February 14, 2019
After Dr. Don Baker received his degree from Cornell University in 1962, the USDA-ARS at Mississippi State University had just opened the Boll Weevil Research Laboratory. There was a vacant staff position for a soil scientist. Baker applied and got the job. When he asked what he could do to help eradicate the evil weevil, the entomologist in charge of the lab said, “You don’t need to do anything. We’ll have the boll weevil eradicated in five years. Continue your research in crop canopy photosynthesis.”
So Baker began studying crop canopy light interception and photosynthesis. Having grown up on a farm, he wanted to render basic science in plant physiology useful in production agriculture — which, even today, is not commonly done. He saw the value in evaluating and quantifying how various physiological processes result in crop growth and yield. Two such processes are the exchanges of carbon dioxide and water vapor.
“We set up a series of chambers called Soil-Plant-Atmosphere-Research (SPAR) units that allowed us to control the plant’s growing environment, including atmospheric carbon dioxide and the measurement of plant process rates including photosynthesis, respiration, transpiration, growth, and development,” explains Baker. “We were able to quantify the way fruit production on a plant slows down when an imbalance occurs between the supply of sugar from photoshythate and the demand from the growing points on the plant — a phenomenon called cutout.”
They recorded the rate of fruit shed in response to “source/sink” imbalance. “Plant development is often confused with plant growth,” adds Baker. “Growth is the increase in plant dry matter — if it gets bigger or heaver. If a plant, say a cotton plant for instance, gets a new node, that’s development.”
Baker began working with producers across the Mississippi Delta to apply his theories. He knew the two primary physiological processes impacting crop growth and yield were the exchange of carbon dioxide and water vapor.
“Water vapor comes out of the plant through stomata. Both water vapor and carbon dioxide enter the plant through the wet surfaces of the cells inside the leaves and are absorbed through the cell walls into the chloroplast,” explains Baker. “They are then combined to make sugar which is converted to starch — and in the case of cotton, cellulose, which is what turns into fiber.”
Leaves are “heliotropic” and follow the arc of the sun’s movement, capture carbon dioxide, exchange the carbon dioxide for water vapor, and so begins the process of plant growth. “Fruit production on a plant slows down when an imbalance occurs between the supply of sugar from photoshythate and the demand from the growing points on the plant,” adds Baker. “If that imbalance is severe enough, the plant will balance its fruit load by shedding the fruit it can’t support.”
Cotton starts developing slowly, but by the time it hits the eighth or ninth node, it really takes off. “Eventually, growth levels off because each one of the growing points on the plant has a certain demand for dry matter, and when the total demand exceeds the supply, delays kick in and nodes form more slowly until cutout occurs,” says Baker. “All these physiological process rate responses were incorporated into predictive models.”
Baker and his team began working with Extension specialists and cotton producers across the Cotton Belt to apply these models as crop management decision support systems. Beyond their value in crop management, these models are useful in predicting the effects of climate change (including higher atmospheric carbon dioxide concentrations) on crop yield and water use.
The SPAR Facility
Today, the North Farm annex of the Plant and Soil Sciences Department at MSU maintains 10 SPAR units. Dr. Raja Reddy, a research professor, oversees the facility. “There is nothing like this anywhere else in the world,” says Reddy. “Our goal is to quantify or add a value to data that can then be used to better understand what influences the environment has on any specific crop.”
Ambient noises from the control room inside the North Farm facility resemble sounds emanating from an operating room, but those sounds are coming from the 60 channel switch boxes controlling each of the individual environments within each SPAR unit. Desktop computers are interfaced with controller mechanisms, each recording 500 different pieces of information every 15 minutes, 24 hours a day, thanks to more than 200 crop monitoring sensors and instruments in the units.
“When I was in graduate school at Cornell, the outside carbon dioxide concentration level was around 310,” remembers Baker. “By the time I retired in 1980, it had risen to 380. Today, it’s around 410.”
Baker knows and wants to emphasize that there is a good side to increased carbon dioxide concentration — higher possible yields for crops. “At higher carbon dioxide concentrations, plants grow and yield much better,” adds Baker. “With these closed-chamber experiments Dr. Reddy is continuing today, we can document proof of that and quantify it as well — which is very important when we give this information to our Extension people who can then relate it to our farmers and policymakers.”
The beauty of this research lies in the ability to look at past weather data, and say with confidence that if weather is similar in the future, a grower might expect a crop to grow a certain way — based on what the models simulated during that weather phase. “Through the use of the models, we can also predict when there isn’t enough of any one particular nutrient,” adds Reddy. “That will allow a producer to know when a crop needs to be side-dressed to counter a nitrogen deficiency, or when to irrigate to avoid drought stress.”
The computers controlling the SPAR units are essentially playing a game, adding or taking away any certain input until the crop no longer responds to it.
Global Food Supply and Policy
Our world’s population will continue to increase. It will increase more rapidly in certain countries than in others. To meet the demands of that rising population, crop yields must increase as well. “A rising population will incorporate diet shifts, higher earning capacities, and increased use of biofuels,” says Reddy. “Based on past trends, a projected rate of yield increase is around 1.2 percent each year, but to meet food demand in the future, we’ll need to double that yield increase rate.”
This problem is not just an agricultural problem, it is a big political concern as well. This type of research can be used to add substantive proof for the need to increase crop yields and help guide policies that will allow and encourage farmers to meet that demand. “By using these SPAR units, we can do in 18 days what it would take three years to do in a field research setting,” says Reddy. “I can show breeders what varietal lines hold the most potential for moving forward and cast aside those that do not.”
Predictive modeling is being used in many applications. It can be used to help a producer decide what varieties to choose for the growing region where the farm is located, and offer a much better understanding of what yield to expect from that variety when it comes time to harvest each year’s crop.
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