Cultivation of kenaf and sunn hemp in the mid-Atlantic United States

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Abstract

Sunn hemp (Crotolaria juncea L.), a legume plant, has potential in the mid-Atlantic region of the U.S. as a renewable source of fiber and pulp, due to its biological nitrogen fixation capability that can help reduce/eliminate N pollution of Chesapeake Bay. Most research in this region has focused on kenaf (Hibiscus cannabinus L.) and little is known about sunn hemp. We evaluated effects of three planting dates (late-May, mid-June, and late-June) and three row spacings (0.3, 0.6, and 0.9 m) on dry matter yields (DMY) of kenaf and sunn hemp during 1997, and 1998 by using three crop treatments (CT1: kenaf grown with 100 kg N ha−1; CT2: sunn hemp grown without inoculation and with 100 kg N ha−1; and CT3: sunn hemp inoculated with Bradyrhizobium but without N fertilization). DMY following CT1 and CT3 (7.8 and 6.4 Mg ha−1, respectively) during 1997 were similar and greater than that following CT2 (5.7 Mg ha−1). However, DMY following CT1, CT2, and CT3 were similar in 1998 and ranged from 12.6 to 13.4 Mg ha−1. Kenaf planting date did not affect DMY during 1997 but during 1998 the highest DMY was obtained from kenaf planted in late-May. The optimal planting date for sunn hemp during 1997 was mid-June, whereas in 1998 it was late-May. Row spacing effects on kenaf DMY were not significant. Row spacings of 0.3 m were optimal for DMY of N-fertilized sunn hemp during 1997 and 1998, whereas row spacing did not affect DMY of non-fertilized, but affected inoculated sunn hemp. We conclude that both kenaf and sunn hemp could produce similar dry matter yields in the mid-Atlantic region of U.S.

Introduction

Kenaf and sunn hemp were identified as alternative sources of cordage material for the United States during the Second World War when supplies from overseas were interrupted and an increased need developed for these fibers (Wilson et al., 1965). Kenaf, an annual plant that resembles cotton (Gossypium hirsutum L.) and okra (Abelmoschus esculentus L.), can be produced in large regions of the United States (Webber et al., 2002) during summer seasons. Sunn hemp, a legume plant, also has great potential as an annually renewable fiber crop and as a green manure and cover crop due to its biological nitrogen fixing capabilities (Cook and White, 1996, Mansoer et al., 1997).

Although both fiber crops possess suitable traits and high yields, kenaf has received more attention than sunn hemp due to its ability to produce consistently greater yields and lower lodging susceptibility (Wilson et al., 1965). Once it was determined that kenaf was a suitable crop for production in the United States, development of high-yielding anthracnose-resistant cultivars and production/harvesting technology soon followed (Nieschlag et al., 1960, Wilson et al., 1965, White et al., 1970). Kenaf has also been identified as an excellent source of cellulosic fiber for the manufacturing of a large range of paper products. Pulping kenaf requires less energy and chemical inputs for processing than standard wood sources (Nelson et al., 1962). Webber and Bledsoe (1993) reviewed the research and development work in the 1990s and concluded that kenaf fiber is suitable for use in building materials, adsorbents, textiles, and composites using new and recycled plastics.

Sunn hemp is also known as Sunnhemp, Indian hemp, Madras hemp, brown hemp, and sannhemp (Duke, 1983). Sunn hemp, a member of the legume family (Fabaceae), has great potential as an annually renewable, multi-purpose fiber crop (Cook and White, 1996). The stems of sunn hemp are composed of two fibers, the bast and woody core. The bast fibers, which are located in the outer bark, are much longer than the core fibers, but the two fiber widths are similar (Cunningham et al., 1978). Duke (1983) observed that bast fiber from sunn hemp is more durable than jute. As the world faces an increased need for fiber, sunn hemp has the potential to be grown on a large commercial scale (Cook and White, 1996). A detailed description of sunn hemp has been provided by Duke (1983) and Cook and White (1996).

Delayed planting reduced dry matter yields of sunn hemp in lower Rio Grande Valley of Texas, especially if planting was delayed by four weeks or longer from late-March to mid-April (Cook et al., 1998), whereas plant population did not influence total stalk yield (Cook and Scott, 1998). Sunn hemp is highly resistant to root-knot nematodes, but not equally resistant to southern root-knot (Meloidogyne incognita) and reniform nematodes (Rotylenchulus reniformis). Robinson and Cook (2001) reported that reproduction of reniform nematode on sunn hemp was nearly undetectable, whereas reproduction of southern root-knot nematode was greater than that on resistant cotton. Scott and Cook (1994) compared the dry matter yields of kenaf, roselle (Hibiscus sabdariffa L.), and sunn hemp at two locations in Rio Grande Valley of Texas during 1992 and 1993 and reported that sunn hemp produced dry matter yields equal to kenaf during 1992, but not during 1993 when sunn hemp yields were significantly lower than kenaf.

In the mid-Atlantic region of the United States, persistent needs for crop diversification and protection of the Chesapeake Bay from nitrogen pollution suggest that leguminous plants that have the potential of reducing/eliminating the use of inorganic nitrogen fertilizers, such as sunn hemp, be studied. However, information about the production and yield of sunn hemp in the mid-Atlantic region of the United States is lacking, whereas considerable work has been done in kenaf (Bhardwaj and Webber, 1994, Bhardwaj et al., 1995, Bhardwaj et al., 1996). Sunn hemp has been researched as a legume cover crop in southeastern U.S. (Mansoer et al., 1997) and as a source of fiber in southern U.S. (Cook and Scott, 1998, Cook et al., 1998, Robinson and Cook, 2001). The objectives of our studies were to identify optimal planting date and row spacing for sunn hemp and to compare the dry matter yields of kenaf and sunn hemp.

Section snippets

Materials and methods

The plant material consisted of sunn hemp cv. ‘Tropic Sun’ and kenaf cv. ‘Everglades-41’. Field experiments were conducted during 1997 and 1998 at the Randolph Farm of Virginia State University, located in Ettrick, Virginia (approximately 37°N and 77°W) on an Abel sandy loam (fine loamy mixed thermic Aquatic Hapludult) soil that typically has a pH of 6.1–6.4, P content of 54–77 mg kg−1 and K content of 52–54 mg kg−1. The experimental design was a split–split plot design of three replications with

Results and discussion

Analysis of variance, from the data combined over two years, indicated that significant interactions existed between year × planting date, and year × planting date × row spacing for dry matter yield. Analysis of data, separately by years, indicated that either the interaction involving crop treatment or the main effects were not significant. Therefore, the crop treatment means were compared by averaging over planting dates and row spacings (Table 1). However, analysis of data, separately by

Conclusions

Our results demonstrate that production of both kenaf and sunn hemp for dry matter production is feasible in Virginia and the mid-Atlantic region of the United States. However, it may be desirable to further study sunn hemp due to its biological nitrogen fixation capabilities. Production of sunn hemp can help in reducing/eliminating use of N fertilizers, and thus, help protect the Chesapeake Bay from pollution.

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Contribution of Virginia State University, Agricultural Research Station Journal Article Series No. 238. The use of trade names or vendors does not imply approval to the exclusion of other products or vendors that may also be suitable.

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