Fertilising practices to reduce nitrous oxide emissions from managed grasslands

Fertiliser and manure applications on grassland are important sources of nitrous oxide (N2O) emissions. This paper assesses strategies to reduce N2O emissions from fertiliser and manure application on grassland, either by reducing the amounts of applied nitrogen and carbon, or by preventing the simultaneous availability of fertiliser nitrate and manure carbon to prevent detrimental interactions. Three mitigation options were tested in three consecutive years on a sandy soil in the Netherlands: (i) application of ammonium based fertilisers, (ii) split fertiliser applications and (iii) separate application of fertiliser and manure. The observed N2O emission factors for the calcium ammonium nitrate were rather low: 0.52%, 0.17% and 0.12% of applied N, in the three consecutive years. Application of ammonium sulphate and split application of calcium ammonium nitrate resulted in a significant reduction of emissions in the first year. In the second and third year however, none of the mitigation strategies resulted in a lower emission. It is concluded that choice of fertiliser type and timing can reduce N2O emissions, but solid recommendations on when to apply these strategies are still lacking.