Submitted to: American Society of Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 8/2/2003
Publication Date: 11/1/2003
Citation: Griffin, T.S., Honeycutt, C.W., He, Z. 2003. The connection between manure carbon composition and nitrogen availability. American Society of Agronomy Abstracts.
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). 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 day aerobic incubation. All of the manures had appreciable NH4 content (at least 20% of total N), and varied widely in fibrous C. The incubation was conducted using two soils (sandy loam and silt loan) at 25 C and 65% 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 amount of NO3 accumulated at the end of the incubation (176 day) and the net rate of nitrification 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. For manures with different NDF:NH4 ratios were also used in a subsequent 56 day incubation that included 15N pool dilution 7 and 49 day after manure incorporation, to estimate gross rates of mineralization, immobilization, and nitrification. These studies demonstrate that increased understanding of manure C and N interactions may lead to improved prediction of manure PAN.