Nitrogen fluxes from irrigated common‑bean as affected by mulching and mineral fertilization

The objective of this work was to measure the fluxes of N2O‑N and NH3‑N throughout the growing season of irrigated common‑bean (Phaseolus vulgaris), as affected by mulching and mineral fertilization. Fluxes of N2O‑N and NH3‑N were evaluated in areas with or without Congo signal grass mulching (Urochloa ruziziensis) or mineral fertilization. Fluxes of N were also measured in a native Cerrado area, which served as reference. Total N2O‑N and NH3‑N emissions were positively related to the increasing concentrations of moisture, ammonium, and nitrate in the crop system, within 0.5 m soil depth. Carbon content in the substrate and microbial biomass within 0.1 m soil depth were favoured by Congo signal grass and related to higher emissions of N2O‑N, regardless of N fertilization. Emission factors (N losses from the applied mineral nitrogen) for N2O‑N (0.01–0.02%) and NH3‑N (0.3–0.6%) were lower than the default value recognized by the Intergovernmental Panel on Climate Change. Mulch of Congo signal grass benefits N2O‑N emission regardless of N fertilization

Limited potential of no-till agriculture for climate change mitigation

The Emissions Gap Report 2013 from the United Nations Environment Programme restates the claim that changing to no-till practices in agriculture, as an alternative to conventional tillage, causes an accumulation of organic carbon in soil, thus mitigating climate change through carbon sequestration. But these claims ignore a large body of experimental evidence showing that the quantity of additional organic carbon in soil under no-till is relatively small: in large part apparent increases result from an altered depth distribution. The larger concentration near the surface in no-till is generally beneficial for soil properties that often, though not always, translate into improved crop growth. In many regions where no-till is practised it is common for soil to be cultivated conventionally every few years for a range of agronomic reasons, so any soil carbon benefit is then lost. We argue that no-till is beneficial for soil quality and adaptation of agriculture to climate change, but its role in mitigation is widely overstated