Soil Moisture Depletion by Irrigated Crops Grown in South Dakota

Abstract

Many of the failures and disappointing results in some of the new irrigation enterprises are a direct result of not meeting the moisture needs of the growing crop. Frequently the failure can be traced back to the under-designing of the distribution system. However, the main causes for failure are insufficient amounts of irrigation water, poor distribution, and applying the water too late to prevent a few clays of high moisture stress in the plant, which results in an inevitable loss in yield. If irrigation systems are designed to cover too many acres, the crops cannot be supplied with adequate water during periods of drouth. Oftentimes too much faith is placed in the probability of rain, and irrigation water is not applied in time to prevent serious effects of dry weather on the crop. The four potential sources of water the plants can use are: precipitation, stored soil moisture, ground water and irrigation water. The availability of water from any or all of these sources is the key to the prevention of drouth periods which may curtail yields and materially lower the quality of the produce. If, for instance, rainfall is inadequate to maintain the supply of stored moisture, then irrigation water must be supplied. For best irrigation results, it is not only important to know how much water to apply and when to apply it, but also where in the soil the plant obtains the moisture. Excessive quantities of irrigation water will cause moisture to pass below the root zone where it cannot be used by plants. Furthermore, it will carry plant nutrients downward and out of reach of the plant, cause additional erosion and aggravate drainage problems. (See more in text