Large Urea Granules for Broadcast Application in Perennial Forage Grasses

This research was conducted using a cool season perennial grass pasture. The grasses have been established for 10 years, and were part of an original pasture rejuvenation project conducted by the Chinook Applied Research Association in cooperation with the land owner. The 2012 growing season was characterized as being close to average in temperature, but much more moist. There were 355 mm of moisture received during the growing period from when spring growth started until when the forage samples were taken compared to only 157 mm normally received. Late June through to mid July is when the first of a possible two seasonal hay cuttings is normally done in this area. After this initial hay sampling, the weather turned warmer and drier than normal and there was insufficient re-growth for a second hay cut, that is normally taken in early September.

The research site was N deficient and there was considerable response to added N. Hay dry matter yield under the zero-N treatment was 0.34 t/ha, and was significantly lower than all treatments receiving N. The highest yielding N treatment was 1.2 t/ha (equivalent of 1.4 t/A of hay at 15% moisture content). Of the three experimental factors, size of urea granules, timing of application, and use of urease and nitrification inhibitors, there was a significant effect of size of granules and timing, but no difference whether urease or nitrification inhibitors were added. The larger forestry grade size granules, 20 mm (0.5 in) in diameter, resulted in greater hay yields compared to the regular sized 3 mm (0.125 in) urea, respectively 1.05 t/ha compared to 0.98 t/ha. Spring applications yielded higher than fall applications, respectively 1.07 t/ha compared to 0.97 t/ha. The pattern of moisture received resulted in conditions that did not seem susceptible to either ammonia volatilization losses or denitrification losses, thus no measurable benefit from using the urease or nitrification inhibitors was observed in the 2012 growing season. It is planned to repeat this experiment for two more growing seasons. AB-30