Changes in nitrogen isotopic compositions during composting of cattle feedlot manure: Effects of bedding material type

Temporal changes in δ 15N of cattle feedlot manure during its composting with either rice hull (RHM) or sawdust (SDM) as bedding materials were investigated. Regardless of the bedding material used, the δ 15N of total N in the manure increased sharply from +7.6‰ to +9.9‰ and from +11.4‰ to +14.3‰, respectively, in RHM or SDM, within 10 days from the commencement of composting. Such increases could be attributed primarily to N loss via NH 3 volatilization and denitrification based on the very high δ 15N values (greater than +20‰) of NH 4 + and NO 3 - in the co-composted manure. The δ 15N of total N in RHM was substantially lower (by more than 3‰) than that in SDM, suggesting that the δ 15N of the composted manure was affected not only by N loss but also by the type of bedding material used. Specifically, the higher N concentration in the rice hull than in the saw dust could lead to a greater 15N isotope dilution.