Water is one of the most important inputs essential for the production of crops. Water management is the planned use for better utilization in agriculture. The application of water is found to be essential for maintaining the optimum soil-moisture balance for better crop production. Soil type is also an important factor. Most soils release at least 50 per cent of their available water by the time this suction is reached.

In swelling clay soils, it is difficult for water to infiltrate unless the soil-mass is in a cracked condition, which does not occur until most of the available water is depleted. If the clay soils are not irrigated immediately after the development of small cracks, these cracks deepen and widen resulting in tearing of roots and accelerate evaporation from the mainfold area exposed due to vertical cracking. Under such situation the frequent application of light irrigation may be needed. Clay soils possess the ability to hold a large amount of water, but moisture extraction by the plant is resisted by greater forces. The additional organic matter in clays, a structural break-up is encouraged. Sandy soil may release 80% of its available water at suctions less than one bar. However, the reserve of moisture at this stage is very small and thus 50% moisture depletion can be regarded as a thumb rule for re-irrigation. Sandy soil, the water holding capacity is therefore, low but the remaining moisture for plant use is easily removed by the roots. The addition of organic matter to sands binds the particles together and causes a reduction in intake rate.

Roots do not penetrate a dry soil and therefore, sufficient water should be applied to wet the soil beneath the existing root-zone during the period of root growth. If the water or soil contains a huge quantity of defloculating agents such as Na, K and Mg or the water is charged with dispersed or suspended substances such as clay particles, infiltration is seriously impeded. A water table near the soil surface reduces the infiltration rate because of the distribution of moisture in the adjecent soil layers. The presence of hard pan or an impervious layer due to puddling affects the infiltration rate.

Loam soils possess good moisture holding properties and have good internal drainage and aeration. The binding of soil particle and structural break-up due to organic matter, both of these effects are beneficial as they increase retention and release water for plant use.

To irrigate efficiently, it is necessary to consider both the water holding capacity of the soil and the water requirement of the crop. Lighter soils require more frequent irrigation than loamy soils. Sandy loams need to be irrigated every fifth day, while clay loams may be irrigated every tenth day.

The humidity and season also affect the water application. In rainy season the humidity is high and the rains may be received just when the crop is in need of water. The effective rainfall is also important while considering water management. It may be taken at 50% of the total rainfall received during the life period of the crop. During winter season the frequency will be longer than in summer because of less evapo-transprition, dew fall, night time humidity and less sunshine. The frequency may be 12 to 15 days in winter and 6 to 8 days in summer.

Ag.
Technologies
(Water Mgmt.)