Sunn Hemp: a New Crop That Controls Weeds.

Sunn hemp (Crotalaria juncea L.) is the fastest growing species of the genus Crotalaria and is the most widely grown green manure in the tropics where is also grown as a forage and fiber  crop. Breeding sunn hemp for adaptation to temperate climates is an ongoing project at Auburn University. It has been observed that sunn hemp can out grow weeds and has the potential to suppress them. An experiment using a breeding population was conducted at Tallassee and Shorter, Alabama, in 2008. Treatments were arranged in a randomized complete block design with four replications. They included a no sunn hemp control and sunn hemp sown at 4.5, 11.2, 17.9, 24.7 and 31.4 kg ha-1 using a drill.  Plots were 3 m wide and 9 m long. Sunn hemp stand and weed biomass was measured when sunn hemp plants had reached their maximum height. Stand count was accomplished by counting the number of plants at three random places (a 1-m-long section of a single row each). Weed biomass was obtained by harvesting all weed foliage in a randomly selected one m2. Non linear regression was used to describe the relationship between weed biomass and sunn hemp plant density. Increasing sunn hemp density from 0 to 100 plants per m2  resulted in a consistent reduction of weed biomass. This reduction was higher at Shorter (96%) than at Tallassee (57%) compared to the control.