| The citrus industry in China has developed rapidly,and the total cultivated area and yield of China have ranked the first in the world.The citrus industry has become one of the pillar industries for rural economic development in the south China,particularly in the Three Gorges Reservoir area.Fertilization is one of the most important factors affecting the yield and quality of citrus.The rational application of nitrogen and new fertilizers is an important measure to promote citrus growth and improve yield and quality.Recent years,the application ratio of nitrogen and phosphorus in Chinese young citrus orchards is general excessive.At the same time,the nitrification inhibitor DMPSA has been little studied on citrus.'Harumi'tangor[Citrus reticulate ×(C.reticulata × C.sinenesis)]is an excellent hybrid citrus variety with high sugar,low acidity and late maturity.It was planted in China's Sichuan province and other citrus production areas.However,it is still unclear about the appropriate nitrogen level for the growth of "Harumi' tangor seedlings,the distribution of nutrients in different parts of the tree,and the influence of root layer nitrogen on the aboveground canopy.Therefore,five nitrogen application ratios during two consecutive years were conducted in this study:T1(control with 0 nitrogen application),T2(control with 125 g tree-1 nitrogen application+DMPSA),T3(control with N156 g tree-1 nitrogen application+DMPSA),T4(control with N156 g tree-1 nitrogen application),T5(control with N234 g tree-1 nitrogen application).The plant height,stem diameter,leaves number and canopy volume of citrus,biomass,nutrient content and cumulative distribution in different parts of citrus were regularly measured,to analyze the linear relationship between root soil nitrogen and aboveground.The aim of this study is the effects of different nitrogen application ratios on the growth and nutrient distribution of 'Harumi'tangor seedlings.Furthermore,the effects of adding DMPSA on root nitrogen regulation and biomass were also explored to provide a reference for determining the appropriate N application rate to citrus seedlings in actual production.This study could lay the foundation for canopy establishment and results.The main results are as follows:(1)Nitrogen(N)application of 156g tree-1(T3,T4)was most suitable for the growth of'Harumi' tangor seedling,which promoted the increase of plant height,stem diameter and leaf number of citrus,accelerated the establishment of aboveground canopy.The increase of leaf area in the aboveground was promoted by nitrogen fertilizer,and the biomass of citrus increased with the increase of leaf area index and canopy volume.Nitrogen can promote the growth of citrus root system.In 508 days after transplanting,the root length,surface area and volume of T3 treatment increased by 80.4%,135%and 81.3%,respectively,compared with the T1 treatment.Under the same N application condition,adding DMPAS can significantly improve the biomass and nitrogen accumulation of citrus.The order of biomass of each part is as follows:leaf>shoot>stem>main root>lateral root.The distribution rate of biomass was different in different parts of citrus seedlings,the aboveground part contributed 64.08-84.26%to the whole plant biomass.The distribution rate of root system to the whole plant biomass was 15.74-35.92%.The distribution rate of aboveground part was significantly higher than that of the underground part.(2)The absorption of macro element nitrogen(N)and medium element calcium(Ca)by young citrus trees were the highest,and the absorption of mico elements iron(Fe)and Manganese(Mn)were the highest.The contents of different nutrient elements were varied from different parts The contents of high mobility elements nitrogen(N),phosphorus(P),potassium(K)and magnesium(Mg)were the highest in the new leaves,which were higher than the old leaves.The contents of Ca and boron(B)in the new leaves were more,while the contents of Fe,Mn and zinc(Zn)with less mobility were more in the lateral roots.Increasing nitrogen application rate can increase the N content in different organs of the young citrus trees,decrease the absorption of copper(Cu)in roots,stem and leaves,and increase the absorption of Fe in shoots.The accumulations of N,P,K,Ca,Mg and B in the aboveground part of citrus were much higher than that in the underground part,accounting for 73.4-96.2%,52.0-95.0%,64.9-87.8%,77.4-90.9%,66.2-87.5%,70.4-93.4%of the plants,respectively,which were mainly distributed in leaves and shoots.Fe,Mn,Cu and Zn were mainly accumulated in the root system,accounting for 62.8%,84.5%,48.0%and 76.0%of the plants respectively.Meanwhile,micro elements(Fe,Mn,Cu and Zn)accumulated in lateral roots much higher than lateral root.(3)T3 treatment can increase the NH4+-N content in the soil,improve the soil pH,while reduce the soil NO3--N content,slow down the conversion process from NH4+-N to NO3--N,significantly inhibit the nitrification of the soil,as a result,improve the nitrogen recovery rate of citrus.(4).Correlation analysis showed that the root length,surface area and volume were positively correlated with nitrogen accumulation and utilization in citrus.The proliferation of citrus root system was beneficial to the absorption,accumulation and utilization of nitrogen,thus promoting the growth of citrus aboveground and the establishment of citrus canopy.In summary,the moderate nitrogen supply level can promote the growth and nutrient absorption of citrus seedlings.Adding nitrification inhibitor at the appropriate nitrogen level can slow down the mineralization of nitrogen fertilizer,further promote the growth of citrus root system,and improve the recovery rate of nitrogen in citrus,which is conducive to the rapid establishment of the canopy of young trees. |
PDF Full Text Request