Response of Valencia orange trees to rock-feldspar applications on in reclaimed soils

Abstract

This investigation was carried out through three successive seasons (2008 & 2009 and 2010) on 20 years old Valencia orange trees budded on sour orange rootstock, cultivated in a private orchard with loamy soil texture, at Giza Governorate. The purpose of this study was to found an alternative source of potassium fertilizer locally termed "Feldspar", obtained as natural rocks which inoculated with dissolving bio-fertilizer. Their effect on leaf growth, mineral contents and yield of Valencia orange trees were checked. Selected trees were fertilized with Fine powder of the rock K-Feldspar at rates (500, 750 and 1000g K 2O/tree) in three dates i.e(October, March and July). Each application rate was applied either once at October or in two equal portions at October & March or in three portions at October, March and July. K-Feldspar substrate was inoculated with the bio-fertilizer silicate dissolving bacteria. Leaf area, leaf fresh weight, leaf dry weight and leaf mineral contents were determined comparing with the traditional fertilizer potassium sulphate at 600g K 2O /tree in two equal portions during February and August. Obtained results revealed that, using feldspar at 1000g K 2O/tree with two or three doses inoculated with Bacillus circulans as soil application had a significant effect on yield kg/tree, fruit weight, leaf area, leaf fresh weight, leaf dry weight and leaf mineral contents. Also, two doses of feldspar at 750g K 2O/tree gave better results where such treatments considered the promising under orchard conditions. Meanwhile, 500g K 2O /tree at any dose recorded generally less response. Therefore, using Bacillus circulans as effective strain of bacillus combined with feldspar at the rate of 1000g K 2O/tree either two or three doses may be recommended instead of chemical fertilizers i.e, (potassium sulphate) to reduce environmental pollution and alleviate the dependence on imported or costly commercial fertilizers.