Fifty acres of corn land for plowing, disking, harrowing, planting, cultivating and harvesting would amount to a total of 1,450 horsepower hours. Thirty acres of wheat would require a total of 330 horsepower hours. Twenty acres of hay would require 110 horsepower hours. In round figures, 1,900 horsepower hours at 121⁄2 cents would amount to $237.50.
Elaborate figures have been worked out theoretically to show that this work can be done by an 8-16 farm tractor in 273⁄4 days at a cost for kerosene fuel and lubricating oil of $1.89 per day. Adding interest, repairs and depreciation, brings this figure up to about $4.00 per day, or a total of $111.00 for the job. No account is kept of man power in caring for either the horses or the tractor. The actual man labor on the job, however, figures 121⁄3 days less for the tractor than for horses. We should remember that actual farm figures are used for the cost of horse work. Such figures are not available for tractor work.
The cost of plowing with a traction engine depends upon so many factors that it is difficult to make any definite statement. It depends upon the condition of the ground, size of the tractor, the number of plows pulled, and the amount of fuel used. An 8-16 horsepower tractor, for instance, burning from 15 to 20 gallons of low grade kerosene per ten hour day and using one gallon of lubricating oil, costs about $1.90 per ten hours work. Pulling two 14-inch plows and traveling 20 miles per day, the tractor will plow 5.6 acres at a fuel and an oil cost of about 30 cents per acre. Pulling three 14-inch plows, it will turn 8.4 acres at a cost for fuel and oil of about 20 cents an acre.
The kind and condition of soil is an important factor in determining the tractor cost of plowing. Comparison between the average horse cost and the average tractor cost suggests very interesting possibilities in favor of tractor plowing under good management.
Aside from the actual cost in dollars we should also remember that no horse gang can possibly do the quality of work that can be accomplished by an engine gang. Anxiety to spare the team has cut a big slice off the profits of many a farmer. He has often plowed late on account of hard ground, and he has many times allowed a field to remain unplowed on account of worn-out teams. Under normal conditions, late plowing never produces as good results as early plowing. Many a farmer has fed and harnessed by the light of the lantern, gone to the field and worked his team hard to take advantage of the cool of the morning. With the approach of the hot hours of midday, the vicious flies sapping the vitality from his faithful team, he has eased up on the work or quit the job.
In using the tractor for plowing, there are none of these distressing conditions to be taken into consideration, nothing to think of but the quality of work done. It is possible to plow deep without thought of the added burden. Deep plowing may or may not be advisable. But where the soil will stand it, deep plowing at the proper time of year, and when done with judgment, holds moisture better and provides more plant food.
The pull power required to plow different soils varies from about three pounds per square inch of furrow for light sand up to twenty pounds per square inch of furrow for gumbo. The draft of a plow is generally figured from clover sod, which averages about seven pounds per square inch. Suppose a plow rig has two 14-inch bottoms, and the depth to be plowed is six inches. A cross section of each plow is therefore 14 by 6 inches, or 84 square inches. Twice this for two bottoms is 168 square inches. Since, in sandy soil, the pressure per square inch is three pounds, therefore 168 times 3 pounds equals 504 pounds, the draft in sandy soil. 168 times 7 pounds equals 1,176 pounds, the draft in clover sod. 168 times 8 pounds equals 1,344 pounds, the draft in clay sod.
The success of crop growing depends upon the way the seed-bed is prepared. The final preparation of the seed-bed can never be thoroughly well done unless the ground is properly plowed to begin with. It is not sufficient to root the ground over or to crowd it to one side but the plow must really turn the furrow slice in a uniform, systematic manner and lay it bottom side uppermost to receive the beneficial action of the air, rain and sunshine.
The moldboard of a plow must be smooth in order to properly shed the earth freely to make an easy turn-over. The shape of the shear and the forward part of the moldboard is primarily that of a wedge, but the roll or upper curve of the moldboard changes according to soil texture and the width and depth of furrow to be turned. Moldboards also differ in size and shape, according to the kind of furrow to be turned. Sometimes in certain soils a narrow solid furrow with a comb on the upper edge is preferable. In other soils a cracked or broken furrow slice works the best. When working our lighter soils a wide furrow turned flat over on top of a jointer furrow breaks the ground into fragments with wide cracks or openings reaching several inches down. Between these extremes there are many modifications made for the particular type or texture of the soil to be plowed. We can observe the effect that a rough, or badly scratched, or poorly shaped moldboard has on any kind of soil, especially when passing from gravelly soils to clay. In soil that contains the right amount of moisture, when a plow scours all the time, the top of the furrow slice always has a glazed or shiny appearance. This shows that the soil is slipping off the moldboard easily. In places where the plow does not scour the ground is pushed to one side and packed or puddled on the underside instead of being lifted and turned as it should be. A field plowed with a defective moldboard will be full of these places. Such ground cannot have the life to bring about a satisfactory bacteria condition necessary to promote the rapid plant growth that proper plowing gives it.
Cultivated sandy soils are becoming more acid year after year. We are using lime to correct the acidity, but the use of lime requires better plowing and better after cultivation to thoroughly mix the trash with the earth to make soil conditions favorable to the different kinds of soil bacteria. Unless we pay special attention to the humus content of the soil we are likely to use lime to dissolve out plant foods that are not needed by the present crop, and, therefore, cannot be utilized. This is what the old adage means which reads: “Lime enricheth the father but impoverisheth the son.” When that was written the world had no proper tillage tools and the importance of humus was not even dreamed of.