Nitrous oxide emission from feedlot manure and green waste compost applied to Vertisols

Application of feedlot manure (FLM) to cropping and grazing soils could provide a valuable N nutrient resource. However, because of its high but variable N concentration, FLM has the potential for environmental pollution of water bodies and N2O emission to the atmosphere. As a potential management tool, we utilised the low-nutrient green waste compost (GWC) to assess its effectiveness in regulating N release and the amount of N2O emission from two Vertisols when both FLM and GWC were applied together. Cumulative soil N2O emission over 32 weeks at 24A degrees C and field capacity (70% water-filled pore space) for a black Vertisol (Udic Paleustert) was 45 mg N2O m(-2) from unamended soil. This increased to 274 mg N2O m(-2) when FLM was applied at 1 kg m(-2) and to 403 mg N2O m(-2) at 2 kg m(-2). In contrast, the emissions of 60 mg N2O m(-2) when the soil was amended with GWC 1 kg m(-2) and 48 mg N2O m(-2) at 2 kg m(-2) were not significantly greater than the unamended soil. Emission from a mixture of FLM and GWC applied in equal amounts (0.5 kg m(-2)) was 106 mg N2O m(-2) and FLM applied at 0.5 kg m(-2) and GWC at 1.5 kg GWC m(-2) was 117 mg N2O m(-2). Although cumulative N2O emissions from an unamended grey Vertisol (Typic Chromustert) were only slightly higher than black Vertisol (57 mg N2O m(-2)), FLM application at 1 kg m(-2) increased N2O emissions by 14 times (792 mg N2O m(-2)) and at 2 kg m(-2) application by 22 times (1260 mg N2O m(-2)). Application of GWC did not significantly increase N2O emission (99 mg N2O m(-2) at 1 kg m(-2) and 65 mg N2O m(-2) at 2 kg m(-2)) above the unamended soil. As observed for the black Vertisol, a mixture of FLM (0.5 kg m(-2)) and GWC (0.5 or 1.5 kg m(-2)) reduced N2O emission by > 50% of that from the FLM alone, most likely by reducing the amount of mineral N (NH (4) (+) -N and NO (3) (-) -N) in the soil, as mineral N in soil and the N2O emission were closely correlated.