The effects of potassium and magnesium fertilizers on yield and composition of successive crops of ryegrass, clover, sugar beet, potatoes, kale and barley on sandy soil at Woburn

In an 8-year field experiment, potassium sulphate and to a lesser extent magnesium sulphate increased yields of all crops both when applied alone and together. Although K/Mg interactions did not affect yields they considerably affected the ratio of concentrations of these elements in the dry matter of the crops. Sodium chloride increased yields of kale but not of barley harvested at ear-emergence.Percentage yield response to potasium followed the orderPotatoes (218%) < clover = barley < sugar beet < kato; < ryegress (17%).Magnesium increased yields from 3 to 10%, most with potatoes.Changes in exchangeable magnesium in the soil reflected differences between applied magnesium and crop uptakes. Changes in exchangeable potassium were less than expected, probably because non-exchangeable potassium was released on plots without added potassium and ‘fixed’ in non-exchangeable forms on plots where much fertilizer potassium had been given.Increase in the incidence of magnesium deficiency symptoms reported recently in South. East England are attributed to the local liming materials containing only small amounts of magnesium and to less F.V.M being applied to crops than previously RESP-5799