Submitted to: Journal of Cotton Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/19/2009
Publication Date: 10/1/2009
Publication URL: http://hdl.handle.net/10113/35240
Citation: Bauer, P.J., Park, D.M., Campbell, B.T. 2009. Cotton production in rotation with summer legumes. Journal of Cotton Science. 13:183-188. Interpretive Summary: Cotton rotations that include winter legumes significantly reduce the amount of nitrogen fertilizer that needs to be applied to the crop. However, winter legumes are not widely used by growers, partly because of the extra time needed to kill with herbicides the legume at cotton planting time. We conducted this study to evaluate the potential of using summer legumes, grown the season before cotton, as a nitrogen source for cotton. We evaluated a common summer legume in the southeast, cowpeas, and a tropical legume, sunn hemp. We grew the crops in late summer and allowed them to be killed by freezing temperatures in the fall. We found that though these two summer legumes accumulate significant amounts of nitrogen, most of the nitrogen is lost during the winter. The amount of nitrogen available was less than half of what was accumulated. It appears that a better rotation with summer legumes would be winter crops such as wheat. This information will be useful to farmers and scientists trying to find ways of reducing nitrogen fertilizer use in crop production systems.
Technical Abstract: Sunn hemp (Crotolaria juncea) is a fast growing tropical legume that can accumulate large amounts of biomass and N in a relatively short period of time during the summer in the southeastern US. This study was conducted to evaluate the potential of using this legume as an N source for cotton (Gossypium hirsutum L.). A field study was conducted in 2004-2005 and 2006-2007. Treatments were summer legume [sunn hemp, cowpeas (Vigna unguiculata), and summer fallow] and fertilizer N rate applied to cotton (0, 45, 90, and 135 kg N ha-1). The summer legumes were planted in mid-summer (July) and cotton was planted the following spring (May). Sunn hemp N accumulation at the first freeze in the fall was 204 kg/ha in 2004 and 98 kg/ha in 2006. Cowpeas accumulated 57 kg/ha in 2004 and 87 kg/ha in 2006. Soil NO3-N was higher in the surface 90 cm following sunn hemp than either cowpeas or summer fallow during the winter in both years. Shortly after cotton planting in May, however; there was no difference among the three summer legume treatments in soil NO3-N. Uppermost fully expanded leaf N concentrations were higher for cotton following the legumes than following summer fallow at seven of nine weekly sampling dates in 2005, but there were no differences in 2007. In 2005, seedcotton yield following cowpeas and summer fallow increased with N rate, but seedcotton yield following sunn hemp was not significantly affected by fertilizer N. Drought conditions in 2007 limited cotton yield and yield decreased with increasing N rates due to the severe stress conditions. Although sunn hemp has the potential for providing substantial biomass and N for soil improvement in the southeast US, potential losses of N through the winter may limit its applicability in cotton rotations.