The value of liquid digested sewage sludge. II. Experiments on rye-grass in South-east England, comparing sludge with fertilizers supplying equivalent nitrogen, phosphorus, potassium and water

Abstract

In a factorial trial comparing liquid digested sludge with equivalent water, and inorganic nitrogen, phosphorus, and potassium fertilizers, almost all the effects observed could be attributed to the uptake of nitrogen or potassium.Over the 2-year period of treatment application, liquid digested sludge and equivalent inorganic fertilizer nitrogen and potassium gave similar responses of 22.3 and 23.8 lb. dry matter per lb. of nitrogen, and 59 lb./acre K increased the response to inorganic nitrogen alone by 5.4 lb./lb. of nitrogen.Over the 2-year period of treatment the amount of potassium absorbed by herbage, in excess of that applied, was greater with fertilizer nitrogen than with liquid digested sludge. Added potassium had no direct effect on crude protein production. Liquid digested sludge and inorganic nitrogen fertilizer increased crude protein to a similar extent.