| Kenton R. Kautman Agricultural Engineering Department North Dakota State University |
LeRoy W. Schaffner Agricultural Economics Department North Dakota State University |
Introduction
A method is needed for controlling weeds that have not been controlled by early
application of herbicides or by cultivation and that subsequently grow taller than the
crop. These weeds area problem because they compete with the crop for nutrients, water and
sunlight. They present a problem for harvesting equipment and cause a decrease in
harvesting efficiency. Control is also needed to prevent weed seed production. A
herbicide, glyphosate (trade name Roundup), will control tall weeds, but glyphosate also
is injurious to the crop and therefore needs to be placed selectively on the weeds.
Present methods for selective placement of herbicides include a herbicide roller, a
recirculating sprayer, or a rope-wick applicator.
A newly developed alternative for control of tall weeds on short crops is the Electrical Discharge System (EDS) weeder marketed by Lasco, Inc. The EDS unit kills weeds electrically on contact with charged probes by forcing the electrolytic solution within the plants vascular system to conduct electrical current. The electricity in the plant, in effect, boils the plant cell solution and ruptures cell walls.
Purpose
To assist farm managers in their decisions regarding these alternate methods of weed
control, North Dakota State University conducted a research program with the following
objectives:
Available time, locations and implements imposed limitations on the scope of this experiment. The results may not represent specific energy requirements for the other weed control methods. However, this study should serve as a basis for general comparisons of the different weed control methods available for future study.
Equipment
The following implement and tractor were used:
Tractor: Allis Chalmers, Model 7045, diesel, equipped with power shift, rated 109 kw (147 hp) at the PTO in Nebraska Tractor Test no. 1308.
The tractor was tested on a Power Take Off, PTO, dynamometer to determine if it was operating properly. The power output at rated engine speed and also at rated PTO speed were checked. In both cases the tractor produced its rated horsepower as reported by the Nebraska Tractor Test. The tractor was operated at rated engine speed for one hour and its fuel consumption was measured. The tractor consumed 9.44 gallons per hour at rated engine speed. Comparing this to the 9.950 gallons per hour which the tractor in the Nebraska Tractor Test consumed, it appears that the tractor was operating properly.
Implement: 1979 Model, Electrical Discharge System Weeder marketed by Lasco, Inc., Vicksburg, Mississippi.
The weeder treated twelve 22 inch rows with a 50 kw, PTO driven generator and transformer. The safety-shielded EDS probe was hydraulically adjusted to pass slightly above the tops of the sugarbeets. The weeds, which are taller, were killed on contact. The EDS weeder was operated by a representative of the Lasco Corp. It was assumed that speeds and voltages chosen were typical of those necessary for proper weed control.
Procedure
Primary energy related measurements made included forward speed, field size, elapsed
time, and fuel consumption.
Field Size: Field size was calculated from length and width measurements. The length of the test plot was measured from end-row to end-row with a Rolatape Model 400 measuring wheel. The width of the test plot was calculated as the product of the width of the machine and tile number of trips through the field.
Elapsed Time and Forward Speed: Elapsed time was measured with a stop watch. Each trip through the field was timed as well as the total time to complete the test plot. Forward speed was calculated from the average of the time readings to travel one-way through the field and the length of the field from end-row to end-row.
Fuel consumption: Fuel consumption was determined by filling the tractor fuel tank before the test was started and refilling it after the test was completed. For both fillings the tractor was parked in the same location with the front end higher than the rear end. This was done to assure that no air bubbles remained in the fuel tank. Temperature measurements using a mercury-in-glass thermometer were taken of the fuel in the tractor tank each time it was filled. Two 5 gallon fuel cans were used to refill the tractor fuel tank at the end of each test. The temperature of the fuel in each of these cans was also observed. The amount of fuel in these cans was determined by weighing them on a portable Hobart Model 45-1000JA scale in the field. The weight of the diesel fuel was obtained from the local distributor (1). It was assumed to be 7.076 pounds per gallon. All fuel consumption measurements were corrected to 60F using the appropriate temperature correction factors (2). This same technique was used to measure fuel consumption on the PTO dynamometer test. From that test it was concluded that the error in measurement using this technique was less than five percent.
Results of Field Test
Energy data was collected on 10 different fields during July 1979. This number of
replications is similar to work done by Frisby and Summers (3) and Smith and Fornstrom
(4). A test plot size of approximately 10 acres was used for each test. The sites were
located in farmers' fields in the Red River Valley of North Dakota and Minnesota.
The primary parameters calculated for each test were gallons of fuel per acre, gallons per hour, acres per hour, speed, and field efficiency. A summary of the results is in Table 1. These results indicate that the weeder on the average used 0.86 gallons of fuel per acre while operating at 2.91 miles per hour in the field. It covered an average of 7.35 acres per hour at a field efficiency of 94 percent. In very heavy weed conditions, the EDS unit consumed 1.35 gallons per acre at a speed of 2.35 miles per hour. It treated 6.03 acres per hour with a field efficiency of 95 percent.
In addition, data was collected to determine the power necessary to pull the weeder through the field without killing any weeds. These data were collected in a summer fallow field. The coulters were in contact with the ground and the PTO was engaged while the tractor drove through the field. The tractor was operated at wide open throttle and in the gear (3rd-slow) most commonly used in the field tests. Three replications were performed. The results are in Table 2. These tests show that the weeder on the average used 0.54 gallons per acre while operating at 3.09 miles per hour in the field and covering 7.97 acres per hour.
Finally, the tractor was driven through the field without the weeder attached. These figures give an estimate of the energy consumed by the tractor alone. These tests were done in the same summer fallow field used for the tests on the tractor and weeder together. The tractor was again operated at wide open throttle and at a speed similar to the field tests using the weeder. Three replications were performed. The results are in Table 3. The outcome shows that the tractor used 0.42 gallons of diesel fuel per acre on the average while operating at 3.19 miles per hour and covering 8.32 acres per hour.
Overall, the data reflect the functions performed. The weed infestations in field Tests #3 and #4 (Table 1) were light. The fuel consumption was 4.63 and 4.65 gallons per hour respectively for these fields. This use of fuel is slightly greater than the highest value of 4.60 gallons per hour (Table 2, Test #3) to power the tractor and unit without killing any weeds. At the same time, the highest value of 3.86 gallons per hour to drive the tractor alone (Table 3, Test #2) is essentially the same as the lowest value of 3.84 gallons per hour (Table 2, Test #l) to operate the tractor and weeder together. So, generally the tests reflect the operations performed.
Conclusions from Field Tests
Several conclusions can be made from the field tests. First, looking at the PTO
performance of the A-C 7045 in the Nebraska Tractor Test there is a strong positive
correlation (R = 0.9997) between the power output of the tractor and its fuel consumption.
This relationship can be used to hypothesize about the power consumption of the tractor
and weeder in the field tests from its fuel consumption.
On the average the tractor used 6.07 gallons per hour or approximately 60 horsepower while operating with the Lasco EDS Lightning Weeder (Table 1). In Test #5, the fuel consumption was 8.11 gallons per hour or about 105 horsepower were used to propel the unit and kill weeds. An average of 4.27 gallons per hour of diesel fuel (Table 2) or approximately 15 horsepower were needed to propel the tractor and weeder through the field. So in Test #5, about 90 horsepower were used to kill weeds. Hence, it seems that in this field the weeder was operating close to its maximum since it takes 100 PTO horsepower to produce 50 kilowatts, the power rating of the weeder (5). Moreover, since it takes about 15 hp to drive the weeder and tractor through the field, a tractor of at least 115 horsepower should be used with the Iasco EDS Lightning Weeder.
Further, the tractor consumed an average of 3.50 gallons per hour (Table 3) while being operated in a summer fallow field without the weeder. This value seems to be a little bit low since the tractor in the Nebraska Tractor Test used 3.552 gph at zero horsepower output. However, looking at Table 3, it appears that less than 5 hp are necessary to propel the tractor in the field. So it could be concluded the 15 hp necessary to propel the tractor and weeder through the field could be broken into two parts of 5 hp and 10 hp. The first part, 5 hp, is needed to propel the tractor alone. The remaining 10 hp is used to pull the weeder through the field and to turn the PTO.
Economic Analysis
Owning a large agricultural machine represents a sizable investment. This investment
can have a significant effect on the profitability of the operation. This part of the
proper is concerned with making purchase decisions for the less costly method of overhead
weed control. The criterion for determination is minimization of the annual equivalent
costs which consists of capital recovery costs or fixed costs and operation and
maintenance costs. Three weed control methods will be considered, a) the Lasco EDS
Lightning 17 Weeder, b) the roller herbicide applicator, and c) the recirculating sprayer.
Estimation of Costs
New Investment: Costs of the roller and the recirculating sprayer were
obtained from their manufacturers. The "Roll-Wipe" herbicide applicator is
marketed by Irrigation Specialties Manufacturing Company, Scottsbluff, Nebraska. The most
popular size is 15 feet. It costs $3,500 and is operated at four to five miles per hour in
the field (6). The type of recirculating sprayer used in this study was the Spray Sickle.
It is marketed by Sprayrite Manufacturing Co., West Helena, Arkansas. The most popular
size is 280 inches, costs $2,900 and is operated at three to five miles per hour in the
field (7).
A 70 hp tractor was selected for the economic analysis on the roller and the recirculating sprayer. This size tractor was used because it is the average small tractor on farms in the Red River Valley (8). A 120 hp tractor was selected for the electric weeder. The costs of these tractors are $13,140 and $27,270 respectively (9).
Machinery Replacement: Machinery replacement is calculated like straight line depreciation except that the purchase price and salvage value for all machines used are in 1979 dollars. Ten percent of new cost was used for salvage value. Obsolescence lives of 10 years were utilized for the weed control machines and 12,000 hours for the tractors (10).
Interest on Investment, Insurance and Housing: An interest rate of 10 percent based on the average investment during the life of the machine was utilized. A charge of 1.3 percent on the initial cost was employed for insurance, sales tax, and housing (11). The tractor was assumed to have an obsolescence life of 15 years resulting in an annual use of 800 hours (10). This was used to calculate the hourly charge for interest on the tractors.
Repairs: The wear-out life of the generator was assumed to be 4000 hours. The repair and maintenance cost over the life of the electric weeder was assumed to be 20 percent of the new cost. The wear-out life for the recirculating sprayer was taken to be 1500 hours as suggested by Smith and Wilkes (10). It was charged a repair and maintenance cost over its life of 30 percent of the new cost (10). The wear-out life and repair and maintenance costs for the roller was presumed to be the same as for the recirculating sprayer.
Additional repair and maintenance was necessary for each machine using herbicides. The mats on the recirculating sprayer needed to be replaced every two years at a cost of $42 (7). The carpet on the roller would need to be replaced every four to five years at a cost of $50 to $60 plus installation (6).
The total repair cost for the tractors was calculated to be 120 percent of the new cost for the life of the machine (10).
Fuel and Lubrication: The fuel requirements for the tractor while operating the Jasco EDS Lightning Weeder were 6.07 gallons of diesel fuel per hour (Table 1). A charge of 80 cents per gallon was made for the diesel fuel. The cost for oil and filters was taken as an additional 15 percent of the cost of the fuel used (12).
The energy requirements of implements not tested in this study were obtained from other studies. The fuel usage by farm operators in Kansas for spraying is 0.31 gallons of diesel fuel per acre (13).The fuel consumption of farmers in Nebraska for spraying is 0.23 gallons of diesel fuel per acre (13). So for this study, an average value of 0.27 gallons per acre was assumed to be the fuel consumption for using the recirculating sprayer or the roller. Judging from the 0.42 gallons per acre to operate the tractor alone in this study (Table 3), the value of 0.27 gallons per acre for spraying might be a little bit low. However, a smaller tractor would be used for spraying, so 0.27 gallons per acre might be realistic.
Herbicide: Recirculating sprayers recycle the excess herbicide that does not hit the weeds. While the amount of chemical that gets recirculated varies according to weed species and infestation levels, 80 to 90 percent recirculated or 10 to 20 percent used is a good estimate based on average conditions. At that rate, the per acre cost of treatment using glyphosate (Roundup) will range from $2.00 to $4.00 for most weeds, with mill weed running about $8.00 due to the higher rate required for control (14). Another estimate states the chemical costs average around $3.00 per acre (15). These costs would be the same for roller applicators.
Hours Per Acre: The man-labor time was estimated to be 15 percent greater than the tractor time. For all the methods, $4.00 per hour was charged for the labor. The tractor time for the roller and recirculating sprayer was calculated using the machine width and an assumed speed of four mph with a field efficiency of 70 percent. This field efficiency was suggested by Vaughan, et al. (16).
A summary of the cost estimates is in Table 4.
Cost Comparisons
This feasibility study of the various weed control methods will consider three
scenarios representative of the Red River Valley. It will consider acreages of 150, 250
and 350 acres. These sizes were selected for two reasons. First, the average size
sugarbeet contract in 1977 was 185 acres (17). Second, there were very few sugarbeet
contracts of less than 100 acres. Additionally, it was assumed that three treatments were
necessary for good weed control with all three implements. Early results indicate three to
four treatments would be needed for optimum weed control in moderate to heavily infested
fields (18).
The first scenario analyzed was the 150 acre farm. The results are in Table 5. The costs per acre for the electric weeder, roller applicator, and recirculating sprayer were respectively $7.86, $6.40, and $5.56. The least cost method of weed control is the recirculating sprayer.
The next scenario studied was the 250 acre contract. The results are in Table 6. The costs per acre for the electric weeder, roller applicator, and recirculating sprayer were respectively $5.75, $5.91, and $5.15. The recirculating sprayer is still the least costly method. The electric method moved from the highest cost to the intermediate cost for the 250 acre scenario.
The final scenario examined was the 350 acre contract. The results are in Table 7. The costs per acre for the electric weeder, roller applicator, and recirculating sprayer respectively were $4.85, $5.70, and $4.98. This grower could choose either the electric weeder or the recirculating sprayer. The final choice would depend on the farmer's preferences. In this case, the fact that the Lasco unit can also be used as a standby generator might persuade him to choose the electric weeder.
The cost comparisons should be reviewed prudently. The machine ownership and operation costs were the only criteria used for making a decision as to the type of machine to purchase. Sugarbeets are sensitive to glyphosate and crop injury has been observed. Experiments on sugarbeets will be analyzed later to observe the crop yield and weed control efficiency of the three methods compared. These results will have a bearing on the type of machine to purchase. This study does not present the complete analysis for a good decision making process.
Other non-economic factors might also be included in the choice of weed control methods. The roller and the recirculating sprayer both involve the handling of chemicals. For safety, any operators of these machines should be trained and certified. The electric weeder may function as a standby power unit. The benefits of having a standby power generator were not considered in the cost calculations but could affect the values used in the decision of which type of overhead weeder to purchase. Nevertheless, safety considerations also apply to the electric unit. With the high voltages and currents being utilized, only knowledgeable operators should run this machine.
Summary
Energy requirements of the Lasco EDS Lightning Weeder were measured. Ten tests were
performed. Field performance results indicate that the weeder on the average used 0.86
gallons of diesel fuel per acre while operating at 2.91 miles per hour in the field. It
covered an average of 7.35 acres per hour at a field efficiency of 94 percent. In very
heavy weed conditions the EDS unit consumed 1.35 gallons per acre at a speed of 2.35 miles
per hour. It treated 6.03 acres per hour with a field efficiency of 95 percent. A
recommended tractor size of at least 115 horsepower should be used to power the Lasco EDS
Lightning Weeder.
Economic comparisons were made between the Lasco EDS Lightning Weeder, the herbicide roller, and the recirculating sprayer. Fixed and variable costs were considered. No adjustments were made for differences in crop yield or effectiveness of weed control. These results will be available later and will have a bearing on the type of machine to purchase. Three cropping situations of 150, 250, and 350 acres were considered. It was assumed that three treatments were necessary for optimum weed control with all three implements. The costs per acre for the electric weeder, roller applicator, and recirculating sprayer were respectively $7.86, $6.40, and $5.56 for the 150 acre grower; $5.75, $5.91, and $5.15 for the 250 acre grower; and $4.85, $5.70, and $4.98 for the 350 acre grower. These are the machine ownership and operation costs. The complete analysis for a good decision making process should include the effectiveness of weed control and variations in crop yield.
References
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1979 Sugarbeet Research and Extension Reports, Volume 10, Pages 72-85
