Submitted to: ASAE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: February 15, 1998
Publication Date: N/A
Interpretive Summary: Crops undergo periods of water stress under both dryland and irrigated production. By quantifying the amount of water stress, it is possible to apply corrective procedures, such as irrigation, or to make assessments of the stress effect on crop yield. An irrigated study of cotton, corn, and soybeans was conducted using multiple irrigation levels where canopy temperatures and weather were measured at the field site. The canopy temperatures and weather factors were used to make daily estimates of water stress indicators that reflect the degree of water stress experienced by the crops. A stress index computed as a summation of time when the plant temperature is above its optimum temperature and a crop water stress index that used a well-watered reference crop were both sensitive to water stress resulting from different levels of irrigation and were indicators of crop yield. Water stress indices that accurately indicate when a crop is experiencing a deficiency of soil water can be used to improve crop production management and increase the efficiency of yield production and profit to the farmer.
Technical Abstract: A field study in 1997 grew cotton, corn, and soybeans using four irrigation levels where canopy temperatures (TC) were continuously measured. The water level treatments were WL1-dryland, WL2-1/3ET, WL3-2/3ET, and WL4-1.0ET. The objective of this report is to compare the accuracy of different stress indices used to describe the crop water stress levels. One procedure for scheduling irrigatation is to estimate water stress level using the Crop Water Stress Index (CWSI). Another method for estimating water stress is daily summation of stress time (ST) when TC exceeded their crop specific optimum temperatures. The CWSI methods included the theoretical procedure, CWSI-T, and two variations of the empirical method that used either calculated values of TCmax and TCmin, CWSI-TC (calc), or a computed TCmax value and a measured value for TCmin, that was the TC in the highest water level treatment WL4, CWSI-TC(WL4). ST were compared for three daily periods s- Midday, Daytime, and Entire Day. The ST values for the Daytime and Entir Day periods increased as amount of applied water declined between WL4 and WL1 and were significantly different among water levels for the same crop. The CWSI-T, CWSI-TC (calc), and CWSI-TC(WL4) values declined as the quantity of water applied to each crop increased. The CWSI values for water level WL1 were highest in corn. The CWSI-TC(WL4) procedure was more accurate than the other CWSI methods because stress value for well-watered treatment WL4 was restricted to zero and values for all water levels remained within the theoretical limit of 0 to 1.0. CWSI values and water level treatments were related with yield in cotton, corn, and soybeans.