An analysis of leaf growth in sugar beet.

SUMMARY The increase of leaf area index ( L ) was examined in a series of sugar‐beet crops grown on different sites (Broom's Barn, Suffolk and Trefloyne, Dyfed) or with different husbandry treatments (sowing dates and nitrogen rates) between 1978 and 1982. The development of L could be described as a function of thermal time using three parameters; D E , which was essentially an estimate of the thermal time required for crop establishment, and rH L and D L , the thermal rate and duration, respectively, of the increase of L . Variations in D E between seasons and with sowing date were small, but significant; they were attributed to factors affecting the condition of the seedbed. There were much larger variations in rH L , especially between seasons, sites and crops given different rates of nitrogen fertiliser, and there was a strong negative relationship between rH L and D L . Much of the variation in rH L was associated with differences in the concentrations of nitrogen in the lamina dry matter. Faster rates for rH L at Trefloyne than at Broom's Barn, and in the crop grown in 1982 as compared with other years, were also partly attributable to particularly warm conditions during the early development of some of the larger, faster‐growing leaves within the canopy. The wider application of the relationships established from these experiments was tested with data from a series of crops grown on other sites between 1960 and 1962. The relationships held particularly well for beet grown on soils with high water‐holding capacity but not for those on soils of low water‐holding capacity.