In order to investigate the effects of different nitrogen addition levels on soil physicochemical properties and available nutrients of drooping paniculus calcareous grassland under alpine ecological condition

the experiment of nitrogen addition was carried out in the 2nd age paniculus calcareous artificial grassland at Tianzhu Alpine Grassland Experimental station. A single factor experimental design was used to determine the nitrogen addition dose in the experiment site according to the nitrogen deposition distribution pattern in China

and five nitrogen addition levels of control N0 (no nitrogen)

N1 (12 kg/hm2)

N2 (24 kg/hm2)

N3 (48 kg/hm2) and N4 (96 kg/hm2) were set

with four times per treatment. Fertilization was performed twice in early July and early August 2021

and rhizosphere and non-rhizosphere soil samples of each treatment were collected for determination in September. The results showed that the nitrogen application level had significant effects on the content of alkali-hydrolyzed nitrogen in rhizosphere soil and the soil bulk density in non-rhizosphere soil (p＜0.01)

and had significant effects on the content of organic matter and available phosphorus in rhizosphere soil (p＜0.05). In rhizosphere soil

soil water content increased with the increase of nitrogen application level. Soil pH value decreased slowly and reached the lowest value under N4 treatment. Under N3 treatment

alkali-hydrolytic nitrogen

available phosphorus and available potassium in rhizosphere soil were significantly increased by 8.92%

44.38% and 16.00% compared with control group (p＜0.05). Soil organic matter content was also significantly higher than that in control group (p＜0.05). In non-rhizosphere soil

with the increase of nitrogen application level

soil alkali-hydrolytic nitrogen and available phosphorus contents increased first and then decreased

and the peak value was reached under N3 treatment (p＜0.05). Soil pH value increased first and then decreased. The content of soil organic matter reached the peak value at the level of N4 (p＜0.05). Under the same nitrogen application level

the contents of water content

available phosphorus and available potassium in rhizosphere soil were lower than those in non-rhizosphere soil except N3 level. pH

organic matter content and alkali-hydrolyzed nitrogen content of rhizosphere soil were higher than those of non-rhizosphere soil. The comprehensive analysis of grey correlation degree showed that N3 treatment and N4 treatments had the greatest effects on physicochemical properties and available nutrients of rhizosphere and non-rhizosphere soil

respectively.