Adaptation of faba bean (Vicia faba L) to dryland Mediterranean-type environments . II. Phenology, canopy development, radiation absorbtion and biomass partitioning

Faba bean (Vicia faba L.) was considered poorly adapted to the low-rainfall environments of south western Australia because of its susceptibility to moisture and heat stresses. As part of a larger study of the adaptation of faba bean to short-season Mediterranean-type environments, faba bean cv. Fiord was sown at three or four dates ranging from early May to early July at two sites in 1993 and 1994 to examine its phenology, canopy development, and biomass partitioning. Faba bean took full advantage of early sowing by producing greater seed yields because it flowered earlier, had longer durations of anthesis, produced more nodes, had greater green area index (GAI), absorbed more photosynthetically active radiation (PAR), greater peak and final biomass, more pods in the upper canopy, and larger harvest index (HI) than when planting was delayed. Rate of leaf appearance on the main stem was consistently 0.19 leaves day(-1) across sowing times, sites, and seasons, and the final numbers of nodes were 20 to 24 with early sowing. Up to 4 stems plant(-1) developed under favorable conditions, but some death occurred and final stem numbers were 2.5 to 3.0 plant(-1) regardless of sowing time. Peak PAR absorbtion was about 75-90% at green area indices of 4 to 5 with early sowing. The estimated radiation-use efficiency (RUE) was 1.85 g MJ(-1) and did not vary with sowing time. Unlike most other crops in this environment, faba bean can be sown in autumn (April) because of its ability to tolerate mild frosts at flowering and podding, and because it partitions assimilates into pods and seeds early in the season before severe drought stress commences in spring. Pod set in this study was adequate for moderate yields and HI was consistently high. The ability of faba bean to partition assimilates into seed was not reduced significantly with late sowings, producing HI of 53 to 62% in 1993 and 33 to 53% in the dry 1994 season.