Root Lodging Affects Biomass Yield and Carbohydrate Composition in Sweet Sorghum (Sorghum bicolor) Grown for Bioenergy.

Sweet sorghum is a promising crop for bioenergy production but is susceptible to lodging, which can significantly affect crop composition and total harvestable yields. Prior research on lodging has typically been conducted on small plots or in pots with experimenter induced lodging, and as an ancillary objective to other work. These studies have failed to provide detailed information on carbohydrate allocation, yields and partitioning of lodged sweet sorghum. Naturally occurring lodging in sweet sorghum plots in 2012 and 2013 in North Florida was exploited to provide a detailed understanding of carbohydrate allocation, biomass partitioning, and the effects of natural lodging. The current research addresses these issues by quantifying yields and partitioning, and identifying differences in carbohydrate allocation as a result of lodging. Fresh biomass yields were not significantly different between lodged and non-lodged plots in 2012 nor 2013, but dry matter content was significantly lower in lodged plots in both years. Carbohydrate allocation was dramatically impacted by lodging, resulting in approximately a 50% decrease in carbohydrate allocation to grain head formation, and a significant but variable decrease in juice Brix, with severely lodged hybrid sorghum losing decreasing from 14.6 to 10, and lodged M81-E decreasing from 11.4 to 9.5. Lodging also reduced machine recoverable biomass at harvest by 40%, which may compound losses due to changes in carbohydrate allocation. Based on morphological and carbohydrate data, lodging appears to extend the period of vegetative growth and delay maturity, potentially as a means to recover from a lodging event.  Overall, severe lodging will significantly impact recovery of soluble carbohydrates from sweet sorghums, due both to dry matter yield loss and a decrease in soluble sugars, potentially decreasing yields of recoverable carbohydrates by almost 50%.