The Response of Crops to Potassium Placement Depth and Band Spacing

We continue to see evidence of responses to additional P, K, or S fertilizer applications in winter and summer crops, with a number of sites responding more strongly to combinations of these nutrients (i.e. P and S, or PK and S) than due to individual nutrients alone. This is especially the case where sufficient N is available to allow higher yield targets to be reached. Factors which affect root system efficiency or the ability of root systems to explore large soil volumes (e.g. lesion nematode activity or water logging) will increase the size of yield responses.

In the recent wet summer and winter crop seasons, the reliance on deep placement of P or K has generally been reduced in favor of overall profile (0 to 25 cm) enrichment, but residual effects of deep P applications are still being recorded six crop seasons after application.

It is proposed that application strategies for P and K fertilizer be developed around periodic deep (15 to 20 cm) applications in bands 50 cm apart (or closer), in addition to the current use of starter P applications in the seeding row when Colwell-P tests in the 0 to 10 cm layer indicate a deficiency. Applications should at least meet likely crop removal in grain until the next application event, while redistribution of deep applied nutrient in crop residue will enrich the topsoil layers. Applications of the more mobile N and S can be made to target individual crops and yield targets as at present. ANZ-13