Does Handling Physically Alter the Efficiency of Polymer-Coated Urea Fertilizer?.

Polymer-coated urea is a form of nitrogen (N) fertilizer that provides controlled-release so that it can be seed-placed at higher rates without rendering toxicity effects on the plant.  The integrity of the polymer coating is often determined by immersing granules in 23^o C water and calculating N released over time, but the results are difficult to relate to field conditions. Field studies were conducted in 2008 and 2009 at two locations in southern Alberta, Canada to determine the impact of handling methods and abrasion on the polymer coating of controlled-release urea (CRU) when seed-placed with canola, wheat or triticale.  Levels of abrasion were created through laboratory simulation (0 to 80% N release after 7d in 23^o C water, calibrated in increments of 10%; Experiment 1), or by collecting material from exit points on delivery implements (9 levels) that were subjected to two contrasting methods of loading and unloading on the farm and at the retail point (9x2x2 factorial; Experiment 2).  Water release data was related to plant and soil responses in the field by seed-placing CRU with spring canola and winter cereals at rates of 45 kg N ha^-1 and 90 kg N ha^-1, respectively.  Compared to the 20% N release control, stand establishment was significantly reduced at 40 to 50% water release in canola, and at 60% water release in winter cereals.  However, acceptable plant populations were maintained up to the 60% release level for all crops.  Similar results were observed for leaf area index (LAI), but cereals were more sensitive to changes in normalized difference vegetative index (NDVI). With respect to retail and on-farm handling, the most serious abrasion occurred when transferring product in equipment containing scaly deposits; topdress applications with an air boom applicator, or with seeders configured with header-manifold systems operating at high air fan speeds.