Phosphorus fertilizer prevents P tie-up

Crystal Green can be blended with MAP or DAP for more readily available P in high- and low-pH soils.

Score one for the good guys in the love-hate relationship with phosphorus (P). Cities must remove the mineral or risk causing algae blooms when the treated water is released. Farmers rely on it as a major nutrient but often find that it becomes tied up in high- and low-pH soils.

Now, a new slow-release, eco-friendly phosphorus fertilizer for mainstream agriculture  and farmers has emerged from the green technology that filters municipal and industrial wastewater. 

Ostara Nutrient Recovery Technologies is using its patented Pearl Technology to extract a pure source of phosphorus called struvite during the final stages of water treatment. 

Under the trade name of Crystal Green, the product contains purified nitrogen, phosphorus, and magnesium. 

It can be blended with MAP or DAP for a safer, more reliable, longer lasting, and more readily available phosphorus source for crops in high- and low-pH soils, say company officials.

Unique Composition 

Chemists have known about struvite for over a century, says Roland Leatherwood, an agronomist with Ostara. The firm was the first to seriously explore its potential as an agricultural fertilizer, he says. 

“We found it fills a need for growers with soils that have a high or low pH,” he says. “A majority of American farms fall into this category, so it’s not an isolated problem.” 

MAP and DAP provide optimal performance in soils with a narrow pH range between 6.4 and 7.2. 

When applied in soils with a pH higher than 7.2 (alkaline), the P from these fertilizers tends to bind with calcium. In lower than 6.4 pH (acidic) soils, it binds with iron and aluminum molecules. Both soil types tie up the phosphorus and restrict availability to the crop, he says. 

In the struvite form, phosphate is already bonded to magnesium. It is prevented from becoming tied up with calcium, iron, or aluminum. 

However, when the plant demands phosphate, this magnesium bond is readily broken by organic acid released from plant roots. That bond also ensures the phosphorus remains plant-accessible throughout the growing season.

Testing by Virginia Tech and the University of Arkansas revealed that Crystal Green remains available to roots for up to nine months, even with heavy irrigation and in porous soil, say company officials. 

In 2017, Joel Ransom, North Dakota State University Extension agronomist, conducted a degradation study looking at phosphorus fertilizer rate of release over an eight-month period starting in the fall. 

Hundreds of sample bags with MAP, DAP, and Crystal Green were buried at five depths in a neutral pH soil. Across all depths, only 5% to 18% of the MAP was recovered, while 94% to 98% of the Crystal Green was recovered in the testing.  

Unlike MAP and DAP, which are water soluble, Crystal Green does not require moisture or precipitation to convert to plant-available phosphate, says Leatherwood. 

When plants require phosphate, roots release organic acids called citrates. Crystal Green is 96% citrate soluble and becomes available on demand throughout the growing season.

“Phosphorus is required at various key growth stages,” says Leatherwood. “Timely access to phosphorus is critical to healthy plant growth. Like all major nutrients, a phosphorus deficiency will have a noticeable impact on yields.” 

Seed safety has long been a concern with MAP and DAP fertilizers due to their high salt index. The salt index for Crystal Green is 70% to 75% lower than MAP and DAP products. This lets you safely apply Crystal Green closer to the seed, which is a big advantage, say company officials.

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