13 Practices that Increase the Amount of Organic Matter
Different approaches are required for different soil and climate conditions. However, the activities will be based on the same principle: increasing biomass production in order to build active organic matter. Active organic matter provides habitat and food for beneficial soil organisms that help build soil structure and porosity, provide nutrients to plants, and improve the water holding capacity of the soil.
By the end of this article, you will be able to: explain 9 practices that increase organic matter content of soils.
13 Practices that Increase the Amount of Organic Matter
Several cases have demonstrated that it is possible to restore organic matter levels in the soil.
Activities that promote the accumulation and supply of organic matter, such as the use of cover crops and refraining from burning, and those that reduce decomposition rates, such as reduced and zero tillage, lead to an increase in the organic matter content in the soil.
The following Practices may increase the organic matter content of soils:
1. Increased Water Availability for Plants
In dry conditions, water may be provided through irrigation or water harvesting. The increased water availability enhances biomass production, soil biological activity and plant residues and roots that provide organic matter. Numerous water harvesting systems have been developed over the centuries, especially in arid areas.
The principle of collecting runoff for crop production is also inherent to many other soil and water conservation technologies that apply the concept of runoff and run-on areas at a micro-watershed level, such as negarims, trapezoidal or “eyebrow” bunds and tied ridges.
2. Balanced Fertilization
Where the supply of nutrients in the soil is ample, crops are more likely to grow well and produce large amounts of biomass. Fertilizers are needed in those cases where nutrients in the soil are lacking and cannot produce healthy crops and sufficient biomass.
Most soils in sub-Saharan Africa (SSA) are deficient in P. P is required not only for plant growth but also for N fixation. Unbalanced fertilization, for example mainly with N, may result in more weed competition, higher pest incidence and loss of quality of the product. Unbalanced fertilization eventually leads to unhealthy plants.
Therefore, fertilizers should be applied in sufficient quantities and in balanced proportions. The efficiency of fertilizer use will be high where the organic matter content of the soil is also high. When soil organic matter levels are restored, fertilizer can help maintain the revolving fund of nutrients in the soil by increasing crop yields and, consequently, the amount of residues returned to the soil.
3. Cover Crops
Growing cover crops is one of the best practices for improving organic matter levels and, hence, soil quality. The benefits of growing cover crops include:
·They prevent erosion by anchoring soil and lessening the impact of raindrops.
·They add plant material to the soil for organic matter replenishment.
·Some, e.g. rye, bind excess nutrients in the soil and prevent leaching.
·Some, especially leguminous species, e.g. hairy vetch, fix N in the soil for future use.
·Most provide habitat for beneficial insects and other organisms.
·They moderate soil temperatures and, hence, protect soil organisms.
A range of crops can be used as vegetative cover, e.g. grains, legumes and oil crops. All have the potential to provide great benefit to the soil. However, some crops emphasize certain benefits; a useful consideration when planning a rotation scheme.
It is important to start the first years with (cover) crops that cover the surface with a large amount of residues that decompose slowly (because of the high C: N ratio). Grasses and cereals are most appropriate for this stage, also because of their intensive rooting system, which improves the soil structure rapidly.
The term green manure is often used to indicate the same plant species that are used as cover crops. However, green manure refers specifically to a crop in the rotation grown for incorporation of the non-decomposed vegetative matter in the soil. While this practice is used specifically to add organic matter, this is not the most effective use of organic matter (especially in hot climates) for two reasons:
·Mechanical disturbance of the soil should be avoided as much as possible.
·When biomass is incorporated in the soil all at one time, there is a short period of high microbial activity in decomposing the material.
This results in the sudden release of a large quantity of nutrients that cannot be captured by the seedlings of the following crop and is thus lost from the system.
4. Improved Vegetative
Stands In many places, low plant densities limit crop yields. Wide plant spacing is often practiced as “a way to return power to the soil” or “to give the soil some rest”, but in reality it is an indicator that the soil is impoverished.
Plant spacing is usually determined by farmers in relation to soil fertility and available water or expected rainfall (unless standard recommendations are enforced by extension). This means that plants are often spaced widely on depleted soils in arid and semi-arid regions with a view to ensuring an adequate provision of plant nutrients and water for all plants.
5. Agroforestry and Alley Cropping
Agroforestry is a collective name for land-use systems where woody perennials (trees, shrubs, palms, etc.) are integrated in the farming system. Alley cropping is an agroforestry system in which crops are grown between rows of planted woody shrubs or trees.
These are pruned during the cropping season to provide green manure and to minimize shading of crops. Alley cropping is an agroforestry practice that places trees within agricultural cropland systems.
This system is sometimes called intercropping, especially in tropical areas. It is especially attractive to producers interested in growing multiple crops on the same acreage to improve whole-farm yield. Growing a variety of crops in close proximity to each other can create significant benefits to producers and help them manage risk. Alley cropping systems change over time.
As trees and shrubs grow, they influence the light, water, and nutrient regimes in the field. These interactions are what set alley cropping apart from more common mono-cropping systems. Some producers plan alley cropping systems to provide additional functions that support and enhance other aspects of their operation.
For example, a livestock producer might grow crops that supply fodder, bedding, or mast crops for their livestock. Other producers may want to produce biomass for on-farm use. Organic producers may choose tree species that fix nitrogen. Like all agroforestry systems, alley cropping systems should be considered as part of the whole farm operation.
Design Considerations Alley Cropping
i. The tree and crop species should be suited to the soils, climate, and the site.
ii. Species and spacing should ensure accessibility for timely management activities such as spraying, pruning, or harvesting.
iii. The size of available equipment used for the alley cropping will in part dictate the width of the alleys.
iv. Take into account growth in both height and width of trees and shrubs on either side of the alleys.
v. Optimal tree row orientation depends on the specific alley crop and alley width. Tree rows planted on contours or aligned in a Keyline system can help reduce soil erosion.
vi. Managing the light for crops is important. As trees and shrubs grow they will create more shade on the companion crops. To address this change, trees can be thinned or crops can be planted that are more shade-tolerant or have a complementary growing season with the trees.
vii. Some plants, most notably black walnut, smooth brome, and some fescue grasses, produce chemicals that inhibit the growth of other plants. Find out which plants are most susceptible to any allopathic species under consideration.
viii. Competition for space, water, and nutrients in the soil is also an issue. Try to choose plants that have root structures that are less likely to compete for valuable resources.
ix. Understand the producer’s goals for the system. Most producers have other goals beyond optimizing or maximizing income. Wildlife and water quality are also common interests of producers.
6. Reforestation and afforestation
Afforestation means the establishment of a forest on land that has not grown trees recently. It can serve two principal soil and water conservation purposes: protection of erosion-prone areas, and vegetation and rehabilitation of degraded land. Afforestation is specifically used to provide protective cover in vulnerable, steep and mountainous areas.
Afforestation helps to replenish timber resources and provide fuel-wood and fodder. The establishment of a forest cover under good management is an effective means of increasing organic matter production.
Why Reforestation and Afforestation
Reforestation and afforestation are two of the leading nature-based solutions for tackling the effects of climate change. For commercial foresters and landowners, these two practices are essential to ensuring they can grow wood for wood products and continuously meet demand in a sustainable way. Reforestation is crucial in combating or preventing deforestation or forest degradation, where forests shrink in size or are completely removed.
As well as reducing a forest’s ability to absorb carbon dioxide (CO2), deforestation can destroy wildlife habitats and contribute to the likelihood of flooding in certain areas. Afforestation can also help avoid desertification, where fertile land turns into a desert as a result of drought or intensive agriculture.
How Reforestation and Afforestation Limit the Effects of Climate
Change Forests are a natural way of keeping the earth’s CO2 levels in check. The more trees there are, the more CO2 is captured and converted into oxygen through photosynthesis. By absorbing CO2, forests help to lower the amount of greenhouse gasses in the atmosphere and reduce the effects of climate change. Reforestation and afforestation help maximize these abilities of forests by increasing the overall amount of forested land on the planet.
The Roles Does Reforestation Play in Commercial Forestry
The global wood products industry depends on sustainable forests to supply the wood needed to make furniture, create construction materials and provide fuel for energy. The supply chain will often start with what’s called a ‘working forest’ – a commercially-run forest which is often privately owned.
The landowner will grow a working forest to a certain stage of maturity and then harvest some or all of the trees to sell the wood. Once the wood has been sold for use as lumber, wood products or fuel, the landowner will reforest the areas to regrow the trees.
Foresters will typically do this in stages across their land to ensure there are multiple stands of forest at different stages of growth across their land, which ensures there is consistent, sustainable growth at all times.
7. Regeneration of Natural Vegetation
Regeneration of natural grasslands and forest areas increases biomass production and improves the plant species diversity, resulting in more diverse soil biota and other associated beneficial organisms. Natural regeneration may be more reliable where land is not very productive.
In some cases, natural regeneration of a given area may lead to the infestation of plots by weeds.
Increasingly, natural vegetation is being recognized for its multipurpose benefits, for example, fuel wood, fibre, bio control (e.g. neem) and medicinal species, as well as restoration of soil fertility (Acacia albida and other leguminous species) and habitats for various beneficial species (pollinators and natural enemies) as well as wildlife.
8. Protection from Fire
Burning affects organic matter recycling significantly. Fire destroys almost all organic materials on the land surface except for tree trunks and large branches.
In addition, the surface soil is sterilized, loses part of its organic matter, the population of soil micro fauna and macro fauna is reduced, and no ready-to-use organic matter is available for rapid restoration of the populations. However, this practice is widely used (e.g. in Africa) in order to enhance pasture regrowth for livestock (using residual P), to control pests and diseases, and even to catch small animals for food.
9. Crop Residue Management
The most appropriate method for managing crop residues depends on the purpose of the crop residues and the experience and equipment available to the farmer. Where the aim is to maintain mulch over the soil for as long as possible, the biomass is best managed using a knife roller, chain or sledge in order to break it down but not kill it. Where the decomposition process should commence immediately in order to release nutrients, the residues should be slashed or mown and some N applied because dry residues have a high C:N ratio.
However, in order to avoid nitrate emission, urea should not be broadcast on the surface but injected where possible.
In systems where crop residues are managed well, they:
· Add soil organic matter, which improves the quality of the seedbed and increases the water infiltration and retention capacity of the soil, buffers the pH and facilitates the availability of nutrients.
· Sequester (store) C in the soil.
· Provide nutrients for soil biological activity and plant uptake
· Capture the rainfall on the surface and thus increase infiltration and the soil moisture content
· Provide a cover to protect the soil from being eroded.
· Reduce evaporation and avoid desiccation from the soil surface.
Depending on the nature of the following crop, decisions are made as to whether the residues should be distributed evenly over the field or left intact, e.g. where climbing cover crops (e.g. mucuna) use the maize stalks as a trellis.
An even distribution of residues will help achieve the following:
(i) Provides homogenous temperature and humidity conditions at sowing time.
(ii) Facilitates even sowing, germination and emergence.
(iii) minimizes the development of pests and diseases; and (iv) reduces the emergence of weeds through allopathic effects.
10. Integrated Pest Management
As with balanced fertilization, proper pest and disease management results in healthy crops. Healthy crops produce optimal biomass, which is necessary for organic matter production in the soil. Diversified cropping and mixed crop-livestock systems enhance biological control of pests and diseases through species interactions.
Through integrated production and pest management farmers learn how to maintain a healthy environment for their crops. They learn to examine their crops regularly in order to observe ratios of pests to natural enemies (beneficial predators) and cases of damage, and on that basis to make decisions as to whether it is necessary to use natural treatments (using local products such as neem or tobacco) or chemical treatments and the required applications.
11. Compost
Composting is a technology for recycling organic materials in order to achieve enhanced agricultural production. Biological and chemical processes accelerate the rate of decomposition and transform organic materials into a more stable humus form for application to the soil. Composting proceeds under controlled conditions in compost heaps and pits.
12. Mulch or Permanent Soil Cover
One way to improve the condition of the soil is to mulch the area requiring amelioration. Mulches are materials placed on the soil surface to protect it against raindrop impact and erosion, and to enhance its fertility. Crop residue mulching is a system of maintaining a protective cover of vegetative residues such as straw, maize stalks, palm fronds and stubble on the soil surface.
Mulching adds organic matter to the soil, reduces weed growth, and virtually eliminates erosion during the period when the ground is covered with mulch.
There are two principal mulching systems:
· In situ mulching systems – plant residues remain where they fall on the ground.
· Cut-and-carry mulching systems – plant residues are brought from elsewhere and used as mulch.
13. Reduced or Zero Tillage
Repetitive tillage degrades the soil structure and its potential to hold moisture, reduces the amount of organic matter in the soil, breaks up aggregates, and reduces the population of soil fauna such as earthworms that contribute to nutrient cycling and soil structure.
Avoiding mechanical soil disturbance implies growing crops without mechanical seedbed preparation or soil disturbance since the harvest of the previous crop. The term zero tillage is used for this practice, synonymously, with terms such as no-till farming, no tillage, direct drilling, and direct seeding.
In Conclusion, Activities that promotes the accumulation and supply of organic matter, such as the use of cover crops and refraining from burning, and those that reduce decomposition rates, such as reduced and zero tillage, lead to an increase in the organic matter content in the soil.
In this article, you have learnt some practices that enhance the organic matter content of soils.
These practices may include the following:
– Increased water availability, balanced fertilization, cover crops, afforestation and reforestation, improved vegetative stand, integrated pest management, compost, mulching, and zero tillage.
