Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 13, 2000
Publication Date: N/A
Interpretive Summary: Inadequate water supply reduces crop yields. By quantifying the degree of water stress corrective procedures such as irrigation can be applied or the effect of water stress on corn and cotton yields can be estimated. A two year field study used multiple irrigation levels where canopy temperatures and weather were measured. These measurements were used to compute daily values of water stress indices that reflect the amount of water stress experienced by the crop. A stress time index and the crop water stress index each had similar relationships across years with yield of cotton, but for corn the relationship differed each year. Water stress indices that accurately indicate when a crop experiences water stress can improve crop production management to either maximize yield or increase the efficiency of water use where water supply is limited. Good production management will increase profitability and sustainability of cotton production.
Technical Abstract: Corn and cotton were grown under multiple stress levels in 1997-1998 field experiments where canopy temperatures (TC) were measured. The water levels in 1997 were WL1-dryland, WL2-1/3*ET, WL3-2/3*ET, and WL4-1.0*ET. The 1998 water levels were WL3 and WL4 in corn and WL1 and WL4 with cotton. An average ET value of 7 mm d^-1 was used as the 1.0*ET water level of each crop. The objective was to compare the accuracy of different temperature- based stress indices for quantifying crop water stress and its relationship with yield. The stress time index (ST) defines water stress as the daily summation of time when TC exceeds the crop specific optimum temperatures. The theoretical, CWSI-T, and empirical, CWSI-TC, forms of the crop water stress index were used. The ST was calculated for three daily periods- Midday, Daytime, and Entire Day, that were determined by threshold levels of net radiation and air temperature. The ST values for the Daytime and Entire Day periods increased as the amount of water applied decreased from WL4 to WL1 and were significantly different among water levels. ST values for the Entire Day were higher than during the Daytime period only in 1998. CWSI-T and CWSI-TC values in both years and crops declined as the quantity of water applied increased. The CWSI value (0.89) for WL1 corn was highest in 1997. The CWSI-TC procedure was more accurate than CWSI-T method because it restricted the stress value for well-watered treatment (WL4) to zero, and all values were within the theoretical range of 0 to 1.0. The yield- water stress index relationships for cotton were similar in both years for each stress indicator, but for corn the relationships differed each year. The yield-total applied water relationship followed the same pattern as that observed for each crop's yield-water stress index.