Soil active carbon as an indicator of nitrous oxide loss potential

Abstract

Improving nitrogen use efficiency in agriculture is crucial to mitigating the greenhouse gas emissions caused by the use of fertilisers whilst increasing production to support the needs of a growing population. Understanding nutrient cycling in agricultural soils informs better land management strategies to achieve these aims. To date, the measurement of key soil properties and estimation of process rates such as nitrogen mineralisation has involved a high cost of labour, equipment and laboratory analysis. A gap exists for simple methods which can be used in the field to quickly assess vital indicators of soil quality and processes.This study tested the viability of a field kit to measure the active or labile soil carbon fraction as permanganate oxidisable carbon and determine its relationship to key soil processes, including denitrification. Fifteen agricultural soils contrasted by land use history and management were incubated in the laboratory at three different water levels, with and without the addition of potassium nitrate, for 100 days.Carbon dioxide and nitrous oxide gas fluxes were calculated at eight intervals over the 100 days. Active carbon and mineral nitrogen availability was determined at days 0, 28 and 100. Resistant C and N were measured from the same composite samples using sodium hypochlorite to enable the fractionation of recalcitrant pools. iv