I hope you enjoyed my previous 5-part series on basic cation saturation ratio concept this winter that you can still read online at https://croptechcafe.org. I ended that series with a call to action to focus on soil acidity and its management using soil pH, buffer pH, and lime to increase soil pH. To that end, this will be a 6-part series on soil acidity management including: 1) soil pH, natural factors, and crop production, 2) impacts of soil acidity, 3) buffer pH and lime quality, 4) lime application, stratification, and tillage, 5) site-specific management, and 6) economics and other considerations. Please follow this series as I walk through soil acidity and management in southeast Nebraska crop production.
Soil pH is an index of soil solution acidity. Technically, soil pH is the negative logarithm of hydrogen ion (H+) concentration in the soil solution. A soil pH value back from the soil testing laboratory of 5.0, compared to a value of 6.0, represents a 10-fold increase in the hydrogen ion concentration. Soils are considered acidic or have more hydrogen ions than when the pH is less than 7.0 (neutral pH). Soils with a pH above 7.0, are basic or alkaline with less hydrogen ions than acidic soils.
Parent material of soil, precipitation (naturally a pH of 5.7), and type of vegetation are natural factors impacting soil acidity across Nebraska. Native vegetation and precipitation are similar locally. Parent materials of our soils are mostly loess and glacial till, and to a lesser extent shale, limestone, and sandstone. For example, Wymore soil series (formed from Peorian loess) is generally more acidic than the Pawnee soil series (formed from calcareous glacial till). Kipson soil series typically would have a higher pH than Pawnee soil series since it was formed out of limestone and shale. In Gage, Jefferson, and Saline counties, soil pH naturally increases with depth from the soil surface into the subsoil for most soil series. Therefore, soil series and historic soil erosion influence soil pH spatially across a field and across the three counties.
Current crop production and management affect soil acidity today too. Nebraska Extension’s NebGuide G1503 Management Strategies to Reduce the Rate of Soil Acidification (https://extensionpubs.unl.edu/publication/99) addresses how long-term intensive crop production results in the gradual soil acidification of the topsoil. There are several management practices to slow the rate of soil acidification including increased crop uptake of applied nitrogen and sulfur fertilizers and minimized leaching of nitrate-N. For example, under continuous corn production, it is estimated that 1.7 tons/ac of ag lime would be needed to maintain soil pH every 10 years. However, even with best management practices and goals, the use of lime will still be needed, but to a lesser extent.
In two weeks, I will address some of the impacts and challenges of soil acidity in crop production. For inquiries about this and other agronomic resources and programs from Nebraska Extension, contact me at nathan.mueller@unl.edu or 402-821-1722. Know your crop, know your tech, know your bottom line at croptechcafe.org