MACHINERY DESIGNS AND ADJUSTMENTS FOR MINIMIZED FIELD LOSSES

Ronald T. Schuler*

Producing quality forage with a minimum field loss requires the proper selection, adjustment, and operation of the forage harvesting equipment. Farm machinery manufacturers continue to make design improvements to increase productivity and minimize losses. Frequently when selecting machinery, a new design may improve productivity but in some cases the producer may have to sacrifice forages losses.

The key machine in the forage harvesting system with respect to field losses is the mower-conditioner. Its performance influences losses directly through shatter losses during its operation and indirectly through its affect on the drying rate after mowing and conditioning. The longer the crop lays in the field until harvesting, the greater the risk of precipitation on the windrow which reduces the forage quality.

Lack of proper machine maintenance and adjustment causes the biggest difference in forage harvest losses from farm to farm. A good operator who maintains losses at a minimum must be familiar with proper maintenance and adjustments to match crop conditions. Some of these harvesting machines have many adjustments that influence the magnitude of the field losses.

MACHINE DESIGNS

One of the biggest changes in forage harvest machine design has occurred in the mower-conditioners where there has been an increase in rotary, also called disk, mowers and, to a lesser degree, impeller conditioners. With respect to balers, the increase in mid-size and large square balers requires drier forage at harvest which can lead to higher losses because a greater risk to weather, the potential for the rain.

Mower-Conditioners

The sickle cutterbar mower has been utilized for over a century but is limited to a forward speed of 7 to 8 miles per hours when well maintained. In the mid 1970’s the rotary mower became more available to the U. S. producers. This European design was used primarily on grasses but has advantages such as greater forward speeds and better performance in lodged crops.

One concern about the rotary mower was the persistence of the alfalfa stand after using this mower. Mueller and others reported no differences in yield and plant stand between mower-conditioners with sickle and rotary cutterbars for the alfalfa cuttings following these machines. Therefore they concluded that rotary mower did not reduce the alfalfa stand when compared to the sickle cutterbar.

Since the mid 1950’s the standard conditioning system was rolls to bend or crimp the alfalfa stems to increase the drying rate. More recently, the impeller, also referred to as finger or tine, conditioning system has created interest. Like the rotary cutterbar, this European design was used primarily on grasses. Instead of crimping the crop, the impeller blades rub or abrade the waxy surface on the stems. The impeller system provides a greater throughput capacity while maintaining effective conditioning. Another advantage was that it allows the large airflow created by the rotary cutterbar to pass through the rear of the machine. This is important in light crops because much of the air discharging from the front of the machine with conditioning rolls causes strips of uncut crop.

Several studies evaluating the losses associated with these cutterbars and conditioning systems have been conducted. In Michigan study, Rotz and others reported the sickle cutterbar had significantly less respiration losses than the rotary cutterbar, Table 1. There was no difference in shatter losses between the two cutterbar designs and two conditioning systems. The conditioning systems, roll and impeller, were very similar with respect to respiration and shatter losses, Table 1.

Table 1. Dry matter losses for three mower-conditioner designs (Michigan study).

Dry Matter Loss

Cutterbar Conditioner Respiration (%) Shatter (%)

Sickle Roll 0.3 3.0

Rotary Roll 4.8 2.9

Rotary Impeller 4.2 2.9

In Wisconsin, Koegel and others compared three machines from mower-conditioning through baling, Table 2. The losses were one percent higher for the rotary mower-conditioner with rolls compared to the sickle mower-conditioner with rolls after raking, but the differences were not considered significant. The impeller conditioner had significantly higher losses after raking when compared to the roll conditioner. At the baler pickup for a small square baler, there were no significant differences between the windrows produced by the three machines. No significant differences were present at the bale chamber of the small rectangular baler although rotary mower machines had more a one-half percent greater loss. For the total field harvesting losses, the rotary machine with the impeller conditioner had losses nearly 3.5 percent larger than the sickle machine with the roll conditioner. The rotary machine with the roll conditioner was in the middle and considered not significantly different from the other two machines.

Table 2. Dry matter losses for three mower-conditioner designs (Wisconsin study).

Dry matter Loss (%)

Cutterbar Conditioner M-C + Rake Pickup Baler Total

Sickle Roll 3.95 2.10 1.48 7.50

Rotary Roll 4.70 2.05 2.22 8.98

Rotary Impeller 6.43 2.38 2.13 10.95

Several types of conditioning rolls are available from the manufacturers and have some influence on losses. Differences are based on the roll material. At Wisconsin, Shinners and others compared four rolls systems: intermeshing molded rubber, intermeshing tire cord, one rubber and one steel roll, and two intermeshing steel rolls. The respective machinery manufacturer representatives completed the adjustments of the rolls with respect to roll spacing and pressure. The system with steel rolls tended to have highest losses and was significantly more than the molded rubber rolls, Table 3. There was no difference in the drying rates.

Table 3. Conditioning roll losses for four types of roll systems.

Roll Type Machine Loss(%)

Molded rubber 5.17

Tire cord 5.38

Rubber and steel 5.72

Steel 5.87

Rakes, Mergers and Tedders

Side delivery rakes have been have been available for nearly century, but wheel rakes and rotary rakes have joined the market place. The wheel rakes primary advantage over the side delivery rakes is the gentle manner which it moves the crop resulting low shatter losses. But because it requires contact with the soil, it tends to mix rocks into the windrow.

The rotary rake is another design brought to the U. S. from Europe where it was very successful on grasses. In Michigan, Rotz and others evaluated rotary rakes and found their shatter losses were nearly twice the side delivery rake. Some these higher losses can be attributed to the high acceleration of the forage when the tines of the rake contact the crop.

As for mergers and inverters, very little information is available with respect losses. The best method to evaluate these machines for potential losses to consider the degree of acceleration of the crop during operation. If the machine gently handles the crop, low acceleration, the shatter losses will be lower. This was true in the rakes where the wheel rakes have the lowest losses.

Harvesting Equipment

Balers and forage harvesters are both included in this discussion of harvesting equipment. All these machines have a pickup in common, which is a point where much of the field loss can occur. For balers, chamber losses can be significant. The two major design factors that influence the loss at the pickup are the pickup speed relative to the ground speed and the speed which the crop is elevated by the pickup into the machine. The forward speed must be reasonably matched to pickup speed. This is especially true when harvesting alfalfa for dry bales. If the forward speed is slow relative to the pickup speed, the pickup fingers will comb the windrow allowing leaves to fall to the ground. If the forward speed is too fast for the pickup, a portion of the windrow may remain on the ground.

Regarding the speed of elevating the crop by the pickup, the apron pickup was designed for windrowed grain. With this apron design, also referred to as the Melroe pickup, the windrow is elevated more slowly than the conventional pickup. Some mergers utilize this design.

On balers, field losses will occur in the chamber area and does vary with design. In a Wisconsin study, Koegel and others compared a small rectangular baler to two round baler designs. One round baler was a variable chamber design where radial pressure on the bale was maintained throughout bale formation. The second round baler had a fixed chamber design where pressure was applied only after the forage fills the chamber. The small square baler had the lowest chamber losses, Table 4. The variable chamber losses were about one percent higher than the rectangular baler but were not significantly different. The fixed chamber had nearly eleven percent chamber losses that were much greater than the other balers.

Table 4. Bale chamber dry matter losses for three types of balers.

Type Loss (%)

Round, variable chamber 3.83

Round, fixed chamber 10.89

Rectangular, small square 2.79

In a Wisconsin study involving mid-size balers, Shinners and others found the pickup losses were much higher for the round baler than the small and mid-size rectangular balers, Table 5. Also they found the mid-size balers had a lower chamber loss than the small rectangular and large round balers, Table 5. Evaluating the forage from 14 to 32 percent moisture, they also found that the bale chamber losses of the mid-size baler was less affected by moisture than the other two balers. The closed bale chamber design on the mid-size baler attributed to the lower losses.

Table 5. Bale chamber dry matter losses for round and square balers.

Type Pickup Loss(%)

Mid-size rectangular 0.7 0.7

Small rectangular 0.4 1.6

Large round 2.6 1.6

In another Wisconsin study, Shinners and others compared two small rectangular balers with bottom feed and side feed chambers with respect to pickup and chamber losses. The bottom chamber feed had lower losses in both cases. For the pickup losses, the bottom feed baler had 1.09 percent versus 1.31 percent for the side feed baler. For the bale chamber losses it was 2.28 percent versus 2.66 percent.

MAINTENANCE AND OPERATION

Proper operation and maintenance of the mower-conditioner is a key to keeping losses at minimum during remainder of the harvesting operations. The mower-conditioner has many adjustments that influence losses directly as shatter losses and indirectly due to its impact on the drying rate in the windrow.

Mower-Conditioners

Some of the mower-conditioners adjustments depend on the cutterbar and conditioner designs. The two primary cutterbar adjustments are height and angle. The cutterbar needs to be adjusted to leave the desired stubble height that will influence yield. The cutterbar angle adjustment is important in lodged crops and depends on the direction of travel relative to the direction of lodging. If operating in the direction of lodging, the cutterbar must be tilted forward or downward. When operating opposite to the direction of lodging the cutterbar angle can be closer to the horizontal.

Another adjustment, which can cause losses if not done correctly, is the support spring tension. The cutterbar, in some cases the conditioning system, is supported by a large spring. If the spring tension is too high, the cutterbar will tend to bounce during operation resulting is uneven or wavy stubble. If the tension is too low, the risk of damage due to striking an obstruction such as a rock is increased.

The sickle mower-conditioner has a reel, which impacts the losses. In most cases, reel adjustments include reel position (vertical and horizontal), speed and timing. These adjustments need to match crop conditions. For example, in a lodged crop, the reel needs to be moved down and forward, reel speed should be increased, and the timing should be delayed.

The cutterbars should receive periodic maintenance to insure minimum losses. The sickle cutterbar will require more frequent maintenance such as sharpening the knives on the sickle and servicing the guards. The knives on the rotary cutterbar will require periodic sharpening even if they appear to continue performing very well.

When adjusting the conditioning system the operator must balance good conditioning against excessive shatter losses. The forage crop must be adequately conditioned to insure rapid drying but not over conditioned, causing high losses. The roll and impeller conditioning systems have different adjustments for obtaining good crop conditioning.

The adjustments on the roll conditioner include clearance, pressure, and timing for the intermeshing rolls. For light crops, the roll clearance and pressure should be reduced. For heavy crops, the clearance and pressure should be increased. The roll timing needs to be adjusted if the intermeshing rolls are interfering causing over conditioning and large bearing loads. The operator should check the conditioned crop to insure the adjustments are correct. The stems should be cracked but no discoloration should be present due to over-conditioning. A dark green color indicates cell walls were ruptured and over-conditioning has occurred.

For the impeller conditioner two adjustments which influence losses and drying rate are impeller speed and clearance between the impeller and conditioning hood. A slower speed is used for alfalfa while a higher speed is used for grasses. For more aggressive conditioning, the hood above the impeller can be lower. On some of the older impeller conditioners, a set of adjustable stationary tines intermeshed with the tines on the impeller. The degree of intermeshing determined the intensity of the conditioning.

Rakes, Mergers and Inverters

The primary adjustment affecting losses of the rakes will be the operating height except for the wheel rake that needs to be in contact with the ground. This height needs to be adjusted to insure the crop is completely picked up without picking up rocks. For the mergers and inverters, the height of their pickups needs to be adjusted to insure the windrow is also completely picked up.

Most of these machines’ performance will be affected by the forward speed. Usually an excessive forward speed leads to high field losses.

Crop moisture content is a major factor in the losses created by this equipment. Raking and inverting should be done with the moisture content over forty percent and tedding should be done at a moisture at sixty percent or more. Although research is very limited on mergers, moisture contents over forty percent should be considered.

Forage Harvesters

The primary adjustment on these machines will be the pickup height to insure the entire crop is harvested. Also the harvesting should be completed in a timely manner before it overdries when losses become larger.

Also consider adding an acid preservative to allow baling dry hay at a higher moisture when losses will be less. This reduces the risk of precipitation causing losses in crop quality as well.

In conclusion, the biggest difference in forage harvesting losses from farm to farm is not the brand or design but how the equipment is adjusted. Time by the operator is well spent checking to insure the crop is being properly mowed and conditioned by the mower-conditioner and adjusting the harvesting equipment to insure the total windrow is harvested. Also these operations should be completed in a timely manner to insure lower field losses and a high quality forage crop.

Equipment design has a key role in shatter losses and productivity. Some of the equipment designed for grasses in Europe increase productivity but increase losses when used to harvest alfalfa. When purchasing this equipment the producer must decide whether they want to sacrifice some losses for improved productivity on mower-conditioners.

*Extension Agricultural Engineer, Biological Systems Engineering Department, University of Wisconsin-Madison.