Nitrous oxide fluxes from Malagasy agricultural soils

Abstract

In Madagascar, no-tillage practices were developed since the early 90s to prevent soil erosion and improve soil fertility. Although such practices have helped to restore soil carbon in most cases, the impact on N 2O emissions has not been investigated yet. The soil N 2O fluxes and concentrations were measured during the growing season of an intercropping maize-soybean on a clayey soil of the Malagasy Highlands. Management treatments consisted of direct seeding mulch based cropping system (DMC) and traditional hand-ploughing after the preceding crop residues were harvested (HP), both with low N inputs (55–57 kg N ha − 1 ). No significant difference in N 2O emissions was observed between treatments (DMC vs. HP). The N 2O fluxes were weakly correlated to soil mineral N contents (R 2 = 0.13; P = 0.03) while no relationship was emphasized with soil water filled pore space (WFPS). N 2O concentrations in the soil atmosphere were correlated to fluxes at the soil surface and to soil WFPS. N 2O emissions at the soil surface were low ranging from 0 to 8.84 g N-N 2O ha − 1 d − 1 , probably due to the low mineral N content of soil. The cumulative annual N 2O emission was 0.26 kg N ha − 1 for both systems. The corresponding N loss as N 2O-N was around 0.5% of applied N. This is in the uncertainty range of IPCC N 2O emission factor (EF), but the IPCC EF mean estimate (1%) would overestimate true N 2O emissions for the soil under evaluation.