Sunn-Hemp Utilized as a Legume Cover Crop for Corn Production

the winter, chemically terminated in the spring, and then corn is planted into the surface residue. Corn is typically The benefits of winter legumes as cover crops for corn (Zea mays planted early in the growing season, which forces an L.) are diminished by the earliness of corn planting in relation to early termination date. A termination date at least 14 d biomass and N production by the legumes. Tropical legumes may before corn planting enables soil surface water recharge offer an alternative to winter legumes because they produce adequate biomass before corn planting. We determined the suitability of ‘Tropic by planting time (Hargrove and Frye, 1987); however, Sunn’ sunn-hemp (Crotalaria juncea L.) as a cover crop for corn on as a result, biomass production for erosion control is a Compass loamy sand (coarse-loamy, siliceous, subactive, thermic limited and N release may not always synchronize with Plinthic Paleudults) in central Alabama using a split-plot treatment rapid N uptake of corn at the six-leaf stage (Magdoff, structure in a randomized complete block design with four replications 1991). Decker et al. (1987) reported higher N percentfrom 1991 to 1993. Main plots were winter fallow and sunn-hemp ages with increased legume top growth the longer the planted in mid-August, and subplots were N (0, 56, 112, and 168 kg legume was allowed to grow in the spring. N ha 1) applied to corn 3 weeks after planting (WAP). Sunn-hemp An alternative to winter legumes are adapted tropical biomass production approximately 14 WAP (first frost) averaged 7.6 legumes, which produce higher biomass contents in temMg ha 1 with an N content of 144 kg ha 1 in the first 2 yr of the perate climates (Mansoer et al., 1997). Yadvinder et al. study. Corn grain yield following sunn-hemp averaged 6.9 Mg ha 1 whereas yield following winter fallow averaged 5.7 Mg ha 1. Grain (1992) showed that tropical legumes could produce their N averaged 16.3 kg ha 1 greater for corn following sunn-hemp than biomass in a shorter time period compared with winter fallow plots. Before first frost, sunn-hemp produced excellent biomass legumes. Reddy et al. (1986) showed mean biomass to serve as a winter cover crop in corn production while producing yields of 10 Mg ha 1 for several tropical legumes across N equivalent to 58 kg ha 1 of N fertilizer during the 3-yr period, based a 3-yr full summer production period with mean N yields on corn yield and N response. Sunn-hemp has potential to be utilized of 200 kg ha 1. as an alternative to winter legumes for ground cover and as an N A tropical legume that has been investigated as a source for a subsequent corn crop in the Southeast. green manure crop and as an intercrop for corn production in the tropics is sunn-hemp (Lales and Mabbayad, 1983; Jeranyama et al., 2000). ‘Tropic Sunn’, a sunnP research highlights the benefits of utilizing hemp cultivar, was jointly released by USDA-NRCS a winter legume in a conservation tillage system for and the University of Hawaii Institute of Tropical Agricorn production (Mitchell and Teel, 1977; Ebelhar et culture and Human Resources in 1983. This legume can al., 1984; Holderbaum et al., 1990; Decker et al., 1994). produce high amounts of biomass and symbiotic N in Winter legumes provide the same benefits of grass cover an 8to 12-wk frost-free period (NRCS, 1999). Therecrops including erosion control, improved water infiltrafore, our objective was to determine if the rapid growth tion, higher organic C contents, and cooler soil temperaand N accumulation of sunn-hemp could serve as an tures (Reeves, 1994), while simultaneously producing a alternative to winter legumes as a cover crop for consersource of biologically fixed N for subsequent crops like vation tillage corn production in the southern USA. corn. The additional N supplied by winter legumes can reduce N fertilizer requirements (Ebelhar et al., 1984; MATERIALS AND METHODS Holderbaum et al., 1990). However, the N contribution We determined the suitability of Tropic Sunn sunn-hemp of legumes is highly variable and depends on species, as a cover crop for corn on a Compass loamy sand at the dry matter production, N concentration of the legume, Alabama Agricultural Experiment Station’s E.V. Smith Reindigenous soil N, and time of termination (Holderbaum search and Extension Center in Shorter, AL, using a splitet al., 1990; Reeves, 1994). plot treatment structure in a randomized complete block deTime of termination has prompted researchers to fosign with four replications from 1991 to 1993. Main plots were cus on the synchrony of N release from legumes with winter fallow and sunn-hemp planted in mid-August, with N the N uptake of corn (Decker et al., 1994; Stute and (0, 56, 112, and 168 kg N ha ) applied as ammonium nitrate Posner, 1995; Mansoer et al., 1997; Vaughan and Ev3 WAP corn as subplots. Three replications from the fallow anylo, 1998). In a conservation tillage corn system, leand sunn-hemp plots, designated to receive no N, mistakenly received 56 kg N ha 1 at 3 WAP in 1993. Consequently, those gumes are planted in the fall, allowed to mature over replications were eliminated from the analysis for that year. Winter weed growth was not controlled in fallow plots. All K.S. Balkcom, USDA-ARS, National Soil Dynamics Lab., 411 S. treatment combinations were in the same location each year Donahue Dr., Auburn, AL 36832; and D.W. Reeves, USDA-ARS, with no re-randomization of treatments. Subplot dimensions J. Phil Campbell Sr.–Natural Resource Conservation Center, 1420 were 3.7 m wide and 13.7 m long with a 0.3-m buffer beExperiment Station Rd., Watkinsville, GA 30677. Received 7 July tween plots. 2004. *Corresponding author ([email protected]). At the initiation of the experiment, in late summer of 1990, each main plot was sampled separately for a routine soil test Published in Agron. J. 97:26–31 (2005). © American Society of Agronomy 677 S. Segoe Rd., Madison, WI 53711 USA Abbreviations: WAP, weeks after planting.