Farm Table says:
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.