1 March 1996

Potash ups silage

GRASS silage yields can be increased by 25% after three years when 200kg/ha (160 units/acre) of potash is applied each year to a sward given 250kg N/ha (200 units/acre).

According to Graham Swift of Scottish Agricultural College, in Signets Beef and Sheep notes, most crops receive optimum nitrogen but rarely receive enough potash. He reminds producers that first-cut silage removes 120kg/ha (96 units/acre) of potash.

He cites SAC trials that show silage yield failed to increase in the first year when 200kg/ha (160 units/acre) of potash was applied. But by year three dry matter yields increased by 26% above fields that received no potash and 7% above fields that had 100kg/ha (80 units/acre) of potash.

SAC now recommends 200kg/ha (160 units/acre) of potash for two silage cuts and aftermath grazing when using 250kg N/ha (200 units/acre).

Half the potash can be applied for first cut, 30% for second and the rest after that. But no more than 100kg/ha (80 units/acre) should be used each time to avoid luxury uptake, he adds.


Dry matter yields from three silage cuts (240kg N/ha) relative to no potash

Total potashTime of1st year2nd year3rd year

rateapplication

None-100100100

100Spring100104114

10033kg/ha/cut99105119

200Spring*98107121

20066kg/ha/cut99110126

* This high level of K in one application is NOT recommended.