Energy Use Efficiency of Biogas Production Depended on Energy Crops, Nitrogen Fertilization Level, and Cutting System
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Energy Use Efficiency of Biogas Production Depended on Energy Crops, Nitrogen Fertilization Level, and Cutting System Marta Oleszek 1
&
Mariusz Matyka 2
# The Author(s) 2020
Abstract The paper evaluates the relation between energy input (Ei) and output (Eo) of biogas production from six energy crops: maize, sorghum, sunflower, triticale, reed canary grass (RCG), and Virginia mallow (VM), cultivated in three different nitrogen fertilization levels. Furthermore, in the case of RCG, the impact of cutting system was examined. The results showed that raised N fertilization dose (in the range of 40–120 kg ha−1 and 80–160 kg ha−1, depending on the crops) increased biomass yield and methane productivity (MP) but simultaneously caused also the increase in Ei. Nonetheless, the application of higher N doses did not cause drastic decrease in energy use efficiency (EUE). The Ei was significantly lower for perennials than for annual crops. For this reason, EUE for RCG harvested in two cuts (5.0–5.2 GJ GJ−1) was close to EUE for maize (5.7–6.8 GJ GJ−1), despite the much lower MP (2027–2903 m3 ha−1 and 4409–5692 m3 ha−1, respectively) and Eo (73–105 GJ ha−1 and 159–205 GJ ha−1, respectively). Furthermore, the collection of RCG in more than two cuts turned out to be unjustified, due to increase in Ei and, simultaneously, decrease in MP. Keywords Bioenergy . RCG . Sida . EUE . Methane . Fermentation . Digestion . Balance
Introduction One of the main requirements for energy crop cultivation is the lack of the competition with food and feed production in arable land areas [1]. For this reason, high biomass yield of properly selected species, and thus, high productivity of energy from unit of cultivation area, is very important. In addition to the right selection of species, appropriate agrotechnical measures are applied, such as increased fertilization doses or more frequent mowing of perennials and grasses. All these measures, however, result in an increase in energy input on cultivation, which in consequence may result in lower energy efficiency. However, we should strive to ensure that the energy input (Ei) and energy output (Eo) ratio, i.e., the so-called energy use efficiency (EUE), is as high as possible.
* Marta Oleszek [email protected] 1
Institute of Agrophysics, Polish Academy of Sciences, Doświadczalna 4, 20-290 Lublin, Poland
2
Institute of Soil Sciences and Plant Cultivation, State Research Institute, Czartoryskich 8, 24-100 Puławy, Poland
At present, there is no complete assessment of the energy efficiency of biogas production from the tested species, which would justify the use of higher doses of nitrogen fertilizers [2]. Jankowski et al. [3] even assessed energy efficiency of biogas production from crops grown in Poland, but Eo was calculated based on calorific value of biomass, not on its biogas yield. They also did not evaluate neither the impact of various nitrogen fertilization levels, nor cutting frequency. Some studies on the influence of nitrogen fertilization on the energy efficiency of biomass
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