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Infrared Thermometry for Scheduling Irrigation of Corn¹

Irrigation scheduling is an increasingly important practice in the management of valuable water resources in agricultural regions. The study reported here was conducted to evaluate the feasibility of scheduling irrigation in corn (Zea mays L.) using canopy temperature data obtained with a hand-held infrared thermometer (IRT).

Specific objectives of the study were: 1) to determine whether irrigations can be scheduled from crop canopy temperature data and 2) to evaluate the effectiveness of various canopy temperature irrigation scheduling methods through their effects on some plant responses and the soil water balance.

The study was conducted at the Sandhills Agricultural Laboratory located near Tryon, Neb. The soil at the site is classified as a Typic Ustipsamment (Valentine fine sand). The range in temperature of six readings made with an IRT—defined as the canopy temperature variability (CTV)—in a fully irrigated reference plot (WW) was less than 0.7 C. As the temperature difference between a water-stressed plot and the WW plot increased so did CTV values until a critical stress level was reached beyond which CTV values stabilized. The onset of water stress can, therefore, be signaled when CTV values exceed 0.7 C.

Observations of CTV were the basis for one type of irrigation scheduling procedure. Irrigation was initiated when the range of six measurments in a plot exceeded 0.7 C. A second procedure consisted of comparing the difference between the average canopy temperature of the well-watered plot (WW) with that of the plot to be scheduled. Irrigations were initiated when plot temperatures became either 1.0 (1SMW; SWM = Stressed Minus Well-watered) or 3.0 C (3SMW) warmer than the well-watered plot.

A total of 283 mm of irrigation water was applied to the WW plot whereas the CTV plot received 127 mm. By the end of the growing season almost all available water had been extracted from the soil in the temperature scheduled plots but the soil profile remained near field capacity in the WW plot. This suggests that during the growing season soil water was most effectively used in the temperature scheduled plots.

Grain yields (Y) were reduced in the order of increasing water stress as follows: Y_WW > Y_CTV > Y_1SMW > Y_3SMW > Y_DL Y_DL is the yield from a dryland (DL) plot which received no supplemental irrigation. Yields of grain in the CTV treatment were slightly lower than in the WW plot, but not significantly so. This suggests that plants in the CTV plot received adequate water. Grain yields in the other temperature-scheduled plots were significantly reduced below those of the WW plot. However, only about 50 to 60 mm of irrigation water were applied to these plots.

Key Words: Canopy temperature • Remote sensing • Water stress • Water use efficiency • Zea Mays L. • Corn yield

² Assistant instructor-research and associate professor, Center for Agricultural Meteorology and Climatology, Institute for Agriculture and Natural Resources, Univ. of Nebraska, Lincoln, Neb. 68583-0728. Contents of this publication do not necessarily reflect the views and policies of the Office of Water Research and Technology, U.S. Dep. of the Interior, nor does mention of trade names or commercial products constitute their endorsement or recommendation for use by the U.S. Government.

Received for publication March 25, 1981.

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