Effect of cultivation method of Panicum virgatum and soil organic matter content on the biomass yield

The relevance of the research lies in tackling an important problem: mitigating anthropogenic environmental impacts. This is achieved by using the biomass of energy crops. The article investigates the impact of sole, strip and mixed crops of switchgrass (Panicum virgatum L.) with red clover (Trifolium pratense L.) on soil organic matter (SOM) content and biomass yield. This enables reduction of the anthropogenic load on agrophytocenoses, improves ecological production as well as increases the yield of the main component switchgrass. The objectives of this experiment were to evaluate the dynamics of the SOM content in energy crops of switchgrass and to determine the impact of SOM content on switchgrass yield. The experiment involved field trials with the introduced switchgrass cultivar 'Cave-in-Rock' during the period of 2011-2018. The experiment was aimed at determining the dynamics of SOM content, the yield level of switchgrass biomass depending on the type of sowing under the conditions of the forest-steppe. The studied factors are experimental years (2011-2018) and three switchgrass sowing methods: sole crop, strip switchgrass with red clover (strip crop) and mixed switchgrass with red clover (mixed crop). In the experiment, general and special methods were used: method of scientific research in agronomy; laboratory methods to determine SOM content and dry matter content in biomass; quantitative-weight method to establish switchgrass yield. The results of the study show that red clover in strip crops survived for 3-4 years and acting as bioherbicides in the row-spacing of switchgrass had a protective function, preventing from weeds germinating. Subsequently, legume aftereffect is observed for 2-3 years after sowing. In general, switchgrass growing in strip crop, in comparison with sole crop, provides the increase (by 0.02-0.045%) of SOM content, which results in the increase (by 0.10-0.13 kg m-2) of dry biomass yield. This is confirmed by a strong correlation between the indicators: the correlation coefficient in strip crop was r = 0.93, in mixed crop - r = 0.92 and in sole crop - r = 0.91 (p < 0.05). Thus, the cultivation of switchgrass by the proposed methods will improve the environment and produce sustainable biomass for the production of biofuels. In the long run, this can reduce the energy dependence of the developing countries, including Ukraine.