Many Australian soils are old and weathered. In fact, many are considered the oldest soils in the world; and the nutrients have been leached, which has resulted in soils of low fertility. For example, average Australian soil phosphorus levels are 40% lower than English soils and up to 50% lower than North American soils.
Improved pasture species allow a much higher stock-carrying capacity; but to maintain this productivity, they require a higher level of soil fertility than do native pasture species.
Nutrient redistribution around the farm and the inherent ability of soils to ‘retain’ applied nutrients; so they are less available for plant uptake, are other reasons for fertiliser applications.
In addition to the loss of nutrients in fodder, grain, and animal products, a significant amount of nutrients can be lost off the farm in runoff from irrigation and rainfall – see Chapters 10.5.2 and 12.3.
There are many factors that need to be considered in working out a profitable fertiliser program for a dairy farm. For details on nutrient planning see Chapter 15.