February 10, 2015 Field Crops 28.33 - 123

How Much Yield Loss Occurs with Corn Hybrids Sold as "Organic"?

Joe Lauer, Corn Agronomist

Farmers growing corn for the organic market often get a premium and rightly so. Organic farmers are required to go through a certification process that requires a fee and extra effort and time for paperwork. They have more expenses due to increased pest control, especially weeds. Organic farmers have also expressed some concern about the genetic yield potential of the commercial hybrids used in organic corn production.

Since 2004, the UW Corn Hybrid Evaluation program has been testing corn hybrids sold for the organic market. A total of 55 organic hybrid trials have been conducted at 10 locations in Wisconsin (see http://corn.agronomy.wisc.edu/HT/). The average yield of the commercial organic hybrids in these trials was 174 bu/A. The average range between the top- and bottom-ranked hybrids was 73 bu/A. These trials are planted early and managed aggressively for pests. All pests are controlled to the best of our ability. Differences among hybrids are likely due to genetic differences, rather than management interaction differences.

In 53 of the trials, a high-performing conventional hybrid check (nontransgenic) was included. Two treatments were applied to the check conventional hybrid. In one treatment the check hybrid was treated exactly the same as the other organic commercial hybrids in the trial. In the other treatment the check hybrid was hand weeded up to 3x during the growing season. No difference was found between the control and hand weeded conventional check hybrids, so data from these treatments were pooled together. Organic hybrids yielded 7% (14 bu/A) less than the conventional hybrids in these trials (Table 1).

Table 1. Yield of commercial organic and conventional hybrids in the UW Corn Hybrid Evaluation program. Data are derived from 53 organic trials conducted since 2004.

Hybrid Grain yield (bu/A)
Commercial organic 174
Conventional 188
LSD(0.05) 3

The organic trials are almost always planted adjacent to the public trials. An estimate of relative performance can be made between these adjacent trials by calculating an average for each trial and treating each environment as a replication. In this analysis, the conventional check hybrid included in the commercial organic trial was dropped so that the mean from the organic trials only represent commercial organic hybrids. Hybrids in the public trials include both conventional and transgenic hybrids.

A total of 48 environments had both organic and public trials planted adjacent to each other. The hybrids in the organic trials yielded 12% (24 bu/A) less than hybrids in the public trials (Table 2).

Table 2. Analysis of average yield for organic and public hybrid trials in the UW Corn Hybrid Evaluation program. Data are derived from 48 environments where both trials were grown.

Trial Grain yield (bu/A)
Organic 175
Public 199
LSD(0.05) 9

In both analyses, organic hybrids yielded less than modern hybrids. In the organic trials, the conventional check hybrid was consistently the top performing hybrid in the trial. However, the commercial organic hybrids were not far behind (7-12% on average). Again, in these trials, all interactions are minimized to the best of our ability, so the trials represent potential genetic differences. As plant stresses increase in organic systems due to management constraints for certification and pest pressure versus the relative ease of controlling some of those same pests in conventional systems, the relative differences between modern organic and conventional systems would also likely increase.

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