Study outcomes could significantly reduce fertilizer costs in greenhouse tomato operations

Controlled-release fertilizer more efficient for plants’ nutrient usage in capillary watering systems

For greenhouse vegetable production, getting the most water and nutrients to the plants with the least amount of time and money is a significant goal. A popular method of greenhouse subirrigation called "capillary wick irrigation" has been gaining approval in Japan. Although the method is labor-efficient and economical for use with ornamental potted plants, it was originally not recommended for long-term use in growing produce, because plants' roots can penetrate the wick over time, disrupting the irrigation system and eventually causing lower fruit yields.

A new root-proof capillary wick irrigation system was developed in Japan in 2008 that makes the wick impenetrable to plants' roots. In this irrigation system, water is stably supplied by capillary action from the side of the substrate without root invasion into the wick. Now, researchers are focused on finding a suitable nutrient concentration for the fertilizer solution to improve tomato cultivation using the improved root-proof wick system.

Researchers from the National Agriculture and Food Research Organization of Japan compare potted tomato plants' ability to absorb nutrients through the root-proof wick system from two methods of fertilization. The scientists used controlled-release fertilizer (CRF) and liquid fertilizer (LF) in the study, which was published in HortScience.

Sample plants were potted in a material conducive to the capillary wick irrigation system with either CRF or LF already mixed in. All of the plants were contained in a greenhouse in which the temperature was closely monitored.

Tomatoes from eight plants of each variation were harvested weekly and weighed. At the end of the experiment the diameter of the stems of six plants per variation was measured under each truss to determine plant growth. Finally, the nitrogen content of leaves, stems, and fruit from four plants of each variation were measured to determine the nutritional use of the plants.

As another method for determining the amount of nutrition being used by the plants, the soil was measured for nutrients every other week. Individual plants were also tested by cutting the top of the plant from its stem, collecting the fluid that was released, and measuring it for concentrations of nutrients on a monthly basis.

"The total and marketable fruit yields from the CRF- and LF-treated plants were not significantly different," the authors wrote. "However, we found that for each element, nutrient uptake per plant and during fruit production was higher with LF, meaning that CRF used the nutrients more efficiently. This finding is very significant with respect to fertilizer cost in tomato cultivation."

None of the plants treated with CRF or LF showed any symptoms of nutritional deficiency. Therefore, either method allowed plants to absorb enough nutrients for healthy growth, but the efficiency of controlled release fertilizer makes it a more economical choice for this type of irrigation strategy.

The complete study and abstract are available on the ASHS HortScience electronic journal web site:

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