Water should never be applied at a rate faster than it can be absorbed by the soil. Soil properties that govern water infiltration (movement of water into the soil) are:
- Texture: The size of soil particles
- Structure: The arrangement of soil particles. Soils exhibiting good aggregation (a measure of structure) permit more rapid infiltration of water.
Texture and structure influences not only the infiltration of water, but also water-holding ability and soil drainage.
- Degree of compaction: Compaction refers to a condition in which aggregation is reduced or absent. The degree of compaction at or near the surface is of special importance insofar as infiltration of water is concerned. It has been shown experimentally that a very thin layer of compacted soil will substantially reduce the rate of infiltration.
- Another very important factor that influences the ability of a soil to absorb moisture is the rate at which the water is applied.
Sprinklers that do not adequately disperse moisture, as well as sprinklers that deliver a large volume of water within a concentrated area, tend to cause surface runoff. Whenever water is applied at a rate faster than it may be absorbed by a given soil, the water is being wasted.
Amount of water to apply
The amount of water to apply at any one time will depend upon:
- The water-holding capacity of the soil: The water-holding capacity of the soil will determine how much water will be needed at any one watering. Loams and clay loams are generally considered to have desirable water-holding capacity, whereas sands display very little water-holding capacity.
- The amount of moisture present when irrigation is started: A sufficient amount of moisture should be applied to insure that the entire root zone will be wetted. Once the soil is already wet throughout the root zone any additional water applied will merely fill the large pores and be excess.
- Drainage: Removal of excess water from soils is referred to as drainage. Unless soil is adequately drained, problems can arise because of the slow removal of excess water.