Evapotranspiration of irrigated and rainfed maize–soybean cropping systems

Authors

Andrew E. Suyker, University of Nebraska - LincolnFollow
Shashi Verma, University of Nebraska - LincolnFollow

Date of this Version

3-2009

Comments

Published in Agricultural and Forest Meteorology 149:3-4 (March 11, 2009), pp. 443–452; doi: 10.1016/j.agrformet.2008.09.010 Published by Elsevier Ltd. Used by permission. http://www.elsevier.com/locate/agrformet

Abstract

We have been making year-round measurements of mass and energy exchange in three cropping systems: (a) irrigated continuous maize, (b) irrigated maize–soybean rotation, and (c) rainfed maize–soybean rotation in eastern Nebraska since 2001. In this paper, we present results on evapotranspiration (ET) of these crops for the first 5 years of our study. Growing season ET in the irrigated and rainfed maize averaged 548 and 482 mm, respectively. In irrigated and rainfed soybean, the average growing season ET was 452 and 431 mm, respectively. On average, the maize ET was higher than the soybean ET by 18% for irrigated crops and by 11% for rainfed crops. The mid-season crop coefficient K_c (=ET/ET₀ and ET₀ is the reference ET) for irrigated maize was 1.03 ± 0.07. For rainfed maize, significant dry-down conditions prevailed and mid-season K_c was 0.84 ± 0.20. For irrigated soybean, the mid-season K_c was 0.98 ± 0.02. The mid-season dry down in rainfed soybean years was not severe and the K_c (0.90 ± 0.13) was only slightly lower than the values for the irrigated fields. Non-growing season evaporation ranged from 100 to 172 mm and contributed about 16–28% of the annual ET in irrigated/rainfed maize and 24–26% in irrigated/rainfed soybean. The amount of surface mulch biomass explained 71% of the variability in non-growing season evaporation totals. Water use efficiency (or biomass transpiration efficiency), defined as the ratio of total plant biomass (Y_DM) to growing season transpiration (T) was 5.20 ± 0.34 and 5.22 ± 0.36 g kg⁻¹, respectively for irrigated and rainfed maize crops. Similarly, the biomass transpiration efficiency for irrigated and rainfed soybean crops was 3.21 ± 0.35 and 2.96 ± 0.30 g kg⁻¹. Thus, the respective biomass transpiration efficiency of these crops was nearly constant regardless of rainfall and irrigation.