Special cases

Sand soils

It is not economic to increase soil K beyond 100 mg/l (upper K Index 1) on these soils because of their very low capacity to hold nutrients. Improvement can be achieved by many years dressing with FYM. Nutrients should be applied 'little and often' on these soils (see PDA Leaflet 22).

Loamy sands

It is not economic to increase soil K beyond 150 mg/l (mid K Index 2-) on these soils because of their low capacity to hold nutrients. Improvement can be achieved by many years dressing with FYM (see PDA Leaflet 22).

Shallow soils

On shallow soils, such as some chalk/limestone soils, there can be greater risk of loss of potash, even though they have a higher clay content than sandy soils, because of their depth and a high proportion of stone in the topsoil (both these factors restricting the volume of soil for nutrient provision) Target fertility in these cases must be adjusted as with other low retentive soils.

K releasing clay soils

Some clay soils can release potash over many years. Normal potash rates can be reduced by 50 kg K₂O/ha (see PDA Leaflet 19).

Manures

Only about 15% of winter cereals and 30% of spring barley nationally receive any manure but it is important that nutrient contribution from this source is estimated and fertiliser use adjusted accordingly. Whilst there are often higher priorities for manure use, e.g. for roots, vegetables and conserved forage crops, regular measured applications of manure will benefit cereal crops, especially on the extremes of soil type - very light or very heavy - by improvement of physical characteristics of the soil of the soil as well as by nutrient supply.