Alfalfa winterkill? Use warm season grasses as emergency forage

As hay prices and demand for forages remain high, incentives have been developed to increase productivity in forage systems, especially alfalfa. In an effort to maximize forage production during the relatively short growing seasons of the upper Midwest, semi-dormant alfalfa varieties have been heavily promoted and widely adopted. Growing later into the fall, and breaking dormancy earlier in the spring, these lines offer potential to capitalize on more growing degree days, but increase the danger of winter injury or winterkill. During the 2012-2013 winter, nearly 750,000 acres of alfalfa in the state of Minnesota experienced winter injury and winterkill.

Very low success has been observed in replanting alfalfa into dead or injured alfalfa stands, due to low establishment year production and autotoxicity. This research, conducted by the University of Minnesota, investigates alternative production strategies employable as quick and effective responses to winter injury. The primary focus is to assess the viability of summer annual grasses as emergency forages when no-till planted into winterkilled alfalfa. These systems are intended to offer forage producers emergency production strategies that could provide forage for both grazing and haylage. Considering unfavorable planting conditions of a cold, wet spring, seeding as late as June or July may be necessary for warm season grasses to establish properly and meet yield potential.

Initial trials of the emergency forage program were conducted near Rosemount, MN, in 2013. This research assessed the following six warm-season grasses on yield potential and response to N fertilization and cutting management: Japanese millet, Siberian foxtail millet, teff, brown midrib (BMR) sorghum, annual ryegrass, and perennial ryegrass. Alfalfa was also seeded but was unsuccessful in establishment (likely due to autotoxicity). Grasses were cut (i.e. early vegetative) one month after the June 5th planting date and again first of September. Nitrogen response was assessed through the application of varying rates to the grasses, along with evaluating the subsequent effects on forage yield and quality.

Brown midrib sorghum yielded the highest of all the grasses, producing over 6 tons per acre. Teff, a warm-weather annual grass adapted to moisture regimes ranging from low desert sands to waterlogged clays, produced above 5 tons per acre, whereas perennial ryegrass was among the lowest yielding species at 1.7 tons per acre. Based on NDFd (neutral detergent fiber digestibility), BRM sorghum was among the highest quality grasses, while Siberian millet was among the lowest. Nitrogen fertilization had no effect on total dry matter production (i.e. yield of tons per acre) across all seven species, which indicated that the winterkilled alfalfa supplied enough N to meet the needs of all grasses. Forage protein content and NDFd were both improved with increasing N rates, ranging from 10% and 13% for Japanese millet and BRM sorghum, respectively.

Adapted from the previous study, the research currently underway maintains the same N rate applications and a fixed, intensive, cutting schedule. According to forage performance in the initial year, this experiment continues to utilize Japanese millet, teff, BMR sorghum, and annual ryegrass, with the introduction of sudangrass, sorghum sudangrass, Italian ryegrass, and a red clover/annual ryegrass biculture. This research is in place at the Southern and Rosemount Research and Outreach Centers at Waseca and Rosemount, MN, respectively, and will be maintained for two years.

Alfalfa was terminated with glyphosate to simulate winterkill at both locations. All species were no-till planted into the alfalfa residue. The research location in Waseca required re-spraying and re-planting due to alfalfa and dandelion persistence after the first glyphosate application. Harvest intervals began 30 days after planting and will take place every 30 days, concluding in early September. Following the final harvest and termination of warm season forages, Forage Plus Oats will be planted across all treatments and harvested in late October to assess yield and quality.

Yield data from the first harvest in Rosemount is available, providing insight to preliminary results. Sudangrass produced the greatest average yield across N rates at 1.41 tons per acre, closely followed by BMR sorghum (1.40 tons per acre). Japanese millet returned the lowest average yield potential (0.67 tons per acre). BMR sorghum, Italian ryegrass, red clover/annual ryegrass mix, and teff showed consistent yield response to increased N (Figure 1). BMR sorghum with 100 pounds N per acre produced the greatest treatment yield (1.64 tons per acre).

Field observations at Waseca indicate that intensive weed management may be critical to stand establishment. Sudangrass and teff appear to have established and maintained the strongest persistence despite heavy weed pressure in all treatments. Higher fertilized treatments of BMR sorghum and Japanese millet also appear to be faring slightly better than other treatments. Sorghum sudangrass, annual ryegrass, Italian ryegrass, and the red clover/ryegrass mixture have generally performed very poorly in this weedy location thus far. This emergency no-till forage research will continue over the next few years with the goal of developing a set of tools for producers faced with extreme winterkill in alfalfa or prevented planting. As the study progresses, future results will be presented at University of Minnesota Extension Forage Website.

(Corresponding author. mswells@umn.edu; office phone: 612-625-3747)

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Alfalfa winterkill? Use warm season grasses as emergency forage