Abstract
Results are given in respect of dry matter yields and potassium contents of an experiment where herbage was cut four times per annum over a threeβyear period. A combination of nitrogen and potassium was essential for maintaining yields and 2 cwt. of muriate of potash/annum was not fully adequate if 12 cwt. of ammonium sulphate were applied each year. Additions of potassium to depleted plots in the third year of the experiment produced large and rapid improvements in yield.
Progressive removals of potassium in the cut herbage were reflected in corresponding falls in exchangeable soil potassium. The mean release of nonβexchangeable potassium over the threeβyear period was 2.7 mg./100 g. of soil which was only 22% of the initial exchangeable potassium value.
Potassium concentrations in the herbage fell to as low as 0.4% K on the plots receiving nitrogen only and to about 1.1% K where nitrogen and potassium were given. The progressive falls in concentrations of the herbage potassium were related to the cumulative removals of potassium in the cut herbage for these treatments, but not for those plots which had received either no fertiliser or potassium only.