EFFECTS OF SINGLE VERSUS SPLIT ANNUAL APPLICATIONS OF NITROGEN ON FORAGE DRY MATTER AND PROTEIN YIELD OF SMOOTH BROMEGRASS

Abstract

A shortage of forage in the spring and autumn is one of the limitations for growth of the cattle industry in the Canadian prairies. Forage grasses respond to nitrogen (N) fertilization and their response is influenced by time and frequency of application. A field study was conducted from 1993 to 1995 on a Black Chernozemic (Udic Boroll) soil in central Alberta to compare the effects of autumn and spring timings, and single versus split annual applications of N at different rates on dry matter yield increase (DMYI), protein content and protein yield increase (PYI) of smooth bromegrass (Bromus inermis Leyss.). The N treatments were combinations of 60, 120, and 180 kg N ha−1 rates, and autumn and spring initiated single (100% in autumn or spring), split50 (applied 50% in autumn or spring, 25% after cut 1 and 25% after cut 2) and split33 (applied 33% in autumn or spring, 33% after cut 1 and 33% after cut 2) modes of application. Bromegrass was harvested in late May to early June (cut 1), early to mid July (cut 2) and mid to late September (cut 3). In cut 1, the DMYI and PYI with single mode were greater from autumn applied N than spring applied N. In cut 2 and cut 3, the DMYI and PYI were usually greater with spring than autumn initiated N application for all modes. The seasonal total DMYI and PYI for the two split N applications were greater with spring than autumn initiated N application. The protein content was higher with spring than autumn initiated N applications for cut 1 forage, while it showed no influence of the initiation time of N application for the cut 2 and cut 3 forage. Single application gave the higher DMYI in cut 1 and lower DMYI in Cut 3 compared to split applications. Split applications thus had more uniform distribution of DMYI and PYI over the growing season than single application. For spring applied N, the seasonal total of DMYI and PYI was greater with split modes than single mode. Overall, the forage yield benefit from applied N was generally greater with spring than autumn initiated N applications, and splitting the N applications normally improved forage production and its distribution in the growing season. However, the savings and workload distribution from autumn application and extra cost of split applications should be taken into consideration to arrive at the appropriate N management practice for bromegrass.