Optimization of silicon and calcium fertilization in grafted cucumber in solar-greenhouse

Objectives Silicon (Si) is beneficial to mineral element absorption, yield and flavor quality of crops. The optimum amount of Si and Ca application in cucumber cultivated in solar-greenhouse was studied to provide a technical guidance for to improve the yield and quality of cucumber.

Methods Microplot experiment was conducted inside solar-greenhouse, the used cucumber cultivar was ‘Jinyou35’, all the treatments were applied the same amount of NPK fertilizers. Using double saturated D-optimal design, 6 treatments containing different Si and Ca rates were setup, and the Si and Ca fertilizer were applied with drip irrigation evenly in four times. The yield and quality of cucumber were investigated. A mathematical model for the optimization was established using SiO₂ and CaO amounts as the independent variables, and the yield and quality of cucumber as objective function.

Results The regression of SiO₂ (X₁) and CaO (X₂) amount with cucumber yield (Y_y) was: Y_y = 108455.82 + 80.27X₁ + 138.91X₂ − 0.15X₁² − 0.40X₂² − 0.05X₁X₂, and that with cucumber quality (Y_q) was: Y_q = 64.113 + 0.116X₁ + 0.237X₂ − 2.167E-04X₁² − 5.552E-04X₂² − 1.741E-04X₁X₂. In the two formulas, the partial regression coefficient for X₁ was 80.27 and 0.12, which were significantly lower than those for X₂ (138.91 and 0.24), indicating that Si has less effect on cucumber yield and quality than Ca. The SiO₂ and CaO amounts for the maximum cucumber yield are 240 kg/hm² and 159 kg/hm², while those for the highest quality grade are 195 kg/hm² and 183 kg/hm².

Conclusion Under the tested conditions, the optimum combination is SiO₂ 195–240 kg/hm², and CaO 159–183 kg/hm², with the suitable ratio of SiO₂∶CaO at 1∶0.78.