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Using Forages as a Rotational Crop

By Trevor Lennox, PAg, Regional Forage Specialist

February 2017

Many grain producers often overlook the possibility of including perennial forages as an important tool to improve the long-term sustainability and profitability of their operation. A few issues that grain producers have faced recently are: herbicide resistance, and the spread of new crop diseases such as Fusarium Graminarium. Perhaps a short-rotation forage crop, such as alfalfa, may be a solution for some producers to help minimize the potential for herbicide tolerant weeds to develop and to reduce the potential for plant diseases such as Fusarium.

The traditional way of thinking that ‘cropland will remain as cropland’ and ‘hayland will remain as hayland’ is being challenged by some producers. These producers are finding excellent benefits to incorporating short-term (3-5 years) alfalfa or alfalfa/grass mixtures into cropping rotations.

Perennial legumes such as alfalfa can contribute large amounts of nitrogen to the soil, reducing nitrogen fertilizer requirements. It is difficult to measure the exact amount of nitrogen left in the soil when alfalfa is terminated, as there are many variables affecting nitrogen fixation in the soil. However, one particular study found that alfalfa contributed an average 45 lbs/ac/year of nitrogen to the following crops. This means that a four-year-old alfalfa stand could potentially contribute a total of 180 lbs/ac of nitrogen towards the annual crops that would follow. Another study found that a five-year-old alfalfa stand provided enough nitrogen for two following crops, with fertility benefits lasting up to seven years following stand termination.

When a perennial forage crop is terminated there is lag time before the nutrients are released into the soil. The delay in nutrient release is a result of nutrients that are tied up in decaying plant material (roots), making them a slow-release type of fertilizer. This delay in nutrient release is challenging when trying to determine the fertility limitations when planting annual crops and makes soil testing an important tool to determine the soil nutrient status. If the soil test shows low levels of nutrients, then additional fertilizer may be required so annual crop yields are not compromised due to low fertility levels.

One challenge with using perennial forages in a crop rotation is that they can dry out the soil profile significantly, more than annual crops. The soil can be dried out to the point that the yield of following grain crops is reduced. One management option to minimize complete depletion of soil moisture levels is to have a short rotation forage crop.  This crop is only left in forage production for approximately three years. In planting a short-rotation forage crop, a producer chooses to plant a short-lived species (3-4 yrs) as they are easier to terminate and go back into annual crop production. Another management option to improve the soil moisture levels prior to planting to annual crops is to fallow the land for a short period of time.

In summary, using perennial forages as a rotational crop can contribute significantly towards improving soil fertility. Alfalfa with its ability to fix nitrogen, offers the greatest fertility benefit to the crops that follow.  

For further information, contact the Swift Current Regional Services office at (306) 778-8294 or trevor.lennox@gov.sk.ca.

 

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