Plant Archives Volume 20 No. 2, 2020 pp. 8613-8621 e-ISSN:2581-6063 (online), ISSN:0972-5210 CALCIUM BORON AND CARPOX-K SPRAYS FOR IMPROVING GROWTH, NUTRITIONAL STATUS AND PRODUCTIVITY OF WASHINGTON NAVEL ORANGE TREES A.A. EL-Khwaga 1 , F.M. Abd El-Latif 1 , M.H.M. Baiea 2 and S.F. EL-Gioushy 1, * 1 Horticulture Department, Faculty of Agriculture (Moshtohor), Benha University, Moshtohor, Toukh, Egypt. 2 Horticultural Crops Technology Dept. National Research Centre. Dokki. Giza. Egypt. *Dr. Sherif Fathy El-Gioushy is an associate professor at the Department of Horticulture Faculty of Agriculture (Moshtohor), Benha University, Moshtohor, Toukh, Egypt. Abstract This study was carried out during the 2018 & 2019 seasons on 9-year-old Washington navel orange trees. These trees were budded on Sour orange rootstock planted at 5×5 meters apart under surface irrigation of a private orchard at Manzala village, Toukh region, Qalubia Governorate, Egypt. The seven treatments were used for comparison as follows: T 1 -100% of chemical NPK (NPK fertilization program adopted at 5, 3 and 1 kg/tree from (NH 4 ) 2 SO 4 , superphosphate and K 2 SO 4 , respectively) according to the Ministry of Agriculture Recommendation (Control or recommended doses RD). T 2 -RD+Calcium boron 2 cm 3 /L, T 3 -RD+Calcium boron 3 cm 3 /L, T 4 -RD+Carpox-K 1g/L, T 5 -RD+Carpox-K 1.5g/L, T 6 -RD+Calcium boron 2 cm 3 /L +Carpox- K 1g/L and T 7 -RD+Calcium boron 3 cm 3 /L +Carpox-K 1.5g/L. The main goal of this investigation was directed towards increasing Washington navel orange trees growth, Nutritional Status and productivity. Moreover, All the obtained data revealed that all investigated treatments increased growth parameters (number, length, the thickness of developed shoots, number of leaves/shoot and leaf area), leaf total chlorophyll and leaf nutritional status (N, K, Ca, Mg, Fe, Mn and Zn) were also positively responded fruit (set % and retention %) and yield/tree was also improved. However, T7- RD + Calcium boron 3 cm 3 /L + Carpox-K 1.5g/L was statistically superior. On the contrary, T 1 - Control or recommended doses (RD) ranked statistically the lowest treatment in this concern. Generally. From the obtained results, it can be concluded that using of RD+ Calcium boron 3 cm 3 /L + Carpox-K 1.5g/L or RD + Calcium boron 2 cm 3 /L + Carpox-K 1g/L could be safely recommended under similar environmental conditions and horticulture practices adopted in the present experiment. Key words: Washington navel orange, Calcium boron, Carpox-K, Nutritional Status, Productivity Introduction According to Annual Reports of Statistical Institute and Agricultural Economic Research in Egypt, (2016) Citrus is one of the most important horticultural crops in Egypt due to its high economic value for the local markets and export. The total exportation of citrus reached 1, 667, 750 and 1, 616, 821 tons of fruits through 2016 and 2017, respectively. The total area occupied by citrus in 2016 was 485, 940 feddans that produced 4, 272, 886 tons of fruits. From such area; 163, 932 feddans were cultivated by Washington navel orange trees representing 33.74% of the total area; producing 1, 489, 536 tons of fruits; representing about 34.86% of total citrus production. Oranges take the foreground of citrus varieties, especially Washington navel orange (Citrus sinensis L. Osbeck). Navel orange plays a dominant role not only in the local market but also for exportation as one of the major citrus fruit crops in Egypt. June drop and pre-harvest fruit drop are extensive in many Egyptian orchards, as the navel orange is a parthenocarpic cultivar and consequently eliminating yield and fruit quality (Saleem et al., 2007). Washington Navel orange is the most favorite and the popular fresh fruits in Egypt due to its seedless, large size, nutritive value, flavor and aroma characteristics. It is also a valuable source of early-season income for citrus growers in some commercial citrus areas of the world. Costs of mineral fertilizers have been significantly going up. As a result, it has become necessary to seek *Author for correspondence : E-mail : sherif.elgioushy@fagr.bu.edu.eg