Phenology, early growth, and yield of planted and ratoon grain sorghum

Abstract

Knowledge is limited on growth and development of ratoon grain sorghum [Sorghum bicolor (L.) Moench] in the field. In efforts to build simulation models of ratoon grain sorghum, modellers have assumed that the planted and ratoon crops grow similarily. This study was undertaken to document the growth of ratoon grain sorghum and test the hypothesis that growth and development of the ratoon crop is similar to the planted crop. Experiments were conducted from 1985 through 1987 under irrigated field conditions using nine hybrids of medium/medium-late maturity on a Houston Black clay: fine, montmorillonitic, thermic Udic Pellustert.In two of the three years, grain-yield of the planted crop exceeded the ratoon while grain-yield was equal in the other year studied. Rapid development of tillers produced much higher leaf-area indexes (L) and vegetative biomass early in the plant's ontogeny for the ratoon compared to the planted crop. Depending on hybrid and year, each primary shoot (PS) of the planted crop produced from 4 to 7 tillers within 20 days of harvest of the planted crop. At harvest, however, only 2–3 tillers/PS remained and only 1.7 tillers/PS (on average) produced grain.The planted crop allocated a higher proportion of its total above-ground biomass to grain than did the ratoon crop. Differences in the degree of tillering and partitioning of biomass to grain were found among hybrids. Yet, a significant hybrid×year interaction suggests that partitioning was dependent on the environment. Phenology of planted and ratoon crops were similar. Grain-forming tillers produced the same number of leaves as the primary shoot of the planted crop, and differences in time to anthesis between the planted and ratoon crops averaged approximately 100 of the 1000 heat units (7°C base temperature). Based on our observations, the assumption that growth of planted and ratoon grain sorghum are similar appears to be in error. However, the phenology of grain-forming ratoon tillers appeared to mimic the phenology of the planted crop's primary shoot.