Improving Hayfield for Forage Quality While Minimizing Nitrate Loading of Tile Drainage.

Most of the 1.1 M ha agricultural land base under Atlantic Canada's humid climate is used for forage or silage production, either in support of the livestock industry or in rotation with other crops. Perennial hayfields with or without a leguminous forage are known for their efficient use of applied nitrogen, whether from inorganic or organic N sources, when compared with other crops such as corn (Zea mays L.). The life span of these perennial forages is not indefinite however, as their quality declines from season to season. Previous work has shown that conventional re-establishment of perennial hayfields every few years (plough down and reseeding) results in a significant release and loss of nitrogen capital from the soil by leaching, denitrification and other N loss pathways. Maintaining the quality of these systems while retaining as much nitrogen capital as possible over the medium term is therefore an important environmental and economic consideration.This study compared the impact of two techniques for improving the quality of existing hayfield on nitrate leaching as well as denitrification losses on a common, tile drained soil in the Annapolis Valley of Nova Scotia. Spring applied liquid dairy manure (LDM) was used as principle N source at a target rate of 150 kg N ha^-1. A randomized block design was used with two hayfield improvement treatments, namely spring interseeding (IS) vs conventional re-establishment (CR), and three replications. Each experimental unit consisted of a 100 m x 12 m tile drained plot. Drainage lines were monitored continuously for drainage volumes and nitrate concentrations. Undisturbed soil cores were taken every 14 days during the growing season to obtain estimates of denitrification using the acetylene inhibition technique. The first year of the experiment (2013 growing season) was used as a time buffer to establish equilibrium soil conditions in all six experimental hayfield units. During this growing season, there were no significant differences in hay yields (two cuts) between each of the three future IS and CR treatment plots which yielded 3,100 and 3,600 kg ha^-1 (dm), respectively. Nitrogen leaching losses to tile drainage were also not significantly different and amounted to 3.1 and 3.6 kg N ha^-1, for the IS and CR plots respectively. Similarly, during the 2013-14 non-growing season, the nitrate leaching losses to tile of 6.9 and 7.4 kg N ha^-1 for IS and CR respectively, were not significantly different. Growing season denitrification losses were however, significantly higher in the plots allocated to the CR treatment (24.8 versus 10.8 kg N ha^-1 for the IS treatment), indicating the possible presence of plot denitrification signatures related to soil moisture conditions associated with differences in micro-topography. In the spring of 2014, LDM was again applied to all plots. The IS treatment was applied by seeding Alfalfa (Medicago saliva L.) at 15 kg seed ha^-1 into an existing Timothy (Phleum pretense L.) / Bromegrass (Bromus arvensis L.) stand using a Hunter rotary strip seeder. In the CR treatment, the Timothy / Bromegrass stand was ploughed under and re-seeded to a mix of Alfalfa, Timothy and Bromegrass at rates of 12, 6 and 10 kg ha^-1, respectively using a Brillian Seeder. The interseeded (IS) treatment resulted in significantly higher (2,405 kg ha^-1, dm) forage yields in the first treatment season when compared with the conventionally re-established (CR) treatment. This was due to a two-cut season for IS versus a one-cut season for CR treatment in the first year. Field inspection also revealed a higher percentage germination and emergence of alfalfa in the IS treatment.  A detailed assessment of yield and quality parameters as well as environmental impacts relating to the fate of applied nitrogen over the course of the 2014 and 2015 growing seasons needs to be undertaken before definitive conclusions can be drawn.