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Cotton Response to Abrupt Change in Water Application

D. F. Wanjura and D. R. Upchurch


Water application to crops is a primary limiting factor to production and thus water status of the crop is essential information required in production management decisions. Cotton was grown under two constant levels of soil moisture and then the water levels were reversed while the change in water status was monitored at Lubbock, TX in 1998. The purpose of the experiment was to compare the sensitivity of leaf water potential, temperature of the crop canopy, and spectral reflectance to the change in water status of cotton. The low water level (WL) was dryland and the high water level (WH) was 1.0 *PET. The transient soil water treatments began on a day of scheduled irrigation which was 21 July (DOY 202). The transient water treatment that relieved water stress was TLH which changed from WL to WH and the treatment which induced water stress was THL which changed from WH to WL. When the transient water treatments were initiated in the WL and WH treatments the growth stage was first bloom plus two weeks. A change in leaf water potential occurred after three days. A change in canopy temperature between the TLH and THL treatments, expressed as the amount of daily time that the temperature was above 28 °C (DST), was detected after four days when the DST of THL became greater than for TLH. Spectral reflectance of the TLH and THL treatments was different between these treatments prior to switching water application input. Then spectral reflectance in the near infrared (NIR) band and the normalized difference vegetative index (NDVI) remained consistently higher in the THL than the TLH treatment for 8 days after water application rates were reversed. This was due to the large leaf area in THL which received water input at the WH level until the transient soil water treatments were imposed. Yields of the THL and TLH treatments of cotton were lower than those from the WH treatment and higher than for the WL treatment. Canopy temperature was sensitive to change in crop water status and can rapidly determine conditions in an entire field compared to leaf water potential which accurately measures water status but can not provide automated spatial measurements with current technology.

Reprinted from Proceedings of the 1999 Beltwide Cotton Conferences pp. 380 - 384
©National Cotton Council, Memphis TN

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Document last modified Monday, Jun 21 1999