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

Abstract Soil salinity negatively affects the mineralization and nitrification processes of the N cycle and may also affect the production of nitrous oxide (N 2 O) and N 2 to N 2 O–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 N 2 O emissions. We studied the effect of organic amendments applied to saline soils on N 2 O emissions and on N 2 to N 2 O–N ratios. Saline soils with electrical conductivity(EC e ) 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 °C. Evolving cabon dioxide (CO 2 –C) and N 2 O–N were monitored along with soil ammonium (NH 4 + –N) and nitrate (NO 3 − –N) concentrations. The results showed that increasing soil salinity increased cumulative N 2 O–N losses but decreased CO 2 –C and N 2 emissions and N 2 to N 2 O–N ratios. Of all the amendments, the highest cumulative N 2 O–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 N 2 O–N ratios at all three salinity levels suggesting that applying active organic materials could be useful in mitigation of N 2 O emissions from salt-affected soils under remediation.