N2O emissions from low and moderately disturbed pasture soils—field tests of minimal and maximal N supply

Abstract

Rates and patterns of nitrogen transformation differ in divergently managed pasture soils. In pastures with low nutrient inputs, N is utilized efficiently and it is assimilated by plants and soil microorganisms for synthesis of biomass. In more intensive pastures, characterized with higher N inputs, significant amounts of N can be lost from the ecosystem in various forms. Two soils of a cattle overwintering area with different levels of cattle disturbance were supplied with a solution of KNO3 in various levels corresponding in range to 0–500 kg N ha−1. Emissions of N2O were measured during 24 h after a NO3−-N application. We hypothesized that under a low disturbance small additions of up to 5 kg NO3−-N are used by plants and soil microbes without an increase in N2O emissions, while a pasture adapted to a moderate disturbance will increase N2O emissions. Results showed that in both soils, the addition of N always increased N2O emissions, while emissions were more pronounced in soil at the location with a higher intensity of cattle traffic. Contrary to our hypothesis, however, NO3––N was not fully metabolized in the soil with low disturbance by the cattle. Probable explanations of such a result were lower intensity of N transformations in this soil and low utilisation of N by grass. Our results suggest that under certain conditions relatively low nitrate-N inputs can also stimulate N2O fluxes from soils.