Effect of various fertilizer doses on soil N2O and CO2 emissions in cropland soils in Hungary

Quantifying greenhouse gas emissions has been a priority for climate scientists for decades. As a result, the spatial and temporal dynamics of emissions have been widely studied, but to date, we still do not fully understand the main drivers of the variation in patterns. The aim of our research is to quantify the spatio-temporal variability of these greenhouse gases under various nutrient supply conditions and different tillage practices (plow or cultivator) on sandy-clay and loam soils.

Our measurements took place near Kartal on loam soil and near Gödöllő on sandy-clay soil, in Central Hungary, in 2022 on winter wheat. CO₂ and N₂O fluxes are analyzed with Li-cor gas analyzers (LI-870 CO₂/H₂O Analyzer and LI-7820 N₂O/H₂O Trace Gas Analyzer) connected to the 8200-01S Smart Chamber. We can track both modest changes brought on by natural factors (precipitation, temperature variations) and the impact of more significant artificial factors (fertilization, type of tillage) on the N₂O and CO₂ flux using these rather sensitive devices. In Kartal, 24, and in Gödöllő 40 KG-PVC rings with a diameter of 20 cm were placed in the study areas and measured on a weekly basis. In Kartal half of the collars received fertilizer, and the other half was covered during the application. In Gödöllő, 8 different treatments can be distinguished, resulting from a combination of 3 different fertilizer doses (0kg/ha, 75kg/ha, and 150kg/ha), 2 tillage methods (plow and cultivator), and soil conditioners. The collars protrude 4 cm from the soil and the inner soil surface has been cleared of vegetation. The gas exchange between soil and air is measured for 3 minutes on each collar, while simultaneously measuring soil moisture, temperature, and vegetation cover (LAI) near the collars. Soil samples were taken monthly to a depth of 15 cm, and 50 cm from the collars.

Based on our observation, in the case of N₂O emission, there are significant differences between the two study areas. On average N₂O emissions in Gödöllő were higher than in Kartal. Cumulative N₂O emissions were significantly higher in areas receiving higher doses of fertilizer. For 150kg/ha, the highest value was 42 g N m², while for 0kg/ha and 75kg/ha, lower values of around 16-20 g N m² were observed. With average emissions of 420–500 g C m², there are no discernible variations in cumulative CO₂ emission across treatments. However, the temporal variation of both GHG emissions shows differences due to the persistent drought in summer. During the rainy season, spring and autumn, a more intense N₂O and CO₂ flux were observed due to soil respiration.