| Chinese fir is a unique species of fast-growing timber in China and plays an important role in the south of China forestry production and commercial materials.Recently,in order to improve the timber production,the plant area of Multi-generation continuous planting Chinese fir becomes bigger and bigger,leading to the decreasing fir production of Woodland unit area,and the soil fertility and Chinese fir plantation decline,which become the key reason for restricting the development of current Chinese fir forestry production.Therefore,the focus of the current fir research is to prevent the decline of Chinese fir plantation and to maintain long-term fir soil fertility and productivity.Reasonable rotation and mixing between fir and other broad-leaved species can supply and improve the soil’s physical and chemical properties in different degrees.It also can significantly improve the soil nutrient content,which has a significant effect on the soil fertility and productivity of Chinese fir woodland,finally contributing to the sustainable management of fir and forest land.Chosen the soil of the second generation fir forest as control factor,the paper studies on the physical properties of different soil layerselements(C,N,P,K,Ca,Mg)and trace elements(Al,Fe,Mn,Zn,Na)in Chinese fir soil,Eucalyptus and Acacia melanoxylon,after the second generation fir forest rotate eucalyptus urophylla and Nitrogen-fixing tree species on the ground for 9 years.The paper also studies how second rotation Chinese fir plantations after rotation Eucalyptus and Acacia melanoxylon influence the soil by correlation analysis and RDA analysis,which can provide the basis for the practice of the second generation of Chinese fir woodland crop rotation.The results are as follows:1.For the different slope position and forest points,soil bulk density,maximum water holding capacity,minimum water holding capacity,pore water holding capacity,non-pore porosity and pore porosity do not reach a significant lever(P>0.05).Chosen the second rotation Chinese fir as the control group,after 9-years rotation,the soil bulk density of Eucalyptus and Acacia melanoxylon decreased by 3.28%and 11.48%respectively;the minimum water holding capacity decreased by 4.44%and 1.92%;pore water holding capacity decreased by 4.24%and 0.95%;pore pores were reduced by 5.16%and 6.94%.Comprared to second rotation Chinese fir,Maximum soil water holding capacity of Acacia melanoxylon improved by 6.81%,non-pore pores increased by 59.1%.Compared to second rotation Chinese fir,the improvement of soil physical properties made by rotation Eucalyptus and Acacia melanoxylon is not obvious.2.With the increase of soil depth,the indicators in the soil of second rotation Chinese fir,Eucalyptus and Acacia melanoxylon,including the water factor,carbon,nitrogen,phosphorus,available potassium,exchangeable calcium,exchangeable magnesium and other indicators,are decreasing.However,other indicators,including nitrate nitrogen,total potassium,calcium,magnesium,aluminum,iron,manganese,and zinc,are improving or make no significant change.There were no significant differences in soil pH,total carbon,total nitrogen,mineral nitrogen,Hydrolyzable nitrogen,total phosphorus,available phosphorus,total calcium,exchangeable calcium,Al,Fe,Mn and Zn in the same soil(P>0.05).There are significant differences between second rotation Chinese fir and Eucalyptus and Acacia melanoxylon on DOC,DON,nitrate nitrogen,ammonium nitrogen,total potassium,available potassium,total magnesium,exchangeable magnesium,Na and other elements.3.Chosen the second rotation Chinese fir as the control group,after 9-years rotation,the soil DOC content of Eucalyptus and Acacia melanoxylon decreased by 4.75%and 16.55%respectively;the nitrate nitrogen content decreased by 68.75%and 44.03%respectively;the total potassium content decreased by 33.96%and 8.08%respectively;the total calcium content decreased by 4.40%and 0.21%respectively;the exchangeable calcium content decreased by 17.51%and 12.13%respectively;the total magnesium content decreased by 34.62%and 12.81%respectively;the A1 content decreased by 5.22%and 7.84%respectively;the Zn content decreased by 7.19%and 10.90%respectively.Comprared to second rotation Chinese fir,the total carbon content of Acacia melanoxylon improved by 42.83%,the total nitrogen content improved by 26.46%,the mineral nitrogen content improved by 13%,the ammonium nitrogen content improved by 24.91%,the Hydrolyzable nitrogen content improved by 7.45%,the total phosphorus content improved by 3.67%,the available phosphorus content improved by 49.29%,the available potassiumcontent improved by 16.62%,the exchangeable magnesium content improved by 49.60%,the Fe content improved by 0.62%,the Mn content improved by 15.93%,the Na content improved by 46.89%;the DOC content of Eucalyptus improved by 28.08%.4.Soil chemical indicators(elements,trace elements)will change with the depth of soil layer,the rotation of tree species and age.To illustrate the relationship between them,the paper has made correlation analysis and RDA analysis by SPSS software and Canoco software.The results shows:There are different degrees of correlation between soil pH,total carbon,DON,total nitrogen,DOC,mineral nitrogen,nitrate nitrogen,ammonium nitrogen,Hydrolyzable nitrogen,total phosphorus,available phosphorus,total potassium,available potassium,total calcium,exchangeable calcium,total magnesium,exchangeable magnesium,Al,Fe,Mn,Zn,Na in the soil of second rotation Chinese fir,Eucalyptus and Acacia melanoxylon,and shows different positive and negative related or unrelated level.they are interact and restrict with each other.5.Soil fertility was higher at 0～10 cm soil layer both in Chinese fir soil,Eucalyptus and Acacia melanoxylon.Comprared to second rotation Chinese fir,soil fertility of Eucalyptus and Acacia melanoxylon were higher,and soil fertility of Eucalyptus was highest.The reason would be continuous plantation of Chinese fir consumed soil nutrient and lead to fertility decline.After rotation Eucalyptus and Acacia melanoxylon,a large amount of litter contain rich nutrients,after microbial decomposition,the nutrient elements can return to the surface soil in time and improve the soil fertility. |
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