Good soil is essential for a good harvest. The soil must have all the nutrients necessary for the growth of the plants, and a structure that keeps them firm and straight. The soil structure must ensure sufficient air and water for the roots of the plant, but must avoid excess water through good drainage.

Most of the nutrients are recycled by the roots of the plant and return to the soil through the leaves that fall from it. Worms, insects, and small organisms like fungi also feed organic matter into the soil and change it to produce humus, which makes the bottom layer of the soil dark and well-structured. Humus is quickly lost if the soil is left exposed to the air for a long time without any cover. The subsoil is generally less fertile.

A commonly used method of determining when to water is to monitor the decrease in water in the soil. When a plant grows, it uses water from the soil around its root zone. As plants use water, soil moisture drops to a level where irrigation is required or the crop begins to become stressed from lack of water. If no water is applied, the plant will continue to make use of the little moisture that remains until it finally uses all the available water in the soil and dies of thirst.

Determining soil moisture by touch has been used for many years by researchers and farmers alike. By squeezing the soil between the thumb and index finger or squeezing the soil into the palm of the hand, a fairly rough estimate of the moisture in the soil can be obtained. It takes a little time and some experience to accomplish this, but it is a proven method. For example, if we look at the soil in our gardens we can see that the wilting point occurs when the sand contains one inch of water per foot of soil, this means that we can hold the soil with our hand and form a compact ball. As the soil dries, it becomes difficult to make a ball of dirt and soon the dirt crumbles between your fingers.