Potassium Loss Mechanisms
See this diagram to understand how the additions and losses of potassium on a typical dairy farm take place.
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This illustration shows the additions and losses of potassium in an intensive dairy production system. |
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The major source of potassium to the system is via fertiliser inputs and imported feed, with a small amount entering in rainfall or irrigation water. As with other production systems, potassium can be lost from dairy pastures by leaching, runoff or by soil fixation. These losses can be minimised by careful selection of rate and time of potassium fertiliser application.
The removal of potassium in animal products from the farm is a relatively small proportion of overall potassium losses in a dairy system. Of the potassium ingested by animals 3% is used to produce body weight, 5% is exported in milk, 10% is expelled in the dung and 80-85% is excreted as urine.
While potassium in urine and faeces is returned to the paddock, much of this potassium can be effectively lost through transfer onto non-productive areas such as stock camps and yards. A high proportion of the potassium in urine is also subject to rapid movement into the profile as urine flows through the soil pores. Some of this potassium will be held in exchangeable or fixed forms and can be accessed by the deeper roots of pasture plants, but the remainder is subject to leaching.
Removal or transfer of hay and silage will have a significant effect on the potassium status of dairy paddocks and may be as high as 100kg potassium/ha for a single crop. Fields which have a history of hay or silage production are likely to have low soil potassium levels in the absence of adequate potassium fertilisation.
The total potassium losses for any dairy system will depend on the intensity of the system, and the herd and pasture management. For example, the OVERSEER™ model developed in New Zealand can predict the effect of changing stocking rate on the magnitude of potassium losses on a dairy farm. (See table.)
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This table shows the effect of stocking rate on the loss of potassium from dairy systems |
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The net result of potassium movement within a dairy system is a wide range in soil potassium levels within individual farms. This has important implications for pasture and grazing management. (See diagram.)
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This diagram shows the distribution of soil potassium within a typical dairy farm. |
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