Effect of iron fertilization through pipe transfusion to trunk on iron nutrition in apple

 Abstract:【Objective】Iron deficiency chlorosis is still causing huge losses to crop yield and quality in cal⁃careous soils. The correction methods using iron fertilizer include soil application, spraying, injection andso on, but there are still some problems. Therefore, exploring new ways of the iron fertilization to improveapple iron nutrition is needed.【Methods】The container for holding iron fertilizer solution was a tankmade of bricks. The main pipe was a PVC pipe, and the branch pipes were made from PE. The soft capil⁃lary pipes had an internal diameter of 0.4 mm. One end of the capillary pipes was inserted into the branchpipe, and the other end connected to a dripper with a flow rate of 2 L·h^-1 that was inserted into the trunk,with one dripper per tree. The iron fertilizer used was Fe-N. The contents of the total iron and active ironin leaves, flowers, xylem and phloem of new shoots and fruits were measured; relative content of chloro⁃phylls (SPAD value), leaf weight, leaf thickness, and chlorophyll fluorescence were determined; and thecorrelation between SPAD and active iron was analyzed.【Results】Leaf SPAD values increased significant⁃ly and the leaves showed no symptom of chlorosis after infusion with iron fertilizer. The leaf SPAD values,leaf weight, leaf thickness, and the contents of total iron and active iron in the treatment with 16.4 ×10-3mol·L^-1 N-Fe (T1) were significantly higher than those in control. The chlorophyll fluorescence parame⁃ters of the leaves were affected by drip transfusion with different concentrations of Fe-N solution. Amongthem, the relative rate of electron transfer (ETR), ΦPSII, the actual quantum yield (Yield), PS potential ac⁃tivity of (Fv/F0), maximal fluorescence yield (Fm), the primary energy conversion efficiency of PS II (Fv/Fm )were higher in T1 than in the control. The total iron content in the shoot xylem had no significant differ⁃ence between treatment and control, but the active iron content in T1 was significantly higher than the other treatments. The active Fe contents in the phloem in T1 and T2 were significantly higher than that in thecontrol. The contents of total iron and active iron in the flower were significantly increased by iron treatments at the three concentrations, and so were those in the fruit. The leaf SPAD value was positively correlated with active iron content.【Conclusion】Iron fertilization through the pipe infusion to the trunk not only prevents leaf chlorosis but also significantly increases the iron content in the fruit and improves fruitquality. This method of iron fertilization has significant advantages such as high utilization efficiency ofiron fertilizer, simple operation, and labor saving, and is currently the best iron fertilizer application meth⁃od. The active iron content in apple flowers and in the phloem can be used to predict chlorosis incidencecaused by iron deficiency, thus iron fertilizer can be applied in time to prevent the disorder. The good correlation between leaf SPAD value and the content of active iron makes it possible to estimate the activeiron content in leaves with SPAD value.