Soil Management Practices and N Fertilization Effects on N2O Emissions in Irrigated Corn in a Mediterranean Agroecosystem.

An adequate choice of agricultural management practices can help to reduce the emission of nitrous oxide (N₂O) from soils, mitigating global warming. The aim of our work was to quantify the emission of N₂O from soils and the corn yields according to different soil management practices and nitrogen (N) fertilization rates in a semiarid area recently transformed to irrigation under Mediterranean conditions.

The study was carried out in NE Spain, in a long-term tillage and N experiment (established in 1996), which was transformed to irrigated corn in 2015 and previously consisting in rainfed barley monocropping during the 1996-2014 period. Three types of tillage (conventional intensive tillage, CT; reduced tillage based on strip-tillage, RT; no-tillage, NT) and three mineral N fertilization rates (0, 200, 400 kg N ha^-1) were compared. During 2015 and 2016, weekly soil N₂O emissions and water-filled pore space (WFPS) were measured (0-5 cm). Corn yield was quantified at harvest to estimate yield-scaled N₂O emissions. For each year, the emission factor (EF) was also quantified.

In 2015, the doses of 200 and 400 kg N ha^-1 in CT showed the lowest cumulative N₂O emission. The highest N rate increased soil N₂O emissions especially just after the application of fertilizer, independently of the tillage system. In 2015, the use of NT and RT led to greater yield than CT. However, only N fertilizer treatments significantly affected N₂O yield-scaled emissions in 2015. The greatest EF was found when applying 400 kg N ha^-1under NT (0.26%). The WFPS was significantly affected by tillage and N fertilization treatments, decreasing in the order NT > RT > CT in 2015 and 2016.

Our preliminary data showed that tillage and N fertilization play an important role on soil N₂O emissions and on corn production in Mediterranean agroecosystems recently transformed to irrigation.