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N Needs By Science
Sam Atwell of the University of Missouri extension, explains the procedure that is the brainchild of
Dr. A.J. Foster, University of Missouri agronomist, on mid-season nitrogen application on rice.
Atwell’s specialty is in rice, and Foster’s is with soil fertility and the Greenseeker nitrogen sensor.
Photo by John LaRose, Jr.
Greenseeker Removes Guesswork From Midseason N Applications
BETTY VALLE GEGG-NAEGER
MidAmerica Farmer Grower
MALDEN, MO.
A research trial demonstration of the mid-season nitrogen application on rice was held recently with Sam Atwell of the University of Missouri extension, explaining the procedure that is the brainchild of Dr. A.J. Foster, University of Missouri agronomist. Foster recently transferred to Kansas State University. Atwell’s specialty is in rice, and Foster’s is with soil fertility and the Greenseeker nitrogen sensor.
“We always have to wrestle with what the mid-season nitrogen rate should be,” he said. “So we will discuss remote sensors, one of which is called a Greenseeker, an instrument that measures the red and green colors by sweeping it over the field or plot.”
By comparing the Greenseeker’s color measurements to a camera photo and lab tissue test of a rice crop in mid-season, it is hoped farmers can get a more accurate estimate of the amount of additional nitrogen needed by the crop.
“So normally we put 120 pounds of N on by mid-season and then we sometimes need to add more, and with these tools we’ll try to calibrate them to use in the field where that sensor will tell us exactly how much extra N is needed to bring the crop through the season,” Atwell explained.
The nitrogen regimes in the fields vary greatly. Each variety has a different shade of green, so by calibrating the tools for the needs of the variety and all the different fertilizer regimes, farmers can take them to the field, either by hand, a drone or by putting the sensor on a sprayer in front of a nitrogen applicator, and get a scientific reading of the amount of fertilizer needed.
“The final summary will be to put this Greenseeker on a fertilizer spreader that’s variable rated and, as you travel through the field, the fertilizer will be applied variable rate according to the in-time data from the Greenseeker,” Atwell said. “The fertilizer that’s applied will be the correct rate to fit that particular spot in the field, so it will actually be a variation of N up and down through the field. We know that already by the work that the University of Arkansas has done with the N-STAR program, where they do a lot of soil and plant sampling to get to the same point that we’re trying to do here with the remote sensors.”
Atwell said the Greenseeker measures the red and green infrared, and works basically opposite of the camera. The camera is taking a picture of the green, while the Greenseeker picks up the flat surface of everything in the field. The camera picks up the color like the naked eye sees it, but when these are downloaded to the computer and overlayed, the pattern of nitrogen needs can be seen.
Several different Universities have been studying these sensors for years on all the crops, not just rice. Scientists are calibrating them to read the desired shade of green of each variety and compare it to the hue picked up by the Greenseeker in the field, then prescribe the correct nitrogen needs to the applicator as it moves through the field.
“The ultimate goal is to determine the extra amount of N that is normally needed mid-season to take the crop to maturity,” he said.
“We do know our recommendation to farmers is 70 pounds of N preflood to 120 pounds,” he said. “That’s a big variation. So a farmer has to guess the correct amount, based on history and what his rate needs to be and on the variety he’s growing to get an optimum yield. We don’t want to put too much N on and cause really serious problems, like enhancing diseases, lodging, environmental issues and wasting money.
“In our studies here, we have applied an extra high N rate plot of 180 pounds; they look great today but my prediction is they’ll be flat on the ground by the time we harvest,” Atwell said. “So our goal is to show that we must get our nitrogen rates correct in the field. I’ve been out here for over 45 years in these fields and I’ve run into a lot of times where there’s heavy lodging, sheath blight and other things caused by too much nitrogen; farmers didn’t want to do that to themselves and they certainly didn’t want to spend the money on fertilizer, but they thought that their soil needed it. That’s what these tools are for, so what we’re going to do is put a basic amount of fertilizer down based on where we think we need to be, a minimum amount, and then shortly after flood we’ll use the sensors and photograph the fields to determine the extra amount of N we need to drop in on the crop to take it to maturity.”
Soil sampling is one way to gauge the nitrogen for the crop, but today’s method is to get the plant to speak for itself.
“The N-STAR program in Arkansas uses extensive, two feet deep soil sampling, even in the fall and winter,” he said. “They’re sampling rice plants, taking them to the lab and analyzing them for the amount of nitrogen in that plant right at that time for mid-season N applications. The lab has the calibration to determine the plant needs of that variety. The comparison is made and the recommendation is relayed to the farmer.
“We’re trying determine the plant needs without sampling in mid-season; we still need to do soil sampling to get the basic levels, but to determine the extra amount of N needed mid-season, we’re hoping that these gadgets, remote sensors and cameras, will assist us and give us the right reading that we want.”
While the lab runs the tests as quickly as possible, the Greenseeker can eliminate a lot of footwork, extra steps, overnight shipping and efforts to get good samples.
“Ultimately we hope to get to where we calibrate all these varieties, get the color schemes made up and give farmers a green colored check point, benchmark if you will, to go to so they can match their color to provide the right rate of N,” Atwell said. “Hopefully, the Greenseeker will tell us in real time the minimum fertilizer rate to still get the maximum yield. That’s the goal.
“I guess the take home message has three elements to it: One is keeping your yields where they’re supposed to be and moving them up; two is environmental, you won’t be applying too much fertilizer which could leave the field and enter the streams; and three, the economics of putting N out, you’re not damaging the environment, you’re not having to undo some things with lodging and all kinds of other things because of excessive N use,” he summed. ∆
BETTY VALLE GEGG-NAEGER: Senior Staff Writer, MidAmerica Farmer Grower
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