The Response of Crops to Potassium Placement Depth and Band Spacing

Two sites were established in central Queensland in 2012, one at Capella and the second at Gindee. Both sites had low soil concentrations of P, K, and S, especially in the subsoil layers. We established trials by adding single nutrients (P or K or S) into the 10 to 30 cm layer, or combinations (P+K, P+S, K+S, P+K+S). These sites were grown under commercial practice through successive crops; sorghum (2012) and the chickpea (2013) at Gindee and chickpea (2012) and wheat (2013) at Capella. No additional fertilizers were added after sowing of the first year.

In year 1 (a good year for moisture), both sites showed a 20% grain yield response to deep-applied P fertilizer. While no other nutrients affected grain yields, there was a suggestion of an additive effect of deep K at Capella in chickpea biomass, There was no S response. 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 very significant additive effect of P + K at Gindie. This suggests that K availability with added P gave a 51% grain yield increase. These experiments show that as soils reserves decline, it is essential to apply the right combination of fertilizer nutrients to maximize crop productivity and seasonal water use efficiency.