Effect of a Temporal Carbon Gradient on Nitrogen and Phosphorus Dynamics and Decomposition During Mesophilic Composting

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Excess carbon (C) can immobilize inorganic nitrogen (N) and phosphorus (P) when composting manure and has been used to reduce the moisture content of liquid manure so they can be composted. A mesophilic composting strategy was previously developed and shown to be an effective method to manage liquid manure without the need for excess C. The objective of this study was to determine if a temporal C gradient would sequester more N and P without the need for excess C. The experiment was conducted in bags. All treatments had arctic char manure applied at the same rate (1.28 g N), every 14 days for 112 days. The C source, ground corn stover, was applied in three batch sizes. The 1X treatment applied 70 g of corn stover every 14 days, the 4X treatment applied 280 g of corn stover at days 0 and 56, and the 8X treatment applied 560 g of corn stover once at day 0. All bags had the same amount of C and N added to them by the end of the experiment at a C∶N ratio of 30∶1. As the C to N or P ratio decreased below 20 and 30, respectively, net mineralization occurred, and the time of this occurrence was similar for all C treatments. The concentration of N and P were relatively low until day 91 when NH4‐N and P and day 105 when NO3‐N started to increase, after which point mineralization occurred at a rate of about 60 mg N and 4 mg P/kg mass/day. Because the temporal C gradient was not in phase with mineralization, it was not effective at immobilizing N and P. Spatial separation of high carbon zones through layering manure and the carbon source may be an effective way to maintain a long‐term C gradient and capture leaching N and P while minimizing C inputs.