Research HighlightsTesting Phosphorus Rates for Better Soil Fertility in North Dakota
In this article, you’ll find details on:
- Researchers are testing different application rates on soils that are low and very low in phosphorus (P) across North Dakota.
- Soybeans need P to help in plant development, especially during seed filling. Knowing how much to add to the field can make a difference.
- After a second season of tests, scientists will have a more accurate picture of proper P application rates, which could help save money or improve crop yield.
By Carol Brown
Soybeans need nutrients including nitrogen (N), phosphorus (P) and potassium (K) to thrive. In North Dakota, soil-test phosphorus levels are generally low or extremely low. Farmers can apply P to increase the soil test values, which might be favorable for soybean growth, but P application rates for soybeans haven’t been reviewed for some time.
Lindsay Malone, an assistant professor at North Dakota State University’s School of Natural Resource Sciences, is conducting P rate tests on soybeans at NDSU Research Extension Centers (RECs) in Minot, Dickinson and Carrington, and on farm fields near the NDSU campus in Fargo. The project is funded by the North Dakota Soybean Council.
“Last summer we conducted two trials in four regions on low and very low P soils with five different rates applied. Each trial was on a field at a REC as well as on cooperating farmers’ fields in each area for a total of eight trials,” Malone explains. “We recorded soybean yield as well as soil P values prior to fertilization and then again after harvest. We hope our outcomes will result in improved P rate recommendations for North Dakota farmers.”
Soybean P uptake increases during the plant’s reproductive stages and seed fill, therefore having adequate amounts of P available for the crop is crucial for seed production. From the biochemical perspective, P is used for many things, Malone says. It is a major component of DNA, a structural component in plant cells, and is essential for chemical energy transfer in nearly all plant processes.
Phosphorus Depletion History
“Dr. David Franzen, an NDSU extension soil specialist, has collaborated with me on this work,” comments Malone. “He has done extensive research on the history of the state’s soil erosion, which includes the loss of topsoil and its nutrients over the last century and a half.”
When settlers began to farm in North Dakota and the land was plowed, two P-related activities took place, according to Franzen1. In the late 1800s, settlers collected the many buffalo bones found on the land they intended to farm. They sold tons of these bones to the eastern part of the country for fertilizer and other products, which helped the settlers earn income as they established their farms. The scavenging of bones from the land reduced the phosphorus going back into the soil — the equivalent of two years of applied P at present fertilizer rates used by farmers.
In addition to the export of P from the land through bone sales, the wind began to erode the plowed fields, taking nutrients with it. Dust storms happened regularly until the agriculture industry deliberately worked to find management practices that kept the soil covered, including no-till, strip-tillage and cover crops. Today, farmers in the state use these methods to slow wind erosion and keep nutrients on the land, but wind erosion remains a major issue in the region.
Determining Phosphorus Application Rates
“Historically, researchers evaluated different P application methods and I think the recommendation rates currently used were based on those studies,” Malone says. “We need to revisit and refine appropriate P application rates.”
Malone and her graduate student, Dayne Tallier, compiled the results from all the sites last year, and they will repeat the experiments again this 2024 crop year. At the end of the project, she and her team hope to recommend profitable application rates of P for deficient soils.
“When looking at phosphorus rates, farmers need to consider their entire cropping system, as there are several crops that don’t need a lot of P, nor do they respond to P fertilizer additions each year,” Malone says. “We hope by testing the different P rates, we can help farmers apply rates that will help their bottom line either by increasing yields or reducing unneeded input costs.”
A related study by colleague Greg Endres is looking at phosphorus application and residual amounts in a corn-soybean rotation, which can also affect a farmer’s application rates and timing.
Farmers can test their soils to find out nutrient levels including phosphorus. Malone says testing time for phosphorus is best prior to planting in the spring or in the fall. She specifies that farmers don’t need to test every season, but if they do, it should always be at the same time of year.
“I’m excited about what we’ll find, as North Dakota soils vary as you travel east to west,” she comments. “Between the five application rates, we hope to build a response curve for phosphorus application, which will help farmers refine their nutrient applications.”
1The History of Soil Erosion in North Dakota – YouTube presentation by Dr. David Franzen
Published: Aug 26, 2024
The materials on SRIN were funded with checkoff dollars from United Soybean Board and the North Central Soybean Research Program. To find checkoff funded research related to this research highlight or to see other checkoff research projects, please visit the National Soybean Checkoff Research Database.
