It can never hurt to review the basics when it comes to crop fertility. No matter what’s going in the ground, whether it is corn, soybeans, sorghum or cotton, it’s important to be aware of the critical growth stages of the crop.
Dorivar Ruiz Diaz, professor of soil fertility and nutrient management at Kansas State University, said several key nutrients in crop production—nitrogen, phosphorus, zinc and sulfur—should always be monitored. But monitoring and managing can only be done if there’s proof of what’s in the soil.
“As a soil fertility specialist, I always want to emphasize collecting good soil samples,” Diaz said. “There are different key points we have to keep in mind for sampling and again, we’re talking about (getting a) good quality sample that we need to collect to generate good information.”
Nutrient management decisions need to be based on the soil test results for fertilizer rates, and having good data is essential in making the most informed decisions. For example, K-State recommends collecting soil samples at 6 inches for immobile nutrients. Some labs ask for 8 inches.
“I’m fine with that as long as it’s consistent,” Diaz said. “Follow through with that lab to get the right recommendation based on that sampling depth.”
Immobile nutrients—phosphorus, pH, zinc, organic matter—are in that surface sample. A profile sample will give chloride and sulfur readings. Those are often mobile and can move within the profile.
“There is a lot of value to collect that profile soil for those mobile nutrients,” Diaz said.
In western Kansas dryland situations, he said losing nitrogen to leaching is not a huge concern.
“Most years we’re going to be able to maintain good levels of nitrogen in the profile so, again collecting that profile can give us a lot of good information,” Diaz said.
Many times Diaz gets the question, “What about more shallow sampling?” The only situation where this would be relevant would be where low pH is a concern.
“We do have some situations already even here in western Kansas,” he said. “I hear some long term no-till fields have started to develop low pH near the surface.”
What happens in that case?
“That would be the point where we want to collect a more shallow sample at 3 inches to have better information in terms of what kind of pH we have there and especially, again, if you’re thinking about applying lime in some of those situations,” Diaz said.
Collecting multiple cores is important to avoid any of the issues when there is variability in the field.
“Try to capture that variability and have an accurate average and mean value for that particular field,” Diaz said. “But, again, always maintain that consistent sampling depth across the entire field.”
It gets a little challenging collecting samples by hand, but with modern equipment it can be done easily and consistently.
Once good samples are collected and tested, management decisions can be made with the information on hand. For example, nitrogen and phosphorus can be limiting nutrients.
“You have to watch those very closely,” Diaz said. “Especially, again, when thinking about return on investment. That’s really the key here.”
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Another two nutrients that are becoming an issue in some cases, chloride and sulfur, both depend on the particular field. Diaz said don’t be too quick putting those in as part of a specific fertility program
“We have to be kind of looking at specific fields that may be benefiting from some of these,” Diaz said. “Of course soil testing is a key tool that we have to do a good job there and basically good information to make good decisions there.”
When issues arise, like those with iron chlorosis in some fields in western Kansas, there are now more tools available to help. Things like improved crop genetics and specific fertilizers can help a high pH soil.
“We have to make sure and we do our research and benefit from some of these products that we have. “
Thoughts on seed
Lucas Haag, Northwest Area agronomist at Northwest Research-Extension Center in Colby, Kansas, said there are a number of things to consider before even getting the crop in the ground. First is row spacing and appropriate seeding rates.
“We get into a lot of conversations about water use and how do we maximize, how do we match water use in order to maximize yields,” he said. “I think this is a common misconception we fall into, and especially when we think about seeding rates.”
For example, if there’s a plant in the field using 1,000 grams of water per day, then two plants must use 2,000 grams. Haag said that is not necessarily true when thinking about field crops. Crops in rows should be considered a community. Water usage is driven by light interception and as there gets to be more plants in the community, leaves don’t get as much sunlight as they want.
“As that canopy starts to close, the per plant water use doesn’t remain constant,” Haag said. “It’s really driven by not how many plants you have out there but by the light you’re intercepting.”
If you’re thinking about cutting seeding rates to save water, think again.
“There’s some truth to that,” Haag said. “But that benefit only exists up until the point where you’ve reached full canopy. If you’re using a full canopy you’re using the same amount of water regardless of how many plants you’ve got out there.”
Crops are either water-limited or light-limited, depending upon seeding rates. For example, if a farmer has a 600-gallon-a-minute well and went out and planted 15,000 seeds of corn or sorghum, they’re likely going to end up being light limited because there’s not enough plants out there.
“We’re leaving yield on the table because we’re not matching our light interception to the water supply that we have,” he said. ‘We’re hoping to find this optimal here.”
When on dryland, if a crop gets planted too thick or rows are too narrow, then water becomes limited.
“We’re intercepting more light than we have water to burn to go along with that,” he said. “So we’re trying to figure out where we’re at on this continuum and matching the resources that we have.”
Haag asked, “How does all this play into management?”
His answer was row spacing.
To explain, he pulled out some old data. In a two-part study, one had two fairly stressful environments with a range of seeding rates, and was planted to sorghum in this case. Yields were around 40 to 80 bushels ranging from 10,000 to 30,000 seeding rates. In the other slightly higher yielding environment, 130-to 160-bushels per acre sorghum was expected. In the higher yielding environment, the lower seeding rate did see some advantages over higher rates.
“We’ve got to match our light interception to our yield potential,” Haag said. “Which for us is going to be water. That’s our limiting factor.”
When moving on to narrower row spacing, Haag questioned the advantages. The biggest one was weed control.
“That competitive effect. The ability to choke out weeds,” Haag said. “It doesn’t replace a herbicide but it certainly can help us. Especially late in season, trying to suppress some of those palmer (amaranth) and restrict their growth a little bit.”
Usually when there’s an advantage to narrow rows, it’s when yield potential was above 70 bushel for sorghum.
“So if you’re in an environment, or we think about irrigated or limited irrigated production, where you’re consistently shooting above 70 bushel, our data would suggest there’s likely an advantage to narrow rows,” he said. “Certainly the higher your yield potential, the greater that advantage is going to be or the more probable it is that you’re going to see a positive response to that.”
He’s seen a similar response in soybeans with narrower rows.
“If you have narrower rows maybe we’re doing a better job,” he said. “Hopefully we’re growing a bigger plant, setting more pods, and with more pods you end up with a little smaller average seed size; because you’ve got more seeds per plant.”
Kylene Scott can be reached at 620-227-1804 or [email protected].
