|Soppe, Richard - UC DAVIS|
Submitted to: Transactions of First International Symposium on Soil Water Measurement Using Capacitance Impedance and TDT
Publication Type: Other
Publication Acceptance Date: October 7, 2002
Publication Date: November 3, 2002
Citation: Ayars, J.E., Soppe, R. 2002. Irrigation scheduling of cotton with fdr probes in the presence of shallow saline groundwater. Transactions of First International Symposium on Soil Water Measurement Using Capacitance Impedance and TDT. No vol. or pgs. on CD ROM. Interpretive Summary: An irrigation scheduling procedure was developed that incorporated continuously measured soil water data and a root development model to determine both the timing and depth of application. A threshold value was set equal to 50 % depletion of readily available soil water stored in the crop root zone. The root zone development was calculated based on days after planting, maximum rooting depth, and days to maximum rooting depth. This provided for a variable storage capacity throughout the season. The water stored was measured with a capacitance probe and only those values within the root zone were included in the calculation. This method was tested on a cotton crop being grown on a field site containing clay soil of moderate salinity and shallow saline ground water. Results of the study indicated that the method was effective providing the soil water data measured by the probe adjusted by a site specific probe calibration curve.
Technical Abstract: This paper describes an irrigation scheduling procedure for a cotton crop grown in the presence of a shallow (1.2m deep) saline (14 dS/m) ground water in the Tulare Lake Basin of California. The field capacity and permanent wilting point values were determined and used to set thresholds for depletion of the available water. The root zone development was modeled using the function developed by Borg and Grimes (1986). Available water data were combined with root zone development to construct a set of curves that were used to determine the application depth and the soil water depletion values to initiate irrigation. Capacitance probes were used to measure the changes in stored soil water in 10 cm increments to a depth of 1 m. These data were then summed to calculate changes in the root zone water content and were the basis for scheduling irrigation. These data are presented for flood, sprinkler, and combined irrigated plots during the 1998 growing season. Results of the study indicated that the method was effective providing the soil water data measured by the probe was adjusted by a site specific calibration curve.