A comparative analysis of the growth of sweet and forage sorghum crops. II. Accumulation of soluble carbohydrates and nitrogen

Abstract

Well-watered crops of sweet sorghum (cv. Wray) and forage sorghum (cv. Silk) were grown in south-eastern Queensland. Treatments consisted of four sowing dates, two intra-row spacings and harvests taken at six physiological growth stages from the third ligule to 3 weeks after grain maturity. Plant density effects on the concentration of sugars and nitrogen were slight, and changes in yields of these components were a function of density effects on dry matter yields. At any growth stage, the concentration of sugars in both cultivars was decreased with delay in sowing date. The delay in sowing date led to an increased nitrogen concentration in cv. Wray, but in cv. Silk the nitrogen concentration was highest in early and late sowings. At maturity, the concentration of sugars in cv. Wray averaged 40'70, 10 times the level in cv. Silk. In both cultivars, accumulation was a near linear function of either time or radiation sum. The partitioning of carbohydrate differed little between cultivars but altered with their ontogeny. The efficiency of light use for sugars production was greater in cv. Wray and altered with ontogeny. In contrast, concentration of nitrogen was similar for both cultivars and decreased curvilinearly with time or degree days. The partitioning of nitrogen altered with ontogeny and the amount partitioned to leaf material was greater in cv. Silk pre-anthesis but was less post-anthesis. Yield of stem sugars in cv. Wray exceeded 10 t ha-1 when the crops were sown early in the season, but was only 3 t ha-1 with late-sown crops.