Radiation interception and biomass and nitrogen accumulation in different cereal and grain legume species

The increasing interest in the sustainability of agricultural systems has emphasised the importance of incorporating legumes into cereal production, in spite of their lower and less reliable grain yields. The basis of the poor performance of legumes has been analyzed in a 2-year comparison between varieties of pea, faba bean, durum wheat and triticale, in terms of resource capture and use. The cereals developed a full canopy 350 °Cd earlier than did the grain legumes, and the triticale more rapidly than the durum wheat. This difference, and the 11-day longer duration of the growing cycle of cereals allowed them to intercept more photosynthetically active radiation (PAR) than grain legumes. This, combined with their higher radiation use efficiency (2.35 ± 0.07 vs 2.10 ± 0.05 g MJ⁻¹), resulted in a biomass greater, on average, by about 500 g m⁻². Within the cereals, triticale accumulated 34% more biomass than durum wheat. Radiation interception and nitrogen uptake are closely tied in both cereals and grain legumes. There was no difference between cereals and legumes in the relationship between the amount of nitrogen assimilated and the fraction of intercepted PAR (FIPAR), but there were differences in the form and in the parameters of the relationship between nitrogen assimilated and PAR intercepted. Below a FIPAR of 0.8, the relationship between FIPAR and N uptake is crop independent, underlining the influence of FIPAR on N uptake. The significance of this FIPAR level is that by the time it has been achieved, the plants will have accumulated most of the N present in their biomass at maturity.