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Use caution with seed-placed N in barley

Research shows benefits to side-banding and higher seeding.

Photos above show the effects of seeding rate (200 and 400 seeds per square metre) when N (90 kg/ha) is placed with the seed. Note the reduced wild oat density at the higher seeding rate. Increasing the seeding rate has partially overcome the negative effects of seed-placed N on barley density thus reducing the wild oat pressure.

In direct seeding and zero tillage systems, nitrogen (N) fertilizer can be placed with the seed in one operation; however, the risk of seedling damage from seed-placed N can be a problem. Researchers initiated a study to compare the effects of seed-placed and side-banded N (urea) applied at different rates on barley density, maturity and yield, and wild oat seed production or fecundity. They also wanted to determine if increasing the seeding rate of barley could reduce the risk of placing N with the seed, improve barley productivity and enable the crop to better compete with wild oats.

This three-year research study was conducted at three western Canadian locations: Beaverlodge and Lacombe, Alta., and Brandon, Man., using a zero-tillage system. Nitrogen was applied as urea at five rates (0, 30, 60, 90 and 120 kg/ha N), either directly with the seed or as a side-band, at three barley seeding rates (200, 300 and 400 seeds per square metre).

“The research results showed that side-banding is much less risky than seed-placed nitrogen in terms of reducing yield and plant numbers, and reducing the impact of wild oat weed issues,” explains Dr. John O’Donovan, research scientist with Agriculture and Agri-Food Canada (AAFC) in Lacombe. “The research also showed that increasing the seeding rate does reduce the risk of seed-placed N, but it doesn’t reduce the risk to as low as side-banding.” 

In all cases, seeding rate had virtually no effect on yield.

Based on the study, researchers recommend the maximum N that can safely be placed with the seed is 30 kg/ha. However, other factors such as soil type, organic matter content and seedbed utilization (SBU) can influence the recommended rate. “All of the research sites had very high organic matter content,” says O’Donovan. “For fields with lower organic matter content, the risk of injury from seed-placed N goes even higher.” The impacts on hulless barley varieties can be even greater from seed-placed N since plant numbers tend to be lower than with hulled barley varieties.

Photos C and D show the effects of seed-placed compared to side banded N (90 kg/ha) at 300 seeds per square metre. Note less wild oat pressure where N is banded. Again, seedling toxicity due to seed-placed N has resulted in reduced barley density and more wild oats compared to banded N. Photos courtesy of Agriculture and Agri-Food Canada.

Seed-placed N also reduced overall plant numbers, which increased the days to maturity. “When the number of plants that emerge are reduced, then the days to maturity increases,” says O’Donovan. “In some cases, the days to maturity can increase quite a bit, which in northern areas like Beaverlodge can be very important.” However, side-banding N did not affect plant densities and had minimal effects on days to maturity. With seed-placed N, the number of days to maturity at the highest N rate increased by 12 days, compared to only two additional days when side-banded.

From this and related studies, researchers are recommending a seeding rate of 300 seeds per square metre for a general purpose hulled type barley that is seeded relatively shallow in reasonably good growing and soil moisture conditions. “Because of the difficulty in trying to estimate a seeding rate in bushels per acre, growers should use seeds per square metre,” says O’Donovan. “All barley varieties have different-sized seeds and seed weights, and even within a variety the size and weights can vary between seed lots.” Therefore, growers are advised to calibrate their seeders based on the weight of the seed and target a barley seeding rate of 300 seeds per square metre.” In most cases this should provide a plant density of 200 to 250 plants per square metre.

In terms of weed management, past research has shown that placing the fertilizer closer to the crop improves crop competitiveness. Banding fertilizer as compared to broadcasting for example, benefits crop growth rather than weeds. “From these studies you could speculate that the closer the N is placed to the seed, the more benefit to the crop,” explains O’Donovan. “However, that is only true to a point and our study shows if you place the N too close to the seed, it backfires. Seed-placed N can injure the seed, reducing the number of barley plants and allowing the wild oats to
take over.”

“The research showed a sharp increase in wild oat densities as N rates increased in seed-placed applications,” says O’Donovan. “There was a six-fold increase in wild oat seed production at the highest compared to the lowest N seed-placed rate, due to reduced barley plant densities.” However, wild oat seed production was not affected by any of the N rates when applied as a side-band.

“Some of our other recent research shows that relatively high barley densities, 200 to 250 plants square metre, are required to optimize herbicide performance and overall weed management,” explains O’Donovan. “Therefore the beneficial effects of high barley densities on weed management would likely be compromised by placing too much N with the seed.”

In conclusion, the research shows that banding a certain distance from the seed is the least risky operation. “In a zero tillage system, seeding at a relatively high seeding rate to achieve around 300 seeds per square metre and seeding relatively shallow, an inch to an inch and a half, will optimize the number of barley plants that emerge, reduce days to maturity and optimize yield and weed management,” says O’Donovan.