Fine tuning deep phosphorus and potassium management

Abstract

Take home message
• 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.