Soil mineral N retention and N 2O emissions following combined application of 15N-labelled fertiliser and weed residues

摘要

RATIONALE: The combination of plant residues with inorganic fertiliser-N provides the potential to increase N-use efficiency in agricultural fruit production systems, such as olive orchards. The development of weeds in the inter-canopy area of olive orchards is encouraged as a novel strategy to reduce soil erosion. However, little is known about soil N retention or N _2O production following the combined application of inorganic-N with the mulched weed residues. METHODS: Emissions of ~15N-N _2O and soil mineral ~15N retention were measured following combined applications of ~15N-labelled fertiliser and a range of olive crop weed residues to a silty loam soil under controlled conditions. These plant residues differed in their C:N ratios, lignin and polyphenol contents. RESULTS: The magnitude of soil ~15N-NO _3 - retention from combining plant residues and fertiliser-N was highly dependent on potential N mineralisation (r = -0.96) and the (lignin + polyphenol)-to-N ratio (r = 0.98) of the residues. Fertiliser-N-derived retention was zero for a legume-based mulch but up to 80% in the treatment containing plant residues with a high (lignin + polyphenol)-to-N ratio. N _2O emissions increased after the addition of residues, and increased further (up to 128%) following the combined application of inorganic fertiliser and residues. Fertiliser-derived ~15N-N _2O was <1.4% of the total ~14+15N-N _2O emission and <0.01% of the applied ~15N-NO ~3 -. Enhanced N _2O emissions following the application of residues and the fertiliser-N values were positively correlated with the C:N ratio of the residue. Thus, combining organic- and inorganic-N immobilised a significant proportion of the inorganic N with little increase in N _2O, especially in low C:N ratio residues. CONCLUSIONS: The results demonstrate that whilst there is potential for N _2O emissions to be controlled by combining weed residues and inorganic fertilisers, this is not easy to achieve as the magnitude and direction of interactions vary between different species due to their varying substrate qualities.