Soil conservation methods are farming practices and management strategies conducted with the objective to curb soil degradation and improve soil productivity. Soil is a valuable resource in agriculture. Proper management is therefore vital in order to sustain long-term agricultural productivity. The most common and easily applicable (in terms of money and resources) soil conservation methods are explained below.
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Mulching is one of the most common soil conservation methods. It is the application of a protective layer of residue from the previous crop, perennial shrubs, straw and wood ﬁbre or similar to the soil surface to protect it against raindrop impact and shallow sheet ﬂow. A mulch can be permanent, for example plastic sheeting, or applied temporarily for example bark chips. It can either be applied around plants, incorporated into the soil or placed on bare soil and is suitable for both commercial and subsistence farms. Mulching provides a cover over the soil which aids in reducing soil displacement caused by the impact of raindrops as well as the volume and velocity of runoff over the soil. Mulch also reduces the intensity of radiation, wind velocity and evaporation. Hay makes the best mulch, however, it should be harvested before the weeds mature. Mulch should be used after late season crops such as potatoes and maize have been harvested. The recommended mulch for effective soil conservation is at a rate of 4 to 6t/ha so as to cover at least 70% of the soil. It is important note that hay and straw will break down over time thus re-application is required. Mulched areas need to be inspected after high winds or heavy rain and mulch reapplied as necessary.
This soil conservation method involves the construction of different types of barriers along contours or horizontally across the slope. Contour ploughing is the most famed among farmers. It consists of cultivating the land on or close to the contour. Each furrow acts as a barrier, catching water as it runs down the hill so that it soaks into the soil. This is commonly practised in areas with gentle slopes and low rainfall intensity. In areas where the land is fragmented, crop residues are stacked in lines along the contour. These lines trap water as it moves down the slope and absorbs it into the soil. The ‘contour principle,’ as it is formally termed, also involves planting vegetation to act as a barrier along the contour. The barriers are usually of grass which is planted in narrow strips along the contour trapping water and soil as it moves down the slope and encouraging it to sink into the soil. Morden contouring techniques include use of trees and shrubs instead of grass and crop residue. Trees and shrubs are grown in contour strips acting as barriers similar to grass and crop residue. The upside of this soil conservation method is that the vegetation that is commonly used are legumes which have the ability to absorb nitrogen from the air into the soil making it available to other plants. This is important in solving the challenge of nitrogen shortage as it is the most common obstacle in the growth of crops.
Cover crops is a soil conversation method that involves growing crops primarily to cover the soil surface thus achieving high infiltration rates and reducing erosion. Cover crops help to improve the soil structure, adds organic matter and uses residual nitrogen from previous crops. They should be planted in time to produce a minimum of 10cm growth before the winter season. Mulching can be used as an alternative if growth is below this level. Ideal plants to be used as cover crops are usually those that grow rapidly and close together. Their dense canopy prevents raindrops from detaching soil particles thereby effectively controlling soil degradation. Cover crops should be grown between cash crops to ensure an adequate cover of vegetation at all times thus guaranteeing effective soil conservation. When selecting the plant to use as a cover crop, the following should be considered:
- How much cover will the crop supply
- Can the crop be harvested the next season?
- The importance of weed control
- Soil improvement
- Nutrient conservation
- Time of seeding
Mixed cropping/Multiple Cropping
The mixed cropping soil conservation method is the practice of growing different types of crops on the same piece of land. The plants to be grown have to be selected with caution such that they complement each other’s growth. Products and refuse from one crop should help in the development of the other crop and vice-versa. This soil conversation method increases soil coverage and enhances the stability of soil aggregates thus reducing soil degradation. Mixed cropping has a positive impact on soil productivity, as such should be considered by both large and small-scale farmers.
Composting is the application of organic fertiliser into the soil. It involves the natural decomposition of organic materials such as crop residues, animal waste and green manures by micro-organisms. This process takes place in controlled environments. Composting is used by many farmers and gardeners as an effective soil conservation methods. Continuous heavy rains lead leaching of nutrients from the soil making it difficult for crops to grow well. Organic fertiliser helps to restore and retain soil nutrients.
Terracing is a soil conservation method that involves converting a steep slope into a series of steps with horizontal ledges called shelves and vertical walls between the ledges termed risers. The wall is susceptible to degradation and so is protected by a vegetation cover and sometimes faced with concrete or stones. There is no channel but a storage area is created by sloping the shelf into the hillside. Terracing increases the rate of infiltration and improves the chemical composition of the soil leading to high yields.
Crop rotation is the practice of growing different crops sequentially on the same plot of land. It is a soil conservation method that improves soil productivity and combats pest and weed pressure. The crops used are usually a mixture of a cultivated crop and a secondary crop that enhances soil health for example a small grain, a grass or a legume. The cultivated crop is highly exposed to erosion, growing a small gain reduces erosion and the grass or legume greatly controls degradation during the period of its use. This soil conservation method is highly recommended when specialising in root crops which are highly destructive to the soil structure. Root crops cause high soil degradation during seedbed preparation and harvest, for this reason, they should not be grown sequentially within a period of 3 years. Crop rotation can be paired other soil conservation methods for example mulching or zero-tillage for maximum productivity. A recommended rotation for a root crop is:
- Year 1 – root crop
- Year 2 – small grain
- Year 3 – forage
Conservation Tillage is a soil conservation method that focuses on field operations aimed at the preserving soil. It involves farming aspects such as using less destructive tillage implements, as well a less or zero tillage.
Zero tillage is among the highly recommended soil conservation methods. Zero tillage is a way of growing crops without tilling the soil. It is designed to leave crop residue on the soil surface to prevent erosion. A permanent cover consisting of residue from the previous crop is maintained on the surface of the land. This system increases infiltration rates, retention of organic matter and recycling of nutrients in the soil.
Soil, rainfall and terrain conditions vary from place to place. For this reason, adoption of proper land use practises is essential. Farmers have to understand the environment they operate in and the appropriate soil conservation methods that will enable them to reap high yields while maintaining health of the soil. It is important to note that some soil conservation methods are most effective in certain areas for example terracing is highly operational in steep slopes.