Sod seeding, where an annual crop is seeded into an untilled, terminated forage stand, has gained popularity over the past decade. Where farmers once had to experiment on their own, now farmers, extension specialists and researchers have developed some best management practices that help ensure success.
Following are 12 tips for success from Ron Heller, former Alberta Reduced Tillage LINKAGES (RTL) agronomist at Vermilion.
1) The best time for forage termination is the year before seeding an annual crop. Heller says there are three typical scenarios when the forage can be terminated with glyphosate. The best time is the typical pre-harvest timing. For sod seeding, that means just before forage harvest in July for a one-cut forage crop.
“Glyphosate translocates best when the forage is actively growing. That is in the early summer just before haying. You will get the best kill of the forage when the crop is almost mature,” explains Heller.
But there are other good reasons for taking out the forage crop 10 months before seeding an annual crop into the terminated sod. Typically, the forage or pasture stand is depleted of moisture, and the early kill-down of the perennial grasses and legumes provides an opportunity to replenish moisture. The sod also has more time to decompose, allowing easier seeding through the sod the next spring. The phytotoxic and allelopathic effects are also reduced because the sod has decayed more.
2) Termination at second-cut hay can work, but increases risk. Heller says in areas with good summer growing conditions, spraying out the forage crop just before the second cut can also work. However, he cautions that waiting for this timing may reduce the chances of successful termination.
“When you wait for the second cut, you need good regrowth. That’s the risk. If the weather turns dry and regrowth is poor, you may not get as good of termination of the stand than if you did it before the first cut,” explains Heller.
3) Pasture termination presents additional timing challenges. If the forage land is used as pasture, there is a temptation to leave the cattle on the land for grazing because it is economically necessary. However, as cattle graze longer into the late summer or fall, the risk of poor forage termination with glyphosate increases because of poor forage regrowth.
“There is a good window in the fall to terminate grasses but alfalfa is harder to terminate in the fall, so timing can become an issue,” says Heller. “You have to get the cows off the land for six weeks to get a good kill. It is tempting to keep cows on as long as possible, but if the cattle are pulled off two weeks before spraying, the forage kill will be poorer.”
4) Spring termination harder to pull off. Heller says that spraying forage out in the spring, and then seeding to an annual crop later that spring is a challenge. He says that the glyphosate application must be delayed in the spring until good forage growth is present. This delay means annual crop seeding will also be delayed.
“Don’t plan on canola or a seed crop. They won’t have time to mature before a fall frost. Choose an early maturing crop like oats or plan a greenfeed crop,” says Heller. “It is tempting to sow Roundup Ready canola because you can spray out any grass regrowing, but growing canola would be risky.”
5) Don’t skimp on the glyphosate. On forages, Heller says using the full 720 gm active ingredient per acre provides the best termination of grasses, legumes and perennial weeds. The 720-gm/acre rate is the two-litre/acre rate for the old Roundup Original formulation and other glyphosates with 360 gm active per litre, or 1.33-litre/ acre rate for Roundup WeatherMax that has 450 gm active per litre. With glyphosate’s low price, he says that cutting back on the rate is a false economy.
“You’re trying to kill perennial plants so you need a high rate to ensure good translocation.” he explains.
6) Observe the pre-harvest interval. Most glyphosate products are registered as a pre-harvest forage treatment. That means they can be sprayed on the forage and then harvested for hay, or grazed by cattle. For hay crops, the forage can be cut three to seven days after glyphosate application. Cattle can also be returned to pasture three to seven days after glyphosate application.
7) Watch nitrogen fertility. Research by Alberta Agriculture in the 1990s found that old pasture and hay fields are usually nutrient deficient. This can be especially true for nitrogen (N) because sod seeding doesn’t till the soil to incorporate the organic matter sod layer, and N mineralization (the converting of organic N to mineral forms of N that the plant can use) takes longer.
“It is hard to get a good soil test on a forage or pasture field that has been terminated, because N mineralization is hard to predict,” says Heller. “Bump up N rates by 25 per cent to make up for the lack of N mineralization.”
8) Pea crops do well. Heller says farmers have recently started seeding peas into sod with good success.
“I like peas because you can seed them early in the spring and they can tolerate being seeded fairly deep. And because the land is usually N deficient because of the lack of mineralization, an inoculated pea crop that fixes its own nitrogen doesn’t need N fertilizer,” explains Heller.
Another advantage is that because N fertilizer isn’t required, a simple, single shoot, narrow knife or disc opener can be used for seeding.
While pea has fewer herbicide choices and isn’t as competitive with weeds as other crops, Heller says weeds typically aren’t a challenge on sod seeded fields, because the land isn’t tilled to stimulate
weed germination. He also says that if the field is rough, it can be rolled. Don’t worry that the seed will be buried by rolling, though, as the roller smoothes out the field but doesn’t close the seeding trench.
9) Oats better than barley and both better than wheat. Oats have also done well when sod seeded, partially because they seem less affected by soil borne diseases, but also because they do not require high rates of N.
Heller says that as a early maturing crop, seeding oats can be delayed to later spring. Many farmers sod seed oats for seed because the land is typically free of wild oats.
10) Canola possible but is riskier. Depending on your risk level, canola can be a good choice. The crop costs more to grow, but with the option to grow a Roundup Ready canola, glyphosate can be used in-crop to clean up any forages that survived.
Heller says that a good double shoot opener will be required to carefully place canola seed into the soil, below the sod layer, and to separate the high rate of N fertilizer from the seed.
“I have seen some good canola crops on sod, but you have to be careful. It is such a high-risk crop to grow. You have to make sure the seed isn’t too deep, or stranded too shallow in the sod. And you can’t get crop insurance for sod seeding, so it is high risk,” says Heller.
11) Seeding equipment is dictated by fertility requirements. For crops other than peas, a double shoot opener is required. Heller says a double shoot opener or the parallel linkage type openers that separate seed and fertilizer can work well as long as they are low disturbance. Wide openers and heavy flat packing may push the sod too firmly back over the seed row, bury the seed too deep or leave exposed seed, so narrow openers with on-row packing is optimum.
Disc openers present a challenge if a high rate of N fertilizer needs to be applied. Heller says the old Barton double shoot disc opener worked well, but hasn’t seen anything come along to replace it.
For single shoot disc or knife openers, Heller says a mid-row type band application is possible to apply extra N fertilizer, although, for reasons unknown, he hasn’t seen good success with mid-row banding in sod seeded crops.
12) Seed slow and maybe seed deeper. No matter what the opener or implement, slower seeding is necessary to help ensure that the sod isn’t disturbed very much. Heller says that if the forage crop was terminated the year before, the sod is usually fairly mellow and easy to seed through.
“You have to place the seed in the moist soil, not the loose thatch. If it is two inches thick, the seed needs to be placed below that to get good seed to soil contact,” Heller explains. “That can be a big reason why sod seeding fails. Otherwise, terminated forage makes a perfect seedbed for almost any annual crop we grow on the prairies”.
This article is courtesy of Reduced Tillage Linkages.