UPCOMING EVENTS
September 8, 1999	WFC Forage Expo – Manitowoc, WI
January 25 & 26, 2000	WFC Symposium & Annual Meeting – Wisconsin Dells, WI
July 16 – 19, 2000	American Forage & Grassland Council Annual Meeting – Madison, WI

IN THIS ISSUE
Page 2	Adding Urea to Corn Silage
Pages 3-4	Here are some tips on corn silage harvest management
Page 5	Corn Silage Yield and Quality Trade-Offs When Changing Cutting Height
Pages 5-6	How Dry is Dry Matter?
Page 8	Forage Spokesperson Contest & Forage Foto Contest

We would like to thank Knowles Produce & Trading Co.

for Sponsoring This Issue of The Forager

Adding Urea to Corn Silage

by Patrick Hoffman, Extension Dairy Specialist, UW-Madison Dairy Science Department

Marshfield Agricultural Research Station

Urea is a manmade feed ingredient containing 46% nitrogen or 287% crude protein equivalents. Urea is a source of dietary nitrogen for use in ruminent feeds. Ingested urea is degraded to ammonia, and the ruminal bacteria incorporate the ammonia into bacterial protein. This type of protein is then digested and becomes available to the ruminant in the lower digestive tract as a source of protein. Urea can supply nitrogen to meet the needs of rumen bacteria in a broad range of diets. Urea is fed at low levels (0–6 oz per head per day) and requires proper mixing and feed delivery. Urea can be toxic if overfed or not properly mixed in the diet. Because corn silage is low in crude protein (8%), there has been continued interest in adding urea to corn silage to increase protein content.

Should I add urea to my corn silage? In most situations, the answer to this question is no. If desired, urea can be easily added to the diet by other methods. Urea can easily be incorporated into grain mixes or protein mixes. Total mixed ration equipment also allows incorporation of urea into diets prior to feeding. When urea is added to corn silage, urea is automatically forced into the diet whenever corn silage is fed. Adding urea to corn silage, therefore, decreases flexibility in feed management.

At what rate is urea added to corn silage? Feed grade urea may be added to corn silage at a rate of 8-10 lb per wet ton (35% DM). Adding 8-10 lb per wet ton of corn silage will increase the protein content of corn silage from 8% to 11-12%.

How do I apply urea to corn silage? In tower silos, urea should be applied at the blower, sing a granular applicator. Producers will need to weigh forage boxes and record unloading times. Dividing the weight (tons) of corn silage in the forage box by the time (minutes) to unload results in an unloading rate (tons/minute). Multiplying the unloading rate by the desired urea application rate (8-10 lb/ton) results in the granular application rate for urea (lb/minute). Adjust the applicator to achieve this rate. Urea can be spread over the top of forage loads, but this method often results in uneven distribution and is labor intensive. It is extremely difficult to add urea to bunker silos and is usually too labor intensive.

Can I use fertilizer grade urea? No. Feed grade urea is a high quality, micro-prilled product that is compatible with other ingredients and mixing processes. Fertilizer grade urea has a larger prill size and may contain contaminants. Use only feed grade urea when mixing and feeding to animals.

What about adding a commercial urea-based silage additive to corn silage? Commercial nutrient-based silage additives may contain urea, slow release NPN (non-protein nitrogen) and true protein sources. Other nutrients such as minerals and vitamins are also commonly added to these products. Companies offering these products usually supply applicators, making application easier. The cost per unit of degradable protein is usually higher with these products when compared to feed grade urea. If desired, similar products can be added to TMR mixers prior to feeding which increases feed management flexibility.

At what stage of maturity should we harvest?

Years ago, it was recommended that corn silage should be harvested at the black-layer stage of maturity. In recent years, research and field experience has shown that this practice usually results in silage that is too dry to be well utilized by dairy cows. Positioning of the kernel milkline is another method of maturity staging that has been used as an indicator of when to harvest whole-plant corn for silage. The best lactation performance by dairy cows has been shown to occur at roughly the one-half milkline stage of maturity. But, recent research and field experience has shown considerable variation in the relationship between whole-plant moisture content and positioning of the

kernel milkline. This variation is related to differences in hybrids and their dry-down characteristics, and differences in growing conditions. Blindly harvesting whole-plant corn for silage at one-half milkline will sometimes result in silage without the right moisture content for good preservation and utilization. It now appears that the best use of kernel milkline positioning is as an indicator of when to start monitoring whole-plant moisture content. Once most of the kernels are dented and the milkline is visible, it is time to chop some whole plants for measurement of moisture content. Whole-plant moisture content should be your trigger for when to harvest corn silage. Special attention must be paid to making an accurate determination of moisture content. Over several years of monitoring the corn dry-down in their counties, our extension agents report a tendency for the microwave oven and Koster-tester methods to over-estimate the dry matter content of whole-plant corn. Considerable care and time must be taken to drive off all of the water and reach a stable endpoint weight before calculating sample dry matter content when using these on-farm methods. Another option is to have the sample dry matter content determined by a commercial testing lab. Analyzing the sample

just for dry matter content is not usually very expensive, and using the near infrared (NIR) method of analysis allows for a rapid turn around time.

At what moisture should we harvest?

The best lactation performance by dairy cows has been shown to occur at 65% to 70% whole-plant moisture. This range in whole-plant moisture content works well for achieving good preservation in horizontal silos. Harvesting whole-plant corn with more than 70% moisture increases seepage losses, increases acidity which can lower dry matter intake and reduces dry matter yield per acre. Whole-plant corn harvested for storage in upright silos may need to be chopped a bit drier than 65% moisture to minimize seepage. But, research has consistently shown reduced fiber and starch digestion along with reduced lactation performance for corn silage harvested at 60% moisture or less. Corn

silage harvested at 60% moisture or less will need to be either chopped fine or processed to minimize losses in starch digestion and lactation performance.

At what length should we chop?

The general recommendation for corn silage harvested with a conventional harvester (without a crop processor) is 3/8” theoretical length of cut (TLC). This recommendation may vary between ¼” to ½” TLC depending upon whole-plant and kernel moisture content, hybrid and forage harvester. To get good breakage of cobs and kernels with a conventional harvester, it is often necessary to chop finer than we would like from an effective fiber standpoint. Unbroken kernels tend to pass through the cow undigested and large pieces of cobs or whole cobs are prone to sorting in the feed bunk. This typically means that only 5% to 10% of the silage should be in the coarse particle fraction or retained on the top screen of the Penn State-Nasco shaker box. Evaluate percent coarse particles and degree of kernel and cob processing to determine the proper TLC setting for your harvester. Corn silage that is harvested past ½ milkline stage of maturity or with less than 65% whole-plant moisture may need to be chopped at ¼” TLC. It may be possible to chop corn silage that is harvested at an immature or wet stage and hybrids that exhibit soft kernel texture at ½” TLC. It appears that brown mid-rib (low lignin) corn silage should not be chopped at less than ½” TLC to maintain effective fiber. Based on our research, the recommended chop length for corn silage harvested with a harvester fitted with a crop processor is ¾” TLC. This normally means that 20% to 30% of the processed silage will be in the coarse particle fraction or retained on the top screen of the Penn State-Nasco shaker box. Processed corn silage that is harvested at the black-layer stage of maturity or with about 60% whole-plant moisture may need to be chopped at ½” TLC. We have no data with processed silage at lengths greater than ¾” TLC, but there have been field reports of excessive equipment wear at TLC of an inch or more.

How can we tell if our crop processing is being done properly?

Based on our research, the recommended roll clearance ranges from 1/16 to 1/8 inch (1 to 3 millimeters). Roll clearance is determined using feeler gauges. If you do not have feeler gauges, lay the blade of your pocketknife flat between the rolls and adjust the clearance until the rolls tighten against the blade. Harvest some whole plants, shake out the chopped material, and visually inspect each screen for the degree of kernel and cob processing. We would like to see all of the kernels broken. Pieces of cob, if discernible, should be no larger than the end of your little finger. If kernel and cob breakage is not complete, then tighten the rolls until kernel damage is complete or consider reducing your TLC. This may be necessary for processed corn silage that is harvested at the black-layer stage of maturity or with about 60% whole-plant moisture. With processed corn silage harvested at an immature or wet stage that tends to mush, you can set roll clearance to 1/8 inch (3 millimeters). Make sure that you follow all recommended safety practices whenever making any machine adjustments.

At what height should we chop?

Silage dry matter yield is reduced about 15% as the row-crop head is raised from 6 to 18 inches. But, estimated milk per ton increases because the more fibrous and less digestible portion of the whole-plant material is left in the field. This results in estimated milk per acre being reduced only about 3%. Prioritize your needs for maximum yield versus high quality to determine the best cutting height for your situation. This may vary from year to year depending upon the inventory and quality of your hay crop silage. From an erosion control standpoint, more beneficial crop residue can be left in the field without sacrificing much milk per acre. Also, because nitrates tend to concentrate in the bottom portion of the stalk raising the crop-head head helps minimize nitrate concerns. This may or may not be an issue depending on your crop growing conditions.

Summary

Harvesting whole-plant corn at the right moisture content and particle size is crucial to making high-quality corn silage that is well utilized by dairy cows. Whole-plant moisture content rather than kernel milkline positioning should be your trigger for when to harvest corn silage. Monitor particle size and kernel and cob breakage to ensure that the forage harvester-crop processor is doing the job. Remember to use additives properly, pack well, and cover securely to minimize storage losses.

Increasing the cutting height of corn silage decreases silage yield. But, what happens to silage quality as the cutter bar is raised? Corn plant parts contain different amounts of fiber and digestible energy. Raising the cutter bar on a silage chopper will leave more of the lower corn stalk in the field, which is typically higher in fiber and lower for digestible energy.

Most of the energy and value of corn silage is in kernels on the ear. Other plant parts differ for fiber and digestible energy. Figure 1 shows the yield and quality trade-off that exists for yield, milk per ton and milk per acre as the cutter bar is raised. Milk per ton is a quality estimate for corn silage that is based on equations predicting intake and animal requirements from data derived from National Research Council (NRC) tables on nutrient requirements of dairy cattle (1978, 1989). Milk per ton approximates a balanced ration meeting animal energy, protein and fiber needs based on forage quality (in vitro digestibility basis). Milk per ton is based on a standard cow weight and level of milk production (1350 lb body weight and 90 lb/d at 3.8% fat). Both milk per acre and milk per ton was calculated using a model derived from the spreadsheet entitled, "MILK95," (Undersander et al., 1993). Milk per acre is simply milk per ton multiplied by yield. Corn silage yield decreased 15% as the cutter bar was raised from 6 to 18 inches above the soil surface. Milk per ton was lowest when the cutter bar height was six inches and greatest at a cutter bar height of 18 inches.

Thus, even though silage yield decreased 15% by raising the cutter bar 12 inches, silage quality (milk per ton) increased. Milk per acre decreased 3-4%. Additionally, more beneficial crop residue would be left in the field without sacrificing much milk per acre.

Literature Cited

Undersander, D.J., W.T. Howard, and R.D. Shaver. 1993. Milk per acre spreadsheet for combining yield and quality into a single term. J. Prod. Agric. 6:231-235.

National Research Council, National Academy of Sciences. 1978. Nutrient requirements of dairy cattle. 5^th rev. ed. Washington, DC.

National Research Council, National Academy of Sciences. 1989. Nutrient requirements of dairy cattle. 6^th rev. ed. Washington, DC.

It would seem that getting an accurate estimate of whole plant dry matter would be somewhat straight forward. However, experiences over the past two years have prompted some questions. Here is why:

Exhibit 1:

In 1997 the Miner Institute reports that Koster tester readings for corn silage and alfalfa haylage were 3 to 5 percentage units higher in dry matter than the same samples run through forced air or convection ovens. Drying time reported was one hour for the Koster and 36 hours for the ovens.

Exhibit 2:

Whole plant corn silage samples from local "burndown days" analyzed with NIR have consistently been 5 to 7 percentage units lower in dry matter (higher in moisture) than the same samples analyzed using only a microwave oven. This was true in 1997 and 1998.

Exhibit 3:

Same whole plant corn silage samples obtained at local "burndown days" and analyzed with a Koster Tester have been about 3 percentage units higher in dry matter (lower in moisture) than when sent to a lab and analyzed with NIR.

Is the 4 to 7 points difference in dry matter determination between testing methods something to be concerned about? Certainly for corn silage it’s too large of a swing when we consider that harvest recommendations are based on whole plant moisture for optimum yield and quality. A difference in moisture of this magnitude translates into a 1 to 2 week difference in optimum harvest date.

Can we account for why these differences occur? Certainly to some degree we can. Most forage labs dry samples to a point using a microwave or conventional oven and then use NIR to read the remaining moisture. The NIR machine reads water chemical bonds very well and easily accounts for ALL of the moisture in a sample. With other methods, it is nearly impossible to account for all of the water. Even long duration oven drying (as most research samples are done and most management recommendations are based upon) leave a few points of moisture in the sample.

As for the "on farm" Koster and microwave methods, it’s clear that the accuracy of the reading will be largely determined by the amount of time and care taken in drying down and weighing the samples. This is especially true for corn silage where whole kernels and cob pieces can be difficult to dry completely without burning the leaf tissue. In a study by Dr. Gary Oetzel, UW School of Veterinary Medicine, corn silage samples run in a microwave were close to those of oven dried samples (within 1 percentage unit) only after about 20 sequential periods of heating (low heat setting). He noted that it was extremely hard to get this level of accuracy without burning the samples and that the entire process took 30 to 40 minutes per sample.

Until this whole moisture dilemma sorts out producers who use "on-farm" moisture determination with a Koster or microwave would be well-served to submit sub-samples for lab analysis in an effort to gauge how self-determined moisture readings compare to those of an NIR machine.

FORAGE SPOKESPERSON CONTEST & FORAGE FOTO CONTEST

Enclosed is an announcement of the 2000 Forage Spokesperson Contest. This activity has become an important part of our Annual Meeting, and we would like it to be a success once again this year. If you are a forage producer, please consider participating. If you are unable to this year but know someone who might be interested, please pass this information on to them. If you work in the commercial or education sector, please consider passing this information on to some of the top producers with whom you work.

As most of our contestants have used 2 x 2 color slides in their presentations, it is important to identify interested individuals soon so good photos can be taken.

The flip side of the enclosure describes a new activity at our Annual Meeting, a Forage Foto Contest. For this activity, we are asking for forage related photographs from WFC members. These photos will be displayed during our Annual Meeting and attendees will vote on the best ones. We think this will add a new and fun dimension to our meeting. Please consider submitting some pictures.

Check us out on the Internet at:

http://www.uwex.edu/ces/forage/wfc.htm

Volume 23, Number 3, August 1999

September 8, 1999

WFC Forage Expo – Manitowoc, WI

January 25 & 26, 2000

WFC Symposium & Annual Meeting – Wisconsin Dells, WI

July 16 – 19, 2000

American Forage & Grassland Council Annual Meeting –

Madison, WI