The Importance of High vs. Low pH in Corn and Soybeans
Although often underrated, the impact of soil pH – the universal measure of how acidic (lower pH) or alkaline (higher pH) the soil is – on production agriculture is real. Processes that are crucial to crop performance, such as soil biological activity and nutrient availability, are very sensitive to soil pH, and many farmers may not realize that it is limiting their yields. Both high and low pH may limit yields in corn and soybean fields.
What causes low pH?
Soil becomes more acidic (drop in pH) when:
- Minerals that control acidity are removed when crops are harvested
- Alkaline minerals leach out of the root zone when soils become saturated during rainy periods
- Acid residues are deposited with the use of some nitrogen fertilizers
- Complete a soil test every 3 to 4 years. If pH levels drop, apply lime at any time that the application does not disturb the crop. Fall applications are preferred to avoid planting delays and compacting soil.
- Make maintaining soil pH at optimal levels (5.8-6.2) a priority. If pH is allowed to fall considerably below this range, it could take years to get it back to target levels and impact yields because pH reacts slowly to conventional liming materials like aglime
Lime rate recommendations vary from state to state. Reference university extension publications for guidance on local recommendations.
What causes high pH?
Soil becomes alkaline (rise in pH) when:
- Soils are formed from calcareous materials, such as limestone
- Soil are saline and contain high levels of soluble salts
- If over-liming was the reason for your high soil pH, simply stop applying lime for several years and pH levels will stabilize
- If other reasons are to blame, apply elemental sulphur, aluminum sulfate or iron sulfate. Unfortunately, it is not economically feasible to treat soils with these materials in soils that have high pH naturally, such as calcareous soils. Adding organic matter with manures or crop residues can lower pH, but it takes several years to impact crop performance.
The best way to manage corn and soybeans in high pH is to plant hybrids and varieties with a high tolerance to high pH. Also, check herbicide labels and adjust application rates for high pH to avoid carryover issues.
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