Nitrogen loss abatement from dairy cow excreta through urine and faeces separation: The effect of temperature and exposure period on NH3 fluxes

Manure management is a crucial aspect warranting attention since a significant proportion of anthropogenic NH3 emissions are derived from it. In dairy cattle, only 20 to 30% of the dietary N is retained in milk, while a relevant amount is excreted in urine and faeces. A substantial proportion (60 to 80%) of the urine-N of high-producing dairy cows exists as urea, which is rapidly converted to NH4+ by the urease enzyme, and volatilizes into the atmosphere as NH3. While extensive literature studied the effects of technical solutions for cattle housing and waste storage, environmental parameters and manure treatments on NH3 emission, limited information exists on its quantification under controlled conditions from isolated and mixed excreta. The aim of the study was to evaluate the NH3 emission reduction potential from maintaining urine and faeces separate in dairy farming systems. NH3 emissions from urine (U) and faeces (F) alone, as well as their mixture (M) were monitored under different environmental conditions and different exposure periods (24 and 72 h). The M samples had significantly higher NH3 emissions (about 100 times higher) than U and F, both in cold and warm conditions and at all exposure periods. Significantly higher NH3 emissions were measured from U, compared to F, after 48/72 h of exposure, probably linked to the higher pH and water content found in U. Separating urine and faeces (before contact) has the potential to reduce NH3 emissions by about 99% during the first 24–72 h of air exposure in dairy cow management systems. This potential approach should also be coupled with accurate urine management, under conditions that prevent environmental urease contamination. Such a strategy could also be an effective solution to improve on-farm N reuse and to reduce the adoption of chemical fertilizers.