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A General System to Measure and Calculate Daily Crop Water Use

Texas A&M Univ. Res. and Ext. Center, Rt. 3, Box 219, Lubbock, TX 79403-9757 and USDA-ARS, 3810 4th St., Lubbock, TX 79415 USA

View larger version (28K): [in a new window]   Fig. 1 Mean monthly rain (1931–1997) and potential evapotranspiration (ETp) for Lubbock, TX. The bars indicate mean monthly rain ± 1 SD

View larger version (31K): [in a new window]   Fig. 2 Connectivity of data acquisition systems to a computer used to measure weather, soil temperature, soil heat flux, crop transpiration, and soil moisture. Also shown is the type of asynchronous connection between the central computer and sensors and synchronous serial from the TDR to the computer (From Lascano et al., 1996)

View larger version (110K): [in a new window]   Fig. 3 Remote instrument monitoring and control software (RIMACS) that provides the user with user functions, irrigation control, soil moisture (TDR) and Flow 32. The User Functions options are shown

View larger version (32K): [in a new window]   Fig. 4 Mean hourly soil (bed) temperature (A) and water content (B) measured at three depths, soil heat flux (C) measured on top of a bed and furrow, and mean stem flow gauge. The crop was irrigated on DOY 209 at 1600 h and a rain fell on DOY 210 at 0400 h

View larger version (28K): [in a new window]   Fig. 5 Measured daily (A) and cumulative (B) soil water evaporation (Es), crop evaporation (Ec) and their sum evapotranspiration (Ec + Es), and calculated potential evapotranspiration (ETp). The crop was irrigated on DOY 208

View larger version (65K): [in a new window]   Fig. 6 Measured and calculated values of soil water evaporation (A) and plant evaporation (B) for a period of 12 d. The measured values are the mean ± SD

View larger version (13K): [in a new window]   Fig. 7 Calculated daily values of Es and Ec as a function of measured ones. Shown is the linear regression equation and coefficient of simple determination

View larger version (40K): [in a new window]   Fig. 8 Calculated daily (A) and calculated cumulative (B) values of soil water and crop, and soil + crop evaporation

View larger version (29K): [in a new window]   Fig. 9 Hourly measured values of crop transpiration (DOY 221, 1996) measured with six stem gauges. Transpiration is expressed in g h-1 (A), per unit leaf area in mm h-1 (B), and calculated values are compared to mean measured ones in mm h-1 (C)

View larger version (22K): [in a new window]   Fig. 10 Daily rain and irrigation as a function of day of year, 1995. Irrigation was applied on a 3-d frequency

View larger version (17K): [in a new window]   Fig. 11 Daily, and 3 and 8 d moving average crop coefficients as a function of day of year, 1995