Drivers of nitrous oxide emissions under crops and natural grasslands in the Pampas region, Argentina

TOMAS DELLA CHIESA; LAURA YAHDJIAN; GERVASIO PIÑEIRO

Conferencia; 100th Annual Meeting of the Ecologial Society of America; 2015

Nitrous oxide (N2O) is one of the major greenhouse gases, responsible for near 6% of global warming, and is the largest stratospheric ozone-depleting substance. The major sources of N2O are soils under natural vegetation and arable lands. Due to the diverse processes involved in the production of N2O from soils, emissions are largely variable in space and time. Understanding the drivers that control these emissions represents a key task when modeling N2O emissions or upscalling from field measurements. Soil variables such as water fill pore space, temperature, and inorganic nitrogen content are usually identified as the main drivers of N2O emissions from terrestrial ecosystems. However, vegetation productivity, which is closely related to these soil factors, has received less attention. In this study two questions were tackled in the main agricultural region of Argentina: Do soils under commercial crops release more N2O than natural ecosystems set aside? And; is vegetation productivity closely related to soil N2O emissions? A manipulative field experiment was settled in two contrasting sites of the Pampas Region. In each site, N2O samples were taken monthly during one year with the static chamber method in soybean, corn, wheat/soybean rotation crops, and natural ungrazed grassland plots. Experimental plots received common agricultural practices like land under commercial production. We also measured soil temperature, vegetation productivity (estimated by the normalized difference vegetation index - NDVI), and we collected soil samples to determine water filled pore space, and NH4+ and NO3- content in each sampling date.