Nitrous oxide concentrations in an Andisol profile and emissions to the atmosphere as influenced by the application of nitrogen fertilizers and manure
A field experiment was conducted to determine N2O concentrations in the soil profile and emissions as influenced by the application of N fertilizers and manure in a typical Japanese Andisol, which had been under a rotation of oat and carrot for the previous 3 years. The treatments include ammonium sulphate (AS), controlled-release fertilizer (CRF) and cattle manure (CM) in addition to a control; all the fertilizers were applied either at 150 kg N ha–1 or 300 kg N ha–1 at the time of sowing carrot. N2O emissions from the soil surface were measured with closed-chamber techniques, while N2O concentrations in the soil profile were measured using stainless steel sampling probes inserted into the soil at depths of 10, 20, 40, 60, 80 and 100 cm. Moreover, soil water potential, soil temperature and rainfall data were also recorded. The results indicated that N2O concentrations in the soil profile were always greater than in the atmosphere, ranging from 0.36 µl N2O-N l–1 to 5.3 µl N2O-N l–1. The relatively large accumulation of N2O in the lower profiles may be a significant source for N2O flux. Taking the changes of soil mineral N into consideration, most emissions of N2O were probably produced from nitrification. The accumulation of N2O in the soil profile and emissions to the atmosphere were differently influenced by the amendments of N fertilizers and manure, being consistently higher in CRF than in CM and AS treatments at the corresponding application rates, but no significant difference existed with respect to the various N sources.
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