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Observations on a general decline in fertility of multiple nutrients

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Declining soil organic matter is resulting in declining organic reserves of nitrogen (N) and sulfur (S), while nutrient removal has also depleted the soil minerals providing slow release reserves of phosphorus (P) as well as K. In most situations we have a reasonable ability to assess and meet N demand, but P inputs continue to be at rates << the rate of removal in grain while K and S inputs are non-existent... At both sites, yields were ~800kg/ha higher when K (Warra) or S (Brookstead) was added in addition to extra P. These responses were quite substantial (16% - 26% increases over adding P alone), and compared to the commercial practice at Brookstead, addressing the combined P and K limitations raised yield potentials by ~50%... The sites will be monitored over coming seasons, and are part of a network of trials across northern NSW and southern and central Qld assessing the responses to addressing multiple nutrient limitations, in addition to examining the most appropriate application strategies for the different nutrients...