Cover crop impacts on soil quality during Miscanthus x giganteus establishment in central Iowa

Abstract

<p>The primary goal of this thesis was to create a baseline for soil conserving Miscanthus establishment in the U.S. Since Miscanthus production is expected to occur on marginal lands with significant erosion potential, we focused our attention on soil quality indicators. The hypotheses of this study were to examine Miscanthus establishment with companion crops by studying: 1) morphological and hydrological soil parameters (soil bulk density, soil aggregate stability, and steady-state infiltration) and 2) percent soil surface cover via photogrammetry (live plant, mulch, and bare soil).</p> <p>Treatments were Miscanthus (Miscanthus x giganteus), rye (Secale cereale), oat (Avena sativa), crimson clover (Trifolium incarnatum), and white clover (Trifolium repens). Five treatments, a control and Miscanthus with a companion crop, were studied in a randomized complete block design on a Webster soil (fine-loamy, mixed, superactive, mesic Typic Endoaquoll) in central Iowa. Measurements began in the 2nd and 3rd growing seasons after Miscanthus transplanting. Morphological soil samples were taken once annually, and hydrological and percent cover were taken monthly throughout the growing seasons. Treatments significantly (p > 0.05) impacted the 1.00 mm (p > 0.0099), 0.50 mm (p > 0.0039), and 0.25 mm (p > 0.0054) aggregate size fractions. Tukey mean comparisons between treatments for 1.00, 0.50, and 0.25 mm aggregate size fractions revealed rye and oat companion crops in all significant comparisons. A temporal effect on intermediate aggregate size fractions showed increased mean weight diameter from 2010 to 2011. Soil bulk density, steady-state infiltration, and all three percent cover parameters were not impacted by treatments. Mulch percent cover was impacted by treatment*month, however this interaction merely suggests treatments impact mulch cover in some months and not others.</p> <p>Changes in the 1.00, 0.50, and 0.25 mm aggregate size fractions indicate changes in the foundation of aggregate stability. Over time these changes influenced by companion crop and Miscanthus treatments could reduce soil bulk density and increase steady-state infiltration. Improvements to soil structure and porosity directly impact soil resistance to erosive events such as intense precipitation. By understanding soil physical parameters and processes, better management decisions can be made about producing bioenergy crops on highly erodible lands.</p>