Nitrogen loss factors of nitrogen trace gas emissions and leaching from excreta patches in grassland ecosystems: A summary of available data.

Patches of excreta voided by grazing animals are nitrogen (N) transformation hotspots in grassland ecosystems and an important source of N trace gas emissions and leaching. Previous studies have focused on individual N losses from excreta, but no quantitative analysis has been performed on all the N losses via N trace gas emissions and leaching. To better understand the fate of N in excreta patches, we summarized 418, 15, 65, 22, 54, 11, and 81 measurements of nitrous oxide (NO), nitric oxide (NO), ammonia (NH), and ammonium (NH) leaching, nitrate (NO) leaching, dissolved organic nitrogen (DON) leaching, and aboveground plant N uptake, respectively. The results based on field studies indicated that the average fractions of N lost via NO were 0.28%, 0.76%, 0.08%, and 0.35% for cattle dung, cattle urine, sheep dung, and sheep urine, respectively. Only 0.01-0.12% of excreta N was lost via NO, whereas 1.69-12.7%, 0-4.58%, 16.4-24.6%, and 1.43-5.91% were lost by NH and NH, NO, and DON leaching, respectively. Aboveground plant parts assimilated 10.4-31.4% of the excreta N. The N lost via NO from urine patches decreased as NH losses increased, and greater NO leaching occurred with lower plant N uptake. The combined NO emission factors for dung and urine from cattle and sheep were 0.59% and 0.26%, respectively. Each N loss factor was much higher in urine patches than in dung patches, irrespective of animal type. This study provides general estimates of N losses and plant N uptake from excreta patches on grazed grassland based on currently available field data. More field studies are needed in the future with longer measurement periods from a wide range of climate zones to refine these N loss factors.