As the weather warms up, high tunnel tomatoes rapidly grow both their vegetative parts (leaves, branches, stems, and roots) and reproductive parts (flowers, expanding and ripening fruit). At this point, adequate supply of mineral nutrients (see figure) is critical for continuous harvest at high yield. To know the status of nutrients in plants, all you need is to conduct a simple tissue test.
To sample, the most recently matured leaf including the blade and its petiole should be used. These leaves are generally the 4th or 5th leaf from the growing point (top), have turned from a light-green juvenile color to a darker-green color, and have reached full size. Sampling should be done at first bloom, early fruit set, first ripe fruit, and during the harvest period (weekly if possible). Eight to ten leaves are required for a good sample. Once collected, leaves should be dried and shipped to a laboratory in paper containers. University of Missouri pro-vides this service (http://soilplantlab.missouri.edu/). The adequate level of minerals is listed below.
NOTE: Boron becomes toxic at approximately 200 ppm. The N-K ration is more important than nitrogen concentration in limiting the effects of high nitrogen, A N:K ration of 1.2 to 1.8 is desirable.
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REVISED: December 1, 2015