Growing Conditions Affect Silage Quality
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By Bill Mahanna
Fantastic weather and soil conditions afforded much of the Midwest and eastern Corn Belt the luxury of early planting. However, since early May, conditions have turned wet across much of the country.
A recent discussion with a consulting nutritionist about how weather patterns affect corn silage quality prompted me to delve into this subject.
Environment is King
The tremendous influence growing environments have on silage quality is depicted in Figure 1. Figure 1 shows the relative silage yields, starch content and 24-hour neutral detergent fiber digestibility (NDFD) of the same hybrid grown in 14 locations in Michigan in 2009.
This clearly demonstrates why it is not valid for nutritionists to attribute hybrid genetics as the primary cause of nutritional differences when comparing hybrids grown on different farms. This is also why seed companies and university plots only compare hybrids grown in the same location (side by side).
One can draw an analogy to proving bulls. Prior to more sophisticated genomic indexing, the artificial insemination industry relied heavily on statistical procedures to factor out the genetics of the dam and the environment (housing, hygiene, nutrition, etc.) to sort out production differences among bull daughters born into herds across the country. This is important because there is no growing environment limitation to where a bull’s daughter can be born.
This is not possible with corn genetics because of growing environment suitability limitations. Therefore, seed companies have to compare hybrids grown next to each other across multiple plots (so they all are in the same environment). It is also important to compare hybrids within the same maturity, seed treatments, technology segment and planting populations (e.g., low populations will result in higher NDFD).
The influence of growing conditions (especially moisture) is a major source of the nutritional variability seen within hybrids across years and locations. A February 2009 Ohio Farmer article cited Dr. Fred Below, a professor of plant physiology from the University of Illinois, attributing 19% of grain yield performance to hybrid genetics, with the remaining influence being the result of weather (27%), nitrogen (26%), the previous crop (10%), plant population (8%), tillage (6%) and growth regulators (4%).
Dry, Moderate Heat
Van Soest (1996) and Van Soest and Hall (1998) suggested that cool, dry years are best for corn silage quality and that slight moisture stress might stimulate seed (grain) production. Cool temperatures, especially at night, may inhibit secondary cell wall development.
These studies suggest that accumulated growing degree days after silking may be most important in affecting a corn silage’s nutritive value because of the nutritional value of enhanced grain yield.
The specific timing of environmental stress during the development of the corn plant also appears to be important. Research by Mertens (2002) indicated that the weather before and after silking may interact to affect the final corn silage nutritive value.
Mertens analyzed unfermented wholeplant corn samples from various genetics grown in multiple locations, with each location geo-referenced to allow for weather station data to be included in the analysis.
Growing conditions prior to silking affected corn plant height (and yield) and fiber digestibility, while growing conditions after silking appeared to exert a stronger effect on corn grain yield and total dry matter digestibility (Mertens, 2002).
It has been proposed that with irrigated crops, silage growers might stress the crop for water during pre-tasseling to increase NDFD, applying the conserved water more liberally during kernel starch filling periods of plant growth.
However, excessive moisture stress during vegetative growth can reduce whole-plant yields by reducing stalk internode length and can possibly reduce grain yield during the sixth leaf and tasseling growth stages by reducing the number of kernels around the ear (ear girth) and the number of kernels per row (ear length), respectively.
Much more research is warranted as to when to irrigate the corn plant to manipulate both silage yield and nutritional value.
Figure 2 shows how five hybrids differed in 24-hour NDFD when grouped by the average growing conditions in Michigan during stalk development. Moisture accumulation and heat exerted an effect on the NDFD of all hybrids, but moisture had a greater influence. Some hybrids (i.e., hybrid C) appear to be more susceptible to environmental influences.
Figure 3 shows more 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.
It was interesting to note that, as expected, the highest NDFD in both seasons was a brown mid-rib (BMR) hybrid, but nearly half of the conventional hybrids grown in the drought year were higher in NDFD than the BMR hybrid grown in the wet year
Interaction
Corn breeders are very interested in the interaction between genetics and the environment. If the genetics-by-environment interaction is significant (in a statistical sense), it means hybrids grown in different environments could rank differently for any particular trait.
Contrast this to an environmental influence on genetics, meaning they will rank similarly across environment, but the relative magnitude of difference will be smaller or bigger depending upon the particular environment. It could also mean that the absolute values will change with no change in the hybrid differences among environments.
While the genetics-by-environment interaction is a very real effect experienced by hybrids — explaining why seed companies do so much testing to determine the area of adaptation of hybrids — there is no indication that nutritional characteristics are any more susceptible to environmental interactions than either grain or whole-plant yield (Coors, 1996).
Research by corn breeders suggests that to be 95% confident in selecting the best hybrid for silage yield or nutritional traits, approximately 20 direct, side-byside comparisons (in the same plots) are required, preferably across multiple years to account for unique yearly environmental effects.
Data from a single plot are almost meaningless due to variability caused by factors such as soil compaction, previous crop history, fertility/manure history, soil type, water availability, tillage and insect damage.
For an average plot with 150 bu.-per-acre yield potential, a hybrid with a two-ton-per-acre (30% dry matter) advantage will have only a 60% chance of being the superior silage-yielding hybrid. The odds of selecting the superior silage-yielding hybrid increase to 95% with a two-ton yield advantage demonstrated across 30 individual silage plots.
The Bottom Line
When it comes to selecting corn silage genetics, university and seed company plots have proven that there are minimal genetic differences (3-4% points) among non-BMR hybrids for NDFD.
The large variation in NDFD nutritionists observe from farm to farm and from season to season is more the result of environmental factors such as growing conditions and harvest timing.
This is why nutritionists working in the Midwest and East, with fewer irrigated acres and more weather variability, struggle with quantifying and managing corn silage digestibility.
In general, dry conditions during stalk development enhance fiber digestibility, and wet conditions, while improving whole-plant yield (taller plants), tend to reduce fiber digestibility.
Most seed companies encourage the nutritionist to be part of the silage hybrid selection process. However, to be an informed participant, a clear understanding of the role of genetics versus growing environment is an important prerequisite.
References
Bolinger, D. 2010. Personal communication.
Coors, J.G. 1996. Findings of the Wisconsin corn silage symposium. In: Proceedings of the Cornell Nutrition Conference for Feed Manufacturers. Rochester, N.Y.
Mertens, D.R. 2002. Fiber: Measuring, modeling and feeding. In: Proceedings of the Cornell Nutrition Conference for Feed Manufacturers. East Syracuse, N.Y.
Van Soest, P.J. 1996. Environment and forage quality. In: Proceedings of the Cornell Nutrition Conference for Feed Manufacturers. Rochester, N.Y.
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Originally published in Feedstuffs, June 14, 2010. Reproduced with permission.