Study On Potassium Nutrient Responses And Its Rapid Detection Techniques In Substrate Cultivated Tomato

Tomato (Lycopersicon esculentum Mill.) is a widely planted, productive and most consumed edible vegetable in world. Potassium fertilizer in greenhouse tomato production is needed more compared with nitrogen fertilizer for high fruit yield. However, unreasonable potassium supply had often happen in the practical production. In order to realize efficient utilization of potassium, potassium control of nutrient solution based on potassium physiological response is available but limited because of shortage in quantitative and rapid detection of potassium nutrition. In this study, via repeated experiments in substrate cultivated tomato under different potassium levels of solution adjusted by nutrient formulation of Japan Horticulture Institute, physiological response indicators of potassium nutrition and its rapid detection techniques of tomato were studied by the growth and development, flowing differentiation, fruit yield and quality.According to the experimental results, better growth and fruit yield were shown in K100 and K150 treatments cultivated under 8 to 12 mmol·L-1 potassium concentration of solution, higher potassium utilization efficiency was shown in K50 treatment cultivated under 4 mmol·L-1 potassium, better fruit quality was shown in K300 treatment cultivated under 24 mmol·L-1 potassium. Considering growth and development, fruit yield and quality, and potassium utilization efficiency in substrate cultivated tomato production, potassium concentration in solution will be suggested to adjust in 4-6 mmol·L-1 at flower bud differentiation prophase,8 mmol·L-1 at fruit stage,12 mmol·L-1 at fruit enlargement period,16 to 24 mmol·L-1 at fruit harvesting stage. On the other hand, the fruit expanding rate and leaf potassium content can be selected as the physioloical indicators responsing to potassium supply of solution.In order to understand effect mechanism of potassium supply of solution on growth and development of substrate cultivated tomato by measuring gas exchange and electron transfer, portable photosynthetic measurement using a conditional method and a rapid photoinduced method were used in this study. The photosynthetic characteristics and chlorophyll fluorescence parameters measured by the conditional method were shown a good sensibility to the potassium supply of solution at 42 and 63 days after transplanting, but did not responsed well at 21 days after transplanting. The CO2 absorption and differential coefficient of intercellular CO2 concentration measured by the rapid photoinduced method can be used to characterize tomato photosynthetic physiological response mechnisium to potassium supply of solution at early stage after transplanting.Leaf potassium content as a potassium physiological response indicator can directly reflect the potassium supply of solution. Using spectral reflectance between 190 to 2500 ran pretreated by using multiple scattering correction was successfully used to construct a partial least squares estimation model for estimating leaf potassium content of tomato at 42 and 63 days after transplanting. For quantitative estimation of leaf potassium content in the early stage after transplanting, spectral parameters with log(T940/T560) based on transmission in 560 nm as a characteristic wavelength and 940 nm as a reference wavelength was precisely used to measure chlorophyll a/b ratio and therefore to regress leaf potassium content with 0.72 in R2 and 0.79 in RMSE as a verification result.In summary, photosynthetic measurement by the rapid photoinduced method, quantitative measurement of leaf potassium content based on spectral reflectance or transmission, and fruit expanding rate measured by fruit transverse diameter can be used to characterize the photosynthetic physiological response to potassium supply of solution at substrate cultured tomato. The above potassium nutrient physiological indicators and its detection techniques are needed more in-depth research in order to looking forward to provide technical support for potassium feedback control of nutrient solution.