KEYS TO HIGHER CORN FORAGE YIELDS

Joe Lauer

University of Wisconsin

This year there is much discussion generated by the high yields produced by Francis Childs at Manchester, IA. If we assume a typical harvest index for corn of 0.50 and back-calculate a grain production level of 442 bushels at 15.5% moisture and 56 pound per bushel test weight, the forage yield produced at this grain yield level is 20.9 tons of dry matter per acre. Many people are asking, “How does Francis Childs do it?” Unfortunately there isn’t an easy answer and is probably a combination of things that when integrated together and sprinkled with patience over a long period of time produces this unique and outstanding yield today.

The highest recorded yield ever measured in the UW Corn Forage evaluation program was 13.5 tons of dry matter per acre at Arlington in 1996. Many factors are important to producing forage yields. Key management practices that make corn forage production profitable include:

1. Hybrid selection

2. Proper timing of harvest

3. Remembering that a trade-off exists between yield and quality for management decisions

4. Early planting date

5. Slightly higher plant populations than what is normally used for grain production

6. Cutting height

7. Adequate soil fertility – predicted by soil sampling

8. Narrower row spacing increases yield

9. Pest control

10. Crop rotation

One of the early decisions that must be made in the production of corn forage is whether yield or quality is to be optimized. The best management practices are slightly different depending upon the objectives of the producer and his operation. For example, bmr corn hybrids differ dramatically for stover quality characteristics than hybrids with the leafy trait. The trade-off between these two hybrid types is between yield and quality. Likewise more milk per ton (better quality) is produced in a field where the population is lower or cutting height is higher than a more normal population or normal cutting heights. The trade-off is reduced yield. The purpose of the paper is to review the above key management practices for producing profitable corn forage.

Hybrid Selection

Numerous hybrids for producing corn forage are available from seed companies today. Since grain is nearly 95 percent digestible most recent breeding activities are concentrating on changing the stover portion of corn forage. Hybrids with special quality traits such as the bmr gene that increases stover digestibility or hybrids that contain the leafy trait with greater leaf numbers above the ear. More examples of these hybrids are being developed by plant breeders that maximize the amount of energy available in the stover portion of corn forage.

In addition to hybrids with special quality traits, numerous hybrids are available with special transgenic traits such as Bt, “Liberty Link” and “Roundup Ready” hybrids. These hybrids allow improved corn production under sometimes difficult field situations.

Regardless of the specialty traits available in corn forage hybrids, the basic objective remains to select a hybrid to maximize the amount of energy available as forage to the animal being fed. Either maximizing energy per ton or maximizing energy from an area of land can achieve maximizing forage energy. Both approaches may be valid depending upon the objectives of the producer. For example, someone buying all their forage from a neighbor would like to by forage with the highest amount of energy per ton because it reduces the costs associated with handling, hauling, storage and feeding the forage. Someone else may be most interested in maximizing energy from their farm land base and should be thinking about energy per acre as a hybrid selection criteria.

A final consideration in selecting corn hybrids for forage purposes is flexibility. A good “dual purpose” hybrid, one that produces good grain and forage yields, gives the producer flexibility at harvest when many forage decisions are actually made. A bmr or leafy hybrid planted in the spring should only be harvested for forage use in the fall because of reduced grain yield potential with these hybrids.

In the UW Corn Performance trials, milk per ton and milk per acre are used to rank corn hybrids (Figure 1). The graph is divided into quadrants Hybrids located in the upper two quadrants are above average for Milk per acre while hybrids located in the right two quadrants are above average for Milk per ton. The best hybrids to pick are located in the upper right quadrant where above average Milk per acre and Milk per ton are measured. The circle represents the amount of error associated with the trial; hybrids outside of the circle are statistically different from one another. Typically hybrids with the bmr trait have been located in the bottom right quadrant, above average for Milk per ton but below average for Milk per acre. Leafy hybrids are typically located in the upper left quadrant, above average for Milk per acre but below average for Milk per ton. Hybrids with transgenic traits are scattered throughout the graph, although as a group Bt hybrids have tended to be above average for both Milk per ton and Milk per acre (upper right quadrant).

Proper Timing of Harvest

Environment influences harvest date. The goal of harvesting is to time harvest so that the forage is at the proper moisture to enable fermentation and preservation of the forage. Too wet the forage will sour, too dry the forage will become moldy. The proper moisture depends upon the storage structure where ensiling will take place. For example, optimal ensiling in a concrete stave silo will take place at 65% moisture. In Manitowoc County, Wisconsin, optimal harvest date for a concrete stave silo has been as early as September 7 (1999) and as late as October 3 (1996).

Currently the only way to predict corn forage harvest date is to use kernel milkline as a guide to timing when a plant moisture sample should be measured for a field (Table 1). Once the moisture of a corn forage field is known use a drydown rate of 0.5% per day to predict when to either check moisture again or begin harvest.

Table 1. Kernel milk triggers for timing harvest for storage structures.
Silo structure	Ideal moisture content	Kernel milk stage "trigger"
	%	%
Horizontal bunker	70 to 65	80
Bag	70 to 60	80
Upright concrete stave	65 to 60	60
Upright oxygen limiting	60 to 50	40
"trigger": kernel milk stage to begin checking forage moisture Forage moisture decreases at an average rate of 0.5% per day during September

Trade-off Between Yield and Quality for Management Decisions

In general, management practices that optimize grain yield will optimize forage yield. The optimum range for a management practice is typically wider for corn forage than for grain production. However, there are some management practices that maximize yield of either grain or forage, but reduces forage quality. Often a trade-off exists between yield and quality. Management decisions that fall into this include planting date, plant density and cutting height.

Early Planting Date

Early planting date is important for maximizing corn grain and forage yields (Figure 3). But, corn of the same maturity grown for forage uses can be planted up to a week later without much change in risk and still be within 95% of the maximum yield. The risk of planting corn in April and May is the same regardless of planting date. In some years early planting will result in low yield, while late planting results in high yield. The opposite can also occur with equal frequency. Thus the recommendation for corn planting is to plant as many acres as possible around the optimum date which is May 1 in southern Wisconsin and May 10 in northern Wisconsin. On either side of these dates yield is reduced, however, by planting on the early side of these dates grain moisture is reduced. For forage use, grain moisture is not as critical, thus corn can be planted a week later when the field is intended for forage use. The general recommendation for planting corn in Wisconsin is to begin planting when field conditions warrant after April 20 in southern Wisconsin and after April 30 in northern Wisconsin.

Ideal Plant Population

The ideal plant population for corn grain yield in Wisconsin is 30,000 harvested plants per acre on most soils and 26,000 plants per acre on lighter soils. For forage yield the optimum plant populations are slightly higher by about 1,000 to 2,000 plants per acre. However, in a recent Wisconsin study (Cusicanqui and Lauer, 1999) greatest Milk per ton corn forage was at 18,000 plnats/A while greatest forage yield was at 42,000 plants/A. Maximum Milk per acre was achieved at 32,000 plants/A. This illustrates the yield and quality trade-off that is often seen when comparing best management practices for grain versus those for forage yield and quality.

Cutting Height

Adjusting cutting height influences yield and quality in corn forage production (Figure 4). This decision is influenced by forage needs of the producer. If forage supply is low, then lowering the cutter bar will result in greatest yields. If supply is adequate to excessive, then raising the cutter bar on the forage chopper will decrease yield, but increase Milk per ton and reduce overall Milk per acre only slightly. Raising the cutter bar will also leave more residue in the field helping to reduce soil erosion potential.

Soil Fertility

Corn grown for forage production requires more soil fertility than corn grown for grain. Greater nutrient removals are taken in forage production with stalk and leaf removal from the field. Fertility recommendations are continuously being fine-tuned for various soils, but yield responses are generally known and can be predicted. The decision to fertilize soil for corn forage production depends upon obtaining a soil test for the field.

Pest Control

Adequate pest control is important for obtaining high yield and uniform quality within a field. In general, economic threshold levels are lower for corn forage than for grain because greater opportunity and grower return is seen when the forage is fed to beef or dairy cattle.

Rotation

Crop rotation has been shown to increase grain yield about 10% over that of continuously grown crops. The yield increase due to the rotation response lasts about two years, and by year three yield levels are similar to continuously grown crops. Similar responses of would be expected for corn grown for forage although this has been little studied. Certainly pest control better in rotated crops compared to continuously grown crops.

Row Spacing

In numerous row spacing trials conducted in Wisconsin, narrower rows (15 or 20 inch row spacing) increases dry matter yield 6 to 9% with no corresponding changes to Milk per ton (Figure 5).

In conclusion, the upper yield potential so far measured for typically managed corn in Wisconsin is approximately 13.5 tons of dry matter per acre. There is quite a bit of difference between this measured yield and the calculated forage yield of 20.9 tons dry matter per acre produced by Francis Childs’ 442 bushels of grain per acre. Numerous factors influence the maximum yield for a farm and each factor contributes not only to yield but also influences quality. Integrating these all these factors into a farm management system is the challenge to the producer.

Literature Cited

Cusicanqui, Jorge A. and Joseph G. Lauer. 1999. Plant density and hybrid influence on corn forage yield and quality. Agronomy Journal 91:911-915.