Wednesday, November 15, 2006

Irrigated Soybean Evapotranspiration in a Semi-Arid Environment.

Terry Howell, Steve Evett, Judy Tolk, Karen Copeland, and Paul Colaizzi. USDA-ARS, P.O. Drawer 10, Bushland, TX 79012-0010

Soybean [Glycine max (L.) Merr.] production is expanding in the Texas High Plains since it has a slightly lower irrigation requirement than corn (Zea mays L.) and supplies feed for an expanding regional swine industry.  Evapotranspiration of irrigated soybean (Group IV) was measured with large, precise weighing lysimeters in 1995, 2003, and 2004 at Bushland, TX.  In 1995, the cultivar, Pioneer 9461, was grown, and in 2003 and 2004 the cultivar, Pioneer 94B73RR®, was grown.  In all three growing seasons, two weighing lysimeters were used to measure crop water use.  Mean evapotranspiration (ET) was 801, 771, and 611 mm, respectively.  Mean lysimeter yields were 407.7, 474.3, and 315.2 g m-2.  The resulting water use efficiencies were 0.509, 0.614, and 0.516 kg m-3.  Maximum daily ET rates were between 10 and 11 mm d-1 in each season.  The crop coefficient (Kc) for the ETr reference (alfalfa base) was nearer a peak Kcb value of 0.75 to 0.85 in 2003 and 2004 and in 1995 was closer in agreement with the peak value of 0.95 for Kcb for beans in Idaho.  The peak Kc in 2003 and 2004 agreed well with the 1.12 peak Kcb for the ETo reference (grass base) for beans in Davis, CA, but the peak Kc was nearer 1.20 in 1995.

Handout (.pdf format, 1023.0 kb)