Djr Cherney

Soil Contamination of Grass Biomass Hay: Measurements and Implications

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.

Biomass Yield and Composition of Switchgrass Bales on Marginal Land as Influenced by Harvest Management Scheme

Switchgrass (Panicum virgatum L.) is well suited to marginal croplands, but is difficult to manage sustainably both for maximum yield and optimal biomass composition. Quality can be improved by overwintering switchgrass in the field, but more information is needed on amount and consistency of yield recovery in spring. Two cultivars of switchgrass were sown on separate fields in Freeville, NY, and mowed and baled in late fall (FALL), mowed in fall and baled in spring (WINTER), or mowed and baled in spring (SPRING), using conventional field harvesting equipment. Samples were collected for analysis of plant morphological components and for determining the influence of harvest stubble height on yield and composition. Recovery of FALL biomass yields the following spring ranged from 52 to 82% and was related to both total winter snowfall and to the spring date when soil was dry enough to allow equipment traffic. Approximately 1% of dry matter yield was left in the field for each centimeter of stubble height following mowing. Bale moisture content was very low in spring, averaging 7.3%, but was much more variable and higher in the fall, averaging 22% for “Cave-in-Rock”. Inflorescence and leaf blade were the primary morphological components lost in standing switchgrass over winter. The SPRING treatment can be mowed and baled on the same day without other field operations and has higher quality than WINTER, with no consistent yield advantage for either spring baling treatment. The large and variable yield loss due to overwintering switchgrass in the field makes the practice questionable.