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1.
《Soil & Tillage Research》2005,80(1-2):159-170
Plough pans have been shown to severely hamper root development, limit rooting depth and reduce crop yields. We evaluated the effect of plough pan re-compaction on root and yield response for winter wheat in a field trial conducted in two neighbouring fields on a sandy loam. Plots were mechanically loosened by a subsoiler to a depth of 35 cm in 1997 and 1998. In 2 years following the loosening operation, perennial grass/clover was grown with limited traffic intensity. Subsequently oats were established and followed by winter wheat. On-land ploughing was compared with traditional mouldboard ploughing. In addition, the plots were either heavy-trafficked (10–18 Mg axle load and ∼200 kPa inflation pressure) or light-trafficked (<6 Mg axle load and <100 kPa inflation pressure). The loosened treatments were referenced by non-loosened soil. Root growth of winter wheat was followed applying the minirhizotron technique. In one of the fields, these measurements were supplemented with core sampling for root length determination approximately at anthesis. Soil water content was followed in one of the fields using time domain reflectometry (TDR). Grain yield and nitrogen content in grain were determined. The adjoining study showed that the combination of heavy traffic and traditional ploughing caused strong recompaction of loosened soil, whereas the combination of light traffic and on-land ploughing produced moderate recompaction. For the loosened plots in one field, the strongly recompacted soil produced 7% lower yield than moderately recompacted soil, whereas no clear difference was found for the other field. No clear difference between the loosened treatments on root growth was observed. Surprisingly, the non-loosened soil performed similar or even better than the loosened and moderately compacted soil. The non-loosened soil facilitated higher root intensity at depth and produced similar yield and N-uptake. Our results suggest that mechanical subsoil loosening of humid sandy loams only is recommendable in case of very severe subsoil compaction. Natural alleviation of subsoil structure induced by changes in soil management may comprise a favourable alternative to mechanical subsoil loosening.  相似文献   

2.
《Soil & Tillage Research》2007,92(1-2):109-119
Soil compaction may affect N mineralization and the subsequent fate of N in agroecosystems. Laboratory incubation and field experiments were conducted to determine the effects of surface soil compaction on soil N mineralization in a claypan soil amended with poultry litter (i.e., Turkey excrement mixed with pine shavings as bedding). In a laboratory study, soil from the surface horizon of a Mexico silt loam soil was compacted to four bulk density levels (1.2, 1.4, 1.6 and 1.8 Mg m−3) with and without poultry litter and incubated at 25 °C for 42 days. A field trial planted to corn (Zea mays L.) was also conducted in 2002 on a Mexico silt loam claypan soil in North Central Missouri. Soil was amended with litter (0 and 19 Mg ha−1) and left uncompacted or uniformly compacted. Soil compaction decreased soil inorganic N by a maximum of 1.8 times in the laboratory study; this effect was also observed at all depths of the field trial. Compacted soil with a litter amendment accumulated NH4+-N up to 7.2 times higher than the noncompacted, litter-amended soil until Day 28 of the laboratory incubation and in the beginning of the growing season of the field study. Ammonium accumulation may have been due to decreased soil aeration under compacted conditions. Application of litter increased soil N mineralization throughout the growing season. In the laboratory study, soil inorganic N in unamended soil was negatively correlated with soil bulk density and the proportion of soil micropores, but was positively related with soil total porosity and the proportion of soil macropores. These results indicate that soil compaction, litter application and climate are interrelated in their influences on soil N mineralization in agroecosystems.  相似文献   

3.
Wheel induced soil compaction is an ongoing concern in mechanized agriculture. This experimental study was performed with the aim to evaluate whether soil compaction is related to stresses induced by towed wheels. Soil bin studies were conducted and soil compaction variables were measured under two towed tires, with different tread patterns, commonly used in Turkey. Tests were carried out at three tire loads (3.5, 5.5 and 7.5 kN) and two forward velocities (0.8 and 1.4 m/s) on a clay loam. To determine soil compaction, surface sinkage, subsurface layer deformation, compaction index, penetration resistance and bulk density were measured. With increasing vertical load, average contact pressure of tires increased from 39.3 to 68.5 kPa. In different trials, surface sinkage, compaction index, penetration resistance and bulk density varied from 46 to 86 mm, 0.18 to 0.48, 1472 to 2530 kPa and 1.31 to 1.70 Mg m−3, respectively. The soil contact projected area of tire 2 was approximately 10% greater than tire 1. The greater contact surface reduced the compaction at the soil surface and subsurface, but the tire load was still the dominant factor in the 0–20 cm depth range used in this study. According to the experimental results, decreasing contact duration with increasing forward velocity decreased soil compaction. Tire load and type affected soil deformation characteristics stronger than forward velocity.  相似文献   

4.
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.  相似文献   

5.
The alteration of mechanical soil properties by a single stress application exceeding all previously applied stresses is analyzed for a conventionally tilled and a conservational managed (since 1992) Stagnic Luvisol. Despite the more pronounced compactness of the plough layer under conventional management, it turned out to be less rigid compared to the “relictic” plough layer under conservation management. We assume that wheeling with a sugar beet harvester (rear wheel 140 kPa, front wheel 110 kPa, total mass 37 Mg) resulted in a break up of the plough pan. This was most obvious in the conventionally tilled soil whereas under conservation tillage, the plough pan seemed to resist the induced forces. Our results suggest that a break up of the compact plough layer and the subsequent re‐arrangement of newly formed fragments results in a smaller mechanical stability of the deformed soil. Soil structural changes within the plough pan are also indicated by the alteration of the anisotropy of cohesion and precompression stress, respectively. Altered mechanical properties induced by heavy soil loading affects the soil response to subsequent loading events, which could be shown by finite‐element simulations of stress‐strain properties. The simulations showed that a decrease in soil stiffness reduces the stress attenuation within the plough pan causing compressive and shear stresses to be transmitted into deeper soil levels, while at the same time shear strain increased.  相似文献   

6.
Growth and symbiotic activity of legumes are reduced by high soil compaction and mediated by Nod factors (LCO, lipo-chitooligosaccharides) application. Our objective was to assess the combined effects of soil compaction and Nod factors application on growth and symbiotic activity of pea. The experiment was two factorial and included soil compaction (1.30 g cm−3 – not compacted (control) and 1.55 g cm−3 – compacted soil), and Nod factors concentration (control without addition of Nod factors and use of 260 nM Nod solution) for each soil compaction. The soil (Haplic Luvisol) was packed into pots, pea (Pisum sativum L.) seeds were soaked with Nod factors solution or water and then plants were grown for 46 days. This study has shown that soil compaction and treatments of pea seeds with Nod factors influenced pea growth and symbiotic activity. Soil compaction significantly reduced pea growth parameters, namely plant height, dry mass, leaf area, root mass and root length and symbiotic parameters, namely mass of nodules, dry mass of an individual nodule, nitrogenase activity and total nitrogen content in plant in comparison to the non-compacted treatment. Treatment of seeds with Nod factors generally improved nearly all of the above parameters. Nitrogenase activity per pot and total plant nitrogen content were significantly reduced by soil compaction and increased by application of Nod factors in plants grown in not compacted soil. Our results demonstrate that increased symbiotic activity resulting from Nod factors addition may mitigate adverse effect of soil compaction on plant growth.  相似文献   

7.
《Soil biology & biochemistry》2001,33(12-13):1869-1872
Population densities of soil macrofauna were assessed in a field experiment with annually compacted treatments (applied to whole plots) and management treatments to repair initially compacted soil. Earthworms accounted for about half the macrofauna recovered during the experiment. Compaction of wet surface soil (water content>plastic limit) by agricultural machinery generally reduced numbers of macrofauna and earthworms. Annual compaction with a 10 Mg axle load on wet soil reduced mean macrofauna numbers from 70 to 15 m−2 and mean earthworm numbers from 41 to 2 m−2. Annual compaction with 6 Mg on soil drier than the plastic limit to a depth of 0.08 m had no adverse effect on the soil macrofauna. A 3-year pasture ley had more macrofauna (211 m−2) than a control treatment under cropping (29 m−2) but numbers declined when cropping was resumed.  相似文献   

8.
《Geoderma》2007,137(3-4):378-387
The burrowing activity of earthworms creates a distinct area around the resulting macropores called the drilosphere, which controls various soil processes. Density and microstructure of the drilosphere were studied and compared with those of the surrounding soil. For this purpose soil cores were separately inoculated with the vertically burrowing earthworm species Lumbricus terrestris. After 70 days some cores were compacted by a hydraulic press (250 kPa) and all cores were analysed by means of X-ray computed tomography. Mean Hounsfield Units were measured for concentric ROI cylinders (ROI = region of interest) of increasing diameters located around vertical macropore sections within selected horizontal slices. Based on these data we estimated stepwise the distribution of bulk density from the inner boundary of the drilosphere to the surrounding soil. In uncompacted soil the bulk density of the drilosphere was increased by 11% over that of the surrounding soil. In cross section, drilosphere and burrow form a concentric area with a total radius up to 2.2 cm. Soil compaction increased the dry bulk density of soil and decreased the diameter of earthworm burrows. Moreover, we found a less dense part of soil between the dense drilosphere and the remaining soil of the compacted core. Scanning electron microscopy revealed that the coarse silt particles of the bulk soil were rearranged to a parallel orientation due to compaction whereas the microstructure of the drilosphere remained unchanged. In any case, the drilosphere revealed a very homogeneous and dense arrangement of silt particles.  相似文献   

9.
Grain yields are presented from a 10-year field trial with four tillage regimes (annual ploughing, harrowing only, ploughing/harrowing alternate years and minimum tillage) on clay loam. We also present soil physical analyses and use the compaction verification tool (CVT) to assess compaction on plots with annual ploughing and minimum tillage, after using slurry tankers with contrasting wheel loads (4.1 Mg, 6.6 Mg) and wheeling intensities (1×/10×) in the 11th trial year, and yields monitored two years after compaction. Winter wheat yields in the period before compaction were strongly affected by tillage, with annual ploughing giving on average 24% higher yield than direct drilling. Both wheat and oats were far less affected in treatments with harrowing only or ploughing/harrowing alternate years, on average within 6% of annual ploughing. Yields after compaction were affected by both previous tillage and compaction intensity. In the first year, single wheeling after annual ploughing gave 23% yield reduction with 4.1 Mg wheel load and 28% reduction with 6.6 Mg wheel load, whilst multiple wheeling gave 14% reduction at 6.6 Mg wheel load. Yield reductions after minimum tillage ranged from 63% (single wheeling with 4.1 Mg) to 100% (multiple wheeling with 6.6 Mg). Similar trends were found in the second year. The soil physical data indicated that all wheeling led to changes in bulk density, pore sizes and permeability in both topsoil and subsoil on both sampled tillage plots. However, effects in the subsoil were partly masked by the soil's high initial bulk density, partly due to its high clay content. The CVT, which plots air capacity against hydraulic conductivity, suggested some harmful compaction on both plots, with the minimum tillage plot being less affected than the ploughed plot. However, yield results did not support this conclusion, indicating that other factors limited yields on the minimum tilled plot.  相似文献   

10.
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.  相似文献   

11.
The aim of this study was to quantify the effects of compaction on water flow patterns at the soil profile scale. Control and trafficked plots were established in field trials at two sites. The trafficked treatment was created by four passes track‐by‐track with a three‐axle dumper with a maximum wheel load of 5.8 Mg. One year later, dye‐tracing experiments were performed and several soil mechanical, physical and hydraulic properties were measured to help explain the dye patterns. Penetration resistance was measured to 50 cm depth, with saturated hydraulic conductivity (Ks), bulk density, and macroporosity and mesoporosity being measured on undisturbed soil cores sampled from three depths (10, 30 and 50 cm). Significant effects of the traffic treatment on the structural pore space were found at 30 cm depth for large mesopores (0.3–0.06 mm diameter), but not small mesopores (0.06–0.03 mm) or macroporosity (pores > 0.3 mm). At one of the sites, ponding was observed during the dye‐tracing experiments, especially in the trafficked plots, because of the presence of a compacted layer at plough depth characterized by a larger bulk density and smaller structural porosity and Ks values. Ponding did not induce any preferential transport of the dye solution into the subsoil at this site. In contrast, despite the presence of a compacted layer at 25–30 cm depth, a better developed structural porosity in the subsoil was noted at the other site which allowed preferential flow to reach to at least 1 m depth in both treatments.  相似文献   

12.
《Geoderma》2007,137(3-4):360-369
Straw residues may be accumulated in isolated zones in the plough layer after mouldboard ploughing. This may limit straw decomposition because of limited nitrogen availability depending on the prevalent water flow pathways induced by tillage. In this study, we used the food dye Brilliant Blue FCF (Color Index 42090) to make visible the flow pathways in the plough layer of a loamy soil after incorporation of 10 tonne of dry mass ha− 1, and to get a qualitative and quantitative interpretation of the small-scale flow behaviour. Approximately 1.3 L of a 4 g L− 1 Brilliant Blue solution was applied at a matric head of − 1 cm with an infiltrometer, equipped with a 25 cm-diameter disk. Horizontal cross-sections of 50 × 50 cm were photographed at 1.5 to 3.5 cm depth intervals. High-resolution spatial maps of Brilliant Blue concentration were derived from the scanned photographs, using separate calibration relationships between the measured Brilliant Blue concentrations and the color spectra and depth for the soil and the straw. Pronounced lateral dye movement was observed through the soil matrix owing to soil sorptivity. In cases of high sorptivity, the dye barely reached the depth of straw incorporation. Otherwise, enhanced preferential dye transport directed towards the incorporated straw was made visible and the stained water eventually ponded on the plough pan which induced lateral redistribution. Although the straw inclusions contributed to dye transport, they did not retain a substantial part of the applied dye mass, owing to the low density and surface area of straw. However, these inclusions may enhance the fast migration of potential pollutants such as nitrate or pesticides out of the tilled layer where much of the transformation occurs due to biological activity.  相似文献   

13.
《Soil & Tillage Research》1987,10(3):213-223
On a silt loam soil, the reaction of crop growth after subsoiling a plough pan was studied during 4 successive years. The mean yield increase for cereals and sugar beets varied between 5 and 10%.In order to determine the duration of the beneficial effects of subsoiling, 2 extra plots were subsoiled on the studied field in the autumn of the fourth year.At that time, penetration-resistance values on the first subsoiled treatment approached 3MPa, the limit-value for non-restricted root growth. Besides penetration-resistance measurements, root growth and nutrient and water uptake from the subsoil by winter wheat also pointed to a slight decline of the previous beneficial effects on the first subsoiled plot during the fifth year.However a yield increase, comparable with the mean increase for the previous 4 years on the studied soil, was still detected during the fifth growing season after the removal of a plough pan.  相似文献   

14.
《Applied soil ecology》2000,14(3):223-229
The effects of different mulch materials applied to compacted and uncompacted soil on the quantity and the quality of deposited earthworm casts were investigated. Biochemical properties and water stability of soil aggregates were compared with the corresponding properties of worm casts. This short-time experiment was conducted in the laboratory, simulating field conditions of mulch management in temperate agricultural systems. In microcosms Lumbricus terrestris and Octolasion cyaneum were inoculated separately. Barley, lupin, maize, or sugar-beet as straw or leaves were applied as mulch in amounts comparable to those usually found in the field. The soil was compacted artificially to a bulk density of 1.0 or 1.5 Mg m−3. In general, plant material and to a lesser extent soil compaction influenced the dynamic processes in the soil affecting microbial activity and water stable aggregation. Higher values of phosphatase activity was measured in compacted soil, while the corresponding enzyme activities in the casts were less affected by compaction. The worm species and the nutritional quality of the food source were factors strongly influencing water stable aggregation. Mulch as well as soil compaction had consequences for the burrowing activity of the worms, which resulted in different rates of cast production depending on the species.  相似文献   

15.
In the Amazon basin, tropical rainforest is being slashed and burned at accelerated rates for annual crops over a couple of years, followed by forage grasses. Because of poor management, the productivity of established pastures declines in a few years so that grazing plots are abandoned and new areas are deforested. Previous studies in the region report higher bulk density in soils under pasture than in similar soils under forest. The objective of this study was to detect changes in the physical quality of the topsoil of nutrient-poor Typic Paleudults in the colonisation area of Guaviare, Colombian Amazonia, and analyse the effect of soil deterioration on pasture performance. Temporal variation of soil compaction under pasture was analysed by comparing natural forest taken as control and pasture plots of Brachiaria decumbens (Stapf) grouped into three age ranges (<3, 3–9, >9 years). Evidence of soil compaction through cattle trampling, after clearing the primary forest, included the formation of an Ap horizon with platy structure and dominant greyish or olive colours, reflecting impaired surface drainage, the increase of bulk density and penetration resistance, and the decrease of porosity and infiltration rate. From primary forest to pastures older than 9 years, bulk density of the 5–10 cm layer increase was 42% in fine-textured soils and 30% in coarse-textured soils. Penetration resistance ranged from 0.45 MPa under forest to 4.25 MPa in old pastures, with maximum values occurring at 3–12 cm depth in pastures older than 9 years. Average total soil porosity was 58–62% under forest and 46–49% under pasture. Basic infiltration dropped from 15 cm h−1 in the original forest conditions to less than 1 cm h−1 in old pastures. Crude protein content and dry matter yield of the forage grass steadily decreased over time. No clear relationship between declining protein content as a function of pasture age and changes in chemical soil properties was found, but there was a high negative correlation (r=−0.81) between protein content and bulk density, reflecting the effect of soil compaction on pasture performance. After about 9–10 years of use, established grass did no longer compete successfully with invading weeds and grazing plots were abandoned. As land is not yet a scarcity in this colonisation area, degraded pastures are seldom rehabilitated.  相似文献   

16.
A well developed macropore network is advantageous in terms of transport processes regarding gas and water, as well as nutrient acquisition and root growth of crops. X-ray computed tomography provides a non-destructive method to visualize and quantify three-dimensional pore networks. Geometrical and morphological parameters of the complex pore system such as connectivity, tortuosity, porosity and pore surface area would be very useful for modeling and simulation of transport and exchange processes by providing quantitative data on relevant soil structural features and their modification by soil management.The scope of this study was to analyze and quantify the development of soil structure in the subsoil depending on three different precrop species (alfalfa A, chicory C and fescue F), at three depths (45, 60 and 75 cm) and cultivation periods (1, 2 and 3 years). Furthermore, morphological (air-filled porosity θa, pore surface area) and geometrical (pore diameter, connectivity, continuity, tortuosity τ) parameters were gathered with X-ray CT and image analysis. From an experimental field trial (Germany) with a Haplic Luvisol as soil type samples were taken and investigated. Air-capacity (θa) was measured in the laboratory for the same cylinders and compared to the results derived by image analysis.Air-capacity was highest for alfalfa (3 years, 75 cm). Tortuosity (τ) ranged between 1.3 and 4.38, while alfalfa (3 years) showed the highest value, which indicated structural development due to crack formation by enhanced root water uptake. Thus, an increase in accessible surface may improve water and nutrient supply for plants, whereas the high τ values may assume that oxygen supply is limited. It was found that the interaction of gas-diffusivity and the calculated parameters should be further investigated in terms of limitations to plant growth.  相似文献   

17.
Mechanically loosened subsoil has been shown to be prone to recompaction. We addressed a sandy loam that had been mechanically loosened by a subsoiler to a depth of 35 cm in 1997 and again in 1998. Perennial grass/clover was grown with limited traffic intensity in 1999 and 2000. A recompaction experiment was conducted in 2001 and 2002 when the soil was grown with oat and winter wheat, respectively. Using the formerly loosened plots, on-land ploughing was compared with traditional mouldboard ploughing with the tractor wheels in the furrow. In addition, the loosened plots were either light-trafficked (<6 Mg axle load and <100 kPa inflation pressure) or heavy-trafficked (10–18 Mg axle load and 200 kPa inflation pressure), respectively. Finally, the soil loosened by non-inversion deep tillage was referenced with a conventional ploughing–harrowing tillage system that never received the subsoil treatment. The conventional treatment was also grown with the grass/clover in 1999 and 2000. On-land ploughing and light traffic was applied in 2001 and 2002 instead of traditional ploughing and traffic for the conventional treatment. Penetration resistance and bulk density was recorded in the field. Undisturbed soil cores were taken in 1998, 1999 and 2002 from the 7–14, 18–27 and 25–30 cm layer and used for measuring total porosity, pores >30 μm and air permeability at −100 hPa matric potential. The results showed that on-land ploughing mitigated recompaction of the upper part of the formerly loosened subsoil. In contrast, only small differences in recompaction between heavy and light traffic were observed. The mitigation of subsoil recompaction was needed for the loosened soil to provide an upper subsoil with similar—not better—pore characteristics than the non-loosened soil in the conventional treatment. The structural conditions in the plough pan improved for the conventional treatment from 1998 to 2002 as indicated by an almost doubling in air permeability. This was interpreted as being related to the growing of grass/clover ley in 1999 and 2000 combined with a shift from traditional tillage and traffic to on-land ploughing and light traffic when growing cereals in 2001 and 2002. Results on root growth and crop yield are reported in an adjoining paper.  相似文献   

18.
Soil compaction caused by traffic of heavy vehicles and machinery has become a problem of world-wide concern. The aims of this study were to evaluate and compare the changes in bulk density, soil strength, porosity, saturated hydraulic conductivity and air permeability during sugar beet (Beta vulgaris L.) harvesting on a typical Bavarian soil (Regosol) as well as to assess the most appropriate variable factors that fit with the effective controlling of subsequent compaction. The field experiments, measurements and laboratory testing were carried out in Freising, Germany. Two tillage systems (conventional plough tillage and reduced chisel tillage) were used in the experiments. The soil water contents were adjusted to 0.17 g g−1 (w1), 0.27 g g−1 (w2) and 0.35 g g−1 (w3).Taking the increase in bulk density, the decrease in air permeability and reduction of wide coarse pore size porosity (−6 kPa) into account, it seems that CT (ploughing to a depth of 0.25 m followed by two passes of rotary harrow to a depth 0.05 m) of plots were compacted to a depth of at least 0.25 m and at most 0.40 m in high soil water (w3) conditions. The trends were similar for “CT w1” (low soil water content) plots. However, it seems that “CT w1” plots were less affected than “CT w3” plots with regard to bulk density increases under partial load. In contrast, diminishments of wide coarse pores (−6 kPa) and narrow (tight) coarse pores (−30 kPa) were significantly higher in “CT w1” plots down to 0.4 m. Among CT plots, the best physical properties were obtained at medium soil water (w2) content. No significant increase in bulk density and no significant decrease in coarse pore size porosity and total porosity below 0.2 m were observed at medium soil water content. The soil water content seemed to be the most decisive factor.It is likely that, CS (chiselling to a depth of 0.13 m followed by two passes of rotary harrow to a depth 0.05 m) plots were less affected by traffic treatments than CT plots. Considering the proportion of coarse pore size porosity (structural porosity) and total porosity, no compaction effects below 0.3 m were found. Medium soil water content (w2) provides better soil conditions after traffic with regard to wide coarse pore size porosity (−6 kPa), air permeability (at 6 and 30 kPa water suction), total porosity and bulk density. Proportion of wide coarse pores, air permeability and bulk density seems to be suitable parameters to detect soil compaction under the conditions tested.  相似文献   

19.
《Soil & Tillage Research》2007,92(1-2):157-163
A loamy sand Acrisol (Aquic Hapludult) that had been microirrigated for 6 years became so severely compacted that it had root limiting values of soil cone index in the Ap horizon and a genetic hardpan below it. Deep and surface tillage systems were evaluated for their ability to alleviate compaction. Deep tillage included subsoiling or none. Both deep tillage treatments were also surface tilled by disking, chiseling, or not tilling. Subsoiling was located in row or between rows to avoid microirrigation tubes (laterals) that were buried under every other mid row or every row. Cotton (Gossypium hirsutum) was planted in 0.96-m wide rows. Cotton yield was improved by irrigation from 485 to 1022 kg ha−1 because both 2001 and 2002 were dry years. Tillage loosened the soil by an average of 0.5–1.3 MPa; but compacted zones remained outside tilled areas. Subsoiling improved yield by 131 kg ha−1 when performed in row where laterals were placed in the mid rows; but subsoiling did not improve yield when it was performed in mid rows. For subsurface irrigation management in these soils, the treatment with laterals buried under every other mid row was able to accommodate in-row subsoiling which improved yield; and this treatment was just as productive as and had been shown to be less expensive to install than burying laterals under every row.  相似文献   

20.
《Applied soil ecology》2007,35(1):128-139
We tested the effect of soil moisture on the performance of four entomopathogenic nematodes species that have recently shown promise for the control of white grubs, i.e., Heterorhabditis bacteriophora, H. zealandica, Steinernema scarabaei, and S. glaseri. Experiments for all four nematodes were conducted in sandy loam, for S. scarabaei also in loamy sand and silt loam. Infectivity was tested by exposing third-instar Japanese beetle, Popillia japonica, to nematodes in laboratory experiments and determining nematode establishment in the larvae and larval mortality. Nematode infectivity was the highest at moderate soil moistures (−10 to −100 kPa), and tended to be lower in wet (−1 kPa) and moderately dry (−1000 kPa) soil. In dry soil (−3000 kPa), only S. scarabaei showed some activity. S. scarabaei was active from −1 to −3000 kPa in all soil types but the range of highest activity was wider in loamy sand (−1 to −1000 kPa) than in loamy sand and silt loam (−10 to −100 kPa). Persistence was determined in laboratory experiments by baiting nematode-inoculated soil with larvae of the greater wax moth, Galleria mellonella. For both Heterorhabditis spp. persistence was short at −10 kPa, improved slightly at −100 kPa, significantly at −1000 kPa, and was the highest at −3000 kPa. Both Steinernema spp. persisted very well at −10 kPa. However, S. glaseri persistence was the shortest at −10 kPa but did not differ significantly at −100 to −3000 kPa, whereas S. scarabaei persistence was not affected by soil moisture. Our observations concur with previous observations on the effect of soil moisture on entomopathogenic nematodes but also show that moisture ranges for infectivity and persistence vary among species. Differences among species may be based on differences in size and behavioral and physiological adaptations.  相似文献   

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