The influence of controlled release fertilisers and the form of applied fertiliser nitrogen on nitrous oxide emissions from an andosol

A laboratory experiment was conducted to determine whether applying controlled release nitrogen fertilisers could reduce nitrous oxide emissions from an andosol maintained at different water contents, compared with applying standard nitrogen fertiliser. The effect of the form of N applied (NH4-N or NO3-N) was also investigated. Soil was collected from an arable field and sub-samples were treated with controlled release or standard fertiliser, applied at a rate of 200 mug N g(-1) dry soil either as NH4+ or NO3-. The soils were maintained at 40%, 55%, 70% or 85% water filled pore space (WFPS) and incubated at 25 degreesC for 50 days. Gas samples were collected and analysed every 3 - 4 days and soil samples were analysed on five occasions during the incubation. Emissions of N2O were much greater from ammonium sulphate than from calcium nitrate fertiliser, indicating that nitrification was the main source of the N2O. Emissions at 85% WFPS were greater than at the lower water contents in all treatments. The use of controlled release NH4-N fertilisers reduced and delayed the maximum peak of emissions, but at 55% and 70% WFPS this did not always result in lower total emissions. Emissions from the controlled release NO3-N fertiliser were very low, but only significantly lower than from standard NO3-N fertiliser at water contents below 85% WFPS. The results demonstrate that choosing the appropriate form of fertiliser in relation to expected soil moisture could significantly reduce N2O emissions. Applying the fertiliser in a controlled-release form could further reduce emissions by reducing the length of time that fertiliser nitrogen is present in the soil and available for nitrification or denitrification.