Abstract
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.