ANRA:Textbook:Soil Water Conservation

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Soil and Water Conservation

by Sion Juu'n, ranger of Pelar, Shemathen Le'Yeritath

Soil Erosion and Soil Conservation:

Soil erosion often occurs where vegetation is sparse, where soil is loose, on sloped lands, and when there is intence rainfall and wind. Soil particles come loose and are carried away by water and/or the wind. When rate of rain fall exceeds soil's water penetration rate, water cannot seep into the soil and will create fast running flows down slope, carrying soil particles with it.

Soil conservation aim to reduce the amount of soil carried away by the erosion and maintain soil fertility. Most methods to protect soil from erosion involves slowing water flow, increasing water penetration rate of soil, and maintaining enough vegetation to protect soil surface.

For a farm to be sustainable, production must be balanced with conservation of the resources it depends on. It must be understood farming should exist in harmony with the land it is dependent on. Soil concervation should aim to: Be able to control erosion. Maintain plant residue in soil. Maintain sufficient level of nutrients in the soil.

Water Conservation:

Water conservation is closely tied to soil conservation. In arid and semi-arid regions, rain often falls in heavy spurts. Causing much of the water to run off the surface, causing erosion.

Water conservation involves storing much of this water as possible on the surface, in tanks or reservoirs, or allowing it to soak into the soil by slowing its flow. In order to raise the water-table and to increase the moisture level of the soil. More water will seep in to the soil if it was managed to spread over large area of soil, rather than being allowed to concentrate into rapid streams.

Conservation Methods:

There are multitude of ways to conserve the soil and water. It can be divided into two broad categories. Vegetative measures, include use of vegetation, buffer zone and soil tillage practices. Physical measures involve construction of permanent structures, most commonly of soil or stone, designed to control the flow of water.

Vegetative measures

Crop management: Appropriate crop management will reduce soil erosion by providing cover for soil from wind and water all year round. Selection of suitable crop rotation is vital in keeping soil covered by vegetation. (see text on Crop Rotation)

Tillage method:

Tillage aim to provide optimal physical and vegetative conditions of soil for crop production, and ensures timely seedbed preparation, and weed control. Taking care not to make the surface soil too fine and powdery. Avoid tilling during rain season, as it can lead to soil compaction. Early tilling will be done before rain season arrives, providing optimal soil condition for water penetration and moisture retention.

Application of organic matter: By adding manure and fertilizers to soil, it can provide required nutrients for vigorous crop growth. This will provide cover for soil from rain and wind erosion and produce higher yields. By tilling cover crop from rest period or leaving crop residue, it can provide plant residue in soil, increasing moisture retention capacity of soil.

Agroforestry:

Agroforestry is planting of trees and shrubs in the farm, or preserving those that are already present. Trees can conserve the soil in multitude of ways. They work as cushion to soften the impact of raindrops, reducing the amount of rain-splash erosion. Roots will bind the soil. When planted along contours of the land, they can interrupt the flow of surface running water. They reduce the soil temperature by shading the soil, thus reducing water loss from evaporation. They provide wind barriers, reducing wind erosion. They can draw nutrients from the deep soil, recycling them to surface. Certain types of trees (leguminous trees) can enrich the soil by fixing certain nutrients into the soil. There are additional benefits to agroforestry. Trees can provide fodder, fuelwood, timber and fruit.

Contour farming:

Contour farming is ploughing, planting and weeding across the slope (contour of slope) rather than up and down. It is most beneficial for farming on moderate slopes, 5~10%. If the slopes are steeper than 10%, contour farming should be used in conjunction with other methods to enhance its effectiveness. In moderate to high rain fall area, contour ridges are used to plant potatoes to reduce erosion by breaking water flow. Grass barrier strips planted to match the contour can be very effective on sandy soils and on slopes as steep as 30%.

Physical measures

Physical conservation structures are permanent features constructed with earth, stones or masonry. They are used to control water flow, to protect soil from erosion and to act as water reservoir where it is needed. However, physical measure is not substitute or alternative to vegetative method. They should be used to supplement vegetative measures, to obtain maximum benefit.

• Cutoff drains: Dug along the contour of slope, it will intercept surface water flow and redirects it to outlet. Protecting cultivated land.

• Infiltration ditch: Used where there is impervious layer below surface. It consists of a ditch, about meter to 1.5 meter deep, dug along contour, upslope from cultivated field. Water is diverted from source of runoff, such as road or rock bed, into the ditch, which has the other end blocked. Water stored in ditch, unable to travel straight down because of impervious layer, it moves downslope towards the crops in the field below.

• Water pit: These pits are used to store runoff and allows water to slowly seep into the soil. Often, series of pits are dug where runoff normally occurs. Using soils from the pits to form banks around the pits. Excess water from one pit is carried to next pit by furrows. The size of the pits will depend on the amount of runoff, but typically they are 1m in depth and 2m square. Tree crops should be planted along the pits to provide shading and other benefits. Never allow livestock to drink from the pits.

• Stone terrace: These terraces are very effective in areas with very steep slopes (as much as 60% or more), and with high population density. Terrace walls are made from stones or masonry. The terraces can be either flat or sloping but slope should be reduced to less than 6%. Several different crops can be planted at sametime to promote better growth and yeild. (Read Terracing Primer for more on terracing)