Effects of soil salinity and carbon availability from organic amendments on nitrous oxide emissions

Soil salinity negatively affects the mineralization and nitrification processes of the N cycle and may also affect the production of nitrous oxide (N2O) and N-2 to N2O-N ratios. Application of organic amendments such as manures and composts improves soil physical, chemical, and biological properties of salt-affected soils. However, because these materials both mineralize N and serve as substrates for denitrifiers, they may also increase N2O emissions. We studied the effect of organic amendments applied to saline soils on N2O emissions and on N-2 to N2O-N ratios. Saline soils with electrical conductivity(ECe) measures of 2.8, 15.2, and 30.6 dS m(-1) were collected from Coachella Valley, California. Treatments included four organic amendments: active greenwaste compost (AGW), cured greenwaste compost (CGW), active dairy manure compost (ADM), and cured dairy manure compost (CDM). Treatments were incorporated at 50 Mg ha(-1) and incubated at 65% water-filled pore space (WFPS) for 60 days at 25 degrees C. Evolving cabon dioxide (CO2-C) and N2O-N were monitored along with soil ammonium (NH4+-N) and nitrate (NW-N) concentrations. The results showed that increasing soil salinity increased cumulative N2O-N losses but decreased CO2-C and N-2 emissions and N-2 to N2O-N ratios. Of all the amendments, the highest cumulative N2O-N and N-2 emissions were produced from the ADM treatment at all three salinity levels. In general, incorporation of active compared to cured amendments increased N-2 to N2O-N ratios at all three salinity levels suggesting that applying active organic materials could be useful in mitigation of N2O emissions from salt-affected soils under remediation. (C) 2014 Elsevier B.V. All rights reserved.