Soil Contamination of Grass Biomass Hay: Measurements and Implications

Abstract

A large area of unutilized or underutilized marginal land in the northeastern USA, some of which currently produce a mature hay crop for use as mulch, is potentially suitable for bioenergy crop production. Mature-mixed grass hay bales (n = 1980) were sampled across New York in late summer and fall of 2011 and 2012 from 65 farms. Chemical analysis of 19 parameters, including gross calorific value, fiber, and elemental analyses, was conducted on the samples. In addition, 156 soil samples, representing 67 soil types, were analyzed for 12 to 14 parameters, using two different extraction procedures. Results indicate that hay composition is extremely variable among bales, and that much of the variation is due to soil contamination. Soil contamination reduced energy content of hay, a reduction best estimated from ash content of the hay. Standard plant analyses of contaminated hay samples determine total elemental content, but the same analyses only partially extract soil elements. A subset of samples showed that fiber analysis of soil-contaminated hay is problematic, with results impacted greatly by soil type and gravimetric filtration method. Aluminum, because of its low plant uptake potential, its high concentration in most soils, and its relatively moderate range in concentration across soil types compared to other soil elemental predictors, is the best indicator of soil contamination of biomass when the soil type is unknown. Evaluation of herbaceous plants for bioenergy parameters should include ash and Al analysis to assess soil contamination, which could significantly bias other compositional analyses.