Inflorescence characteristics, seed composition, and allometric relationships predicting seed yields in the biomass crop Cynara cardunculus
Cynara (Cynara cardunculus) is a perennial C(3) herb that has its potential as bioenergy crop. This paper aims (a) to derive empirical relationships to predict cynara seed yield per head and per unit area, avoiding laborious extraction of seeds from the complex structure of its inflorescences; (b) to determine the head-weight distribution per unit area, the seed composition and the oil profile of cynara seeds; and (c) to estimate the range of cynara biomass, seed and oil yield in representative parts of Greece. We analyzed 16 field experiments, varying in crop age and environmental conditions in Greece. Seed yield per head (SY(head)) can be accurately predicted as a linear function of dry head weight (H(w)): SY(head)=0.429 center dot H(w)-2.9 (r2=0.96; n=617). Based on this relationship, we developed a simple two-parameter equation to predict seed yield per unit area (SY): SY=HN center dot(0.429 center dot mu-2.9), where mu is the mean head weight (g head-1) and HN is the total number of heads per unit area, respectively. The models were tested against current and published data (n=180 for head-level; n=35 for unit area-level models), and proved to be valid under diverse management and environmental conditions. Attainable cynara seed yields ranged from 190 to 480 g m-2 yr-1, on dry soils and on aquic soils (shallow ground water level). This variation in seed yield was sufficiently explained by the analyses of head-weight distribution per unit area (small, medium and large heads) and variability of seed/head weight ratio at head level. Seed oil concentration (average: 23%) and crude protein concentration (average: 18.7%) were rather invariant across different seed sizes (range: 26-56 mg seed-1) and growing environments.