Autor:innen:
Matthias Claß | Forschungszentrum Jülich | Germany
Prof. Dr. Nicolas Brüggemann | Forschungszentrum Jülich | Germany
Sustainable agriculture capable of meeting the global demand for more food with less resource input is an important challenge, especially in view of climate change and the need to reduce nitrate losses to the groundwater and greenhouse gas emissions to the atmosphere. Within-field heterogeneity of the soil nitrogen (N) status due to differences in soil properties leads to differences in N losses that require analysis of the soil nitrogen status with high spatial and temporal resolution. Based on spatially highly resolved soil mineral N data, agricultural N use efficiency can be improved by applying N fertilizer according to crop demand and local soil mineral N content. Here we present a new approach for highly sensitive detection of reactive N gases emitted from soil as proxies for the soil N status, which could make destructive soil sampling dispensable.
To correlate reactive N soil gas emissions with the soil N pool, we conducted a two-pronged approach combining laboratory and field experiments. The main purpose of the laboratory experiments was to gain a general understanding of the relationship between soil N gas emissions and soil mineral N content. For this purpose, we conducted incubation experiments using a fertilizer gradient (0, 10, 30, 50, 70, 90 kg N/ha) and a soil water gradient (0, 20, 40, 60, 80% mWHC) on five soils with different pH values (4.3, 5.5, 6.3, 6.8, 7.7) and measured the corresponding gas emissions (NH3, NO, NO2, HONO, N2O, CO2, H2O) and soil parameters (pH, water content, NH4+, NO2-, NO3-). In addition, field experiments were conducted in 2021 and 2022 with a mobile system including a multi-compound infrared laser analyzer to determine the control variables for the emissions of the different N gases, and the limitations of the measurement method.
At this stage, we can demonstrate that it is possible to determine the ammonium pool in the soil by measuring ammonia emissions from the soil. In addition, we found positive correlations between soil pH, water content, and NH3 emissions, which must be considered when calculating soil ammonium concentrations from soil NH3 emissions. In the majority of the cases, measured HONO concentrations were low ( < 1ppb), which made reliable measurements challenging due to the detection limit of the analyzer. In contrast, NO turned out to be a more suitable and reliable proxy for NO2- concentration in the soil.