Potassium Requirements for Grass Cut for Silage – A Review

Keywords: grassland fertilisers, potassium, nitrogen-potassium interactions, manures.

The management of productive grass swards is primarily driven by the appropriate use of relatively large dressings of nitrogen, both from fertilisers and manures. The basis for current fertiliser recommendations was laid by a large number of experiments carried out in the UK between the 1940s and 1960s. These experiments are identified and their findings reported. Both costs and outputs must be assessed. Increasingly aspects relating to water quality and pollution hazards to the environment must be considered. High yields of conserved grass inevitably remove large quantities of potassium from the field when harvested. This potassium must be replaced if soil fertility is not to decline. The percentage of potassium in the herbage DM (especially late in the previous season) is a good indicator of the essential need for potassium fertilisation. Values below 2.0% potassium are indicative of serious depletion which should receive attention. UK experiments suggest that optimum yields can be obtained when herbage potassium concentration remains above 3.0% DM at the end of the previous season.

The critically important relationship between the requirements for nitrogen and potassium by high-yielding grass swards is discussed and the extensive experimental evidence is reviewed.

Emeritus Professor Gordon Hemingway, Glasgow University Veterinary School, Bearsden, Glasgow G61 1QH, UK.

16 pages, 12 tables, 22 references.