Abstract
Perennial crops, like switchgrass (Panicum virgatum L.), are important for bioenergy production and long-term carbon sequestration. Biochar, a byproduct of certain bioenergy production processes, is also identified as a potential tool for carbon sequestration and soil quality improvements, especially in marginal soils. Despite the focus on switchgrass, soil health characteristics under switchgrass production for biomass are unclear. This study focused on identifying the effects of four N rates (0, 17, 34, and 67 kg N ha−1) and biochar application (0 and 9 Mg ha−1) in a 3-year switchgrass field study on a silt loam soil. Soil active carbon (AC) and wet aggregate stability (WAS) were the indicators used to assess soil health. Our results indicated a decline in both AC and WAS over the study period, similar to other studies. Wet aggregate stability declined from 32% in 2018 to 15% in 2019. There were some significant differences between treatments, but no defined trends were observed. A decline in AC from 301 mg C kg soil−1 to 267 mg C kg soil−1 was also observed over the three-year period. Nitrogen rate also affected AC in the last year of study. Several possible explanations for the observed changes are proposed; however, a definitive mechanism is still unknown, thus future research is essential to improve our understanding and provide wider acceptance.
Highlights
Biofuels are considered an important component to reach the renewable energy goals of the United States; the sustainability of biofuel crop production remains questionable [1,2,3]
The multiple benefits of biochar make it a potentially attractive tool for sustainable soil health; research far has many contradictions, which may imply the variable nature of biochar and its inability to be applied across multiple different landscapes
Based on the results of our study, application of biochar increased total carbon content of the soil and did not negatively impact the measured soil health indicators, showing its potential to be used as a soil amendment
Summary
Biofuels are considered an important component to reach the renewable energy goals of the United States; the sustainability of biofuel crop production remains questionable [1,2,3]. Since large areas of land will be needed for switchgrass production to meet such goals, it is important to understand its impact on soil health to maintain its sustainability. Evaluation of the sustainability of switchgrass production practices and assessment of soil health using various indicators of soil quality are needed. Soil health or quality can be assessed by making observations and measurements of various soil processes and properties called soil health indicators [7] These indicators can help assess soil health by linking functional relationships of different soil characteristics and correlating their changes with changes in land management and environmental impacts [8]. Soil aggregate stability and active carbon content are key indicators of soil health and the environmental sustainability of various agricultural management practices [9].
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