Climate change will be an interesting topic over the next several years, Jerry Hatfield says — not because the government says it is, but because it will impact farming like never before. Weather variability is the biggest problem, the plant physiologist from the National Soil Tilth Research Laboratory in Ames, Iowa, says.
“We are already seeing extreme weather variability in the eastern United States and it’s beginning to move west,” Hatfield says. “We are seeing a change in the frequency and the intensity of precipitation, but little change in the overall amount.
“We saw this last year in central Iowa with an inch of rain in June and July before we got 18 inches in August, which came in three storms of 6 inches each.
“The rainfall distribution we see today in the growing season is not what we’re used to farming with. That offers new challenges of how we manage our ag system tomorrow.”
In addition, Hatfield says we are currently in a warming cycle that will place more stress on farming systems.
“If we don’t have the water available to that plant, these warming cycles will cause even more stress on plants, he says. “And if it occurs during the reproductive stage, it will cause a real impact on yield.”
Finally, Hatfield points out that carbon dioxide levels are increasing in the atmosphere, which is not bad for plant growth. However, he points out that you need very little water stress for plants to use carbon dioxide.
Water Is Vital
According to Hatfield, water is required for optimum plant growth and yield, and that requires a soil system that can store water. Temperature extremes can negatively impact both plant growth and soil microbial systems, but water is the most important variability.
“Unless we have soil under proper conditions, we will be more subjective to the extremes that occur in the environment,” Hatfield says.
Early in the growing season, water is typically not a limiting factor for the growth of the plant, and plant growth is extremely uniform. But variance typically begins in June and continues through to harvest.
“When we move into the reproductive stage, it’s our biggest water-use season and we are relying on what is stored in that soil profile,” Hatfield says. “We are dependent upon one rainfall event to another unless we have the proper water stored in the soil.
“How many people have too much money in their checking account? Think of water in the soil in the same way. When you have too little water in the soil, it’s like going from paycheck to paycheck. Without proper water in the soil, you are dependent upon rainfall-to-rainfall events.”
Hatfield says yield patterns within fields are caused by lack of soil water during the grain-fill period. The yield variation within a field can be as large as 100 to 150 bushels per acre due to the water-holding capacity of soils. And unless you can irrigate, or afford to irrigate, you can’t control the weather.
Organic matter is important since it increases the capability of the soil to hold water like a sponge, Hatfield reports.
“We are organic-matter poor in our soils,” he says. “We need to build them up because it allows us to hold more water. It’s like increasing the size of your checking account. It basically prevents that soil from allowing the water to fall through it.
“Sandy soils have little water-holding capacity. Water runs rights through it. Add some organic matter to those soils, and you’ll see a dramatic response in the water-holding capacity of that soil.”
Recovery Through Residue
Crop residue holds the key to changing the overall soil structure, Hatfield says.
“It increases the infiltration rate because organic matter begins and the residue buffers the soil from the beating it can take from raindrops,” he says. “It acts as a momentum absorber. This happens immediately.”
Changing the water-holding capacity with residue may take 3 or 4 years, Hatfield says, but it’s important to note that it increases the biological activity that improves soil quality and reduces compaction.
“When we layer residue rather than have a bare surface, we change how much energy is absorbed from rain events, and the amount of water that is evaporated back into the atmosphere,” Hatfield says. “Think about residue on the soil surface just as if you were wearing a coat on a cold winter day. That coat is a barrier of resistance that changes the rate of what the cold air does to you.
“It’s the same with residue. If you take on an inch of water, the evaporation rate is reduced because of residue. You can take care of a half to six-tenths of an inch of moisture that goes back out with bare soil. We maintain that soil surface and manage evaporation rates that are very low under residue.
“If we have smaller rainfall events, such as a quarter to a third of an inch, the moisture evaporates quickly with bare soil. But in no-till, it moves down into the soil and becomes available to the soil.”
Use Water Efficiently
In trials conducted in Iowa’s Clarion soils, which are considered poor soils for water-holding capacity, Hatfield sees dramatic yield swings due to poor water-use efficiency. In fact, he pointed to one field trial that showed 20 inches of water use produced 318 bushels per acre, so he’s confident that efficient use of water can lead to high yields.
“We see a lot of poor yield points in our data with Clarion soils. That’s because they are running out of water during the grain-filling period,” Hatfield says. “They grew very well up to tassel. Due to a lack of rainfall and to keep that corn plant growing, they have suffered a lot of yield loss.
“Plus, we are not getting the value of that nitrogen we applied because we ran out of water. We can have a yield potential above 350 bushels per acre in these fields, but when we suffer water stress, we can watch kernels disappear from week to week, or they become very small. In poorer soils, we can lose 150-plus bushels in the grain-filling period.”
When comparing corn plants in no-till vs. conventionally tilled fields, researchers consistently find that plants in conventional-till fields have less available water. They see them shut down earlier in the day, with leaf curling sooner, under stressful conditions than plants in no-till fields.
The water-holding capacity of no-till fields, and the protection offered by crop residue, places plants under less stressful conditions.
When plant stands are measured early in the season, Hatfield finds more variability in plant spacing and population with conventional till than no-till.
“Every time you till in the spring, it’s roughly a half-inch of water that has evaporated back into the atmosphere,” Hatfield says. “That half-inch doesn’t come from the whole soil profile. It comes from the top several inches, and it increases the risk of poor early stand establishment.
“We make stand establishment more risky when we cultivate because it dries out the environment.”
He adds that it’s not uncommon to see yields in a 17.5-foot row of corn that’s been conventionally tilled to have yields ranging from 20 to 400 bushels per acre.
“That’s how variable we make yield by drying it out a little bit or creating a sod clump that interferes with plant establishment,” Hatfield adds. “A uniform seeding environment is very important.”
In fact, no-tillers will see half the yield variation of conventional-till fields, due to more moisture being available during the growing season in drier conditions, says Hatfield. Those trials were conducted in areas of 35 to 36 inches of rainfall annually.
“We lose 50 bushels per year on short-term water stresses that we don’t even see occurring to the plant with the eye,” he says. “You see the plant shut down its photosynthetic ability and that impacts yield. If we can change the water dynamics, that’s an extra 50 bushels per acre. At $5 per bushel, that’s real money.”
What this proves, Hatfield says, is that growers who argue that they need to dry out their fields in the spring with cultivation in order to plant need to rethink what they are doing to the water-carrying capacity of their soils throughout the growing season.
“I often hear that I can’t have crop residue because it reduces the ability of the soil to dry. I can’t get out there. I can’t seed on time,” he says. “This is a management opportunity and not a barrier to no-till.”
Moderate Soil Temperatures
Placing a layer of residue on the soil surface creates more moderate and fewer extreme temperatures. In previous work he conducted in Lubbock, Texas, Hatfield said temperatures in the top half-inch of soil could go from 40 F in the morning to 140 F by the afternoon.
“It’s not real comfortable walking across that field in bare feet and realizing that the soil temperature is coming back up the plant and causing stress on the plant, influencing it negatively more so than positively,” he says.
Residue in a no-till system acts as a temperature buffer for the soil and helps create an environment that allows the biological system of the soil to work.
“If a conventionally tilled biological system belonged to a union, it would sue you for unfair practices,” Hatfield says. “It’s cold, it’s hot; it’s wet, it’s dry. Think about how that soil biology is screaming at you because it can’t work in those conditions.
“When we went to no-till in those sandy soils of Texas, in just 2 years we saw a change in soil color and structure of those poor soils.”
The biological activity of no-tilled soils promotes stable soil aggregates that can withstand the forces of nature or tillage, he adds.
No-Till Provides Buffer
With the buffer that crop residue provides in no-till soils, Hatfield says no-tillers’ fields will be better able to withstand the severe weather situations we’re bound to see in the coming years.
“Better infiltration will enhance water availability. You’ll decrease soil water evaporation and increase the water-holding capacity of your soils with no-till,” Hatfield says. “And more water will equal higher yields.
“No-till offers the potential to reduce the impact of climate variation. And it will vary over the next 10 to 20 years. How we manage to get there will be interesting.”