Skip to content
Grain Farmers of Ontario is the province’s largest commodity organization,
representing Ontario’s 28,000 barley, corn, oat, soybean and wheat farmers.
Search
Ontario Grain Farmer Magazine

Long-term strategic management of P and K: Phase Two

Principal Investigator: David Hooker1 and Horst Bohner2

Research Institution: University of Guelph1 and Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) 2

Timeline: January 2018 – February 2022  

Objectives:

  • To determine the economic responses of various starter fertilizer strategies in corn, soybean, and wheat performance on side-by-side plots with inherently varied background soil test phosphorus (P) and potassium (K) levels and other soil health indicators
  • To determine whether economic responses are maintained with built P and K fertility compared to crop responses achieved in Phase One of this study. (Relatively high applications of P and K were applied during Phase One for build-up purposes.)
  • To determine if soil test P and K levels stabilize at moderate-high levels following several years of high rates of P and K for buildup purposes, and how much fertilizer P and K are needed to raise soil test P and K by one ppm, based on fertilizer application rates and crop removal estimates.
  • To construct a database to improve understanding between crop removal (grain) vs. contrasting background soil test P and K and starter treatments, and to address environmental sustainability; use the Phosphorus Loss Assessment Tool (updated P Index) for Ontario (PLATO) to further develop the tool and to evaluate risk for P losses.

Impacts:

  • Impact to Growers. Phase II will enable an economic comparison of sufficiency (current OMAFRA) vs. build & maintain fertilization approaches during a ‘drawdown’ phase across various environments. This information will be used to potentially update the official fertilizer recommendations for corn, soybean, and wheat, pending review and recommendations by the Soil Management Research Committee (SMRC). This research will provide farmers with better guidance on more optimal approaches for managing P and K on a site-specific basis, which may also depend on soil health indicators.
  • Impact to Environment. If the results show that the build & maintain approach is superior to the sufficiency approach, technology transfer activities will emphasize the role of nutrient application timing and placement on the potential for environmental losses. Data were generated to validate the P-index through PLATO. By following best management practices with respect to timing and placement, some of the increased environmental impact of maintaining higher soil test levels can be mitigated by building up P and K and maintaining levels through sub-surface placement of starters.

Scientific Summary:

Phase One of the long-term project was established on 4 sites between 2010 and 2012, depending on the site, to compare various starters (some starter treatments meet OMAFRA sufficiency recommendations) on a patchwork of various background levels of P and K, and to compare two fertilizer strategies: the sufficiency approach (current OMAFRA recommendation) vs. a build & maintain approach. Remarkable grain yields of all 3 crops were achieved with the build approach with moderate background soil test P and K levels (P<0.001). The high yields could not be achieved using any starter alone, even when some starters exceeded the OMAFRA sufficiency recommendation. This is strong evidence that the current OMAFRA recommendations are outdated. Due to the long-term nature of building soil tests over several years, crucial questions remained unanswered. Were yields responding to the “build phase”, where P and K may be more extractable with new fertilizer applications? Why did it take less P and K to increase soil tests by one ppm than was anticipated? These questions needed to be addressed before different P and K management strategies for the province are considered.

This project, namely ‘Phase Two”, is the next phase – a drawdown phase – which enabled an economic comparison of sufficiency and build & maintain fertilization approaches. It will provide farmers with better guidance on more optimal approaches for managing P and K. During this phase, the only fertilizers applied were the starter treatments; background levels of P and K were established in Phase One. Very few datasets exist in North America that examine the drawdown phase. There are also few datasets in existence where fertility responses consider the effects of soil health processes. Four field sites were uniquely established for side-by-side comparisons. If the highest economic yields are still produced with moderate background levels of P and K during Phase Two, then this evidence would favour the build & maintain approach, rather than simply being an artifact of the buildup phase in Phase One. This will have implications on site-specific management. Soil health influences on fertility responses were also investigated. Phase Two also tested the relationship between the amount of P and K needed to increase soil tests by one ppm (important for the economic analysis of building), tested the new P-index tool (PLATO) for environmental sustainability, and updated current data on crop removal and uptake. It should be noted that the opportunity to compare starters across a patchwork of various levels of background P and K in side-by-side plots is rare in North America.

Results

In 2018, a ‘drawdown phase’ was initiated, which validated crop responses of the sufficiency and build/maintain fertilization approaches. During this phase, the only fertilizers applied were the starter treatments; the build levels of P and K were established in Phase One. Very few datasets exist in North America that examine the drawdown phase in side-by-side plots. During the Build Phase, it was determined that corn, soybean, and wheat yields using higher-rate starter (at approximately replacement rates) were 10, 3 and 11 bu/ac higher, respectively, in the P+K built regime, compared to the no-build regime. The drawdown phase showed that yield responses to built P and K levels were indeed lower compared to those in the build phase, so the crops were responding to the applied fertilizer that was used to build P and K fertility levels in addition to the P and K starters close to OMAFRA recommended rates according to soil test levels. In the drawdown phase, corn, soybean, and wheat yields were numerically 5.9, 0.8 and 6.7 bu/ac higher, respectively, in the P+K built regime with replacement-rate starter compared to the same rate starter that was applied in the no-build regime. Because the starter rates in the no-build regime tended to be higher than OMAFRA recommendations, it may be speculated that starter rates in the no-build regime across the field sites in this study should have been higher, especially for corn and wheat, since the yields were higher in the P+K build regime. Moreover, soils low in both P and K did not respond to P fertilizer unless potash was applied. This was particularly evident at the Elora site. In a MSc thesis produced by Harpreet Hanzra, no trends of soil health on P and K responses were identified. The thesis also investigated crop removal rates; grain concentrations of P and K were higher in the built P and K regime, compared to the no-build regime.

Ontario farmers struggle with the problem of declining soil fertility because fertilizers are expensive. The results of this project can help maximize corn, soybean and wheat productivity while saving costs. Our research findings have the potential to revolutionize farming practices in Ontario. By adopting the updated recommendations and leveraging the build-and-maintain approach farmers can improve crop yields, optimize nutrient management, and maximize farming investments. Here are our key findings and recommendations:

1.       Declining Soil Fertility: Soil test results across Ontario have shown decreasing levels of P and K, party due to costly fertilizers and insufficient nutrient replenishment.

2.       Higher Yields. By using a P+K build regime instead of the recommended starter in the no-build regime, we achieved significantly higher grain yields in corn, soybean, and wheat.

3.       Starter Limitations: Even when the P and K starters exceeded the OMAFRA sufficiency recommendation, they were unable to achieve the same high yields as the P+K build regime.

4.       Using high-rate starter fertilizers at replacement rates in the build phase, we achieved 10, 3 and 11 bu/ac more corn, soybean, and wheat, respectively, in the P+K built regime compared to the no-build regime. This indicates a strong response to P and K fertilizers applied during the build phase.

5.       When comparing the same rate starter applied in the no-build regime with the P+K built regime after the soils were built with P and K, we observed numerical yield increases of 5.9, 0.8 and 6.7 bushels per acre in corn, soybean, and wheat, respectively, in the P+K built regime. These yield increases are returns on the investment for the fertilizer applied during the build phase; an analogy is the initial investment of tile drainage followed by yield increases in future years. This supports the need for updated OMAFRA recommendations, pending review by the Soil Management Research Committee (SMRC).

6.       Update OMAFRA Recommendations. Based on the evidence, we strongly recommend revising the current OMAFRA recommendations for corn, soybean, and wheat to reflect the benefits of the build-and-maintain approach. The data will need to be reviewed by the SMRC.

7.       Multiple Approaches. Both the sufficiency and build-and-maintain approaches have their merits. The sufficiency approach suits short-term land rental agreements, for example, while the build-and-maintain approach is more favourable for long-term leases or owned land.

8.       Soil Health Investigation. Although we didn’t identify any specific trends, we examined the impact of soil health on fertility responses. Further research is needed in this area.

9.       Rare Opportunity. It’s important to note that the opportunity to compare different starters across a patchwork of varying P and K levels in side-by-side plots is rare in North America, making these findings particularly valuable.

External Funding Partners:

This project was funded in part through Fertilizer Canada and Grain Farmers of Ontario.

Project Related Publications:

Bohner, H. 2019. Soybean school: Building up soil offers best return on nutrient investment. Realagriculture.

Bohner, H. 2017. P and K management for corn, soybean and wheat. Field Crop News.

Bohner, H and Hooker, D.C. 2018. P and K Management. Ontario Grain Farmer.