|Soppe, Richard - VISITING RESEARCH SCHOLAR|
Submitted to: Agricultural Research International Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: November 3, 1996
Publication Date: N/A
Interpretive Summary: Improved water management in irrigated areas with shallow ground water requires knowledge of crop water use from ground water. In the past this data has been obtained either by inference or through the use of lysimeters, both drainage and weighing. Data from small above ground lysimeters demonstrated the interaction of ground water quality and depth on crop water use. These data were used to develop crop coefficients for cotton which were suitable for use in areas with shallow ground water. The developed coefficients need to be evaluated under more realistic conditions. Two weighing lysimeters (2 m by 4 m by 3 m deep) were constructed to evaluate the proposed crop coefficients and shallow ground water use by other crops. The lysimeters were built in two pieces with the top section containing undisturbed soils and the bottom section containing disturbed soil. This procedure maintained the integrity of the salinity profile in the top 1.7 m of the soil profile. The lysimeters were instrumented to measure changes in soil water content in the profile and to monitor root development. One lysimeter is well drained and the second lysimeter has a water table at a depth of 1.1 m. Initial studies indicate that the lysimeters will provide the data needed to evaluate the crop coefficients and to quantify crop water use from shallow ground water.
Technical Abstract: Lysimeters are routinely used to develop crop coefficients for crops grown in well drained soils. This paper describes the construction and operation of a pair of lysimeters being used to develop crop coefficients for irrigation scheduling of crops grown in the presence of shallow ground water. The soil tanks were constructed with an undisturbed top (1.7 m) and disurbed bottom layer (1.3 m) in order to maintain the integrity of the salinity profile in the top 1.7 m of soil. A Marriotte bottle is used to maintain a constant water table in one lysimeter, and the second lysimeter is a well drained soil. Instrumentation is installed to monitor water use from shallow ground water, soil water content, and root development in addition to mass changes of the lysimeter. The crop is irrigated with a subsurface drip irrigation system. With the exception of the soil water and root observations, the data collection and control is fully automated. In initial studies with cotton the system responded with the drained lysimeter showing higher evapotranspiration values than when a water table was present.