Kenaf: A Multi-Purpose Crop for Several Industrial Applications

This chapter discusses the origin and taxonomy of kenaf, the description of the plant parts (stems, leaves, flowers, seeds, and root), the importance of the crop worldwide, the cultivation area, as well as its importance. Kenaf (Hibiscus cannabinus L.) is an annual spring crop cultivated for long (4000 BC). It originated from Africa, disseminated in the 1900s in Asia (in India and then in China) and in the 1940s from Asia to northern and central USA. Kenaf belongs to the Malvaceae family and section Furcaria. It is closely related to cotton, okra, hollyhock, and roselle. Nowadays it is being cultivated in 20 countries worldwide and its total production (kenaf and allied crops) is 352,000 tons (2010/2011). Currently, China and Pakistan are the main producers. In the last part of the chapter the importance of the crop is discussed. Kenaf is an annual non-food fiber crop that used to be cultivated for numerous uses (paper pulp, fabrics, textiles, building materials, biocomposites, bedding material, oil absorbents, etc.). Recently, it is also considered as an important medicinal crop as its seed oil is recorded to cure certain health disorders and help in the control of blood pressure and cholesterol.

This chapter describes the physiology of kenaf from seed germination and root development till the effects of water and nutrients stress on grown plants. Review on kenaf agro-physiology of experiments carried out worldwide are presented and discussed mainly at the canopy and whole-plant level with the aim to help producers to make decisions and planning of production. However, few literature reports experimental results on the physiology of this multipurpose crop especially in terms of assimilation rate and its relation with environmental and agronomic factors. Knowledge on gas exchange rate and stomatal conductance may be a key support in understanding the physiology of Kenaf in terms of water requirements, its ability of light conversion into carbonaceous molecules influencing crop production potential and, indirectly, the carbon sequestration activity. In kenaf seedling development takes place when temperatures are higher than 10 °C, supporting the idea that kenaf is a macrothermal plant and optimal sowing has to be carried out during spring-summer, depending on the area of cultivation. Kenaf is very sensitive to reduced soil water availability, however, under moderate water stress conditions the crop maintains root development while reducing final biomass yield. Recent studies from Greece and Italy showed that even though kenaf uses CO₂, solar radiation, water, and nitrogen less efficiently than C₄ crops its assimilation rates can reach 50–58 kg of CO₂ ha⁻¹ h⁻¹. However, great differences in terms of net photosynthesis have been reported by various authors, which may be related to the different environmental variables and agronomic managements during field and controlled experimental environments, such as air temperature, light intensity, water supply, nutrients availability, relative humidity, wind, cultivar, plant density, and soil type. Similar results were reported in the literature regarding stomatal conductance and transpiration rates. In experiments carried out during the night, stomatal conductance and transpiration rate determined water looses probably affecting the water requirement of the crop. Kenaf could be described as opportunistic in relation to water availability, with a high rate of stomatal conductance and transpiration when soil water is available but with markedly reduced leaf conductance and transpiration rate when water is limited. Extinction coefficient for light (K _L ) and nitrogen (K _N ), under water limited conditions, were found to be always smaller than under irrigated conditions, as a result of irregular adjustment of leaf orientation to incident radiation particularly during midday. Vertical Specific Leaf Nitrogen (SLN) distributions were found in canopies when leaf area index (LAI) was >1.5. It was observed a strong association between SLN and PAR distributions in irrigated kenaf canopies. Due to its tropical origin, kenaf behaves as a short-day plant remaining vegetative until daylength falls below 12.9 or 12.45 h. Flowering of late-maturity cultivars is under photoperiodic control; conversely, photoperiod does not influence the flowering of early maturity cultivars. Radiation use efficiency (RUE) in kenaf is positively associated with specific leaf nitrogen. RUE decreased under water deficit and nitrogen supply. Water use efficiency (WUE) decreased as the level of irrigation increased. It was higher than other C₃ crops, but lower as compared to C₄ crops tested in the same environments. Information on nutrient use efficiency (NUE) for kenaf is scarce and not well quantified to date. Higher NUE values were reported for micronutrients than for macronutrients. This last characteristic needs further investigation, since improvement of NUE is an essential and challenging prerequisite for the expansion of bioenergy crop productions into less fertile soils and marginal lands.

The main purpose of breeding new kenaf is developing new varieties that are higher yielding, resistant to pests and diseases, drought-resistant or regionally adapted to different environments and growing conditions. Kenaf breeding can be accomplished through many different techniques ranging from simply selecting plants with desirable characteristics for propagation, to more complex molecular techniques. Classical kenaf breeding uses crossing of closely or distantly related individuals to produce new kenaf varieties or lines with desirable properties. Plants are crossbred to introduce traits/genes from one variety or line into a new genetic background. Modern plant breeding may use techniques of molecular biology to select, or in the case of genetic modification, to insert, desirable traits into kenaf. The main methods which have been used in kenaf are introduction and breeding, system selection, crossbreeding, mutation breeding, transgenic breeding, and so on.

The determination of the appropriate crop management is a key factor for the successful insertion of the crop in the existing cropping systems with economic benefits. Research on crop management has been conducted when kenaf was evaluated as an excellent cellulose fiber source for a large range of paper products (in 1960s). The most important parameters in the crop management that should be followed are the site of its cultivation and the final end use. New kenaf varieties have been released that were resistant to pests and diseases with improved resistant to drought, and with higher yields. The plant density and the fertilization need to be varied according to its final use of the crop. When it is cultivated for its fiber stem the plant population should be from 170,000 to 350,000 plants per ha and with row spacing 35–50 cm. In areas where the precipitation is limited irrigation is needed to achieve high yields. It is a crop very sensitive to nematodes, especially when it is cultivated in areas with sandy soil and this should be taken under consideration on the rotation system that will be followed. Harvesting time and methods can be adjusted according to the use of the crop (fiber, seeds, fiber and seeds, forage).

This chapter outlines the environmental aspects of kenaf production and utilization, focusing on the impact on biotic and abiotic resources, through the analysis of the crop’s interaction with its environment and management practices. In this study, the assessment of data retrieved from literature was supplemented with results obtained from the Biokenaf project. As a bioenergy and biomaterials carrier, kenaf offers ecological advantages over fossil sources by contributing to reduction of greenhouse gases and energy savings. Nevertheless, a negative impact may be perceived in terms of acidifying emissions. Although the different indicators did not yield a common pattern, overall results suggest that kenaf crop have an advantage over other annual energy crop systems, namely regarding pesticides and fertilizers inputs. However, risks associated with soil quality, erodibility, use of resources, and biodiversity are equivalent to most annual energy crops. Crop management options can influence the outcomes, but site specific factors should be accurately assessed to evaluate the adequacy between crop and location. In addition, environmental hot spots in the systems are detected and options for improvement are presented.

The purpose of this chapter is twofold. First, to introduce the reader to some simple basic economic concepts used in financial analysis and project evaluation, and second to bring together in a new analytical framework, significant pieces of information from recently published research findings on the economics of kenaf production. The BIOKENAF research and experimentation project (QLK CT2001 01729, 2003–2007), which is the most relevant recent scientific work from the point of view of geography and approach, has provided most of the basic material for this chapter. The findings of BIOKENAF are updated and compared with other related bibliographical evidence, concentrating on the farmer’s point of view. This chapter will objectively re-examine the financial implications of kenaf production and hopefully guide the reader on how to make his own budgets and set up business plans for his farm.

This chapter summarizes the most important achievements of the European research project entitled “BIOKENAF—Biomass Production Chain and Growth Simulation Model for Kenaf” (www.​cres.​gr/​biokenaf) that carried out for 2003–2007. The overall objective of the BIOKENAF project was to introduce and evaluate kenaf as a non-food crop through an integrated approach for alternative land use in South EU that will provide diversified opportunities for farmers and biological materials for the “bio-based industries” of the future. Several fields’ trials were carried out in South EU aiming to identify the appropriate crop management for yields maximization (sowing dates, plant densities, best varieties, irrigation and fertilization needs, harvesting time). A dynamic crop-growth simulation model was developed to produce quantitative estimates of the yielding potential of kenaf at regional level. The model was based on the detailed crop data that were collected from the field trials and were included in photosynthetic capacity, respiratory losses, phenology, dry matter distribution, and data on leaf area. The appropriate harvesting time for south EU countries that ensure the highest possible yields with the lowest possible moisture content investigated as well as best storage method in order to the minimum losses in the quality and quantity of the feedstock to be achieved. The suitability of kenaf for both selected industrial products (composites, building materials, nonwovens, paper, and board and absorption particles) and for thermo-chemical energy applications (combustion, gasification, and pyrolysis) was investigated. Following an environmental/economic assessment and market studies insight in the feasibility of kenaf for industrial and energy applications was provided that was used not only for comparison of the crop with other conventional crops with similar cultural practices but also for the development of scenarios for alternative land use and diversified opportunities for farmers in order to produce industrial bio-products that will supply the “bio-based industries” of the future.