After reading this article you will learn about the biological and mechanical methods for the management of land eroded by water.
A. Biological Method:
I. Agronomial method, and
II. Agrostological method.
I. Agronomical Method:
1. Growing Cover Crops:
Sod-like crops, such as grass, sannhemp, berseem, groundnut offer excellent soil protection against erosion by water. Such crops are effective primarily because they provide a cushion against the raindrops. The denser the vegetation the more effective is the cushioning effect.
Close growing crops also help to control erosion by providing root channels thorough which water moves downwards more freely. In addition, plant roots aid in making a desirable soil structure. Vegetation also encourages the growth of earthworms and other desirable forms of soil life. These in turn help to keep the soil open and receptive to raindrops.
This practice consists of growing erosion- permitting crops (e.g., jowar, bajra, maize), in alternate strips with erosion checking close-growing crops (e.g., grasses, pulses). The erosion checking strips check and held the flowing water and soil (Fig. 23.2).
Contour strip cropping is one of the type of strip cropping. Contour strip cropping is the growing of erosion-permitting and erosion-resisting crops alternately in strips across the slope and on the contour.
3. Crop Rotation:
Growing of two more different crops in sequence in a field for maintaining the soil fertility. Continuous growing of clean-cultivated crops (e.g., tobacco) causes more erosion. A good rotation should include densely planted small grains, spreading legume which may check soil erosion.
Mulches of different kinds minimise evaporation and increases absorption of moisture. Stubble mulching is based on merely stirring the soil with implements that leaves considerable part of vegetative materials i.e., crop residue or vegetative litter on the land as a surface protection against erosion and for conserving moisture by favouring infiltration and reducing evaporation.
5. Organic Manures:
Incorporation of organic manures in the soil improves the soil structure. Granular and crumby structures increase infiltration and permeability in the soil and conserve soil water.
II. Agrostologial Method:
Dense canopy and profuse root system of grasses fightly bind the soil against erosion. Grasses increase water infiltration and improve physical conditions of soil.
Grasses can be grown on lands which are otherwise not suitable for cultivation. They are also used in protecting bunds, waterways, badly eroded areas and gully control.
The grasses commonly grown are:
(i) Dubâ€”Cynodondactylonâ€”Checks run-off water.
(ii) Kudzu vineâ€”Checks gully erosion.
(iii) Kansâ€”Sachharumspontaneumâ€”Checks water erosion on the bank of rivers and. streams.
(iv) Dinanathâ€”Pennisetumpedicellatumâ€”Checks bunds and water outlet.
B. Mechanical Methods:
Mechanical measures constitute various engineering techniques and structures. These practices reduce run-off velocity, impound water for a longers me and provide more absorption opportunity. Following mechanical practices are adopted for checking water erosion.
1. Contour Tillage:
On hilly land (slope) all tillage operations and the sowing of crops should be done at right angles to the slope of the land. On long slopes, the field may be laid out in narrow strips across the slope rather than with it. In contour tillage, each furrow which lies intercept flowing water and holds it and allows it to soak into the soil (Fig. 23.3).
2. Contour Bunding:
The slope of the land is broken up into smaller, more level compartments by constructing earthen embankments of suitable size on contours. Each bund thus, holds the rain water within each compartment. Farmers in the plains could raise level bunds around their fields for holding the rain water and conserving the soil. The maintenance of bunds is very important. Planting useful grasses, strengthening the bunds at weak points, closing rat holes and closing small breaches in time are the most important items in bund maintenance.
On steeper slopes terraces or flat platforms are constructed in steps like series across the slope. It is like a level benches or table top for retaining and distributing rainfall for controlling run-off (Fig 23.4).
4. Outlet Channel:
For safe removal of excess run-off water, it is essential to provide suitable outlet structure at proper places so that no harmful effects of waterlogging, eroding, gullying or damage to other conservation structures are caused. Some of the important surplusing arrangements are grass waterways and diversion ditches.
5. Basin Listing:
Scooping out small basins at regular intervals on slopes, checks run-off.
6. Pan Breaking and Sub-Soiling:
Pan breaking and sub-soiling permit infiltration and percolation. This increases the water storage capacity of the soil, thus, decreasing run-off and erosion.
7. Water Harvest:
At suitable places with possibilities of storing water, ponds and tanks are recommended water conservation practices. They are also very useful to some extent as flood control measures.
8. Conservation Tillage Practice:
In the conventional tillage practice, run off and erosion pressure is greatest due to extensive soil tillage and the soil remain bare after ploughing. The conservation tillage system vary from no-tillage (zero-tillage) to reduced tillage system. This system permits direct sowing or planting in the residue of the previous crop and uses only that localized tillage necessary to plant the seed.
A prime objective of the conservation tillage is to keep some plant residues on the soil surface. Surface run off is decreased due to soil cover by the plant residues, simultaneously, soil erosion is reduced.
No-tillage or reduced tillage plots are generally somewhat higher in soil water, especially in the upper portion of the profile, than the conventionally tilled plots. This is likely due to increased water infiltration from no-tillage systems and reduced evaporation losses, which are characteristics of any residue-covered plots. Organic matter are higher in the upper few centimeters of no-tillage and reduced tillage plots.
The conservation tillage systems also can significantly reduce losses of nitrogen and phosphorus. The finer fractions of soils, which are among the first to be carried away through erosion, contain most of these nutrients.
Control of Gully Erosion:
Gully control is necessary in order to prevent complete destruction of cultivated lands and grasslands. In the first step, water flowing into the gully should be diverted away by means of a bund. The second step is to build several instructions in the gully such as rock dams.
Invariably, the gullies should be established under permanent grass and tree vegetation. Sometimes a gully may be adequately established by converting it into a paddy field.