Showing papers in "Soil & Tillage Research in 2004"

A history of research on the link between (micro)aggregates, soil biota, and soil organic matter dynamics

Abstract: Since the 1900s, the link between soil biotic activity, soil organic matter (SOM) decomposition and stabilization, and soil aggregate dynamics has been recognized and intensively been studied. By 1950, many studies had, mostly qualitatively, investigated the influence of the five major factors (i.e. soil fauna, microorganisms, roots, inorganics and physical processes) on this link. After 1950, four theoretical mile-stones related to this subject were realized. The first one was when Emerson [Nature 183 (1959) 538] proposed a model of a soil crumb consisting of domains of oriented clay and quartz particles. Next, Edwards and Bremner [J. Soil Sci. 18 (1967) 64] formulated a theory in which the solid-phase reaction between clay minerals, polyvalent cations and SOM is the main process leading to microaggregate formation. Based on this concept, Tisdall and Oades [J. Soil Sci. 62 (1982) 141] coined the aggregate hierarchy concept describing a spatial scale dependence of mechanisms involved in micro- and macroaggregate formation. Oades [Plant Soil 76 (1984) 319] suggested a small, but very important, modification to the aggregate hierarchy concept by theorizing the formation of microaggregates within macroaggregates. Recent research on aggregate formation and SOM stabilization extensively corroborate this modification and use it as the base for furthering the understanding of SOM dynamics. The major outcomes of adopting this modification are: (1) microaggregates, rather than macroaggregates protect SOM in the long term; and (2) macroaggregate turnover is a crucial process influencing the stabilization of SOM. Reviewing the progress made over the last 50 years in this area of research reveals that still very few studies are quantitative and/or consider interactive effects between the five factors. The quantification of these relationships is clearly needed to improve our ability to predict changes in soil ecosystems due to management and global change. This quantification can greatly benefit from viewing aggregates as dynamic rather than static entities and relating aggregate measurements with 2D and 3D quantitative spatial information.

Soil structure and the effect of management practices

Abstract: To evaluate the impact of management practices on the soil environment, it is necessary to quantify the modifications to the soil structure. Soil structure conditions were evaluated by characterizing porosity using a combination of mercury intrusion porosimetry, image analysis and micromorphological observations. Saturated hydraulic conductivity and aggregate stability were also analysed. In soils tilled by alternative tillage systems, like ripper subsoiling, the macroporosity was generally higher and homogeneously distributed through the profile while the conventional tillage systems, like the mouldboard ploughing, showed a significant reduction of porosity both in the surface layer (0–100 mm) and at the lower cultivation depth (400–500 mm). The higher macroporosity in soils under alternative tillage systems was due to a larger number of elongated transmission pores. Also, the microporosity within the aggregates, measured by mercury intrusion porosimetry, increased in the soil tilled by ripper subsoiling and disc harrow (minimum tillage). The resulting soil structure was more open and more homogeneous, thus allowing better water movement, as confirmed by the higher hydraulic conductivity in the soil tilled by ripper subsoiling. Aggregates were less stable in ploughed soils and this resulted in a more pronounced tendency to form surface crust compared with soils under minimum tillage and ripper subsoiling. The application of compost and manure improved the soil porosity and the soil aggregation. A better aggregation indicated that the addition of organic materials plays an important role in preventing soil crust formation. These results confirm that it is possible to adopt alternative tillage systems to prevent soil physical degradation and that the application of organic materials is essential to improve the soil structure quality.

Effects of compost, mycorrhiza, manure and fertilizer on some physical properties of a Chromoxerert soil

Abstract: Addition of organic materials of various origins to soil has been one of the most common rehabilitation practices to improve soil physical properties. Mycorrhiza has been known to play a significant role in forming stable soil aggregates. In this study, a 5-year field experiment was conducted to explore the role of mycorrhizal inoculation and organic fertilizers on the alteration of physical properties of a semi-arid Mediterranean soil (Entic Chromoxerert, Arik clay-loam soil). From 1995 to 1999, wheat ( Triticum aestivum L.), pepper ( Capsicum annuum L.), maize ( Zea mays L.) and wheat were sequentially planted with one of five fertilizers: (1) control, (2) inorganic (160–26–83 kg N–P–K ha −1 ), (3) compost at 25 t ha −1 , (4) farm manure at 25 t ha −1 and (5) mycorrhiza-inoculated compost at 10 t ha −1 . Soil physical properties were significantly affected by organic fertilizers. For soil depths of 0–15 and 15–30 cm, mean weight diameter (MWD) was highest under the manure treatment while total porosity and saturated hydraulic conductivity were highest under the compost treatment. For a soil depth of 0–15 cm, the compost and manure-treated plots significantly decreased soil bulk density and increased soil organic matter concentration compared with other treatments. Compost and manure treatments increased available water content (AWC) of soils by 86 and 56%, respectively. The effect of inorganic fertilizer treatment on most soil physical properties was insignificant ( P >0.05) compared with the control. Mycorrhizal inoculation+compost was more effective in improving soil physical properties than the inorganic treatment. Organic fertilizer sources were shown to have major positive effects on soil physical properties.

Long-term tillage and crop rotation effects on microbial biomass and C and N mineralization in a Brazilian Oxisol

Abstract: Crop rotation and tillage impact microbial C dynamics, which are important for sequestering C to offset global climate change and to promote sustainable crop production. Little information is available for these processes in tropical/subtropical agroecosystems, which cover vast areas of terrestrial ecosystems. Consequently, a study of crop rotation in combination with no tillage (NT) and conventional tillage (CT) systems was conducted on an Oxisol (Typic Haplorthox) in an experiment established in 1976 at Londrina, Brazil. Soil samples were taken at 0–50, 50–100 and 100–200 mm depths in August 1997 and 1998 and evaluated for microbial biomass carbon (MBC) and mineralizable C and N. There were few differences due to crop rotation, however there were significant differences due to tillage. No tillage systems increased total C by 45%, microbial biomass by 83% and MBC:total C ratio by 23% at 0–50 mm depth over CT. C and N mineralization increased 74% with NT compared to CT systems for the 0–200 mm depth. Under NT, the metabolic quotient (CO2 evolved per unit of MBC) decreased by 32% averaged across soil depths, which suggests CT produced a microbial pool that was more metabolically active than under NT systems. These soil microbial properties were shown to be sensitive indicators of long-term tillage management under tropical conditions. © 2003 Elsevier B.V. All rights reserved.

Tillage and cropping effects on soil quality indicators in the northern Great Plains

Abstract: The extreme climate of the northern Great Plains of North America requires cropping systems to possess a resilient soil resource in order to be sustainable. This paper summarizes the interactive effects of tillage, crop sequence, and cropping intensity on soil quality indicators for two long-term cropping system experiments in the northern Great Plains. The experiments, located in central North Dakota, were established in 1984 and 1993 on a Wilton silt loam (FAO: Calcic Siltic Chernozem; USDA 1 : fine-silty, mixed, superactive frigid Pachic Haplustoll). Soil physical, chemical, and biological properties considered as indicators of soil quality were evaluated in spring 2001 in both experiments at depths of 0–7.5, 7.5–15, and 15–30 cm. Management effects on soil properties were largely limited to the surface 7.5 cm in both experiments. For the experiment established in 1984, differences in soil condition between a continuous crop, no-till system and a crop–fallow, conventional tillage system were substantial. Within the surface 7.5 cm, the continuous crop, no-till system possessed significantly more soil organic C (by 7.28 Mg ha −1 ), particulate organic matter C (POM-C) (by 4.98 Mg ha −1 ), potentially mineralizable N (PMN) (by 32.4 kg ha −1 ), and microbial biomass C (by 586 kg ha −1 ), as well as greater aggregate stability (by 33.4%) and faster infiltration rates (by 55.6 cm h −1 ) relative to the crop–fallow, conventional tillage system. Thus, soil from the continuous crop, no-till system was improved with respect to its ability to provide a source for plant nutrients, withstand erosion, and facilitate water transfer. Soil properties were affected less by management practices in the experiment established in 1993, although organic matter related properties tended to be greater under continuous cropping or minimum tillage than crop sequences with fallow or no-till. In particular, PMN and microbial biomass C were greatest in continuous spring wheat (with residue removed) (22.5 kg ha −1 for PMN; 792 kg ha −1 for microbial biomass C) as compared with sequences with fallow (SW–S–F and SW–F) (Average=15.9 kg ha −1 for PMN; 577 kg ha −1 for microbial biomass C). Results from both experiments confirm that farmers in the northern Great Plains of North America can improve soil quality and agricultural sustainability by adopting production systems that employ intensive cropping practices with reduced tillage management.

Temporal variation of soil compaction and deterioration of soil quality in pasture areas of Colombian Amazonia

Abstract: 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 ( 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.

Effects of tillage on soil microrelief, surface depression storage and soil water storage

Abstract: Conservation of soil water is an important management objective for crop production in the semi-arid tropics where droughts are persistent. Identification of the best tillage methods to achieve this objective is thus imperative. The integrated effects of conservation tillage on soil micro topography and soil moisture on a sandy loam soil were evaluated. The field experiment consisted of five tillage treatments, namely tied ridging (TR), no till (NT), disc plough (DP), strip catchment tillage (SCT) and hand hoe (HH). Data measured in the field included soil moisture content, surface roughness, infiltration and sorghum grain yield. A depth storage model was used to estimate depression storage TR treatment and the higher the surface roughness, the greater the depression storage volume. Regression analysis showed that random roughness decreased exponentially with increase in cumulative rainfall. Higher moisture contents were associated with treatments having higher depressional storage. Infiltration rate was significantly higher in the tilled soils than the untilled soils. The DP treatment had the highest cumulative infiltration while NT had the lowest. The Infiltration model which was fitted to the infiltration data gave good fit. Grain yield was highest in TR and least in NT, whereas DP and HH had similar yields.

Productivity and soil response to plastic film mulching durations for spring wheat on entisols in the semiarid Loess Plateau of China

Abstract: Plastic film mulching is an important agricultural practice in semiarid areas of the Loess Plateau in northwest China to improve crop productivity by changing soil properties. We conducted field experiments using spring wheat ( Triticum aestivum L. cv Longchun 8139-2) to examine the effect of film-mulching with varying durations on crop yield and soil properties in 1999 and 2000 on Loess Orthic Entisols in the semiarid Loess Plateau of China. The three mulching treatments with varying durations were applied: (1) M30: mulching for 30 days after sowing (DAS); (2) M60: mulching for 60 DAS; (3) Mw: mulching for the whole growth period, as well as the control; M0: without mulching. In 1999, seedlings from the three mulching treatments emerged 8 days earlier than those from unmulchingly treated. In 2000, a very dry year, emergence of seedlings in the mulching treatments occurred only 1–2 days earlier compared to control. Moreover, mulching treatments also significantly increased the total root biomass before 90 DAS in 1999 and before 30 DAS in 2000. There was a sharp increase in soil respiration in the mulching treatments. Soil microbial biomass nitrogen content in the Mw treatment was significantly lower at 43 DAS than that in control. Accumulation of total mineral nitrogen in the soil at harvest was clearly higher in Mw than in the other treatments and the control. Highest yields were recorded from wheat treated with M60 (3305 and 1203 kg ha −1 in 1999 and 2000, respectively). By contrast, no significant difference in yield was found among the three-mulched treatments in 1999. In 1999 the water use efficiency in all mulching treatments was significantly higher than in control, while in 2000 it was significantly higher in M60 and Mw than in M30 and control. These findings therefore suggest that mulching for 60 DAS increased grain yield by increasing the mineral nitrogen, soil water and the efficiency of water use and avoiding the over-decomposition of organic matter and over-mineralization of organic nitrogen.

Aggregate distribution and soil organic matter under different tillage systems for vegetable crops in a Red Latosol from Brazil

Abstract: Several management systems can improve soil productivity. By studying aggregate stability it is possible to quantify whether or not the management is ameliorating the natural soil properties and the land capability for agriculture. The effect of three tillage systems on the stability of soil aggregates and soil organic carbon was studied in comparison to reference plots with grass and bare soil. Samples were collected at the Pesagro Experimental Research Station in Paty do Alferes, state of Rio de Janeiro, Brazil, from an experiment that has been carried out from 1995 to 2001, on a Dystrophic Red Latosol (Typic Haplorthox). Aggregate size distribution mean weight diameter, geometric mean diameter of the aggregates, and total organic carbon in each aggregate size fraction were determined. The proportion of aggregates with diameter ≥2 mm appeared to be a suitable indicator of the influence of tillage systems on aggregation. At a depth of 0–5 cm, aggregates ≥2 mm were 50% of soil under no-tillage, which was greater than under animal traction (35%) and conventional tillage (30%). Total organic carbon concentration was greater under no-tillage (19 g kg −1 ) than under conventional tillage (11 g kg −1 ) at a depth of 0–5 cm, but not significantly different (average 13 g kg −1 ) at a depth of 5–10 cm. Soil exposure with tillage and lack of residue inputs caused declines in aggregation and organic carbon, both of which make soil susceptible to erosion. Adoption of no-tillage led to a decline in aggregation compared with grass reference, but did significantly alter soil organic concentration, suggesting it was a valuable conservation practice for vegetable production on sloping soils. © 2003 Elsevier B.V. All rights reserved.

Bulk density as a soil quality indicator during conversion to no-tillage

Abstract: Producers often identify compaction as an important problem, so bulk density is usually included in minimum data sets used to evaluate tillage and crop management effects on soil quality. The hypothesis for this study was that bulk density and associated water content would be useful soil quality indicators for evaluating the transitional effects associated with changing tillage and crop management practices on deep-loess soils. The study was conducted on three deep-loess, field-scale watersheds located in western Iowa, USA. The soils are classified as Haplic Phaeozems, Cumulic-Haplic Phaeozems, and Calcaric Regosols. Watersheds 1 and 2 were converted in 1996 from conventional tillage to no-tillage, while watershed 3 was maintained using ridge-tillage and continuous corn (Zea mays L.), a practice implemented in 1972. Watershed 1 was converted to a corn—soybean (Glycine max (L.) Merr.) rotation while watershed 2 was converted to a 6-year rotation that included corn, soybean, corn plus 3 years of alfalfa (Medicago sativaL.). Bulk density and water content were measured at three landscape positions (summit, side-slope, and toe-slope), in 20 mm increments to a depth of 300 mm, five times between September 1996 and May 2000. Organic C and total N were also measured to a depth of 160 mm during the initial sampling. Neither bulk density nor water content showed any significant differences between the two watersheds being converted to no-tillage or between them and the ridge-till watershed. There also were no significant differences among landscape positions. Bulk densities and water contents showed some differences when adjacent sampling dates were compared, but there was no overall or consistent trend. Our results show that bulk density is not a useful soil quality indicator for these soils within the bulk density range encountered (0.8–1.6 Mg m 3 ). Our results also confirm that producers do not necessarily have to worry about increased compaction when using ridge-tillage or changing from conventional to no-tillage practices on these or similar deep-loess soils. Published by Elsevier B.V.

Soil hydraulic properties as related to soil structure

Abstract: Soil structure is one of the main attributes of soil quality. It influences the soil pore system and through it all parameters of equations describing the transport processes in soil. Soil pore size distribution is either log-normal, or the log-normal distribution is an acceptable approximation. Kosugi [Water Resour. Res. 30 (1994) 891] has applied the log-normal distribution to data on the soil water retention curve and has replaced the empirical equation by the physically-based model. Log-normal pore size distributions were used for the estimation of the unsaturated hydraulic conductivity function. This paper deals with the application of Kosugi's model to the description of the retention curve and of the unsaturated conductivity function in soils exhibiting a bi-modal distribution of pores, typical for all soil horizons having a certain type of structure. The domain of structural pores and the domain of matrix pores are defined in these structured soils. Results from this study show that two hydraulic functions, the retention curve and the unsaturated conductivity are well described by models based on a log-normal distribution of pores in both the structural and the matrix domains of the soil porous system. The exponents α, β defined as parameters of the unsaturated conductivity are different for the structural and matrix domains. It is therefore, assumed that the configuration of soil pores including the tortuosity differs in these domains. The destruction of soil structure changes distinctly the configuration of soil pores which is demonstrated by the change of parameters α, β Consequently, the saturated and unsaturated conductivity is changed, too.

Transport of labile carbon in runoff as affected by land use and rainfall characteristics

Abstract: The mobilization of organic carbon (C) by water erosion could impact the terrestrial C budget, but the magnitude and direction of that impact remain uncertain due to a lack of data regarding the fates and quality of eroded C. A study was conducted to monitor total organic C and mineralizable C (MinC) in eroded materials from watersheds under no till (NT), chisel till (CT), disk till low input (DT-LI), pasture and forest. The DT-LI treatment relies on manure application and legume cover crops to partly supply the N needed when corn is grown, and on cultivation to reduce the use of herbicides. Each watershed was instrumented with a flume and a Coshocton wheel sampler for runoff measurement. Carbon dioxide (CO2) evolved during incubation (115 days) of runoff samples was fitted to a first-order decomposition model to derive MinC. Annual soil (6.2 Mg ha −1 ) and organic C (113.8 kg C ha −1 ) losses were twice as much in the DT-LI than in the other watersheds (<2.7 Mg soil ha −1 , <60 kg C ha −1 ). More than management practices, rainfall class (based on intensity and energy) was a better controller of sediment C concentration and biodegradability. Sediment collected during the low-intensity (fall/winter) storms contained more organic C (3 7gCk g −1 ) and MinC (30–40% of sediment C) than materials displaced during the high-intensity summer storms (22. 1gCk g −1 and 13%, respectively). These results suggest a more selective detachment and sorting of labile C fractions during low-intensity storms. However, despite the control of low-intensity storm on sediment C concentration and quality, increased soil loss with high-energy rainfall suggests that a few infrequent but high-energy storms could determine the overall impact of erosional events on terrestrial C cycling. © 2003 Elsevier B.V. All rights reserved.

Soil properties following cultivation and non-grazing of a semi-arid sandy grassland in northern China

Abstract: Cultivation and overgrazing are widely recognized as the primary causes of desertification of sandy grassland in the semi-arid region of northern China. Very little is known about the effect of cultivation and overgrazing on soil physical, chemical and biological properties in this region. The objective of this study was to quantitatively evaluate the magnitude of changes in soil properties due to 3 years of cultivation (3CGS) and 5 years of ungrazed exclosure (5RGS) in a degraded grassland ecosystem of the semi-arid Horqin sandy steppe. Short-term cultivation resulted in a 18–38% reduction in concentration of soil organic C, and total N and P in the 0–15 cm plow layer. Cultivation had a significant influence on N and P availability and soil biological properties, with lower basal soil respiration (BSR) and enzyme activities than the grassland soils. This was mostly due to strong wind erosion when sandy grassland was cultivated. Data indicated a considerable difference in soil particle size distribution between the cultivated and grassland soils, and fine fraction (

Effects of tillage method and crop rotation on non-renewable energy use efficiency for a thin Black Chernozem in the Canadian Prairies.

Abstract: Producers in the Canadian Prairies have begun to extend and diversify their cereal-based rotations by including oilseed and pulse crops, and by managing these newer cropping systems with minimum- and zero-tillage practices. This study examined the implications of these land use changes on non-renewable energy requirements (both direct and indirect), energy output, and energy use efficiency for monoculture cereal, cereal–oilseed, and cereal–oilseed–pulse rotations, each managed using conventional (CT), minimum (MT), and zero (ZT) tillage practices on a thin Black Chernozem in Saskatchewan, Canada. The crop rotations included: spring wheat (Triticum aestivum L.)–spring wheat–winter wheat–fallow (Ws–Ws–Ww–F), spring wheat–spring wheat–flax (Linum usitatissimum L.)–winter wheat (Ws–Ws–Fx–Ww), and spring wheat–flax–winter wheat–field pea (Pisum sativum L.) (Ws–Fx–Ww–P). The findings, based on 12 years of data, showed that non-renewable energy use for the complete cropping systems was largely unaffected by tillage method, but that it differed significantly with crop rotations. Energy requirements were lowest for Ws–Ws–Ww–F (average 6389 MJ ha−1), intermediate for Ws–Fx–Ww–P (11% more), and highest for the Ws–Ws–Fx–Ww (28% more). The substitution of pea for spring wheat in the Ws–Fx–Ww–P versus Ws–Ws–Fx–Ww rotation reduced total energy use by 13%, reflecting the minimal requirement for N fertilizer by pulses due to their ability to biologically fix N, and from the lower fertilizer N rate that was applied to spring wheat grown after the legume. The use of MT and ZT practices provided significant energy savings (compared to CT) in on-farm use of fuel and in machine operation and manufacture for some cropping system components (e.g., summerfallow preparation, spring wheat grown on pea stubble, and for pea grown on cereal stubble), but these savings were often offset by higher energy requirements for herbicides and for N fertilizer with conservation tillage management. Gross energy output averaged 32 315 MJ ha−1 for Ws–Ws–Ww–F, 41 287 MJ ha−1 (or 28% more) for Ws–Ws–Fx–Ww, and 42 961 (or 33% more) for Ws–Fx–Ww–P. Tillage method had little overall influence on energy output for the monoculture cereal and cereal–oilseed–pulse rotations, but it was generally lower with CT than with MT or ZT management for the cereal–oilseed rotation. Energy use efficiency, measured as grain produced per unit of energy input and as the ratio of energy output to energy input, was highest for the cereal–oilseed–pulse rotation (373 and 6.1 kg GJ−1, respectively) and lower, but generally similar, for the cereal–oilseed and monoculture cereal rotations (298 and 5.1 kg GJ−1, respectively). The use of conservation tillage management enhanced overall energy use efficiency for the two mixed rotations, but not for the monoculture cereal rotation. We concluded that adopting diversified crop rotations, together with minimum and zero tillage management practices, will enhance non-renewable energy use efficiency of annual grain production in this sub-humid region.

Modern forestry vehicles and their impacts on soil physical properties

Abstract: “Close-to-nature forest stands” are one central key in the project “Future oriented Forest Management” financially supported by the German Ministry for Science and Research (BMBF). The determination of ecological as well as economical consequences of mechanized harvesting procedures during the transformation from pure spruce stands to close-to-nature mixed forest stands is one part of the “Southern Black Forest research cooperation”. Mechanical operations of several typical forest harvesting vehicles were analysed to examine the actual soil stresses and displacements in soil profiles and to reveal the changes in soil physical properties of the forest soils. Soil compaction stresses were determined by Stress State Transducer (SST) and displacement transducer system (DTS) at two depths: 20 and 40 cm. Complete harvesting and trunk logging processes accomplished during brief 9-min operations were observed at time resolutions of 20 readings per second. Maximum vertical stresses for all experiments always exceeded 200 kPa and at soil depths of 20 cm for some vehicles and sequences of harvesting operations approached ≥500 kPa. To evaluate the impacts of soil stresses on soil structure, internal soil strengths were determined by measuring precompression stresses. Precompression stress values of forest soils at the field sites ranged from 20 to 50 kPa at soil depths of 20 cm depth and from 25 to 60 kPa at soil depths of 40 cm, at a pore water pressure of −60 hPa. Data obtained for these measured soil stresses and their natural bearing capacities proved that sustainable wheeling is impossible, irrespective of the vehicle type and the working process. Re-occurring top and subsoil compaction, increases in precompression stress values in the various soil horizons, deep rut depths, vertical and horizontal soil displacements associated with shearing stresses, all affected the mechanical strengths of forest soils. In order to sustain naturally “unwheeled” soil areas with minimal compaction, it is recommended that smaller machines, having less mass, be used to complete forest harvesting in order to prevent or at least to maintain currently minimal-compacted forest soils. Additionally, if larger machines are required, permanent wheel and skid tracks must be established with the goal of their maximum usefulness for future forest operations. A first step towards accomplishing these permanent pathways requires comprehensive planning with the Federal State Baden-Wurttemberg. The new guideline for final opening with skid tracks (Landesforstverwaltung Baden-Wurttemberg, 2003) proposes a permanent skid track system with a width of 20–40 m.

Effects of traffic on soil aeration, bulk density and growth of spring barley

Abstract: This paper reports the results of field experiments on several different soils to quantify the effects of different numbers of passes of vehicular traffic on soil aeration status (measured in terms of oxygen diffusion rate, ODR and redox potential, Eh), soil bulk density and development of spring barley. In a further series of field experiments, the effects of single and dual wheels were compared and the effectiveness of a soil loosener operating behind the wheels was evaluated. Additionally, some microplot experiments are reported in which a range of known values of soil bulk density were produced and the effects on soil aeration and development of spring barley were evaluated. It is shown that repeated wheeling, even by a tractor of only about 2 tonnes weight, can produce soil conditions in which aeration can be limiting for crop growth. The use of dual wheels resulted in lower values of soil bulk density and associated greater soil aeration. The loosener alleviated the compaction produced by wheels and also improved soil aeration. For a sandy loam soil, greatest root growth and crop yield occurred at a bulk density of 1.43 Mg m −3 . Soil aeration as a component of soil physical quality is discussed.

Integrating no-till into crop–pasture rotations in Uruguay

Abstract: Crop–pasture rotations (CPR) are unusual around the world but have been the predominant cropping system in Uruguay since the 1960s. Uruguay has a temperate sub-humid climate, 80% of its landscape (16 Mha) is climax grasslands C3 and C4 species. Beef, wool, and dairy are the main commodities. Crops occupy a portion of the remaining 20% land area, primarily on Argiudolls and Vertisols, rotated with seeded grass and legume pastures. Continuous cropping (CC) with conventional tillage (CT) has proven unsustainable due to decreased soil productivity. Seeded pasture periods increased soil productivity. CPR adoption created less variable inter-annual economic results, but soil degradation remained a major concern during the crop cycle using CT. Farmers and technicians became interested in no-till (NT) to reduce erosion and production cost. Currently, approximately 52% of crop producing farms and 25% of dairy farms have adopted NT. This paper synthesizes research results (mainly from long-term experiments) contrasting CC versus CPR with CT (1960–1990) and NT (from 1990). Soil erosion was reduced more than six times with NT in CC, and almost three times in CPR compared with CC using CT; but combining the use of CPR and NT resulted in the same low erosion rate as under natural pasture. The transition from CT to NT is not always easy. The time between herbicide application to pasture and planting of the first crop of the rotation crop cycle with NT is a critical transition factor to optimize N and water availability, and soil tilth. Chiseling or paraplowing can alleviate plow-pans inherited by NT from previous CT; but higher soil strength at the soil surface under NT contributes to better forage utilization under grazing. Soil organic carbon (SOC) content in CC decreased with CT, and was maintained with NT only if grain was harvested. In CC systems with harvested forage, SOC decreased even with NT. CPR with NT maintained or increased the original SOC content. The paper concludes with a discussion on the relative sustainability of CC versus CPR with NT. Both are sustainable from the soil quality and productivity standpoints. But compared with CC, CPR is a more economically and climatically buffered system, due to higher diversity. Also, CPR systems are more environmentally sustainable since fuel and agrochemicals usage is reduced approximately 50%.

Tillage effects on compaction, earthworms and other soil quality indicators in Hungary

Abstract: The philosophy toward tillage throughout the last century in Hungary can be characterized as a fight against extreme climatic and economic situations. The ‘Hungarian reasonable tillage’ approach that was promoted by Cserhati at the end of the 1800s was aimed at reducing tillage without increasing the risk of crop failure in arable fields. Recently, new tillage trends and systems have been introduced because of the rise in energy prices and because of the need to cut production costs, conserve soil and water resources and protect the environment. In Hungarian relation, the rationalized plowing, loosening and mulching systems are counted to the new tillage solutions. There are new steps in the sowing methods too, such as seedbed preparation and plant in one pass, till and plant, mulch-till and plant and direct drilling, which are environment capable, throughout improving soil condition and avoiding the environment harms. The applicability of various soil conservation tillage methods is currently being tested in research projects and discussed in workshops throughout the country. In this paper, soil quality problems such as compaction, trends in soil tillage, and factors affecting soil quality or condition as well as improvement and maintenance are summarized. The data show that annual disking and plowing causes subsoil compaction at the depth of tillage within 3 years and that the compacted layer expanded both in surface and deeper layers after the 5th year. Soil quality deterioration by tillage-pans was improved by subsoiling and maintained by direct drilling and planting soil-loosening catch crops. Within a loam and a sandy loam soil there were close correlations between earthworm activity and soil quality. Earthworm numbers increased on undisturbed but noncompacted soils and soils that included stubble residues remaining on the surface, but did not increase on soils that were deteriorated by tillage-pans or left bare by the absence of mulch. Our goal for the new millennium, is to use only enough tillage to create and maintain harmony between soil conservation, soil quality and crop production.

Long-term tillage system effects under moist cool conditions in Switzerland

Abstract: How do different soil tillage systems influence soil quality over the years? Under moist cool conditions is it possible in the long term to reduce dramatically soil tillage intensity without experiencing reductions in yield or other problems? In 1987, the Swiss Federal Research Station for Agricultural Economics and Engineering in Tanikon initiated a long-term soil tillage trial to clarify these questions. The trial compared mouldboard plough, chisel, paraplow, shallow tillage and no-tillage systems on a well-drained Orthic Luvisol with 160 g kg −1 clay, 310 g kg −1 silt, and under a climate that has a mean annual precipitation of 1180 mm. The tillage treatment effects were evaluated by measuring several biological, chemical, and physical soil quality indicators. Reduced soil tillage increased earthworm populations, reduced Pseudocercosporella herpotrichoides infection in wheat ( Triticum aestivum ) and increased plant colonisation by arbuscular mycorrhizal fungi. Yields for no-tillage and other ploughless cultivation techniques were on par with those obtained by ploughing. An exception was direct-drilled maize ( Zea mays ), where no-tillage decreased yield by more than 10% over the course of 14 years. In the first 7 years of the trial, the level of soil organic carbon in all the tillage regimes was approximately 40% lower than natural grassland (initial situation 1987=75 Mg SOC ha −1 ). The no-tillage method did not differ from the others in respect of bulk density, but it showed an increased preconsolidation stress and hence better trafficability. Under Switzerland’s moist cool climatic conditions, it is possible to reduce soil tillage intensity without substantial reductions in yield, and at the same time improve soil quality.

Influence of cultivation and fertilization on total organic carbon and carbon fractions in soils from the Loess Plateau of China

Abstract: To evaluate the degradation of soil quality and find ways to maintain soil fertility on the Loess Plateau of China, the effects of cultivation time on total organic carbon (TOC), light fraction of organic carbon (LFOC), and microbial biomass carbon (MB-C) in two soil chronosequences comprised of Huangmian (Calcaric Cambisols, FAO) and Huihe (Haplic Greyxems, FAO) soils were investigated. The effects of fertilization on the TOC and its fractions were also studied using samples from a long-term experiment on Heilu soil (Calcic Kastanozems, FAO). Upon cultivation, Huangmian soil (0–20 cm) lost 77% of TOC within 5 years, at a reduction rate of 2.15 Mg C ha−1 per year. The Huihe soil (0–20 cm) lost 70% of TOC at a rate of 0.96–1.06 Mg C ha−1 per year over 42 years. In the Huangmian soil, water and tillage erosion are likely the main reasons for organic carbon decline, while organic matter decomposition and water erosion appear to be dominant factors in the Huihe soil. The LFOC decreased by 73 and 90% for the Huangmian and Huihe soil for the corresponding period. Changes in microbial biomass carbon (MB-C) showed the same trend as TOC and LFOC. The results of the long-term experiment on the Heilu soil indicated that manure alone and manure plus nitrogen and phosphorus fertilizer treatments restored TOC and MB-C to the level of the native sod, indicating the importance of manure addition in maintaining soil fertility over the long term (20 years). The straw return plus nitrogen and phosphorus fertilizer treatment had a significantly higher TOC than nitrogen plus phosphorus fertilizer alone. Organic matter additions in the form of manure or straw, either alone or in combination with chemical fertilizers, appears to be more effective in maintaining or restoring organic matter in Heilu soil on the Loess Plateau than chemical fertilizer alone.

Least limiting water range indicators of soil quality and corn production, eastern Ontario, Canada

Abstract: The least limiting water range (LLWR) attempts to incorporate crop-limiting values of soil strength, aeration, and water supply to plant roots into one effective parameter (on the basis of soil water content). The LLWR can be a useful indicator of soil quality and soil physical constraints on crop production. This study focused on assessing dynamic cultivation zone LLWR parameters between different cropping/tillage/trafficked clay loam plots at Winchester, Ont., to identify potential management impact on surficial soil physical conditions for contrasting growing seasons. This study also evaluated dynamic cultivation layer LLWR variables as indicators of corn ( Zea mays L.) plant establishment and corn yield. The results suggest that no-till soils had lower average air-filled porosities (AFP) and O 2 concentrations than respectively managed tilled plots for both years of study. Potential trafficking effects on aeration properties were most evident in no-till relative to till; preferentially trafficked no-tilled plots had lower AFP and O 2 concentrations than respective non-preferentially trafficked no-till plots for both years of study. Corn establishment and yield variability were principally explained by cumulative differences between daily AFP and aeration threshold values, and the cumulative number of days daily AFP was below an AFP aeration threshold for specific corn growth stage periods. Lower AFP was linked to lower yields and plant establishments. Soil strength, as measured by cone penetration resistance, was important over certain sites, but not as important globally as AFP in predicting crop properties. Overall, conventional tilled soils that were not preferentially trafficked had most favorable aeration properties, and subsequently, greatest corn populations and yields. No-till soils were at greater risk of aeration limiting conditions, especially those in continuous corn and preferentially trafficked.

Erodibility of agricultural soils on the Loess Plateau of China

Abstract: Soil erodibility is thought of as the ease with which soil is detached by splash during rainfall or by surface flow. Soil erodibility is an important factor in determining the rate of soil loss. In the universal soil loss equation (USLE) and the revised universal soil loss equation (RUSLE), soil erodibility is represented by an erodibility factor ( K ). The K factor was defined as the mean rate of soil loss per unit rainfall erosivity index from unit runoff plots. Although high rate of soil loss from the Loess Plateau in China is well known and widely documented, it is remarkable that there is little systematic attempt to develop and validate an erodibility index for soils on the Loess Plateu for erosion prediction. Field experimental data from four sites on the Loess Plateau were analyzed to determine the K factor for USLE/RUSLE and to compare with another erodibility index based on soil loss and runoff commonly used for the region. The data set consists of event erosivity index, runoff, and soil loss for 17 runoff plots with slope ranging from 8.7 to 60.1%. Results indicate that the K factor for USLE/RULSE is more appropriate for agricultural soils on the Loess Plateau than the erodibility index developed locally. Values of the K factor for loessial soils range from 0.0096 to 0.0269 t h/(MJ mm). The spatial distribution of the K value in the study area follows a simple pattern showing high values in areas with low clay content. For the four sites investigated, the K factor was significantly related to the clay content, ( K =0.031−0.0013 Cl, r 2 =0.75), where Cl is the clay content in percent. The measured values of the K factor are systematically lower than the nomograph-based estimates by a factor of 3.3–8.4. This implies that use of the nomograph method to estimate soil erodibility would considerably over-predict the rate of soil loss, and local relationship between soil property and the K factor is required for soil erosion prediction for the region.

Effects of soil management practices and tillage systems on surface soil water conservation and crust formation on a sandy loam in semi-arid Kenya

Abstract: The effect of different soil management practices on crust strength and thickness, soil water conservation and crop performance was investigated on a ferric lixisol in a semi-arid environment of eastern Kenya. The study proved that manure and mulching with minimum tillage have a greater effect on the water balance of crusted soils and maize emergence. There was increase in steady infiltration rates, amount of soil water stored in the soil and better drainage. The physical effect of mulch was less important in the rehabilitation of crusted soils in the study site when it was incorporated into the soil. Manure and surface mulch with minimum tillage should therefore be taken into account in land management and water conservation in the semi-arid areas of Kenya. The response of crops to the improved water availability due to manure with minimum and with conventional tillage and surface mulch was very clear. These management practices should be recommended when considering the effectiveness of soil and water management techniques in the study area.

Simulation of soil–blade interaction for sandy soil using advanced 3D finite element analysis

Abstract: In this paper a finite element investigation of the tillage of dry sandy soil, using the hypoplastic constitutive material model, is described. In most earth moving machinery, such as bulldozers or tillage tools, the working tool is a blade. Hence for tillage systems, accurately predicting the forces acting on the blade is of prime importance in helping to enhance productivity. The initial conditions, such as blade geometry or soil type, and operating conditions, such as cutting speed and cutting depth, have been shown experimentally to have a great effect on machine productivity. Experimental studies give valuable insights but can be expensive and may be limited to certain cutting speeds and depths. Results are also highly dependent on the accuracy of the measuring devices. However with increasing computational power and the development of more sophisticated material models, finite element analysis shows more promise in analyzing the factors affecting soil-blade interaction. Most of the available finite element studies in the literature are two-dimensional or if three-dimensional (3D), are limited to a certain blade displacement depending on the element distortion limit before the solution has convergence problems. In this study, a 3D finite element analysis of soil-blade interaction was carried out based on predefined horizontal and vertical failure surfaces, to investigate the behavior of the soil-blade interface and study the effect of blade-cutting width and lateral boundary width on predicted forces. Sandy soil was considered in this study and modeled using the hypoplastic constitutive model implemented in a commercial finite code, 'ABAQUS'. Results reveal the validity of the concept of predefined failure surfaces in simulating soil-blade interaction and the significant effect of blade-cutting width, lateral boundary width and soil swelling on cutting forces.

Morphological characterisation of soil structure in tilled fields: from a diagnosis method to the modelling of structural changes over time

Abstract: Characterisation of soit structure within the tilled layer of cultivated fields is crucial because the importance of this soil characteristic on the biological, chemical and physical properties of the soil and its repercussions on water cycle, root growth and functioning. We present in this paper a method for field characterisation of soil structure. This method, practised since the 1970s, was designed for field diagnosis of the effects of cropping systems on soil structure. It is based on a stratification of the observation face of a pit dug perpendicular to the direction of tillage and traffic: spatial compartments are distinguished, according to the nature of the mechanical stresses they have been submitted to during tillage and crop management. Characterisation of soil structure is performed on a morphological basis, using two criteria, each of them addressing a specific organisation level of the soil: firstly, clods size distribution, proportion of fine soil and the way the clods are brought together are considered; then, secondly, the clods are classified in three types, on the basis of the importance and the origin of their internal structural porosity. Physical measurements (bulk density, compaction test, and water retention) are presented, which demonstrate that physical behaviour is different between clod types. These results justify the use of the method to model changes with time in soil structure, under the effects of the main factors affecting soil structure dynamics in tilled fields: compaction, fragmentation, climate and biological activity. A model which simulates at the field scale the changes overtime of the proportion of compacted clods within the tilled layer is presented. In this model, the tilled layer is represented as a set of 1 cm2 pixels, regularly located on a square grid. Each pixel is defined by its co-ordinates and a specific structure, compacted or non compacted. The pixel co-ordinates are modified during ploughing, for which the model calculates the lateral and vertical displacement of the soil. The structure of any individual pixel can be changed, depending on the soil condition and the operation type. This model was evaluated by comparing its outcomes to measurements obtained from a long term field experiment designed to study soil structure dynamics. (Resume d'auteur)

Tillage and crop management effects on soil erosion in central Croatia

Abstract: Soil erosion continues to be a primary cause for soil degradation and the loss of soil quality throughout the world. Our objectives were to quantify soil erosion (referred to as erosional drift) and to assign erosion risk to six tillage and crop management treatments evaluated from 1995 to 1999 for a 5-year maize ( Zea mays L.), soybean ( Glycine hyspida L.), winter wheat ( Triticum aestivum L.), oil-seed rape ( Brassica napus var. oleifera L.), and spring barley ( Hordeum vulgare L.) plus double-crop soybean rotation on Stagnic Luvisols in central Croatia. Standard black fallow (tilled, unsown, and without any vegetative cover) Universal Soil Loss Equation (USLE) plots were used to establish the erosion potential associated with the rainfall pattern for each year. Soil loss from the check plots was several times greater than the T value, which is estimated to be 10 t ha −1 per year. During the 2 years when spring seeded maize or soybean were grown (1995 and 1996) erosion risk was extremely high, especially for treatments where tillage and planting (row direction) were up and down the slope. When autumn seeded winter wheat or oil-seed rape were grown (1996/1997 or 1997/1998), soil erosion was insignificant. Also, except when plowing and sowing were up and down slope, erosion loss for the spring barley plus double-crop soybean crops in 1999 was insignificant. With no-tillage, soil erosion from the maize and soybean crops was reduced 40 and 65% compared to plowing up and down slope, even though the planting direction was still up and down the slope. With the exception of maize in 1995, erosion losses were moderate to insignificant when plowing and planting were performed across the slope. We conclude that erosion risk can be used as a reliable indicator of sustainable land management and that using no-tillage or plowing and planting perpendicular to the predominant slope are effective soil conservation practices for this region.

Structural heterogeneity of the soil tilled layer as characterized by 2D electrical resistivity surveying

Abstract: Our research was aimed at analysing the possibilities of using a geophysical method, the electrical resistivity method, to describe the structure of a cultivated loamy soil. Soil electrical resistivity was measured in laboratory conditions on two soil blocks (0.30 m x 0.30 m x 0.20 m) with 2D Wenner configuration using an inter-electrode spacing of 0.015 m. The two soil blocs exhibited different structure: one with a compacted structure (bulk density equal to 1.59 Mg m -3 with a standard deviation of 0.05 Mg m -3 ) and the second with a porous structure (bulk density equal to 1.39 Mg m -3 with a standard deviation of 0.04 Mg m -3 ). The electrical resistivity results showed a significant 10 Ω m difference between the compacted block (30 Ω m) and the porous block (40 Ω m) due to the difference in their bulk density. This structural distinction by electrical resistivity needs temperature correction using the Campbell equation. The soil electrical resistivity was also measured in the field with a 2D Wenner configuration using an inter-electrode spacing of 0.10 m along a 3.20 m transect. After the electrical measurements, a pit was dug and the contours of porous and compacted zones in the ploughed layer were identified, the boundaries between the ploughed layer, the plough pan and the pedological horizons were defined. Comparisons between inverted electrical resistivity maps and visual morphological descriptions showed the ability of electrical resistivity to detect wheels tracks. However, electrical surveying in a heterogeneous field after ploughing did not correspond to the visual morphological description, the latter being 2D whereas the electrical resistivity map is a 2D projection of a 3D sensing. As a non-destructive method, the electrical resistivity method could improve the quantitative description of the tilled layer and permit a temporal survey.

Soil precompression stress - I. A survey of Swedish arable soils

Abstract: In determining stress limits to prevent soil compaction, it is important to know the mechanical properties of soils. One important parameter is the precompression stress, which is often used as a criterion for soil susceptibility to compaction. A series of uniaxial compression tests on Swedish arable soils was conducted by Eriksson [Markpackning och rotmiljo (soil compaction and root environment), Report 126, Division of Agricultural Hydrotechnics, Department of Soil Sciences, Swed. Univ. Agric. Sci., Uppsala, Sweden, 1982 (in Swedish, with English summary)]. The objective of the present study was to derive precompression stress values from these data. Eighteen soils, generally classified as Eutric Cambisols and with clay contents ranging from 62 to 863 g kg−1 were used. Soil cores (25 mm high, 72 mm in diameter) were sampled at 10 cm intervals to a depth of 1 m and equilibrated at 0.5 or 60 kPa water tension. The cores were then compressed in an oedometer by sequential stresses of 25, 50, 100, 200, 400 and 800 kPa. Precompression stress was determined according to Casagrande [The determination of the pre-consolidation load and its practical significance, in: Proceedings of the International Conference on Soil Mech. and Found. Eng. (ICSMFE), vol. 3, Cambridge, MA, 22–26 June 1936, pp. 60–64] and by regression methods. Precompression stress was higher for subsoils than for topsoils and higher at higher soil water tension, but was difficult to relate to soil physical properties. Values determined according to Casagrande were generally between 100 and 200 kPa. Values determined by regression methods had a smaller range compared to the Casagrande method. The values of precompression stress indicate a low risk for subsoil compaction on Swedish soils, which is not in line with practical experience in compaction experiments. The concept of precompression stress as a clear transition from small, elastic deformation to larger, plastic deformation could not be supported by the stress–strain relationships obtained in this study. There is an urgent need to design laboratory tests that reflect soil behaviour in the field.

Specific draught for mouldboard plough, chisel plough and disc harrow at different water contents

Abstract: The objective of the present study was to measure the specific draught (force per cross-sectional area of worked soil) and energy use for soil fragmentation for different tillage implements and soil conditions. Draught was calculated from measurements of fuel consumption and speed during tillage with a mouldboard plough and a chisel plough set to working depths of 13, 17 and 21 cm, and a disc harrow. Tillage was carried out at three different water contents (“Wet”, “Moist” and “Dry”) on two sites. The average working depth was calculated from weighing the loose soil within a 0.25-m 2 frame. Specific area of the soil was determined by sieving. Soil strength was measured in situ using a shear vane and a penetrometer. Average working depth was much less than the set working depth for the chisel plough. Specific draught was generally the lowest for the mouldboard plough and the highest for the chisel plough, and increased with decreasing soil water content. The specific draught was strongly correlated to soil cohesion, but not to penetration resistance. The proportion of coarse aggregates after tillage was the highest for the mouldboard plough and the lowest for the moist soil. The energy use for soil fragmentation was in most cases the lowest for the disc harrow, while there were small differences between the chisel and the mouldboard ploughs. The results show that the mouldboard plough is energy efficient for loosening soil, while the disc harrow is energy efficient for soil fragmentation during primary tillage. Tillage at an intermediate water content, close to the plastic limit, gave the largest proportion of small aggregates and consequently the lowest energy use for soil fragmentation.

Technical solutions to reduce the risk of subsoil compaction: effects of dual wheels, tandem wheels and tyre inflation pressure on stress propagation in soil

Abstract: The use of heavy machinery is increasing in agriculture, which induces increased risks of subsoil compaction. Hence, there is a need for technical solutions that reduce the compaction risk at high total machine loads. Three field experiments were performed in order to study the effects of dual wheels, tandem wheels and tyre inflation pressure on stress propagation in soil. Vertical soil stress was measured at three different depths by installing probes into the soil horizontally from a dug pit. In one experiment, also the stress distribution below the tyre was measured. Beneath the dual wheels, vertical stresses at 0.15 and 0.3 m depth were lower between the two wheels than under the centre of each wheel, despite the gap between the wheels being small (0.1 m). At 0.5 m depth, vertical stress beneath the wheels was the same as between the two wheels. The stress interaction from the two wheels was weak, even in the subsoil. Accordingly, measured stresses at 0.3, 0.5 and 0.7 m depth were highest under the centre of each axle centre line of tandem wheels, and much lower between the axles. For a wheel load of 86 kN, tyre inflation pressure significantly affected stress at 0.3 m depth, but not at greater depths. Stress directly below the tyre, measured at 0.1 m depth, was unevenly distributed, both in driving direction and perpendicular to driving direction, and maximum stress was considerably higher than tyre inflation pressure. Calculations of vertical stress based on Boussinesq's equation for elastic materials agreed well with measurements. A parabolic or linear contact stress distribution (stress declines from the centre to the edge of the contact area) was a better approximation of the contact stress than a uniform stress distribution. The results demonstrate that stress in the soil at different depths is a function of the stress on the surface and the contact area, which in turn are functions of wheel load, wheel arrangement, tyre inflation pressure, contact stress distribution and soil conditions. Soil stress and soil compaction are a function of neither axle load nor total vehicle load. This is of great importance for practical purposes. Reducing wheel load, e.g. by using dual or tandem wheels, also allows tyre inflation pressure to be reduced. This reduces the risk of subsoil compaction.