HOW DOES THE LAND USE AFFECT SOIL NITROUS OXIDE EMMISIONS IN THE SUBHUMID CHACO?: PRELIMINAR STUDY

Abstract

Agriculture is responsible of a significant part of the anthropogenic nitrous oxide emissions that are released into the atmosphere from the soil. There is a lack of information on N2O emissions for different regions of the world that allow the assessment and comparison of emissions under different land uses. – The objectives were: 1-Quantify in three sampling dates the emissions of nitrous oxide under different land uses and 2- Determine the soil and environmental variables that best explained the variability of the N2O emissions. Three sites of the most common type of land use in the region: natural forest, soybean crop at the headland (high soil bulk density) and center of the field (low soil bulk density) and pastures of Panicum maximun cv. Gatton Panic. The gas measurements were carried out in three moments: 3/2016, 4/2016 and 8/2016 and soil samples of the first 10 cm were extracted to determine bulk density (BD), total organic carbon (TOC), particulate organic carbon (POC), nitrates and water filled pore space (WFPS). For agricultural fields, both at the headland and at the center of the lot, emissions were low in the first two samples (1.1 - 2.3 ugN-N2O m-2 h-1), in August the values were negative (-3.5 ugN-N2O m-2 h-1). In pastures the emission was high at the first (20 ugN-N2O m-2 h-1) and last sampling dates (12 ugN-N2O m-2 h-1), in April the emission rate was similar to that of the agricultural fields (1.6 ugN-N2O m-2 h-1). The natural forest has the highest N2O flow during the entire period, 13 ugN-N2O m-2 h-1 in March, 10.5 ugN-N2O m-2 h-1 in April and 20.2 ugN-N2O m-2 h-1 in August. There was a positive relationship between the flux of N2O and the contents of nitrates, POC, TOC. Most of the variability of N2O flux was explained quadratic relationship between soil nitrates and N2O emissions (R2 = 0.43; P<0.01). The physical properties (WFPS and BD) did not correlate with the emission rates.