Biomass and Sugar Yield Response of Sweet Sorghum to Lime and Fertilizer1

Abstract

AbstractSoil fertility requirements for sweet sorghum [Sorghum bicolor (L.) Moench] as an alcohol fuel crop have not been well defined. The primary objective of this study was to determine the biomass and sugar (% Brix ✕ extracted juice) yield response of sweet sorghum to N‐P‐K and lime. The study was conducted for 2 years on a Wynnville silt loam (fine‐loamy, siliceous, thermic Glossic Fragiudult) soil in the Cumberland Plateau region of northern Alabama. Experimental design was a split‐plot with 0 or 8 Mg ha−1 dolomitic limestone and combinations of 0, 45, 90, or 180 kg ha−1 N, 30 or 90 kg ha−1 P, and 40 or 120 kg ha−1 K. Liming significantly increased yields of fresh and dry biomass, grain, and juice sugar extracted from stalks. The lime also greatly reduced exchangeable soil Mn and Al and increased Mg and decreased Mn concentrations of the biomass. Due to the dominant effect of lime and other interactions, biomass and juice sugar yields were not consistently related to applied N, P, or K. In nonlimed soil, biomass and sugar yields decreased with high N in the presence of low P‐K, but not with high P or K. This suggests an acidity ✕ P and/or K interaction related to toxicity of soil Mn and/or Al. In the limed soil the maximum dry biomass and sugar yields occurred with 180‐90‐120 (1981) or 90‐90‐120 (1982) kg ha−1 N‐P‐K, however yields from some treatments with lower levels of N, P, or K were often not significantly different at the 0.05 level. Inherent soil acidity and related Mg deficiency must be corrected to obtain maximum response of sweet sorghum to fertilization in Wynnville and associated soils of the Cumberland Plateau region.