Effect of reducing phosphorus dosage in nutrient solution on soilless culture of grafted tomato crops

The application of phosphorus fertilizers in liquid form has been developed in recent years to produce high yields of tomatoes. The liquid form easily penetrates to growing substrate and fasten the access of nutrients into plant, but it is considered as a major source of eutrophication when running off into water environment. Therefore, efficient use of phosphorus fertilizer is important for cost benefit as well as minimizing environmental risks. For this reason, we have been conducting an investigation at large scale (3.5 ha) tomato production greenhouse (Inochio Farm, Japan) to clarify the adequate dosage of phosphorus fertilizer for tomato growth. Tomatoes were graftage of two popular fruity species in Japanese commercial farms, cultivated in soilless growing media filled with coconut coir, and connected with a supply system of water and nutrient solutions. The proportion of phosphorus fertilizer in nutrient solution was gradually reduced by 10, 20 and 30% while the growth parameters including photosynthesis and transpiration at canopy level, number of leaves, leaf area index, contents of chlorophyll were carefully being monitored. The results showed well monitoring of the photosynthetic rate and transpiration of tomato at canopy level. There was not adverse effect on tomato even when the phosphorus content in fertilizer solution was remarkably reduced by 30%. However, the values of chlorophyll tended to decrease as lack of nutrient. The leaf area decreased while the number of leaves increased. The research is in progress but the results implied promising prospects to reduce phosphorus fertilizer dosage in tomato commercial greenhouse.