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Fluid Journal : Winter 2017
12 The Fluid Journal Winter 2017 The Fluid Journal • Official Journal of the Fluid Fertilizer Foundation • Winter 2017 • Vol. 25, No. 1, Issue #95 Joseph J. Weeks Jr. and Dr. Ganga M. Hettiarachchi Summary: Including small amounts of polyphosphates when applying fluid MAP to calcareous soils could potentially allow growers to apply less total phosphorus to agricultural systems without compromising plant performance. While more work is necessary, our group believes the blending approach possesses tremendous potential to reduce total P inputs to calcareous soils in the future, simultaneously saving grower capital, conserving a non-renewable resource, and protecting freshwater ecosystems. The challenge of efficiently managing phosphorus (P) in cropping systems on high pH, calcareous soils is one that many farmers are well acquainted with. Faced with high input costs, low commodity prices and stringent scrutiny from regulatory organizations, the Media and the general public, those who grow our food, find themselves in a frustrating situation. While the food culture in the United States continues to mature, one way progress can be made to benefit the collective as a whole is to find ways to produce low cost, environmentally friendly fertilizers that provide growers’ crops with the nutrients they need, when they need them--no more, no less. In the drier regions of the World, high pH calcareous soils are very common (FAO 2016). When P fertilizers, especially orthophosphate (OP) fertilizers, are applied to these soils much of the element that was intended for the plant quickly reacts with calcium (Ca) to form insoluble compounds that are not plant-available essentially wasting money and the non-renewable, vital resource. Unfortunately, the plant unavailable compounds, although not helping the farmer, can still erode into freshwater bodies and contribute to eutrophication along with its concomitant slew of human and environmental health consequences. Use of polyphosphates (PP), instead of OP, drastically improves fertilizer acquisition efficiency (FAE), but PP must undergo an enzyme mediated hydrolysis reaction before becoming useable by plants, causing growers to fear P deficiency in the early part of the growing season when soils are still cold (Holloway et al. 2001). Further investment into fertilizer research and development of new technologies is required to prevent or retard Ca-P “fixing” reactions to keep P plant- available in high pH calcium-rich soils. Much work has already been done in this arena. As mentioned above, use of PP instead of OP in fertilizers can improve FAE. Additionally, fluid fertilizers prove superior to their granular counterparts in that they allow P to diffuse greater distances from the point of application. Greater diffusive distances give the fertilizer application a greater “footprint” and decrease the P concentration at any discrete point in the soil. High P concentrations promote the formation of plant-unavailable Blending MAP, APP Reduces Fluid Fertilizer Input Costs ▼ DOWNLOAD Ca-P compounds. Because fertilizer granules are very dry in comparison to the surrounding soil when they are applied, soil water, rich in Ca, rushes into the granule causing fixation to take place within the granule itself, severely arresting P diffusion (Lombi et al. 2004 and Pierzynski and Hettiarachchi 2016). In response to the benefits and drawbacks of OP versus PP, some farmers blend fluid sources such that monoammonium phosphate (MAP), an OP source, accounts for 80% of the total P added and ammonium polyphosphate (APP) makes up the remaining 20%. The small addition of PP possibly allows for P to diffuse further into the profile, while the majority of OP mitigates the risk of early-season P deficiency. While this sounds like a reasonable approach, no controlled research of the actual chemical behavior of this mixture, compared to full applications of fluid MAP or APP, has been reported. To the surprise of the investigators, this initial study indicates potential for significant FAE increases when blending P sources compared to 100% OP applications, suggesting that this approach may actually be best. While mitigating environmental impact in high pH soils.