The Response of Crops to Potassium Placement Depth and Band Spacing

Two field experiments were established in central Queensland at Capella and Gindie to investigate the immediate and the residual benefit of deep-placed (20 cm) nutrients in this opportunity cropping system.

The field sites had factorial combinations of P (40 kg P/ha), K (200 kg K/ha), and S (40 kg S/ha) and all plots received 100 kg N/ha. No further K or S fertilizers were added during the experiment but some crops had starter P. The Capella site was sown to chickpea in 2012, wheat in 2013, and then chickpea in 2014.

The Gindie site was sown to sorghum in 2011/12, chickpea in 2013, and sorghum in early 2015. There were responses to P alone in the first two crops at each site and there were K responses in half the six site years. In year 1 (a good moisture year) both sites showed a 20% grain yield response only to deep P. In year 2 (much drier) the effects of deep P were still evident at both sites and the effects of K were clearly evident at Gindie. There was a suggestion of an additive P+K effect at Capella and a 50% yield increase for P+K at Gindie. Year 3 was dry and chickpeas at Capella showed a larger response to P+K but the sorghum at Gindie only responded to deep K.

These results indicate that responses to deep-placed P and K are durable over an opportunity cropping system, and meeting both nutrient requirements is important to achieve desired yield responses.