Determining the critical level of soil available zinc through DTPA and SB-DTPA extractants in peach orchards of Golestan province

To determine the critical level of zinc in soil and evaluation of the zinc nutritional status in peach orchards, composite soil samples (depths of 0-30 and 30-60 cm) were collected from 39 peach orchards of Golestan province. Soil samples of 24 gardens were selected for the following experiments on the basis of basic experiments results and extracted soil zinc contents. The extractants applied in the study were DTPA and SB-DTPA. An experiment was carried out as a split plot in randomized complete block design including two factors, with four replications. The main plots included 24 orchard soils and sub plots contained three levels of zinc treatments from zinc sulphate (34% Zn) source in 0, 10 and 20 kg/ha rates utilized in banded application on the shade area of tree. Leaf samples were randomly collected from all treatments in mid-season growth and their zinc contents were analyzed. Visual zinc deficiency symptoms were recorded in the orchards at the time of leaf sampling. Critical levels of soil zinc for DTPA and SB-DTPA were estimated by visual inspection method 0.90 and 1.00 mg/kg, respectively and by Cate-Nelson graphical method 0.70 and 0.85 mg/kg, respectively.