Effects of nitrogen and zinc on quantitative and qualitative of sweet lime (Citrus limmetta Tan.) fruits grafted onto Mexican lime rootstock in calcareous soil condition

Balanced fertilization of organic matters and macro- and micro-nutrients is the most important effective factors on the fruit quality and the yield of the citrus trees (Hao et al., 2007). A very large area of land under cultivation in the south of the Iran is calcareous, and as a result, the absorption of elements such as zinc, phosphorus, iron, etc. in these soils is done slowly, which is one of the agricultural problems of these areas (Aboutalebi and Hassanzadeh, 2007). In the subtropical regions, flowering in citrus occurs after the infancy period and exposure to low temperatures and short days of winter (Nebauer et al., 2006). This study was conducted with the aim of investigating the effect of nitrogen and zinc on increasing the fruit quantity and quality of the 6-old-years sweet lime.

This investigation was performed as factorial arrangement in randomized complete block design with nine treatments and three replications and one 6-years-old sweet lime tree budded on the Mexican lime rootstock in each replication in two separate parts of the big research orchard of Islamic Azad University of Jahrom branch. The experiment factors included the foliar application of urea at three concentrations of 0, 3 and 5 gL-1 and the foliar application of zinc sulfate at three concentrations of 0, 3 and 5 gL-1. The foliar application of urea and zinc sulfate was performed before flower induction of the trees, in October. After spraying, in the time of the fruit harvesting, the parameters including fruit juice pH, TSS, vitamin C, average fruit weight, texture firmness, single tree yield and fruit ripening were measured.

Based on the results, in the present study due to foliar application of urea and zinc sulfate particularly combined treatments, all traits significantly influenced compared to control treatment. Totally, the treatments without urea were in the lowest levels in viewpoint of quantitative and qualitative characteristics of the fruit. The use of 5 gL-1 zinc sulfate without urea and/or 3 gL-1 urea without zinc sulfate as well as combined treatment of 3 gL-1 urea and 5 gL-1 zinc sulfate caused to improve qualitative characteristics of the fruit. The use of 5 gL-1 zinc sulfate without urea led to increase the peel thickness and fruit firmness. Combined treatment of 5 gL-1 urea and 5 gL-1 zinc sulfate increased average fruit weight and plant yield.

In the present study, the foliar application of urea and zinc sulfate, particularly in the combined treatment, significantly affects all parameters compared to control treatment. On this basis, it can be recommended the foliar application of 5 gL-1 urea + 3 gL-1 zinc sulfate in the October to improve qualitative traits of the fruit and the combined treatment of 5 gL-1 urea + 5 gL-1 zinc sulfate to increase the yield of sweet lime.