There is nothing worse than having cattle to feed and then being caught off guard by low forage yields due to winter injury. If you have not already done so, walk alfalfa fields and dig some plants to assess for winterkill, heaving, frost damage and plant health. Watch for crown and root rots, brownish disclouration, spongy texture and lack of secondary roots and nodulation. Plant health can be more significant than plant density to a successful yield. http://www.omafra.gov.on.ca/english/crops/facts/info_alfalfa_stand00.htm
Nitrogen can dramatically increase the yield of grass stands, as well as forage protein levels. Optimum rates depend on the cost of nitrogen, anticipated value of the hay, thickness of stand, moisture conditions, and whether it is pasture or hay. Good grass stands with less than one-third legume, can generally benefit from at least 70 kg/ha (63 lbs/acre) of actual nitrogen (Table 3-6, OMAFRA Publication 811, Agronomy Guide www.omafra.gov.on.ca/english/crops/pub811/3fertility.htm#nitrogen ). The first application of nitrogen for hay should be made at green-up, as soon as possible in the spring when soil conditions are suitable.