Fine Tuning Deep Phosphorus and Potassium Management

GRDC - Author: Doug Sands (Queensland Department of Agriculture and Fisheries), Prof. Mike Bell (University of Queensland), Dr. David Lester (Queensland Department of Agriculture and Fisheries)

Type: Research Paper
Knowledge level: Advanced

Farm Table says:

The authors of this paper note in the conclusion: “While chickpea residues can contribute to the mineral N pool, they rarely leave large amounts of surplus N behind – especially if grain yields have been reasonable. As discussed in the associated paper, ‘Strategies to improve efficiency of use of applied N,P and K fertiliser in Central Queensland’ (Bell et al, 2020),nitrate applied at planting can get stranded in the top soil and be unavailable for crop uptake in the season of application.”. Please access the full paper via the link below if this research interests you.

The take home messages from this GRDC funded research are below. Please access the full paper via the link below for methodology, references, acknowledgements and discussion.

  • The re-application interval for the deep placement of phosphorus (P) and potassium (K) will depend on the most limiting nutrient and crop type
  • Residual effects of deep P bands applied 5 years previously were still evident in the 2019 chickpea crop on a site with very low soil P status, with yield increases of 500 (20P) to 1000 (40P) kg/ha compared to sites where no deep P had been applied
  • However, yield increases of a further 900 kg/ha were recorded when a 2nd deep P application was made during the preceding fallow, clearly augmenting the P supply from the residual P bands
  • In contrast, there was no evidence of any residual benefits from deep K bands applied 3-5 years ago shown in chickpea crops at two low K sites, but yield increases of 500 kg/ha were recorded when K was re-applied during the preceding fallow
  • Potassium-limited sites may require shorter re-application intervals than sites where the main limit is phosphorus
  • Legume grain crops export more K/t grain than cereals, but cereals can quickly redistribute deep K back to surface soil layers in stubbles, due to their low rates of removal.

Figure 11. Mean accumulated grain yields (kg/ha) over the farmer reference (FR) treatment for all 4 crops (wheat 2016, chickpeas 2017, mungbean 2018 and chickpeas 2019) on the Dululu potassium (K) trial.

2020 - Australia - GRDC - Author: Doug Sands (Queensland Department of Agriculture and Fisheries), Prof. Mike Bell (University of Queensland), Dr. David Lester (Queensland Department of Agriculture and Fisheries)
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