Investigation On Nutritional Deficiency Yellowing Leaves And Reason Analysis Of Top-grafting Hybrid Citrus Trees In Chongqing

In this study,the trees of yellowing and normal top-grafting hybrid citrus orchards were used as experiment objects in Chongqing's main citrus production areas?Zhongxian County,Changshou district and Tongliang District?.A total of 61 samples were collected the orchards of Fengheng and Hengcai company in Xinli Town,Hengcai and Chunken company in Bashan,Chunken company in Shibao,Xinshuo company in Wuyang,Xiangheng company in Dongxi at Zhongxian county,Huifeng,Xuntai company and Erdengyan cooperative in Longhe at Changshou county and Zhongbang in Bachuan at Tongliang county.The fertilization of orchards,leaf physiological indicators and yield were investigated.Meanwhile,mature leaf and soil samples were collected for mineral element measurement;fruit at maturation period were collected for internal and external quality analysis.Several methods of statistical analysis were used to assess significant differences among fertilization status,leaf physiological indexes,soil physical and chemical conditions,leaf mineral nutrients and fruit quality in the yellowing and normal hybrid citrus orchards.The aim was to find out the key factors affecting the occurrence of yellowing in top-grafting hybrid citrus.The main results are as follows:?1?Different orchards showed the large differences in fertilization levels,and fertilization method in all top-grafting hybrid citrus orchards such as irrational fertilizations of less application,multiple application and partial application.The annual average fertilization of organic manure was at high level?>300 kg/667 m²?in all?Orah‘[?C.reticulate×C.sinensis?×C.tangerine cv Orah]orchards.However,it was at low level?<200 kg/667 m²?in the?Harumi‘[C.reticulata×C.sinenesis cv Harumi]orchards,except for company of Fengheng and Xiangheng.The excessive problem of annual average fertilization of nitrogen?N?,phosphate?P₂O₅?and potash?K₂O?were existed in all?Orah‘orchards,such as excessive fertilization of Chunken company,improper proportion?1:1:1?of Xiangheng company,less application?P₂O₅?of Xinshuo company and bias fertilization of K₂O?Fengheng and Xinshuo?.Some problem was similar to fertilization of?Orah‘orchards in?Harumi‘orchards.Fertilization of N,P₂O₅and K₂O were the most abundant and were even in excess of the?Harumi‘orchards?40.29 kg/667 m²,18.29 kg/667 m² and 41.71 kg/667 m²?of Huifeng company.The fertilization proportion of Xiangheng was inappropriate?1:1:1?and the amount of N application was insufficient.The amount of P₂O₅ fertilizer application in Xuntai was below the suitable range?<6.67 kg/667 m²?.?2?Leaf physiological indexes of top grafting hybrid citrus orchards display considerable variability between different types and varieties.The length of the normal leaves exhibited as?Harumi‘>?Jinqiushatangju‘[C.reticulate×C.reticulate cv?Jinqiushatangju‘Shatangju]>?Orah‘,the width was?Jinqiushatangju‘>?Harumi‘>?Orah‘,the thickness was?Jinqiushatangju‘>?Orah‘>?Harumi‘,the relative chlorophyll content?SPAD?was?Orah‘>?Jinqiushatangju‘>?Harumi‘.The yellowing leaves of three citrus cultivars showed a decrease in leaf length,an increase in leaf width or thickness,and a significant decrease in SPAD.According to the normal/yellowing ratio of leaf physiological indexes,the effects of yellowing on SPAD of three cultivars were as follows:?Orah‘?2.55?>?Harumi‘?2.24?>?Jinqiushatangju‘?1.80?.?3?Analysis of soil physical and chemical properties showed that alkaline soil accounted for a relatively low proportion?39.39%?in normal orchards,and a much higher proportion?60.71%?in yellowing orchards.The results indicated that yellowing orchards were more alkaline than normal orchards.Overall,top grafting hybrid citrus orchards was at low level of the organic matter.The distribution proportion of organic matter?content below 1.5%?was 30.30%in normal hybrid orchards,which was higher than that of yellowing orchards.In the half of yellowing hybrid orchards,the content of organic matter was below 1.5%.?4?Analysis of soil available nutrient showed that the average content of available P and Mg in yellowing orchards soil was significantly lower than that in normal.However,the average content of soil available Ca was significantly higher than that in normal?P<0.05?.The distribution frequency of soil available P and Mg showed a higher percentage?>60%?at deficiency or low level in yellowing orchards compared with the normal orchards.All orchards showed an insufficient of soil available N and excessive of soil available K and Ca.Soil available Fe in yellowing orchards was significantly lower than that in normal?P<0.05?.The results of distribution frequency of micro elements showed that,excessive 20%yellowing orchards with an insufficient of available Fe and all the orchards were short of available Zn,Cu and B?28.57%-75.00%?.However,soil available Fe?66.67%?and Mn?42.42%?of normal orchards,soil available Mn?28.57%?of yellowing orchards were excessively high.?5?Analysis of leaf macro or middle nutrients showed that the average values of N,S and Ca existed significantly difference in both yellowing and normal orchards.The average values of normal orchards were significantly higher than those of yellowing?P<0.05?.According to leaf nutrient classification standard of Chongqing,the N content of leaf?3.06%?in the normal orchards was at high level,the Ca content of yellowing orchards?2.96%?was at low level,the Mg content of both normal?0.22%?and yellowing?0.21%?orchards was at low level,the average values of other macro or middle elements were at the appropriate range.The coefficient of variation of Mg?>40.00%?was larger than that of other macro or middle elements.Except S,the coefficient of variation showed a trend that the yellowing orchards was larger than in those of normal.The distribution frequencies of N,P,K in yellowing orchards leaves and K in normal orchards leaves were showed a bipolar phenomenon.The distribution frequencies of leaf Ca was relatively high in yellowing orchards?42.86%?,but distribution proportion of leaf Mg was very high in all orchards?>80%?.From the analysis of leaf micro nutrients,the content of Fe and Mn in normal orchards was significantly higher than that in yellowing orchards,while the content of Cu in normal orchards was significantly lower than that in yellowing?P<0.05?.The Fe and Mn were at the suitable level in most normal orchards.However,the contrary results gained in yellowing orchards,especially Fe deficiency?>70.00%?.Leaf Zn deficiency was at very high level in both two types of orchards?close to 100%?and Cu and B deficiency was slightly lower.The main difference of micro element distribution between normal and yellowing orchards was Fe,followed by Mn.?6?Cluster analysis of soil pH and organic matter showed that all the orchards were divided into five categories.Among different categories,soil pH and organic matter showed significant differences and negative correlation.All the orchards were divided into five categories using the cluster analysis of soil available macro and middle nutrients.Significant and even extremely significant differences of soil available nutrients including macro or middle nutrients were also observed among different classifications.Cluster analysis of soil available micro elements were divided into six categories,and the difference of soil available micro nutrients gained the similar result of macro and middle nutrients.Cluster analysis of leaf macro or middle elements showed all orchards were classified into four categories.Category ? was the normal orchards type with typical Mg deficiency.Category ? was a typical Ca insufficient.Category ? showed deficiency of N,Ca and Mg.Category ? showed deficiency of N and Mg,and Ca was slightly lower.Category ? and ? were the yellowing orchards type.Cluster analysis of leaf micro elements showed all the orchards was classified into six categories.The normal and yellowing orchards existed in all six types of orchards.?7?The results of correlation analysis among soil,leaf nutrients and fruit quality showed that,some correlations between soil available nutrients and leaf nutrients,soil available nutrients and fruit quality,leaf nutrients and fruit quality.There was a strong correlation between soil available nutrients and leaf nutrients in?Harumi‘and?Orah‘orchards,followed by leaf nutrients and fruit quality,soil available nutrients and fruit quality.Based on the above results,the comprehensive effect determined preliminarily was the main cause of yellowing that including multiple factors in top-grafting hybrid citrus orchards.The first reason was soil physical and chemical properties,which include high pH level,alkaline soil and low content of soil organic matter.And the seconde reason was irrational fertilization and low input of organic fertilizer.Thirdly,the contents of available P,Mg,Zn,Cu and B were low in soil,and the leaf nutriention of N,Ca,Mg,Fe and Zn were relatively deficient at the yellowing orchards.In order to avoid or correct the yellowing of leaves and achieve high yield and good quality of top grafting hybrid citrus orchards,it is should be applied many measures such as regulating the soil pH,adding organic fertilizer,the rationalizatal fertilization,and alkali-resistant rootstocks in hybrid citrus production.