الفهرس 
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Abstract
A pot experiment was carried out during the autumn season of 2017 under alluvial soil conditions at the green house of Soils Dept. Faculty of Agriculture, Mansoura University. The aim of this experiment is to study the response of squash (cucurbita pepo L .) plant to different rates of potassium phosphite and potassium fulvate as single treatments or in combination with each other. The experiment treatments included; potassium phosphite as a single treatment at four concentrations (C1: 0,0 (control), C2: 0.1 ml plant-1, C3: 0.2 ml plant-1 and C4: 0.4 ml plant-1), potassium fulvate as a single treatment at four concentrations (C1: 0,0 (control), C2: 6 kg fed-1, C3: 9 kg fed-1 and C4:12 kg fed-1), and the combined treatment of potassium phosphite with potassium fulvate at four concentrations (C1: 0,0 (control), C2: 0.05 ml plant-1+ 3 kg fed-1, C3: 0.1 ml plant-1+4.5 kg fed-1 and C3: 0.2 ml plant-1+6 kg fed-1, respectively) using soil and foliar applications. The used experimental design was a split split plot design with three replicates for each treatment. The parameters investigated were: 1- Plant length, total leaf area plant-1, fresh weight and dry weight and NPK content of squash plants at the flowering stage (after 40 days from planting) and the harvesting stage (after 70 days from planting). 2- Total yield, dry weight, fruit content of NPK %, fruit characteristics ( length , diameter and weight). 3- Some chemical properties of the studied soil after harvesting of squash plant ( Available N, P and K mg kg-1) and organic matter in soil (g kg-1)). The results obtained could be summarized as follows: 1- At the flowering stage The results of the present study showed that the highest values of fresh, dry weight (g pot-1), total leaf area (cm2) and the nutrients content N, P and K (%) of squash plant were achieved with the combined treatment of potassium phosphite with potassium fulvate at C3 (0.1 ml plant -1+4.5 kg fed -1, respectively) at the flowering stage after 40 day from planting using soil application. The highest values of plant length were achieved with the combined treatment of potassium phosphite with potassium fulvate at C3 (0.1 ml plant -1+4.5 kg fed -1) and potassium fulvate as a single treatment at C2 (6 kg fed-1) using soil application, respectively. 2- At the harvesting stage The highest values of fresh, dry weight (g pot-1), total leaf area (cm2) and the nutrients content N, P and K (%) of squash plant were obtained by the combined treatment of potassium phosphite with potassium fulvate at C2 (0.05 ml plant -1+ 3 kg fed -1), the highest value of plant length (cm) was achieved with the combined treatment of potassium phosphite with potassium fulvate at C3 (0.1 ml plant -1+4.5 kg fed -1) at the harvesting stage after 70 day from planting using soil application. 3- Yield and characteristics fruit The highest values of total yield, dry weight of yield and characteristics (length, diameter and weight) of squash fruit were achieved with the combined treatment of potassium phosphite with potassium fulvate at C3 (0.1 ml plant-1+ 4.5 kg fed-1, respectively) using foliar method of application, while the highest values of the nutrients content N, P and K (%) were obtained by the combined treatment of potassium phosphite with potassium fulvate at C2 (0.05 ml plant -1+ 3 kg fed -1, respectively) using soil method of application. 4- Chemical properties of soil The highest values of available N, P and K (mg kg-1) and OM (g kg-1) in soil after harvesting were recorded with the combined treatment of potassium phosphite with potassium fulvate at C4 (0.2 ml plant -1+ 6 kg fed -1, respectively) using soil method of application. Conclusions Based on the obtained results of this study it could be concluded that the addition of potassium phosphite in a combination with potassium fulvate is considered the most suitable treatment as a biostimulate to increase the growth , parameters and nutrients content of squash plant, in addition to yield, characteristics and nutrients content of squash fruit. Also, the combined treatment of potassium phosphite with potassium fulvate has positive effects on chemical properties of the studied soil. We also recommend in the following studies to study the effect of applying potassium phosphite and potassium fulvate while reducing the levels of mineral fertilizers (NPK) recommended required for squash plant growth.