Sustainable soil and land management for climate-smart agriculture in practice
This chapter provides examples of sustainable soil and land management practices that are designed to protect and restore soils and soil biodiversiy, control soil erosion control, sequester soil carbon and optimize water management in the soil.
B7-3.1 Preventing and mitigating land degradation
The world’s soils are seen as having a high potential for carbon sequestration because soil organic carbon content can be conserved, restored and increased through appropriate land uses and agricultural management practices that can be applied at the landscape level (Corsi et al., 2012). However, initiating the carbon sequestration process on degraded soils is a slower process as the soil microbial population that drives the soil organic carbon and nutrient cycling requires specific nutrient ratios that take time to achieve (Stevenson, 1986). In addition, degraded soils are at much greater risk from the damaging impacts of mismanagement and climate change. Their vulnerability is a result of serious losses in soil organic matter and soil biodiversity, which undermine soil resilience; greater soil compaction; and increased rates of soil erosion and a higher incidence of landslides. Land degradation is itself a major cause of climate change (Scherr and Sthapit, 2009b).
Unsustainable land management practices that degrade soils include tillage-based crop production systems; simplified crop rotations that lead to soil nutrient mining; the improper application of fertilizers; inappropriate irrigation practices; overstocking, overgrazing and burning of rangelands; inefficient grazing methods; and the overexploitation or clearance of wooded and forest lands.
The widespread restoration of degraded soils is crucial for sequestering carbon and supporting the productive capacities of the world’s croplands, rangelands and forests. Soil organic carbon sequestration can be achieved by reducing erosion (Chapter B7-3.2) and preserving and increasing soil organic matter in the soil (Chapter B7-3.3).
Equally important is the prevention of the conversion of vulnerable land for unsustainable uses. Intensive land uses are expanding into areas where soil organic carbon stocks are less resilient.
- Semi-arid savannas and grasslands, tropical rainforests and peatlands are being converted to arable land at an increasing rate.
- Temperate humid grasslands release about 30 percent of their soil organic carbon after 60 years of cultivation (Tiessen and Stewart, 1983; Guo and Gifford, 2002).
- In semi-arid environments, the cultivation of tropical forest soils causes more than 60 percent of original soil organic carbon stocks to be lost in only a few years (Brown and Lugo, 1990). Converting native vegetation or pastures to cropland depletes soil carbon stocks by 30 percent in less than five years (Zach et al., 2006; Noellemeyer et al., 2008). In the Amazon rainforest, establishing pastures on cleared forest emits between 8 and 12 tonnes of carbon dioxide per hectare (Fearnside and Barbosa, 1998; Cerri et al., 2007).
- In arid and semi-arid areas, soil organic carbon is undergoing significant changes in the aftermath of series of different combinations and sequences of land-use changes.
Changes in soil organic carbon depend on the management practices associated with land use and the time since the current land-use system was established (Mohawesh et al., 2015). Assessments of land resources (Chapter B7-2.1) are needed to help identify the effects of land-use changes and associated management practices on the dynamics of soil organic carbon and support the formulation of sustainable land management plans. Such assessments will identify hotspots in terms of the degradation of soil, water and biodiversity) and climate change, and bright spots where sustainable land management practices are generating multiple ecosystem benefits. Land-use planning can then be used to determine the most suitable land uses and provide policy support or incentives to reduce land conversion and promote the adoption of sustainable practices, with particular attention given to peatlands (Box B7.2 and drylands that are more vulnerable to human intervention and climate change. See also module C3 on policy and programmes for climate-smart agriculture.
Box B7.2 Peatlands as climate change mitigation hotspots - towards wiser management
Peatlands are ecosystems where greenhouse gas emissions can often be reduced in a cost-effective manner. Peatlands or ‘organic soils’ have a substantial layer of organic matter near the surface. Unlike mineral soils, most pristine peatlands are wet during most of the year. Peatlands, which are found in almost every country in the world, contain 30 percent of the world’s soil carbon but cover only three percent of the global land area (Joosten, 2009; Victoria et al., 2012). Draining a part of a peat dome or excessive irrigation lowers the water table in the entire peatland area and causes greenhouse gas emissions. Drained peatlands and fires in drained peatlands are responsible for almost one-quarter of the carbon dioxide emissions from the land-use sector (Joosten, 2009; Victoria et al., 2012).
There has been a rapid growth in emissions from peatlands as they have been drained for forestry, food crops and cash crops, such as oil palm. In many cases, for example in Ukraine and Southeast Asia, the cultivation of peatlands has led to their serious degradation, subsidence and abandonment. Abandoning peatlands significantly increases the risk of fires.
To reduce greenhouse gas emissions from peatlands, it is essential to determine their status; whether they are pristine, drained, abandoned or in productive use. The main approaches for reducing emissions from peatlands include:
- conserving undrained peatlands;
- rewetting drained peatlands using blocking canals and grids;
- increasing the productivity on the existing farmland to reduce the pressure to drain peatlands for agriculture or forestry; and channelling the expansion of agricultural land to areas with mineral soils; and
- managing peatlands, if they cannot be rewetted, in ways that maintain soil carbon. (FAO, 2014)
Rewetted peatlands (Figure B7.4) can provide income and other benefits to local communities by supporting forestry and agricultural cultivation under wet conditions, a practice known as paludiculture. Paludiculture, which can be carried out wherever there are marketable plants and animals living in wet conditions, can produce biomass for bioenergy, feed for livestock, fibre, building materials and food, such as nuts and berries. In Southeast Asia, natural rubber is collected from Jelutung paludiculture. Local communities are earning up to half of their income from raising fish in the blocked grids alongside the rubber production (FAO and Wetlands International, 2012). Paludiculture represent the only sustainable mode of agricultural production on peatlands. There are, however, technical and socio-economic constraints that can prevent drained peatlands from being rewetted. In such cases, the negative environmental and socio-economic impacts of peatland use can be limited, for example, by choosing crops that are adapted to high soil moisture; minimizing drainage as much as possible to reduce peat oxidation and land degradation; and reducing the use of fertilizers.
Source: Hans Joosten and Maria Nuutinen
Figure B7.4. Raising the water levels on drained peatlands by blocking ditches can be done with low-cost techniques and local materials. Dam in a channel in Mentangai, Indonesia
- Source: Marcel Silvius, Wetlands International
B7-3.2 Controlling soil erosion
Soil erosion is process that is causing widespread and serious environmental degradation. Erosion removes a field’s original topsoil, reducing the thickness of the soil surface, which is the most productive part of the soil profile, and causing losses of soil organic matter (Mohawesh et al., 2015).
Tillage-induced soil erosion is a major cause of the severe soil carbon loss and soil translocation in upland landscapes (Lobb et al., 1995; Lobb and Lindstrom, 1999; Reicosky et al., 2005). Even on gradual slopes, alkaline soils for example, may suffer from dispersion or crusting that will increase surface runoff and the risk of soil erosion. The redistribution of soil within fields caused by tillage erosion may lead to high erosion rates on knolls, exceeding 30 tonnes per hectare per year and to deposition rates in hollows and at downslope field borders, exceeding 100 tonnes per hectare per year. These rates are not directly comparable to wind or water erosion rates, as soil eroded by tillage will not leave the field. However, tillage erosion may significantly reduce crop productivity on knolls and near downslope field or terrace borders (FAO and ITPS, 2015b).
Intense rains can cause devastating soil erosion on cultivated lands on moderate to steep slopes where runoff rates are high and the ground has inadequate vegetative cover. Increased incidences of windstorms accelerate the loss of fertile soil by blowing soil particles off the fields or onto other fields.
Soil erosion by rainfall and surface runoff, and wind can be prevented or substantially reduced with conservation agriculture, and minimum- or no-tillage farming, combined with a range of soil and water conservation measures that include optimizing vegetative cover with adapted species; using rotational grazing to sustain the quality of rangeland vegetation; enhancing the roughness of the soil surface with clods and tied ridges; contour farming using bunds and diversion ditches; and planting windbreaks perpendicular to the prevailing winds.
On steeper slopes, soil erosion control requires additional measures, including reducing the degree and length of slopes with progressive and bench terracing; planting cross-slope vegetation; using soil and water conservation structures, such as terraces, earth bunds and tied ridges to optimize water capture and infiltration; and creating grassed waterways to convey excess water safely off the slopes. Erosion control mats and blankets (geotextiles), preferably biodegradable ones, offer immediate soil protection, and in some cases, these products may be an economic option for erosion control. In different parts of the world, biological geotextiles have proven to be highly effective for controlling soil erosion and supporting above-ground biomass production (Bhattacharyya et al., 2009; Bhattacharyya et al., 2011; Bhattacharyya et al., 2012a; Ghosh et al., 2016).
B7-3.3 Managing Soil Organic Matter for soil carbon sequestration
Organic matter in the soil is made up of dead plant and animal materials in various stages of decomposition. It does not include fresh and undecomposed plant material lying on the soil surface, which is known as litter. As explained in Box B7.3, soil organisms break down the organic matter so they can use it as food. In doing so, they release excess nutrients into the soil in forms that plants can use. The organic matter that these organisms cannot digest is reorganized into soil organic matter, which is less decomposable than the original plant and animal material (Figure B7.5). Soil organic matter primarily contains organic carbon (on average 58 percent), but also nutrients that are essential for plant growth, and some inorganic carbon. Soil organic matter acts as a sink for atmospheric carbon, in that it sequesters carbon from the atmosphere. Soil organic matter also enhances soil structure by binding the soil particles together as stable aggregates, which influence the soil’s physical properties (e.g. aggregation, water holding capacity, water infiltration and aeration) and chemical fertility (e.g. nutrient availability). The characteristics of soil organic matter have an impact on the overall biological resilience of agricultural ecosystems. The greater the soil organic matter content, the greater the soil biodiversity. Higher levels of biodiversity in the soil accelerate the processes involved in breaking down dead and decaying organic matter into humus and making nutrients available for plant growth (Charman and Roper, 2000; Bot and Benites, 2005; Bhattacharyya et al., 2012b; Bhattacharyya et al., 2012c).
Soil carbon stocks and the mitigation potential they provide depend on the agro-climatic zone, the type of land use and the intensity of use (Figure B7.2). The rate of soil organic matter decomposition and turnover depends primarily on the combined effects of the soil organisms, temperature, moisture and the soil's chemical and physical composition. It is also affected by the previous land use and natural resource management practices, particularly the mechanical disturbance of the soil. When assessing carbon sequestration, rates should always refer to the specific association of soil and vegetation and definite carbon pools, as each carbon category has a very different turnover rate. For instance, carbon accumulated in the first ten years is young and highly oxidizable, but becomes more stable over time. To assess the effects of management practices on soils, it is also necessary to use a reference base for similar soil types under the same climatic conditions. Undisturbed soils under natural vegetation should be used as a benchmark and used when making a comparison with the soils affected by human activities. In this context, it is important to emphasise that only data from similar agro-ecological zones can be compared because the rate of conversion of the carbon content in crop residues into soil organic matter is strongly related to the climate, and the rates achieved under different climatic conditions are not directly comparable (Corsi et al., 2012).
Box B7.3 Nutrient turnover and terrestrial carbon sequestration
Terrestrial carbon sequestration occurs in standing biomass (e.g. trees), long-term harvested products (e.g. lumber), living biomass in soil (e.g. perennial roots and microorganisms), recalcitrant soil organic matter in soil (e.g. humus), and inorganic carbon in the subsoil (e.g. carbonates) (Johnson et al., 2007). Organic and inorganic carbon pools in soils are generally the most long-lived terrestrial reservoirs for sequestering carbon (Figure B7.5).
Photosynthesis represents the largest transfer of carbon (through carbon dioxide) in the carbon cycle. Through photosynthesis, plants draw carbon dioxide out of the air to form plant tissues (carbohydrates). When dead plant and animal material (i.e. organic matter) is returned to the soil, it decomposes. The decomposition of organic matter is a biological process carried out by soil organisms that involves a series of steps that lead to the mechanical breakdown (comminution), the chemical breakdown (mineralization), and the biochemical reorganization of complex structures and molecules (polymers). Only the indigestible fraction of carbon (i.e. carbohydrates, lignins, tannins, aromatic amino acids and waxes) enters into the formation of stable soil organic matter (humification).
By transforming organic compounds into inorganic compounds, and breaking down carbon structures and rebuilding new ones or storing carbon into their own biomass, the microbial population acts as functional engine for the turnover of organic matter and the release of nutrients to the soil. It is this microbial population that is responsible for enabling the soil to provide crops with nutrients.
When decomposing soil organic matter, the soil organisms release nitrogen in the form of ammonium ions, potassium, calcium, magnesium and a range of other nutrients necessary for plant growth and the organisms' activities. Plants obtain many of their nutrients from soil by ‘cation exchange’, whereby root hairs exchange hydrogen ions with the cations (positively charged ions) adsorbed in the soil particles. Clay soils have a higher cation exchange capacity and a structurally greater potential chemical fertility than silty soil and sandy soils.
Nitrogen is a nutrient that deserves special attention. It plays a key role in plant metabolism and growth, but it can also be a cause of pollution when it leaches in the form of nitrates into the water table. Nitrogen can also be released from the agricultural ecosystem in the form of nitrous oxide - a potent greenhouse gas.
Source: Sandra Corsi, Feras Ziadat
Figure B7.5. Organic matter turnover
- Source: Gupta et al., 1997
Mainstream agricultural production systems that do not rely on biogechemical cycles do not ensure the sustained productivity of soils.
- Over the past 50 to 100 years, tillage-based agricultural practices have caused soil organic carbon levels in many regions to decline by one to three percent, which has caused soil degradation. As shown in Table B7.1, a three percent loss in soil organic carbon not only represents a significant loss of water storage (432 000 litres per hectare), but also represents nearly 400 tonnes of extra carbon dioxide per hectare emitted into the atmosphere. The loss of soil organic carbon and water holding capacity is associated with a range of practices, including the elimination of perennial groundcover, repetitive cultivation and tillage, continuous grazing, bare fallows, the removal of crop residues and grassland burning.
- Intensive monoculture, in combination with the high use of external inputs, has been an approach farmers have adopted to achieve the highest possible yields with minimal labour. However, the production of energy-intensive mineral fertilizers and pesticides is a major source of greenhouse gas emissions. Moreover, when incorrectly applied, these inputs leach into water resources, and the resulting water contamination has seriously harmful effects on ecosystems and human health.
With agricultural intensification, farmers are increasingly supplementing organic fertilizers (e.g. manure, compost and plant residues) with inorganic or synthetic fertilizers, which deliver the required crop macronutrients (e.g. nitrogen, phosphorus, potassium, calcium, magnesium and sulphur) and micronutrients (e.g. boron, chlorine, copper, iron, manganese, molybdenum, zinc and nickel). Nitrogen fertilizers are the most widely used fertilizers and deliver huge benefits in terms of productivity, especially in nutrient-depleted soils. However, as indicated in Table B7.1, these fertilizers can cause environmental damage in the form of greenhouse gas emissions and nitrate pollution (Scherr and Sthapit, 2009b).
Table B7.1. Capacity of a soil with a bulk density of 1.2 g/cm3 to store water as affected by soil organic carbon content to 30 cm soil depth
The calculation of these figures is based on a conservative estimate that one part of soil organic carbon retains four parts of soil water.Change in soil organic matter content.
Change in soil organic matter content | Extra soil organic matter |
| Carbon dioxide sequestered | |
|---|---|---|---|---|
[%] | [kg] | [litres/m2] | [litres/ha] | [t/ha] |
1 | 3.6 | 14.4 | 144 000 | 132 |
2 | 7.2 | 28.8 | 288 000 | 264 |
3 | 10.8 | 43.2 | 432 000 | 396 |
Source: Jones, 2006a and 2006b
Integrated soil fertility management practices seek to maximize the efficiency in the use of nutrients and water. They does this by balancing the use of organic matter obtained on the farm or from other sources as a soil amendment with the judicious use of nutrients from mineral fertilizers; and reducing nutrient losses by synchronizing the supply of nitrogen with crop demands through sound agronomic practices, including soil and water conservation measures. Examples of integrated soil fertility management practices include:
- making changes in the rates, timing and type of nitrogen fertilizer applications; and using slow release fertilizers that control the formation of nitrates;
- adding nitrification inhibitors containing ammonium to fertilizer;
- practicing no-tillage farming, while maintaining continuous soil cover and rotating cropping patterns, which provides enough structural carbohydrates (e.g. lignin) along with nitrogen to allow the nitrogen produced from decaying surface residues to be released more slowly and contribute to the growth of the following crop and minimize nutrient losses (Huggins et al., 1998; Gregorich et al., 2001; Gál et al., 2007).
This form of agriculture, known as conservation agriculture, considerably reduces nitrate leaching (Macdonald et al., 1989). This is because, unlike mechanical tilling practices, conservation agriculture does not disrupt the stabilization and formation of soil aggregates (Bhattacharyya et al., 2013). Soil aggregates protect the nitrogen from microbial enzymes, decreasing mineralization and the subsequent production of nitrates. The cover crops in the rotation take up the nitrogen and keep it from being lost from the soil. At the same time, unused mineralized nitrogen remains distributed within smaller pores and is not washed out of the soil (Gors et al., 1993; Bergström, 1995; Davies et al., 1996). However, where no-tillage is used without cover crops and with herbicides to manage weeds, the effects on nitrogen uptake and reduced leaching, as well as on yields, may be less evident (Das et al., 2014).
Greater efficiency in the management of production inputs reduces wastage and the amounts used, which can lower greenhouse gas emissions. Additional efficiency gains can be achieved through the climate-smart practices presented in module B1 for crop production, module B2 for livestock production and module B5 for integrated systems and summarized in Table B7.2. The use of biochar as a carbon sequestration practice may be an option, but it remains controversial (see Box B7.4).
Box B7.4 Biochar
Biochar is a stable, carbon-rich form of charcoal that can be produced by pyrolysis, a process in which biomass is heated with little or no oxygen (Sparkes and Stoutjesdijk, 2011). Possible biomass sources for biochar include milling residues (e.g. rice husks, sugar cane bagasse); crop and logging residues; biofuel crops; municipal wastes; and animal manure. The suitability of biomass for biochar production depends on its lignin content (Eagle et al., 2012).
Biochar, due to its porous nature, high surface area and its ability to absorb soluble organic matter and inorganic nutrients, is thought to offer benefits for sustainable agricultural productivity. It increases biological activity and improves the efficiency of nutrient use, which reduces nitrous oxide emissions and increases carbon sequestration. Prommer et al. (2014) found that biochar increased total soil organic carbon but decreased the extractable organic carbon pool and soil nitrate. They concluded that the addition of inorganic nitrogen fertilizer in combination with biochar could compensate for the reduction in organic nitrogen mineralization.
Biochar is a relatively new, and the physical properties of biochar are highly variable. The cost effectiveness of using biochar depends on the biomass source and distance to the pyrolysis plant. In many contexts, it is not an economically viable option. Also, not all soils or crops show the same improvements when biochar is applied, and there may be risks associated with increased soil alkalinity. In the long term, the application of biochar may affect soil fertility, reduce the efficacy of some agricultural chemicals, and inhibit microbial processes due to the production of ethylene. More research is needed on the potential benefits and risks of its use in agricultural soils.
Source: FAO, 2013
B7-3.4 Improving water use and management in agriculture
As climate change has an impact on every element of the water cycle, particular attention should be placed on using water efficiently.
Water storage in the soil depends on many factors, including the amount and intensity of rainfall, soil depth, soil texture (e.g. clay content), soil structure, soil temperature, and the content and type of soil organic carbon. Different soil types, textures and structures have different degrees of water permeability and offer different levels of protection for soil organic matter. Within the soil, stable forms of soil organic carbon, such as humus, can hold up to 7 times their own weight in water. A soil that has a crumbly structure, which breaks easily into separate lumps and clumps, will absorb water more quickly than one that is compacted. Sandy soils are the least productive soils. They have a non-reactive chemical nature and, as they are highly permeable, have a low capacity for retaining water. They also offer limited protection to soil organic matter compared to soils with a higher proportion of silts and clays, which can attract and retain water and nutrients through chemical processes.
Soil management can increase water infiltration, strengthen the capacity of the soil to store water and reduce soil water evaporation.
- Groundcover management can have highly significant effects on soil surface conditions, soil organic matter content, soil structure, porosity, aeration, bulk density. This has a direct influence on infiltration rates, the water storage potential of the soil and water availability to plants.
- Roots, and the organisms that thrive in undisturbed soils create channels that improve soil porosity and the water infiltration rate.
- Minimizing soil compaction increases the effectiveness of rainfall, enhances productivity, reduces erosion and the dispersion of soil particles, and lowers the risks of waterlogging. Compacted soils or soils with a hardpan may waterlog easily and then dry out quickly.
- Sandy soils can be managed productively even in hot, dry climates by adding organic matter (e.g. green manure, animal manure, composted material) and, in irrigated systems, supplying nutrients through drip irrigation.
The good management of soil-crop-water interrelations can maintain and increase soil organic matter, improve the soil’s nutrient retention capacity and enhance soil biodiversity. This integrated management can create optimal conditions for crop production, while simultaneously increasing the resilience of production systems to climate change.
In crop production systems, good management practices to increase soil organic matter include:
- direct seeding (no-tillage) in combination with protective soil cover, crop diversification and crop rotation;
- the elimination of the burning of crop residues;
- integrated soil fertility management to increase the soil's nutrient retention capacity and the availability on nutrients to plants;
- the precise management of nitrogen;
- integrated pest management, which includes the sustainable use of herbicides.
- the construction of soil conservation structures, such as stone and earth terraces and bunds, and check dams;
- irrigation or partial irrigation where needed or possible (see module B6 on water management);
- the harvesting and proper use of rainwater;
- the development of reliable sources of information and extension services that are tailored to local conditions; and
- appropriate soil erosion control practices
In grazing systems, soil organic matter can be increased through controlled grazing, which reduces the degradation of vegetation and restores grassland diversity. Reducing burning to the absolute minimum also increases soil organic matter. However, on common property lands, burning is often a preferred strategy to enhance phosphorus and encourage the growth of young plants for grazing animals (also see module B2 on livestock). Case study B5.2 presents details on the ‘Quesungual Slash and Mulch Agroforestry System’, an alternative to slash and burn practices.
Integrated crop and livestock systems can be used to enhance soil fertility. An example of an integrated system on sloping uplands is presented in case study B7.2. Pasture cropping, a practice where an annual crop is grown out-of-phase with perennial pasture, builds soil at higher rates than perennial pastures alone. This is due to the fact that there is a year-round transfer of soluble carbon to the root zone and the humification process is maintained during the period when the perennial crop is not growing (Cluff and Seis, 1997).
To increase the amount of water in the soil, rainwater harvesting and irrigation can be used. These are addressed in module B6 on water management. Case study B7.3 presents an indigenous system of soil and water management for rice production.
Table B7.2. 'Business-as-usual' practices verses climate-smart practices
The following practices and approaches have been selected as good management practices that can contribute to climate change adaptation and mitigation. Progress in this area will require embracing an ecosystem approach that fosters the integrated management of soil and land resources and takes into consideration the interactions among water, crops, forests, livestock and other components of the ecosystem.
'Business-as-usual' practices | Climate-smart practices for climate change adaptation | Climate-smart practices for climate change mitigation |
|---|---|---|
Soil fertility management through synthetic fertilizers | Integrated soil fertility management | |
|
|
|
Soil tillage for annual crops | ||
Tillage is done to control weeds and loosen the soil. However, when loose soil is left under the impact of rain, wind and heat, the topsoil gets eroded. This lowers the natural content of soil organic matter, reducing soil fertility and releasing carbon dioxide. It also reduces the presence of soil organisms (e.g. earthworms, fungi), which limits the soil's capacity to regain its fertility. Tillage also typically develops a compacted layer (hardpan), which impedes plant root growth and rainwater infiltration. | Conservation agriculture increases the resilience of the farming systems in a number of ways.
| Conservation agriculture reduces:
These 'carbon savings' exceed the carbon costs related to the use of chemical herbicides for weed control. Conservation agriculture also has the potential to sequester soil organic carbon. Maximum rates of sequestration are achieved in the first 5 to 20 years after carbon-enhancing changes in land management have been implemented. Sequestration rates then decrease until soil organic carbon stocks reach a new equilibrium after 20 to 30 years (Lal, 2004; IPCC, 2007; FAO, 2017). The point at which equilibrium is reached depends on soil texture and composition. Until this point is reached, an exponential relationship between the application and accumulation of soil organic matter can be expected in most soils (Jacinthe et al., 2002; Six et al., 2002).
|
Soil puddling in rice paddy systems | ||
Flooded rice fields represent one of the main sources of methane emissions. | Systems of Rice Intensification, which reduce the use of water, also bring benefits in terms of productivity and adaptation. | Systems of Rice Intensification reduce greenhouse gas emissions in rice cultivation. Also the timely flooding of rice paddies, or the cultivation of rainfed lowland rice in flooded fields with periods of non-submergence can help save water and reduce methane emissions. However, this practice also may have the potential to increase nitrous oxide emissions. |
Extensive grazing | Improved grazing management (see module B2 for more details) | |
Many extensive grazing systems are suffering from overgrazing and serious reductions in the biodiversity of above-ground vegetation. This is a result of declining land availability and overstocking due to inadequate livestock management. This is leading to a decline of soil quality in rangelands, which is marked by a depletion of biomass, the erosion of topsoil by water and wind, the loss of soil organic carbon and a reduction of ecosystem services. This is accompanied by a decline in soil structure and resilience (e.g. through loss of deep rooting species that can cycle nutrients and water from deep in the soil profile). Excessive trampling of the soil by livestock, particularly around watering points, further damages the soil structure and inhibits its ecosystem functions. |
| Compared with more highly productive pasture, rangelands have low carbon sequestration rates when measured on a per unit of production basis. However, because of the vast areas they cover, their carbon sequestration potential remains high. |
Livestock waste management | Sustainable mixed farming systems | |
When conventional stockless arable farms become dependent on the input of synthetic nitrogen fertilizers, manure and slurry from livestock become an environmental problem. In these livestock operations, the availability of nutrients becomes excessive and over-fertilization may occur. In this situation leaching is likely to lead to water pollution and high emissions of carbon dioxide, nitrous oxide and methane. | Mixed farms or close cooperation between crop and livestock operations—a common practice in most forms of sustainable farming, especially organic ones— can contribute considerably to climate change mitigation and adaptation. Different forms of compost, especially composted manure, are also particularly useful in stimulating soil microbial processes and building up stable forms of soil organic matter (Fließbach and Mäder, 2000). On-farm use of farmyard manure, which is a practice that has been increasingly abandoned in conventional production, needs to be reconsidered in light of climate change. | |