Relationships between biomass of the Juglans regia trees in different stand ages and soil nutrients in karst peak-cluster depression

The objective of this study is to explore the change process and the relationships between biomass and soil nutrients for different-aged J uglans regia plantation in karst peak-cluster depression in the north-west of Guangxi Province.Based on a combination of field investigation and laboratory analysis,this study analyzed the change in biomass and soil nutriens and the influence of soil nutrients on the biomass of the J uglans regia trees in different stand ages.It also discussed the biomass of the J uglans regia trees and asso-ciated soil nutrients;and established relationship between soil nutrients and environmental factors (e.g. slope aspect,gradient and position and bare rock rate).The biomass of the J uglans regia trees increases a-long with the stand age,of which the trunk and root accounted for more than 60% of the total biomass.Ex-cept for the available potassium,the soil nutrients have such a trend as rich fruiting period (33 years)>seedling stage (2 years)> early fruiting (10 years).The result of correlation analysis showed that there was no significant relationship between soil nutrient,slope position and bare rock rate.However,there was neg-atively significant correlation between soil nutrient,slope,and vegetation coverage.The biomass of the J uglans regia trees is a result of the combined influence of various factors and their growth at different sta-ges is affected by different factors.For example,in seedling period the biomass of the J uglans regia trees is controlled by total phosphorus;but that is controlled by available phosphorus in early fruiting and by availa-ble nitrogen in rich fruiting.Based on these findings,soil nutrient should be considered as one of key factors in the J uglans regia plantation cultivation in karst regions.