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.
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