The Effects of Magnesium Deficiency on the Yield and Quality of Glasshouse Tomatoes Grown at Two Levels of Potassium

Abstract

Tomato plants of two varieties (Potentate and Immuna) were grown for four seasons with different combinations of magnesium and potassium sulphate in heated glasshouses. Magnesium sulphate was applied either to the soil or as a foliar spray, with untreated plots as controls ; these treatments were combined factorially with two levels of soil potassium. The effects of the treatments on the magnesium and potassium contents of the soil, as extracted by 0 5N-acetic acid, are recorded.Chlorosis of the leaves was widespread where magnesium was not applied. Foliar spraying effectively controlled the deficiency symptoms; treatment of the soil with magnesium sulphate was only partially successful in the first season but increasingly satisfactory thereafter.In only one of the four seasons was there a significant increase in yield J due to the correction of magnesium deficiency. In that year (1959) the yields at the higher level of potassium were increased by 15%and 12%by the soil and spray treatments respectively (P=0·001).The magnesium treatments slightly improved fruit quality as assessed by visual grading, mainly at the very low level of potassium in the last two seasons. The dominant factor affecting fruit quality was potassium, however, which markedly increased the proportion of uniformly coloured fruit and reduced the incidence of ripening disorders.It is suggested that magnesium deficiency should be controlled by supplying this nutrient rather than by reducing the application of potassium salts below the quantity necessary for high fruit quality.Variety Immuna gave higher yields and better quality fruit than Potentate throughout the trial.