- Total yield. Fruit were harvested at the commercial harvest time (SSC=16-17%). The number of clusters per vine and the average weight of cluster were recorded and the total yield per hectare was calculated (ton/ha).

- Cluster physical characteristics. During harvest, a sample of 6 clusters per each replicate was randomly taken and then cluster lengths as well as the two first shoulders length per cluster were measured (cm).

-Berry physical characteristics. Berry length and diameter (mm) were determined in ten berries/cluster using vernal clipper. Berry firmness and berry shattering force in gram force (gf) were measured in ten berries per cluster using a hand dynamometer apparatus model FDP1000 with a 1 mm thump.

-Berry chemical characteristics. Juice soluble solids content (SSC %) was estimated using a hand refractometer (Atago, Japan) apparatus and titratable acidity (%) was determined as mg of tartaric acid equivalent using NaOH (0.1 N) in 100 mL of berries juice ( AOAC, 1995 ). The SSC/acid ratio was calculated. Total anthocyanine content of berries was determined according to Ranganna (1986) using 50 g as a sample of each replicate that blended with 50 mL of ethanolic HCl solvent (150 mL of 1.5 N HCl + 850 mL of 95% ethanol) for 24 h at 4ºC, and the absorbance was recorded using spectrophotometer (Nebraska, USA) at 535 nm wavelength; then values were expressed as mg/100 g fresh weight. In addition, nitrate and nitrite content in the berry juice (mg/kg) were determined in a sample of fruit extracted with 2% acetic acid, and then measured colorimetrically according to Sen & Donaldson (1978) .

Leaf N, P and K content were determined in mature leaves (5-7 ^th leaves from shoot top) using the acid digesting solution method described by Chapman & Pratt (1961) . Nitrogen (%) was determined by the modified Microkjeldhal method ( AOAC, 1995 ), P (%) was determined colorimetrically ( Murphy & Riley, 1962 ), and K (%) was estimated using the flame-photometer method ( Cottenie et al. , 1982 ).

Data were subjected to analysis of variance according to Snedecor & Chocran (1980) , and treatment means were compared using DMRT at 5% level according to Duncan (1955) .

Table 6 shows that the combination of compost, natural rocks and mineral fertilizers affects leaf mineral content (NPK) in both locations. The highest significant percentage of N was obtained in vines fertilized with T ₁ , T ₂ , T ₃ and T ₄ in both seasons of sandy soil and first one of clay soil location. However, the highest values of P were detected with vines grown in clay soil that received T ₁ , T ₂ or T ₃ treatments. Meanwhile, vines treated with T ₁ or T ₃ showed the highest values in both seasons of sandy soil. Concerning leaf K concentrations, the vines treated with T ₁ , T ₂ or T ₃ as well as T ₁ , T ₂ , T ₃ or T ₄ showed the highest values in both seasons, respectively, in the clay soil location. A similar trend was found in sandy soil during both seasons. On the other hand, the lowest leaf N, P and K content were generally showed in vines treated with T ₆ under both study locations. These results are in line with the findings of Shaheen et al. (2013) , who concluded that application of 50% (compost + phosphate rock + feldspar) + 50% of NPK mineral fertilizers + bio-fertilizer showed the best vegetative growth characteristics and leaf mineral content.

Table 7 shows that cluster physical characteristics were positively affected by the partial replacement of mineral fertilizers with organic and natural rocks. Cluster number per vine significantly increased in vines treated with T ₃ or T ₄ in clay soil during both seasons; in vines receiving T ₄ or T ₅ in the first season and treated with T ₂ , T ₃ or T ₄ in the second one significantly increased under sandy soil condition. On the other hand, vines that were completely treated with organic and natural rocks (T ₆ ) produced the lowest number of clusters in both locations and seasons.

Cluster length and the first two shoulders length of cluster increased significantly in vines fertilized with T ₃ in comparison with other treatments in both locations. The lowest cluster length was detected in vines treated with T ₆ in both locations and seasons. However, the lowest length of the first two shoulders was recorded in vines fertilized with T ₅ and T ₆ in both locations and seasons, except in the second season of the sandy soil location. The positive effect of partial replacement of mineral NPK with natural rocks and bio-fertilizers might be due to the effect of these materials on soil physical and chemical properties, which is reflected on plant growth and productivity ( Ahmed et al. , 2012 ; Abdelaal et al. , 2013 ; Shaaban, 2014 ). These results are in line with those of Masoud (2012) and Ahmed et al. (2015) that showed a remarkable enhancement in the yield and clus­ter characteristics of 'Superior' seedless grapes using 50% mineral N + 50% manures + 30 mL of a commercial bio-fertilizer named EMas fertilizer program.

Table 8 shows that 'Flame' seedless grapevines receiving T ₃ or T ₄ treatments had a significant in­crease in cluster weight under sandy soil condition in both seasons, whereas the highest cluster weight was recorded with vines receiving T1 and T3 in the first season and T3 in the second one in the clay soil location. The enhancement effect on total yield was more pronounced under the sandy soil condition, where the highest values were detected in vines treated with T ₄ in both seasons. As for clay soil, the vines treated with T ₂ , T ₃ or T ₄ in 2017 as well as those treated with T ₃ or T ₄ in 2018 showed a significant increase in total yield. On the other hand, the vines that received the recommended dose of T ₆ showed the lowest values of both cluster weight and total yield in both locations and seasons. The positive effect of organic and bio-fertilization combined with mineral NPK fertilization on fruit trees were discussed by Dahama (1999) and David (2002) . Also, these results are in accordance with those reported by Abdelaziz et al. (2014) who stated that the application of mineral N in combination with plant compost enriched with algae was as effective as the use of mineral sources on yield and cluster quality characteristics; however, reducing the mineral N below 50% of recommended doses was associated with a reduction in total yield.

Table 9 shows that berry characteristics were greatly affected by the partial replacement of mineral fertilizers with the natural ones in both locations and seasons. Vines fertilized with T ₃ produced the highest significant values of berry diameter, firmness, and removal force in both locations during both seasons. However, berry length data did not show a clear trend under both soil study locations. The lowest values of berry physical characteristics were recorded in vines treated with T ₅ and T ₆ in both locations and seasons in most cases. The positive effect of combination of compost, bio-fertilizers, natural rocks and mineral fertilizers may be related to the richness in essential nutrients increasing the availability of soil nutrients and uptake by plant roots, which in turns is reflected on vines nutritional status and total yield ( Nijjar, 1985 ). Similar results were reported by El-Rawy (2007) and Mostafa (2008) , who found that application of inorganic N greatly improved the berry quality characteristics of various grapevines cultivars respect to using mineral N fertilizers only. Abd El-Wahab (2011) reported that 'Red Globe' grapevines fertilized with 50% compost and chicken manure combined with the application of 50% mineral N resulted in the highest yield, yield components and physical properties of bunches and berries.

Nitrate and nitrite contents

Table 10 shows that berries content of nitrates, nitrites and their total greatly decreased with increa­sing rates of natural fertilizers. The highest significant values were recorded in berries of vines treated with T ₁ , followed by those treated with T ₂ in both locations and seasons. On the other hand, vines treated with T ₃ , T ₄ , T ₅ or T ₆ showed the lowest values of nitrites with no significant differences among them in both locations during the first season. The lowest values of nitrates were recorded in berries harvested from vines treated with T ₆ in the first season as well as T ₅ or T ₆ in the second one under the clay soil location. The same trend was found in vines treated with T ₅ or T ₆ in 2017, as well as in those treated with T ₄ , T ₅ or T ₆ in 2018, in the sandy soil location. The lowest significant values of total nitrites and nitrates were showed in vines treated with T ₅ or T ₆ in both locations and seasons in most cases. This effect could be related to the slowly releasing of N from organic fertilizers which make it available for plant uptake for long time ( Hallberg & Keeriey, 1993 ). Similar results were reported by Ahmed et al. (2016) on 'Superior' seedless grapes. Abd El-Wahab (2011) reported that the application of compost mixed with chicken manure and 50% of the recommended mineral N fertilizers improved the chemical characteristics of berries and reduced nitrate and nitrite content of 'Red Globe' grapes.

SSC, SSC/acid ratio, acidity and anthocyanine

Table 11 shows that juice SSC was enhanced with the use of natural fertilizers in moderate rates. The vines treated with T ₃ resulted in the highest significant percentage of SSC in both locations and seasons. On the other hand, the lowest values were recorded in vines fertilized with T ₁ or T ₅ in the clay soil vineyard in 2017 and 2018, respectively. However, the differences among treatments were not significant in most cases in sandy soil during both seasons.

Data of juice acidity generally showed a reduction trend with increasing natural fertilizers as compa­red with application of 100% mineral fertilizers. The highest values were noticed with vines that received T ₁ in clay soil location during both seasons. The lowest significant values of acidity were noticed with T ₅ or T ₄ in clay soil in 2017 and 2018, respectively. Regarding sandy soil vineyard, the lowest acidity percentage was recorded with vines treated with T ₃ and T ₄ in the second season only.

The highest SSC/acid ratio was recorded in vines treated with T ₅ and with T ₃ & T ₄ in 2017 and 2018, respectively; meanwhile the lowest ratio was found in vines that received T ₁ in clay soil in both seasons. Concerning the sandy soil, the highest values were recorded in vines treated with T ₃ or T ₄ in both seasons. Berries anthocyanine content showed the highest significant values in 'Flame' seedless grapevines fer­tilized with T ₂ under clay soil condition as well as T ₂ and T ₃ in sandy soil vineyard in the second season of both locations. These effects may be due to the richness of natural fertilizers in macro and microelements, which enhance plant photosynthesis and led to more available sugars that can be used for growth and fruit ripening ( Belal, 2006 ). Similar results were reported by Abd El-Wahab (2011) on 'Red Globe' grapes. Masoud (2012) concluded that the use of bio-fertilizers or organic manure, or even the combined mixture, greatly improved total soluble solids and anthocyanine content of 'Flame' seedless and 'Ruby' seedless grapes in comparison to using mineral N fertilization only.

It can be concluded that the application of 60% mineral NPK + 40% organic fertilizers and natural rocks effectively enhanced the nutritional status of 'Flame' seedless grapevines and gave the optimum yield and fruit quality. Using natural fertilization reduced nitrate and nitrite content of the berries. This mixture can also reduce the use of mineral fertilizers by about 40%, reducing then soil and environmental pollution.