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Beating the heat on seed-placed fertilizer

Lack of soil moisture may give pause when it comes to hot seedbeds

Farmers are being reminded to watch their seed-placed fertilizer rates if they want to avoid burning off profits.

Placing phosphate with soybeans has not typically given a yield response, according to Dennis Lange, provincial pulse specialist. He urged farmers to monitor their soil phosphorus and determine whether they should be drawing down, maintaining or building up the nutrient in their soils.

Why it matters: Seeding is wrapping up for most of the province, but for those farmers still on the field, seed-placed fertilizer is a perennial question in crops like soybeans.

Those opting for seed placement rather than side or mid-row banding should set their limit at around 20 pounds per acre for soybeans, Lange said.

The Manitoba Fertility Guide sets that number lower. The guide suggests that limit is on track for canola, but that soybeans should top out closer to 10 pounds of actual phosphate per acre in 15-inch bands, and that seed-placed phosphate in wide soybean rows may not be safe at all.

That 20-pound-per-acre recommendation is also based on adequate soil moisture, Lange cautioned.

Soil moisture has also been on provincial oilseed specialist Dane Froese’s mind. He warned that lack of moisture also means lack of water to dilute and dissipate fertilizer.

“We have had decent conditions. We do have some seedbed moisture, but it’s not excessively wet in most areas of the province,” he said in the first week of May.

Some farmers are bemoaning a dry start to the 2019 growing season. Farmers near Pierson say they have seen less than 20 mm of rain this growing season, while the nearby Manitoba Agriculture weather station reports only six per cent moisture five centimetres deep as of May 17. Much of western Manitoba and the Interlake (a region hit hard with dry conditions last year), saw soil moisture percentage in the high teens to low ’20s at the same depth, although more northern regions near Swan River hovered around 39 per cent.

Other parts of the province saw rain in the second week of May, and provincial weather stations noted soil moisture increased past 30 per cent five centimetres down in much of central and eastern Manitoba as of May 17.

Farmers may have to forgo seed-placed fertilizer altogether in dry soil, Lange said.

“(Drop) the phosphorus and the sulphur rates or find an alternative placement strategy,” Froese suggested. “Band it on ahead of time. Side band it. Mid-row band it. Put the minimum amount, or what’s considered a safe amount, with the seed and then put the rest elsewhere.”

Froese also urged farmers to consider their seeder’s seed distribution spread (a knife having a narrower spread than a hoe opener, etc.) divided with row width.

The higher that number, the higher the safe seed-placed fertilizer rate, he said.

Froese has similar worries when it comes to nitrogen and sulphur on sandy hilltops. Sulphur is particularly dangerous in the seed row, Froese said, “given that that has a fairly high ammonium and salt toxicity factor.”

Manitoba tends to be conservative on seed-placed urea, said John Heard, provincial crop nutrition specialist, since the typically higher soil pH moves more nitrogen from ammonium to ammonia.

Building phosphorus

Even the ideal seed-placed limit of phosphorous under ideal moisture conditions will not be enough to replace what canola and soybeans take out of the soil.

Lange suggests that farmers look past a single growing year to build phosphorus in the soil.

“A better recommendation for managing phosphate in soybeans is not necessarily managing it in soybeans themselves, but manage it as a whole rotation,” he said.

That echoes advice given during last year’s CanoLAB and SoyLAB event in Dauphin. Ray Dowbenko, senior agronomy specialist with Nutrien and one of the event speakers, urged producers to put down more phosphate during a cereal year, when crops are more resistant to phosphorus toxicity than either canola or soybeans.

Manitoba Agriculture suggests that up to 50 pounds per acre of phosphate can be laid down with cereal seed without worry.

At the time, Heard tagged the strategy for farmers who do not have the ability to side or mid-row band.

Farmers looking at newer products may be on to something when it comes to sulphur, although Heard warns that MicroEssentials products have proven less safe than normal MAP (mono ammonium phosphate).

Those products do have a lower salt index, he acknowledged, although, “salt effect is one of the two considerations in seed-placing safety of fertilizer sources. The other I consider more critical is the ammonia or (nitrogen) content.”

A cross-Canada study in 2014 found a blend of MAP and ammonium sulphate (36 and 18 pounds per acre, respectively) produced almost double the damage to canola than equivalent levels of a low salt index product (MicroEssentials ME S-15). Both, however, stunted stands more than MAP alone. One site out of 17 showed seven less plants per square metre with only MAP, while the low salt index product grew 11 less plants per square metre at two of 17 sites, and the blend reduced stand by 20 plants per square metre at seven sites.

At the same time, a half-rate of that blended mix provided better yield than either the equivalent low salt fertilizer or MAP alone, and on more sites, while higher rates saw about equal yield boosts with both the blend and novel fertilizer (between 10.6 to 10.8 more bushels an acre, compared to a 7.7 increase with only MAP.

“In summary, for this study S-15 fertilizer is safer in the seed row than MAP/AS blends providing similar amounts of (phosphate) and (sulphur). But S-15 is not safer than MAP alone, should growers find another method to meet the sulphur needs of the crop,” Heard said.

About the author

Reporter

Alexis Stockford is a journalist and photographer with the Manitoba Co-operator. She previously reported with the Morden Times and was news editor of  campus newspaper, The Omega, at Thompson Rivers University in Kamloops, BC. She grew up on a mixed farm near Miami, Man.

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