Put It Down To Get It Up!

Many areas in the Northern Great Plains are considered deficient in P₂O₅, where soil samples are commonly taken at depths of 6”. When looking at adequate levels, the results are often represented in ppm, or parts per million. This is meant to use as a gauge, not as an absolute value. Below is a guide to soil tests and ratings.

The Bourgault farm is situated near St. Brieux Saskatchewan, which is located in a pocket of Grey Wooded, sandy loam soil. These types of soils are typically low in soil phosphorus, with many soil test levels coming in with single digit ppm. A composite sample was taken to a depth of 8” in the spring of 2023 on a fi eld on the Bourgault farm with a result of 5 ppm.

However, the core 8” sample was also segregated into depth layers and tested separately. Below is the breakdown of the results.

The highest concentration of phosphorus was found in the top 2” of the soil, and declined rapidly as it went down to 8”. The reason for this layering of differing concentrations, also known as stratification, of phosphorus in the soil profile is due to the properties of phosphorus itself, as well as the history of the phosphorus application. There are several factors that have played a role:

• Phosphorus does not move very far in the soil, perhaps an inch a year,
• The most common application of phosphorus over the years has been to apply all phosphorus close to the seed in the seed row, typically 1-2” in the soil,
• The roots are capable of pulling phosphorus from deep in the soil profile, where it is either taken off in the grain, or it is deposited on the soil surface as crop residue,

• Phosphorus is taken up by direct contact with plants roots, which needs soil moisture to take in nutrients. As the soil dries out during the summer, or in a drought, the top of the soil profile is the first to dry out, which is where the majority of the phosphorus is located, leaving it stranded.

The result of these factors is a higher concentration of phosphorus in the top few inches of the soil profile. This compounds the issue of having low soil test phosphorus, which uses composite depth sampling because a good portion of that already low amount is stranded in the top 2” of the soil if it dries out!

A multi-year trial was established on the Bourgault farm in the spring of 2023 to test the effects of a deep application of phosphorus. The soil test shown above was from the area this trail was established on.

TRIAL LAYOUT:

• The standard seeding practice was done perpendicular to the direction of the treatments.
  • A TriMax™ system was used where seed was placed on its own, 50 lb of P₂O₅ was placed in a side band, and 125 lb of N was placed in a mid row band.
• Four Treatments were established:
  • Control,
  • Deep Application (5” depth),
  • Broadcast (No incorporation),
  • Worked Only (5" depth - same as Deep Application but without phosphorus application to determine effect of increased mixing of concentrated top layer).
  • Treatments were 420’ long by 35’ wide.
  • To complete the treatments, a Bourgault L7550 Air Cart was coupled with a SPS360 equipped with an air kit to apply the phosphorus fertilizer on May 5, 2023.
  • 192 lb of 11-52-0 was used in the Deep Application and Broadcast Treatments equating to 21 lb of N and 100 lb of P₂O₅.
  • Treatments were swathed and harvested with weights collected via weigh wagon and equalized to 10% moisture based on individual samples taken.

OBSERVATIONS:

As the year progressed, it became evident there were differences amongst the treatments. At the end of June there were flowering differences where the BROADCAST treatments were first into flower. By mid July, as seen below, the DEEP APPLICATION treatments were showing prolonged flowering.

RESULTS:

There were significant differences in yield between the treatments, where the deep application of phosphorus had a significant 6.8 bu/acre increase in yield over that of the control. The broadcast treatment also had a 3.7 bu/acre yield increase over the control.

ECONOMICS:

Below are the additional costs and revenue of each treatment compared to the control (does not include the cost of the standard seeding practice).

SUMMARY:

With the significant increase in yield in the deep application of phosphorus, it’s safe to say that the canola crop utilized the fertilizer from being placed deeper in the soil. One valid argument is that there was also nitrogen being applied with the phosphorus fertilizer, which may have contributed to yield. The fact that the deeper application of phosphorous fertilizer produced a significant increase in yield compared to the control or the broadcast application shows a definite benefit to this treatment.

When looking at the economics of this trial, there was no benefit to putting down the extra fertilizer once the additional pass and cost of fertilizer was calculated and weighed against any increase in yield. However, this was in the first year of this multi-year trial. Next year wheat will be seeded perpendicular to the fertilizer treatments and yields taken again. With phosphorus being a relatively non-mobile nutrient, it should theoretically still be available to the following crops. The treatments in the following years of this application won’t have any additional cost and any increase in yield will be all profit.

Bourgault offers tillage equipment such as the 9500 chisel plow or a SPS360, like the unit used in this trial, capable of applying nutrients when coupled with an air tank. Another option to apply phosphorus deeper in the soil profile at the time of seeding is through Mid Row Bander® or Mid Row Shank™ fertilizer applicators. A split application with some in the seed row and the rest in a mid row band allows for two feeding sites, and puts phosphorus at a greater depth in the soil.

By Curtis DeGooijer, PAg, CCA Agronomy Team Leader