Analysis of growth dynamics of Mediterranean bioenergy crops

In spite of the rapidly growing bioenergy production worldwide, there is lack of field experience and experimental data on the cultivation of bioenergy crops. This study aims to advance crop management operations and modelling studies by providing essential information on phenology, agronomy and crop physiology of three Mediterranean bioenergy crops: Helianthus annuus (sunflower), Hibiscus cannabinus (kenaf) and Cynara cardunculus (cynara). These crops cover a wide range of bio-industrial applications and fit into different cropping strategies. For these crops, we identified the most important knowledge gaps and performed a series of field experiments to fill some of those, particularly for cynara. Information on phenology and seed yield potential for cynara was missing mainly due to its complex inflorescence structure. This thesis codifies and describes cynara’s phenological growth stages according to the universal BBCH coding system. This scale can be used by everyone involved in the production of this crop under all circumstances. In addition, we present a robust allometric model for estimating seed yield under diverse management and environmental conditions. Inputs to the model are two easily quantifiable inflorescence traits: total weight and number of seed-bearing heads per unit area. Additionally, this thesis investigates factors at leaf, canopy and crop level that determine biomass production for all tested crops and provides key parameters for crop growth modelling. Leaf photosynthesis and respiration rates in response to light, temperature and leaf nitrogen were quantified. Based on such data, a biochemical model for C3 leaf photosynthesis and an empirical model for respiration were parameterized and validated. Then, to upscale these rates from the leaf to the canopy level, light- and nitrogen extinction coefficients over time and in response to water availability were determined in detail. It was shown that the light extinction coefficient changes under water stress conditions and time of year, while leaf nitrogen only shows a strong vertical distribution within crop canopy during the mid-season. Relevant agronomic data, such as biomass production over time and leaf area index in response to management practices, are also presented for the three crops. This thesis contributes to the general objective of gaining more insight into bioenergy production from crop species. The findings can help farmers, researchers and modellers to better evaluate agricultural land uses and to improve biomass quantity and quality. Among the studied species, the perennial cynara shows the greatest potential for energy production in the Mediterranean region because a significant part of the production is achieved in the winter–spring period relying on natural rainfall. Key words: cynara, kenaf, sunflower, phenology, agronomy, crop physiology, modelling, biomass production, crop growth, growth stages, BBCH code, seed yield, oil/seed ratio, leaf area index, leaf nitrogen, light and nitrogen extinction coefficients, photosynthesis, respiration, respiration acclimation, bioenergy, Greece, Mediterranean region.