Effect Of Subirrigation And Nitrogen Fertilizer On Seedling Quality And Outplanting Performance Of Quercus Variabilis Seedlings

Fertilization and irrigation are the crucial management parts of cultivating seedlings during the nursery stage because of the limited container volume affecting the absorption of water and nutrition.Researches show that fertilization and irrigation have a great effect on regulating seedling quality,but the mechanism of the combination of the two methods affecting seedling quality is still unclear.Usually,the morphological attributes and nutrient status of seedlings are evaluated to indicate seedling quality in the nursery.However,evaluating seeding quality according to their outplanting performance is rare.Therefore,it is meaningful for improving seedling quality and outplanting performance by carrying out the modified techniques through studying the relationship between fertilization,irrigation and outplanting performance of seedlings.We study the containerized Chinese cork oak(Quercus variabilis Blume)seedlings in the following experiments:(1)by comparing the nitrogen(N)absorption of seedlings under different nitrogen rates,nitrogen forms,and irrigation methods,to find out the pattern of nitrogen absorption and utilization of Chinese cork oak seedlings with different irrigation methods;(2)by comparing the effect of nitrogen rates and irrigation methods on seedlings growth and physiology,to study the mechanism of irrigation methods affecting seedling quality;(3)by analyzing the response of growth and nutrient status of seedlings to controlled-release fertilizer and irrigation methods,to determine the optimal combination fertilizer rate and irrigation method when cultivating Chinese cork oak seedlings;(4)seedlings cultivated in the nursery for 1 year with different irrigation schedules,fertilizer rates,and container sizes were outplanted in the field,by analyzing the relationship between outplanting performance and seedling quality in the nursery,to estimate the seedling quality considering plants performance in the nursery and field.The main conclusions of this research are as follows:(1)In June and August,15N content of seedlings aboveground part was significant higher than that of seedlings underground part.In October,15N content of seedlings underground part was increased.The distribution of 15N content in seedling root was top root>middle root>bottom root.The nitrate nitrogen content was higher by 10%?52%than ammonium nitrogen content in the leaf with two fertilizer rates.The absorption of stem to nitrate nitrogen and ammonium nitrogen were similar.High fertilizer rate and subirrigation enhanced seedlings to assimilate nitrate nitrogen.Subirrigation improved the nitrate nitrogen fertilizer utilization of Chinese cork oak seedlings by 5%?21%comparing to overhead irrigation.(2)Nitrogen fertilizer and subirrigation promoted the growth and nitrogen.phosphorus,and potassium accumulation of Chinese cork oak seedlilngs.Nitrogen fertilizer accelerated the seedlings photosynthesis efficiency.The leaf incellar CO2 concentration with 125 mg N·plant-1 and subirrigation was lower than other treatment combinations by 15%?22%.125 mg N·plant-1 and subirrigation increased leaf chlorophyll a and total chlorophyll content by 12%-281%and 4%-321%,respectively.The leaf chlorophyll b and total chlorophyll content with subirrigation were 79%and 18%higher than those with overhead irrigation.Subirrigation reduced non-photochemical quenching coefficient with 20%comparing to overhead irrigation.It reduced the consumption of energy to dissipate heat and enhanced the captured light be used in photosynthesis.High nitrogen fertilizer significantly increased substrate nitrogen concentration and EC,and reduced substrate pH.The substrate nitrogen concentration with subirrigation was significant higher than that of overhead irrigation.Subirrigation reduced the middle substrate pH and improved bottom substrate pH.The substrate EC with subirrigation and nitrate ammonium fertilizer was 0.5 1?1.35 dS m-1,however,did not have negative effect on seedling growth.(3)The optimal combination of fertilizer rate and irrigation method to cultivate Chinese cork oak seedlings was 125 mg N·plant-1 and subirrigation.The maximum EC of top and bottom substrate under subirrigation with controlled-release fertilizer was 4.69 dS· m-1 and 0.56 dS· m-1,which did not poison the seedlings.(4)Subirrigation improved plants survival,stem biomass,and stem phosphorus concentration by 23%,22%,and 17%after outplanted 1 year in the field,respectively.The height,root-collar diameter,and biomass of seedlings cultivated in D60 containers were 10%,8%,and 18%larger than those cultivated in D40 containers,respectively.Considering the growth and nutrient status of seedlings in the nursery and field,Subirrigation and D60 were variable alternation for Quercus variabilis seedlings cultivated in nursery.Subirrigation at 65%-75%TSWC in D60 could serve as a feasible option for producing high quality Chinese cork oak seedlings.(5)The effect of controlled-release fertilizer on height and root-collar diameter of outplanted seedling lasted at least 2 years.Subirrigation improved seedling height and root-collar diameter after 1 year outplanting.