If you want to know if you should top dress fertilizer in season, a great place to start is with just how much soil moisture is available.
Knowing the answer to that question will tell you if there’s any opportunity still out there to be captured, says Ryan Hutchison, of South Country Equipment.
South Country’s Crop Intelligence is an app that collects and interprets weather station data by using crop-available moisture, accumulative rainfall, and expected precipitation to model water-driven yield potential (WDYP) throughout the growing season.
“We wanted to develop a baseline of crop-available water,” says Hutchison.
In other words, what does the farmer start with, what does he end up with, and how does that compare year after year. From that data the aim is to help farmers determine if they should make certain management decisions, or simply keep the money in their pockets.
Maximum yield potential is defined by crop variety and genetics, but actual yield is influenced by management and environment, including water availability and use efficiency.
Generally, a moist soil should have about two to four inches of water available in the soil. Most crops use water more efficiently from the upper root zone than the lower root zone.
“Over time, the top 10 cm of our sensors are showing that’s where 39 per cent of the in-season water usage is coming from, so it’s matching what long-term research is showing,” says Hutchison.
Over the last three years, Crop Intelligence has determined that farmers can grow 5.7 bushels of canola and 7.5 bushels of wheat on average for every available inch of water in Western Canada.
Crop differences, soil texture, root development versus activity, rain timing and nutrient distribution all have an impact on water-driven yield potential.
The sensors can tell a lot about plant health from the rooting signature of the crop.
“A minus-eight frost stalls root activity; we can see that in the moisture probes,” says Hutchison, who adds the outcome of being able to forecast yield potential could be making better marketing decisions.
Different crops will have different rooting signatures, that can be detected by the moisture sensors and give an idea of whether the crop is growing as it should be.
How are producers using this data in season?
Hutchison presented some examples of how the data can potentially inform in-season fertility decisions.
A producer with 17,000 acres near Regina has been using Crop Intelligence since 2014. After seeding canola in 2018, the capacitance moisture probes read how much crop-available water was in the soil, which in this case was 7.3 inches. Crop Intelligence then factors in how much rain the farm would normally get from this stage to season end date based on a 30-year average.
“He may have a normal in-season rainfall of eight inches of rain, so he is at 15 inches of available water to grow his crop,” says Hutchison. “Based on water and his management, we’re suggesting he’s got a water-driven yield potential of 15 bushels over his goal of 45 bu./ac. Does he make decisions at that time or not? Likely not, but it’s a report card right after seeding to take a look.”
The farm received timely rain events in May, which added a good yield opportunity, because it was the right time of the year for additional moisture for that stage of the crop.
“He has a chance to look at his field, the uniformity of it, talk to his agronomist and make a decision of whether he may want or may not want to add nutrition for added yield potential,” says Hutchison. “The available water in the soil is actually higher now than 10 days after seeding, so there is more water in the bank to use. He’s sitting at 150 per cent of normal rainfall from the seeding date to that current date. We’ve given him some things that he should already know, but making it easy to see.
“This producer, in consultation with his agronomist chose to top dress some liquid 20-0-0 and some sulphur.”
That upped the yield potential, based on water availability to 25 bu./ac. over the goal.
“It’s about a 70 bu./ac. canola crop, right, based on water and his management practice,” says Hutchison.
At harvest a weigh wagon verified that where the producer applied the additional top-dressed fertilizer, he did get up to 70 bu./ac.
Agronomists making recommendations need to look below the soil, says Hutchison.
“You can learn, regardless of the type of capacitance moisture probe, the net daily moisture changes at each sensor depth,” he said. “When you look at root activity, the sensor at 10 cm in the ground, shows water used during the day. When it gets dark at night, there’s no transpiration so there’s not much change in water use. We’ve spent a lot of time proving that if we suggest a probe is saying there’s root activity, that the roots are actually there doing something.”
Hutchison says the soil moisture probes aren’t new technology, but says this system is looking a bit differently at how to apply the information they provide to practical planning and in-season decisions.