| Several problems exist in irrigated agriculture on the west side of the San Joaquin Valley, California. Most of them are related to the presence of a shallow saline groundwater. Crop use of shallow groundwater depends on many factors, including the depth to the water table, soil hydraulic properties such as water holding capacity and hydraulic conductivity, evapotranspiration demand, the root growth and distribution of a crop, and salinity and toxicity levels in both soil moisture and the groundwater (Talsma, 1963; Grimes and Henderson, 1984). In a detailed weighing lysimeter study the potential for crop use of shallow groundwater, crop and root response to shallow groundwater use, root water uptake in the soil profile and from shallow groundwater are quantified. A field study describes two different irrigation methods and drainage management over a four-year time span. Through measurement of the water balance components, an indication of the potential for shallow groundwater use was obtained at the field scale. Problems associated with the water balance are discussed.; Processes affecting crop water use from groundwater are identified in the lysimeter and field study. The effect of soil type, crop, and irrigation management are discussed in more detail. Loam soils have a large potential for shallow groundwater upflux. Deep rooted crops that are salt tolerant and have a high evaporative demand create a large potential of crop water use from the groundwater. A low frequency irrigation method maintains a higher potential for groundwater upflux than a high frequency irrigation method.; Increasing shallow groundwater use solves existing short term agronomical problems. Long term solutions to shallow groundwater tables will be found in improved irrigation and drainage management, and environmentally friendly ways of discharging drainage water. |
