Productivity and energy balance of maize and sorghum grown for biogas in a large-area farm in Poland: An 11-year field experiment
K. Jankowski, Bogdan Dubis, Mateusz Sokólski, Dariusz Załuski, Piotr Bórawski, W. Szempliński
Abstract
The biomass yield and energy efficiency of maize and sweet sorghum were evaluated based on the results of an 11-year experiment conducted in a large-area farm in north-eastern Poland. The demand for energy in the production of maize biomass was estimated at 24.4–25.5 GJ ha−1. Energy consumption in the production of sweet sorghum biomass was 2.8 GJ ha−1 lower on average. Mineral fertilization was the major energy input (72–73 %) in the cultivation of both crops, mainly due to the high energy value of mineral fertilizers (66–71 %) and, to a lesser extent, the demand for energy during fertilizer application. The average maize yields in north-eastern Poland reached 21.7 Mg ha−1 dry matter (DM). The biomass yield of sweet sorghum was 4.0 Mg ha−1 DM lower on average. The variability in sweet sorghum biomass yields was nearly 1.5- to 2-fold higher relative to maize. The energy output of maize biomass ranged from 197 to 290 GJ ha−1 y−1, whereas the average energy output of sorghum biomass was 61 GJ ha−1 lower. The energy gain and the energy efficiency ratio of maize biomass were determined at 172−265 GJ ha−1 and 7.7–11.3, respectively. The above parameters were 58 GJ ha−1 and 14 % lower in sweet sorghum biomass, respectively. In north-eastern Poland, sweet sorghum yields exceeded maize yields, and sweet sorghum was characterized by a more favorable energy balance only in years with above-average precipitation.