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phosphates

Catalogue: GRDC Updates
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...
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Catalogue: GRDC Updates
S requirements should be locally assessed on a paddock to paddock basis; consider fertiliser history, cropping rotation, product removal and soil test data... Overall, N was the key nutrient driving early growth responses at all sites (Table 3) in 2012, and the N balance was more important than S. Similar yields were achieved from applying N as Urea alone, as SoA, or as a Urea and gypsum combination (Figure 1) at all sites, except at Lameroo where an additional response to combined N and S was found... The response is not uncommon in Mallee farming systems, as DAP/MAP will supply a proportion of the N requirement, and the ongoing crop demand for N can be assessed throughout the growing season to better match seasonal conditions (soil moisture) with N supply...
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