Engineering efficiency for field operations is defined as actual amount of useful work performed versus the amount of work theoretically possible.
Consider a field that is infinitely long (many miles), so equipment never needs to be turned at field ends. The maximum amount of field area covered per hour by the implement is simply equipment swath width times field travel speed. For example, a 30-foot-wide implement traveling 5 miles per hour (26,400 feet per hour) covers 792,000 square feet or about 18.2 acres per hour, if the implement never has to turn or stop. This is the theoretical (maximum) field capacity.
In actual practice, however, implements need to be turned and often raised at field ends, slowing field speed and creating unproductive time in the field. Theoretical field capacity is reduced to a lesser, actual field capacity. In addition to turns and minor in-field stops, many field operations also need to be “tended.” Tending can be operations like filling the equipment with supplies, such as seed or fertilizer hoppers or filling spray tanks, or removing harvested grain or crop from the field. Unproductive time accumulates during both turns and tending equipment.
Measurements of equipment such as tillage implements or a mower-conditioner that doesn’t require tending, show that time for turns, etc. reduces actual field capacity to about 80% of theoretical capacity. From the earlier example, a 30-foot- wide implement traveling 5 miles per hour would only cover about 14.5 acres per hour. Field efficiency for equipment that requires tending, such as planters, application (fertilizer, pesticide) or harvest equipment is closer to 60% of theoretical capacity. For the example situation, (such as a 12-row, 30-inch planter that is 30 feet wide traveling 5 miles per hour), this reduces actual field capacity to about 10.9 acres per hour.
Although larger (wider) equipment and/or faster field speeds increase the number of acres covered per hour, somewhat unexpectedly, field efficiency is often slightly reduced a couple of percentage points. With wider equipment, turns at headlands are longer with raised implements not in use, and headland areas are often larger.
Wider equipment may also occasionally result in a smaller number of acres covered per hour if travel speed must be slowed due to limited tractor horsepower available or too much tractor wheel slippage. Increased travel speed also comes with some cost (e.g., harvest field losses, seed placement during planting as equipment is being required to perform at a higher rate), and equipment must also slow down from a faster speed at headlands to accommodate turns, further adding to the percentage of turning time.
The term “efficiency,” as used by many farmers, actually can be thought of as “capacity” (i.e., how many acres per hour are being covered by equipment). Both increasing equipment width and speed improve capacity and the number of acres covered per hour, even if field efficiency is slightly reduced.
Returning to the objective mentioned at the beginning (covering acreage in the least amount of time), as farm operations have become larger and more scattered geographically, other factors besides in-field efficiency are becoming significant factors affecting time management for many farmers. Two of these factors are:
- Transportation time between field locations
- Supplying or tending equipment (e.g., seed, fertilizer and pesticide in spring and taking away harvested crop during fall or summer)
Both of these can be more broadly considered as logistical requirements of field operations.
Monitoring crop and soil conditions in scattered field locations frequently dictates order of operations such as tillage, planting, pest control and harvest in various fields. Technology is beginning to assist this management with real-time tracking of equipment locations, which can be coupled with consideration of local traffic patterns and “rush hour” on more heavily trafficked roads.
Field operations that require a significant portion of time for tending suggest careful attention to how inputs are being supplied or crop taken away during harvest. Consider a planting operation where 25% of the time (15 minutes per hour) the planter is parked while seed hoppers are filled. Even if planter travel speed is doubled, only ¾ of the total time period is being improved. The amount of time the planter remains parked for loading seed becomes an even more significant drag on productivity.
Taking this concept a step further, the greater percentage of time a tending operation requires, the more it should be considered for improvement. Consider seed tending for planting corn at 35,000 seeds per acre or soybeans at a significantly greater seeding rate of 175,000 seeds per acre. Because five times as many seeds must be loaded per acre, return and payback for using a mechanical seed tender are much faster as capacity increases during soybean planting than during corn planting (Figure 1).
Also, the impact of tending improvement is greater for wider equipment with more seed required to be loaded each time the planter is stopped.
Contrasting grain harvest operations to planting, because the volume of corn grain harvested per acre is three to four times that of soybean grain, return and payback of additional grain cart and truck capacity are greater during corn than soybean harvest. On-the-go grain cart loading, commonly used to keep combines harvesting, can have longer-term detrimental effects on soil compaction and ultimately lower ultimate crop profitability if soil is wet.
Additional capacity of larger combines frequently outstrips the ability of grain transport systems and at times grain receiving systems, particularly during falls with significant corn drying requirements. Careful attention to these downstream requirements to tend harvest by removing crop may have a greater effect on increasing capacity than simply using a wider or faster combine.
Although increasing travel speed of field operations generally increases field capacity, keep in mind the overall objective is to maximize crop profitability. Being the first operator in the neighborhood back to the machine shed doesn’t do any good if seed has not been properly planted or crop has been left in the field during harvest as it bounces out of the gathering head. Poorly calibrated or maintained equipment, in addition to excessive speed, also reduces profits. 
Mark Hanna is a agricultural engineer. Email Mark Hanna.
