Analysis of the causes of leaf yellowing in Harumi and Orah mandarins in Chongqing
Leaf yellowing of Harumi and Orah mandarins top-grafted on sweet orange occurred in Zhongxian,Changshou,Tongliang of Chongqing.To find out the main causes of leaf etiolation,soil and leaf samples were collected from normal and etiolated orchards of Harumi and Orah.The soil physical and chemical properties,leaf mineral elements contents and leaf SPAD value were compared,and the relationship between soil physical and chemical properties,leaf SPAD value with leaf mineral nutrition was analyzed.The results showed that the average soil pH value(8.09)of the yellowing orchard of Harumi was significantly higher than that of the normal orchard(6.89),with the soil available iron content(average)significantly lower than that of the normal garden,the exchangeable calcium content significantly higher than that of the normal orchard,and the leaf iron content significantly lower than that of the normal garden.The content of soil exchangeable calcium in leaf yellowing Orah orchard was higher than that in normal orchard,with the content of available iron significantly lower than that in normal orchard,and the average content of nitrogen,sulfur and iron in leaves significantly lower than that in normal orchard.Leaf SPAD value was significantly positively correlated with leaf nitrogen and leaf iron content,respectively.The boosted regression trees analysis showed that the contribution of leaf iron content to leaf SPAD was 35.23％,which was the highest,followed by 22.29％of nitrogen.Excluding natural disasters or diseases factors,it was considered that the etiolation of leaves in top-grafted hybrid citrus orchard was due to the high soil pH value and exchangeable calcium,which led to the reduction of soil available iron content,and inhibited the absorption of Fe by trees,resulting in the etiolation of leaves.In addition,the low content of N in leaves was one of the factors leading to the etiolation of Orah.
万方数据
维普
