Biomass Production From Sweet Sorghum Under Different Soil Type and Nitrogen Rate.

Due to (1) the high cost and negative environmental impact of such nutrients, (2) the scale of energy needed to face worldwide demand, (3) the need to make the biofuel production system sustainable and profitable, it is very important to study how to make biofuel plants more efficient and how to create an environment that better suits their production. Up to today, very little research has been done to test how nitrogen fertilization affects the production of ethanol from sweet sorghum grown in the field.  To provide data on these issues, 7 nitrogen rates were applied to sorghum planted in 3 types of soil. As the stalk is the organ from which the juice is squeezed to produce ethanol, any effects on the stalk yield will also affect the ethanol yield. The distribution of the total biomass between the leaves and the stalk is highly affected by the nitrogen rates applied (P=0.01)   and also by the soil type (P=0.0005). There is a highly significant effect of the soil type on both the fresh and the dried biomass yield of sweet sorghum (P<.0001). The N rate did not significantly affect either the fresh biomass yield (P=0.06) or the dried biomass yield (P=0.27). A highly significant difference was found among soil types when analyzing the stalk yield (P<.0001) and N rates (P=0.02). The water content in sorghum stalk is highly affected by the soil type (P<.0001) whereas the N rate has no effect (P=0.89). The highest water content was obtained in the clay soil (74%) whereas the loam has the lowest value (70%). The amount of water accumulated in sorghum stalk was related to the soil type (P<.0001) and to the N rate applied (P=0.01). So, using only the total biomass to access the impact of N fertilization on sweet sorghum production for biofuel purposes is a misleading method. Indeed, unlike what many people think, although sweet sorghum is N efficient, in order to maximize feedstock yield while using it for biofuel production, great attention needs to be paid to the soil type and N fertilization.