Eggplant dry matter composition fruit yield and quality as affected by phosphate and total salinity caused by potassium fertilizers in the irrigation solution

Eggplant (Solanum melongena L.) grown under winter conditions in unheated polyethylene covered greenhouse displays unmarketable red color fruit skin. The purpose of this work was to study the effect of potassium (K), phosphate and total salinity levels in the irrigation solution on the quality of eggplant fruit grown at winter and spring seasons. Eggplant was grown in containers filled with basalt erupted tuff scoria. The fertigation solutions were composed of three levels of P: 18, 36, and 54 g P m^-3, using mono K phosphate (MKP). Each level of P was applied on two levels of total K concentrations, 475 and 920 g K m^-3 composed of K nitrate, MKP, and K chloride (KCl). The KNO₃ fertilizer was used in all treatments at 150 g N m^-3. Increasing the KCl concentration increased the average electrical conductivity (EC) in the irrigation solution from 2.3 to 3.9 dS m^-1, reduced class A fruit number and weight, but had no effect on the skin color. During the cold winter period the intensity of the skin color was weaker than in the normal hot growing period. Increasing the average phosphorus (P) concentration in the irrigation solution throughout the growing season from 36 to 54 g m^-3 increased the number of fruit per plant, the number of class A fruits but has no significant effect on total fruit yield. Increasing the total electrical conductivity of the nutrient solutions by K fertilizers above 3.8 dS m^-1 decreased fruit yield and total dry matter in the spring growth period.