Studies On Optimal Fertilization And Annual Nitrogen,Phosphours And Potassium Cycle Of Pear Trees In Yongchuan,Chongqing

Pear(Pyrus L.)is globally widely cultivated in ~85 countries including China(except the Hainan Island),which is one of the earliest countries to grow pear.With 1.12 M harvest area and 19.50 M tons pear fruit production in 2016,China accounts for about 70% of the total world‘s harvest area and fruit production.However,the average fruit production was 17 t/hm~2 in China only(ranking at 23 th globally).Through both the field surveys and literature review,we have found that most of the pear orchard lands in Chongqing are in poor plant growth conditions,including shallow soil layers,low soil fertility,and un-rational fertilization,etc..Meanwhile,excessive input of chemical nitrogen(N)and phosphorus(P)for pursuing high pear fruit yield has resulted in the nutrients surplus in the pear orchard,which not only has caused resource waste and cost increase,but also seriously environmental pollution problems.By combined data from the questionnaire survey collected in 2016 in Chongqing with literature reviews,a mature fruiting stage of pear(Huanghua variety)orchard in Huanggua Hill of Yongchuan District has been selected for a field experiment to mitigate the input of chemical fertilizers while increasing the fruit production and quality with five optimized fertilization treatments and seven N fertilization rates.Stable isotope of 15 N labelling technique was also employed to understand N uptake and distribution in leaves and fruits.The objectives of these experiments were to provide a theoretical win-win basis for decreasing the use of fertilizers while increasing fruit yield and/or quality.The main results are as follows:(1)Data from the questionnaire survey showed that soil available nutrients in Chongqing‘s pear orchards(p H 4-5)we generally relatively good and ranged from poor,medium to rich,but 93% of the orchards were lack of soil organic matter.Meanwhile,the averaged nutrient input to the pear orchards in Chongqing was 604(N),319(P2O5)and 355(K2O)kg/hm~2.The Yongchuan District of Chongqing had highest N fertilization of 1,027 kg N/hm~2.In general,the excessive N fertilization in the pear orchards in Chongqing is serious,and an optimal chemical fertilization is timely needed.(2)Soil available N,P and K(potassium)positively correlated with total N,P and K,and fruit N,P and K positively correlated with leaf N,P and K,respectively.Significantly positive correlations were displayed between leaf N,P and K,and a significantly negative correlation between leaf calcium and magnesium.(3)Among the five optimal fertilization treatments(applications of N,P2O5,K2 O were OPT1: 271,154,244 kg/hm~2;OPT1-25%N: 203,154,244 kg/hm~2;FP: 521,334,334 kg/hm~2;OPT2: 321,194,264 kg/hm~2;OF: 50% chemical N was replaced by organic manure on the basis of OPT1),no significant differences were observed for the taste of pear fruit,fruit shape,quality index.While leaf nutrients were in an appropriate range,significantly greater fruit yields among these five fertilizations ranked as OPT1(25.1 t/hm~2)> FP(24.8 t/hm~2)> OPT2(23.3 t/hm~2)> OF(22.4 t/hm~2)> OPT1-25%N(17.7 t/hm~2),indicating that the OP1 was the best fertilization practice.In addition,the annual variation of leaf N,P and K showed a decreasing trend,with the maximum decrease during the flowering and fruit expansion stage.(4)The soil available N and K at 0-20 cm depth were decreased during the flowering,expansion and vigorous fruiting stage,while rose again during the maturity stage,but the nutrient concentrations were higher in the full bloom stage than in other stages.Similar soil nutrients changes were observed between the 20-50 cm and 0-20 cm depth.(5)Results from soil 15 N labelling showed a 15 N competition between adjacent trees,but the 15 N absorption was higher in the central 15N-donor pear tree than in its adjacent trees.After absorption 15 N was transported to the nutrient priority demand organ,the leaf and fruit bud had less N absorption form the spring fertilizer application,while speeding up the N absorption and utilization during the fruit development period.The Ndff%(N derived from fertilizer)was higher in the fruits than in the leaves since the beginning of the young fruit stage,indicating that a high N-demand in the flowers or fruits than in the leaves.(6)No significant differences were observed among the seven fertilization treatments(Fertilization as 71,203,230,271,311,338 and 406 kg N/hm~2,P2O5 and K2 O was 154 and 244 kg/hm~2)for the fruit hardness,soluble solids and stone cell.The number of stone cells and titratable acid were firstly decreased and then increased with the increase of N fertilization rate,while fruit VC was increased with the increase of N fertilization rate.Meanwhile,the single fruit weight and yield were increased,but not the fruit shape,with the increase of N fertilization rate,while the excessive N application(OPT1+50%N)decreased the pear yield.The fruit number had singnificant effects on pear yields.Significantly greater fruit yields among the seven fertilization treatments patterned as OPT1+15%N(25.2 t/hm~2)> OPT1+25%N(25.2 t/hm~2)> OPT1(25.1 t/hm~2)> OPT1-25%N(18.3 t/hm~2)> OPT1+50%N(17.1 t/hm~2)> OPT1-15%N(16.8 t/hm~2)> OPT1-N(14.9 t/hm~2).