Decline In Soil Organic Matter Research Articles

Scope of nanotechnology in future agriculture-an overview

To address the challenges in agriculture such as stagnation in crop yields, low nutrient use efficiency, declining soil organic matter, multinutrient deficiencies, climate change, shrinking arable land and water availability and shortage of labour besides exodus of people from farming and to attain a sustainable growth in agriculture to meet the food security challenges, application of nanotechnology in agriculture has the potential to revolutionize the agricultural scenario to increase the farm productivity with reduced resource costs and higher input use efficiencies while ensuring environmental safety. The application of nanotechnology to agriculture and food industries is getting attention nowadays. Investments in agriculture and food, nanotechnologies carry increasing weight because their potential benefits range from improved food quality and safety to reduced agricultural inputs and improved processing and nutrition. Nanotechnology-based products and its applications in agriculture include nanofertilizers, nano herbicides, nano-pesticides, recalcitrant contaminants from water, nano-scale carriers, nanosensors, detection of nutrient deficiencies, preservation, photocatalysis, etc. While nanotechnologies offer many opportunities for innovation, the use ofnanomaterials in food and agriculture has also raised a number of safety, environmental, ethical, policy and regulatory issues. This review is focused on modem strategies used for the management of seed germination, fertilizers, herbicides, pesticides, water, carriers, sensors and potential of nanomaterials in sustainable agriculture management as modem approaches ofnanotechnology.

Soil organic matter in Northern Ethiopia, current level and predicted trend: a study case of two villages in Tigray

AbstractSoil degradation resulting from permanent and high pressure on natural resources is a threat for the present and future of agricultural production in Ethiopia. Mono‐cropping, cultivation on steep slopes, use of cattle manure and crop residues as an energy source for cooking are common practices that have led to declining soil organic matter (SOM) contents. The objective of this research was to evaluate the current status of SOM in farmlands and exclosures (areas protected from grazing to allow their natural restoration) in Northern Ethiopia and to explore the long‐term effects of current agricultural practices and an improved scenario on SOM. At present, the SOM content of farmland soils is small, ranging from 2.1% to 2.9%, while exclosures showed a significant recovery after 20 yr of protection, with SOM contents ranging from 2.6% to 5.6%. However, the level of SOM in farmland soils is envisaged to decline given current agricultural practices, that is removal of crop residues and use of manure as an energy source for cooking. We found that applying manure alone appeared to be insufficient to revert this trend, due to limited availability and its alternative uses. Therefore, a multidisciplinary approach including improved manure and compost management needs to be supplemented with energy saving techniques, as fuel use is currently the largest competing claim for organic matter in the area.

Organic matter dynamics in an intensive dairy production system on a Dutch Spodosol

In many studies, possibilities are being explored to adjust farm management to increase or maintain soil organic matter (SOM) contents in agricultural soils. Some options may be conflicting with efficient nutrient (N and P) management, i.e. management aiming at maximum conversion of imported nutrients into exported products (milk and meat in the case of dairy farms). This study explored long term effects of efficient nutrient management on SOM dynamics on an experimental dairy farm with three types of land use: permanent grassland, a 3year grass–3year arable crop rotation (ROTI), and a 3year grass–5year arable crop rotation (ROTII). The arable phase in the crop rotations consisted predominantly of maize. The experimental farm, called ‘De Marke’, is located on a Spodosol with an Anthropic Epipedon in the Netherlands. The study consisted of: i) trend analyses based on data of measured SOM mass percentage (SOM %) from 1989–2010, and ii) simulations of long term (50years) SOM dynamics for four management alternatives. Three alternatives were related to manure digestion: no digestion; ‘mild anaerobic digestion’ (degrading 35% of organic matter) and; ‘strong digestion’ (degrading 70% of organic matter). The fourth management alternative was similar to the first (no digestion) but differed in that no catch crop was grown after maize. The trend analyses showed that SOM % of the 0–0.2m layer was approximately stable under permanent grassland. In ROTI, SOM % decreased on average by 0.04y−1 and in ROTII by 0.03y−1. The decline did not slow down over time. SOM decline was more severe on plots with relatively high initial SOM %. Decomposition was described using a mono-component model with a time dependent relative decomposition rate. Decomposition rates in the rotations with arable crops were not higher than those for permanent grassland indicating that tillage did not affect decomposition rate and that SOM dynamics were dominated by the quantity and quality of the substrate input. Simulations indicated that in the long term, decline of SOM must be expected both under arable crop–grassland rotations and under permanent grassland, even in the case of permanent grassland receiving undigested manure. Our results further indicate that strong manure digestion puts pressure on future SOM levels suggesting a trade-off with bio-energy production, and that the contribution of a catch crop to long term SOM is marginal.

Combined effect of tillage and organic fertilization on soil quality key indicators and indices in alluvial soils of Indo-Gangetic Plains under rainfed maize–wheat system

Inceptisols in the submountainous region of Indo-Gangetic Plains in India are known as low productive areas due to several constraints like decline in soil organic matter and fertility, deterioration of soil physical and biological properties. The present study was conducted with tillage as main treatments and integrated nutrient management as subtreatments to improve soil quality and to identify the key indicators of soil quality after 5 years of experimentation in maize–wheat cropping system at Ballowal Saunkhri. Conventional tillage (CT) + interculture (IC) maintained significantly higher soil quality indices (SQI) of 1.12 which was at par with 50% CT + IC + chemical weed control (CWC) (1.08). Application of nitrogen (N) through 50% (organic) + 50% (inorganic) maintained higher soil quality with SQI of 1.10 followed by application of 100% N through organics (1.08). The results indicated that reduction in the intensity of tillage to 50% with interculture practices and combined use of organic and inorganic fertilizers maintained higher soil quality in these degraded Inceptisols. The methods of principal component analysis and computation of SQI adopted will be highly useful to future researchers, land managers, and students at locations across the world having similar climatic and edaphic conditions.

Productivity, economics, and fruit and soil quality of weed management systems in commercial organic orchards in Washington State, USA

Organic tree fruit producers often rely on tillage in the tree row to control weeds and disrupt rodent pest habitat. This inexpensive practice can potentially damage the trees’ trunk and roots, thereby reducing yield and fruit quality. In contrast, mulching under the trees to suppress weeds often improves tree performance but at a high initial installation cost, whereas flame weeding and organic-compliant herbicides can control weeds without disturbing the soil. These three systems of weed management in the tree row were compared in commercial, certified organic apple and pear orchards in Washington State, USA, to determine the effectiveness for weed control and the impacts on tree performance, soil organic matter, and economic return of each system when taking into account both the cost of the weed control itself and its impact on fruit yield and quality. Mulching produced a large net economic benefit relative to tillage, more so in the apple orchard that had sandier soil than in the pear orchard on a loam soil. Flame weeding was similar to tillage in cost, whereas organic herbicides proved extremely expensive and relatively ineffective. Tillage did not lead to a decline in soil organic matter over three seasons, nor did mulching increase it. Overall, mulching led to better tree performance and economic returns but was not a successful stand-alone weed control practice over 3 years. A combination of flaming and tillage and/or mulch may offer the best overall results.

The effect of understory removal on microclimate and soil properties in two subtropical lumber plantations

Understory vegetation is an important component in forest ecosystems. However, the effects of understory on soil properties in subtropical forests are not fully understood. We thus conducted an experimental manipulative study in two young fast-growing plantations—Eucalyptus urophylla and Acacia crassicarpa—in southern China, by removing understory vegetation in both plantations, to estimate the effects of understory vegetation on microclimate, soil properties and N mineralization. Our data showed that, after 6 months, understory removal (UR) in both plantations had greatly increased soil surface luminous intensity (90–500 cd) and temperature (0.5–0.8 °C); soil moisture was reduced in the Eucalyptus plantation but not in the Acacia plantation. Understory removal also reduced soil organic matter (SOM), but had little impact on other soil chemical properties, including total phosphorus, C/N, pH, exchangeable cations (K, Ca, Mg), available P, ande extractable NH4–N and NO3–N. We found a significant decline of soil N mineralization and nitrification rates in the 0–5 cm soils of UR in both plantations. The decline of SOM in UR may contribute to the lower N transformations rates. This study indicates that a better understanding of understory vegetation effects on soil N cycling would be beneficial to forest management decisions and could provide a critical foundation for advancing management practices.

An exploration of spatial risk assessment for soil protection: Estimating risk and establishing priority areas for soil protection

Methods for the spatial estimation of risk of harm to soil by erosion by water and wind and by soil organic matter decline are explored. Rates of harm are estimated for combinations of soil type and land cover (as a proxy for hazard frequency) and used to estimate risk of soil erosion and loss of soil organic carbon (SOC) for 1km2pixels. Scenarios are proposed for defining the acceptability of risk of harm to soil: the most precautionary one corresponds to no net harm after natural regeneration of soil (i.e. a 1 in 20 chance of exceeding an erosion rate of <1tha−1y−1 and SOC content decline of 0kgt−1y−1 for mineral soils and a carbon stock decline of 0tha−1y−1 for organic soils). Areas at higher and lower than possible acceptable risk are mapped. The veracity of boundaries is compromised if areas of unacceptable risk are mapped to administrative boundaries. Errors in monitoring change in risk of harm to soil and inadequate information on risk reduction measures' efficacy, at landscape scales, make it impossible to use or monitor quantitative targets for risk reduction adequately. The consequences for priority area definition of expressing varying acceptable risk of harm to soil as a varying probability of exceeding a fixed level of harm, or, a varying level of harm being exceeded with a fixed probability, are discussed. Soil data and predictive models for rates of harm to soil would need considerable development and validation to implement a priority area approach robustly.

Soil organic matter stability in organo-mineral complexes as a function of increasing C loading

Soil carbon (C) saturation behavior predicts that soil C storage efficiency observed under field conditions decreases as a soil approaches C saturation. This may be due to a decline in soil organic matter (SOM) stability as the result of changes in the type, strength or turnover time of organo-mineral interactions with increasing organic C input. The goal of this study was to test whether the stability of organic matter bound to soil minerals decreases as organo-mineral complexes approach C saturation with increasing C loading. A series of batch sorption experiments with natural dissolved organic matter (DOM) and soil mineral components was conducted to obtain organo-mineral complexes with a range of organic C loadings. The relative stability of C in these organo-mineral complexes was subsequently assessed using evolved CO2 gas analysis during thermal analyses and laboratory incubations. Results indicated that differences in dissolved organic C before and after sorption overestimated the amount of sorbed C when compared to differences in solid-phase C concentrations. Values of C/N, δ13C, and δ15N of the organo-mineral complexes were significantly smaller or more negative than initial soil samples or the stock DOM solution, consistent with the concept of molecular fractionation by sorption to minerals and suggesting that the composition of the organic matter in the organo-mineral complexes may have changed as the amount of sorbed organic matter increased. Observations that organic C loadings at maximum sorption did not substantially exceed 1 mg C m−2 and linear rather than asymptotic relations between sorbed C and initial DOM concentrations suggest that organo-mineral complexes may not have reached C saturation under the conditions in the batch sorption experiments of this study. The temperature at which half of the CO2 evolved during thermal analysis (i.e., CO2-T50) increased with increasing C loading, suggesting the sorbed C required greater energy input for combustion. Results of the laboratory incubations to determine relative biological stability of sorbed C were not consistent with the initial hypothesis. The size of potentially mineralizable C pool relative to the total sorbed C decreased with increasing C loading, even though this pool was being degraded more rapidly. Overall, the results did not support the hypothesis that SOM stability decreases with increasing C loading. In spite of generating a wide range of C loadings substantially greater than previous studies, the conditions of the DOM sorption experiments conducted in this study appeared unable to generate organo-mineral complexes exhibiting C saturation behavior. We speculate that measurable decreases in SOM stability may occur only once the threshold of C saturation is reached.

Characteristics and management options for rice–maize systems in the Philippines

In the Philippines, maize (corn) is the second major cereal crop after rice. Around 0.12 million ha of maize are grown in rice–maize (R–M) systems, mostly situated in the lowlands, and the area of this system is growing fast. The objectives of this study were to describe the targeted cropping system, to test several management options that could help to optimize it and reduce the production risk, and to develop a simple nutrient balance as a sustainability indicator. For this, we conducted participatory on-farm trials in Pangasinan province, where about 33,600ha of yellow maize are grown, mostly in R–M systems. Combined grain yields of the system reached 14tha−1 in the first year and 21tha−1 in the second year, depending on the treatment. Yield differences were mostly due to climate-induced stresses in the first year and very favorable conditions in the second year. Varietal choice in rice was an option to reduce production losses by selecting the variety according to average field-specific characteristics (drought-prone, favorable, flood-prone). Balanced fertilizer applications reduced stress-dependent rice yield losses considerably, and helped to maximize grain yield in the favorable season. The rice fertilizer treatment without any application caused lower yields in the subsequent maize crop but the effect was not significant. No effects of field topography on soil characteristics or on grain yields of rice or maize were detected. The nutrient balance indicated the considerable danger of soil nutrient mining in this cropping system, which could aggravate possible trends of declining soil organic matter concentrations in R–M systems that have been shown in previous studies. We concluded that a combination of adjusted management components can reduce production risk and optimize system productivity. To maintain system productivity, it seems most promising to combine different management elements, including balanced NPK fertilizer rates with limited PK mining, recycling of waste products from residue use on the farm as much as possible, and only limited removal of residues from the fields.

How Important is the Quality of Organic Amendments in Relation to Mineral N Availability in Soils?

Wastes generated from municipal and agricultural activities have the tremendous potential for application in agriculture as a source of nutrients and as amendments to improve soil organic matter (SOM). A decline in SOM can represent a serious threat to soil fertility and quality. Nitrogen (N) mineralization from organic amendments is important for understanding the N dynamics in terrestrial ecosystems. In this review, quality of the amendments such as C/N ration, N content, and biochemical compositions, etc. are discussed. Since, C/N ratio cannot explain all differences in N mineralization; emphasis has been laid on characterizing different compounds in organic amendments that govern the mineralization process. The importance of simulation models has also been described in modeling N mineralization from some complex materials like compost, animal manures and farmyard manures. These complex simulation models once modified according to the quality of the organic amendments can simulate N mineralization and thus, they can be used for simulating N dynamics in terrestrial eco-systems.

Predicting pH buffering capacity of New Zealand soils from organic matter content and mineral characteristics

Information on the pH buffer capacity of soil is required to estimate changes in pH due to acidic or alkaline inputs, and to model pH-dependent processes within the soil nitrogen (N) cycle. The objective was to determine whether a model based on soil organic matter (SOM) and mineral characteristics (clay content, extractable iron (Fe) and aluminium (Al)) would be adequate to estimate the buffer capacities of New Zealand soils. We measured pH changes in 34 soils, representing a range of SOM and texture, after equilibration with several rates (range 0–15 cmol OH– kg–1 soil) of either KOH or Ca(OH)2. The Ca(OH)2 method often yielded higher buffer capacity values than the KOH method, possibly because of incomplete reaction of Ca(OH)2, especially at high addition rates. Buffer capacity (measured using KOH) of the soils was strongly correlated with soil carbon (C) (R2 = 0.76), and weakly (but significantly, P &lt; 0.05) with clay content, and with dithionite extractable Fe and Al. A regression with soil C, clay, and P-retention (a surrogate for extractable Al and Fe) as independent variables explained 90% of the variability in pH buffering. The role of organic matter was further evaluated by measuring buffer capacity of soil from research plots at Lincoln, Canterbury, New Zealand, that differed in C (21–37 g C kg–1 in the top 7.5 cm; 19–26 g C kg–1 in the 7.5–15 cm) as a result of the treatments imposed during the 12-year trial period. A substantial decrease in pH buffering (by up to 24% in top 7.5 cm) was associated with a decline in SOM following the conversion of permanent pasture (pre-trial land use) to arable cropping. Across all treatments and sampling depths, buffer capacity was linearly related (R2 = 0.84, P &lt; 0.001) to soil C; the estimated buffer capacity of SOM was 89 cmolc kg–1 C pH unit–1, similar to the value calculated from the previous study with different soil types. After 12 years, treatments with low soil C concentrations tended to be more acidic, possibly partly because of weaker pH buffering.

Effect of long-term agricultural cultivation and land use conversion on soil nutrient contents in the Sanjiang Plain

The cultivation patterns in the Sanjiang Plain of Northeast China have changed over the last three decades, resulting in variations in the land use and soil properties. Changes in cultivation patterns are an important concern for agricultural development in China. In order to highlight the impact of long-term land use on soil quality, the spatial pattern of permanent wetland, permanent forest, permanent dryland, wetland converted to dryland, wetland converted to paddy land, dryland converted to paddy land, and forest converted to dryland in the Sanjiang Plain from 1979 to 2009 was identified. Forty-one soil samples from these seven permanent and converted land use types were collected and eight indexes were analysed. The soil nutrient content of permanent forest, dryland reclaimed from forest, permanent wetland and dryland reclaimed from wetland was not significantly different. However, the soil nutrient content of permanent wetland, except for the available phosphorus, was higher than those of dryland and paddy land reclaimed from wetland. Compared to the permanent wetland, the soil organic matter and total nitrogen of dryland reclaimed from wetland decreased by 55.8% and 59.6%, respectively. For paddy land reclaimed from wetland, the decline in soil organic matter and total nitrogen was 63.6% and 67.6%, respectively. However, the total potassium and available phosphorus of permanent wetland were significantly lower than the amounts in dryland. After permanent forest and wetland were changed to dryland, the available phosphorus increased by 107.7% and 103.2%, respectively. The one-way ANOVA was applied to assess the effect of different changes in land use patterns on the soil nutrient contents. This study suggests that the reclamation of wetland decreased soil nutrient content, but the conversion of dryland to paddy land and forest to paddy land increased the nutrient content. The findings can provide advice for agricultural land use managers and also enhance the understanding of nutrient balance.

Estimating soil organic carbon in Europe based on data collected through an European network

Under the European Union Thematic Strategy for Soil Protection, the European Commission Directorate-General for the Environment (DG Environment) and the European Environmental Agency (EEA) have identified decline in soil organic matter and soil losses by erosion as priorities for the collection of policy-relevant soil data at European scale. To support EU policies related to soil conditions the data collected on corresponding indicators requires establishing agreed datasets for the EU Member States on these themes.In 2010, the Joint Research Centre of the European Commission (JRC), which is charged with the collection of soil data at European scale and hosts the European Soil Data Centre (ESDAC), conducted a project to collect data on soil organic carbon and soil erosion in Europe using the European Environment Information and Observation Network for soil (EIONET-SOIL). The data submitted by participating countries are their best estimate and represent an official point of view. The technical approach taken allows a country to easily update the records when new data become available.This paper presents the first results obtained from analyzing the soil organic carbon data submitted to EIONET-SOIL. The collected data were compared with the modelled data of the European topsoil organic carbon content developed at the JRC. The modelled data follow the general pattern of the geographic distribution of collected data, but show higher values compared to the EIONET-SOIL data. The important role of soil organic carbon (SOC) as an indicator of soil quality underlines the need for using common methods of sampling, analysing and reporting soil organic carbon to provide a standard product, such as EIONET-SOIL.

Impact of soil tillage and land use on soil organic carbon decline under mediterranean conditions

Soils under Mediterranean climate conditions frequently have low to very low levels of soil organic matter (SOM), as a result of low biomass production under the predominantly rainfed conditions and the intensive tillage operations commonly practiced. In order to assess both short and long-term impacts of soil tillage and land use on soil organic carbon, two sets of experiments were performed. One consisted in the identification and soil analysis of 3 pairs of sites under different soil types and land use over 5 to 30 years; in the second experiment a long-term fallow area was repeatedly submitted to different types of soil tillage management (mouldboard plough + disc harrow; non-inversion tine cultivation; no-till) over 3 years. Soil texture, bulk density and SOM were analysed along the whole soil profile in the first experiment, whereas bulk density and SOM to a depth of 30 cm was measured before the first tillage operations and at the end of the observation period in the second experiment. The results clearly indicate that tillage based land use, irrespective of the type of land use, caused a considerable decline in SOM content in the tilled soil layer. Very small and inconsistent differences in SOM between paired soil profiles were observed in the lower part of the profiles. In the second experiment with three types of tillage systems, SOM content decreased with tillage intensity. Avoidance of soil disturbance is an important step towards halting SOM decline under Mediterranean climate conditions.

Conservation agriculture for small holder rainfed farming: Opportunities and constraints of new mechanized seeding systems

Small holder farmers in rainfed agriculture believe that soil tillage is needed to maximize crop yields. However, as cropping intensity, and hence tillage intensity, increases there may be a decline in particular physical, chemical and biological properties of the soil which limit crop yield. This is primarily caused by declining soil organic matter, its oxidation being accelerated by tillage, particularly in warmer climates, and exacerbated by the limited return of above-ground biomass to the soil due to its competing use for other purposes. In large-scale commercial agriculture declining soil quality has been effectively addressed by conservation agriculture—cropping systems based on minimum tillage, crop residue retention and appropriate crop rotations and associations, preferably including legumes. This has required development of minimum tillage planting equipment along with herbicide technology to achieve weed control that is traditionally achieved through tillage. However, a shortage of mechanized options suitable for small holder farmers is creating an impediment to the adoption of conservation agriculture practices that would arrest the decline in soil quality in their fields. In South Asia, two-wheel tractors are replacing animal-drawn ploughing in small holder plots. This speeds the tillage operation and hence the turnaround time between crops, which may increase opportunities for crop intensification, but the problems associated with full tillage remain. Over the previous decade planter attachments to two-wheel tractors have been developed which permit seed and fertilizer placement with minimum to zero tillage in a single-pass. Recent tests have demonstrated that use of these implements can produce crop yields equal to or better than conventional tillage involving hand broadcasting of seed and fertilizer. Further, fuel and labour costs, seed and fertilizer inputs and turnaround time between crops can be reduced. In Africa, the introduction of animal-drawn rippers and direct seeders, originally developed for small-scale farmers in Brazil, is considered as a major breakthrough to small-scale farmer mechanization. It significantly reduces labour required for planting and benefits may be even greater if herbicides can be effectively used for weed control. Nevertheless, movement towards minimum tillage with two-wheel tractor mounted planters and animal-drawn direct seeding equipment is constrained by weed management issues. There are problems of availability and of safe and effective use of herbicides by resource-poor farmers and there is a need to develop more integrated weed management strategies that can be combined with small-scale planters. There is also a need to optimize the performance of small-scale planters to suit farmers’ needs in different agro-ecological environments. Tools and concepts are now available to implement conservation agriculture for small holders and thereby increase profitability of their cropping practices and at the same time improve soil quality and sustainability of their livelihoods. However, much more adaptive research and on-farm evaluation is needed across a diverse range of soils, cropping systems and agro-ecological regions to bring conservation agriculture to more small holders.

Impact of soil tillage and land use on soil organic carbon decline under mediterranean conditions

Soils under Mediterranean climate conditions frequently have low to very low levels of soil organic matter (SOM), as a result of low biomass production under the predominantly rainfed conditions and the intensive tillage operations commonly practiced. In order to assess both short and long-term impacts of soil tillage and land use on soil organic carbon, two sets of experiments were performed. One consisted in the identification and soil analysis of 3 pairs of sites under different soil types and land use over 5 to 30 years; in the second experiment a long-term fallow area was repeatedly submitted to different types of soil tillage management (mouldboard plough + disc harrow; non-inversion tine cultivation; no-till) over 3 years. Soil texture, bulk density and SOM were analysed along the whole soil profile in the fi rst experiment, whereas bulk density and SOM to a depth of 30 cm was measured before the fi rst tillage operations and at the end of the observation period in the second experiment. The results clearly indicate that tillage based land use, irrespective of the type of land use, caused a considerable decline in SOM content in the tilled soil layer. Very small and inconsistent differences in SOM between paired soil profiles were observed in the lower part of the profiles. In the second experiment with three types of tillage systems, SOM content decreased with tillage intensity. Avoidance of soil disturbance is an important step towards halting SOM decline under Mediterranean climate conditions.

Role of Nitrogen Fertilization in Sustaining Organic Matter in Cultivated Soils

Soil organic matter (SOM) is essential for sustaining food production and maintaining ecosystem services and is a vital resource base for storing C and N. The impact of long-term use of synthetic fertilizer N on SOM, however, has been questioned recently. Here we tested the hypothesis that long-term application of N results in a decrease in SOM. We used data from 135 studies of 114 long-term experiments located at 100 sites throughout the world over time scales of decades under a range of land-management and climate regimes to quantify changes in soil organic carbon (SOC) and soil organic nitrogen (SON). Published data of a total of 917 and 580 observations for SOC and SON, respectively, from control (unfertilized or zero N) and N-fertilized treatments (synthetic, organic, and combination) were analyzed using the SAS mixed model and by meta-analysis. Results demonstrate declines of 7 to 16% in SOC and 7 to 11% in SON with no N amendments. In soils receiving synthetic fertilizer N, the rate of SOM loss decreased. The time-fertilizer response ratio, which is based on changes in the paired comparisons, showed average increases of 8 and 12% for SOC and SON, respectively, following the application of synthetic fertilizer N. Addition of organic matter (i.e., manure) increased SOM, on average, by 37%. When cropping systems fluctuated between flooding and drying, SOM decreased more than in continuous dryland or flooded systems. Flooded rice ( L.) soils show net accumulations of SOC and SON. This work shows a general decline in SOM for all long-term sites, with and without synthetic fertilizer N. However, our analysis also demonstrates that in addition to its role in improving crop productivity, synthetic fertilizer N significantly reduces the rate at which SOM is declining in agricultural soils, worldwide.

Land use and soil organic matter in South Africa 2: A review on the influence of arable crop production

The decline of soil organic matter as a result of agricultural land use was identified for a review with the ultimate aim of developing a soil protection strategy and policy for South Africa. Such a policy is important because organic matter, especially the humus fraction, influences the characteristics of soil disproportionately to the quantities thereof present. Part 1 of this review dealt with the spatial variability of soil organic matter and the impact of grazing and burning under rangeland stock production. In this second part of the review, the impact of arable crop production on soil organic matter is addressed. A greater number of studies have addressed the degradation of soil organic matter that is associated with arable crop production than the restoration. However, cropping under dryland has been found to result in significant losses of soil organic matter, which is not always the case with cropping under irrigation. Restoration of soil organic matter has been very slow upon the introduction of conservational practices like zero tillage, minimal tillage, or mulch tillage. Reversion of cropland to perennial pasture has also been found to result in discouragingly slow soil organic matter restoration. Although increases or decreases in soil organic matter levels have occurred in the upper 300 mm, in most instances this took place only in the upper 50 mm. The extent of these changes was dependent inter alia on land use, soil form and environmental conditions. Loss of soil organic matter has resulted in lower nitrogen and sulphur reserves, but not necessarily lower phosphorus reserves. Depletion of soil organic matter coincided with changes in the composition of amino sugars, amino acids and lignin. It also resulted in a decline of water stable aggregates which are essential in the prevention of soil erosion. Although much is known about how arable crop production affects changes in soil organic matter, there are still uncertainties about the best management practices to maintain and even restore organic matter in degraded cropland. Coordinated long-term trials on carefully selected ecotopes across the country are therefore recommended to investigate cultivation practices suitable for this purpose.

Land use and soil organic matter in South Africa 1: A review on spatial variability and the influence of rangeland stock production

Degradation of soil as a consequence of land use poses a threat to sustainable agriculture in South Africa, resulting in the need for a soil protection strategy and policy. Development of such a strategy and policy require cognisance of the extent and impact of soil degradation processes. One of the identified processes is the decline of soil organic matter, which also plays a central role in soil health or quality. The spatial variability of organic matter and the impact of grazing and burning under rangeland stock production are addressed in this first part of the review. Data from uncoordinated studies showed that South African soils have low organic matter levels. About 58% of soils contain less than 0.5% organic carbon and only 4% contain more than 2% organic carbon. Furthermore, there are large differences in organic matter content within and between soil forms, depending on climatic conditions, vegetative cover, topographical position and soil texture. A countrywide baseline study to quantify organic matter contents within and between soil forms is suggested for future reference. Degradation of rangeland because of overgrazing has resulted in significant losses of soil organic matter, mainly as a result of lower biomass production. The use of fire in rangeland management decreases soil organic matter because litter is destroyed by burning. Maintaining or increasing organic matter levels in degraded rangeland soils by preventing overgrazing and restricting burning could contribute to the restoration of degraded rangelands. This restoration is of the utmost importance because stock farming uses the majority of land in South Africa.

The influence of climate change on the soil organic carbon content in Italy from 1961 to 2008

Soils are the biggest carbon store in the world (1500 Gt, e.g. 1.5 × 10 21 g). The European Commission indicates the accounting of soil organic carbon (SOC) variations in space and time as the first step in the strategy for soil protection. It is indeed necessary in evaluating the risk of soil organic matter decline and soil biodiversity decline, and when evaluating the role played by soils in global CO 2 accounting. Previous maps of SOC variations in Italy did not consider the direct effect of climate. There is a marked inter-dependence between SOC and climate. SOC increases with the increase in precipitations and decreases with a rise in temperatures. It is also known that land use and management have a bigger impact on SOC than climate. The aim of this work is to understand to what extent the SOC variations occurring in Italy from 1961 to 2008 could be explained by climate change. The soil database of Italy was the source of information for SOC content: 17,817 observations (3082 before and 14,735 after 31 Dec 1990). SOC content was referred to the first 50 cm of soil depth, one single data obtained by weighted horizon thickness. SOC content was expressed as percentage by weight (dag kg − 1 ) analyzed by the Walkley–Black procedure and converted to ISO standard. The CRA–CMA (Research Unit for Climatology and Meteorology Applied to Agriculture) database was the source of information for climatic data. We considered the mean annual temperature (MAT) and mean value of total annual precipitation (MAP) of the two periods 1961–1990 and 1991–2006, and we mapped them by regression kriging with elevation and latitude as predictors. The climate change between the two periods was characterized by a general MAT increase, which was greater at lower altitudes and higher latitudes. The precipitation generally decreased, with some local exceptions. Some linear regression analyses were used to investigate the relationship between SOC content and climate/land use. Temperatures had most relevant impact on SOC with an inverse correlation. SOC content was directly correlated with precipitations on arable lands and inversely in forests and meadows. Two general multiple linear regression analyses considered all the pedogenesis factors and: either by time periods (1979–1990; 1991–2009), model 1; or by MAT and MAP, model 2. The two models both had low precision (multiple R-squared = 0.26–0.27; RMSE = 1.42; IoA = 0.61), but very different accuracies. Model 1 correctly predicted the mean SOC values for the 3 land uses in the 2 periods, detecting a significative decrease in all three land uses. Model 2 was not accurate every time. SOC decreases estimated with model 2 were always significatively lower than the observed ones. Model 2 did not estimate a significative SOC decrease in forests. Climate change had a general low influence on SOC variations. The relatively higher climatic influence occurred in meadows and in agricultural areas with a moderate or high MAP decrease (<−100 mm/y) and a moderate to high MAT increase (> 0.62 °C). Other changes, probably linked to land management, need to be investigated to explain SOC variations.