Cropping

A natural supply of potassium in both the exchangeable and fixed soil pools has historically been available in much of Australia and New Zealand's most productive cropping areas.  On the other hand, some soils do not have a natural supply of slow-release fixed potassium, such as the sandy soils of Western Australia. Once the exchangeable potassium pool is depleted, there is no natural replenishment from soil supplies.  But as soil reserves are depleted over time, even the more fertile soils will begin to lack sufficient potassium and will fail to meet the large potassium demand of high-yielding crops.

Some important points to remember about potassium in cropping include:

• Potassium is removed from fields through grain and hay. Since vegetative plant material is often much richer in potassium than grain, more potassium is lost when hay is removed.

• Potassium is needed early in the life cycle of most annual crops. This results in a rapid uptake period in which crops take up potassium at a very high daily rate. Different crop species have differing maximum uptake rates, although maize and cotton are particularly high.

• As improvements in plant breeding and farming systems develop - as well as the use of other limiting nutrients - crop requirements for potassium will increase.

• Sometimes chronic potassium deficiency can occur. This usually happens in severely deficient soils where yields are extremely low. In these cases, small potash applications do not produce any yield responses, but large applications do. This is probably due to soil fixation of added potassium before any is available for plant growth.

Move on for more information about:

Nutrient Removal in Grain and Hay >>
Potassium Uptake Rates >>
How Requirements Increase with Yield Potential >>
Chronic Deficiency >>
Potassium Deficiency Symptoms >>
Research Projects >>