Establishment of Short-Rotation Willow Crop on Claypan Soil Landscapes.

<align="center">ABSTRACT

Short-rotation willow crop (SRWC) is being considered as a cellulosic alternative biofuel in the United States. While willow (Salix sachalinensis) naturally grows predominately on floodplains and stream banks, the objective of this study was to determine if establishment and production of SRWC for biofuel could be adapted to upland claypan soil landscapes of central Missouri.  Three plot repetitions, where each plot contained summit, backslope, and footslope landscape positions -defined by topsoil depth to claypan layer- were planted in 2011 with cuttings at a density of 1.26 plants per square meter. To determine establishment, yearly mortality assessments were conducted as well as destructive sampling to determine yield.  In 2011 plots experienced droughty conditions and heavy weed pressure. Willow mortality averaged 35% across all landscape positions, with the highest mortality found in the summit position. In the spring of 2012 dead willows were replanted with new cuttings.  Severe drought conditions from June through late August of 2012 resulted in competition from drought-tolerant weeds contributing to extensive mortality of the SRWC.   Nearly all 2012 replant cuttings died.  Survival, averaged across plots, was 17, 51, and 54% for summit, backslope, and footslope positions, respectively. Oven-dry biomass yield of available harvest after two growing seasons (one year growth after coppice), was highest for the footslope position (0.14Mg ha^-1), lower for the backslope position (0.13 Mg ha^-1), and negligible for the summit position (0.017 Mg ha^-1). These yields were <15% of comparable SRWC studies. Low precipitation, extreme heat, weed pressure, and landscape position are all stress factors that contributed to the unsuccessful establishment of SRWC on this claypan soil. Without irrigation the results of this two-year study suggest the risk is high for establishing a SRWC on a claypan landscape.