Charlotte Ward, MSc, PAg – Regional Forage Specialist - Yorkton
The typical production schedule for a perennial forage crop usually consists of 3 to 5 years of high yield (honeymoon period) followed by a rapid decline in productivity. Once this 3 to 5 year honeymoon period is over, factors such as declining soil fertility and decreasing plant numbers typically result in lower production. Another key factor that will affect long-term stand productivity is timing and frequency of harvest – whether or not producers take a 2nd cut of hay or grazing and the timing of that harvest.
Proper management of these stands from now until freeze up can help to mitigate the natural decline in productivity.
How can soil fertility affect stand productivity and why should be thinking about it this fall?
As we harvest perennial forages and remove the plant material from the field, we are also removing a tremendous amount of nutrients from the soil as well. High yielding forages will remove more nutrients than low yielding forages, which will in turn likely remove more nutrients than if the stand were grazed. Over time we need to replenish these nutrients. Manure, commercial fertilizer and even feeding livestock on the field can all be used as tools to import nutrients.
If alfalfa makes up 50% or more of the production in the stand and was properly inoculated at seeding, nitrogen is generally not a concern in the forage stand as the alfalfa will fix all the nitrogen that the stand needs. Phosphorus, potassium and sulphur are the three nutrients that we tend to focus more on in stands that contain a significant portion of legumes as legumes are high users of these nutrients. Phosphorus and potassium are of particular importance as they contribute to root and nodule health and the over-wintering capability of the plants. Both of these nutrients can be fall applied as they are relatively immobile in the soil and they will not leach or volatilize to the atmosphere like nitrogen will. Fall application of these nutrients can also help to decrease the work-load next spring. The most cost-effective way to know where your stand is at in terms of soil fertility is to do a fall soil test.
How does the timing of harvest and frequency of harvest affect forage yield?
Improper cutting of alfalfa stands can lead to winter kill. Understanding alfalfa physiology can help to avoid this problem. In the plant, energy is produced in the leaves through the process of photosynthesis and is used to fuel plant growth. As the plant produces excess energy, it is stored in various plant parts such as the roots and crown. The stored energy is used for regrowth following cutting, plant maintenance over winter and growth during early spring.
When an alfalfa plant is cut, few leaves remain and the plant may draw on stored energy reserves for regrowth. Generally the plant will need 6 weeks to replace leaves and replenish stored reserves to pre-cutting levels. Thus there is a 6-week critical period after cutting that the plant needs to ensure that it has good energy reserves going into winter. This is of particular importance to producers looking to take a second harvest off their fields, either through mechanical harvest or grazing livestock.
Plants harvested after August 15th may not obtain six weeks of good weather of replenish reserves before a hard frost and can go into winter with low energy levels. Plants with low energy levels are more susceptible to winter kill. If it is necessary to take a second harvest, producers should wait until after a killing frost as the plants will shut down and will not try to mobilize energy reserves.
Fall harvests should be approached with caution as harvesting plants after August 15th reduces the stubble height of the field which is important for trapping snow and spring moisture next year. Standing alfalfa will not only trap snow this winter, but will also cover the soil next spring and summer to minimize moisture lost through evaporation.
What can producers do this fall to optimize forage yield next year?
· Avoid cutting between August 15th and the first killing frost
· Ensure there is adequate soil fertility, including phosphorus and potassium which is particularly important for root health and development as well as nodule health
· Manage stubble for maximum snow cover