Tillage Management for Sunn Hemp.

Sunn hemp (Crotolaria juncea L.) is a tropical legume used as a summer cover crop in the US because it grows fast, fixes large amounts of N, and is resistant to root knot nematode. Sunn hemp also has potential to be used for grazing and as a biomass source for energy. In the southeastern coastal plain, grain crops benefit from subsoiling which loosens an inherent hardpan. Our objective was to determine tillage practices that optimize sunn hemp biomass production when grown in a double crop system with flax (Linum usitatissimum L.) grown for fiber. Experiments were conducted in 2014 and 2015 near Florence, SC. All plots were conventionally tilled with a disk harrow prior to planting flax in the previous fall. Treatments in the experiment were a) deep tillage with a paratil before flax planting (subsoil or none); b) surface tillage before sunn hemp planting (disk harrow or none); and c) deep tillage with a paratil before sunnhemp (subsoil or none). After flax harvest in the spring, sunn hemp was planted in late May or early June. Aboveground biomass of the sunn hemp was determined in late August and in early October each year. Average over both years, sunn hemp biomass yield was 9881 kg ha^-1 in late August and 14561 kg ha^-1 in early October.  Subsoiling (either before flax, before sunn hemp, or both) had a small impact on biomass yield at both sampling times. There was no difference between surface tillage treatments at either sampling time.  Results suggest that tillage (either subsoiling or disking) does not substantially improve sunn hemp yield when following a flax crop harvested for fiber.