Variation characteristics and rules of nitrogen and phosphorus contents throughout the slurry movement from scaled dairy farms in Tianjin

Abstract: Both nitrogen and phosphorus were abundant in the dairy manure, which were ideal water and fertilizer resources in agriculture. However, influenced by the change of environmental conditions, there were great differences in manure collection and transportation methods and treatment processes in different dairy farms, resulting in unclear characteristics and varying rules of nitrogen and phosphorus components and contents in numerous links of slurry movement, which was harmful to the sustainable management on the manure. Based on the long-term monitoring on the complex manure rotation system of 33 large-scale dairy farms in Tianjin, the variation characteristics of nitrogen and phosphorus contents were uncovered in the whole chain of slurry movement along with the time and space, and the variation rules of nitrogen and phosphorus contents were explored under different management modes in different dairy farms. The results showed that there were 6 single or combined manure cleaning ways and 5 slurry treatment technologies in 33 dairy farms distributed in 6 main dairy industry districts. Therein dry clean plus slurry flush and dry clean were the main cleaning ways of manure in Tianjin. Sbs_L (storage of biogas slurry plus lagoon) and Af_Sbs_L (anaerobic fermentation plus storage of biogas slurry plus lagoon) were the main combined treatment processes adopted by the dairy farms. Great variability was appeared to the overall distribution of nitrogen and phosphorus in the slurry movement, and positive skewed distribution was showed on the data of total nitrogen (TN) and total phosphorus (TP). The range of TN content was 100.4-6 207.4 mg/L, the average value plus minus standard deviation was 1 691.5 ± 1 279.1 mg/L, and the coefficient of variation was 0.76, and great variability was showed on the data. The highest probability of TN content was around 750 mg/L. The range of TP content was 2.0-184.0 mg/L, the average value plus minus standard deviation was 69.0 ± 44.2 mg/L, and the coefficient of variation was 0.64. The highest probability of TP content was in the range of 20-40 mg/L, while the degree of variation of TN was greater than that of TP. The characteristics and rules of nitrogen and phosphorus content were focused on slurry movement under different space-time conditions and management conditions in this study. The analysis of linear mixed effect model showed that, 1) the contents of TN and TP in the slurry were significantly different in 4 seasons (P < 0.001); 2) the contents of TN in the slurry was no significantly different in 6 districts (P > 0.05), but the contents of TP in the slurry was significantly different in 6 districts (P < 0.05); 3) the contents of TN (P > 0.05) and TP (P > 0.79) in the slurry were no significantly different under 6 cleaning ways of manure, but the contents of TN and TP in slurry under DC_DC (dry clean + dry clean) were slightly higher than those in other approaches; 4) the contents of TN (P > 0.05) and TP (P > 0.17) in the slurry were no significantly different under 5 slurry treatment technologies, but the contents of TN and TP after Af_Sbs (anaerobic fermentation plus slurry storage) treatment were slightly higher than those of the other 4 technologies; 5) the contents of TN and TP in the slurry were significantly different in 19 migration processes (P < 0.000 1). In the combined processes of dry clean plus dry clean and anaerobic fermentation plus storage of biogas slurry, the highest content of TN and TP was yielded, while during the dry clean plus slurry flush /deep litter and lagoon, the lowest content of TN and TP was yielded. In conclusion, this study systematically illuminated the variation characteristics and rules of nitrogen and phosphorus contents in the whole chain of slurry movement under complicated environmental and management conditions, which provided a theoretical basis for the research and development of practical technologies and pathways selection of manure management.