Achievement of the target set by the Energy Independence and Security Act (EISA) of 2007 to produce 60 billion liters (16 billion gallons) of cellulosic biofuels annually in the United States by 2022 will require around 200 million tons (dry) of cellulosic feedstocks each year [1
]. The fact that the cellulosic feedstocks are harvested within a short span of time, usually between 1–2 months, and are required by the biorefineries over the whole year necessitates their effective and efficient storage. Different types of cellulosic feedstocks, including agricultural residues, such as corn stover and soybean (Glycine max
L. Merr.) straw, and energy crops, such as switchgrass (Panicum virgatum
) and miscanthus (Miscanthus
), are being stored in different ways, such as bales, piles and silos, in different parts of the United States. Collection of cellulosic biomass as bales in a single-pass is one of the options for in-field biomass collection. The single-pass collection method is advantageous compared to the multi-pass method due to their reduced ash content, and the biomass collection as bales has advantage over bulk collection due to their enhanced bulk density. In addition to these notable advantages, single-pass bales have some disadvantages, primarily the inability to control moisture content prior to harvest. This may adversely affect the bale storage characteristics. Therefore, this study focuses on the storage characteristics of large square single-pass corn stover bales in Iowa, one of the principal, Midwestern corn growing states.
Most related previous studies [2
] were based on the storage of multi-pass bales formed with different types of biomass under different conditions and at different geographical locations. Blunk et al.
] found the dry matter loss (DML) of large square rice straw bales stored under different indoor and outdoor storage treatments for a year to be in the range of 10 to 60%. Huhnke [3
] found the DML of large round multi-pass wheat hay bales stored under different conditions (storage inside barn and several combinations of outdoor storage) for 10 months in Chickasha, Oklahoma to be in the range of 6.4 to 19.3%. Sanderson et al.
] found the storage DML of large round bales of switchgrass stored either outdoor unprotected above grass sod or gravel pad, or indoor above concrete for 6 and 12 months in Stephenville, Texas to be in the range of 0 to 13%. Shinners [5
] investigated the storage characteristics of large square alfalfa bales under treatments with propionic acid, bacterial inoculant and formation of 0.08 or 0.12 m diameter vent hole through the bale center, and found that the storage DML didn’t significantly change under any treatment, when compared to the control bales. Shinners et al.
] studied the wet and dry storage characteristics of corn stover bales stored for around 9 months, at the University of Wisconsin Arlington Agricultural Research Station. They found the storage DML for wet tube-wrapped, and dry indoor and outdoor stored bales to be 2.4, 3.3 and 18.1%, respectively. Shinners et al.
] investigated the storage characteristics, including DML, of large round and square alfalfa bales stored as individually and tube-wrapped. They found that the average DML of bales with initial moisture in the ranges of 30 to 40 and 40 to 55%wb
were 3.5 and 2.3%, respectively. Shinners et al.
] studied the effects of wrap types and storage methods on the preservation of large round alfalfa bales stored for 5 to 11 months, and found the DML for outdoor stored bales with different wrap types to be between 7.2 and 19.5%. Additionally, they found the DML of outdoor stored plastic covered and indoor stored bales to be 4.5 and 1.9%, respectively.
All of the studies discussed so far were based on the storage of multi-pass bales, but to meet the biorefineries’ quality demands, alternative methods for feedstock storage need to be evaluated. Single-pass bales have advantages over multi-pass bales in that they have significantly lower ash levels, but to date, storage characteristics of single-pass bales have not been determined. The objective of this study was to investigate the storage characteristics of low and high moisture, single-pass corn stover bales stored either outdoors on wooden pallets and under two different types of cover [tarp or a breathable film (brand name Tyvek) through which water vapor can pass, but which does not allow liquid water to penetrate], or on a concrete floor within a metal building for short (3 months) or long (9 months) durations. The DML, changes in moisture, biomass composition (as determined by fiber and ultimate analyses and heating values during storage were investigated.