Density Effect Of Soil Nutrientand Stoichiometry Of Cunninghamia Lanceolata Plantationsin Naxi,Sichuan Province

Five densities(2m×3m(A)、2m×1.5m(B)、2m×1m(C)、1m×1.5m(D)、1m×1m(E)respectively)and five soil layers(0-20cm20-40cm、40-60cm、60-80cm、80-100 cm respectively)of 30-year-old Chinese Fir Plantations were used to study the characteristics of soil nutrient elements and their stoichiometry in Naxi,Sichuan Province.And we explored the indicators of soil nutrient content on forest site index.The main conclusions were as follows:(1)The initial density had a significant effect on the soil nutrient of Chinese Fir Plantations.The contents of organic matter and organic carbon in the surface soil(0-20cm),hydrolyzed nitrogen and total calcium increased first and then decreased with the increase of density,which were the highest at B density(2m×1.5m,3333 strain·hm-2).The contents of total phosphorus,total potassium and available potassium increased first and then decreased with the increase of density,which were the lowest in B density.The total phosphorus and total potassium content was the highestin E density.The total magnesium content and pH increased with the increase of density.Organic matter,organic carbon beneath 20 cm soil layers and the total nitrogen content didn’t affect by density obviously.The results showed that B density was beneficial to the accumulation of organic matter and organic carbon in the surface soil,which was beneficial to the accumulation of hydrolyzed nitrogen and total calcium in different layers of soil.And E density was conducive to the rise of total phosphorus,total potassium,total magnesium accumulation and pH value.The density effect of nutrient contents was weakened with the increase of soil layers.(2)The contents of total nitrogen,hydrolyzed nitrogen,total phosphorus,organic matter and organic carbon were significantly decreased with the increase of soil depth.The effect of total potassium,available potassium,total calcium,total iron and total magnesium content on soil layer was not obvious.The soil pH value increased with the increase of soil depth.The effect of soil depth on nutrient contents and pH value was weakened beneath soil depth of 60 cm.(3)The average of C:N ratio of five kinds of Chinese fir plantations was 19.44,which was higher than the average of 11.9 in China.The average of N:P and C:P ratio were 2.89 and 43.07,which were lower than the average of 5.2 and 61.The average of C:N:P is 43:3:1,which was lower than the average of 60:5:1.The initial density had a significant effect on soil C:N,N:P,C:P ratios,especially in the surface soil.The ratio increased first and then decreased with the increase of the density,which were the highest in B density.N:P and C:P showed a linear decline and C:N first descended and rised with the increase of soil depth.(4)The available phosphorus and total magnesium contents had a good indicative of the productivity of Chinese fir plantation.The higher content of soil available phosphorus,the lower the total magnesium content,the higher the quality of forest site.The soil available phosphorus content in 0-100 cm soil layer or the total magnesium content of 0-20 cm soil layer could be used as an indicator of the quality evaluation of Chinese fir plantation in experimental area.