Real Time Crop Sensing
What is Opt RX?
OptRx uses sensors, usually mounted on the sprayer’s booms, to assess reflected light to determine plant strength and health (vigor). It assigns numeric values to the varying levels of vigor to create a Vegetative Index (VI).
Using the VI, OptRx calculates nitrogen application rates, to apply a variable rate on the go. OptRx creates nitrogen rates either by using the N Algorithm or by using the user-defined Application Rate Table. OptRx can also be used for scanning purposes.
OptRx does not require an unlock and can be utilized on Ag Leader InCommand 1200, Integra and InSight displays.
Common OptRx Questions
How do OptRx Crop Sensors define plant health?
OptRx Crop Sensors pulse light at 40,000 Hz to detect raw plant vigor. The raw plant vigor feedback is reflected back to the sensor then the NDRE algorithm uses a combination of NIR and RedEdge measurements to define the vegetative index (VI).
NIR looks at plant biomass while RedEdge focuses on evaluating Chlorophyll. Looking at these two factors, plants express stress by stunted growth and deceases in Chlorophyll efficiency.
When OptRx determines plant health, will it tell me plant stress is from water or potassium deficiencies?
There is a possibility that OptRx can incorrectly diagnose an unhealthy plant. Ag Leader recommends that users do regular soil sampling and maintaining agronomic best practices on the other nutrients to the best of their ability. Since nitrogen moves so easily with water and into the air, we are assuming that to be the cause of most variability in the field caused by plant nutrition.
That being said, if there is too much water that has caused the plants to appear sick, there has been enough water to cause leaching and denitrification. Applying more N in these situations will likely be a big return on investment. If it is lack of water like in a sandy soil in the heat and dry spell of the summer, an extra shot may not help here. If you are familiar with this area of the field, take over for OptRx and switch to manual to apply a flat rate in this spot of your choosing.
When is the appropriate growth stage to begin using OptRx crop sensors for corn?
V5 is the earliest recommended growth stage to operate OptRx sensors in corn. The crop canopy is just not adequate enough for identifying crop needs before then.
OptRx can be used from V5 until tassel in corn. Tasselling interferes with the sensor’s ability to accurately identify plant vigor.
Does OptRx account for nitrogen available in the soil before side-dressing?
Yes. OptRx allows growers to enter known nitrogen credits so the algorithm can take into account the existing nitrogen levels. Nitrogen can come from a previous nitrogen application or organic material in the field. For example, if a plant is growing in a high organic matter soil or a soil that has an abundance of pre-plant nitrogen, the corn plant will typically be a taller healthier looking plant. OptRx senses this and applies less nitrogen because the plant shows little to no stress. If a plant is growing in a low organic matter area or has been in soils saturated long enough to cause denitrification, the plant will often be a smaller weaker looking plant. OptRx senses this and applies more nitrogen to compensate for the lack of nitrogen available to the plant.
How much Pre-plant Nitrogen should I use with OptRx?
It is recommended that 1/3 to 1/2 of the total amount of nitrogen that will be applied throughout the entire year is applied to corn at or before planting. The reason is the corn plant determines both kernels per row and number of rows by growth stage V5. Any stress on a plant this early can result in yield losses that cannot be recovered. Therefore, it is best to supply enough nitrogen to sustain the corn plants through V5. Any stress shown by a corn plant between V5 and V12 can be recovered by side-dressing nitrogen with OptRx.
Why don’t I just apply the whole year’s worth of Nitrogen at pre-plant and not risk stressing the corn plants?
The management of nitrogen can mean the difference between great yields and great losses of profit. If all of the nitrogen that is needed by a plant is applied at or before planting, there is a great risk that the nitrogen will be lost to the environment and not used by the corn plants. Loss of nitrogen in the soil will happen every year due to weather and other variable conditions. Minimizing those losses by splitting the application into two applications is vital to controlling the amount of lost nitrogen. Split applications also provide an opportunity to provide more nitrogen to plants that do not have enough nitrogen for optimal growth.
Recent studies at the Illinois Crop Physiology Laboratory have shown that side-dressing nitrogen can be one of the biggest factors in yield improvement.
Does dew/standing water affect crop sensor readings?
Yes, it will have a minimal affect. Wait for leaves to dry or perform a separate calibration with wet conditions. Keep an eye on the recommended rates as conditions dry and revert to the dry calibration as soon as possible.
Does the temperature of the day affect the crop’s VI readings?
Yes. In summer’s intense heat, the plant’s leaves will start to roll and respiration/photosynthesis will slow down. This can significantly affect the sensor’s readings. A user can continue to operate in these conditions if they re-calibrate to compensate for this plant behavior.
What if the low crop vigor in plants is due to a nutrient deficiency other than nitrogen?
If a plant is shorter and has less crop vigor than a reference value plant, OptRx will respond by applying more nitrogen. OptRx is a tool used to help with recommendations on one of the most vital and difficult nutrients to maintain, nitrogen. Other issues such as a lack of potassium, phosphorus, sulfur or even low or high soil PH must be in balance in order for corn to grow optimally and for OptRx to perform its best.
How does OptRx account for variable rate seeding zones?
The sensor doesn’t know anything about the variable rate seeding in that field. Typically, variable rate seeding is directed by yield environments and a lot of times, nitrogen availability in those environments has a large bearing on why that area yields higher or lower than other regions. Higher populations go in more productive soils and where there tends to be more water availability. There is naturally less need for additional nitrogen except when we put more seeds in that zone by VR seeding. If VR seeding was done right, the plants shouldn’t be stressed beyond what you would normally see, but the sensors may notice increased vegetation. This would be viewed as healthier plants. OptRx may call for less N on regions where there may be higher demand and work in the same way except opposite in areas where there are few plants. Fewer plants that are stressed results in OptRx thinking it should apply more than it needs to in reality.What to do? Here are some suggestions:
- High population zones – Assume these zones are going to be read as the least stressed regions. Evaluate the season so far and potentially set your minimum rate slightly higher than you would normally to make sure you adequately feed those additional plants.
- Low population zones – Assume these zones are going to be read as the most stressed areas. Evaluate the season so far and set your maximum rate potentially lower than you would normally to make sure you aren’t overcorrecting the stress in a condition with fewer plants
Is a nitrogen-rich strip required for calibration?
N rich strips are not required with the OptRx system. University research and broad scale field testing have proven that nitrogen sufficient areas almost always exist in passes not treated with nitrogen-rich strips. OptRx selects the highest crop vigor readings from the nitrogen sufficient areas and sets them as the reference value during the Virtual Reference Strip scan. This produces the same result as scanning a nitrogen rich strip, only without the hassle of installing nitrogen-rich strips.
How frequently do I need to create a Virtual Reference Strip?
It is best to create a Virtual Reference Strip in every field. It is critical that the application is done with a reference value of the same growth stage. However, a previous field-s reference value may be used in place of creating a new reference value. Selection of previous reference value should be based on crops that are in similar growth stages as the field about to be applied to ensure accurate nitrogen recommendations.
Example of Setup for Wheat
The exact values for these settings are up to the grower, ideally after consulting with an agronomist. Ag Leader does not provide agronomic advice.
- Minimum Rate: The lowest amount of nitrogen the operator wants to apply. If OptRx prescribes a lower rate, the system will default to the minimum rate value.
- Maximum Rate: The highest amount of nitrogen the operator wants to apply. If OptRx prescribes a higher rate, the system will default to the maximum rate.
- Rate Increment: Increments of rate change. This setting will be in kg of N/ha.
- Managed Rate: Amount of nitrogen the crop will uptake throughout a single season.
- Number of Applications: Times per season that N will be top-dressed.
- Planned Rate: Intended rate of N application if sensors were not used.
- Application Trend: Tells the system whether to increase rate for high biomass or decrease rate for high biomass.