Nonirrigated corn production is a high-risk enterprise in the Mid-South.

According to the Mississippi State Budget Generator, specified costs for growing glyphosate-tolerant corn in the Delta are about $310 per acre.

With an estimated land cost of at least $80 per acre, it can easily cost more than $400 per acre to produce a crop that is subject to yield reductions caused by Delta drought in nonirrigated systems. With $3 per bushel corn, yields would have to exceed about 135 bushels per acre to cover costs.

Obviously, the thin profit margin from nonirrigated corn production leaves little room for production errors or uncontrolled weather stresses. Producers who do not irrigate can do little to alleviate the effects of drought, but they can use available tools and resources to make production decisions that lead to the greatest probability of success.

One decision that can make a big difference in corn yields is hybrid selection. Within that process lies the decision of what maturity class a hybrid should be chosen from to provide the greatest chance for success from nonirrigated corn production.

Data from nonirrigated corn variety trials conducted in Tennessee, Mississippi, and Louisiana were summarized to assess the effect of relative maturity (used here to replace days-to-maturity) on corn yield. Yields from studies conducted in 2005 and 2006 at the locations shown in the accompanying table were used. Missouri and Arkansas do not conduct nonirrigated hybrid trials in the Delta.

For purposes of comparison, relative maturity is divided into the three levels shown in the table. These designations correspond to what is commonly referred to as early- (110-113 days), medium- (114-116 days), and full-season (117-120 days) categories.

Within each maturity class and test location of each year, yields of the top five hybrids were averaged to obtain the yields shown in the table. The number of hybrids from each of the three maturity classes that yielded in the top 15 at each test location in each year is also shown.

At all locations shown in the table, the trend was for average yield of the best medium-season hybrids to be equal to or greater than average yield of the best full-season hybrids. In all but one trial, the five best medium-season hybrids showed a trend toward yields that were equal to or greater than yields of the five best short-season hybrids.

The Ames Plantation (Tenn.) trial in 2006 showed an apparent advantage for early-season hybrids. This trend is probably the result of drought during the 100-day period from planting through early August when rain totaled about one-half the long-term average. All yields in this test were unprofitable.

It is noteworthy that many of the average yields in the table are below those needed to make a profit. This is especially significant because the averages shown here are for the best hybrids in each trial, and production practices in these trials are assumed to be optimal for a nonirrigated production system.

This assessment of 2005 and 2006 variety trial results using available hybrids (no experimentals) indicates that corn producers throughout the lower Mississippi River Valley should be planting medium-season hybrids to ensure the greatest profit opportunity from nonirrigated production systems.