| Fertilization is an important way to promote the growth of trees,but the current research on forest fertilization is mainly focused on the fast-growing tree species,while the research on forest fertilization of precious tree species is less,which limits the recovery and cultivation of precious tree species.This study chose a 10 years old and a 15 years old Fraxinus mandshurica plantation forest stands from Shangzhi Xiaojiu experimental forest farm in Heilongjiang province as the research object and set nitrogen fertilizer(N1:5 g/m2、N2:12.5 g/m2、N3:20 g/m2),phosphate fertilizer(P1:7.5 g/m2、P2:15 g/m2),nitrogen and phosphorus fertilizers(N1P1,N1P2,N2P1,N2P2,N3P1,N3P2)and contrast(CK)with a total of 12 fertilization treatments.Measured the indexes of trees height,diameter at breast height,leaf chlorophyll and the nutrient concentration,as well as forest stands soil nutrients after fertilization,we conclude the following conclusions:(1)Nitrogen and phosphorus fertilization could significantly improve the contents of ammonium nitrogen and available phosphorus in the surface soil of the 10-year-old and 15-year-old ash and reach max 2.99 mg·g-1、1.98 mg·g-1 and 2.50 mg·g-1、3.49 mg.g-1 under N2P2、N3P3 treatment and N3P2、P2 treatment.However,it only had a significant effect on the ammonium nitrogen in the deep soil of the 10-year-old ash plantation and reach max 2.09 mg·g-1 under N3 treatment,but had no significant effect on the available phosphorus in the deep soil,nitrate nitrogen in the surface and deep soil,and the total NPK in the surface and deep soil.Fertilization for 3 consecutive years had a significant effect on the total phosphorus content in the surface soil of the 15-year old ash plantation and reach max 4.51 mg·g-1 under P2 treatmen,but had no significant effect on the total nitrogen and potassium in the surface and deep soil and total phosphorus in the deep soil.(2)Each fertilization treatment of 10-year-old and 15-year-old ash increased the growth of DBH of ash,among which,N2P1 and N1P2 treatments of two forest ages were significantly different from CK treatment and higher 57.4%、53.7%and 44%、34.7%respectively;and the contents of chlorophyll a,chlorophyll b,total chlorophyll and SPAD value(CI)in the leaves of 10-year-old ash were increased by each fertilization treatment,and under the condition of different fertilizations,SPAD value and chlorophyll content changing trend is consistent,the maximum are both processed in N2P1 where SPAD value and chlorophyll a,total chlorophyll are 40.20 and 2.51 mg·g-1,3.47mg·g-1,showed that fertilization has promoting effect to the growth of ash,especially nitrogen and phosphorus fertilization.(3)On the whole,the N content in the leaves of both 10-year-old and 15-year ash could be significantly increased by each fertilization treatment,in particular,high level N and N plus P treatment,and the two stand ages’ max 28.13 mg·g-1 and 41.81 mg·g-1 appear in the N3 and N3P2 treatment respectively.However,each treatment had no significant effect on the contents of P,K,Fe,Mn,Cu,Zn in the leaves.Compared with CK,the concentrations of Ca and Mg in the leaves of 10-year-old ash under each fertilization treatment decreased,but there was no significant effect on the contents of Ca and Mg in the leaves of 15-year-old ash under each fertilization treatment,indicating that the stand age was small and the demand for Ca and Mg was large.(4)Through the DRIS graphic method in the diagnosis of 10 years old and 15 years old ash elements ratio scope of different nutrition status,found that 10 years N/P、K/P、K/N balance status are 12.083-19.733,3.58-6.498,0.286-0.348 and 15 years P/N、K/P、K/N balance status are 0.061-0.105,2.818-5.030,0.245-0.331,and compared with the diagnosis of 10 years old ash,15 years at various nutritional status of ash K/P and K/N are smaller,showed that with the increase of forest age,compared to K,ash has increased the demand for N,P.According to both DRIS diagram method and index method,the order of fertilizer demand of 10-year-old ash forest stand is P>N>K.However,the index method showed that the fertilizer order of the 15-year old ash stand was N>P>K through accurate digital diagnosis.In this study,the growth and physiological response of ash under different ratio of nitrogen and phosphorus fertilization were measured,and it was found that fertilization could significantly promote the growth of ash,especially the N2P1 and N1P2 treatment.And diagnosis systems of N,P,K nutrient balance status of the two stand ages were established based on nutrient content in leaves of high yield group after fertilization treatment. |
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