Weeds are an invasive pest that competes with crops for nutrients, water, and light. If not treated properly, weeds may reduce the yield significantly, especially during early crop growth stages, thus causing financial losses to the farmer. Since weed control is a labor-intensive farm activity, farmers must constantly improve weed control techniques. Using a hoe and a field cultivator for years, farmers now have a modern and efficient solution for successful weed control.
Modern weed control includes the use of farm machinery with a real-time kinetic-global positioning system (RTK-GPS) and mapping techniques.
An RTK-GPS system is used to correct the lateral deviation of the combined row crop cultivator and band sprayer implement.
Additionally, mapping techniques provide information about the position of individual crop plants to steer the cultivator with an acceptable level of selectivity. In this regard, the system can automatically detect crop planting geo-positions, based on weed knives placed between crop plants along the row’s centerline.
Passing over the crops, cameras within the system distinguish weeds from the crop based on spectral color analysis techniques and textural properties of leaves and shapes of plants, thus automatically removing the weeds with intra-row mechanical weed knives.
These mechanical weed control machines are designed to precisely remove as many weeds in the seed line as possible, while not damaging crop plants. They are mainly used in vegetable and arable crops grown from transplants, which are initially larger than the weeds.
Farm machinery with a real-time kinematic GPS system are used not only for mechanical weed removal but also for agrochemical application. Providing a row-positioning accuracy of ±25 mm, this system can greatly enhance the precision of the application. In this regard, weed-infested patches are treated selectively while weed-free patches are not treated at all.
The activity of simultaneous inter-row cultivation and intra-row band is possible due to an electro-hydraulic side-shift frame controlled by the RTK-GPS system. A side-shift frame has the ability to center the narrow band treatments of agrochemicals above the rows and parallel to the crop rows with a minimum of lateral drift (cross-track error). The side-shift frame is attached to both the tractor and the implement.
In order to determine the position of crop plants and appropriately remove the weeds and apply protection agents, farmers can use different sensors. These include:
- Sensors which reflect the near infrared wavebands to determine the spectral differences between weeds and bare ground
- Sensors which employ light emitting diodes to assess the ratios of red and near-infrared reflectance of weeds and background
- Sensors that identify weeds based on color, basic shape, and size properties using video image analysis
- Non-contact laser treatments
They are all either attached to the tractor or are independent autonomous machines used for these purposes.
After the sensor determines the unwanted weed, it can destroy using three methods; mechanical, chemical, or thermal by using the laser.
The development of farm machinery with RTK-GPS systems for weed control benefits both the farmer and the crop. Moreover, they may greatly enhance overall crop production performance in the following ways:
- Saves for manual weeding
- Reduces damage to crops by manual weeding
- Cultivates and sprays weeds in a single pass
- Saves fuel
- Minimizes soil compaction
- Decreases pesticide rate
- Applies pesticides with more precision and more cost effectively
- Reduces farm cost
By providing high temporal measuring resolution, real-time data transfer, and high spatial resolution of sensor data that shows in-field variations, sensor technology provides an added value to the crop production.
The only disadvantage of RTK-GPS systems at this time is the high capital cost due to the requirement that a base station must be located within 10 km at all times.
Unlike sensors for weed detection, farmers can use a variety of sensors for the tracking of different crop conditions. These can be ground-based crop sensors, drones, and/or satellites.
These sensors can measure diverse crop conditions and anomalies such as; Photochemical Reflectance Index (PRI), Moisture Stress Index (MSI), Normalized Difference Water Index (NDWI), Chlorophyll Index (CI), Normalized Difference Vegetation Index (NDVI), and many others.
All sensors have one thing in common. They provide the farmer with detailed information about crop conditions.
Today, farmers have another tool in remote sensing to improve yields even further while simultaneously reducing farm costs. The old-fashioned ‘walking down the field’ monitoring system has been replaced with the automatical field survey as a part of precision approach to crop management.
Text sources: NCBI – PMC3658748 || NCBI – PMC3231660 || MDPI
Image sources: Nanne Kooiman || University of California || NCBI || MDPI
