Bench Talk

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Field crop production is labor and energy intensive. Traditional methods for growing commodities such as corn, wheat, soybeans, cotton, alfalfa, vegetables, or fruits typically require making multiple passes over the field with human-driven, diesel-powered tractors pulling various implements. These implements perform functions such as plowing, soil preparation, seed planting, cultivation, agrichemical application, and harvesting. A single growing year of alfalfa (harvesting multiple crops of growth per field) can take 15 or more tractor passes, potentially using thousands of gallons of fossil fuel and hundreds of hours of labor for a large field. Self-driving tractor experiments have tried to reduce the labor investment, but they’ve had limited success. Attempts to electrify tractors are proving difficult because available battery technologies do not have the energy density to provide nearly half a megawatt (big modern tractors are rated at more than 600 horsepower) for a 10-hour or longer shift. This is on the order of 50 times the battery capacity of a Tesla Model S electric car. Tethering an electric tractor to the grid with what amounts to a long extension cord has severe reliability, safety, and practicality problems.

But, what if we could eliminate the tractor entirely by employing robotics and Internet of Things (IoT) technologies? One interesting way to do this can be inspired by center-pivot irrigation systems, where a central tower supplies water, and one end of a long string of pipes is attached to it with a pivot, while the other end slowly travels around to make a large circle. Segments of pipe are suspended by trusses between a series of towers, with variable-speed drive wheels that are controlled to keep the pipeline straight. Sprinkler heads distributed along the pipe irrigate the crops below. Typical center-pivot systems are a quarter of a mile (400 meters) in radius. To see this technology in action, take a look at a satellite image of the croplands in the region of Ogallala, Nebraska.

The robotic system suggested here beefs up the trusses and wheeled towers to allow a heavy implement to be hung on a rail where the water pipe is located in traditional center-pivot systems. A motorized carriage moves across the entire length of the rail, carrying a turntable that in turn carries the interchangeable implement. To place the implement at the exact position the field the system commands, the wheels of the towers are driven at coordinated speeds to pivot the rail to the correct angle, the carriage moves the required radial distance from the center pivot, and the turntable orients the implement so that it’s positioned to do the required work and can follow rows of plants no matter what their orientation in the field. Rails can be 10 feet (3 meters) or more above ground level to accommodate tall crops.

The system has several technical innovations. An electrical busbar parallel to the rail delivers electrical power from the pivot to all elements of the system—something on the order of 100kW (kilowatts), 440V (volts), 3 phase. Sliding contacts on the carriage connect the busbar to the implement, supporting electrical loads in excess of 100hp (horsepower). Data networks interconnect the implement, carriage, motors, valves, and sensors to the central pivot, where fiber-optic links connect to the internet and cloud-based control. A water pipe irrigates the field, but individual valves and perhaps robotic sprinkler heads apply the water with much greater precision than traditional irrigation systems. Conveyer systems can run on top of the rail to deliver seeds and agrichemicals to the implement as well as remove the harvested crops. Hundreds of sensors, actuators, and distributed computers manage the system and integrate its functions.

A Use Case

Here’s a use case for the system. First, the central pivot is anchored in the middle of the field, and various power, computer network, conveyer, and water-distribution systems are buried fairly deep to supply it. Then, the pivot is assembled to segments of rails and wheeled drive towers to achieve the radius needed to cover the field. A grading implement is attached to the rail that levels and grades the land, moving soil from high spots to low spots. Plow and soil-conditioning implements till the soil, preparing a planting bed. Next, a planting implement is attached, which is periodically refilled with seed from the overhead conveyer. It precision-plants the entire field. Planting in rows is unnecessary if different patterns, such as hexagonal grids, are better for the specific crop. As the crops grow, cultivator implements make passes to control weeds and pests. This task can be mechanical or chemical or use video analytics and high-tech solutions such as lasers, water jets, or ice darts to selectively destroy weeds and harmful insects. Irrigation is done by the robotic system as needed based on sensors that measure the soil moisture with square-meter precision and apply exactly the required amount of water.

At harvest time, an implement suitable to the crop is mounted on the rail, gathers the crop, cleans and sorts it, and delivers the harvest to the conveyer system, where it’s moved to the central pivot, and then to storage or market. Unlike traditional harvest practices, this system can efficiently support multi-pass harvesting implements that use sophisticated vision systems to analyze the crops and robots to pick only the portion that has achieved optimal ripeness.

This system has several advantages over traditional agricultural techniques. It’s all electric, avoiding emissions, carbon, and petroleum cost volatility. It requires a fraction of the labor that human-driven tractors need. It can efficiently use seed, water, and agrichemicals. It supports selective harvesting to improve product quality. Soil compaction and erosion can be greatly reduced. It can enable organic farming by eliminating chemicals in favor of advanced weed and pest control practices. As the global population increases, these electronic, robotic, and IoT technologies should be valuable in improving the efficiency, productivity, and environmental responsibility of farming.