Soil Structural Decline Research Articles

Current nature and problems of agricultural land management in the Republic of Crimea

The main problems of the nature and management of agricultural land under the conditions of modern soil management have been considered. Among the processes which cause soil structure decline on the Crimean peninsula, predominate: erosion, deflation, dehumification, secondary salinization and alkalinization of previously irrigated areas, overgrowing of agricultural land with shrubs and light forests, and some other processes leading to loss of soil fertility. Considerable attention has been paid to the problem of developing a system for soil resources monitoring. It has been noted that the main problems in the rational management of agricultural land in the region are: the imperfection of the regional monitoring system for the nature, conservation, management and protection of soil cover, and the lack of reliable and complete information on the nature of agricultural land.

The long-term role of organic amendments in addressing soil constraints to production

The use of organic amendments such as composts and manures in agricultural production can be traced back to at least the 3rd millennium BC (Wilkinson 1982), where evidence of urban refuse being used in intensive cultivation was found in Iran, Oman and Syria. Foxhall (1998) also reports on historical scrolls that describe the use of cereal byproducts such as straw and chaff in composts and soil amendments for crop production in ancient Greece and Rome. The role of composts and other organic amendments in modern agriculture has perhaps taken a backseat to practices such as the application of synthetic fertilisers, herbicides and mechanical tillage. Arguably, the development of the Haber–Bosch process and synthetic nitrogen (N) fertilisers is the key driver for improved agricultural productivity worldwide. But numerous reports describe a decline in soil quality from intensive tillage practices and a focus on inorganic fertilizer amendments. These include soil acidification, loss of soil organic carbon (SOC), soil structural decline, heavy metal contamination and off-site nutrient effects including emissions of greenhouse gases from soil. There is no question that recycled organic residues are currently underutilised in modern farming systems. This could be due to any number of factors such as uncertainty around benefits and consequences, economic considerations, and lack of supply or supply chains outside of urban areas or regions with intensive animal production facilities. This special issue focuses on identifying and explaining the long-term mechanisms by which composts, manures and other organic amendments can influence crop productivity, profitability and soil fertility.

Towards incorporation of potassium into the disaggregation model for determination of soil-specific threshold electrolyte concentration

Use of non-traditional irrigation sources will increase with industry water demand, with many industry wastewaters (e.g. agri-industry processes such as milk factories, piggeries, wineries and abattoirs) containing appreciable potassium (K), which is known to result in soil structural decline if the concentration is sufficient. The threshold electrolyte concentration (CTH) is generally understood to represent the electrolyte concentration (directly proportional to electrical conductivity) at which a soil will remain stable when subjected to a solution of given sodium adsorption ratio, without limiting dispersion. However, current approaches to determine CTH do not incorporate K. Hence, this work seeks to investigate incorporation of K into the disaggregation model for CTH and validate this against equivalent sodium (Na) systems using an ionicity approach. A single generalised coefficient of equivalence for K relative to Na did not appropriately describe the system changes; this coefficient was specific to a soil and appeared to vary with the percolating electrolyte concentration. Incorporation of K into the disaggregation model, although not accurate with a universal coefficient of equivalence for K, was considered reasonable where no other approach could be used. This conclusion was drawn on the basis that the model would produce a conservative CTH under such circumstances, which would not cause undue degradation to the soil environment.

The impacts of expansion and degradation on Australian cropping yields—An integrated historical perspective

Using a ‘stocks and flows’ model of Australian cropping we show that the expansion of aggregate cropping area has effectively masked landscape degradation impacts associated with continual production activity on “ageing” land. We estimate yield loss from combined land degradation to have increased to 9%, though the aggregate impact has effectively been masked by the introduction of new land. The model tracks the vintage of land since its first introduction to the agricultural system and calculates landscape degradation for four modes (dry-land salinity, irrigation salinity, acidification, and soil structure decline) according to historical production and ameliorating activities on each vintage. The model is calibrated with over 140years of varied historical data from the 1850s. Modelled farm-gate production volumes also incorporate technological factors, such as genetic and other yield increases. Despite the introduction of many technological advances in the cropping industry through the middle of the 20th century, production yields of Australian cereal grain remained relatively unchanged for decades. This can be explained by the rapid ageing and degradation of the cropping land due to a period of halted expansion. This perspective has important implications for future scenarios of the Australian cropping industry, which are unlikely to maintain land expansion at the long-term average of about 2%pa. Without major change, land degradation in our model results in yield loss of nearly 30% by 2060.

Pasture degradation decreases organic P content of tropical soils due to soil structural decline

Degradation of tropical pastures on highly weathered soils is linked to soil structural decline and associated losses of organic matter, which could both also affect soil phosphorus (P) dynamics and availability. Our aim was to elucidate these linkages by examining the effect of pasture degradation on the contents and forms of P contained within aggregate size classes and macroaggregate fractions (collectively referred to as soil structural components). We conducted a study on nine farms in a deforested part of the Colombian Amazonia, each farm with degraded and productive Brachiaria spp. pastures. Topsoil (0–10cm) samples were separated by wet-sieving into aggregate size classes, and macroaggregates were further separated into occluded fractions. Soils and structural components were analyzed for concentrations of total P, available P (extracted using anion exchange resins), NaOH–EDTA extractable organic and inorganic P, and enzyme-hydrolyzable organic P (simple monoester-like, DNA-like, myo-inositol hexakisphosphate-like) in the NaOH–EDTA extracts. Degraded pasture soils had significantly fewer large macroaggregates and more microaggregates, both with significantly lower organic P concentrations (in mgPkg−1 of structural component) than those in productive pasture soils. At the same time, total and extractable inorganic P concentrations in bulk soil and structural components did not differ between pasture types, suggesting a shift from organic to non-extractable P upon degradation. Soils under productive pastures contained 37% more organic P than degraded pasture soils (in mgPkg−1 soil), mainly in large macroaggregates. The organic P concentrations were strongly correlated with C concentrations across all soil structural components, suggesting similar stabilization mechanisms for organic P and C. In bulk soil and most structural components, around 60% of organic P was enzyme-hydrolyzable. The lower contents of all enzyme-hydrolyzable as well as enzyme-stable organic P in degraded vs. productive pasture soils indicate a reduction of all organic P classes during pasture degradation. The large macroaggregates and, in particular, microaggregates occluded within this fraction were identified as an important site for organic P storage. Our results highlight a linkage between soil structure and organic P, both of which can play an important role in maintaining the productivity of pastures established on highly weathered soils.

Impact on soil hydraulic properties resulting from irrigating saline–sodic soils with low salinity water

Irrigation-induced salinity is a serious problem facing irrigated areas in the Murray–Darling Basin of Australia. Groundwater pumping with farm re-use for irrigation is a key strategy for controlling salinity in these irrigation areas. However, the re-use of highly saline–sodic groundwater for irrigation leads to accumulation of sodium in the soil profile and can result in sodic soils. Leaching of saline–sodic soils by winter rainfall and low salinity irrigation waters are 2 management scenarios likely to exacerbate sodicity problems. Characteristic to sodic soils is poor soil structure and potentially reduced soil permeability. Two indicators of soil permeability are infiltration rate and hydraulic conductivity. A replicated plot experiment was conducted to examine the long-term impact of irrigation with saline–sodic water on soil permeability. High levels of soil sodicity (ESP up to 45%) resulted from 10 years of saline irrigation. Over this period, leaching by winter rainfall did not result in long-term impacts on soil hydraulic properties. Measured soil hydraulic properties increased linearly with the salinity of the applied irrigation water. Leaching by irrigating with low salinity water for 13 months decreased soil salinity and sodicity in the topsoil. The resulting reduction in steady-state infiltration indicates soil structural decline of the topsoil. This trial shows that groundwater re-use on pasture will result in high sodium levels in the soil. Sodicity-related soil structural problems are unlikely to develop where there is consistent groundwater irrigation of pasture. However, structural decline of these soils is likely following the cessation of groundwater re-use.

Impact of cultivation and sugar-cane green trash management on carbon fractions and aggregate stability for a Chromic Luvisol in Queensland, Australia

Technological advances in sugar-cane harvesting and processing is bringing about rapid changes in production systems which could impact on soil physical conditions. An increasing incidence of soil structural decline and depletion of soil carbon levels has increased the risk of soil erosion and crop yield reductions. Soil carbon (C) and aggregate stability were studied on a sugar-cane ( Saccharum officinarum L.) green trash blanket trial that had been established on a Chromic Luvisol soil at Mackay, Qld, Australia in 1992. The experiment consisted of blocks with two blocks being harvested early and the remaining two blocks harvested late in the crushing season. Within each block, treatment combinations of trash burnt or green trash blanket, which are either cultivated between rows or not cultivated after harvest, were included. Cropping and cultivation of the soil reduced the different C fractions in the surface 0–100 mm layer by 66–67% when compared to an adjacent uncropped reference soil. The labile C (C L) concentration was 11% lower in the burnt treatment compared to the trash returned treatment but the opposite was found for total C (C T). After four years, the no cultivation treatment had higher concentrations of all C fractions measured, compared to the cultivated treatment. When compared to the uncropped reference soil, cropping resulted in marked reductions in aggregate mean weight diameter (MWD) and aggregates >250 μm and an increase in aggregates <125 μm determined by both immersion and tension wetting. The return of the green trash resulted in a 30% greater MWD and a 28% increase in aggregates >250 μm and an 18% reduction in aggregates <125 μm compared to the burnt treatment when immersion wetting was used. Four years of cultivation reduced the MWD, as determined by immersion wetting, by 26% compared to the no cultivation treatment. No significant correlations were found between any measured C fraction and aggregate stability. This study indicates that sustainable sugar-cane cropping systems will likely be those where cultivation is kept to a minimum and trash is retained in the system.

Temperate Eucalypt Woodlands: a Review of Their Status, Processes Threatening Their Persistence and Techniques for Restoration

Temperate eucalypt woodlands were once widespread throughout southern Australia and Tasmania. Following European settlement, woodlands were cleared for agriculture, or grazed and converted to pasture. In the wheatbelts of south-western and south-eastern Australia, woodlands have been almost completely eliminated from the landscape with as little as 3% of some woodland types remaining. As a consequence, some temperate eucalypt woodland communities are amongst the most poorly conserved ecosystems in Australia. The main effect of widespread clearing and grazing has been the loss of habitat. This has had a devastating impact on the woodland flora and fauna. A number of species have become extinct and many are threatened; many others have undergone regional and local population declines. Woodlands now occur throughout much of their former range as remnants of varying size, quality and isolation. Many of these are under threat from further clearing, rising saline water tables and increased inundation, livestock grazing, nutrient enrichment, soil structural decline, altered fire regimes and the invasion of exotic weeds. The degradation and loss of biodiversity in temperate eucalypt woodlands will continue unless clearing stops and the management of remnants changes; this will invariably involve ecological restoration both at the patch and landscape level. The review discusses approaches to restoration and reveals that there are few data in the published literature describing techniques for reversing degrading processes and restoring diversity structure and function in remnant woodlands. This information is urgently needed. Past research on temperate eucalypt woodlands has focused on identifying the processes of degradation and these are now relatively well documented. There is a need to shift the focus of research to developing solutions for these problems.

Amelioration of soil compaction by a cover-crop for no-tillage lettuce production

Excessive cultivation in many horticultural areas results in soil structural decline and poor utilization of water and nutrients. There are no reliable techniques for growing irrigated vegetables without cultivation. This work explores the hypothesis that a winter legume cover-crop can overcome the soil limitations of no-tillage and provide an alternative to excessive cultivation in the vegetable industry. We grew lettuce (Lactuca sativa) under no-tillage in field trials on a sandy loam soil following a bare winter fallow or a cover-crop of subterranean clover (Trifolium subterraneum), and compared this with cultivation by rotary hoe. The clover died naturally in early summer or was desiccated in the spring to form a mulch of at least 5 t ha-1 on the soil surface. The experiment was carried out over a 2.5 year period. The first crop was grown during hot weather and the soil in the no-tillage treatments was only moderately compacted. The yield of lettuce was similar in the no-tillage and cultivated treatments, and increased by about 30% when a mulch was added to each treatment. The soil was artificially compacted after the first crop. The second crop was grown 18 months later, during cooler spring weather, and following two further cover-crops. The yield of no-tillage lettuce was only 40% of that obtained with cultivation. Yield in the no-tillage treatment was doubled in two different ways: (1) by the addition of a surface mulch, and (2) through changes to soil structure stimulated by a cover-crop in the absence of a mulch. The experiments showed that a well-managed cover-crop can significantly ameliorate a compacted sandy soil by modifying soil temperature, soil strength, and by stimulating the formation of biopores.

Can perennial pastures provide the basis for a sustainable farming system in southern Australia?

Abstract Land degradation, associated with farming systems based on annual pastures and crops, is threatening the long‐term viability of Australian agriculture. Perennial pastures could play a significant role in reducing some forms of land degradation i.e. dryland salinity, erosion, and soil structure decline. In terms of sustainability, the key differences between perennial and annual pastures relate to rooting depth and the water uptake pattern throughout the year. Deep‐rooted perennials can use water when annual pastures are dead, recover leached nitrate (and reduce acidification), and can provide soil cover and root mass to restrict wind and water erosion. Deeply penetrating roots also create biopores and improve soil structure and drainage. In addition, problems normally associated with water repellency are reduced as perennials are not required to germinate each year. There is an urgent need to breed plants that can colonise hostile Australian subsoils characterised by high soil strength, acidity, ...

Effects of subsurface drainage, cultivation, and stubble retention on soil porosity and crop growth in a high rainfall area

Wheat, triticale, and rapeseed growth and yield were studied under various tillage (conventional, deep ripping, direct drilling) and stubble-handling (burnt, retained) regimes with and without drainage at Hamilton in south-western Victoria from 1985 to 1987. Grain yield was increased from about 2 to &gt;4 t/ha by drainage in both years; however, effects of other treatments, although significant, were much less. Soil structure (as measured by fractional air-filled porosity at -5 J/kg) deteriorated during winter and recovered during spring and summer. A laboratory experiment showed that this variation in soil structure resulted from saturation per se and redrying. In the field, the decline in porosity was most pronounced with cultivation and the absence of drainage, but overall, the effects of stubble retention and tillage treatments were small. There was a significant positive relationship between yield and porosity on undrained areas, but not where drains were present. Drainage reduced soil structural decline during winter, while stubble retention reduced the decline in porosity in the cultivated-undrained treatment in 1987.

The distribution of sodic soils in Tasmania

It is estimated that sodic soils (ESP&gt;6) occupy at least 23% of Tasmania's land area based on the present limited soil data set. Sodic soils are mostly restricted to lower rainfall areas (&lt;800 mm/y) of eastern Tasmania, occurring primarily in the Launceston Tertiary Basin, the Derwent, Coal, Jordan and Huon River Valleys and on Flinders Island. In Tasmania, sodic soils have formed predominantly from Triassic and Permian mudstones and sandstones, Tertiary clays and unconsolidated Quaternary deposits. However, profiles with sodic features have also developed above granite, Jurassic dolerite and Tertiary basalt. Sodic soils most commonly occur on lowland plains, river terraces and in valley floors. In Tasmania, sodic soils are characterized morphologically by: (i) abrupt separation of a sandy, bleached A2 horizon from a moderately sodic (ESP 6-15) clay subsoil; (ii) coarse prismatic, columnar and/or angular blocky pedality in the subsoil, which may exhibit vertic properties; (iii) hardsetting sandy A2 horizons in some profile classes; (iv) fine sandy crack infills and clay-organic coatings on ped faces in the upper B2 horizon; and (v) thick, sticky and greasy fine clay argillans on ped faces, and clay infills in cracks and other voids in the lower B2 horizon that contribute to reduced porosity and permeability. Sodic soils in Tasmania have traditionally been utilized for pasture production with occasional cultivation for fodder crops and pasture renewal. Under a pastoral system, few sodicity problems have been recognized as such. However, in the last 10 years there has been increased cropping, particularly for poppies and more recently potatoes. Soil structure decline and drainage problems have become key factors limiting production. Management problems are mainly due to poor internal and external drainage, with poor structure in the A2 horizons which liquefy in winter and often set hard in summer. Salinity in associated drainage depressions is a problem gaining increasing recognition.

Survey of land degradation in New South Wales, Australia

A survey of land degradation was undertaken in New South Wales, Australia during 1987–1988. The aims of the survey were to assess the location, extent, and severity of ten forms of degradation and to present the data in map and statistical form. Sample points were located on a regular grid. The method was designed so that data could be acquired from aerial photographs, expert local knowledge, and limited field checking. Individual statewide maps were prepared for each form of degradation. Map data were shown in pixel form. Sheet and rill erosion and soil structure decline were confined mostly to lands used for cropping. Gully erosion was commonly found across the state, while mass movement was confined to steeper lands. There were three severe areas of dryland salinity; irrigation salinity was mapped in parts of the southern irrigation lands. Induced soil acidity was severe in some cropping and pasture lands. Absence of tree regrowth was a noticeable feature of lands used for cropping. The survey enabled community awareness of the problems of land degradation to be increased, in addition to assisting regional land managers in resource allocation. The survey also provided the basis for the future location of sites that could be used to monitor the trends in the status of land degradation.

Management of excess water in duplex soils

Excess water in duplex soils can be removed by drains. In soils in which drainage is impractical, some success has been obtained by deep ripping and by gypsum amendment. These practices can increase profile storage or drainage. Interceptor drains are suitable for duplex soils with slopes of more than about 1.5%. On more gentle slopes, relief drains are used to remove excess water. Subsurface tube and mole drains have been used successfully to drain cereal crops in Victoria, but in Western Australia open drains are preferred because they can carry storm runoff as well as seepage waters. The greatest cost of open drains is the land removed from production. Over 35% of the rain falling during the growing season has been removed by drains in Victoria and Western Australia in wet years. Drainage was almost entirely downslope of monitored interceptor drains in Western Australia, which is not predicted from the theory. Simulation of water levels between drains and of drain flows using the DRAINMOD model indicated significant, preferred pathways for water flow to drains. The pathways explain the predominantly downslope effect of interceptor drains and the wide drain spacings which can be used. Deep ripping and the incorporation of gypsum can reduce waterlogging in some soils, but has had no effect in several others. The effect of deep ripping on recharge is unclear. Drains may decrease groundwater recharge, water and wind erosion, and soil structure decline. Their effect on phosphate export from catchments is unclear.