Effects of biochar on yield and nitrogen nutrition of warm-season biomass grasse

Majority of the global energy supply depends on fossil fuel sources such as coal, petroleum, and natural gas. Energy production by these sources has significant environmental impacts such as air and water pollution, global warming, and environmental degradation. These issues have become the driving forces of searching for cleaner burning fuels. Bioenergy is a form of renewable energy, produced from plant and animal based materials which are called biomass feedstocks. Switchgrass (Panicum virgatum L.), Big bluestem (Andropogon gerardii Vitman), and Indian grass ( Sorghastrum nutans (L.) Nash) are perennial (C4) warm-season grasses native to North America with great potential as energy crops. They are highly adapted to growing under diverse growing conditions with low inputs, particularly on marginal lands. Improving water holding capacity and soil fertility of marginal lands could potentially increase biomass yield of energy crops on marginal lands. Biochar is a carbon-rich solid material produced by thermal decomposition of biomass under limited supply of oxygen (O2), and at relatively low temperatures (<700 °C) that can be applied as an organic soil amendment, for improving water and nutrient retention in marginal sandy soils. The hypothesis tested was N fertilization with biochar application to low fertile soils would increase biomass production for switchgrass, big bluestem, and Indian grass. I conducted two greenhouse experiments one in 2014 and one in 2015, to evaluate the effects of biochar amendments with different N rates on growth and biomass production of warm-season grasses and water holding capacity of the potting media. The experimental design was a randomized complete block design (RCBD) with four blocks. In the first study, potting media was prepared by homogenously mixing PromixRTM starter mix and sand at the volume ratio of 3:1, and 0, 5, 20, 35 Mg ha-1 rates of biochar. In the second study, the potting mix and sand (1:9 by volume) were mixed to create sandy marginal soils found along floodplains of major rivers. Four nitrogen (NH4NO3 fertilizer) application rates (0, 60, 120, 180 kg N ha-1) were used in both experiments. Above and belowground biomass yield, net photosynthetic rate, and water holding capacity of the potting media were measured in both years. Biochar and nitrogen interactions were not significant with relative to aboveground biomass and photosynthetic rate for any species in both years. However, interaction effect was significant for belowground biomass of switchgrass in 2014 where 20 Mg ha-1 biochar and 60 kg N ha-1 resulted the highest belowground biomass. Root:shoot ratio of both switchgrass and Indian grass declined significantly with increasing N rates in 2015. Water holding capacity of the potting media did not increase with increasing rates of biochar in both media, however there was a positive trend observed in the medium with 90% sand for volumetric water content at field capacity with increasing biochar rates. Further studies should include long-term experimentation in marginal sandy soils to explore the benefits of using biochar for herbaceous biomass crop production at field and regional scale.