| The construction of artificial grassland can not only obtain high-yield and high-quality forage grass,effectively alleviate the contradiction between grass and livestock,but also help reduce the pressure on natural grassland,and protect and maintain the ecosystem services of natural grassland.This study was conducted on the concentrated planting area of Alfalfa artificial grassland in the south of Ar horqin banner,Chifeng City,Inner Mongolia.Using multi-temporal satellite remote sensing digital images of GF-2 and Sentinel-2,combined with field investigation,we established the evaluation models for the resume growth and nitrogen and phosphorus content of alfalfa artificial grassland,and monitored the resume growth status of alfalfa artificial grassland in 2020.Then,the temporal and spatial dynamics of nitrogen and phosphorus content and N:P ratio in different cutting periods were evaluated,and the effects of the resume growth status on content of nitrogen and phosphorus for alfalfa artificial grassland were analyzed.The main results are as follows:1.The planting area of alfalfa artificial grassland was extracted based on the summation of NDVI approaches.The results showed that there were 597 alfalfa artificial grassland planting patches in the study area,the extraction accuracy was 84.3%,and the total area is 16535.6 hm~2.2.A method for evaluating the resume growth status of alfalfa artificial grassland was proposed.Based on the field investigation data in 2019 and the GF-2 remote sensing digital image over the same period,the perpendicular vegetation index（PVI）was used to establish the vegetation coverage inversion model.And the vegetation coverage was graded to evaluate the resume growth status of alfalfa artificial grassland.Furthermore,the above methods were used to monitor and evaluate the resume growth status of alfalfa artificial grassland in the study area in 2020.The fully,moderately and poorly resume growth areas were 11211.1 hm~2,4453.9 hm~2 and 870.6 hm~2,respectively.Fully or moderately resume growth areas accounted for 94.74%of the total artificial grassland,indicating that the resume growth was overall good in this area in 2020.3.A method for evaluating the nitrogen and phosphorus content of alfalfa artificial grassland was proposed.Based on the field investigation data in 2020 and the Sentinel-2 remote sensing digital image over the same period,the difference vegetation index（DVI）was used to establish the model of nitrogen and phosphorus content.Monitoring the area change in nitrogen and phosphorus content of alfalfa artificial grassland in 2020 found that both the nitrogen and phosphorus content showed maximum value a during the second cutting,The estimation results of the N:P ratio of alfalfa artificial grassland showed that the growth and development of alfalfa was mainly limited by nitrogen.4.The effect of the resume growth status on the nitrogen and phosphorus content of alfalfa artificial grassland was analyzed.At the first cutting,the nitrogen content between different resume growth grades was significantly different,and the phosphorus content of the fully and poorly resume growth status was significantly different;for the second cutting,whether it was the nitrogen content or the phosphorus content,there was a significant difference between fully and moderately and poorly resume growth status;when the third cutting,there was no significant difference between the nitrogen and phosphorus content under different the resume growth grades.To sum up,this study puts forward a method to evaluate the resume growth status of alfalfa artificial grassland through a combination of field observation and satellite remote sensing technology,and establishes an estimation model of nitrogen and phosphorus content of alfalfa artificial grassland,which is useful for field management of alfalfa artificial grassland.It provides theoretical and technical support,and also has the potential to be promoted in similar regions. |
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