The response of bearing navel orange trees to some sources and rates of potassium fertilizers and silicate bacteria

Abstract

This study was carried out through two successive seasons (2011 and 2012) in a private orange orchard in Qalubia Governorate, Egypt on 40 years old Navel orange trees budded on sour orange-rootstock grown in a clay loam soil (Typic Torriorthents). Planting distance was 5×5 meters apart and flood irrigation was used by river Nile water. Under this orchard conditions no sources of potassium fertilizers were added from many years ago. In the present study, potassium fertilizers were added at three rates (300, 450 and 600 g K2O/tree/year) as potassium sulphate 48% K2O and K-feldspar, 10% K2O plus inoculation with Bacillus circulans KSB8 (silicate bacteria). This strain was isolated and identified by 16S rRNA gene sequence. It releases high amount of available K in broth medium supplemented with K-feldspar through the production of organic acids. As well as, it is able to solubilize phosphorus, produce auxins, cytokinin and siderophore which are known to stimulate the growth of plant. The obtained results showed that, inoculation with Bacillus circulans KSB8 only and orchard conditions treatments were not sufficient for giving high yield from Navel orange trees while adding potassium fertilizers irrespective the source and level the yield was increased. The trend was clear in the second season than in the first one due to increases potassium percentage and biological activity, in the soil. The best values of yield, TSS, TSS/acid ratio and leaf mineral content in most cases were observed by the highest levels from potassium (600 g K2O) as potassium sulphate+silicate bacteria or K-feldspar+silicate bacteria treatments followed closely by the second rate (450 g K2O) from each potassium source. Regarding the effect of potassium source on soil biological activity, it is clear that fertilizing the inoculated plants with potassium sulphate or feldspar at 600 g and 450 g K2O gave the greatest values of dehydrogenase and CO2 evolution followed by the treatments amended with 300 g K2O in second growing season. Thus it could be safely concluded that, using silicate bacteria as effective strain combined with feldspar at the rate of (450 g K2O/tree/year) may be recommended instead of chemical fertilizers (potassium sulphate) to reduce environmental pollution and alleviate the dependence on imported or costly commercial fertilizer.