Modeling Biomass Production of Sweet Sorghum

Sweet sorghum [Sorghum bicolor (L.) Moench] is a leading contender in biomass production energy systems because of its high biomass yield, high percentage of easily fermentable sugars and combustible organics, tolerance to water stress, and low fertilizer requirements. However, scientific information on growth factors is limited and precludes establishing valid interrelationships for predicting biomass production. With that objective in mind, a field study on sweet sorghum was conducted to investigate the relationships among stalk length, leaf area index, and dry biomass. Cultivar Mer 71-7 was planted using two row configurations of single rows on 71-cm centers and double rows on 142 cm centers on Pahokee muck (Lithic Medisaprist). The spacing between double rows was 30 cm. Leaf area, stalk length, and dry leaf biomass were periodically monitored. Six equations involving leaf area were developed. The first equation estimated leaf area (A) from the length of leaf (L) and the maximum width of leaf (W), i.e., A = 0.741 LW. The second equation estimated leaf area from the length of leaf alone, i.e., A = 0.083 L². The third equation estimated leaf area per stalk (Y) from stalk length (X), i.e., Y = Exp[X/(2.106 + 0.093X + 0.629X × 10⁻⁴X²)]. The fourth equation showed the dry leaf biomass accumulation (DAR) as a function of time (T), i.e., DAR = 0.764 × 10⁻³T⁰.⁴⁸¹. The fifth equation predicted the leaf dry biomass (LOB) from DAR and leaf area index (LAI), i.e., LDB = DAR × LAI. The sixth equation estimated total dry biomass (TDB) from LDB and ratio of dry leaf biomass to total dry biomass (DBPL), i.e., TDB = LDB/DBPL. The relationships developed appeared to be useful for estimating sweet sorghum biomass. However, further testing is needed to evaluate the effects of diverse growing conditions and varieties and to determine the utility of the method in comparison to determining the mean plant weights and populations.