Wider rows can increase damage from seed-placed N

Going to wider rows? Many new drills are set at 12” and 14” row spacing. Wider row spacing means higher concentrations of seed and fertilizer through each opener — based on the same per-acre rates. This can increase fertilizer damage to seedlings and lead to a thinner stand, particularly for openers that place fertilizer and seed together.

Nitrogen is usually the greatest challenge to manage. It is typically required in the greatest quantities and tends to be the most damaging macronutrient when placed with the seed. Safe levels of nitrogen fertilizer in the seed row are as low as 10 to 15 pounds of actual nitrogen per acre. The wider the row spacing, the lower the number. For example, jumping from 8” to 16” row spacing means the amount of nitrogen per seed row doubles, as does the amount of seed per row. With wider rows, seed and nitrogen are that much closer together, which increases the risk of seedling death and thinner stands.

Ways to limit damage from seed-placed nitrogen:

Use more of the seedbed. Wider openers spread seed and fertilizer over more of the seedbed, increasing separation. Keep in mind that wider openers also require wider packers, may lead to less precise depth of placement, and take more horsepower to pull — especially in wet soils. Double shoot openers are designed to place nitrogen away from the seed, but if growers seed too fast or if the openers are worn, these openers may not achieve the desired separation.

At higher speeds, double shoot openers may not place seed where desired. Seed will often bounce down into the fertilizer furrow. This can lead to seedling damage and a thin stand, as shown in the photo below.

Use a urease inhibitor (Agrotain) or polymer coated nitrogen (ESN). These products slow the release of ammonia and ammonium from urea fertilizer, which increases seed safety and allows for higher rates of nitrogen to be placed with the seed. They work in different ways to achieve this result.

ESN’s polymer coating wraps urea prills in plastic that lets water in slowly, and then slowly releases ammonia and ammonium back out into the soil. This keeps the concentration of ammonia and ammonium lower early in the season when seedlings are most sensitive.

The urease inhibitor in Agrotain slows the hydrolysis of urea into ammonia and ammonium, reducing concentrations early in the season. Agrotain, the company, says Agrotain allows for safe seed placement of nitrogen at rates up to 50% higher than provincial recommendations for seed-placed nitrogen.

A study by Saskatchewan Soil Conservation Association in 2000 compared seed-placed nitrogen treatments, and found that Agrotain and polymer-coated urea reduced seedling mortality and improved crop yield when compared to untreated urea. “Polymer coating tended to be more effective for improving emergence, seed yield and N uptake than the Agrotain coating and the effect was significant in some cases,” the study report says.

A current nine-site Alberta study, led by Alberta Agriculture in Lethbridge, is looking at canola stand establishment and yield for seed-placed ESN compared to seed-placed untreated urea. The researchers have completed only three of the four years and the study results are not yet published, but so far it appears that ESN provides a significant improvement in seed safety with higher rates of seed-placed nitrogen. (A recent but as yet unpublished study from AAFC in Saskatchewan came to the same conclusion.) Ross McKenzie, lead researcher in the Alberta study, says growers could safely apply up to 60 pounds of ESN per acre in the seed row. This is based on 10% seedbed utilization, which would be a one-inch knife on 10-inch centres — for example. A drill with one-inch knives on 12- or 14-inch centres will need lower ESN rates to maintain the same degree of seedling safety.

Seed into moisture. With moist soil conditions, water dilutes the concentration of nitrogen molecules around the seed and seedling. Water also disperses nitrogen molecules throughout the soil, reducing concentrations around the seed. In dry conditions, seed-placed nitrogen fertilizer tends to produce higher concentrations of ammonia and ammonium that can damage young seedlings. Seed placed nitrogen rates should be lowered when conditions are drier than normal.

Remember, thinning can occur with any rate of nitrogen placed with the seed, so seed-placed nitrogen, in general, does have an element of risk. The higher the rate, the higher the risk.

Published on February 7, 2011