Fertilizer for soybeans – does it pay?

NEW RESEARCH GIVES DIFFERENT FERTILIZER OPTIONS MIXED REVIEWS

traditionally, soybeans do not received much, if any, fertilizer. Soybeans are efficient in providing their own nitrogen through biological nitrogen fixation and typically, there has been enough residual phosphorus and potassium left behind by previous crops to provide essential nutrients.

Good prices for corn and soybeans have many Ontario growers moving to shorter rotations between soybean crops and high fertilizer prices have resulted in lower application rates in corn and wheat. With more soybean acres and less fertilizer applications, many fields have seen nutrient deficiencies. In many fields soil test values have now slipped to the point where precious soybean yield is being lost.  In those situations it may be time to feed the beans.

measuring fertilizer impact
For the past two years OMAFRA has been conducting a few preliminary trials across high fertility and low fertility sites to see where yield could be gained. In 2009 there were two field scale trials with three replications, and three trials in 2010. Treatments are listed below in Table 1.

TABLE 1: Summary of fertility trial treatments conducted in ontario (2009-2010)

Treatment Description
Untreated No fertilizer added
3 gallons 6-24-6 Liquid fertilizer applied in row with the seed
40 P + 70 K Inc. Fertilizer blend broadcast and incorporated to apply 40 lbs P2O5 and 70 lbs K2O
25 P with seed 50 lbs of MAP granular fertilizer applied in row with the seed at 25 lbs P2O5
40 P + 70 K Inc. + 3 gallons 6-24-6 Dry fertilizer broadcast and incorporated as well as liquid fertilizer applied in row with the seed
40 P + 70 K 2”x2” Band Fertilizer applied in a band 2 inches to the side and 2 inches below the seed

Treatments were 20 feet wide, 1000 feet in length and replicated three times within each trial.  Trials were planted using a Kearney 15 inch vacuum planter and yields were measured at harvest time using a calibrated weigh wagon. Soil test values are listed in Table 2. The Stratford location was a high fertility site, while the rest were considered low fertility sites.

cost effective results
At all the low fertility locations, each treatment showed some improvement over the untreated check.  At the high soil testing site only the 2”X 2” band showed a yield benefit.  Table 3 shows the average yield results, as well as a breakdown of cost versus expected return from the least profitable to the most profitable.

While the treatments that were the most economical were not necessarily the treatments with the highest yields, they were the ones with the lowest input costs.

In the case of soybeans, we know that it is difficult to increase yields by more than a few bushels per acre for any particular input. In the case of the most intensive and costly input, we’d be hoping for a yield advantage of over seven bushels per acre at $10 per bushel beans to break even!  A response of seven bushels per acre is very difficult to achieve unless the soil test is very low and we did not get that large a response at any of our sites. The cheapest inputs were effective because they give a reasonable yield advantage, but the costs were more in line with the yield benefit.

The yield advantage at the high fertility site was not significant, except for the
2” X 2” band.  This has lead us to wonder if an economic advantage to banding dry fertilizer at lower rates could be achieved even in fields with reasonably good soil tests.  One thing is clear, soybeans respond to banded fertilizer more than broadcast fertilizer.

TABLE 2: Soil test values for fertility trials in ontario (2009-2010)

Location Soil Test Values (P) Soil Test Values (K) Tillage
Dufferin 2009 25 103 Spring Cultivate
Monkton 2009 7 118 Spring Cultivate
Lucan 2010 8 147 Spring Cultivate
Stratford 2010 47 200 No-Till
Bornholm 2010 19 89 No-Till

TABLE 3: Average economic benefit based on soybean yields and fertilizer input costs in ontario (2009-2010)

Treatment Average Yield (bu/ac) Yield Advantage (bu/ac) Cost ($/ac) Net Response ($/ac @ $10/bu Soys
Untreated 48.7
40 P + 70 K 40 P + 70 K Inc. + 3 gallons 6-24-6 52.3 3.6 $67.00 -$31.00
40 P + 70 K Inc. 51.0 2.3 $51.50 -$28.50
40 P + 70 K 2”X2” Band 52.3 3.6 $51.50 -$15.50
3 gallons 6-24-6 50.8 2.1 $15.50 $5.50
25 P with seed 51.8 3.1 $12.50 $18.50

practice caution
Adding 50 pounds of MAP with the seed was the most profitable treatment in these trials. However, there is concern that any dry fertilizer with the seed can cause burn.  Potassium is too risky to put with the seed but even MAP is questionable.  In 2010 various Ontario growers applied 50 pounds of MAP with the seed and had mixed results; in some cases they actually experienced a small yield loss. It’s unclear why there was such a discrepancy in the test results.  There were no obvious plant stand losses or burn issues.  Because there were such variations in the results when using 50 pounds of MAP with the seed, we would caution producers from adopting this practice wholeheartedly. More experimentation is necessary. 

Overall, adding fertilizer was an effective way to raise soybean yields in fields with lower soil tests. However, only two treatments showed a large enough yield gain, compared to the cost of the input, to make them economical.  In higher testing soil sites we could find no additional yield except to banding.  We will expand these trials in 2011 to assess more options with the aim to find more economically viable fertilizer options. •

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