Taking a field out of forages is a decision that should first examine why it was put into a forage in the first place.
If you bought or rented the field when it was already in grass or alfalfa, you may be in for a surprise.
There were probably good reasons for the field being planted to a perennial crop, and they might still be there. These could include stones or rocks, salinity or sandy soil with a very high water table. Or it may have been seeded simply for the forage.
Soil sampling is a good way to determine salinity. Make sure you get a zero to 60 centimetre sample and ask the lab to look at the electrical conductivity in both the surface zero to15 cm and subsurface samples. This should give an indication of salt issues.
It should also provide an indication of stones and rocks. I separate these two items using the rational that a stone is something smaller and can be picked using a stone picker, while a rock is bigger than a stone and will need specialized equipment for disposal. I am sure that a soil sampler will give you feedback if he encounters an abundance of stones and rocks in the field.
The first point that needs to be discussed is the method of termination. Here we have three choices: tillage, chemical and a blend of the two.
Tillage can be effective in removing a forage stand but will require a number of operations to be effective.
I have seen growers till six or seven times and end up with a very rough and lumpy seed bed. I have also seen fields that are denuded of any residue and the field blew when the wind came up in the fall and spring.
The results will depend on the equipment used, the soil texture, the age of the forage stand and the weather. The use of a tandem disc will create in a blacker, residue-free field quicker than a couple of passes with a chisel plow or cultivator.
Herbicides are another way to terminate a forage crop.
Glyphosate is the most common product used. It can be quite effective if applied when the forage is actively growing, but results can vary depending on species in the forage mix and weather conditions.
Alfalfa and smooth brome can be the most difficult species to control. They may take 1,020 to 1,750 grams per acre, 2.8 to 4.9 REL, to obtain affective control.
A timing option is to apply the glyphosate 4.5 days before cutting or when the alfalfa is starting to wilt. The crop can be baled or ensiled as usual because there is no restriction to feeding glyphosate-treated crops. A touch-up can be made again in the fall to any regrowth. The following year, a crop can be seeded directly into the standing residue.
Moisture is a big issue when planting a crop into a previous perennial forage field. There is almost always very dry soil following perennial forage termination. These crops use moisture from spring melt to freeze-up. This is probably the number one reason why, once established, a farmer resists breaking up a perennial forage field, no matter how poor the stand is.
As for fertilizing following a forage crop, you can bet phosphate, potash and sulfur are going to be deficient. These nutrients have been removed and fed to your cattle or sold for years.
A tonne of forage hay will remove approximately 35 to 50 pounds of nitrogen per acre in addition to 10 to 15 lb. of phosphate and 40 to 50 lb. of potassium. This means that a lot of nutrients have been hauled away over the life of a stand.
I suggest broadcasting a significant amount of your fertilizer needs in the fall when managing potash, phosphorus and sulfur.
For phosphorus and potassium, this can be done before tillage. A rate of at least 50 lb. of each of P2O5 and K2O is recommended.
As for sulfur, elemental sulfur can be an effective product choice. I recommend broadcasting it during the summer or fall if using herbicides and in the fall if using tillage, after the last tillage pass. This will allow the elemental sulfur particles to disperse and oxidize into plant-available sulfate (S04) more quickly.
In the spring I recommend seed-row application of the same rates of these products that would be normally used. When growing canola, I would suggest using a sulfate form of the nutrient. This will ensure there are adequate quantities for crop growth.
This leaves us with nitrogen.
If you have a significant amount of alfalfa in the stand, you can expect the breakdown of this to provide a significant amount of nitrogen to your crops for the next three years.
However, there are a number of variables determining how much and when this will show up. A healthy alfalfa stand with five or more crowns per sq. foot may provide more than 100 lb. per acre of nitrogen for the next crop. The amount available will decrease with the amount of alfalfa crowns to approximately 30 to 40 lb. if the number of crowns is one to two per sq. foot.
Terminating the stand will also effect the availability of the nitrogen. A field that is terminated at the time of the first cut may provide the entire amount of nitrogen to the following crop, while a field terminated in September may only provide half that amount.
The method of termination will affect the mineralization rate of the nitrogen. A field terminated after the first cut in late June or early July that is disked and cultivated a number of times during the summer will see most of the nutrient mineralized for the next crop.
Compare this to a field that is terminated by herbicides, where only 30 to 40 lb. will be available. However, the next year, there will be a flip with more being mineralized in the herbicide-terminated fields than the tilled fields.
The long-term benefits of a perennial forage are numerous. One of these is that they help to reverse soil compaction. The effect of a deep-rooted perennial crop can be seen for two to three years following termination because water infiltration and crop rooting depth are both improved.
Managing the crop following forage termination will make a forage in your rotation more profitable.
Thom Weir PAg is a certified crop advisor and professional agrologist in the Yorkton, Sask., region. You can reach him at firstname.lastname@example.org.