PS5-7. In-situ Evaluation of Forage Grown in Soil Amended with Manure from Cattle Fed Different Types of Biochar.

Abstract Biochar is produced by pyrolyzing organic materials - primarily agricultural or forestry waste - at high temperatures (400-800 °C) under low-oxygen conditions, yielding a carbon-rich product with a large surface area. Biochar has been investigated as a soil amendment to improve soil health and promote plant growth; however, its incorporation into soil can be labor-intensive. As biochar passes through the gastrointestinal tract mainly intact, there is potential to feed it to grazing cattle, which then inoculate it with rumen microbes and deposit it with manure. However, there remains a deficit of research investigating the effects of biochar-amended manure on plant growth and quality for ruminant animals. The objective of this study was to evaluate how manure from cattle fed different types of biochar affects forage growth and rumen degradability. Beef steers (n = 5) consuming ad libitum forage were provided one of five treatments at 1.6% of the previous 3-d intake for 7-d: no biochar (CON); and biochar derived from pecan shells (PEC), bamboo (BB), mixed brush (MB), or pine (PN). Manure was collected from each steer over a 48-h period and mixed with native soil at a 0.02:1 ratio. Rye grass was grown in manure/soil mixtures, in soil treated with organic fertilizers (ORG), or soil without manure or organic fertilizers (SOL) for seven treatments total. Rye grass was harvested at 2.5 cm (grazing length), dried, ground, and ruminally incubated in cannulated beef steers (n = 3, 625.2 ± 97.9 kg) consuming ad libitum hay and receiving CSM (0.5 kg/d) in reverse order for 0, 4, 6, 12, 24, 48, and 72 h. Upon removal, bags were rinsed and dried at 55 °C for 96 h then air-equilibrated for 24 h to determine partial dry matter (PDM). Dry yields of rye grass were affected by treatment such that there were significant differences (P ≤ 0.05) between yields for biochar/manure-based treatments (25.9 ± 4.57 g) versus SOL (6.83 ± 2.56 g) and ORG (4.33 ± 1.63 g), but there were no differences across the various biochar/manure treatments or for SOL versus ORG. There were not adequate quantities of rye grass from SOL or ORG for in situ analysis. Across biochar/manure treatments, there were no differences in fractions of rye grass categorized as Instantly Degradable (18.1%; P = 0.98), Potentially Degradable (70.3%; P = 0.42), or Undegradable (11.6%; P = 0.13). Treatment also did not affect rate of degradability (kd; P = 0.30), which averaged 5.3%/h, or partial DM degradability (PDMD; P = 0.31). However, there were numerical differences in PDMD that may translate to biologically meaningful differences - i.e., MBB had lower PDMD (42.8%) than CON (50.1%) which was lower than MBP (58.2%), MBM (59.6%), and MBS (60.0%). These findings suggest that manure enhances rye grass yield and the presence of biochar within manure may enhance rumen degradability.