Potential of Bioenergy Cropping Systems for Soil Organic Matter Restoration, Potassium and Magnesium Recycling, and Water Quality Protection.

Periodic oil price spikes, concerns about the ever-growing world consumption of crude oil and its environmental collateral impact, the quest for mitigating global climate change, have triggered among agriculturalists a compelling interest in alternative, renewable sources of energy. Research has mostly focused on genetics, fertilization requirements, soil organic carbon and soil structural properties responses, weed control, and growth and development of warm-season perennial grasses and short-rotation woody crops. The effects of these non-traditional cropping systems on soil fertility properties and nitrate scavenging have not been fully investigated. Here, we studied the mid-term impact, on selected soil fertility properties, of the change from a conventional small grain cereal land-use to conservation corn-soybean, C₄ perennial grass, and short-rotation woody crop land-uses. For the first time, these three distinct land-uses are evaluated together in the same experimental field for soil organic matter, total nitrogen, residual nitrates, available phosphorus, exchangeable potassium and magnesium, and cation exchange capacity. Seven years after the establishment of the new cropping systems, we observed that SOM significantly increased by 17% in the 0-15 cm layer of soils cultivated with switchgrass or Miscanthus, and average residual nitrate levels significantly dropped by 55%, 75%, 82%, and 88% in the plough horizon of the corn-soybean rotation, switchgrass, Miscanthus, and willow cropping systems, respectively. Furthermore, soil exchangeable K decreased in the corn-soybean rotation and switchgrass plots by 16% and 8%, respectively; it remained constant in Miscanthus plots, but increased by 12% in willow plots. Average soil exchangeable Mg in the plough horizon significantly increased by 17% in the willow cropping system, while it remained similar to the 2008-levels in the corn-soybean, switchgrass, and Miscanthus cropping systems. This study highlights the ecosystem services provided by switchgrass, Miscanthus, and willow cropping systems: restoration of organic matter, protection of water quality, and K and Mg recycling.