Just Get pH Right? Does getting soil pH “right” lead to more nutrient availability? Yes, but also no. Life in the soil is not one dimensional. When considering pH, we should also be considering Eh (soil redox potential). There are management decisions that can influence both pH and Eh, and these two metrics should be thought of together. Redox Potential (Reduction and Oxidation) Reduction= gain of electrons (H+) Oxidation= loss of electrons or gain of Oxygen To make it easier to understand, I think about a plant oxidizing the atmosphere (adding oxygen) and the roots reducing (adding H+) to the soil. Reference the Pourbaix diagram I’ve attached to see how pH and Eh relate. There are more of these charts you can find to see where different nutrients may become available to the crop. You can find this by looking for Olivier Husson’s work. It makes sense why pH is considered and Eh is not. pH can actually be measured on a soil test. But even pH is not static even though we treat it like it is. Either way, there are management choices that will impact both. Here are some examples of an overly oxidized, reduced, and a more balanced system. Overly Oxidized: -frequent tillage -dry soil conditions, low residue cover -low OM/low WEOC -nitrate based fertility -low biological activity All results in high Eh and slightly alkaline conditions plus nutrient tie-ups Overly Reduced: -heavy clay w/ poor drainage -high OM and/ or manure inputs -compacted, anaerobic subsoil -waterlogged for extended periods of time All results in low Eh and more acidic conditions plus anaerobic microbial activity. Blueish gray looking soil that might smell rotten. A more balanced system: -living roots as much as possible -minimal tillage -mixed nitrogen sources -good biological activity -ground cover -aggregated soil All results in moderate Eh and slightly acidic to neutral pH. Leads to nutrient cycling and resilience.

What could fertilizers be doing to the soil? Example: 10-20 years of corn-soybean rotation. 10 CEC soils with a 225 bushel yield goal for corn and a 55 bushel yield goal for soybeans. With adequate soil test levels, you biennially spread Potash (220#) and MAP (230#) 0.9 NUE goal on corn (203#) in the form of UAN 28 w/ majority at side dress. This is a basic example but aims to paint a picture of what might be happening in soils. So what happens? •The soil acidifies over time until lime is needed •The soil oxidizes over time •Oxidized Mn and Fe tie up P •Oxidative stress on crops •Higher levels of disease •Lowered WEOC •Decline in microbial diversity •Decline in aggregate stability •Poor nutrient cycling that requires more synthetic fertilizers See the illustrations for pH and Eh trends (key word is trends). All of this leads to a cycle of needing higher rates of fertility, more -cides, and crops being more dependent on us.