this over-simplifies a complex situation in which the relationship between these variables depends on spatial scale and location. We used the wavelet transform to assess this scale- and location-dependence. We established a transect on an arable field in Eastern England, and studied the correlations of soil strength (top- and subsoil) with crop yield. The transect comprised 267 contiguous 0.72 m × 0.72 m plots. Measurements were taken during two consecutive growing seasons of winter wheat (harvest dates of August 2004 and 2005). Soil strength was measured with a penetrometer in the spring of each growing season. As expected, the overall correlation of soil strength with yield was negative but weak. Wavelet analysis revealed that, at fine spatial scales, topsoil and subsoil strength were correlated more or less equally with yield; however, at coarse spatial scales, topsoil strength had a stronger correlation with yield than did subsoil strength. The correlation of topsoil strength with yield at fine spatial scales (corresponding to about 1 m on the ground) was negative. A likely source of this fine-scale variation was the soil compaction associated with tractor wheelings. The correlation of topsoil strength with yield at the coarsest spatial scale (corresponding to about 50 m on the ground) was positive. This correlation was temporally stable, and might have reflected how soil strength can act as a proxy for other soil attributes. In the 2005 growing season, we found evidence that, at intermediate spatial scales, the correlation of soil strength with yield changed depending on the position on the transect. This was probably due to an interaction between the compaction associated with tractor wheelings and the local soil conditions. There was no evidence of such location-dependence in the correlation of soil strength with yield in the 2004 growing season. In summary, the effect of soil strength on crop yield was not expressed in a constant negative correlation across all spatial scales and locations: the negative correlation occurred mainly at fine spatial scales, and the correlation changed according to the position in the landscape and the prevailing local soil conditions.     

Effects on some clay soil qualities following the passage of rubber-tracked and wheeled tractors in central Italy

There is increased use of rubber-tracked tractors for ploughing on clay soil (Vertic Cambisol) in central, south and insular Italy instead of metal-tracked tractors, because they allow travel on public roads. Field tests were carried out on arable soil previously ploughed and harrowed to compare two types of tractors, one rubber-tracked (CAT Challenger Ch 45) and one wheeled (New Holland 8770) in order to establish the compacting effects resulting from 1 and 4 passes of the tractors in the same track. The following parameters were studied: soil penetration resistance, bulk density and its increment ratio, soil shear strength, soil macroporosity and hydraulic conductivity. Multiple passes made by the two tractors induced very similar effects on the soil in regards to soil penetration resistance. Mean values of penetration resistance (0–0.20 m depth) were 1.15 MPa for the rubber-tracked tractor and 1.11 MPa for the wheeled tractor; mean values of penetration resistance (0.21–0.40 m depth) were 1.07 MPa for the rubber-tracked tractor and 1.17 MPa for the wheeled tractor. The decrease in macroporosity, in particular that of elongated pores in the soil surface layer (0–0.10 m depth) was greater in treatments involving the rubber-tracked tractor (from 20.2 to 2.7%) than for the wheeled tractor (from 20.2 to 10.3%). Following traffic of the two tractors, hydraulic conductivity decreased and the following values were found for the five treatments: control, 18.48 mm h⁻¹; wheeled tractor 1 and 4 passes, 11.15 and 7.45 mm h⁻¹, respectively; rubber-tracked tractor 1 and 4 passes, 3.25 and 1.1 mm h⁻¹, respectively. Highly significant correlations between shear strength and dry bulk density, and between hydraulic conductivity and elongated pores and total macroporosity were found. Significant linear relationships between macroporosity and penetration resistance for 1 and 4 passes of both tractors were found in the soil layers (0–0.10 m). A significant difference was found between tractors and for correlations of penetration resistance values above control values. However, in the soil layer (0–0.20 m depth), with respect to the higher degree of macroporosity and low values of penetration resistance, treatments involving wheeled tractor (1 pass) showed a lower degree of soil compaction than was observed after 1 pass of the rubber-tracked tractor.     

Soil compaction effects on soil bulk density and penetration resistance and growth of spring barley (Hordeum vulgare L.)

Abstract

The weight of the tractor is not the only factor affecting soil compaction. Soil-management practices, such as the use of fertilizers and pesticides, also affect soil properties through an increased number of overriding. The aim of the current study was to investigate compaction effects on soil physical properties, such as dry bulk density and penetration resistance, and the growth of spring barley (Hordeum vulgare L.) as a monoculture. The five-year experiment was conducted on the Estonian University of Life Sciences’ research field at Eerika, near Tartu in 2001–2005. The soil of the experimental site is sandy loam Stagnic Luvisol. The treatments included were no compaction, one pass, three passes, and six passes. All passes were track-by-track. Measurements of soil and plant were made in the earing phase of barley and measurements of yield in the maturity phase of barley. The compaction treatment was conducted using an MTZ-82 tractor (total weight 4.84 Mg). Neither fertilizers nor herbicides were used. 5 years after compaction distinguishable subsoil and topsoil compaction was detected. Soil deformation increases with the number of passes; in the case of six passes soil bulk density increased by 0.15 Mg m^?3 and penetration resistance by 3 MPa. However, there were no significant differences in the soil bulk density and penetration resistance between treatments compacted with one and three passes. The effect of compaction on soil bulk density was higher when the soil was compacted under wet conditions. Compaction decreased the quantity of barley shoots, their phytomass, and grain yield by more than 80%. In the second year of the experiment the dry weight of above ground biomass decreased by almost three times and shoots’ density by 1.5 times, compared with the first year results. In the third year of the experiment the biomass, plant density, and grain yield of barley were stabilized and no further decreases were detected in the following two experimental years. The results from the experiment revealed that even a low weight tractor can induce subsoil compaction and a high decrease of plant productivity by repeated passes over time.     

Changes in some physical properties of a clay soil in Central Italy following the passage of rubber tracked and wheeled tractors of medium power

The aim of this study was to evaluate the compacting effect of rubber tracked tractors in comparison to that of the traditional wheeled tractors. Macroporosity, pore shape and size distribution, bulk density, penetration resistance and saturated hydraulic conductivity were analysed in a clay soil (Vertic Cambisol) near Rome (Italy) following one and four passes on the same track of rubber tracked and wheeled tractors of medium power. The soil structure attributes were evaluated by characterising porosity by means of image analysis of soil thin sections prepared from undisturbed samples. Macroporosity decreased in the 0–10 cm layer of compacted soil, particularly after four tractor passes, due to a large reduction in the proportion of elongated pores and in their vertical continuity. The rubber tracked tractor had a more pronounced compaction effect in the surface layer (0–10 cm) than the wheeled tractor both after one and four passes; the latter treatment producing the lowest soil porosity. The same trend was observed for hydraulic conductivity, which showed a highly significant correlation with elongated pores. In the 10–20 cm layer the porosity was significantly decreased following traffic, apart from in the soil under one pass of the rubber tracked tractor. Again in this layer, the lowest values of porosity were found in soil after four passes of the rubber tracked tractor. Single and multiple passes made by the two tractors induced different effects regarding soil penetration resistance and bulk density. Increment ratio of penetration resistance after tractor passes with respect to the control was: 12.5 and 49.9% with the wheeled and 34.4 and 39.8% with the tracked after one and four passes, respectively. Increment ratio of dry bulk density values after tractor passes with respect to the control was 7.9 and 11.7% with the wheeled and 7.5 and 8.3% with the tracked after one and four passes, respectively. The tractor passes transformed the initial subangular blocky structure into a massive structure with sometimes a platy structure in the upper few centimetres. The results indicated that soil compaction following traffic with the rubber tracked tractor was generally the more pronounced. However the compacting effect of this tractor after one pass seemed to be limited to the surface layer only.     

Effects of agricultural machinery with high axle load on soil properties of normally managed fields

In a field study, conducted on 10 conventionally managed field sites in Germany, the effects of high axle loads (15–25 Mg) on soil physical properties were investigated. Soil texture classes ranged from loamy sand to silty clay loam. All sites were annually ploughed, and one site was additionally subsoiled to 40 cm depth. In the context of common field operations wheeling was performed either by a sugar beet harvester (45 Mg total mass, 113 kPa average ground contact pressure) or a slurry spreader (30 Mg total mass, 77 kPa average ground contact pressure). Soil moisture conditions varied from 3.2 to 32 kPa water tension during this pass. Penetration resistance was measured before the pass. Soil cores were collected in a grid scheme at each site before and after the machine passed. Bulk density, aggregate density, air-filled porosity and air permeability at seven distinct soil water tensions ranging from 0.1 to 32 kPa were determined in these cores taken from three layers (topsoil, plough pan and subsoil).At most sites, a pass by the sugar beet harvester or slurry spreader strongly affected topsoil properties. Bulk density and aggregate density increased while air-filled porosity and air permeability decreased. The plough pan was already severely compacted before wheeling: therefore changes were small. The subsoil showed no changes or only minor signs of compaction. Only at one site, which was subsoiled the year before, significant signs of compaction (i.e. changes in bulk density, air-filled porosity and air permeability) were detected in subsoil layers.The results show that using present-day heavy agricultural equipment does not necessarily lead to severe subsoil compaction in soils where a compacted plough pan already exists. However, fields which were subsoiled leading to an unstable soil structure are in serious danger of becoming severely compacted.     

Pipeline right‐of‐way construction activities impact on deep soil compaction

A 762‐mm‐diameter pipe 1,886 km long was installed to transfer crude oil in the USA from North Dakota to Illinois. To investigate the impact of construction and restoration practices on long‐term soil productivity and crop yield, vertical soil stresses induced by a Caterpillar (CAT) pipe liner PL 87 (475 kN vehicle load) and semi‐trailer truck (8.9 kN axle load) were studied in a farm field. Soil properties (bulk density and cone penetration resistance) were measured on field zones within the right‐of‐way (ROW) classified according to construction machine trafficking and subsoil tillage (300‐mm‐depth tillage and 450‐mm‐depth tillage in two repeated passes) treatments. At 200 mm depth from the subsoiled surface, the magnitude of peak vertical soil stress from trafficking by the semi‐truck trailer and CAT pipe liner PL 87 was 133 kPa. The peak vertical soil stress at 400 mm soil depth appeared to be influenced by vehicle weight, where the Caterpillar pipe liner PL 87 created soil compaction a magnitude of 1.5 greater than from the semi‐trailer truck. Results from the soil bulk density and soil cone penetration resistance measurements also showed the ROW zones had significantly higher soil compaction than adjacent unaffected corn planted fields. Tillage to 450 mm depth alleviated the deep soil compaction better than the 300‐mm‐depth tillage as measured by soil cone penetration resistance within the ROW zones and the unaffected zone. These results could be incorporated into agricultural mitigation plans in ROW construction utilities to minimize soil and crop damage.     

Cumulative effect of annually repeated passes of heavy agricultural machinery on soil structural properties and sugar beet yield under two tillage systems

The aim of this study was to determine potential cumulative effects of repeated passes with current heavy agricultural machinery on topsoil (0–0.3 m) and subsoil (below 0.3 m) physical properties of a Luvisol as affected by long-term tillage (annual mouldboard ploughing to 0.3 m depth (MP), shallow-mixing conservation tillage to 0.1 m depth (SM) with a wing-bladed rigid tine cultivator). Moreover, sugar beet yield was determined. Wheeling was conducted with a six-row self-propelled sugar beet harvester representing contemporary heavy agricultural machinery (wheel load 7.8–11.7 Mg, average ground contact pressure 100–145 kPa). Wheeling was applied once per year over three consecutive years after harvest of sugar beet, cereal and cereal, and moreover, independent from regular plot management with light experimental machinery. Soil moisture at wheeling (0–0.6 m depth) was around 100% field capacity in most years, which was secured by irrigation before wheeling if necessary.Repeated wheeling negatively affected penetration resistance, macropore volume (equivalent diameter >50 μm) and air permeability of topsoil (0.05–0.1 m, 0.18–0.23 m) and subsoil (0.4–0.45 m) layers, while biopore number and surface water infiltration remained unaffected. SM compared to MP tillage increased penetration resistance while decreasing macropore volume and air permeability in the 0.18–0.23 m layer, whereas reverse effects occurred in 0.4–0.45 m depth. Sugar beet yield was decreased by wheeling and SM tillage compared to the control treatments. No significant interactions between wheeling and tillage occurred in any parameter investigated.Conclusively, SM tillage did not provide better subsoil resistance against compaction compared to MP treatment under wheeling and soil conditions prevalent in our experiment. Repeated wheeling with heavy agricultural harvest machinery is obviously at risk to exceed the bearing capacity of susceptible soils. Although (i) under regular harvest conditions just small parts of arable fields (except headlands) are wheeled with high loads, (ii) harvest is by far not every year conducted under high soil moisture, and (iii) effects in the subsoil were small, such risks have to be taken into account. Reduction of tillage depth to <0.1 m is not recommended for high yielding sugar beet crops grown on loessial soils.     

Effect of tractor weight, depth of ploughing and wheel placement during ploughing in an organic cereal rotation on contrasting soils

The relative effects of using light (2–3 Mg) versus heavier (5–7 Mg) tractors, shallow (15 cm) versus deeper (25 cm) ploughing and on-land versus in-furrow wheel placement during ploughing were investigated from 2003 to 2006 in organic rotations (wheat or barley, green manure, oats with peas) and conventionally fertilized barley. Trials were located on loam soil in south-eastern Norway and silty clay loam in central Norway. Ploughing was performed in spring, when the topsoil moisture content was at or below field capacity, using single furrow ploughs that allowed alternative wheel placement and resulted in complete coverage of the surface by wheels each year (ca. 3 times the normal coverage during ploughing). Low tyre inflation pressures (≤80 kPa) were used throughout. The use of a heavy tractor increased topsoil bulk density slightly in the loam soil, and, in combination with in-furrow wheeling, it reduced air-filled pore space and air permeability at 18–22 cm. On the silty clay loam, the use of a heavy tractor did not increase bulk density, but it reduced air-filled pore space throughout the topsoil. In-furrow wheeling reduced air-filled pore space in this soil also, compared to on-land wheeling. Penetration resistance was in this soil always greater at 15–25 cm depth after shallow than after deep ploughing, especially with in-furrow rather than on-land wheeling. Shallow ploughing led on both soils to marked increases in perennial weed biomass compared to deep ploughing. Earthworms were hardly affected by the treatments, but in the loam in 2006 a higher number of individuals were found where the light rather than the heavy tractor had been used. Few significant treatment effects were found on grain yield and quality. Deep ploughing with a light tractor gave the highest wheat yield and protein content in 2 years on the loam soil, and on the silty clay loam the yield of conventionally fertilized barley was higher after deep than after shallow ploughing. In summary, limited evidence was found to support the use of on-land rather than in-furrow wheeling when ploughing is performed at favourable soil moisture and with tractor weights < 5 Mg. There is, however, reason to be wary of using heavy tractors (>5 Mg), even under such conditions. With regard to ploughing depth in organic rotations dominated by cereals, the need to combat perennial weeds by deep ploughing weighs probably more heavily than any possible beneficial effect of shallow ploughing on stimulating nutrient turnover.     

Subsoil improvement in a tropical coarse textured soil: Effect of deep-ripping and slotting

In many coarse textured soils, limited root development and biomass production are attributed to adverse physical conditions in the subsoil. The current study was undertaken on an Arenic Acrisol located in Northeast Thailand (i) to assess whether subsoil physical characteristics influence crop rooting depth, and (ii) to compare the benefits associated with conventional tillage with that of localised subsoil loosening on crop performance and selected soil attributes. Control plots consisted of disk ploughing; the implemented treatments were conventional deep-ripping and localised slotting below the planting line. A crop rotation consisting of a legume followed by maize was established annually to assess the impact of these treatments on crop performance. In the control treatment, root development was restricted to the topsoil (0–20 cm) due to high subsoil bulk density (>1.6 Mg m⁻³). After deep-ripping, no improvement was observed in bulk density, rooting depth and in crop performance. The implementation of a slotting treatment systematically improved root development in the slotted subsoil, root impact frequency increasing from <0.2 to 0.6–0.8 (P = 0.01) despite no change in the bulk densities of the subsoil. This systematic improvement in root development could be explained by (i) reduced slumping that enable root development prior to recompaction and/or (ii) preferential drainage in the slot and therefore decreased resistance to root penetration. In a dry year maize yield was improved by 78% (P = 0.01); the deep-rooting legume Stylosanthes was tested only a wet year and its biomass production increased by >40% (P = 0.03). This study highlights the detrimental impact of subsoil compaction on root development and the potential role of slotting in coarse textured soils as a long-term management tool in addressing adverse subsoil physical characteristics that limit deep-rooting.     

土壤压实对土壤物理性质及小麦氮磷钾吸收的影响

为了研究土壤压实对土壤物理性质以及小麦养分吸收情况的影响,在2006和2007年进行了两轮田间试验.试验中,先用旋耕机对田块进行旋耕,耕深10cm,然后使用手扶式、轮式、履带式拖拉机在旋耕后的田块中通过1次(T1)、2次(T2)、4次(T3)以对土壤进行压实处理,对照组(T4)不作任何压实处理.压实处理后再次对土壤表层进行浅旋耕,耕深5 cm,耕后用播种机进行小麦播种,小麦品种为南京-601.试验结果发现,次表层土壤的压实处理显著影响次表层土壤的容重,孔隙度,小麦蛋白质含量以及植物中N、P、K的含量.除次表层的土壤容重在T3组中最大,T4组中最小外,其他参数值在T4组中最大,T3组中最小.并且,随着次表层土壤压实程度的增加,几乎所有的参数(土壤容重除外)都有所减少.不过,与第一年相比,参数值在第二年略有增加.总之,土壤压实严重破坏土壤结构,不利于小麦对养分的吸收.     

The installation of underground pipelines: effects on soil properties

Since the 1970s a network of underground pipes, up to 1200 mm diameter, has been installed in the UK to transmit crude oil to refineries and gas from onshore terminals for distribution. Chosen routes are subject to significant constraints. Current techniques for pipe installation involve topsoil removal and storage. Trench depth is set to allow a cover of 1200 mm overburden after pipes have been installed. The heavy machinery involved results in severe compaction of exposed subsoil. Subsoil is loosened comprehensively and topsoil replaced. Existing field drains are reconnected, and, if necessary, new drains with gravel backfill installed. Pipe installation usually takes place between April and October. Preventative measures to limit compaction during installation are not a practical option. If subsequent arable crops or grass are poorer or drainage more defective than before disturbance, the loss is assessed and compensation paid. To determine the cause of the loss >60, investigations have been made throughout the UK. Soil physical properties were assessed in an open trench using visual and tactile methods. Consistently, severe compaction in the subsoil was identified as the cause of poor crop growth or drainage; it was not observed in the topsoil. Specific recommendations for remedial action were made based on location, depth and severity of the compaction. These included the installation of additional land drains, increasing the amount of gravel above the drains, or further subsoil loosening orientated to cross gravel backfill. After appropriate remedial action, net compensation for crop losses was frequently small or negligible.     

Soil stress as affected by wheel load and tyre inflation pressure

The relative importance of wheel load and tyre inflation pressure on topsoil and subsoil stresses has long been disputed in soil compaction research. The objectives of the experiment presented here were to (1) measure maximum soil stresses and stress distribution in the topsoil for different wheel loads at the same recommended tyre inflation pressure; (2) measure soil stresses at different inflation pressures for the given wheel loads; and (3) measure subsoil stresses and compare measured and simulated values. Measurements were made with the wheel loads 11, 15 and 33 kN at inflation pressures of 70, 100 and 150 kPa. Topsoil stresses were measured at 10 cm depth with five stress sensors installed in disturbed soil, perpendicular to driving direction. Contact area was measured on a hard surface. Subsoil stresses were measured at 30, 50 and 70 cm depth with sensors installed in undisturbed soil. The mean ground contact pressure could be approximated by the tyre inflation pressure (only) when the recommended inflation pressure was used. The maximum stress at 10 cm depth was considerably higher than the inflation pressure (39% on average) and also increased with increasing wheel load. While tyre inflation pressure had a large influence on soil stresses measured at 10 cm depth, it had very little influence in the subsoil (30 cm and deeper). In contrast, wheel load had a very large influence on subsoil stresses. Measured and simulated values agreed reasonably well in terms of relative differences between treatments, but the effect of inflation pressure on subsoil stresses was overestimated in the simulations. To reduce soil stresses exerted by tyres in agriculture, the results show the need to further study the distribution of stresses under tyres. For calculation of subsoil stresses, further validations of commonly used models for stress propagation are needed.     

Compaction of loamy soils due to tractor traffic in vineyards and orchards and its effect on infiltration in southern France

Viticulture and fruit culture in Mediterranean areas demand frequent tractor traffic in vineyards and orchards for tillage and for the application of herbicides and pesticides, resulting in soil compaction. The aim of this study was to investigate the extent of soil compaction and its effect on infiltration in vineyards and orchards in an area in southern France, known for its wine and fruit production (Vaucluse). Compaction of both the topsoil and the subsoil was demonstrated with measurements of bulk density, penetration resistance and water retention characteristics. Subsoil compaction was attributed to wheel load, not to tillage, and was alleviated within 5 years after termination of tillage operations in vineyards. No effects of topsoil compaction on infiltration were expected on account of the slight differences in the values of infiltration parameters between wheel tracks and inter-rill areas. Effects of subsoil compaction on infiltration were examined with rainfall simulation tests. Under wet initial conditions and high rain intensities, no effect of soil compaction on infiltration was observed. This implies that the frequent tractor traffic associated with viticulture and fruit culture does not enhance run-off on loamy soils in Mediterranean areas.     

Soil compaction produced by tractor with radial and cross-ply tyres in two tillage regimes

The aim of this paper was to quantify soil compaction induced by tractor traffic on two tillage regimes: conventional tillage and direct drilling. Traffic was simulated with one pass of a conventional 2WD tractor, using four configurations of cross-ply rear tyres: 18.4–34, 23.1–30, 18.4–38 and 24.5–32, and four configurations of radial tyres 18.4R34, 23.1R 30, 18.4R 38 and 24.5R 32, with two ballast conditions used in each configuration. The experiment was conducted in the east of the Rolling Pampa region, Buenos Aires State, Argentina at 34°25′S, 59°15′W; altitude 22 m above sea level. Rut depth after traffic and soil bulk density and cone index in a 0–450-mm profile were measured before and after traffic. Considering topsoil level, in two tillage regimes, all treatments induced significant values of soil compaction as compared to the control plot without traffic. Subsoil compaction increased as total axle load increased and was independent of ground pressure. For the same tyre configuration, radial tyre caused less soil compaction than the cross-ply.     

Effects of subsoil compaction on yield and yield attributes of wheat in the sub-humid region of Pakistan

The prolonged use of vehicular traffic for farming creates subsoil compaction, which reduces crop yield and deteriorates the physical conditions of the soil. Field experiments were conducted during 2002–2003 and 2003–2004 in Pakistan to study subsoil compaction effects on soil bulk density, total porosity, yield and yield components of wheat. Soil compaction was artificially created at the start of the experiment using 7.0 t roller having length of 1.5 m and diameter of 1.22 m. Treatments consisted of T₁ = control (no compaction), T₂ = two passes of roller, T₃ = four passes of roller, T₄ = six passes of roller. The experiments were arranged in randomised complete block with four replications. Results indicated that subsoil compaction adversely affected the bulk density, total porosity of soil and root length during both the years. Soil compaction increased the bulk density (BD) from 1.37 for T₁ to 1.57, 1.61 and 1.72 Mg m⁻³ whereas decreased the total porosity from 47.3% for T₁ to 40.0, 37.4 and 34.5% for T₂, T₃ and T_4, respectively. Similarly grain yield decreased from 4141.7 for T₁ to 3912.8, 3364.5 and 3010.3 kg ha⁻¹ for T₂, T₃ and T_4, respectively. The deteriorating effect of compaction depended upon the degree of compaction. Subsoil compaction adversely affected the yield and yield attributes of wheat during both years of experiments. The subsoil compaction adversely affected soil physical conditions, which substantially decreased the yield of wheat. Therefore, appropriate measures of periodic chiselling, controlled traffic, conservation tillage, and incorporating of crops with deep tap root system in rotation cycle is necessary to minimize the risks of subsoil compaction.     

Soil microbial community structure affected by 53 years of nitrogen fertilisation and different organic amendments

The Ultuna long-term soil organic matter experiment in Sweden (59′82° N, 17′65° E) was started in 1956 to study the effects of different N fertilisers and organic amendments on soil properties. In this study, samples were taken from 11 of the treatments, including unfertilised bare fallow and cropped fallow, straw with and without N addition, green manure, peat, farmyard manure, sawdust, sewage sludge, calcium nitrate and ammonium sulphate, with n = 4 for each treatment. Samples were taken from topsoil (0–20 cm) and subsoil (27–40 cm depth) and analysed for concentrations of phospholipid fatty acids (PLFAs), organic C, total N and pH. The results showed that the subsoil samples reflected the total PLFA content of the topsoil, but not the microbial community structure. Total PLFA content was well correlated with total organic C and total N in both topsoil and subsoil. Total PLFA content in topsoil samples was highest in the sewage sludge treatment (89 ± 22 nmol PLFA g dw⁻¹). This contradicts earlier findings on microbial biomass in this sewage sludge-treated soil, which indicated inhibition of microorganisms, probably by heavy metals added with sludge. A switch towards microbial growth and faster decomposition of organic matter occurred around 2000, coinciding with lowered heavy metal content in the sludge. According to the PLFA data, the microbial community in the sewage sludge treatment is now dominated by Gram-positive bacteria. A lack of Gram-negative bacteria was also observed for the ammonium sulphate treatment, obviously caused by a drop in pH to 4.2.     

拖拉机田间行走对土壤特性及冬小麦生长的影响

农业机械的过度使用、密集轮作以及不适当管理等都会造成土壤压实。试验研究了拖拉机行走对土壤特性和小麦生长的影响。试验所使用的耕作机械包括轮式、履带式和手扶式三种拖拉机，分析了土壤压实对小麦生长以及土壤结构不连续性的影响。试验数据表明，土壤密度、土壤阻力以及土壤水分一般会随拖拉机行走次数增加而增大。同时，文中给出了小麦根系与秸秆间蕴涵的机理关系。试验数据还表明，小麦发芽率在显著性水平P≤0.05时，不同处理组之间无明显差异。但是，2、4、6、8、10、12、18周以及收割时的小麦秸秆高度在显著性水平P≤0.01时，各处理组之间却存在显著差异，其中轮式和手扶式拖拉机处理组高于履带式拖拉机处理组。当显著性水平分别为P≤0.05和 P≤0.01时，不同处理组的小麦根长度和密度间也存在显著差异，其中轮式和手扶式拖拉机处理组同样表现出更好的结果。总之，拖拉机行走会显著影响干物质、谷物产量等小麦生长参数。然而，作物产量不仅受土壤压实的影响，同时很大程度上也取决于天气以及土壤初始压实等因素。