Pasture Production and Composition

Highly productive dairy pastures require inputs of potassium fertiliser to maximise dry matter production and maintain the legume component of mixed swards.  This table shows a series of production measurements that were taken during spring from New Zealand pastures with a variety of initial QTK values. (See table.)

Spring pasture production responses to the addition of potassium fertiliser.

Even where soils have significant fixed potassium reserves, it may not be released at a rate sufficient to meet plant requirements.  For instance in North Canterbury, New Zealand, dairy pastures on sedimentary soils with fixed potassium reserves produced 16% more dry matter during the milking season from potassium application of 50kg potassium/ha. All other nutrients such as phosphorous, sulfur and nitrogen were in adequate supply.

Potassium nutrition will influence the composition of mixed pastures.  Grasses, in particular perennial grasses, are more efficient than legumes in obtaining potassium from the soil.  In situations where potassium supplies are low, grasses can out-compete pasture legumes leaving them susceptible to potassium deficiency and poor growth.  As a result the legume composition of mixed pastures will decrease. (See photo.)

The effect that potassium nutrition can have on mixed pasture composition.

Often the increase in pasture production from potassium fertilisation is almost exclusively due to improved legume growth. (See table.)

The effect of phosphorous and potassium fertiliser on the botanical composition of an old pasture in Victoria.

<< Back