Welcome to the Spring 2000 Forager

Volume 25, Number 3, September 2001

elcome to the Fall 2001 Forager. It has been a summer of extremes with long periods of wet, cool weather followed by very dry conditions. First crop alfalfa was good, but rainy weather made it very hard to put up. This was followed by dry conditions, which made for a short second cutting. The result has been yields of both alfalfa and corn silage (due to generally late planting) will be below average. Much of first cutting alfalfa was also less than desired quality due to the rain occurring during harvest.

In This Issue:

The WFC Forage Expo was held this summer in conjunction with the Farm Progress Tri State Hay Show and the Agronomy Field Day at Arlington. It was a successful day with over 1,000 attendees. Thanks to all who helped with this event.

Mark January 21 and 22, 2001 on your calendar as the dates of the next Wisconsin Forage Council Symposium in Appleton. We will be holding a joint meeting with the Custom Forage Harvesters and the Professional Nutrient Applicators. We feel that the three groups have many issues in common. The annual symposium will have almost continuous concurrent sessions so that all attendees will find many topics of interests.

Upcoming Events

Introduction

Accurately determining corn whole plant moisture is important when harvesting for corn silage. Harvesting corn for silage too early (high moisture content) or too late (low moisture content) can affect forage yield, quality and silage fermentation.

Whole plant moisture content typically changes by 0.5 units per day and in dry conditions can change by up to 1.0 unit per day. In the past, growers have used benchmark stages of kernel maturity (black-layer development or kernel milkline position) to estimate when to harvest corn for silage. Because of the variability associated with these methods, growers have been encouraged to periodically check actual whole plant moisture of plants from various fields on their farm. The success of this strategy is dependent on obtaining an accurate moisture content measurement in a timely manner.

This article discusses the accuracy of several on-farm moisture measurement techniques based on a study conducted by the UW Soil & Forage Analysis Lab at Marshfield.

What factors affect moisture content and dry-down rates of corn?

Several factors affect moisture content of corn plants and the rate at which they dry down in the field.

· Geographic location – Corn silage is grown in virtually all areas of the state. The length of the growing season and average temperature varies significantly, particularly from north to south. This will affect the rate of dry down of similar maturity varieties, necessitating local monitoring of moisture levels.

· Stage of maturity – As the corn plant matures, whole plant moisture content decreases. A killing frost will also speed up the drying process.

· Hybrid selection – Both relative maturity and hybrid choice will significantly affect moisture content of corn. Hybrids differ in dry-down rates, which means that each hybrid should be tested separately.

· Crop management - Factors such as soil fertility, weed control, and pest management will also influence whole plant moisture content and dry down rates. Healthy, vigorous plants will tend to stay photosynthetically active for a longer time and be wetter than less healthy plants.

· Landscape position and soil type - Changes in soil types or significant changes in landscape throughout a field can influence how a plant grows and dries down. Soil moisture levels may be adequate in one part of a field and excessively dry in another part of the same field leading to differences in plant maturity and moisture content.

What factors affect measurement of whole plant moisture content?

When measuring corn whole plant moisture the following factors can affect the accuracy of the test.

· Fineness of chop – To accurately measure corn whole plant moisture, samples need to be chopped. Our studies indicate that the finer this material is chopped, the more accurately moisture content can be measured. The goal of chopping is to achieve a more homogenous material that can be subsampled more accurately.

· Method of determination – On-farm options for moisture determination include microwaves ovens, koster moisture testers, and traditional kitchen ovens. Kitchen ovens are seldom used because of inconvenience, odor, risk of burning at a high temperature, and slower completion time at low temperatures.

· Operator technique – For both the microwave method and Koster dryer system, operator technique is critical in getting an accurate estimate of corn silage moisture content. Properly drying a sample using a microwave is especially difficult for an inexperienced person.

What moisture measurement methods were compared?

· Microwave – samples (80-125 grams) were dried on high for two minutes, then on medium-low in three-minute increments until sample weight stabilized.

· Koster – samples (100 grams) were dried for thirty minutes.

· Laboratory oven –sample (80-125 grams) dried in lab oven set at 55^oC overnight.

· NIR – sample tested using Near Infrared instrumentation with a corn silage moisture calibration.

What did the study show?

Residual Moisture

In a lab setting, approximately 2% residual moisture content was found in samples after using the microwave or Koster drying methods. Another study conducted on-farm using several different operators, showed that residual moisture content ranged from 3% to greater than 6% (Ballweg and Rankin, 1998; Figure 1). Error levels of this magnitude are unacceptable for growers needing to make a corn silage harvest decision.

All methods require an additional laboratory step to determine residual moisture content of a sample for complete accuracy. This can be accomplished using either a NIRS-based moisture determination or a standard high temperature (135^oC) lab oven method.

Fineness of Chop

Sample grind and fineness of chop is important in determining sample moisture content. This is particularly important when using the microwave drying method. The variability among samples was higher for coarsely chopped samples when compared to those ground to a smaller particle size. In addition, the moisture remaining after drying was greater for coarsely chopped samples versus using a fine grind (Figure 2).

Drying Method

The drying method affected the variability of moisture determination. Specifically, the microwave method was more variable than the Koster drying method was, while the laboratory oven method was least variable (Figure 2).

Figure 1. Effect of drying method and number of operators on residual moisture content of corn silage samples.

Figure 2. Effect of drying method and grind type on residual moisture content of corn silage samples.

Summary

Accurately determining the moisture content of corn silage on the farm is a difficult process. One of the limitations to on-farm testing is the availability of an accurate scale (+/- 1 gram). In addition, operators need to maintain a consistent protocol when drying samples so that the residual moisture content is consistently in a range of 2-5%. Finally they need to have a laboratory determine the average residual moisture content of dried samples.

If the on-farm test would consistently result in 2-3% residual moisture when calibrated with a laboratory result, the operator could then make reasonable management decisions about when to harvest corn for silage.

A better option is to submit samples to a laboratory for dry matter analysis. Using a laboratory greatly reduces sample-to-sample variability and results in a more accurate number.

References

Ballweg, M. and M. Rankin. 1998. Verification of On Farm Moisture Determination.

As we approach fall, the likelihood of good drying weather decreases. This becomes particularly critical when making medium square bales (600 to 1000 lb) because hay must be 16% moisture or less to avoid spoilage in storage unless the bale is treated with preservative or wrapped in plastic.

Wrapping bales in plastic costs about the same as using a preservative and has the advantage of working regardless of moisture content of the forage. We have preserved square bales wrapped in plastic from 18 to 63% moisture. Unlike using a preservative, no adjustment in rate must be made for moisture content of the silage. We believe the preservation of wrapped bales involves fermentation when forage moisture is above 55% and involves development and maintenance of an anaerobic condition at lower moisture contents.

We have been researching wrapping medium square bales with plastic at the UW Lancaster Research Station for the past several years. Though I will present only one year’s data here, our findings over the years have been very consistent and the conclusions are based on several years’ data. The first question we asked was how much plastic was needed to preserve the wrapped bales. We did several studies with 1 ml and 1.5 ml plastic with varying wrapping numbers. This first basic finding is that number of wrappings was not as significant as the thickness of the plastic. The plastic is not completely impermeable to oxygen and a certain thickness is necessary to keep oxygen out so that spoilage does not occur. The data is summarized in figures 1 and 2 as millimeter thickness of plastic. It becomes apparent from the data that wrapping with at least 6 millimeters (and 8 is preferred) of plastic is necessary to adequately preserve the hay. When hay was wrapped with less thickness, the temperature of the hay remained elevated for a longer time. It is apparent that with adequate plastic thickness (over 6 mm) that oxygen becomes limiting almost immediately and the temperate rapidly begins to fall and reaches ambient temperature in about 10 to 11 days. The rapid stop of respiration, both of plants and molds, is reflected in the lesser increase in ADF (fig 2) from baling in July to sampling in December. When adequately wrapped, bales increased about 2% in ADF due to loss of cell solubles during the respiratory processes. If the plastic was too thin, ADF increased 7 to 8%. This increase above 2% represents a loss of cell solubles that are high in energy and readily digestible in the rumen.

We did these studies with bales both in the 25 to 35% and in the 55 to 60% moistures ranges and found the same results. Therefore our recommendation is that, if preserving hay or silage with plastic wrap, the bales be wrapped with at least 8 mm thickness of plastic. This can be accomplished with 8 wraps of a 1 mm plastic or fewer wraps of a thicker plastic. It is important to avoid tears in the plastic; either during wrapping or after the bales are being stored.

Since most bale wrapping is a custom operation, the question often becomes: how soon after baling should the bales be wrapped in plastic for adequate preservation. Studies that we have done suggest that bales should be wrapped no longer than 24 hours after bailing. As can be seen in figure 3, the bales wrapped immediately remained the coolest and the longer one waited to wrap bales, the hotter they got. Further, bales wrapped within 24 hours tended to cool off faster. This temperature data is further supported by the acid detergent fiber of the forages, shown in figure 4. The 63% moisture silages (or the hay at 36% moisture, data not shown) showed a slight increase in ADF from wrapping to sampling after in storage for three months regardless of when wrapped. However, more mold was observed in bales wrapped after 48 hours.

Thus, our recommendation is to wrap large square bales within 24 hours after baling whether preserving wet hay (20 to 35% moisture) or making silage (55to 65% moisture). It is sometimes advantageous to wait until after due has settled on bales to increase toughness and decrease likelihood of brittle stems breaking the plastic.

Corn being grown for silage is quite variable across the state this year due to the poor planting conditions this spring, which resulted in many late plantings, and then generally dry weather following that greatly reduced growth in spots. While corn silage can make an excellent forage, it must be harvested properly to produce the desired forage quality.

It is critical to harvest corn at the appropriate moisture for good silage. For corn in near normal growing conditions, you can go to the corn silage drydown web site, operated by the UW Cooperative Extension Service, to find the moisture content of what corn is generally in your region. The website is:

http://cf.uwex.edu/ces/ag/silagedrydown/

However, due to different planting dates and growing conditions the information on this site should be used only to alert you to when you should begin checking your own silage for moisture content to determine when it is ready to harvest.

Much of the late-planted corn may not be ready to harvest before frost. Forage quality can still be good. As the data (from Wiersma et al., 1993) on page 7 shows, there is only slight change in forage quality whole plant corn silage from soft dough to early dent and almost no further change in forage quality to no milkline. The quality of the corn silage stover changes almost none after the beginning of kernel fill except as leaf loss occurs. The major issues in forage quality of corn silage with advancing maturity are the availability of nutrients (which declines as the kernel hardens) and whether or not the whole plant is at the appropriate moisture content for ensiling.

The good news is that this means corn silage that was planted late and did not fully form ears can be reasonably high quality silage, if it can be harvested in a good moisture content range for ensiling. One consideration for farmers this year could be that silage can be harvested at a higher moisture content (up to 70%) if put into bunkers or silo tubes. Vertical silos require dryer silage to avoid seepage.

Another issue facing many farmers is the unevenness of many fields. Some portions of many fields were severely stunted by the drought that occurred in July and August. To the extent possible when harvesting a cornfield of differing maturities, the different portions should be harvested separately. This may not be possible in many fields where a portion of many rows are two differing maturities. One should harvest so that the entire mixed silo is in an appropriate moisture range. Harvesters should take care to mix the two different maturities while chopping and while filling the silo. Some seepage may occur from the wet spots, but if it does not leave the silo, nothing is lost. Of great concern are dry spots that may heat and either produce some mycotoxins, or through spontaneous combustion, cause a silo fire.

In many cases, farmers will have to wait until after a killing frost for the corn silage to dry down sufficiently to harvest in an appropriate moisture range for ensiling. The killing frost for corn silage can be anything below 32^oF. Whether or not a killing frost occurs depends on the length of time the coldest temperature occurred, the humidity and wind speed. Corn silage can be killed by a frost at 32^o F if it lasts for several hours, humidity is low and wind is moderate. More often though, all conditions do not exist together and temperatures must fall below 32^o F to actually kill the corn.

Frost killed corn can be harvested anytime after a frost. Frost does not cause buildup of nitrates or any other toxic compounds that would cause animal health problems. Often producers will need to wait a few days after frost to allow continued drydown so that the corn is in the correct moisture range for ensiling. One should not wait any longer than necessary because corn leaves, even when brown, are relatively high in forage quality and will be lost by wind as time goes on after a frost. Frost killed corn will have similar quality to corn harvested without frost at the same stage of maturity when the frost-killed corn is harvested with minimal leaf loss.

The last issue to consider for corn silage this year is the potential for nitrate poisoning. This is caused by an accumulation of nitrate in the plant (stems primarily) that is not metabolized into protein. Nitrate accumulation generally occurs when a field is fertilized for normal yield and then yield is greatly reduced, e.g. by drought. Many farmers forget to take the nitrogen credits for the manure applied or legumes plowed down and have nitrate accumulations in drought-stressed corn even though no nitrogen fertilizer was applied.

Any silage that is suspected of having high nitrate should be sampled and analyzed to determine nitrate concentrations. Analysis is much cheaper than losing cattle. Most high nitrate silage can be fed with caution once the nitrate level is determined, either to appropriate animals or with adequate dilution in a balanced ration. Generally, small, young animals are most sensitive to nitrate and animals on high-energy diets are least sensitive. For a thorough discussion of nitrate in forage and nitrate toxicity see the article on the my website at:

http://www.uwex.edu/ces/forage/pubs/nitrate.htm.

Volume 25, Number 3, September 2001

WRAPPING SQUARE BALES TO PRESERVE THEM

By Dan Undersander, Forage Agronomist, UW-Madison

NEW MILK2000 RELEASED