Assessing the Impact of Non-Urea Ruminant Urine Nitrogen Compounds on Urine Patch Nitrous Oxide Emissions

Abstract

Urea, the dominant form of N in ruminant urine, degrades in soil to produce NO emissions. However, the fate of non-urea urine N compounds (NUNCs) in soil and their contribution to urine patch NO emissions remain unclear. This study evaluated five NUNCs: allantoin (10%), creatinine (3%), creatine (3%), uric acid (1%), and (hypo)xanthine (0.6%), where numbers in parentheses represent the average percentage of total urine N. The fates of NUNCs in a pasture soil were determined using N-labeled NUNCs in a laboratory trial. Two NUNCs, hypoxanthine and creatine, were added to the soil with perennial ryegrass ( L.) present and sampled over time for soil inorganic N, NO emissions, and plant N dynamics. The N enrichments of soil inorganic N and plant N were significantly increased within 24 h of NUNC application, indicating rapid microbial degradation and plant uptake of NUNCs in pasture soil. An autumn field trial was also conducted to evaluate the in situ impact of varying concentrations of NUNCs on urine patch NO emissions. Increasing the proportion of urine N excreted as NUNCs did not alter the urine patch NO emission factor, soil inorganic N concentrations, or plant N uptake. It is concluded that NUNCs rapidly degrade in pasture soil and that an increased ruminant excretion of urine N as NUNCs does not significantly alter the urine patch NO emission factor.