N Rates Compared by Corn Producers in 2007

Greg Stewart, OMAFRA Corn Specialist
Ken Janovicek, University of Guelph

Last year 35 producers from across Ontario tested N rates on their corn fields in order to
evaluate new OMAFRA recommendations compared to more traditional N rates.

Background
The most recent development in OCPA’s ongoing efforts to boost profitability and improve environmental sustainability has involved the funding of a project to allow producers to test the N Calculator. The plan for this project was pretty simple. Use the N Calculator to determine the recommended nitrogen rate for a producer’s specific corn field. Contrast that against what the producer has typically used as an N rate to grow corn. Set up plots and/or sections within the fields to grow corn using both of the aforementioned rates. Soil texture, soil fertility levels (including soil N tests), GPS site mapping of the field, yields and harvest moistures for most fields were obtained over the 2007 growing season. The results allowed us to compare the impact of the various N rates on the yield, the nitrogen costs and the net impact of following the Calculator on each field.

2007 Results
The results from last year highlighted the potential risks and benefits of fine tuning nitrogen rates. In 2006, 12 producers in the Southwest estimated their expected yield to be 148 bu/ac; however, the actual yield from these fields using the grower N rate was 190 bu/ac! The 2007 yields, in the Southwest sites were more in line with the expected yields producers entered into the Calculator.

Table 1. indicates that on average, if producers applied 50 lbs more N than the Calculator recommended yields increased only slightly on average. Perhaps a better way of assessing the results is based on the number of producers that came ahead economically by following the Calculator. In the Southwest, 9 of the 13 participating producers did so. Variability on heavier soils is still an issue that we continue to sort out. The Calculator does recommend more N on heavier soils (29 lbs/acre more on clay than on silt loams, for example) but on occasion the results still have the Calculator scratching, especially if yields are higher than expected.

In the Central sites (roughly from London to Guelph) the Calculator recommendations did very well (see Table 2.). 10 of the 12 sites showed improved net returns by applying the Calculator rate. Interestingly, the silt loam/loam sites where the Calculator gives the lowest recommendation (compared to other soil types) seems to be very reliable. Questions have arisen over the red clover credit. The Calculator gives a 73 lb credit for red clover that is plowed. This is based on data where the stands of red clover would be considered good, that is uniform and at least 12” (30 cm) at season’s end. Based on results from the last two years this credit is too large for spotty stands or stands with poor fall growth.

In Eastern Sites (Ottawa Valley) the N Calculator, with an average recommendation of 98 lbs N per acre, faired better than the producer’s rate only half the time (see Table 3.). We continue to gather data to verify the original conclusion taken from research done in this area. This is, that the region needs significantly less fertilizer N, all other things being equal, than the rest of the province. The 2007 results show quite high yields with relatively modest N applications, but does not support the Calculator as being more reliable than producer estimates. One
complicating factor is that over both years, the actual yields have been considerably higher than expected. Additional field testing will aim to improve recommendations in the east.

Where Now?
This specific project is concluded. However, if you would like further information regarding N rates for corn, or to see what the Calculator recommends for your fields, please go to www.gocorn.net.

One criticism occasionally made of general nitrogen recommendations is that a uniform N rate is recommended over fields which will have variable requirements. Are there significant advantages to using variable rate N recommendations across a field? The research information has been quite unclear as to the possibilities, and it is difficult to actually verify that the variable rate was a net improvement over uniform rates.

It is possible to obtain variable rate information from the N Calculator in regards to changes in either soil texture or yield. If you attempt to do this, care should be taken to ensure that N rate adjustments above or below the field average rate are done only in sections of fields with a known stable history of producing yields that are significantly below or above the field average. For example, if a sandy knoll almost always
produces yields that average 75 bu/ac below the rest of the field which is a loam, then recommendations would suggest that N rates on the sandy knoll may be reduced by 40 lb-N/ac when compared to the rest of the field.

Future development and refinement of recommendations for corn will focus on how reliably variable N rate recommendations can be predicted using the current Calculator recommendations but apply them in a sitespecific pattern.

Acknowledgements
Appreciation is expressed to the following sponsors of this project: the Ontario Corn Producers’ Association, the Agricultural Adaptation Council (CORD IV), AGRICORP, and the Ontario Ministry of Agriculture, Food and Rural Affairs. Appreciation is expressed to all of the farm co-operators.