The attached PDF is a summary of the results from this trial.

As has been our experience with conducting many on-farm trials over the past 5 years around Indiana, the statistical quality of the data from this trial was excellent. One measure of that "quality" is the value of the coefficient of variation (aka C.V.), which was only 1.8 for this trial (the lower the value, the better the data quality).

The summary focuses on the predicted "best" N rate based on the yield response curve and not on the yields of the individual N rate treatments. This is the statistically appropriate way to analyze trials that include rates of an input because it allows us to identify an optimum N rate that may not have actually been used in the trial.

So, even though the best numerical yield in the trial was 200 bpa at 230 lbs N / ac, the analysis of the yield response curve indicates that the yield response in a practical sense leveled out at a total N rate of about 179 lbs N / ac. Furthermore, the N rate that resulted in the greatest $$ return was 170 lbs N / ac (using $6 corn and $855 anhydrous). 

These results compare favorably with those of a similar trial with "rebuilder" the previous year where we saw maximum yield occurring at 203 lbs N and maximum $$ at 185 lbs N. You might say... "but there's about 15 lbs difference one year to another!". Yes, but this is the fact of life for N rate variability one year to another. Optimum N rate for a given field can easily vary plus/minus 20-30 lbs over years due to differences in rainfall timing/amount and the consequences for loss of soil nitrate-N. The value of the trial for "rebuilder" is that the results identify the range of N rates that will maximize yield and dollar returns for him in the future.

Jim Camberato and I use results from on-farm trials like these to develop and re-fine our N rate guidelines for Indiana. Since 2006, we have been involved with more than 165 field-scale trials around Indiana and more than 60% of them have been collaborative on-farm trials. Every year we publish an updated set of guidelines at:

http://www.kingcorn.org/news/timeless/NitrogenMgmt.pdf

Folks like "rebuilder" represent a tremendous resource that greatly enables us to develop such guidelines quicker and more reliably than we could in the "old days" of small-plot research.  Anyone out there who would like to collaborate with us by putting out N rate or seeding rate trials in 2012, take a look at our protocols available online at:

http://www.agry.purdue.edu/ext/ofr/protocols.html

THANKS, REBUILDER!

Harv_Summary.pdf (12KB - 119 downloads)