9 May 1997

Potash warning

POTASH deficiency could be the cause of poor grass growth and reduced silage yields.

So warns seedhouse Nickersons. It has started trials to examine the effect of potash inputs on silage swards on one of its sites which is inherently low in potash.

According to the companys forage specialist, Peter Schofield, potash deficiency is not perceived to be a concern. But he says that it is the cause of 90% of cases of poor grass growth in swards which are three to four years old.

"Soil test results back this up, and applying muriate of potash helps growth. Where potash is low, nitrogen is not used properly, and you will lose the benefit of fertiliser, nitrogen deficiency is often the first obvious symptom."

The cut-off for adequate potash levels is 180mg potash/litre, equivalent to ADAS indices of 2 minus to 2, he says. "Above that and it is fine to use the normal N:K silage ratio of 2:1. Any less than 180mg/litre, and it is best to use a 1:1 ratio until levels return to their optimum."

The trials at its Humberside site are examining different fertiliser ratios, from 25:10:10, which provides just enough for plants, to 25:0:16, which should be enough to increase yields and soil indices. Trials looking at the 1:1 ratio are likely to be included next year.

, says Mr Schofield.