Characterizing water holding capacity and total solids of manure-bedding mixtures

Beef producers in the Midwestern United States, driven by environmental regulations, have shown an increased interest in solid manure bedded-pack systems (BPS). BPSs can be an economically and environmentally sound alternative for animal housing, and an efficient manure management alternative for beef production systems, as manure is stored and handled as a solid and eliminates the need for runoff control. Bedding materials are used to absorb excess moisture, improve animal comfort and reduce negative environmental impacts from these livestock facilities. Various biomass types can be used as potential bedding material, such as corn stover, wheat straw and soybean stover. When choosing a bedding material, a number of factors must be considered. Initial moisture content and particle size distribution play an important role in selecting a media for bedding. However, the most important design criteria to consider is the water holding capacity (WHC) of the material and the total solids (TS) of the manure-bedding mixture at saturation. WHC is the moisture a material can retain at the point of saturation. The main objective of this experimental study was to characterize properties of manure-bedding mixtures that might be found in BPS. These property characterizations included evaluating the impact of several bedding materials and manure TS mixtures on WHC. Seven organic bedding materials were evaluated (corn cobs, corn stover, pine shavings, switchgrass, miscanthus, wheat straw, and soybean stover) and they were characterized for their particle size distribution, bulk density and initial total solids. The first goal of this project was to develop a Standard Operating Procedure (SOP) for measuring WHC with manure addition and the minimum time needed to reach that value. Furthermore, the effect on bedding WHC when beef manure is used in place of water for substrate was determined. To meet this objective, the WHC was evaluated using beef manure at 5 TS levels total solids contents (0%, 4%, 8%, 12% and 16% TS). An SOP for measuring WHC with manure addition was developed, based on a standard method for non-manure systems in literature. The results of this study, WHC increased significantly with manure addition. Furthermore, the outcomes of this work indicated that, for the majority of the bedding materials tested, high TS manure slurry (12% or 16%) resulted in lower WHC than did 4% and 8% TS slurry, but all are substantially greater than the baseline WHC without manure slurry addition. All bedding materials WHCn ranged from 2.4 to 8.8 g H2O (g of dry mixture)-1. These values were for soybean stover at 16% manure TS and corn stover at 4% manure TS, respectively. If using corn stover and wheat straw the total bedding required per animal per day ranged from 0.6 to 6.6 kg. Compared to current bedding mass recommendations in Illinois the amount of bedding suggested for use in BPS was up to 90% lower, while the total manure-bedding mixture storage volume were greater or lower, depending on the bedding materials bulk density