The Response of Crops to Potassium Placement Depth and Band Spacing

Central and southeastern Queensland cropping systems are driven by water availability, and in these summer rainfall areas either winter crops (wheat or chickpea) or summer crops (cotton or sorghum) will be selected depending on the amount of stored soil moisture. It has been shown that in these systems, the subsoil nutrient levels are moderately to severely depleted due to the rainfall and root development patterns. Low levels of P, K, S, and micronutrients are routinely seen in the subsoil (>20 cm), but soil testing is usually from surface soils (0 to 10 cm) except on irrigated (bedded) cotton which is sampled 0 to 30 cm. Field experiments on cotton, sorghum, chickpea, and wheat are investigating the placement and type of nutrients to meet the demands of these crops. Because these are grown with minimum tillage, the investigations are considering supplying large amounts of nutrients (e.g. 200 kg KCl/ha) in the subsoil to meet crop demand over several seasons. Nitrogen management is tactical in these systems, as it is in these experiments. Row spacing, placement depth and balancing nutrients are treatments being used.

Results indicated that much of the cropping region faces multiple nutrient deficiencies, particularly with low P, which then constrains the response of K and S. There appears to be little penalty from having wide rows (100 cm) and deep placement (30 cm), and some growers are investigating using specialized deep placement equipment to establish these bands in the field. There are still problems with getting reliable soil K tests, and other work in the region is investigating both sampling depth, clay mineralogy and extractants. ANZ-13