Water Use by Five Warm-Season Legumes in the Southern Great Plains

Authors: Rao, Srinivas; Northup, Brian

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/26/2009
Publication Date: 11/15/2009
Citation: Rao, S.C., Northup, B.K. 2009. Water use by five warm-season legumes in the Southern Great Plains. Crop Science. 49:2317-2323.

Interpretive Summary: Growing winter wheat is an important agricultural practice in the southern Great Plains (SGP). Wheat is grown during the fall through spring, and the land is fallowed during the summer to conserve soil water for the next wheat crop. However, recent increases in production costs have resulted in interest in modifying the traditional system of production by growing annual grain legumes (pulses) during the fallow period to provide low cost nitrogen (N), produce summer forage for livestock, or produce another grain crop to sell. Though double cropping wheat and pulse crops is rarely used in the SGP due to farmers’ fears of using soil water needed to produce the next wheat crop. We undertook a study to describe how five species of summer pulse crops, pigeon pea, guar, cowpea, mung bean and soybean, affected soil water. We found that mung bean, cowpea and guar used less soil water than pigeon pea or soybean in three of four years, and available soil water under cowpea and mung bean was similar to fallowed lands at wheat planting (October) in two of four years. These results indicate some pulse legumes could be double-cropped with winter wheat for short periods without causing large-scale reductions in soil water. The best use of pulse crops during the fallow period of winter wheat would be in years with predicted high amounts of rainfall during spring and summer.

Technical Abstract: Growing warm-season legumes during fallow periods of traditional systems of continuous winter wheat (Triticum aestivum L.) in the Southern Great Plains (SGP) can provide supplemental forage, biological N, and protection from soil erosion, provided they can tolerate drought stress and not deplete available water in the soil profile. Our objective was to quantify water use by five species of pulses {pigeon pea [(Cajanus Cajan (L.) Millsp.) cv. ‘GA-2’], guar [(Cyamopsis tetragonobloba (L.) Taub.) cv. ‘Kinman’], cowpea [(Vigna unguiculata (L.) Walp.) cv. ‘Chinese red’], mung bean [(Vigna radiata (L.) Wilcz.) cv. ‘Berkins’] and soybean [Glycine max (L.) Merr.) cv. ‘Hutcheson’ (the control)]} in comparison to summer fallow. Seeds were inoculated and planted after wheat harvest in mid-June 2003 through 2006. Amount of water in the upper 65 cm of the soil profile was measured on nine dates [from 45 d before planting legumes (mid-April) to 195 d after planting in late-December]. Significant (P<0.01) differences in amounts of soil water were recorded among treatments, dates, and years. Differences in amount of soil water among fallow, cowpea and mung bean were less following the 2003 and 2004 summer seasons and most noticeable in 2005 and 2006. Mung bean, guar, soybean and pigeon pea used the greatest amounts of water in 2005, the wettest growing season, while cowpea and mung bean used the least in 2003. Mung bean, cowpea and guar generated smaller water deficits in three of four years, and available soil water with cowpea and mung bean was similar to fallow at wheat planting (October) in two of four years. These species could be effective components of wheat-summer legume rotations in the SGP, provided the system is used during years with precipitation capable of optimizing production.