Large Urea Granules for Broadcast Application in Perennial Forage Grasses

Urea is the most common N fertilizer for surface broadcast applications for perennial forage grass production in the Northern Great Plains (NGP). There is interest to know whether various N fertilizer additives, specifically a urease inhibitor alone or in conjunction with a nitrification inhibitor, can increase N availability and the production of forage grasses. There is also interest in whether larger urea granules (e.g. 0.5 in. diameter) could supply N more efficiently than regular-sized granules (0.125 diameter). This study consisted of two years (2012 and 2013) of experiments evaluating both large and regular-sized urea granules, with or without treatment with urease and nitrification inhibitors. The urea treatments were broadcast on the soil in both the fall and spring. Some band-applied urea fertilizer treatments were also included, with and without urease and nitrification inhibitor, using a no-till disc drill in both the fall and spring. The research site was a mixed grass stand pasture that had been previously established for eight years (near Youngstown, Alberta). The N application rate for all treatments was 36 lb N/A (40 kg N/ha), except for a unfertilized treatment. A broadcast application of 25 lb P₂O₅, 20 lb K₂O, and 4 lb S/A were also applied to all plots. The fall treatments were applied in mid October of each year, and the spring treatments were applied in mid April of each year. A forage cut was taken from the middle of each plot at the end of June.

In 2012, there were higher forage yields from both the larger urea granule treatment compared to regular sized urea, and from spring urea applications compared to fall applications. There were no differences in forage yield between untreated urea and yields from grass fertilized with urea treated with urease and nitrification inhibitors. In 2013, there were no yield differences between the two sizes of urea granules, or the timing of applications. The use of combined urease plus nitrification inhibitor on the urea resulted in greater forage yields than the use of untreated urea or urea treated only with a urease inhibitor. The research experiment will be continued at this site for one more growing season. There appears to be potential for improved grass forage yields from using urease and nitrification inhibitors with urea fertilizer, and a potential benefit from larger a granule size, but more research is needed to verify this finding.