Nitrogen Emission from Livestock Housings Quantified Combining a Mass-Balance Model and Low-Field NMR Sensoring

Environmental pollution through nitrogen (N) emission needs to be reduced for green transition of modern agriculture and for sustainable agricultural expansion to meet increasing global food demands. While on-site monitoring is essential for systematic minimization of emission, gas emission measurements are challenging for naturally ventilated livestock housings. Addressing this challenge, we propose a sensor-based mass-balance model based on the ratio between N and an internal tracer (e.g., phosphorus [P], potassium [K], or sodium [Na]) driven by on-site NMR slurry measurements. For demonstration, we conducted a full-scale barn experiment with 32 dairy cows housed in two identical mechanically ventilated barn units, allowing for the measurement of gaseous emissions, while inputs/outputs were quantified and full mass balances for N, P, K, and Na were established. We found Na to be an appropriate tracer and that a N/Na-based mass-balance model may provide valuable measurements of N emissions in naturally ventilated barns under the condition that extensive, careful sampling and accurate analysis is performed as demonstrated here using mobile NMR sensor technology.