Three Years of Nitrogen Plots - What Can Nitrogen Rate Strips Do For You?

Results from the Quinte and St Clair Regional Soil and Crop Improvement Association Nitrogen Projects

The St. Clair District Soil and Crop Improvement Association project was initiated to develop a method that would allow a farmer to assess the profitability of current rates of N application on a field. Nitrogen rate strips were used and nitrogen soil tests were taken. The Quadratic plateau statistical model was used to calculate the maximum economic rate of nitrogen (MERN). The Quinte project focussed on the pre-side-dress nitrogen test (PSNT) and used nitrogen rate strips to determine the MERN.

The following shows typical response curves from a couple of the plots.

The table below summarizes the results from both projects for the 2002 season.

Some of the St. Clair sites were not included in the table as the dry weather made it difficult to determine the MERNs.

The results from the 3 years of the two projects show some interesting information. In the St. Clair project, many cooperators were able to identify opportunities to reduce the rate of nitrogen applied to the field. There were opportunities for a 10 to 40 lbs per acre reduction with many showing the opportunity to reduce rates by about 30 lbs. N /acre. The St. Clair project the also used the Quadratic plateau model to determine MERNs. It fit the response curve better (in many cases) than the quadratic statistical model and tended to give a lower N recommendation.

Both projects showed that nitrogen rate strips in a field can be a useful tool for assessing how accurately a producer's traditional nitrogen application rate meets the actual N requirements of the crop. Nitrogen rate strips are relatively easy to set up in a field. There are several ways the strips can be setup. It can be as simple as leaving a strip of corn without any nitrogen, other than the starter, in the field. This can be useful on fields that receive a lot of manure or have legumes in the rotation. If you can't pick out the strip in the field through the season then the manure or legumes are supplying the corn's nitrogen requirements.

Multiple rate strips are useful for fine-tuning a nitrogen rate. Four or five rates (the typical rate for the field, one above and two or three below typical) can provide enough information to determine the maximum economic rate of nitrogen. Place one set of rate strips in a representative area of the field. Better still put a couple of sets in the field to see if different parts of the field have different MERNs. A simplified version of this would include a zero (no sidedress and no more than 30lbs. N in the starter), a two-thirds rate and a full rate.

At the end of the season look at the yield gain versus the amount of nitrogen applied. If the additional nitrogen applied isn't paid for by the gain in yield then it didn't pay to apply it.

Concerned about the cost of yield loss from the lower rate strips? In most cases once you factor in the nitrogen not applied, it doesn't cost that much. If you are able to reduce your rates, the savings nitrogen will more than pay for it.