Irrigation in the Great Plains

ABSTRACT Kanemasu, E.T., Steiner, J.L., Biere, A.W., Worman, F.D. and Stone, J.F., 1983. Irrigation in the Great Plains. Agric. Water Manage. , 7: 157–178. Irrigation scheduling answers the question of when to irrigate and how much. The techniques used for scheduling include the monitoring of soil moisture, physiological indicators and water balance models. The areas of major concern are: (a) a soil moisture sensor which is inexpensive, rapid and accurate; (b) a means of assessing the upper and lower limits of soil water content in the changing root zone; (c) development of a rapid technique for estimating leaf area; and (d) a means of measuring canopy transpiration. A major research thrust that can be identified is the separation of evaporation from the soil surface and transpiration by the canopy. As one manipulates the canopy geometry to assess the cultural practices and irrigation systems, the need to clearly identify the contribution of evaporation and transpiration becomes increasingly important. The objective for irrigation for the farmer is to maximize his net returns. There are three components of an economic model for determining that decision: (a) a water balance; (b) a growth response function; and (c) an economic optimization function. A few of the problem areas in such a scheme are: (a) adaptation by the plant to water stress; (b) dynamics of the root system; (c) interaction between fertility and water; and (d) risk analysis.