1.3 Water

Water is the most essential substance for life and it is also indispensable for agriculture. Effeective use of water is very important in agricultural practice, so it is necessary for us to understand the water cycle and the factors which aid effective use.

1.3.1 The Water Cycle

Water cycles on the planet through the force of sun energy as the diagram shows. Fi8rst, clouds are formed be evaporation from the sea and forest. The cloud moves and falls on the land in the form of rain. The rainfall stays on the land temporarily in the vegetation and the soil, and goes in many ways like evaporation and run-off (the source of rivers). Finally the rainwater goes back to the sea and into the clouds.

The Water Cycle

1.3.2 Actual and Effective Rainfall

The source of water for the land is rainfall. However, only part of rainwater is used by the plants while the rest is lost in many ways. Actual rainfall is the total quantity of all rainwater on the land. Effective rainfall is the total quantity of rainwater which is reserved in soil, used by plants and others and excluding that lost in run off and evaporation. The effective rainfall is the resource for plants, animals and agriculture.

1.3.3 Factors which Increase Effective Rainfall

Whether or not effective rainfall increases depends on the allocation of rainfall, the type of soil, density of vegetative cover, land shape, etc. Soil with a high organic matter content can absorb more water. The vegetation diminishes the beating effect of rainfall on the soil surface by intercepting it and water is gradually soaked into the soil from where plants use it for a ling period. In flat terrain, rainwater stays longer than in sloping terrain.

Ways to increase effective rainfall for agriculture:

1. Supply organic matter to the soil which increase water-holding capacity.
2. Plant permanent trees and grasses which hold much water.
3. Cover the soil with vegetation and organic matter to decrease the beating effects of rainfall
4. Make water catchments such as ponds which are very useful for preserving water for the dry season
5. In sloping land, terrace cropping or contour cropping reduces water loss.

Though it is indirect in effect, preserving the forest and aforestation is actually the most effective way to increase the effective rainfall in an area. The forest preserves huge quantities of rain water and releases it gradually which is the source of rivers. Furthermore, the forest increases and sustains the actual rainfall through formation of clouds as a result of evaporation, especially inland, for from the sea.