Smart agriculture, also known as precision agriculture, allows farmers to maximize yields using minimal resources such as water, fertilizer, and seeds. By deploying sensors and mapping fields, farmers can begin to understand their crops at a micro scale, conserve resources, and reduce impacts on the environment. Smart agriculture has roots going back to the 1980s when Global Positioning System (GPS) capability became accessible for civilian use. Once farmers were able to accurately map their crop fields, they could monitor and apply fertilizer and weed treatments only to areas that required it. During the 1990s, early precision agriculture users adopted crop yield monitoring to generate fertilizer and pH correction recommendations. As more variables could be measured and entered into a crop model, more accurate recommendations for fertilizer application, watering, and even peak yield harvesting, could be made.

Figure 1. A drone performs high definition soil mapping using infrared light. (credit: MONOPOLY919/Shutterstock)

In this article, we will explore how these sensing technologies have been woven into modern large agribusiness and discuss how progression of the technology both to small farms at home as well as globally can increase our capacity to feed the world.

Agricultural Sensors

A number of sensing technologies are used in precision agriculture, providing data that helps farmers monitor and optimize crops, as well as adapt to changing environmental factors.

Location Sensors use signals from GPS satellites to determine latitude, longitude, and altitude to within feet. Three satellites minimum are required to triangulate a position. Precise positioning is the cornerstone of precision agriculture. GPS integrated circuits like the NJR NJG1157PCD-TE1 are a good example of location sensors.

Optical Sensors use light to measure soil properties. The sensors measure different frequencies of light reflectance in near-infrared, mid-infrared, and polarized light spectrums. Sensors can be placed on vehicles or aerial platforms such as drones or even satellites. Soil reflectance and plant color data are just two variables from optical sensors that can be aggregated and processed. Optical sensors have been developed to determine clay, organic matter, and moisture content of the soil. Vishay, for example, offers hundreds of photodetectors and photodiodes, a basic building block for optical sensors.

Electrochemical Sensors provide key information required in precision agriculture: pH and soil nutrient levels. Sensor electrodes work by detecting specific ions in the soil. Currently, sensors mounted to specially designed “sleds” help gather, process, and map soil chemical data.

Mechanical Sensors measure soil compaction or “mechanical resistance.” The sensors use a probe that penetrates the soil and records resistive forces through use of load cells or strain gauges. A similar form of this technology is used on large tractors to predict pulling requirements for ground engaging equipment. Tensiometers, like Honeywell FSG15N1A, detect the force used by the roots in water absorption and are very useful for irrigation interventions.

Dielectric Soil Moisture Sensors assess moisture levels by measuring the dielectric constant (an electrical property that changes depending on the amount of moisture present) in the soil. Airflow Sensors measure soil air permeability. Measurements can be made at singular locations or dynamically while in motion. The desired output is the pressure required to push a predetermined amount of air into the ground at a prescribed depth. Various types of soil properties, including compaction, structure, soil type, and moisture level, produce unique identifying signatures.

Agricultural Weather Stations are self-contained units that are placed at various locations throughout growing fields. These stations have a combination of sensors appropriate for the local crops and climate. Information such as air temperature, soil temperature at various depths, rainfall, leaf wetness, chlorophyll, wind speed, dew point temperature, wind direction, relative humidity, solar radiation, and atmospheric pressure are measured and recorded at predetermined intervals. This data is compiled and sent wirelessly to a central data logger at programmed intervals. Their portability and decreasing prices make weather stations attractive for farms of all sizes.

Figure 2. Remote weather stations can be placed at strategic locations in a field. (credit: Budimir Jevtic/Shutterstock)

Sensor Output Applied

Sensing technologies provide actionable data to be processed and implemented as need be to optimize crop yield while minimizing environmental effects. Here are a few of the ways that precision farming takes advantage of this data:

Yield Monitoring Systems are placed on crop harvesting vehicles such as combines and corn harvesters. They provide crop weight yield by time, distance, or GPS location measured and recorded to within 30 cm.

Yield Mapping uses spatial coordinate data from GPS sensors mounted on harvesting equipment. Yield monitoring data is combined with the coordinates to create yield maps.

Variable Rate Fertilizer application tools use yield maps and perhaps optical surveys of plant health determined by coloration to control granular, liquid, and gaseous fertilizer materials. Variable rate controllers can either be manually controlled or automatically controlled using an on-board computer guided by real GPS location.

Weed Mapping currently uses operator interpretation and input to generate maps by quickly marking the location with a GPS receiver and datalogger. The weed occurrences can then be overlapped with yield maps, fertilizer maps, and spray maps. As visual recognition systems improve, the manual entry will soon be replaced by automated, visual systems mounted to working equipment.

Variable Spraying controllers turn herbicide spray booms on and off, and customize the amount (and blend) of the spray applied. Once weed locations are identified and mapped, the volume and mix of the spray can be determined.

Topography and Boundaries can be recorded using high-precision GPS, which allows for a very precise topographic representation to be made of any field. These precision maps are useful when interpreting yield maps and weed maps. Field boundaries, existing roads, and wetlands can be accurately located to aid in farm planning.

Salinity Mapping is done with a salinity meter on a sled towed across fields affected by salinity. Salinity mapping interprets emergent issues as well as change in salinity over time.

Guidance Systems can accurately position a moving vehicle within 30 cm or less using GPS. Guidance systems replace conventional equipment for spraying or seeding. Autonomous vehicles are currently under development and will likely be put into use in the very near future.

Large-scale farming gained an early foothold in the practice of precision farming. Expensive sensors, infrastructure, and processing equipment could only be realistically put to work by agribusinesses with sufficient capital available to invest. Those that invested in precision farming saw handsome paybacks in terms of crop yields.