Maintenance and improvement of soil quality in continuous cropping systems is critical to sustaining agricultural productivity and environmental quality for future generations. This review focuses on lessons learned from long-term continuous cropping experiments. Soil organic carbon (SOC) is the most often reported attribute from long-term studies and is chosen as the most important indicator of soil quality and agronomic sustainability because of its impact on other physical, chemical and biological indicators of soil quality. Long-term studies have consistently shown the benefit of manures, adequate fertilization, and crop rotation on maintaining agronomic productivity by increasing C inputs into the soil. However, even with crop rotation and manure additions, continuous cropping results in a decline in SOC, although the rate and magnitude of the decline is affected by cropping and tillage system, climate and soil. In the oldest of these studies, the influence of tillage on SOC and dependent soil quality indicators can only be inferred from rotation treatments which included ley rotations (with their reduced frequency of tillage). The impact of tillage per se on SOC and soil quality has only been tested in the ‘long-term’ for about 30 yrs, since the advent of conservation tillage techniques, and only in developed countries in temperate regions. Long-term conservation tillage studies have shown that, within climatic limits: Conservation tillage can sustain or actually increase SOC when coupled with intensive cropping systems; and the need for sound rotation practices in order to maintain agronomic productivity and economic sustainability is more critical in conservation tillage systems than conventional tillage systems. Long-term tillage studies are in their infancy. Preserving and improving these valuable resources is critical to our development of soil management practices for sustaining soil quality in continuous cropping systems.

The role of soil organic matter in maintaining soil quality in continuous cropping systems

Recent literature on no-till is reviewed with particular emphasis on research results and commercial uptake in northern, western and southwestern Europe. Increased interest in no-till, as well as minimum or reduced tillage, is the result of changes in the economic circumstances of crop production, the opportunity to increase the area of more profitable autumn-sown crops and increased concern about environmental damage associated with soil inversion by ploughing. Highly contrasting soil and climate types within and between these regions exert a strong influence on the success of no-till. While no-till may often result in crop yields which equal or exceed those obtained after ploughing, modest reductions in yield may be tolerated if production costs are appreciably lower than with ploughing. The relative costs of fuel and herbicides have changed appreciably in recent years making no-till more attractive commercially. While effective weed control is an essential aspect of no-till, current herbicide technology may not yet fully achieve this. No-till soils will usually have lower temperature and higher moisture content at the time of drilling, delaying drilling of spring-sown crops in northern regions. Their bulk density and bearing capacity are greater than for ploughed soils but the pronounced vertical orientation of macroporosity will allow encourage penetration of roots and water, especially in view of the increased population of deep-burrowing earthworms. Particular care must be taken to minimise soil damage at harvest and to ensure the even distribution of crop residues prior to drilling. Reduced erosion and runoff under no-till are widely observed and are of particular importance in southwestern Europe. No-till reduces losses of phosphorus in runoff and the loss of nitrate through leaching. Emissions of greenhouse gases CO2 and N2O from no-till soils are highly variable and depend on complex interactions of soil properties. Emission of CO2 from fuel during machinery usage is always appreciably reduced with no-till. Increased soil organic carbon in surface layers of no-till soils may not be associated with increased carbon sequestration throughout the profile. All relevant factors must be included in the evaluation of the relative overall climate forcing effects of no-till and ploughing. Adoption of no-till could be encouraged by government financial assistance in recognition of environmental benefits, although future restrictions on the use of herbicides may be a deterrent. Opportunities for further research on no-till are outlined.

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No-till in northern, western and south-western Europe: A review of problems and opportunities for crop production and the environment

http://www.nurserycropscience.info/water/managing-runoff/technical-pubs/reichenberger-et-al.-2007.-mitigation-strategies-to-reduce-pesticide-inputs-into-ground-and-surface-water-and-their-effectiveness-a-review

Mitigation strategies to reduce pesticide inputs into ground- and surface water and their effectiveness; A review

The structure of soil can determine both the effectiveness and the impact of farming practices. Soil structure influences the extent to which crop breeding and the management of weeds, insects, disease, soil fertility, and water are manifested in increased crop yields. Soil structure also influences the loss of agricultural chemicals through erosion and leaching and can, therefore, have a significant bearing on the environmental impact of some agricultural practices.

Rates of Change of Soil Structure Under Different Cropping Systems

Pores and organic matter take a multitude of forms in soil and their characteristics change in space and time following a change in tillage practices as a new “steady state” is approached. Information on the variation with depth (stratification) in the characteristics of pores and organic matter and the rates of change in these characteristics is vital to interpreting the short- and long-term impacts of a reduction of tillage on the productivity and hydrology of agricultural soils. This information is also of value in estimating the effect of a reduction in tillage on the sequestration of carbon in agricultural soils. Recent literature comparing conventional tillage (CT) with no-till (NT) in temperate agroecosystems with varying soil textures and climates was reviewed for the purpose of assessing rates of change in the magnitude and stratigraphy of bulk density, porosity, pore size classes, organic matter content and organic matter fractions. The influence of tillage on bulk density, macroporosity and organic matter content was found to be documented more extensively than the effects on pore size distribution, soil organic matter fractions and their interactions at different soil depths. Many of the reports documenting tillage-induced changes in soil porosity and organic matter were based on measurements at a specific time after initiating the tillage trial. Results obtained by different investigators were found to be most consistent when measurements were made ≥15 years after initiating the tillage trial. Data from different studies were used to generalize trends in pore and organic matter characteristics with depth and time. However, few studies provided measurements that permitted accurate prediction of either the rates of change or the maximum change that will occur following a change from CT to NT. Future research must enhance our ability to make these predictions if we wish to garner a better understanding of the effects of NT on the quality and productivity of agricultural soils and their ability to sequester carbon.

Conservation tillage and depth stratification of porosity and soil organic matter

A replicated, long-term field drainage experiment on a clay soil was started in 1978 to investigate the effects of mole drainage on land that had been direct-drilled or ploughed. We here describe the background and the need for this work, details of the experiment and summarize the results for the first 2 years. The main factors causing point-to-point variability in the soil at the experimental site and their relative contributions were assessed. Variations in inherent soil properties were small, except for depth to calcareous clay. Site hydrology was also generally uniform, especially soil water content, and was little affected by the presence of subsoil drainage schemes dating from the 19th century. There were some variations in micro-relief. The drained and undrained plots were hydrologically separated. Equipment was installed to measure separately surface runoff, lateral flow at the bottom of the cultivated layer (the interflow) and deep drainage from the mole and pipe system (in the drained plots only). The design and performance of that equipment is described. In both years much of the undrained soil became saturated in winter, but a residual cultivation pan limited the effect of the mole drains in 1978–9. In 1979–80, after disrupting the pan, the water table in the moledrained plots was about 25 cm deeper than in the undrained plots, root growth was greater and yield of winter wheat 11% heavier. About 90% of water and nutrients draining from the drained plots were carried in the mole and pipe system. The results on water balance, nutrient losses, crop growth and yield are fully reported in companion papers (Harris et al. 1984; Ellis et al. 1984).

A study of mole drainage with simplified cultivation for autumn-sown crops on a clay soil: 1. Background, experiment and site details, drainage systems, measurement of drainflow and summary of results, 1978–80

The soil water regimes, flow paths of water and concentrations of nutrients in this water were measured for a clay soil growing winter wheat in 1978–9 and 1979–80. The soil was either drained with mole drains at 2 m spacing connected to plot drains 46 m apart or undrained. In the 1st year a compacted layer at about 20 cm depth caused a perched water table in the Ap horizon in both drainage treatments, and prevented the mole drains at 60 cm from affecting the water table. In 1979–80 after cultivation to disrupt the compacted layer, midway between the mole drains the depth to the winter water table was 20 cm greater than in undrained soil.Surface flow, interflow at the depth of the plough layer and deep drainflow from mole and pipe drains responded rapidly to winter rainfall events. During both winters the mole and tile system removed most of the rainfall on the drained plots and the peaky hydrographs were typical of a mole system in a clay soil. In the undrained plots only a small proportion of the winter rainfall was accounted for in flow from the top 30 cm, and up to 75% of the water was able to percolate downwards possibly to below the barriers that separated the plots. Long-term water-balance studies indicated that a proportion of the water moving to depth in the undrained plots was probably entering the deep drainage system of the drained plots. As a result, the mole and pipe drainage system often removed more water than the rainfall input less evapotranspiration. This problem did not affect the depth to the water tables.For each flow component concentrations of nitrate, ammonium, nitrous oxide, phosphorus, potassium and calcium were measured in the drainage water. Concentrations of nitrate-N from all drained plots were largest in autumn, being in the range 50–95 mg N/1, but then decreased to 1–5 mg N/1 by the end of March. Losses of nitrate-N were mainly through the mole drains and amounted to 43·6 and 59·7 kg N/ha in the 2 years. The quantities of nitrate-N lost in surface runoff or in flow in the cultivated layer were small on both treatments. Gaseous nitrous oxide, ammonium and phosphorus contents were very small. Potassium concentrations were somewhat larger, but not exceeding 3·5 mg/1. The calcium concentrations were in the range 40–210 mg/1. Concentrations of herbicides measured in November 1980 were negligible.In the 2nd year water was taken up from a greater depth in the drained than in the undrained plots from April onwards. These results are discussed in relation to water supply to the crops at this site.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0021859600042118

A study of mole drainage with simplified cultivation for autumn-sown crops on a clay soil: 2. Soil water regimes, water balances and nutrient loss in drain water, 1978–80

SUMMARY

In the United Kingdom silty soils have been classified as unsuitable for direct drilling since these soils may produce seed-beds that are inadequate for satisfactory crop emergence. This judgement was based on problems encountered in the first 2–3 yr of direct drilling as well as on an appreciation of soil physical properties. Longer-term experimentation (10 yr) has indicated that, subsequent to that initial period, soil conditions after zero-tillage are not a major limitation to growth of autumn-sown cereals. This eventual parity between simplified and conventional tillage can be attributed largely to improvement in the surface of direct-drilled land. In the tenth experimental year this layer comprised more strongly developed aggregates, of greater stability, than those from the annually ploughed soil. Porosity and soil strength measurements did not indicate that root growth would be severely restricted below this depth. When this soil was wet in winter it was weak and relatively unstable and so it would most likely be unsuitable for sequential direct drilling of spring-sown crops.



At the same site soil that had been continuously under grass throughout the same 10 yr period developed better structure than that in the arable area, in part because of a greater earthworm population and an increased organic matter accumulation. In any subsequent change to arable usage this improved structure would best be conserved by avoiding soil inversion and using direct drilling or some other simplified method of cultivation.

Structure of a silty soil in relation to management

Cultivation systems and the leaching of nitrates.

Nearly half the soils of England and Wales on which cereals are grown have a clayey texture and many are subject to seasonal waterlogging. Use of close spaced mole drains 1–3m apart drawn at about 0.5m depth and discharging into permeable gravel fill above pipe drains on a 40–50m spacing is considered to be the most effective way of draining such land (Trafford and Massey, 1975).

K. R. Howse

Papers

A study of mole drainage with simplified cultivation for autumn-sown crops on a clay soil: 1. Background, experiment and site details, drainage systems, measurement of drainflow and summary of results, 1978–80

A study of mole drainage with simplified cultivation for autumn-sown crops on a clay soil: 2. Soil water regimes, water balances and nutrient loss in drain water, 1978–80

Structure of a silty soil in relation to management

Cultivation systems and the leaching of nitrates.

Nitrate in Water Draining from Arable Land Under Autumn Sown Crops and the Influence of Cultivation