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 C4crops its assimilation rates can reach 50-58 kg of CO2ha-1h-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 (KL) and nitrogen (KN), 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 C3crops, but lower as compared to C4crops 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.
|Titolo:||Crop Physiology in Relation to Agronomic Management Practices|
|Data di pubblicazione:||2013|
|Appare nelle tipologie:||2.1 Contributo in volume (Capitolo o Saggio)|