In tougher times, make your soil pay you

By Luke Schulte, CCA, Beck’s Hybrids field agronomist

It is undeniable that 2025 currently looks to be much leaner economically than farmers have experienced in several years. In tighter times, inputs like dry fertilizer are often some of the first to be scrutinized because their potential impact is less obvious than skimping on herbicide use, for example.

Over the years, annual rainfall accumulation throughout the eastern U.S. has increased modestly.  However, the intensity of those rain events has increased dramatically.

While it may seem subtle, how we receive a large portion of our rain today has impacted how our soils function altogether, mainly due to sustained periods of limited soil oxygen.

Contrary to what may appear to be the case in agronomic textbooks, soil fertility is more complex than a mathematical equation. The state of soil nutrients, available vs. unavailable or “tied up,” is continually evolving. 

Take phosphorous (P) for example. The average recovery rate or volume of P that leaves the field the year following a fertilizer application is approximately 17-18%. So, if we apply 200 pounds of 11-52-0 this fall, approximately 35-40 pounds is all that will be removed from the harvested grain next year. Where did the remaining 160 pounds go? The remaining P largely contributes to the organic phosphorus (OP) pool and is temporarily unavailable. OP accounts for approximately 30-65% of all soil P. This is like having an operating loan of $100,000 accruing interest, but only $20,000 is liquid.

One of the primary mechanisms for maximizing nutrient availability is maintaining soil test calcium (Ca) levels. Years ago, simply maintaining soil pH often meant Ca levels were sufficient. However, as the Clean Air Act has reduced sulfur deposition (less acid rain), soil pH is not declining as rapidly. In turn, the need to apply lime or Ca to maintain pH has also diminished. In the 1980s, our rainwater had a pH of 4.0-4.5, but it is much higher today. I’ve been testing the rainwater at our home in central Ohio throughout the spring and summer for three years and I’ve never found the pH to be less than 6.2.

High calcium lime is an ideal source of Ca. However, as soils require less frequent lime applications to elevate pH, what are soil test Ca levels doing? We can no longer rely on maintaining soil pH to also provide sufficient Ca to maximize soil functionality. Think of it this way: the higher the base saturation Ca level, the higher the soil oxygen content.

Evidence:

2016- Ohio PFR- Pelletized Lime Study

**Soybeans: $10.00/Bu.  **High Calcium Pelletized Lime: $205/ton                                                                                       

While soil pH was optimal, a yield advantage of 5.3 bushels per acre led to an ROI increase of $22.25 per acre in a 2016 Beck’s Ohio PFR Pelletized Lime Study. Ideally, we need to maintain a base saturation Ca level > 70%. The addition of pelletized lime (Ca) to fall-applied P on soils with a pH of 7.0 increased available P the following spring by 14-53%.

2021- University of Illinois

Why did the added Ca lead to a yield benefit or increase in nutrient availability when soil pH was already optimal?

• ↑ Ca = ↑ soil oxygen = ↑ soil microbial activity → converting OP to plant available P
• ↑ Ca = ↑ microbial activity → improved aggregate stability/soil structure → increased water infiltration
• ↑ water infiltration → reduced soil crusting
• ↑ water infiltration throughout the soil profile = ↓ seedling diseases
• ↑ Oxygen = ↑ biological activity = ↑ nutrient release = ↓ dependency on applied nutrients

The bottom line is, as our weather has evolved, soil oxygen has inherently become the most yield-limiting element year in, year out. Maximizing soil functionality and reducing dependency on applied fertilizer primarily comes down to increasing soil oxygen. Products to influence soil Ca levels include pelletized lime, high calcium ag lime, and gypsum.