The Effects of Nitrogen, Phosphorus, Potassium Magnesium and Lime in Factorial Combination on Ripening Disorders of Glasshouse Tomatoes

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Abstract
The effects of nutrition on the incidence of fruit ripening disorders are described, based on studies of three varieties of tomato (Potentate, Moneymaker and J168) grown with 72 combinations of fertilizers in heated glasshouse borders. The treatments included three levels each of nitrogen and potassium in factorial combination with two levels of phosphorus, magnesium and lime. Potassium sulphate markedly decreased the overall percentage of unevenly ripened fruit from all three varieties. Magnesium sulphate had a similar but smaller effect; the response to magnesium was greatest at low levels of potassium. The higher level of phosphorus increased the proportion of unevenly ripened fruit, the combination of low potassium and high phosphorus having a particularly adverse effect. The responses to nitrogen were complex and differed between varieties. Lime increased the proportion of unevenly coloured fruit from varieties Moneymaker and J168, significantly in the high nitrogen plots. Numerous other interactions between nutrients were found. The effects of the treatments on specific forms of ripening disorder were recorded, including greenback, yellow and green blotch, and waxy fruit. Potassium decreased the incidence of all forms of ripening disorder. High phosphorus increased the proportion of blotchy and waxy fruit, but significantly decreased the incidence of greenback in variety Potentate. Although the intermediate level of potassium in this trial (871 lb. K2 0 per acre) had previously been found sufficient for maximum yield, significant improvements in fruit quality were obtained at the highest level (1,742 lb. K2O per acre).