12/9/2022

Can Potassium Fertilizer Rates Be Reduced in Strip-Till?

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Written by Lauren E. Schwarck and Dr. Tony J. Vyn, Agronomy Department, Purdue University

Key Findings

A field-scale experiment was conducted to evaluate potassium (K) uptake and corn yield with banded application in a strip-till system.

Tissue samples taken at the V6 stage showed differences in K concentration between full- and half-rates of K, but not until the second year of corn in the rotation.

Results suggest the possibility of longer-term negative consequences if a reduced rate is maintained over several years.

Objectives

The ability to band fertilizer into the tilled strip where most corn roots are located has led some adopters of strip-till to question if potassium (K) fertilizer rates could be reduced.
Previous research has suggested rate can interact with placement; i.e., lower rates in a band generally have greater nutrient uptake efficiency than a higher rate broadcast (Randall and Hoeft, 1988), but some research has not found rate differences in maize response to K placement (Bordoli and Mallarino, 1998).
There are concerns that reduced rates used over an extended period of time may negatively impact grain yield and plant health.

Purdue University Research

A four site-year field-scale experiment was conducted at the Agronomy Center for Research and Education (ACRE Farm) near West Lafayette, IN to evaluate K uptake and corn yield with full and reduced rates of K fertilizer with banded application in a strip-till system.
This research was led by Dr. Tony Vyn and Lauren Schwarck of Purdue University and partially supported by the Pioneer Crop Management Research Awards (CMRA) Program.

Study Description

Strip-tillage was done in either the spring or fall using an Environmental Tillage Systems 6-row SoilWarrior coulter-type strip-till unit.
Potassium and boron fertilizer (Aspire®, 0-0-58-0.5B) was banded in the strips at rates of 0, 58, or 116 lbs K₂O/acre, representing non-treated, half-rate, and full rate treatments, respectively.
Research alternated between two fields planted in a corn-soybean rotation, with one field in corn in 2016 and 2018 and the other in 2017 and 2019.
Treatments were only imposed before corn in the corn-soybean rotation and applied in the same location in the fields during the corn years of the rotation. This methodology allowed responses to K rates to be observed for both first- and second-year corn.
Whole-plant tissue samples were taken at V6 and ear leaf samples at R1 to evaluate differences in potassium concentration among treatments.
The distribution of plant-available K for each site year and the critical level based on the average CEC for the area currently recommended in the Tri-State Fertilizer Recommendations (Vitosh et al., 1995) is shown in Figure 1. All study locations were close to meeting the recommended critical level based on the CEC; however, a majority of locations had portions of the field area that were considered insufficient.

Distribution of plant available K - ppm - to a depth of 8 inches.

Figure 1. Distribution of plant available K (ppm) to a depth of 8 inches for each site year (minimum, maximum, and average). Orange bars indicate critical values calculated using the Tri-State Fertilizer Recommendation Guide based on the average CEC for the control plots.

Results

Whole-plant tissue samples taken at the V6 stage did not show a difference in K concentration between the 58 and 116 lbs K₂O/acre rates in first-year corn; however, second-year corn showed a greater K concentration for the 116 lbs K₂O/acre rate versus the 58 lbs K₂O/acre rate (Figure 2).
Ear leaf sampling at R1 for both the initial and second years did not show a difference in K concentrations between the intermediate and high rates (data not shown).
Grain yield also did not show a significant difference between the 58 and 116 lbs K₂O/acre rates for either field year, but in the second year, 58 lbs K₂O/acre did not significantly differ from either the 0 or 116 lbs K₂O/acre (Figure 3).
Results from this experiment suggest that, initially, there may be few negative consequences (possibly lower initial K concentration at the beginning of the growing season) to cutting K fertilizer rates when utilizing strip-till in soils that are already near the soil-test K critical level.
However, results also suggest the possibility of longer-term negative consequences if a reduced rate is maintained for several years.
Reducing fertilizer rates with strip-till incorporation (and particularly at rates below actual crop removal) should only be considered when soils are well above the critical levels and when soil and tissue K concentrations are monitored closely to prevent considerable mining of exchangeable soil K supplies.

Average concentration of K in whole plant tissue samples taken at V6 in the first and second year of corn in a rotation with zero, half and full rates of K fertilizer.

Figure 2. Average concentration of K in whole plant tissue samples taken at V6 in the first and second year of corn in the rotation with zero, half and full rates of K fertilizer. Letters indicate significant differences in rate for strip-till (average of fall and spring) treatments within a specific field year at p<0.05.

Corn grain yield for the first and second year of corn in a rotation with zero, half, and full rates of K fertilizer.

Figure 3. Corn grain yield for the first and second year of corn in the rotation with zero, half, and full rates of K fertilizer. Letters indicate significant differences in rate for strip-till (average of fall and spring) treatments within a specific field year at p<0.05.

Conclusions

Strip-till is growing in adoption across the Midwest, and research to identify optimal management using strip-till is ongoing.
As with any tillage operation, strip-till needs to be completed under the correct soil conditions to prevent short- and possibly long-term damage to soil structure.
Reduction of K fertilizer rates when utilizing strip-till showed signs of reducing early-season uptake but did not negatively affect grain yield in the short term.
However, repeated use of that practice, especially at rates well below crop removal (for a rotation cycle) on moderate K testing soils, may still be negative.
More research is needed to better understand the long-term impacts of fertilizer rate reduction with placement in the intended crop row.

References

Bordoli, J.M., and A.P. Mallarino. 1998. Deep and shallow banding of phosphorus and potassium as alternatives to broadcast fertilization for no-till corn. Agronomy Journal, 90(1), 27-33.
Randall, G.W., and R.G. Hoeft. 1988. Placement methods for improved efficiency of P and K fertilizers: a review. Journal of Production Agriculture, 1(1), 70-79.
Vitosh, M.L., J.W. Johnson, and D.B. Mengel. 1995. Tri-State Fertilizer Recommendations for Corn, Soybeans, Wheat, and Alfalfa. Extension Bulletin, 2567, 1-4.