Interactive effect of irrigation and blend ratio of controlled release potassium chloride and potassium chloride on greenhouse tomato production in the Yellow River Basin of China

Soil water and fertilizer are two main factors affecting tomato yield and quality, and their optimization management is crucial for sustainable production. There are many studies about the response of tomato growth and fruit yield formation to irrigation level and potassium (K) fertilizer, but few studies have been conducted on the responses of irrigation level and controlled release potassium chloride (CRK), not to mention the different irrigation levels and CRK to KCl blending ratios. In this study, two consecutive growing seasons (2020–2021) tomato pot experiments were presented with three irrigation levels (W₁₀₀, W₈₀, and W₆₀) and three blending ratios of CRK to KCl (100%, 80%/20%, 60%/40%) under the condition that the amount of potassium fertilizer was reduced by 40% compared with conventional application rate. The results revealed that under W₈₀ water conditions, 80% CRK mixed with 20% KCl application led to a significant increase in tomato yield by 4.1–11.9% and 4.6–18.9%, K use efficiency by 11.5–34.2% and 6.1–32.3%, fruit vitamin C content by 9.3–25.3% and 5.6–28.3%, fruit soluble sugar content by 10.2–20.0% and 10.2–24.1% in 2020 and 2021, respectively, compared with the other K fertilization treatments. Meanwhile, the water use efficiency and fruit soluble solid content of W₈₀K₈₀ treatment were also maintained at a high level. Molecular analysis shows that the W₈₀K₈₀ treatment had a higher photosynthetic rate, rubisco content, cytokinin content, and osmotic regulation substances content, and lower abscisic acid (ABA), malondialdehyde (MDA), and hydrogen peroxide (H₂O₂) contents. Our results indicated that 80% irrigation level and 80% CRK-20% KCl blending ratio were the optimal water and K supply mode for tomato production in this study. The result provided useful information regarding greenhouse tomato production that would allow the achievement of higher fruit yield, quality and resource use efficiencies, and provided theoretical and technical support for greenhouse tomato irrigation and K fertilizer application technologies.