Phosphorus: Deficiencies and its added ecological soil benefits

In 2018, Replenish Nutrients Chief Technology Officer Neil Wiens bought some land to study the company’s proprietary products. On his land – and using his money and time – he compared what would become Rebuilder, the company’s regenerative fertilizer product, against a zero additional phosphorus strip (control) and one with MAP, or synthetic phosphorus.  

After five years of testing, he noticed a few changes – most markedly, delayed maturity among the control sections. 

The delayed maturity from the control strips is clear. 

We recently sat down with Neil, a generational farmer, to understand the importance of phosphorus, symptoms of phosphorus deficiency, and how you can ensure your crops have the required fill of phos… or, if we may, are well ph-ed.  

The right balance of phosphorus is vital to plant health. 

Phosphorus in plants is key in capturing, storing, and converting the sun’s energy into biomolecules that drive biochemical reactions (e.g., photosynthesis) from germination through grain formation to maturity. 

Phosphorus promotes early root growth, winter hardiness, and seed formation, stimulates tillering, and increases water use efficiency. Plants deficient in phosphorus are stunted in growth and often have an abnormal dark-green color. 

After noticing these symptoms and others, Neil began speculating that the soils were low in phosphate. “Delayed maturity in the barley was the first sign,” Neil explained. “We saw small, spindly plants with poor hybrid vigor. Over three years, it was getting progressively worse.” 

While many attributed the results to smoke, cold spring, fungicides, or just poor hybrid vigor causing the delayed maturity, Neil remained unconvinced and later realized his hypothesis was correct.  

“It continued to happen year after year, and we had a different excuse agronomically. I started to wonder if the delayed maturity across the prairies was related to low phosphorus. We started to play with the phosphate levels in the soil, and in our test plots, we noticed a clear trend.”  

Symptoms in the soil. 

Phosphorus is absorbed by plants in the ionic forms H2PO4– and HPO4=. General knowledge of ion exchange in soils would predict that these anions are not retained by the negatively charged soil colloids but move in the soil like nitrogen. However, phosphorus does not leach. It moves very little, even with large amounts of precipitation or irrigation.  

Phosphorus is present in the soil in organic and inorganic forms. In fact, as Neil explains, “it’s not true that all soils are deficient in phosphorus.” However, the amount of phosphorus available for plant uptake is very low compared to the total amount of phosphorus present in the soil.  

“Agronomically we’re seeing decreased phosphorus levels on soil tests,” added Neil. “It’s difficult to show this decrease in tissue samples as there’s still just enough phosphorus left that test results are within range.” Even in more technical tests like infrared, signals are skewed due to increased soil biological activity.  

Worse still, Neil explains that the recommended phosphorus application rate “hasn’t changed over the years – we keep removing it, but we aren’t adding it back in.” And that’s the basic phosphorus problem — how do we adequately re-supply the soil solution as the crop roots remove available phosphorus from the soil solution? 

As the data from Neil, and his co-investigator Elston Solberg, suggested, “there is an average annual soil deficit in NA of 5.2 M MT of P205 in the soil. That is what we are taking off and not replacing as we continue to chase high yields.” 

Phosphorus test plot labeled as (R)ebuilder, (M)AP, (C)ontrol
Test plot labeled as (R)ebuilder, (M)AP, (C)ontrol

As crop roots remove soil solution phosphorus, more phosphorus becomes available from the slowly soluble sources. However, if soluble fertilizer phosphorus is placed in the soil, it reverts into slowly soluble or insoluble forms, removing soluble phosphorus from the soil solution. This phenomenon is often called “fixation.”  

But you can do many things to liberate what is already in the soil and overcome fixation.    

Application of phosphorus 

Fixation of soil phosphorus increases with time of contact between soluble phosphorus and soil particles. That’s the primary reason why the placement and application of phosphorus fertilizer are important to limit fixation.  

The lack of available phosphorus in soil solution necessitates phosphorus applications via organic sources such as manure or inorganic sources such as synthetic fertilizers. Additionally, more efficient utilization of phosphorus fertilizer is generally obtained by applying fertilizer shortly before planting. In some areas, you may apply fertilizers several months before planting with little to no decrease in the availability of the fertilizer phosphorus to the crop. 

Replenish Nutrients: Your Rockstar Rock Phos 

There’s a common misconception that rock phos doesn’t break down in the soil. In fact, from a nutrient management standpoint, the source of phosphorus does not matter; however, what separates different sources is their ability to release phosphorus and increase the availability of phosphorus in soil solution for plant uptake.   

Delayed maturity due to phosphorus deficiency in control strip versus Replenish Nutrients test strip.
Delayed maturity due in control strip versus Replenish Nutrients Rebuilder test strip.

Neil tested three areas when running his trial: one without additional phosphorus, one with conventional amounts (41 lbs per acre) through Rebuilder, and one with MAP. Results confirmed that Replenish Nutrients products releases at the same rate or better than conventional fertilizer without salt. With Rebuilder and MAP, Neil’s team saw the field reach 120 bushels per acre.  

If you, like many other farmers, are concerned with high prices or considering decreasing the amount of applied phosphorus in your fields this year, remember the lasting effects of phosphorus deficiencies and the added ecological soil benefits our fertilizer provides.  

If you’re ready to increase the micronutrients and biology in your soil and improve nutrient density, contact your local authorized dealer today to order.  

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