Multiple Studies in Soil P

Multiple Studies in Soil P

Use of a maleic-itaconic copolymer fertilizer additive can have a positive effect on the solubility and potential plant availability of applied phosphate, depending on soil conditions, according to recently published studies conducted by North Carolina State University and Kansas State University.

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Phosphorus (P) is a challenge to manage. Soils used for agricultural production usually contain 0.005% to 0.15% P in an acre furrow slice (about 2 million pounds of soil). That is equivalent to 100 to 3,000 pounds of total P. Unfortunately, only one to two pounds of the total P in an acre furrow slice of soil is soluble and available to the crop at any point in time due to P fixation. This necessitates the use of P fertilizers; however, the processes of P fixation also make application inefficient, allowing less than 40% of applied P to be taken up by plants in the cropping season when the fertilizer is applied. Sometimes, depending on soil and environmental conditions, the percentage of applied P that actually makes its way into crops can be much less than 40%. These research findings showing improved P solubility using a copolymer fertilizer additive are significant.

“Phosphorus fixation happens when negatively charged phosphate from fertilizers reacts with calcium, magnesium, iron, and aluminum in soils,” says Todd Carpenter, Technical Development Manager for Verdesian Life Sciences. “The result of this fixation is that 60% to 95% of the P fertilizer you apply this year will not be used by this year’s crop, and no one can predict when it will be available.”

Unfixing Soil Fixation

The maleic-itaconic copolymer product examined at the two universities is AVAIL Phosphorus Fertilizer Enhancer from Verdesian Life Sciences. According to Carpenter, AVAIL shields applied P from fixation by binding with the soil elements that would otherwise attach to the P and render that nutrient unavailable for plant uptake.

“Just because soil tests might show high levels of P in the soil doesn’t mean the nutrient is available to the crop,” Carpenter says.

There are three pools of P in the soil: soluble P; labile P and fixed/stable P. Soluble P is the P that is dissolved in the soil solution and is easily accessed by the plant. This represents the 1 to 2 pounds per acre that is available to the plant at any point in time. Labile P is the soil fraction of P that continually replenishes the soluble pool. This fraction is somewhat available to the plant through active transport mechanisms facilitated by root exudates and symbiotic mycorrhizal associations. The fixed or stable P pool is the P that is unavailable to the plant. This P may eventually be converted into labile forms, but it is impossible to predict how much will be converted or when.

A study conducted by Kansas State University indicates that AVAIL applied to fertilizer results in more soluble phosphate minerals being formed in soils than in soils where untreated P fertilizers were applied. “These more soluble minerals are easier for the plant to access and use,” says Carpenter. Work conducted at North Carolina State University indicates that AVAIL binds to mineral surfaces, keeping more P in solution. The work also suggests that AVAIL complexes with metals in the soil solution, keeping P more soluble.

“This work may mean that AVAIL can help to solubilize bound P in the soil with sufficient rates of the polymer added to soil,” Carpenter says.

Practically, under favorable soil conditions, the NC State study suggests that treated P fertilizer granules will dissolve into a greater volume of soil, making it easier for plant roots to intercept. This would be especially impactful in banded or knifed applications of granular or liquid P.

Increased P Availability

Improved availability and early-season uptake of P translates into faster root development, improved root structure and stronger stalks, meaning a more robust crop that can better manage environmental stresses of the growing season, Carpenter adds.

“We are seeing the potential for 30% more P available to the crop on average when AVAIL has been applied in numerous independent, dealer, and company field trials,” he says. “In some of these trials, the rate of applied P was reduced by 20% to 50% with little or no adverse effect on yield.”

These trials and test plots demonstrate the use of AVAIL is especially valuable if soil tests show low P levels, when pH is below 6.0 or above 7.0, and for use in starter fertilizer applications. “If you would expect a response to your P fertilizer, you should expect a response from AVAIL,” Carpenter says.

Carpenter emphasizes that the increase in P efficiency that AVAIL provides has a direct correlation to improved return-on-investment (ROI) from every pound of P applied. “Ninety percent of our corn trials have shown an increase of 10 bushels per acre, on average, when AVAIL is applied,” he says. “At $3.25 per bushel corn, the ROI could be as high as 5:1. Getting 30% more of the P applied this season into this season’s crop makes a big difference.”

Sustainability Considerations

Improving the efficiency of applied P also offers benefits to the environment and farmers’ sustainability that must be considered part of the equation. Obviously, the greater amount of P that is taken up by the crop, the less P is left behind in the soil where it is subject to off-site movement into waterways.

Ag retailer Ben Hushon knows this equation well. His company, The Mill (a member of the CropLife 100) has six locations in Maryland and eastern Pennsylvania. All of his approximately 500 grower-customers are located within The Chesapeake Bay watershed. Many of them treat their P with AVAIL to help better address nutrient run-off issues and a number of stringent environmental regulations directed at agriculture, especially in Maryland.

“Given the proximity to the Chesa­peake Bay, our service area is in the national spotlight where sustainability is concerned,” Hushon says. “Our farmers are environmentally focused at a level not yet seen in the Midwest. What we can accomplish here will be a model for the rest of the country.”

Hushon says that the research studies from both North Carolina and Kansas State Universities will make his agronomists more likely to recommend that P fertilizer is treated with AVAIL. “We will also feel comfortable recommending reduced P application rates in some situations when AVAIL is used,” he adds.

“If I can tell them they can increase their P efficiency and plant uptake and, at the same time, meet some pretty strict environmental regulations, that is a key point that most of them can see and understand,” says Hushon.

The economic ROI also works as a selling point for AVAIL. “I tell my customers they can reduce their P rate by up to 20% and off-set that with the price of AVAIL,” Hushon says. “I can then promise them that the reduced P rate combined with AVAIL will outperform applying the full rate of P without AVAIL.”

The Mill firmly believes that run­ning a profitable farming operation and being environmentally proactive are not mutually exclusive. “Farmers can have the best of both worlds,” Hushon emphasizes. “If you don’t take care of your soil and water, your cropping efforts won’t be profitable in the long run.”

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