Effects of different mixed ratios on the growth and soil nutrient of oak mixed plantations

This article was designed to study the effect of different mixed ratios on the growth and soil nutrients of oak mixed plantations and explore the best mixing mode of oak.

Five types of oak mixed plantations were selected in Batangzhen Forest Farm of Ningxiang County in Hunan Province: Pure oak (L10), Oak-Liquidambar formosana mixed (L3F7), Oak- Liquidambar formosana mixed (L7F3), Oak- Cunninghamia lanceolata mixed (L5S5) and Oak- Cunninghamia lanceolata mixed (L7S3), and the oak pure plantation of Eucalyptus was used as the control (CK). Growth factors and soil nutrient indexes were determined and analyzed after 12 years.

1) There were extremely significant differences in the DBH and individual volume of oak in the 5 stands. The average DBH of the other 3 mixed models was higher than that of the L10 mode except for the L5S5 mode, and the order of average individual volume was L7F3 > L3F7 > L7S3 > L10 > L5S5. The diameter distribution range of the L10 mode was 1-2 grades wider than that of the other 4 mixed plantation modes, but the average individual volume was smaller than that of other modes. The order of the volume of each mode was L7S3 > L10 > L7F3 > L5S5 > L3F7. 2) Compared with the L10 mode, the soil nutrient content of forest land had changed, especially the organic matter was significantly improved after mixing with Liquidambar formosana or Cunninghamia lanceolata. With the increase of soil depth, the total phosphorus and total potassium content did not change significantly, while the total nitrogen, organic matter, alkaline nitrogen, available phosphorus and available potassium decreased gradually, and the pH value increased gradually. In addition to the significant difference of available phosphorus between each soil layer, the changes of other available nutrients in the 20-40 cm soil layer were significantly greater than that in the 40-60 cm soil layer. It showed that the changes in soil nutrient content slowed down below the 40 cm soil layer. 3) On the whole, the stand growth was significantly correlated with the 5 factors of pH, total nitrogen, total potassium, available phosphorus and organic matter, and the correlation with soil available potassium was not significant. The comprehensive scores of soil nutrient quality in all modes were ranked as follows: L7F3 > L3F7 > L7S3 > L5S5 > L10.

The mixed plantations of Oak+Liquidambar formosana or Cunninghamia lanceolata were better than that of Oak pure plantation. The research results can provide a theoretical basis for the practical production of mixed afforestation of oak.