Soil Cation Balance Affects Tomato Fruit Color Disorders

Abstract

A survey of 140 processing tomato fields throughout central California was conducted in 1996–97 to determine whether soil factors affect the occurrence of the tomato (Lycopersicon esculentum Mill.) fruit color disorders “yellow eye” (a halo of yellow tissue around the stem scar) and white core (an abnormal amount of internal white tissue); these disorders render fruit unsuitable for use as peeled or diced product. All fields were planted in `Halley' or `Heinz 8892'. Soil samples (0–30 cm) were analyzed for pH, texture, TKN, bicarbonate extractable P, and ammonium acetate-extractable K, Ca, and Mg. Ripe fruit were rated for the incidence (%) of fruit affected by one or both of the disorders, blended color, and % soluble solids (SS). Soil K (in meq., expressed as a % of base exchange) was negatively correlated with the incidence of the disorders, while soil Mg was positively correlated. Fields with extractable K <2% of base exchange averaged 21% of fruits affected by one or both disorders, compared to only 4% of fruits affected in fields with K >2.5% of base exchange and a Mg/K ratio (meq. basis) <12. Percent SS was weakly correlated with extractable K, but blended color was unrelated to any soil factor. In 1997 field trials, both gypsum application (to displace soil Mg) and K fertilization significantly suppressed the color disorders but did not affect yield, blended color, or % SS.