by Bill Mahanna and Ev Thomas
Mahanna is with Pioneer, a DuPont Business, and is an adjunct professor at Iowa State University; Thomas is retired from the William H. Miner Agricultural Research Institute and president of Oak Point Agronomics Ltd.

yield/nutritional value chart
Surplus moisture during vegetative growth appears to have the greatest effect on reducing NDFD (neutral detergent fiber digestibility). Meanwhile, growing conditions right after pollination primarily affect corn silage starch content.

There are good reasons why dairymen in the Midwest and on the East Coast spend more time figuring out how to feed new-crop corn si­­­­­­lage than many of their counterparts in the West - and those reasons are soil variability and Mother Nature.

The tremendous influence of growing environments on corn silage's yield and nutritional quality is illustrated in Figure 1.

yield/nutritional value chart

It shows silage yield, starch content, and 24-hour NDFD (neutral detergent fiber digestibility) of the same hybrid grown in 14 locations in Michigan during 2009.

This demonstrates that, while hy­­­­­­brid genetics set the foundation for the crop potential, growing environment has the final say. Corn grain research from the University of Illinois attributes 19 percent of the grain yield performance to hybrid genetics, with the remaining influence a result of weather (27 percent), nitrogen (26 percent), previous crop (10 percent), plant population (8 percent), tillage (6 percent), and growth regulators (4 percent).

Dry, moderate heat best
Temperature and moisture are the primary drivers of the yield and nutritional variability seen within hybrids across years and locations. Moderate temperatures and relatively dry growing conditions appear best for overall corn silage quality in terms of fiber digestibility and starch content.

The timing of environmental stress during the development of the corn plant is also important. Growing conditions during corn vegetative growth (prior to pollination) affect corn internode length (thus plant height and yield) and fiber digestibility. Excessive moisture and heat exert a negative impact on NDFD. However, surplus moisture during vegetative growth appears to have the greatest effect on reducing NDFD.

Wet versus dry environment

Figure 2 shows data from Michigan State University silage plots harvested in a relatively wet growing season (2006) compared to the same hybrids harvested from the same plot in a relatively dry growing season (2007). Hybrids averaged 6.5 points higher in 24-hour NDFD in the drought year. Cool temperatures (especially at night) appear to inhibit secondary cell wall development and can somewhat offset the negative impact of excess moisture on NDFD.

Growing conditions after pollination primarily affect silage starch content. The accumulation of heat units after silking is important because of the nutritional value gained by increasing starch deposition. Some have proposed that moderate stress of irrigated corn prior to tasseling may boost NDFD and allow for shifting water supplies to the kernel starch filling period. More research is needed regarding when to irrigate corn to manipulate silage yield and nutritional value. We do know too little moisture during vegetative growth can reduce tonnage. This is done by reducing stalk internode length and possibly reducing starch by causing stress during sixth leaf stage (when ear girth is determined) and tasseling (when ear length is determined).

The more the better
The relationship between genetics and environment (GxE) is why seed companies spend so much time and money evaluating silage genetics in lots of different growing environments. If the interaction between GxE (in a statistical sense) is significant, it means hybrids grown in different environments could rank differently for any particular trait.Contrast this to the environmental influence on genetics, meaning they would rank similar across environments, but the relative magnitude of difference will be smaller or bigger, depending upon the particular environment. It could also mean the absolute values will change with no change in the hybrid differences between environments.

This is why nutritionists and dairymen need to be cautious about hybrid testimonials about how cows are milking on a specific hybrid. Research by corn breeders suggest that, to be 95 percent confident in selecting the best hybrid for silage yield or nutritional traits, a minimum of 20 direct, side-by-side comparisons (in the same plot) are required, preferably across multiple years to account for unique yearly environmental effects. Data from a single plot is almost meaningless due to the variability caused by factors such as soil compaction, previous crop history, fertility/manure history, soil type, water availability, tillage, and insect damage. It is also important to compare hybrids within the same maturity, seed treatments, technology segment, and planting populations.

To put one plot in perspective, on average, soils with a 150 bushel/acre yield potential, a hybrid with a proven 2-ton per acre (30 percent DM) advantage has only a 60 percent chance of being that plot's top-yielding silage hybrid. The odds of selecting the superior-yielding silage hybrid goes up to 95 percent with a 2-ton yield advantage demonstrated across 30 different silage plots. Put another way, would you trust a sire proof with one daughter record? No, that is why A.I. studs strive to get many daughters spread across the most herds possible.

Dairyman and their crop/nutrition advisors should consult reliable silage hybrid data and agree on the attributes they desire in the "ideal" corn silage crop, but don't be surprised when Mother Nature decides to influence the final results.

This article appeared on page 565 of Hoard's Dairyman's September 10, 2011 issue