Study On Fertilizer Requirement Regularity For Seedlings Of Carya Illinoinensis In Response To Different Exponential Regimes

An exponential fertilization experiment was conducted with six dose levels(applying a total of 0,100,200,400,600,800 mg·seedling^-1 in this experiment)of nitrogen to assess the effects of different nitrogen levels on growth dynamics,root morphology,photosynthetic characteristics and nutrient accumulation of one-year-old pecan seedlings.The objective of this study was to reveal the nitrogen demand and determine the optimal nitrogen amount for pecan seedlings.Results indicated that:?1?The height,ground diameter and biomass of pecan seedlings increased as the nitrogen fertilization increased from 0 to 600 mg·seedling^-1and then decreased with the nitrogen fertilization increased from 600 to 800 mg·seedling^-1.The maximum values were 33.4cm,5.08mm and 9.33g,which were 1.48,1.45,2.17 times of the CK treatment respectively..The root shoot ratio decreased with the nitrogen fertilization increased.?2?Chlorophyll a,chlorophyll b and total chlorophyll increased with the nitrogen fertilization increased.The root to shoot ratio of the pecan seedlings decreased with the increase of the amount of nitrogen.The SPAD values of the pecan seedlings increased with the increase of the amount of nitrogen.?2?The root length,root surface area,root volume and root biomass of pecan seedlings decreased with the increase of N supply.Effect of N total 100 mg for a plant was best to pecan seedlings,by the end of the study,the root length,root surface area,root volume and root biomassofpecanseedlingswere4882cm,830cm2,12.29cm3,3.84g,whichwere1.53,1.55,1.79,1.59 times of the CK treatment respectively.The specific root length of the pecan seedlings decreased with the increase of the amount of nitrogen.?3?The content of chlorophyll a,chlorophyll b and total chlorophyll increased with the increase of the amount of nitrogen.The net photosynthetic rate,stomatal conductance,intercellular CO₂ concentration and transpiration rate of pecan seedlings increased as the nitrogen fertilization increased from 0 to 600 mg·seedling^-1 and then decreased with the nitrogen fertilization increased from 600 to 800 mg·seedling^-1.The maximum values were 10.53?mol·m^-2·s^-1,0.192 mol·m^-2·s^-1,241.7?mol·mol^-1and 2.85 mmol·m^-2·s^-1,respectively.The?Fv/Fm?,Yield,Qp,ETR were increased until the nitrogen application rate of 600 mg/seedling,with the highest values of 0.795,0.356,0.379 and 23 respectively.?4?For exponential fertilization treatments the N accumulation increased 297%-692%,P accumulation increased 313%-536%and K accumulation increased 268%-485%with N concentration increasing 98%-335%,P concentration increased 107%-250%,and K concentration increased 84%-180%;The nutrient accumulation and total biomass of pecan seedlings increased as the nitrogen fertilization increased from 0 to 600 mg·seedling^-1 and then decreased with the nitrogen fertilization increased from 600 to 800 mg·seedling^-1;The nutrient concentration of pecan seedlings increased with the increase of with the increase of the amount of nitrogen;Critical level approach was used for identifying N,P and K deficiencies by means of foliar analysis in pecan seedlings,and the critical values of N,P,and K(were 22.58,1.89and12.71 g·kg^-1,while their optimal concentrations ranged from22.58 to 32.73,1.89 to3.15,12.72to 22.05 g·kg^-1,respectively.Based on these data,it could be concluded that 600 mg·seedling^-1 would be the optimal nitrogen amount for pecan seedlings in greenhouse.