Foliar Nutrient Diagnosis For Litchi(litchi Chinensis Sonn.vs.Feizixiao) In South China

Feizixiao（Litchi chinensis Sonn.）is the most widely cultivated litchi species in China.Twenty-two typical Feizixiao orchards,located in the main production regions of South China including Guangdong,Guangxi,Hainan,Yunnan and Fujian,were chosen in this study.193,186 and 159 leaf samples were collected at the fruit swelling stage（FSS）of2016,the last autumn branch maturing stage（LABMS）of 2016 and FSS of 2017,respectively.And the foliar nutrient（N,P,K,Ca,Mg,S,Zn and B）concentrations of all samples were detected.The fruit yield was recorded for each tree at harvest of 2016 and2017,and the high yield levels for nutrient diagnosis in both years were determined by squared Euclidean distance.The relationship between leaf nutrient concentration and fruit yield was fitted,and five methods such as Critical Value Approach（CVA）,Sufficiency Range Approach（SRA）,Deviation from Optimum Percentage（DOP）,Diagnosis and Recommendation Integrated System（DRIS）,and Compositional Nutrient Diagnosis（CND）were used to evaluate the foliar nutrient status.While the vantages of diagnosis results of five approaches were evaluated,suitable diagnosis norms for foliar nutrients in Feizixiao were established to assess the nutrition status and improve nutrient management in litchi.The results were described as follows:（1）The yield calculated by multiplying fruit yield per tree in one orchard and plantation density,reflected more widely yield coverage than that obtained by multiplying mean fruit yield of all sampled trees in one orchard and plantation density.The fruit yield（yield per tree multiplied by plantation density）varied from 113 to 38520 kg·hm^-2 and from 832 to48878 kg·hm^-2 in 2016 and 2017,with the means of 12560 and 15473 kg·hm^-2,respectively.The high yield levels were designated as 19710 kg·hm^-22 and 19785 kg·hm^-2 for both years,based on the classification of fruit yield subjected to squared Euclidean distance and the commonly-acceptable high yield(18750 kg·hm^-2 for Feizixiao)in practice.（2）In contrast to the foliar nutrients at FSS of 2016,foliar K,Ca,Mg,S and Zn concentrations at FSS of 2017 were significantly increased,however,foliar P concentration was significantly decreased（p<0.05）.Foliar Ca,Mg,S,Zn and B concentrations at FSS of2017 were significantly higher than those at LABMS of 2016,but foliar N,P and K concentrations were significantly lower（p<0.01）.The discrepancies of foliar nutrients between the high yield population at FSS of both years were considerably decreased,but those between LABMS of 2016 and FSS of 2017 were still significant（p<0.01）,indicating that various foliar nutrient indices are needed for different growth stages.（3）Regression analysis showed that close relations were calculated between fruit yield versus foliar Ca,Zn and B at FSS in 2016,and between fruit yield versus foliar N and Ca at LABMS in 2016 and foliar N,P,K,S and Zn at FSS in 2017.（4）Based on the relation between fruit yield versus foliar nutrient,diagnosis indices of some foliar nutrients were achieved by CVA.The necessity of litchi tree nutrients was qualitatively,but not quantitatively evaluated by DOP,DRIS and CND.Moreover,the diagnostic accuracy for FSS was higher than that for LABMS by these three methods.And the most deficient or abundant nutrients were more precisely assessed than the others.Finally,diagnosis indices calculated by SRA were accepted as the norms for foliar nutrient diagnosis in Feizixiao,due to their stability and versatility for all nutrients.（5）The optimal foliar nutrient ranges for Feizixiao are recommended as N 16.7¹9.2g·kg^-1,P 1.06¹.25 g·kg^-1,K 5.1⁶.7 g·kg^-1,Ca 7.7¹1.0 g·kg^-1,Mg 2.5³.7 g·kg^-1,S1.51¹.81 g·kg^-1,Zn 19.6³2.6 mg·kg^-1,B 11.5¹9.2 mg·kg^-1 at FSS,and N 19.7²2.0g·kg^-1,P 1.69¹.95 g·kg^-1,K 10.8¹2.7 g·kg^-1,Ca 3.0⁴.1 g·kg^-1,Mg 2.5².9 g·kg^-1,S1.38¹.57 g·kg^-1,Zn 15.0¹8.9 mg·kg^-1,B 10.8¹6.8 mg·kg^-1 at LABMS.（6）As evaluated by the above diagnosis norms,the trees of optimal foliar nutrients accounted for less than 50%of the total sampled trees in both years,and nutrient deficiency and surplus coexisted in the sampled trees.This phenomenon highlights the necessity of foliar nutrient diagnosis in litchi production in South China.