Balady mandarin trees grown under Qena region during 2012, 2013 and 2014 seasons were investigated to find the best NPK fertilization through 0 to 100% of natural or bio-fertilizers along with a mineral source. The experiment was arranged in a complete randomized block design with five replications, one tree for each, and it consisted of seven treatments. Filter mud cake and calcium super-phosphate, as well as rock phosphate and feldspar were added once in the middle of December. Biostimulants i.e., nitrobien, phosphoren and potassiumage were added in two equal doses in March and May. Potassium sulphate was applied in two equal doses in March and June, where mineral-N fertilizer was added in three equal doses in March, May and July. The obtained results could be summarized as follow: Using the recommended N, P and K via two forms or three forms (mineral, natural plus bio) resulted in an obvious promotion on all growth traits and leaf area and its nutrients, as well as shoot carbohydrates and C/N ratio compared to using them as a mineral fertilizer source only. Amending the trees with natural or bio-fertilizer singly or a mixture of natural, bio and mineral NPK fertilizers significantly improved the yield and fruit quality. No significant differences were noticed on most studied traits among all different treatments except with the mineral source (the check treatment). The improvement in the fruit quality and the reduction in the juice nitrite content were associated with reduction in the mineral NPK source and, at the same time an increase in the mineral or bio-fertilization sources. It is evident from the foregoing results that using either three fertilization forms or any two fertilization forms produce healthy trees, with the highest yield and the best fruit quality. In addition, it reduces the environmental pollution as well as produces organic farming products.
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