Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2004
Publication Date: 6/1/2005
Citation: Griffin, T.S., He, Z., Honeycutt, C.W. 2005. Manure composition affects net transformation of nitrogen from dairy manure. Plant and Soil Journal. v. 27. p. 29-38. Interpretive Summary: The amount of nitrogen (N) available from dairy manure is usually estimated by assuming that all of the ammonium N and a portion of the organic N will be transformed to nitrate during the growing season. However, this approach does not take into account large differences in manure composition, including the possibility that fibrous material might result in N being tied up rather than released. We looked at the connection between fibrous carbon (C) and ammonium in nine dairy manures, for 176 days after stirring them into two different soils. Even though all of the manures contained ammonium at the time of application, some resulted in accumulation of nitrate and some tied up N. We found that the ratio of fibrous C to ammonium was strongly related to the rate of nitrate formation at early and middle stages of the incubation, and to the total amount of nitrate formed by the end of the incubation. This is a promising approach for refining our estimates of manure N availability, taking into account differences between dairy manures.
Technical Abstract: The plant available nitrogen (PAN) content of dairy manure is commonly calculated using concentration and availability coefficients for organic nitrogen (N) and ammonium N (NH4), but the carbon (C) fraction of the manure also influences the availability of N over time. We evaluated the interactive effect of manure C and N from nine dairy manures during a 176 d aerobic incubation. All of the manures had appreciable NH4 content, and varied widely in fiberous C. The incubation was conducted using two soils (sandy loam and silt loam) at 25oC and 60% water-filled pore space. There were clear differences in nitrate (NO3) accumulation over time, including manures that resulted in net nitrification and net immobilization. For both soils, the rate of nitrification at 7 and 56 d after application, and the amount of NO3 accumulated at the end of the incubation (176 d) were closely tied to the ratio of neutral detergent fiber (NDF) to NH4, demonstrating that recalcitrant C controls the availability of inorganic N. The addition of manure C also resulted in significant net immobilization, compared to addition of mineral N fertilizer alone. These studies demonstrate that increased understanding of manure C and N interactions may lead to improved prediction of manure PAN.