Trends in tillage practices in relation to sustainable crop production with special reference to temperate climates

The concept and some definitions of sustainable agriculture are reviewed. Most of these definitions include economic, environmental and sociological aspects. The finite area of land emphasizes the need for consideration of soil conservation and of soil quality in relation to sustainability. An important element of soil quality is rooting depth. Therefore loss of soil by erosion is a dominant factor in long-term sustainability. The effects of tillage on soil parameters in minimum data sets that have been proposed to describe soil quality are reviewed. Soil organic matter may be one of the most important soil quality characteristics in relation to tillage because of its influence on other soil physical, chemical and biological properties. Conservation tillage practices can increase the organic matter content, aggregate stability and cation exchange capacity (CEC) of the topsoil. However, bulk density and penetrometer resistance are also increased, especially with zero tillage. Although such soil quality parameters may form a basis for describing some of the consequences of particular tillage practices, they do not provide a basis for predicting the outcome in terms of crop growth and yield. This is both because critical values of soil quality parameters have not been defined and because in some soils biopore formation in zero or minimally tilled land can modify the soil for water movement and for root growth and function.

The effects of tillage on crop growth and yield in long-term experiments are reviewed. The review only includes experiments in North America, Europe and New Zealand that have lasted 10 years or more to allow for seasonal variation in weather, possible progressive changes in soil conditions and the learning phase often experienced when new tillage methods are used. While there is a good deal of variation in the results of these tillage experiments some patterns have emerged. In long-term experiments, yields of maize in Europe and the US and soybeans in the US have been similar after ploughing and no-tillage, especially on well-drained soils. In Europe, yields of winter cereals have also been similar after traditional and simplified tillage but yields of spring cereals have sometimes been less after direct drilling than ploughing.

Trends in tillage practices are reviewed. Conservation tillage in the US is increasing and is used on about 30% of cropland, including no-till on about 10% of cropland. This increase in use of conservation tillage is mainly attributed to the legal requirement for farmers who are in government price support programs to adopt conservation plans which may involve conservation tillage. However, the allowable rates of erosion in these plans are likely to be in excess of rates of erosion for long-term sustainability. Survey information on tillage practices needs to be considered in relation to predictions on suitability of conservation tillage based on experimental results. In the semi-arid prairies of Canada there is a trend toward fewer cultivation operations, but in eastern Canada the mouldboard plough is still the dominant tillage method. In Europe although erosion is less obvious it is believed to be increasing, but minimum tillage is not widely used. This is because of the need to remove at least some straw for successful minimum tillage in sequential winter wheat and barley crops, but there are few economic uses for straw, and burning is illegal in many countries. In the more moist cooler conditions of Europe grass weed proliferation is another constraint, at least with present technology. So far, the overall success of conservation tillage has not been limited by the growing problem of genetic resistance of weeds to herbicides. Societal attitudes to the continued use of herbicides may pose longer-term problems for some conservation tillage practices.     

Effect of long-term conservation tillage on soil biochemical properties in Mediterranean Spanish areas

In semi-arid Mediterranean areas, studies of the performance of conservation tillage systems have largely demonstrated advantages in crop yield, soil water storage and soil protection against wind and water erosion. However, little attention has been given to interactions between soil biochemical properties under different tillage practices. Biochemical properties are useful tools to assess changes caused by different soil tillage systems in long-term field experiments. This study deals with the effect of long-term tillage practices (reduced tillage and no-tillage vs. traditional tillage) on soil chemical properties and microbial functions in three different sites of Spain (two of them located in the Northeast and one in the Southwest) under semi-arid Mediterranean conditions. Soil biological status, as index of soil quality, was evaluated by measuring microbial biomass carbon (MBC) and dehydrogenase (an oxidoreductase) and protease (a hydrolase) activities at three soil depths (0–5, 5–10 and 10–25 cm). In the three experimental areas, increases in soil organic matter content, MBC and enzymatic activities were found at the superficial layers of soil under conservation tillage (reduced tillage and no-tillage) in comparison with traditional tillage. Values of the stratification ratio of some biochemical properties were significantly correlated with yield production in Northeast sites.Conservation tillage has proven to be an effective strategy to improve soil quality and fertility in Mediterranean areas of Spain.     

Some major developments in soil science since the mid-1960s

Although the science of soil was established about 150 years ago with the modern soil science taking off after the Second World War, the new Millennium has brought other challenges and new opportunities. Rapidly increasing population in countries that can least afford it have made them food-insecure. With inadequate inputs in agriculture, developing countries are degrading their lands rapidly and destroying ecosystems. Affluence in the richer countries has precipitated other problems hampering ecosystem functions and quality of land resources. These changing conditions have placed new demands on both the society and the soil science community. The latter has resulted in new areas of soil sub-disciplines such as land and soil quality, land degradation and desertification, cycling of bio-geochemicals, soil pollution assessment and monitoring etc. Advances in information technology have also enabled the science to meet the new demands of the enviro-centric world. In the last decade, noticeable changes are evident in methods and research priorities in the discipline. Soil resource assessment and monitoring is entering a new era, in terms of quality of information produced by new information technologies through the innovative use of Geographic Information Systems and remote sensing and significantly improving the acceptance and use of soil survey information. Electronic technology has dramatically increased the demand for and ability to process more data. Other innovations have resulted in quantitative approaches in soil genetic studies and demonstrated the integral role of soils in ecosystems. For global and regional resource assessment, concepts and procedures were refined. The World Reference Base for soil classification and the Global Soil and Terrain Database are the first steps towards standardisation and a more detailed assessment of global soils. The global assessment of human-induced land degradation and vulnerability to desertification are benchmark products of the databases. Environmental pollution and its effects on human and ecosystem health have become public concerns and soil science has contributed to localising, quantifying, and developing mitigation technologies to address the problems. The challenges of climate change and the charge to maintain ecological integrity have been met with technologies such as conservation tillage, agroforestry, precision agriculture etc. New concepts such as multi-functionality of land, soil quality, sustainability of agriculture and carbon sequestration, have emerged leading to new management strategies and an enhanced quality of life.     

Tillage systems and soil properties in North America

This paper reviews current knowledge on the range and extent of various tillage systems used in North America with special reference to the effects on soil properties, the erosion hazard and water quality. The increasing adoption of conservation-tillage systems since their introduction in the early 1960s follows an enhanced awareness of the increasing risks of soil erosion and non-point source pollution and the high cost of fuel with conventional tillage. Most “conventional tillage” systems encompass complete inversion tillage along with several secondary and tertiary tillage methods. In contrast, conservation-tillage systems involve streamlining various farm operations, thereby reducing the frequency and intensity of the soil manipulative operations. Reduction in tillage intensity has been accompanied by the development of rotations and cropping systems, methods of surface and internal drainage, fertilizer technology and pest management alternatives.

The status of antecedent soil physical properties is an important factor affecting the choice of tillage systems. Important soil physical properties governing the choice of tillage systems include soil wetness and anaerobiosis, soil temperature and soil structure including its susceptibility to compaction, crusting or erosion. Tillage systems affect soil physical, chemical and biological properties. Among drastic tillage-induced changes in soil properties are bulk density, infiltration rate, aggregation and aggregate size distribution, soil organic carbon and nutrient profile, microbial activity and species diversity, and the population of earthworms. Macropores and biochannels are usually more prevalent in conservation-tillage than conventional-tillage systems. Conservation tillage induces stratification of soil organic matter and related nutrients, enhances the activity of soil fauna and leads to acidification. The magnitude of these changes depends on the soil type, the cropping systems and the type of conservation tillage adopted. Soil organic carbon and nutrient stratification are generally more pronounced in coarse-textures than in clayey soils. Conservation tillage is also associated with greater biomass pool size. The latter affects the nutrient response curves of the soil. Nitrification and denitrification are other important processes affected by tillage systems.

The widespread adaption of conservation-tillage systems, although beneficial in controlling off-site sedimentation, has raised concerns about the potential for increased leaching of nutrients and pesticides to groundwater. Important pollutants associated with conservation tillage are nitrate and pesticides. Some studies have shown little effect of tillage on losses of pesticides. Conservation tillage may suppress crop yields, especially on heavy textured soil with poor internal drainage and in those prone to soil compaction caused by vehicular traffic.     

耕作方式对土壤螨类群落结构的影响

土壤螨类是土壤生态系统中重要的指示生物之一。为探讨耕作方式对土壤螨类数量、类群数、群落结构以及垂直分布的影响, 试验选取位于东北黑土区中国科学院海伦农田生态系统国家野外科学观测研究站中5种耕作方式(免耕耕作、少耕耕作、平翻耕作、组合耕作和旋耕耕作)试验区内土壤螨类为研究对象, 采用改良干漏斗(Modified Tullgren)法, 于2009年5月、6月和7月3个时期分离0~15 cm土层中的土壤螨类。结果表明: 耕作方式对土壤螨类数量和类群数存在显著影响, 3个时期共捕获土壤螨类2 441只, 免耕耕作、少耕耕作、组合耕作、旋耕耕作和平翻耕作分别捕获土壤螨类366只、436只、553只、819只和267只, 分别隶属于13科、18科、13科、14科和11科。传统的旋耕耕作具有最高的土壤螨类个体数量, 而保护性耕作中的少耕耕作具有最高的土壤螨类类群数。不同时期耕作方式对土壤螨类垂直分布的影响不同, 5月除免耕耕作外其他4种耕作方式均较好地保持了土壤螨类垂直分布的表聚特征, 即0~5 cm土层中土壤螨类的数量显著(P<0.05)高于其他两层(5~10 cm, 10~15 cm), 其中组合耕作和少耕耕作在3个时期中均较好地保持了土壤螨类的表聚特征, 且少耕耕作较好地保持了土壤螨类的多样性。MGP分析结果表明: 土壤甲螨群落随季节的变化在组成上发生变化, 从最初的高等甲螨为优势类群转化为低等甲螨为优势类群, 免耕和少耕的这种趋势较其他耕作方式更为明显, 少耕耕作3个时期土壤甲螨的组成类型分别为P型、G型和O型, 而免耕耕作3个时期土壤甲螨的组成类型分别为P型、O型和G型。少耕和免耕两种保护耕作方式较其他耕作方式更有利于土壤螨类群落结构的稳定性及多样性的保持, 有利于农田土壤生态环境的保护。     

Reducing tillage in cultivated fields increases earthworm functional diversity

Alternative cropping systems such as conservation agriculture have been implemented to limit the harmful effects of intensive conventional cropping systems. Conservation agriculture is known to modify the structural diversity of earthworm communities, but no data have been reported so far on their functional diversity. Structural and functional indices of community were used to study the effects of different soil tillage intensity on earthworm diversity in arable soils.Field data were collected in four agricultural trials across France representing different soiland climatic conditions. Three types of soil tillage were assessed: plowing, superficial tillage and direct seeding. Earthworm abundance, species richness and ecomorphological group abundance were investigated. Seven functional traits, i.e. body length, body mass/length ratio, epithelium type, cocoon diameter, typhlosolis type, carbon preferences and vertical distribution, were selected according to their hypothesized link with mechanisms of tillage impact. Functional diversity indices were then computed. Soil tillage intensity decreased functional diversity and modified the functional trait profile within the earthworm community whereas neither structural diversity (species number) nor abundance changed with tillage intensity. Differences between plowing and direct seeding were significant in each trial, and superficial tillage often showed intermediate trait values. Regarding ecomorphological groups, anecic abundance was positively influenced by a decrease in soil tillage, contrary to epigeic and endogeic earthworms that showed no response. Tillage acts as an environmental filter, and decreasing its intensity caused a lesser convergence of traits and thus higher functional trait diversity. We demonstrated that a trait-based approach better permitted comparisons of community responses across sites than species number or abundance.     

Global achievements in soil and water conservation: The case of Conservation Agriculture

In response to the dust bowls of the mid-thirties in the USA, soil and water conservation programmes involving reduced tillage were promoted to control land degradation, particularly soil erosion. The farming and land management practices that were considered to adequately address soil and water conservation objectives were based on no-till seeding and maintenance of soil mulch cover. This collection of practices led to what became known as conservation tillage, although no-till systems by definition avoid soil disturbance by no-till direct seeding, and maintain an organic mulch cover on the soil surface.This article is an overview of achievements in soil and water conservation on agricultural lands through the experience derived from the adoption and spread of Conservation Agriculture (CA) world-wide. CA is an agro-ecological approach to sustainable production intensification. It involves the application of three inter-linked principles that underpin agricultural production systems based on locally formulated practices: (i) permanent no or minimum mechanical soil disturbance, which in practice entails direct seeding through mulch into no-till soils; (ii) maintenance of soil cover with crop residues and green manure crops, particularly legumes; and (iii) diversified cropping system involving annuals and perennial in rotations, sequences and associations.In 2011, CA had spread over 125 million hectares (9% of the global cropped land) across all continents and most agro-ecologies, including small and large farms. In addition, there is a significant area of CA orchards in the Mediterranean countries. CA is now considered to be a practical agro-ecological approach to achieving sustainable agriculture intensification. It offers environmental, economic and social advantages that are not fully possible with tillage-based production systems, as well as improved productivity and resilience, and improved ecosystem services while minimizing the excessive use of agrochemicals, energy and heavy machinery. While there are challenges to the adoption of CA, there is also increasing interest from producers, the civil society, donors and private sector institutions to further promote and service the uptake and spread of CA globally.     

Tillage systems for the West African Semi-Arid Tropics

The West African Semi-Arid Tropics (WASAT) is characterized by a monomodal rainfall pattern, and based on the amount of annual rainfall it can be divided into three ecologies: Sahel, Sudan and Northern Guinea savannahs. The major soil groups of the WASAT are Alfisols, Inceptisols and Entisols and Vertisols, with the former three predominating. The major soil constraints to crop growth are: soil compaction, low fertility, high temperature and low soil water retention, available water holding capacity and infiltration rate. Tillage in traditional farming systems is manual. However, mechanization of tillage operations has received emphasis in the recent past. The accelerated soil degradation which is a feature of mechanized-tillage systems under rainfed agriculture can be minimized with no tillage. However, lower yield have been reported to occur with no tillage. Some possible reasons are: the absence or low amounts of residue mulch, high soil compaction, the presence of harmful soil insects in crop residues, the creation of stable pores by tillage in soils of high organic matter, silt and fine sand contents. Unavailability of crop residues in a major impediment to the adoption of no tillage. The use of heavy and intensive mechanical tillage in irrigated agriculture leads to the formation of plow soles. Deep tillage such as subsoiling does not ensure the elimination of plow soles. While no tillage appears to hold promise for use in the irrigated agriculture of the WASAT much research remains to be done.     

Impact of perennial pasture and tillage systems on carbon input and soil quality indicators

Soil degradation associated with tillage is a major problem in Uruguayan agriculture. Either rotation of crops with pastures (ROT) or no-till (NT) cropping have been proposed as alternatives to minimize the impact of agriculture on soil quality. The combined impact on soil properties of ROT and NT has not been evaluated. In this study, we report results of the first 12 years of a long-term experiment established on a clay loam soil in western Uruguay. The objective was to determine the influence of conventional tillage (CT) and NT on systems under continuous cropping (CC, two crops per year) or ROT (3.5-year annual crops/2.5-year pastures). Soil samples taken at the beginning of the experiment in 1994 and in 2004 were analyzed for organic carbon (SOC), total organic carbon (TSOC) and total nitrogen content (STN), and for water-stable aggregation (WAS). Soil loss and erodibility indicators were studied using microrain simulator. With 12 years, the cumulative carbon (C) inputs of aboveground biomass were similar between tillage, but C input in CC was 50% higher than ROT. This difference was explained because 84% of the pastures dry matter was consumed by animals. Nevertheless we estimated a higher below ground biomass in ROT compared to CC systems (24.9 Mg ha⁻¹ vs. 10.9 Mg ha⁻¹). NT presented 7% higher SOC than CT (0–18 cm) with no differences between rotation systems. While all treatments declined in STN during 12 years, ROT had 11% and 58% higher STN and WAS than CC systems, with a large impact of the pasture under CT. Runoff and erosion were minimized under NT in both rotations systems. Thus, including pastures in the rotation, or switching from CT to NT improved soil quality properties. The expected benefit of combining NT and ROT will likely require more years for the cumulative effect to be detectable in both C input and soil properties.     

Controlled traffic farming—From research to adoption in Australia

Efficient mechanisation is a major factor underlying the high productivity and low cost of most Australian crop production systems. Efficiency has generally been associated with greater work rates, achieved by using equipment of greater power and weight. This trend has continued until very recently, despite a reduction in tillage for weed control.

Scientists have warned of erosion and soil structural degradation caused by tillage and traffic, but tillage, rather than field traffic was seen as the major problem, and reduction of tillage as the solution. Reduced tillage has provided major benefits, but adoption has occurred slowly and sustained zero tillage is still rare, except in controlled traffic farming systems.

The first part of this paper presents research evidence of the direct cost, practical impact and long-term effects of wheel traffic on cropped soil. Direct cost is associated with the energy requirements of disturbing wheeled soil. Practical impact occurs as a result of the lost opportunities and additional operations associated with wheel ruts. Long-term productivity and environmental impact occur because wheel traffic reduces plant available water and increases runoff and erosion.

In controlled traffic all equipment wheels are restricted to compacted permanent traffic lanes, so that soil in the crop beds and traffic lanes can be managed respectively for optimum cropping and optimum trafficability. Controlled traffic farming recognizes the symbiosis between controlled traffic and zero tillage in providing opportunities for more productive and sustainable farming of soil uncompromised by wheel effects.

The beneficial effects of controlled traffic have been demonstrated in widely different soils and mechanisation systems (e.g. Australia and China), and it has been vigorously advocated in both the USA and Europe, but large-scale adoption has been rare. The second part of this paper discusses cropping system response to controlled traffic farming, and the program which led to large-scale adoption in Australia. This happened first in extensive grain production, but adoption has since occurred in many Australian farming systems, supported by the availability of high-precision field guidance systems and a greater range of compatible equipment.

Controlled traffic farming reduces soil degradation and the energy requirements of cropping. It is also more productive, and its practicality and economic viability have been clearly demonstrated in enthusiastic farmer adoption, and the formation of an Australian Controlled Traffic Farming Association.     

Long-term impact of conservation tillage on stratification ratio of soil organic carbon and loss of total and active CaCO3

Under semi-arid conditions, the properties of many soils are influenced by the presence of organic matter and calcium carbonate (CaCO₃). However, the influence of different tillage systems on the development of these properties has scarcely been studied under semi-arid Mediterranean conditions. We studied the effect of long-term conservation tillage (CT) and traditional tillage (TT) on the stratification ratio of soil organic carbon and on CaCO₃ content. The study was conducted in a wheat (Triticum aestivum L.)–sunflower (Helianthus annuus L.) crop rotation established in 1991 under rainfed conditions in Southwestern Spain. As is traditional in this area, wheat was fertilised, but sunflower was not. Conservation tillage was characterised by reduced number of tillage operations and leaving crop residues on the soil surface, while TT was with mouldboard ploughing. Stratification ratio of soil organic C was calculated from C contents in the 0–5 and 5–10 cm soil layers divided by that in the 25–40 cm. Stratification ratio of soil organic C under the CT (>2) was significantly greater than under TT (<2); values >2 indicating better soil quality. Our results show a loss of CaCO₃ under both tillage systems. However, the loss of CaCO₃ was significantly higher under TT than under CT. Also, P and K accumulated in the soil surface and stratification ratio for both nutrients was greater in CT than in TT.     

Tillage effects on microbial biomass and nutrient distribution in soils under rain-fed corn production in central-western Mexico

Quantifying how tillage systems affect soil microbial biomass and nutrient cycling by manipulating crop residue placement is important for understanding how production systems can be managed to sustain long-term soil productivity. Our objective was to characterize soil microbial biomass, potential N mineralization and nutrient distribution in soils (Vertisols, Andisols, and Alfisols) under rain-fed corn (Zea mays L.) production from four mid-term (6 years) tillage experiments located in central-western, Mexico. Treatments were three tillage systems: conventional tillage (CT), minimum tillage (MT) and no tillage (NT). Soil was collected at four locations (Casas Blancas, Morelia, Apatzingán and Tepatitlán) before corn planting, at depths of 0–50, 50–100 and 100–150 mm. Conservation tillage treatments (MT and NT) significantly increased crop residue accumulation on the soil surface. Soil organic C, microbial biomass C and N, potential N mineralization, total N, and extractable P were highest in the surface layer of NT and decreased with depth. Soil organic C, microbial biomass C and N, total N and extractable P of plowed soil were generally more evenly distributed throughout the 0–150 mm depth. Potential N mineralization was closely associated with organic C and microbial biomass. Higher levels of soil organic C, microbial biomass C and N, potential N mineralization, total N, and extractable P were directly related to surface accumulation of crop residues promoted by conservation tillage management. Quality and productivity of soils could be maintained or improved with the use of conservation tillage.     

A conservation tillage research update from the Coastal plain soil and water conservation research center of South Carolina: A review of previous research

In the U.S. Southeastern Coastal Plains conservation tillage (CT) became useful as a management system with the development of in-row subsoiling systems capable of planting into heavy residues. Research priorities associated with the development of CT included: reducing cover crop water loss, improving stand establishment, assessing nutrient and water management requirements, determining optimal subsoiling strategies, understanding long-term conservation tillage effects on soil properties, evaluating the interaction of crop residue removal with tillage systems, and documenting tillage impact on pests and beneficial organisms. Since the late 1970s the Coastal Plains Soil and Water Conservation Research Center in Florence, SC has made a concerted effort to study these interactions and alleviate them as obstructions to the use of CT management. These studies showed that for Coastal Plain soils such as Norfolk sandy loam (fine-loamy, siliceous thermic, Typic Paleudults) winter cover crops such as rye (Secale cereale L.) desiccated the soil profile by evapotranspiration in the spring. This delayed emergence and early season growth of corn (Zea mays L.) but not full-season soybean (Glycine max (L.) Merr.). Conservation tillage helped manage soil strength by gradually increasing soil organic matter content, restricting traffic patterns and maintaining higher soil water contents. Laboratory studies demonstrated a negative correlation (R²=0.85) between proctor soil strength and organic matter content. Conservation tillage affected nematode, Bradyrhizobium japonicum and Heliothis species populations. Alternate cropping systems using rapeseed (Brassica napus L.) as a winter crop or sunflower (Helianthus annuus L.) either before soybean or after corn provided crop cover against potential soil loss from late autumn through early spring, when bare soil is exposed to intense rainfall. Water quality questions associated with CT have been raised but remain unanswered. Although CT can reduce runoff and erosion, the crop residues can support higher insect populations and pathogen inoculum levels, and thus prompt greater pesticide use. Quantifying relationships between soil strength, macropore formation and persistence, and water infiltration with surface and subsurface water quality is the focus of new long-term evaluations. The findings of these studies, published to date, are summarized in this paper.     

Abandonment of soil and water conservation structures in Mediterranean ecosystems: A case study from south east Spain

Traditional rainfed agriculture in semi-arid regions heavily relies on soil and water conservation (SWC) structures to supplement the sparse rainfall. As referring to the ecosystem functions of these constructions, when extensive such systems prevent any runoff into the fluvial system. The extent to which these dams and terraces resist major events is variable, and earthen dams can be major sediment sources. Extensification and increasing mechanization of rainfed agriculture in marginal areas have led to a change in cropping systems. Large-scale almond and olive plantations with widely spaced trees do not rely on runoff water, but draw the soil water from a large soil volume of bare soil maintained by regular shallow tillage. The high density of terraces has now become a nuisance to the farmers. The aim of this paper is to i) demonstrate the degradation of SWC structures and the relative importance of the driving forces, ii) assess the limits of the protection that earthen dams can provide by surveying their resistance during a heavy storm (return period 8.2 years) and iii) demonstrate the implications of the abandonment of SWC structures over the period 1956–2005 for the hydrological connectivity between croplands and the ephemeral rivers system. The headwaters of a marl catchment with a continuous area treated with SWC structures in Murcia region (Spain) already had a very high density of step terraces and check dams (182 m ha^− 1) in 1956. This density decreased by 27% in the period 1956–2005. Furthermore, many terraces have not been maintained and flow traces indicate that they no longer retain water. This is particularly true for the check dams in abandoned lands. The distance between the step terraces has increased over time, making them vulnerable to erosion. The mean drainage area of the dams that failed during the heavy storm was significantly (3.16 ha) higher than that of the ones that remained intact (1.11 ha). The probability of failure increases with drainage area from P = 0.16 for an area of 1.8 ha to P = 0.8 for an area of 20 ha. The percentage of cropland draining directly on the river system without interference of a check dam has increased from just 9% in 1956 to 31% in 2005 and 40% after the storm in November 2006.     

Soil sustainability indicators following conservation tillage practices under subtropical maize and bean crops

Conservation management systems such as no tillage may enhance sequestration of soil C. The soil properties that contribute to soil C storage under such systems are still largely unknown, especially in subtropical agroecosystems. We investigated the influence of tillage [mouldboard plough (MP) and no tillage (NT)] on soil organic C, microbial biomass and activity, structural stability and mycorrhizal status of a field cultivated with maize (Zea mays L.) or bean (Phaseolus vulgaris L.) on a Vertisol in Northern Tamaulipas, Mexico. Crop type, tillage system and soil depth had a significant effect on soil organic C, aggregate stability and bulk density. Soil organic C, microbial biomass C and N and dehydrogenase and phosphatase activities were greater with NT than with MP, particularly under bean cultivation. In the 0–5 cm layer, microbial biomass C and N were, on average, about 87 and 51% greater in the soils cultivated with bean and maize, respectively, under NT than under MP. Higher levels of mycorrhizal propagules, glomalin related soil protein (GRSP) and stable aggregates were produced under NT than under MP in both crops. The no-tillage system can be considered an effective management practice for carrying out sustainable agriculture under subtropical conditions, due to its improvement of soil physical and biochemical quality and soil C sequestration.     

Soil tillage for crop production and for protection of soil and environmental quality: a Scandinavian viewpoint

Based on experience from 35 years of tillage research in Sweden, future development of soil tillage is discussed and some research problems are identified. Tillage and seeding methods must be more carefully adapted to conditions at individual sites and occasions. Low-pressure typres, better weed control and improved seed coulters favour the increased use of reduced tillage. In order to diminish the impact of agriculture on the environment, it is necessary to develop methods for establishment of crops in the early spring or immediately after harvest, even in soils with large amounts of crop residues or high moisture content. The roles of tillage methods, and of soil compaction and structure on environmental impact of agriculture must be investigated. World food production must increase, since the world population is rapidly increasing. Therefore, it is necessary to develop improved crop production systems, including crop establishment systems, which favour efficient use of basic crop growth factors, while protecting or increasing soil productivity. Compaction, decreased organic matter content, and erosion are important long-term threats to soil productivity.     

陇中黄土高原不同耕作措施下土壤磷动态研究

依托陇中黄土高原旱作农田已实施13 a的保护性耕作试验,研究传统耕作、免耕、传统耕作秸秆还田、免耕秸秆覆盖、传统耕作地膜覆盖和免耕地膜覆盖6种耕作措施下土壤全磷及磷组分动态变化特征。结果表明:试验期各处理土壤全磷和总无机磷均逐年增长;两个秸秆还田处理总有机磷逐年增长,免耕地膜覆盖和免耕处理总体增长,传统耕作和传统耕作地膜覆盖处理相对稳定;各无机磷组分均总体增长,其中氢氧化钠提取态无机磷、水溶态无机磷和碳酸氢钠提取态无机磷涨幅较大,平均涨幅分别为253.6%、128.6%和66.9%;保护性耕作可不同程度地提高水溶态无机磷、碳酸氢钠提取态无机磷和氢氧化钠提取态无机磷含量,相同覆盖条件下免耕较传统耕作效果明显,尤其免耕秸秆覆盖处理最明显;耕作方式对浓盐酸提取态无机磷和残留磷的影响不明显;保护性耕作可提高碳酸氢钠提取态有机磷和氢氧化钠提取态有机磷含量,两个秸秆还田处理最明显,两处理也可提高浓盐酸提取态有机磷含量,但免耕、传统耕作地膜覆盖和免耕地膜覆盖处理下该组分含量降低。综上,采取保护性耕作可适当减少磷肥用量,保护性耕作尤其是免耕秸秆覆盖方式值得在该区推广。     

Tillage systems for a cotton–peanut rotation with winter-annual grazing: Impacts on soil carbon, nitrogen and physical properties

Integrating livestock with cotton (Gossypium hirsutum L.) and peanut (Arachis hypogaea L.) production systems by grazing winter-annuals can offer additional income for producers provided it does not result in yield-limiting soil compaction. We conducted a 3-year field study on a Dothan loamy sand (fine-loamy, kaolinitic, thermic plinthic kandiudults) in southern Alabama, USA to determine the influence of tillage system prior to cotton–peanut planting on soil properties following winter-annual grazing. Two winter-annual forages [oat (Avena sativa L.) and annual ryegrass (Lolium mutiflorum L.)] and four tillage practices [chisel + disk, non-inversion deep tillage (paratill) with and without disking and no-till] were evaluated in a strip-plot design of four replications. We evaluated cone index, bulk density, infiltration, soil organic carbon (SOC), and total nitrogen (N). Paratilling prior to cotton or peanut planting, especially without surface soil tillage, reduced compaction initially to 40 cm and residually to 30 cm through the grazing period in winter. There were no significant differences in cone index, bulk density, or infiltration between forage species. No-tillage resulted in the greatest bulk density (1.65 Mg m⁻³) and lowest infiltration (36% of water applied), while paratilling increased infiltration in no-tillage to 83%. After 3 years, paratilling increased SOC 38% and N 56% near the soil surface (0–5 cm), as compared to concentrations at the beginning of the experiment, suggesting an improvement in soil quality. For coastal plain soils, integrating winter-annual grazing in a cotton–peanut rotation using a conservation tillage system of non-inversion deep tillage (paratill) with no surface tillage can improve soil quality by reducing cone index, increasing infiltration, and increasing SOC in the soil surface.     

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

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 Cserháti 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.     

Methods for predicting the optimum and the range of soil water contents for tillage based on the water retention curve

Information is needed on the range of soil water contents for tillage. The objective of the work was to develop methods for the prediction of the soil water contents at which tillage may be done satisfactorily. Three water contents are considered: the lower (dry) limit, the optimum water content, and the upper (wet) limit. This paper makes a synthesis of published results from tillage and soil physics experiments and also includes some new experimental results. The effects of tillage are considered in relation to some “fixed points” including the lower plastic limit, field capacity and a new fixed point “the inflection point”. These considerations lead to methods for prediction of the lower (dry) tillage limit, the optimum water content, and the upper (wet) tillage limit in terms of the parameters of the van Genuchten equation for soil water retention. Predictions can be made in terms of soil composition through the use of pedotransfer functions for the parameters of the van Genuchten equation. The new methods will enable the effects of soil degradation and climate change on tillage work days to be estimated. The results are potentially mappable using geographic information systems.