Top Soil Conservation Methods: Why & How to Protect Your Land

Soil conservation can be defined as the science and art of looking after the land in such a way that soil is retained in one place and not carried away by agents such as water, wind, and animals, including man. To a certain degree, soil conservation is the same as erosion control.

When effective soil conservation measures are practiced, soil nutrients and organic matter are held in place, and the soil structure is not destroyed. Consequently, soil fertility and productivity are maintained.

Soil conservation practices are tools farmers can use to prevent soil degradation and build organic matter. These practices include crop rotation, reduced tillage, mulching, cover cropping, and cross-slope farming, among others. These increase soil organic matter content, soil structure, and rooting depth.

Understanding and Controlling Soil Erosion for Soil Conservation

Soil erosion is the denudation or wearing away of the upper layer of soil. This natural process is caused by the dynamic activity of erosive agents, that is, water, ice (glaciers), snow, air (wind), plants, and animals (including humans).

Types of Soil Erosion

1. Rill erosion: Water flows in tiny rills (channels) down the slope. It occurs in areas where there is little vegetation or in fields where land has been ploughed. Some of the rills are as shallow as 0.6cm.
2. Sheet erosion: This is the type of erosion that occurs on large areas of land. Water flows over the whole field at a slow speed, carrying relatively little soil from the top layer.
3. Gully erosion: Gully erosion is the result of sheet erosion. It is characterized by deep, usually long ditches dug by running water.
4. Wind erosion: Wind erosion occurs when the wind is the causal agent, and its effects are encouraged or aggravated by a lack of vegetation cover, such as forests or grasslands. Although wind erosion is relatively unimportant in most parts of the world, it can be a significant issue in areas such as Karamoja and Turkana, where vast areas are devoid of vegetation due to overstocking and overgrazing. The severity of wind erosion is influenced by factors such as wind velocity, soil structure, soil texture, and the quality of vegetation cover.

Soil erosion in a field

Causes of Soil Erosion

a). Overgrazing:

This is usually a result of overstocking or keeping a few animals on a piece of land for a very long time.

b). Over-cropping (over-cultivation):

The same crop is repeatedly grown on a piece of land without rest. The organic matter content and soil fertility run down, and, as a result, the crops grown cannot form a dense cover. When it rains, water erodes a lot of soil.

c). Removal of vegetation:

Careless removal of vegetation, such as cutting down forests (deforestation) and burning bushland, can lead to erosion. The vegetation, which acts as a barrier against soil erosion, is lost. A vivid example is Karamoja in Uganda, where large gullies are a common feature.

During rainy seasons, water runs down the slope at high speed, causing great damage to crops before it enters large gullies, and improper farming methods, such as ploughing along the slope, that is to say, ploughing up and down sloping land, planting crops along the slope, and planting annual crops on very steep slopes.

Methods of Controlling Soil Erosion

1. Afforestation

This is the practice of planting forests in areas where forests did not exist before. Trees are usually planted on hilltops and mountainsides where land is too steep for cultivation. The trees are planted to reduce wind erosion, and the debris from rotten leaves and branches that fall off the trees absorbs water and reduces soil runoff. The roots of the trees have a binding effect on the soil.

2. Cover Cropping

Leguminous crops, such as beans, peas, Centrosema pubescens, Stylosanthes gracilis, and Calapogonium mucunoides, are useful as cover crops. They reduce the speed of rainwater and are easily propagated by seed. Cover crops that tolerate shade, suppress weeds, are resistant to pests and diseases, and grow vigorously without competing with the main crop should be selected.

3. Mulching

If the mulch is laid well, it acts as a barrier and thus prevents soil and water from being carried down the slope.

4. Stop-wash Lines

Single lines of grass, such as vetiver grass (Vetiveria zizanioides) or lemon grass (Cymbopogon species), are planted across the slope to stop soil erosion.

5. Constructing Bunds

Bunds are heaps of soil along a contour. Sometimes offshoots (called tie bunds) are constructed emanating from the main bunds to facilitate better erosion control. Paspalum notatum is sometimes planted on top.

6. Contour Ridging

Ridges are constructed using either a tractor, an ox-drawn ridge, or a hand hoe to conserve both water and soil. The practice is carried out in growing both sweet and Irish potatoes. Sometimes tie ridges are used instead of the usual straight ridges used in potato growing. The practice is referred to as contour tie ridging and is used in the growing of cotton in Usukuma land in Tanzania and the Gezira area in Sudan.

7. Contour Ploughing and Planting

The main aim of contour ploughing and planting is to encourage water to be absorbed by the soil. Soil erosion is encouraged when ploughing and planting are done along a slope, that is, up and down the slope.

8. Grassed Waterways

All waterways should be covered with grass to reduce the speed of the water and water wash.

9. Intercropping

In this method, two or more crops are grown on one piece of land. Cover crops are grown between rows of annual crops, such as maize, and perennial ones, such as coffee, bananas, and citrus, to provide nitrogen, as well as to reduce soil erosion. Commonly used cover crops are beans, cowpeas, Centrosema pubescens, and Stylosanthes gracilis.

10. Terracing

Terracing is a soil conservation practice applied to prevent rainfall runoff on sloping land from accumulating and causing serious erosion.

Terracing is done in hilly or mountainous areas where the slope is steep, for instance, Kigezi in Uganda and the Kenya Highlands. In Kigezi, terraces are laid in horizontal strips about 15 meters wide and less in steeper areas.

They are separated from one another by bunds on which elephant grass is grown. They are constructed using hand hoes. In the Kenya Highlands, broad-based terraces are constructed mechanically.

Terracing on a rice field

In all types of terracing, it is necessary to conserve the topsoil as it contains more plant nutrients, soil organic matter, and micro-organisms, among others, than any other layer of the soil profile.

During construction, topsoil should be scraped off and placed in one place. After leveling, the soil is evenly distributed to every part of the terrace. The main objectives of constructing terraces are to reduce the surface flow of water and carry away surplus water that cannot be absorbed by the soil.

Types of Terraces

a). Broad-based Terraces:

Broad-based terraces are wide at the base, three meters or more, and usually about two-thirds of a meter high at the crest. They have a shallow drain (channel) on top.

They are normally about 250 meters long and are costly to construct, as graders are needed to level the terrace. They are mostly found in arable land with deep soil. They are slightly sloping in high-rainfall areas, but they level in low-rainfall areas.

b). Narrow-based Terraces:

These are usually level and shorter, but are put closer together than broad-based terraces. In Kenya, the width of strips for narrow-based terraces is just half that of broad-based terraces.

They are usually constructed by hand. The terraces are planted with grass or long-term crops, like pigeon peas. They are built along the contour or on a slight gradient with channels on the upper and lower sides. They are suitable for land with a 12 to 20 percent slope.

c). Bench Terraces:

These are usually constructed on steeper slopes and are only justified when high-value crops are grown, or there is an acute shortage of suitable land. During construction, the surface layer should be set aside and then spread on top. At the top of each terrace, there is a channel that is planted with grass.

The top bank is protected by a stone wall or grass and is built as vertically as possible. However, the banks may harbor weeds, and the upper part of the cultivated area usually becomes unproductive because of exposed soil. Bench terraces are common in Sri Lanka, Ethiopia, and China. Bench terraces look like a bench in appearance, with slopes.

11. Crop Rotation

Crop rotation is a system of growing different crops on a piece of land in a sequence or definite order to preserve and maintain soil fertility and productivity.

Crops that have different growth habits and nutrient requirements are grown on the same piece of land in an ordered sequence. Rotation depends on the type of crops to be grown and the fertility of the land.

In the past, there was a lot of land for cultivation, and rotation was not practiced. Instead, shifting cultivation used to be carried out. The land was planted with crops for several years, and whenever a cultivator detected that yields and soil fertility had started declining, they moved to another area.

They continued to grow crops on the new land until it was exhausted. Thereafter, the area was abandoned for a long time during which the land got back to bush or forest through natural regeneration.

These days, shifting cultivation is not feasible because of the following factors:

1. Land shortage due to population increases.
2. Introduction of perennial crops, as these take a long time to die.
3. Permanent buildings would be expensive to replace.

The following points should be observed when designing a crop rotation (principles of crop rotation)

1. Crops with deep roots (deep rooters) should alternate with shallow rooters.
2. Crops with similar pests or diseases should not follow one another.
3. A resting phase (fallow period) should be included in the rotation.
4. Crops with high nutrient requirements, for example, maize and cotton, should be planted first on newly cultivated land.
5. Legumes such as beans, groundnuts, and cowpeas often alternate with other crops.

Advantages of Crop Rotation

Good crop rotations break the life cycle of crop pests and diseases. In most cases, pests and diseases that attack one crop do not attack others, unless the crops are of the same family. Nematodes, which tend to build up after continuous monocropping, can be controlled by following a good rotation.

Legumes included in the rotation add organic matter and nitrogen to the soil, consequently maintaining soil fertility. During the ley phase/fallow period, soil erosion is minimized due to the heavy vegetative cover provided by legumes and grasses. Crops have different feeding habits and varied root systems.

By following good rotation, deep-rooted crops like cotton can bring up mineral nutrients from lower layers. This is an advantage for shallow-rooted ones such as finger millet, which can make use of the nutrients brought up by the cotton plant after the latter has decomposed and released the nutrients in the soil.

In this way, the depletion of nutrients from one depth is minimized. Good crop rotation evens out labor requirements over the year.

Rotations spread financial risks over several crops, and parasitic weeds, such as Striga species that are specific to cereals, can be controlled by planting crops that are not cereals.

Agronomic Factors Limiting Productivity of Crops.

a). Timely opening up and preparation of land:

Land should be opened up early to allow a breakdown of organic matter before crops are planted. The practice is to allow at least 6 weeks between opening up the land and planting.

If planting is done immediately after plowing, seedlings suffer from a shortage of nitrogen. Microorganisms use it in the process of decomposing organic matter. The plants that are affected are chlorotic and stunted.

b). Proper selection of seed:

Seeds should be of good quality, free from pests and diseases, or mechanical damage, to encourage germination. It is advisable to dress seeds with insecticides. For example, carbon tetrachloride and lindane are used to dress sorghum and maize to control seedling pests, respectively.

Furthermore, fungicides and bactericides are sometimes used in dressing seeds. A good example of a bactericide is cuprous oxide, which controls bacterial blight, a bacterial disease of cotton.

c). Early or timely planting:

This is important because it enables a proper program of farming activities to be carried out. Unless food crops are planted early, the whole farming calendar gets delayed. Early planting enables crops to have enough moisture during critical stages of growth, namely at germination, flowering, and fruiting.

This is of particular importance in Africa, where rainfall is generally poor. It also enables crops to get nitrate-nitrogen (NO3-N), which accumulates in the soil during hot and dry weather.

During that time, there is usually an equivalent of 22 kg N/ha (nitrogen per hectare).

If planting is delayed, the nitrate-nitrogen will not be available to crops because it will have been leached down the regolith (defined as the soil material above the parent rock).

d). Row cropping:

Row cropping is the same as row planting. It is the practice of planting crops in rows or lines. When crops are grown in rows, it is possible to achieve the optimum plant population per unit area, which leads to high yields.

It becomes easy to carry out agronomic practices such as planting, weeding, spraying, and harvesting, either by hand or mechanically. In the case of weeding, this practice is particularly useful in small grains such as oats, finger millet, wheat, and barley, which demand much labor on weeding if broadcast.

Close spacing is achieved, which can help in controlling certain diseases in some crops. For example, groundnut rosette. A lower seed rate is used than if seeds are broadcast, and mechanization is only possible when crops are grown in rows.

e). Recommended spacing:

Every crop has a recommended spacing at which it should be planted. For example, Arabica coffee is planted at 2.7 m x 2.7 m, while sorghum is spaced at 60 cm x 15 cm.

In recommended spacing, weeds are smothered - weeds do not grow big enough to lead to a considerable reduction in yield. It provides the optimum plant population per unit area, which, in turn, leads to high yields.

Although wide spacing encourages bigger plants, it wastes a lot of land and results in low yields. On the other hand, close spacing encourages the etiolation of crops - that is to say, crops become tall and weak with fewer flowering points, resulting in a reduction in yield.

Recommended spacing strikes a balance between these two extremes. Each crop gets enough plant nutrients, and therefore, crop growth and production are adequate. In some crops, such as groundnuts, close spacing is recommended to reduce the incidence of diseases.

In this case, if groundnuts are widely spaced, aphids (Aphis craccivora) that transmit the groundnut rosette virus move from one plant to another in search of food. However, when the crop is closely spaced, feeding of the aphids will be confined to a small area, and thus rosette will not spread much.

f). Weeding:

One of the primary aims of weeding is to reduce competition for various factors of growth, namely air (oxygen), sunlight (solar radiation), soil moisture, plant nutrients, and space.

Young crops are especially sensitive to weed competition; early weeding is, therefore, essential, particularly during the first month after planting. Delayed weeding reduces the growth and yield of crops.

Properly weeded crops

g). Thinning:

Thinning is done to enable crops to grow laterally. When crops are crowded together, they shoot upwards in an attempt to obtain enough air and sunlight. Such crops are etiolated (long, weak stems) and are liable to be blown by the wind. They are also susceptible to disease.

Thinning enables the right number of crops per unit area to tap as much water and nutrients from the soil as possible, which leads to good growth and yield.

h). Pest and disease control:

Failure to control pests and diseases leads to reduced yield. For example, several attacks of maize stock borer (Busseola fusca), a major pest of maize, may lead to as much as a 50% loss in yields.

i). Harvesting and drying:

Crops should be harvested on time to reduce field losses through destruction by rain, birds, and rodents. Proper drying is essential to avoid the rotting of the produce. When seeds are completely dry, they should be stored in well-ventilated, rat-and leak-proof stores, preferably with a concrete floor.

j). Application of fertilizers and manures:

The type and quality of fertilizer and manure to use vary from crop to crop. However, in all crops, phosphatic and potassic fertilizers are always incorporated into the seedbed. Among other things, phosphorus encourages root establishment, while potassium boosts the growth of meristematic tissues.

Nitrogenous fertilizers are applied later in the growing season to encourage vegetative growth. Organic manure, such as farmyard manure and compost, is applied to specific crops, for example, vegetables, flowers, and fruits, such as pineapples.

Recommended fertilizers and manure are a must, and they should be applied at the right time to realize high yields.

Methods of Fertilizer Application

1. Broadcasting.
2. Foliar application/ spraying.
3. Starter solutions.
4. Ring, aerial application, and injection into the soil.
5. Band/ side application.
6. Through irrigation water (Fertigation).
7. Through drilling/ row placement/ base/ bottom application.

Qualities of a Good Fertilizer Are;

1. It should be easy to apply.
2. It should be easy to handle and consistent in particle size with smooth and hard granules.
3. It should be easy to store and easily spread, ensuring even distribution patterns.
4. It should have a long-lasting effect.
5. It should have a high nutrient content.
6. It should supply the required nutrients readily to the soil.
7. It should be able to quickly dissolve when in contact with moist soil or water (avoid run-off) and be free from contaminants and additives.

Problems Associated With the Use of Fertilizers

Fertilizers can burn/ scorch plants when improperly used.

Fertilizers may be washed into the rivers and lakes, where they encourage the growth of algae, and they may pollute the environment and may be dangerous to the person applying them if mishandled.

Excessive application of fertilizers may cause improper plant growth. Fertilizer application may alter the PH of the soil, and excessive application of fertilizer may encourage the lodging of crops.

Fertilizers may be toxic to beneficial microorganisms in the soil and may be easily leached/ lost from the soil/causing a short-lived effect in the soil.

Fertilizers may be expensive to buy. Some fertilizers may be a source of pests and diseases, especially organic fertilizers, and some organic fertilizers may encourage the multiplication of weeds.

Effects of Excessive Application of Nitrogen Fertilizers on Crops

It causes excessive vegetative growth at the expense of fruit production and delayed maturity of crops.

It causes scorching of leaves, excessive succulency/ excessive sap production, reduced quality of the crops, reduced resistance to diseases, and weakening of the stems/ lodging in grains/ cereals and crops.

It also causes a deep green color in some plants, reduced tuber production, and reduced quality in tubers.

Factors Favoring the Growth of Root Crops in Most Parts of The World

1. Root crops stand a variety of soil conditions.
2. Root crops grow under different climatic conditions.
3. Root crops require little attention/ labor once established.
4. Root crops can stay in the ground till it is required.
5. Root crops do not need elaborate processing before they can be eaten.
6. Root crops have fewer pests and disease problems.

Characteristics of Plants That Make Them Suitable For Green Manure

1. They have a fast growth rate.
2. They are easy to plow into the soil.
3. They are leafy/ highly vegetative.
4. They are rich in nitrogen content.
5. They have a rapid decomposition/carbon: nitrogen ratio.

Conclusion

In conclusion, soil conservation plays a crucial role in maintaining soil fertility and productivity, preventing soil degradation, and mitigating the negative effects of soil erosion. By implementing effective soil conservation practices such as crop rotation, reduced tillage, mulching, cover cropping, and contour farming, farmers can increase soil organic matter content, improve soil structure, and enhance rooting depth. These practices help to retain soil nutrients, prevent soil erosion, and promote sustainable agriculture.

Soil erosion, caused by various agents such as water and wind, is a significant challenge in soil conservation. Different types of erosion, including rill erosion, sheet erosion, gully erosion, and wind erosion, can result in the loss of topsoil and the degradation of agricultural land. To address soil erosion, it is crucial to address its underlying causes, such as overgrazing, over-cultivation, and the removal of vegetation.

Implementing methods of controlling soil erosion is essential for effective soil conservation. Techniques such as afforestation, cover cropping, mulching, constructing bunds, contour ridging and ploughing, grassed waterways, intercropping, terracing, and crop rotation can help to prevent soil erosion and promote sustainable land management. By adopting these practices and understanding the principles of crop rotation and agronomic factors that affect crop productivity, farmers can contribute to the conservation of soil resources and ensure the long-term sustainability of agricultural systems.