Effects Of Mowing And Fertilization On Productivity And Carbon/Nitrogen Input Of Reseeding Grassland In Semi-Arid Areas

In this study,reseeding legumes to improve and restore degraded grassland was the starting point,and alfalfa and bromeless grasses in reseeding grassland were taken as the research object.Different alfalfa reseeding ratios(reseeding 30%,reseeding 15%,not reseeding)and different management measures(control,fertilization,mowing,fertilization + mowing)were set as experimental treatments.Through studying the effects of different reseeding ratios and management measures on the performance of grassland,the biological nitrogen fixation of alfalfa,the transfer of nitrogen with the associated Brome,the characteristics of litter decomposition,and the characteristics of soil nutrients.Explore the internal influence mechanism of biological nitrogen fixation,nitrogen transfer and litter decomposition on natural grassland ecosystem carbon and nitrogen input,and clarify the influence mechanism of reseeding legumes on the key process of nitrogen input in degraded grassland.The main results are as follows:(1)Mowing and fertilization measures have significantly changed the biomass of reseeding grassland.In 2019 and 2020,the combination of 30% reseeding and fertilization + mowing has the highest total biomass above ground;the combination of fertilization and reseeding 15% has the highest total biomass below ground,and the combination of fertilization + mowing and reseeding 30% has second.The management measures of fertilization + mowing after reseeding can significantly increase the proportion of alfalfa.In the second year of reseeding,the proportion of alfalfa in the control treatment reached 15.02%～16.12% of the total above-ground biomass,which increased to 41.46%～50.8% after fertilization +mowing treatment.(2)The density of alfalfa in the year of reseeding was the highest under the combination of reseeding30% and fertilization + cutting,accounting for 54.6%;the density of bromeless was the highest under the combination of reseeding 30% and cutting,accounting for 75.7%.In the second year of supplementary sowing,the density of alfalfa was the highest in the combination of reseeding 30% and fertilization +mowing,accounting for 54.2%;the density of bromeless bromegrass was the highest in the combination of supplementary sowing 30% and fertilization,accounting for 77.3%.(3)Reseeding 15% and fertilization + mowing treatment can significantly increase the biological nitrogen fixation rate of alfalfa.The combination of reseeding 15% and fertilization + mowing had the highest nitrogen fixation rate,which was 21.95%,and the combination of reseeding 30% and control had the lowest nitrogen fixation rate,which was 16.58%.The nitrogen transfer rate was the highest under the treatments of reseeding 15% and fertilization + mowing,which was 11.12%.(4)The decomposition time has a significant effect on the mass loss rate,carbon concentration,nitrogen concentration,and C/N ratio of alfalfa and Bromegrass litter.With the increase of decomposition time,the mass residue of litter fell rapidly first,and the rate of decline gradually slowed down after 140 days of decomposition.After 288 days of decomposition,the mass loss rate was about 36.25%～39.77%and 45.1%～42.16%.The N concentration of alfalfa and bromegrass litter decreased significantly with the increase of time,and dropped to about 1.46%～1.63% and 1.44%～1.69% after 288 days of decomposition.The C content of alfalfa and bromegrass litter showed a trend of first increasing and then decreasing with the increase of decomposition time,and was about 49%～54% and 46%～53% after 288 days of decomposition.The C/N ratio increased significantly with time.(5)The content of soil organic matter was the highest under the treatment without reseeding,which was 40.64 g/kg;the total nitrogen content of the soil was the highest under the treatment with 15%reseeding,which was 0.21 g/kg,which was significantly higher than that under the treatment of 30%reseeding.The contents of alkali hydrolyzed nitrogen,total phosphorus and total potassium were the highest without reseeding treatment,which were 57.62 mg/kg,0.28 g/kg,and 35.99 g/kg,which were significantly higher than the 15% reseeding treatment.The soil available phosphorus content was the highest under the fertilization treatment,which was 10.75 mg/kg,which was significantly higher than the control and mowing treatments.The content of available potassium was the highest under the 30%reseeding treatment,which was 1134.23 mg/kg,but there was no significant difference from the other treatments.