Optimum levels of nitrogen and potassium in the irrigation water for best growth and quality of tomato in soilless culture

Objectives Reasonable N and K nutrition supplementation is an important strategy to improve tomato growth and fruit quality. In this study, we attempted to optimize N and K supplement levels for tomato precision management in substrate cultivation system.

Methods In greenhouse, a soilless culture experiment was conducted using sand and pearlite mixture in ratio of 1∶2 in volume as growth substrates, and potato cultivar A20 as tested materials , the irrigation treatments were composed of two factors (N and K) and five levels. The basic levels of N and K in irrigation water were 244 and 313 mg/L respectively, and the designed steps were 120 mg/L for N and 150 mg/L for K, respectively. The yield, chlorophyll content and net photosynthetic rate in leaves, the soluble sugar and titratable acid contents, the sugar/acid ratio, vitamin C, and lycopene contents in fruits were measured.

Results Within the N levels of 74–414 mg/L in the irrigation water, both the yield and chlorophyll content increased first and then decreased. Within the K supply levels of 101–525 mg/L, the net photosynthetic rate in leaves, lycopene contents in fruits increased first and then decreased, the soluble sugar content, sugar/acid ratio and Vc content in fruit kept increasing. N supplying levels mainly affected yield, chlorophyll content and net photosynthetic rate, while K supplying levels mainly affected soluble sugar, titratable acid, sugar/acid ratio, Vc and lycopene contents. There were significant interaction between N and K levels on yield and chlorophyll content. Adequate K supplement promoted the uptake and assimilation of N nutrition and increased the leaf chlorophyll content and yield. Appropriate N supplement was conducive to K uptake and utilization. According to the principal component analysis, the comprehensive performance of tomato yield and quality reached the optimum at the N 378 mg/L and K 391 mg/L with the highest net photosynthetic rate in tomato leaves.

Conclusions Using sand and pearlite as growth substrate, the optimum N and K supplying levels in irrigation water for tomato production are 378 and 391 mg/L, respectively, and the comprehensive performance of tomato yield and quality reached optimum level. The fertilization strategy may serve as reference for the precise management of nutrient solution for tomato cultivation in production practice.