Corn Hybrids’ Response to Fertilizer
Ken Janovicek, University of Guelph and Greg Stewart, OMAFRA Corn Specialist

Previously reported research conducted by the University of Guelph indicated that including 50 lb/ac of potassium (K) in a planter-band can lead to substantial increases in corn yields. This has prompted many corn producers to conduct side by side comparisons to evaluate whether similar increases can be obtained on their farms. When interpreting yield results from side by side fertilizer comparisons, you should be aware that there is evidence that all hybrids do not necessarily respond similarly to applied fertilizer. This article highlights some University of Guelph and U.S. research which indicates that hybrids can differ significantly in their response to applied fertilizer.

Hybrid Response to K Application
A 3-year study was conducted by the University of Guelph from 1997 to 1999 to evaluate the yield response of five corn hybrids to spring-applied potash in a no-till system. These trials were conducted on a well-drained silt loam located near Paris, Brant County. The fields had a Fig1low exchangeable K rating, which averaged between 50 and 60 ppm.

Three methods of potash application were evaluated. Potash in the deep-band treatment was placed in a band 6” deep and corn was planted directly on top of the deep-placed band. In the broadcast + planter-band treatment, half of the potash was broadcast-applied, and the rest was applied in a 2” by 2” band at planting. The amount of potash applied was 110 lb-K2O/ac.

The 3-year average yields presented in Table 1 suggest that hybrids differed in their yield response to spring-applied potash. The size of the yield response for two of the five hybrids (Pioneer 3893 and Novartis Max 357) was relatively small, often not exceeding 5 bu/ac. For the three more responsive hybrids, potash usually increased yields by 15-20 bu/ac. The differences in yield response to K fertilizer were mostly due to the ability of the non-responsive hybrids (Pioneer 3893, Novartis Max 357) to produce greater yields when K fertility levels were low.

There is also evidence that hybrids differed in their response to method of potash application. For example, the Novartis hybrids tended to produce the highest yields when potash was deep-banded, while the Dekalb hybrid tended to produce higher yields when at least part of the potash was broadcast-applied.

The differences in corn hybrid response to K fertilization suggest that K fertility management for corn based on the results of a single hybrid may not necessarily represent the best K fertility management option for another hybrid. Unfortunately, it is not possible to predict how a particular hybrid will respond to a specific K fertility management option. Decisions for the best K fertility option for no-till corn should be based on the results of many hybrids in order to select the management option which has the greatest likelihood for maximizing profitability among a wide range of hybrids.

Hybrid Response to Starter Fertilizer
Corn research work conducted in Kansas in the mid-1990s also examined the response of a series of 5 hybrids to starter fertilizer over a three-year period. This study was conducted on soils testing high for phosphorous, and where fertilizer would not generally be recommended. Corn was planted early within a no-till system and starter fertilizer (30 lb/ac N + 30 lb/ac P2O5) was placed in a band through the corn planter (2” deep and 2” beside the corn row). This starter treatment was compared to a ‘no starter’ system. For all 5 hybrids, starter fertilizer caused a significant increase in early growth. In three of the hybrids, grain yields were significantly enhanced over the ‘no starter’ treatment by an average of 13 bu/ac. However, two of the hybrids showed no yield gain.

Growers using side by side comparisons to fine-tune their fertility programs are advised to be aware of the potential that not all hybrids respond as expected to applied fertilizer. The intent of this article is not to discourage on-farm evaluation of corn response to fertilizer application, but rather to suggest that caution be used when interpreting yield responses that differ from those that are expected. It may be that in some instances where unexpected results are obtained, it is the result of a non-responsive hybrid. More reliable information is obtained when multiple sites and multiple hybrids are used to evaluate fertilizer options.

Research reported from the University of Guelph was conducted under the direction of Dr. Tony Vyn. Funding for this research was provided by the Potash and Phosphate Institute of Canada, Ontario Corn Producers’ Association and Grow Ontario.

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