The john innes composts: Some effects of increasing the base-fertiliser concentration on the growth and composition of the tomato

Summary The effects of increasing the strength of the base fertiliser in John Innes composts on the rates of growth, development, and the chemical composition of tomato Potentate, and also on the levels of available nutrients within the composts, has been examined. Comparison has also been made between plants grown in the JIP1, JIP2, and JIP3, composts and those grown in sand cultures receiving Hoagland's nutrient solution at each irrigation.For an initial period after pricking out an inverse relation between plant-growth rate and base-fertiliser concentration was found. This was later changed to a positive relationship. A significant interaction was shown between the length of the initial period during which the growth rate was depressed due to fertiliser concentration and the light intensity.The high rate of base-fertiliser application did not however extend the period of high growth rate or significantly reduce the rate of the fall in the nitrogen concentration within the plant. It is conlcuded that, from a practical point of view, plants grown in all three strength composts will require supplementary feeding at the same period.Whilst approximately 75 per cent of the ammonia extracted by Morgan's solvent was also water soluble this form of nitrogen did not significantly influence the specific conductivity of saturated extracts. Nitrates were highly correlated with the specific conductance.