Soil PH: The Big ElePHant in the FieldPosted in: Farming By Elston Solberg June 24 2015
Across Western Canada there are roughly 20 million acres affected by low soil pH.
To put this in perspective, this is more than all the land farmed in Indiana or the UK, and ten times all the farmland in the Netherlands. In Indiana, the UK and the Netherlands, the first thing a grower looks at on a soil test is pH.
The map in Figure 1 represents ~14,000 randomly sampled fields extrapolated across the 0.5 million fields across Western Canada. Within the higher pH areas, there will be many fields with significant portions of low pH.
Low soil pH is due to a number of factors — low pH parent material, organic matter breakdown and nitrogen fertilizer. It’s just a natural consequence of growing crops.
My question is…why not here? We know that pH affects pretty much everything — crop growth, nutrient efficiencies, herbicide carryover, clubroot risk and, when limed correctly, the positive effects can last for upwards of 10 years.
Yet, we are still hesitant to tackle the elepHant.
Cost is the most likely cringe factor. However, a number of factors have changed, making liming a more economic option. These include VR capabilities of the application equipment and the availability of alternative liming sources.
If you have a field with a pH of 5.8, you can be sure that parts of the field are pH 4.8 and other parts are pH 6.8. This means that 20-40% of the field likely has a pH low enough to negatively affect yield potential, nutrient use and water use.
In very simple terms, this means that 20-40% of the 20 million affected acres need liming. Obviously variable rate liming makes tremendous sense.
This spring, Agri-Coaches Matt Gosling and Andrew Clements, owners of Premium Ag Services Ltd, grid sampled a 477-acre field near Calgary (see Figure 2). The pH (0-6") on this field ranged from 4.4 to 7.7. Doug McKay, Geo-Coach with Cervus Equipment Corp. out of Calgary, built the prescription map for the spinner floater with VR capabilities and a by-product lime material was VR applied across the field. The range of VR lime application was 0 to 8,600 lbs/ac with about 21% of the field receiving little or no lime.
The beauty of liming in this manner is that while it is VR, it doesn’t have to be precise. If we get close and improve the pH issue by 80%, the ramifications are huge.
Here’s my rough ‘napkin math’ for this situation:
A responsive crop such as barley should have 30-50% more yield potential and grow at least 30% more crop on the low pH areas. Plus, there is the increased NPKS fertilizer efficiency, so factor in at least a $20 nutrient benefit. Note: increasing pH will reduce micronutrient availability (all except Mo).
In this case, over 50% of the field (purple to light blue areas on Figure 2) will give these responses:
•Barley – 30+% yield potential increases – say 27 bu for this farm @ $4.50 = $120 – total = $140
•Canola – 20% – say 9 bu @$10 = $90+ $20 = $110
•Wheat – say 15% – 11 bu @ $7 = $77 + $20 = $97
•Peas – say 30% – 18 bu @$4.72 = $85+ $20 = $105
Conservatively, this is an additional $100 crop revenue averaged across crops. If we assume the effect lasts 10 years, that’s $1,000/ac for a $107/ac investment. If you think it’s closer to five years, we are still talking about a 5+:1 payback.
To summarize, here is my advice: Don’t ignore the elepHant in the field any longer! Tackle it head on — it’s a fix that keeps on paying back.
Elston Solberg is the director of Agri-Trend’s Agri-Knowledge Division and can be reached at email@example.com.
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