Effects Of Harvesting Residues And Fertilization Managements On The Growth Of Chinese Fir And Soil Nutrient Availability

Chinese fir is the one of most important timber forest species in southern China.Chinese fir plantation covers subtropical region of China,and has an important strategic position in forestry construction.Although the clones of Chinese fir with different traits have been breeded out through tissue culture,cuttings and molecular techniques for a long time,the research on the effects of plantation management techniques on the growth and soil nutrient in different clones of Chinese fir is still less.After cutting,the fir can produce a large of harvesting residues such as branches,leaves and roots.How to rationally use the harvesting residues and improve the soil nutrient availability of reforest land is key to the cultivation of Chinese fir plantation.In addition,fertilization is an important management technique to effectively alleviate the decline of soil fertility in Chinese fir plantations.In recent years,with the continuousdevelopmentofslow-releasefertilizertechnology,slow-release compound fertilizer has been widely used in agricultural production,but the research on the effect of slow-release fertilizer on soil nutrients in the cultivation of Chinese fir plantation is still lacking.Therefore,this paper will carry out research on the effects of Chinese fir clones,residue treatment methods and fertilization techniques on forest growth and soil nutrient contents,and providing a theoretical basis for the sustainable management of Chinese fir plantations.We selected one Chinese fir plantation newly reforested in spring of2018.The 3×2 split-plot experiment design is used to compare of Chinese fir clone,harvesting residue crushing and slow release compound fertilizer application on the growth of Chinese fir seedlings and nutrients in plant and soil at the early stage of afforestation.We set up eight treatments:"Yang-020"and"Yang-061"clones of Chinese fir,harvesting residue placed in situ and crushed,and fertilization and no fertilization,and each treatment had 6 replications.The plant height,ground diameter and leaf C,N,P,K,Ca and Mg contents,soil C,N,P,K,Ca and Mg contents and soil NH₄⁺-N and NO₃^--N nutrient contents were measured.At the same time,soil water solution collector was buried at 30 cm and60 cm depth in each plot,and soil water solution was collected in June,July,September and November,respectively,and then DOC,SIN?NH₄⁺-N and NO₃^--N?and ion contents such as K⁺,Na⁺,Ca²⁺,Mg²⁺,and SO₄^2-were determined.The results are as follows:?1?Height and root collar diameter were 80.62 cm and 10.04 mm in“Yang-061”,and 68.13 cm and 8.35 mm in“Yang-020”,indicating clones of Chinese fir had significant impacts on seedling size.However,there were no differences in growth of Chinese fir by fertilization and harvesting residue crushing managements.There was no significant interaction between Chinese fir clones,residual crushing and fertilization on the growth and leaf nutrient content in Chinese fir.?2?Leaf N,P and Mg contents were 20.38,0.87 and 0.92 mg/g in“Yang-020”clone,and 17.33,0.75 and 1.02 mg/g in“Yang-061”clone.Leaf N and P content in“Yang-061”clone decreased 14.97%and 13.79%compared to“Yang-020”,but leaf Mg increased 10.87%.In addition,the addition of slow-release fertilizer increased leaf P,but decreased leaf Mg,and implying soil P nutrition might be key limit of growth of Chinese fir.Harvesting residues management did not change leaf nutritions.?3?The effects of Chinese fir clones,harvesting residues,slow-control fertilizers and their interaction on soil C,N,P,K,Ca and Mg contents and soil NH₄⁺-N and NO₃^--N nutrient contents were not significant.?4?Fertilization can immediately affect DOC and NO₃^--N,and ion contents in soil water solution in new reforested Chinese fir plantation.Fertilization increased NO₃^--N contents in soil water solution at 30 cm depth and DOC content at 60 cm depth.In addition,fertilization decreased SO₄^2-and increased Na⁺at 60 cm depth.Similarly,the nutrients of soil water solution between two Chinese fir clones were also different,and K+content at 30 cm and Na+at 60 cm in“Yang-020”clone were higher than that in“Yang-061”clone.But harvesting residue crushing treatment had no significant effect on nutrients of soil water solution.In addition,the nutrient contents in soil water solution has obvious monthly dynamic characteristics.Our results suggested that clones and fertilization had significant impacts on the growth and soil nutrients,but not for harvesting residues management.Considering a short-term experiment of six months,the impacts of siviculture and managements on the growth and nutrients in Chinese fir plantation should be further studied for a long-term period.