| Chinese fir[Cunninghamia lanceolata(Lamb.)Hook.]is one of the most important of fast-growing timber species in southern China and plays an important role in forestry.It has become a consensus that continuous planting of Chinese fir will lead to fertility decline.Burning and other traditional silvicultural measures were questioned and the shortcomings had constantly been reported.So the development of Chinese fir industry needs to seek new ways of silviculture that help maintains soil fertility,long-term productivity and sustainable development.Logging residue is the product of forest regeneration,and the management of it has profoundly influenced the development of the next generation of artificial forest land.Develop appropriate management measures for logging residues has great significance for maintaining soil fertility level and promote long-term development of plantation productivity.Available nutrients are nutrients that can be directly absorbed by plants and it can indicate the level of soil fertility.Experiments in Xiayang forest farm,Nanping City,Fujian Province,China,were established to investigate the effects of harvest residue management on soil available nutrients.The aim is to further explore the impact of residue management on soil nutrient in Chinese fir plantation.Five logging residue treatments include:(1)whole tree harvest and forest floor removal,(2)whole tree harvest,(3)stem only,(4)double residue,(5)stem only and burning.Available nutrients include:ammonium nitrogen(NH4+-N),nitrate nitrogen(NO3--N),available phosphorus,available potassium,exchangeable calcium and magnesium(Ca2+,Mg2+).soil samples were collected at 3,6,9,12,15 and 19 years after tree replanting.The results are in the following:(1)The diameter of the 19-year-old second-generation Chinese fir plantations was range of 19.38-22.44 cm,with 20.76 cm on average and the tree height range of 16.81?18.94 m,with 18.01 m on average.Growth status of Chinese fir was better than that of other Chinese fir forests at the same latitude.There was an extremely significant difference between the four blocks in growth(P<0.01),but five kinds of logging slash treatments had no significant effect on the growth of 19-year-old second-generation Chinese fir plantations(P>0.05).Under the five treatments,the size of forest stock volume was BL1>SB>BL3>BL2>BL0,and the individual volume was BL2>BL1?BL3>BL0>SB.(2)The changes of soil available nutrients were different from the sampling year.Multiple comparisons ANOVA showed that there were significant(P<0.05)or extremely significant(P<0.01)differences in the contents of other available nutrients in each sampling period,except available phosphorus.Ammonium nitrogen and available potassium,exchangeable magnesium all decreased with the increase of age.Ammonium nitrogen increased abruptly in 11-year-old and it may be caused by extreme hypothermia.6-year-old Chinese fir plantations soil available potassium content was significantly lower than that of 3 years old and it may be related to the decomposition rate of the logging residue.The soil nitrate nitrogen and exchangeable calcium increased with age first decreased and then increased,with the maturation of young stage to return to the basic level.The content of available phosphorus in the soil was stable in the whole growth process.Vertical variance analysis showed that the contents of available nutrients in the soil layer was significant or extremely significant and the contents of Ammonium nitrogen,available phosphorus,available potassium,exchangeable calcium and exchangeable magnesium decreased with the increase of soil depth,but the nitrate content increased with the increase of soil depth.(3)There were no significant differences in the content of available potassium,exchangeable calcium and exchangeable magnesium in surface soil among five logging residue treatments and this difference decreased with soil depth.Treatments had no significant effect on nitrate nitrogen content and had significant effect on ammonium nitrogen in only part of the year(12 years),and also had extremely significant or significant effect on available phosphorus content of 6 year old,12 year old,15 year old and 19 year old in Chinese fir plantations.The order of the contents of available nutrients in soil under different treatments as followers,with soil ammonium nitrogen was BL3>BL0>BL2?BL1>SB,Soil available phosphorus was BL3>BL1>BL0>BL2>SB,soil available potassium was SB>BL1>BL3>BL2>BL0,soil exchangeable calcium was SB>BL3>BL2>BL 1>BL0,soil exchangeable Mg was SB>BL2>BL3>BL1>BL0.There was no significant difference of soil nitrate nitrogen content among treatments.Analysis of repeated-measures ANOVA showed that available nutrients concentrations for the three depth layers varied between years(P<0.01),except available phosphorus in surface soil.Harvest residue management had extremely significant effects of on available phosphorus,available potassium,exchangeable calcium and exchangeable magnesium in 0-10cm soil.The interaction of sampling year and harvest residue management had extremely significant effects of soil ammonium nitrogen,available potassium,exchangeable calcium and exchangeable magnesium and this effect decreases with increasing soil depth.(4)Correlation analysis indicated that there was a significant correlation between soil available nutrients,but between nitrate nitrogen and other elements,between ammonium nitrogen and exchangeable calcium excepted.Ammonium nitrogen,available potassium,exchangeable calcium and exchangeable magnesium were extremely significantly positively correlated with pH.(5)Principal component analysis showed that the order of the effects of five treatments on soil available nutrients was as follows:SB>BL2>BL3>BL1>BL0.Under the treatment of burning,the content of nitrate nitrogen and available phosphorus in the soil was the lowest,but these two elements were the highest under the treatment of double residue.Based on the actual significance,the treatment of burning is not suitable for Chinese fir plantations,because phosphorus is the limiting factor for the development of Chinese fir plantation productivity.Comprehensively,The treatment of double harvest residue was the most beneficial to soil available nutrients,followed by stem only.These observations suggested that harvest residue management had no significant effects on the growth of 19-year-old Chinese fir in subtropical China.The soil available nutrients varied between years.The management of harvest residue had a significant effect on soil available potassium,exchangeable calcium and exchangeable magnesium,and less impact on available phosphorus and ammonium nitrogen,and no significant effect on nitrate nitrogen.Treatments of double harvest residue and stem only are conducive to maintaining soil nutrient status. |
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