Planting date and cultivar effects on growth and stalk yield of Sunn hemp

Due to the accelerated harvesting of forest resources, there is an international need to identify alternative fiber sources to meet increasing consumer demands. Sunn hemp (Crotalaria juncea L.) has potential as an annually renewable, nonwood fiber source for industrial use. A 2-year study was conducted in the Lower Rio Grande Valley of Texas to evaluate the effects of four planting dates (2-week intervals) and two cultivars (Tropic Sun and PI248491) on stalk height, basal diameter, and dry matter yield. Results indicated that in the Lower Rio Grande Valley delayed planting generally reduced yield, especially when planting was delayed by 4 weeks or longer from late March to mid-April. The Hawaiian cultivar, Tropic Sun, produced the greatest mean stalk yield (16.2 Mg ha(-1)) across the 2-year study, averaging 2.2 Mg ha(-1) more stalk yield than the Brazilian plant introduction, PI248491. Plant height consistently showed a strong, positive correlation with stalk yield, whereas, the association between basal diameter and stalk yield was generally weaker and often erratic. Single year results from the fiber analyses conducted in 1995 indicated that bast and core fiber lengths were not significantly affected by planting date. Since most sunn hemp cultivars have short-day flowering response, delays in planting will shorten the growing season and could result in lower stalk yields. (C) 1998 Elsevier Science B.V. All rights reserved.