Deep P and K - Outcomes from 8+ years of research: the good, the bad and the ugly

Abstract

Take home messages
• Stratified soil testing guides fertility and constraint identification. These tests do not need to be conducted annually for immobile nutrients and constraints
• Research experiments with subsurface placement of fertiliser phosphorus (P) at around 20-25 cm on low Colwell P subsoil tests has significantly increased grain yield in central Queensland (CQ) across range of wheat, chickpea and sorghum crops. Winter cereals across southern Qld are generally also positively responding, but chickpeas and sorghum responses in this region have been mixed, ranging from positive to no effect. Data for northwest slopes and plains of NSW is very limited
• The relationships between crop P uptake and grain yield for chickpea, wheat and sorghum are robust. As you get more P into the plant, yields are increasing
• Potassium is an emerging yield constraint, but data sets are not yet as extensive as for P.