Potassium fertilization effects on processing tomato yield and fruit quality

Sixteen field trials were conducted in central California from 1994 to 1998 evaluating the effects of potassium fertilization on processing tomato (Lycopersicon esculentum Mill.) yield and fruit quality, Ammonium acetate exchangeable soil K ranged among fields from 0.26 to 0.83 cmol kg(-1). K application methods included pre-plant or sidedress soil application, foliar spray, or application in irrigation water. Seasonal K application rates varied from 55-560 kg ha(-1). Significant fruit yield increases were observed in only two fields, both with soil exchangeable K < 0.35 cmol kg(-1). At no site did K fertilization increase fruit soluble solids content (SSC) or the color of blended juice. The percentage of fruit affected by the color disorders yellow shoulder (YS, a disorder characterized by a ring of tissue surrounding the stem scar that remains yellow at fruit maturity) or internal white tissue (IWT, an objectionable level of white tissue in the mature fruit) was evaluated in trials conducted in 1997 and 1998. K application reduced YS in two fields and IWT in another but did not eliminate either disorder. The relatively modest reduction in YS and IWT in response to K fertilization was partly attributed to high K fixation capacity of these soils. A laboratory assay estimated that soil fixation of more than 50% of applied K was likely in some trial fields.