Emissions of CO2 and N2O from a pasture soil from Madagascar-Simulating conversion to direct-seeding mulch-based cropping in incubations with organic and inorganic inputs.

In the highlands of Madagascar, agricultural expansion gained on grasslands and cropping systems based on direct seeding with permanent vegetation cover are emerging as a means to sustain upland crop production. The objective of this study was to examine how such agricultural practices affect greenhouse-gas emissions from a loamy Ferralsol previously used as a pasture. We conducted an experiment under controlled laboratory conditions combining cattle manure, crop residues (rice straw), and mineral fertilizers (urea plus NPK or di-NH₄-phosphate) to mimic on-field inputs and examined soil CO₂ and N₂O emissions during a 28-d incubation at low and high water-filled pore space (40% and 90% WFPS). Emissions of N₂O from the control soil , i.e., soil receiving no input, were extremely small (< 5 ng N₂O-N (g soil)^-1 h^-1) even under anaerobic conditions. Soil moisture did not affect the order of magnitude of CO₂ emissions while N₂O fluxes were up to 46 times larger at high soil WFPS, indicating the potential influence of denitrification under these conditions. Both CO₂ and N₂O emissions were affected by treatments, incubation time, and their interactions. Crop-residue application resulted in larger fluxes of CO₂ but reduced N₂O emissions probably due to N immobilization. The use of di-NH₄-phosphate was a better option than NPK to reduce N₂O emissions without increasing CO₂ fluxes when soil received mineral fertilizers. Further studies are needed to translate the findings to field conditions and relate greenhouse-gas budgets to crop production. [ABSTRACT FROM AUTHOR]