Abstract
The rate of growth and the potassium content of seedlings of carrot, lettuce and onion was greater on plets which had received applications of farmyard manure (FYM) than on those which had received only mineral fertilisers (including potassium sulphate at 150 Ib. of K per acre).
To find the reasons for these differences the effects of applications of potassium sulphate at rates of up to 800 lb. of K per acre on the availability of potassium in the soil, and on the growth and mineral composition of the seedlings, have been studied.
The exchangeable potassium content and the energy of exchange for the replacement of calcium with potassium (ΞF value) after application of 400 lb. of K per acre were similar to those in soil which had received FYM annually for 8 years.
Seedlings took up similar amounts of potassium whether the soil had received FYM or 400 lb. of K per acre. Growth of seedlings on the fertiliserβtreated soil was adversely affected when the rate was more than 200 lb. of K per acre. The interactions K/Ca and K/Mg are discussed in this connexion.
Fixation of added fertiliserβK could explain the relatively poor growth response of crops at Wellesbourne to rates of application of fertiliserβK of about 100 lb. of K per acre.
The need to maintain soilβpotassium reserves at a high level for vegetable growing is emphasised.