High soil test phosphorus effect on corn yield
Low corn prices have farmers scrutinizing their nutrient dollar return on investment (ROI). A recent University of Nebraska–Lincoln study examines phosphorus (P) application level ROI in continuous corn over six years. The most cost-effective method of fertilizer P use proved to be a P-replacement approach with the P rate equal to the P removed from the previous harvest. The research also found that maintaining soil P availability levels above 25 ppm (Bray-1) wasn't justified
Phosphorus (P) is the second most commonly applied nutrient in corn production after nitrogen (N) for the U.S. Corn Belt and Great Plains. Applied P is not subject to as many loss mechanisms as N, but loss of P to erosion and runoff, leaching to tile drains, and eventually movement to surface waters is of environmental concern. Researchers from the University of Nebraska–Lincoln (UNL) examined P application strategies across 12 irrigated and five Nebraska rainfed site-years with and without tillage. The sites had silt loam and silty clay loam soils with initial Bray-1 P below 11 ppm. All sites had a history of conservation tillage. The research was conducted at Haskell Agricultural Laboratory (HAL) near Concord, Eastern Nebraska Research and Development Center (ENREC) near Mead, and Western Central Research and Development Center (WCREC) near North Platte. The research objective was to determine whether another fertilizer P management strategy is superior to the currently recommended deficiency correction strategy and whether there's a yield benefit to maintaining soil test P above 25 ppm.
This article was adapted from the Soil Science Society of America Journal article, “High Soil Test Phosphorus Effect on Corn Yield.” For the full text, including References (omitted here due to space constraints), view the original article: https://doi.org/10.2136/sssaj2018.02.0068.
Below are the five P application levels and approaches evaluated. The third one proved to be the most cost effective:
- 0P: No P applied.
- UNL_P: P applied according to the UNL deficiency correction recommendation. Corn yield was 3.3% less on average with UNL_P compared with Replace_P and Bray_35 (below).
- Replace_P: P applied to replace P removed in the previous harvest.
- Bray_25: Bray-1 P increased and maintained at 25 ppm.
- Bray_35: Bray-1 P increased and maintained at 35 ppm.
Corn yield was similar for Replace_P, Bray_25, and Bray_35 methods. These had 9.6% higher yields than the control (Table 1). Replace_P was the most cost-effective choice overall. Replace_P had 3.4% and 5.6 bu/ac higher corn yield than UNL_P with 30% or 15 lb/ac more P2O5 applied (see Table 2). It had an agronomy efficiency ratio of 26 lb grain yield increase per pound of P2O5 applied. This method was economically justified only for Bray1-P below 20 ppm. Study results don't justify maintaining soil-test P for the 0- to 8-inch depth above 20 ppm Bray-1 P for high continuous corn yield production. For Bray-1 P above 20 ppm, the P rate should be reduced or Replace_P should be withheld in some years to save money and to avoid excessive surface soil-test P (STP) and P-runoff losses.
Table 1. Corn grain yield (bu/ac) as affected by the year × tillage interaction at Haskell Agricultural Laboratory
| Corn grain yield | |||||
|---|---|---|---|---|---|
| Tillage | 2011 | 2012 | 2013 | 2014 | 2015 |
| bu/ac | |||||
| Disk | 186 | 39 | 156 | 144 | 184 |
| No-till | 168 | 60 | 152 | 105 | 174 |
Table 2. Bray-1 P initially and after five years of treatment application as affected by soil depth, location, and P application according to 0P with no P applied, University of Nebraska–Lincoln recommendation (UNL_P), to replace harvest P (Replace P), and to build and maintain Bray-1 P at about 25 ppm (Bray_25) and 35 ppm (Bray_35). Bray-1 P in 2011 was from soil sampling in the spring before application of fertilizer P practices. Location × P practice × soil depth interaction (LSD0.05 = 11.8)
| Soil depth, inches | 2011 | 2015a | ||||
|---|---|---|---|---|---|---|
| 0P | 0P | UNL_P | Replace_P | Bray_25 | Bray_35 | |
| Eastern Nebraska Research and Extension Center | ||||||
| 0-2 | 10.5 | 14.6 | 29.7 | 32.2 | 48.5 | 48.2 |
| 2-4 | 7.1 | 9.8 | 16.4 | 13.7 | 16.2 | 24.3 |
| 4-6 | 6.1 | 7.9 | 9.9 | 14.4 | 11.6 | 14.3 |
| 6-8 | 7 | 11.2 | 9.2 | 8.4 | 10.5 | 10.2 |
| Haskell Agricultural Laboratory | ||||||
| 0-2 | 17.9 | 14.2 | 78.7 | 59.7 | 68.4 | 86.9 |
| 2-4 | 7 | 6.2 | 19.5 | 13.8 | 18.4 | 28.3 |
| 4-6 | 4.5 | 4.4 | 5.9 | 4.8 | 6 | 6.7 |
| 6-8 | 4.2 | 4.6 | 5.5 | 4.6 | 5.3 | 5.3 |
| West Central Research and Extension Center (WCREC)b | ||||||
| 0-2 | 18.3 | 21.8 | 36.1 | 59 | 72.1 | 77.2 |
| 2-4 | 10.6 | 9.1 | 12.9 | 15.1 | 25.3 | 33.9 |
| 4-6 | 8 | 6.4 | 7 | 8 | 9.1 | 18.2 |
| 6-8 | 6.6 | 5.7 | 6.3 | 7.6 | 8.4 | 11.7 |
Yield Hit without P Applied
Not applying any P (0P) cut corn yields by 9.3% (14 bu/ac) compared with the other P application treatments. Fertilizer P application for continuous corn should use the Replace_P method rather than the current UNL P when Bray-1 P is below 20 ppm for the 0- to 8-inch soil depth. Approximately 26% of plant P uptake appears to be from below the 8-inch depth. Gradual depletion of this P source may eventually require higher STP maintenance at the 8-inch soil depth.
Corn yield response to P practices was similar for all site-years. There were no site-years with greater response to Bray_25 and Bray_35 compared with Replace_P, including with the unusually 2011 cool and wet spring conditions at ENREC.
Latitude and Other Considerations
There's no economic justification for maintaining high soil-test P for corn at the Nebraska sites studied. More northern latitudes, and maybe higher elevations, may justify maintaining high STP (Wagar et al., 1986). At Waseca, MN, corn and soybean yields were 14 and 28% higher, respectively, with Bray-1 P of 25 ppm compared with 7 ppm, coupled with P applied as recommended for the lower STP. On calcareous western Canada soils, large infrequent P applications had higher wheat yields than did annual P applications had higher wheat yields (Wager et al., 1986).
Tillage did not affect yield response to applied P. Over all trials, grain yield was 2.5% higher with disk compared with no-till. Corn grain yield wasn't affected by tillage at ENREC and WCREC, but yield was on average 7.4% more with disk compared with no-till at HAL. This effect at HAL was especially great in 2014 when disk yielded 40 bu/ac more than no-till, but yield with disk compared with no-till yield was 24 bu/ac less in the dry year of 2012.
Phosphorus application increased grain P concentration by 28% at WCREC, 9% at ENREC, and 18% at HAL (Table 3). The tillage × location × year interaction effect on grain P concentration was due to higher grain P concentration with disk compared with no-till in 2012 at ENREC, 2012 at HAL, and 2014 at WCREC while P concentration was low with disk at ENREC in 2015 (Table 3). Phosphorus concentration wasn't affected by tillage with other site-years. The P application effect on grain P concentration was also greater in 2015 compared with 2011, 2012, and 2013.
Table 3. Corn grain P concentration (%) as affected by the location × P practice (L × P), the year × P practice (Y × P), and location × year × tillage interactions (L × Y × T) for three Nebraska locations
| 0Pa | UNL_P | Replace_P | Bray_25 | Bray_35 | ||
|---|---|---|---|---|---|---|
| Location × P practice | ||||||
| Location | ||||||
| ENREC | 0.28 | 0.29 | 0.3 | 0.31 | 0.32 | |
| HAL | 0.25 | 0.28 | 0.3 | 0.3 | 0.31 | |
| WCREC | 0.25 | 0.29 | 0.31 | 0.32 | 0.35 | |
| Year × P practice | ||||||
| Year | ||||||
| 2011 | 0.28 | 0.3 | 0.29 | 0.33 | 0.33 | |
| 2012 | 0.26 | 0.27 | 0.29 | 0.31 | 0.34 | |
| 2013 | 0.26 | 0.28 | 0.3 | 0.29 | 0.32 | |
| 2014 | 0.28 | 0.32 | 0.35 | 0.34 | 0.35 | |
| 2015 | 0.22 | 0.26 | 0.27 | 0.28 | 0.3 | |
| Year × location × tillage | ||||||
|---|---|---|---|---|---|---|
| ENREC | HAL | WCREC | ||||
| Disk | No-till | Disk | No-till | Disk | No-till | |
| Year | ||||||
| 2011 | 0.26 | 0.25 | 0.26 | 0.27 | 0.38 | 0.39 |
| 2012 | 0.42 | 0.39 | 0.27 | 0.23 | 0.23 | 0.23 |
| 2013 | 0.34 | 0.36 | 0.23 | 0.22 | 0.29 | 0.31 |
| 2014 | 0.24 | 0.41 | 0.44 | 0.44 | 0.34 | 0.3 |
| 2015 | 0.25 | 0.26 | 0.26 | 0.28 | 0.28 | 0.28 |
Why Revisit P Rates?
Public scrutiny of P loss to erosion, runoff, and contaminating surface waters brings renewed interest to efficient P management and corn yields. And P removal has increased since many land grant university recommendations were formed. However, high-yielding crops typically have well-developed root systems and mycorrhizal associations for efficient P uptake (Marschner and Dell, 1994; Baligar et al., 1998).
For more than 50 years, fertilizer P recommendations were based upon a soil P availability test (STP) calibrated with crop response to applied P (Olson et al., 1954).
Land grant universities differed in how they interpreted and calibrated results. Some states’ P recommendation strategy is deficiency correction, and others advocate building STP well above the critical value and then supplementing at harvest P-removal rates. This build-and-maintain approach ensures adequate P in exceptional years with a yield benefit from STP above the critical level. It also allows skipping P application when P is costly (Leikam et al., 2010).
The build-and-maintain approach delays returns on the build investment, and more P is lost to runoff, erosion, and leaching into surface waters (Sharpley et al., 2001; Wortmann et al., 2013). In Nebraska and some other states, the build approach had less profit potential than basing P rates on deficiency-correction calibrations (McCallister et al., 1987; Olson et al., 1987; Wortmann et al., 2008).
Applied P efficiency is less than for N during the application year (Baligar et al., 2007). However, the eventual recovery of applied P equivalent can be high in the long term as indicated by soil test P increases with application rates near the P removal rates (McCallister et al., 1987). Applied P contributes to various P pools’ equilibrium.
Text © . The authors. CC BY-NC-ND 4.0. Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.
