Sign up for email alerts of new Fluid Journal issues!
Fluid Journal : Winter 2016
What About Fluid P Fertilizers In Moderately Calcareous Soils? Do they excel? . Joy Pierzynski and Dr. Ganga Hettiarachchi T DOWNLOAD The Fluid Journal · Official Journal of the Fluid Fertilizer Foundation · Winter 2016 · Vol. 24, No.1, Issue #91 Summary: Overall, in a controlled laboratory experiment on the 3 calcareous soils it did appear that fluid P ferlilizer was superior over the P granular in terms of enhanced movement away from the point of application and/or remaining extractable. However, field studies on mild to moderately calcareous soils will be needed to gauge whether the laboratory results hold up under scrutiny in the field and actually enhance or influence plant growth. T he lack of soil phosphorus (P) availability in soil is one of the major reasons for less than optimal crop growth over the course of a growing season. When P fertilizer is added, it can rapidly undergo chemical transformations that make this macronutrient unavailable for crop uptake. It necessitates frequent or heavy applications of P to maintain crop productivity, which can be costly and also increase the potential for P runoff. This is a common problem in many agricultural areas of the world. The mechanisms responsible for decreased P availability in soils are quite complex and vary depending on soil mineralogy, pH, climate (such as soil moisture), and the form of P fertilizer added to the soil. Calcareous soils present a unique challenge because we know the addition of granular P fertilizer to these soils can cause the rapid formation of insoluble calcium (Ca) P reaction products within and near the fertilizer application point. This greatly reduces the release of dissolved P of the fertilizer into the surrounding soil and also decreases the potential plant availability of applied fertilizer P. Winter 2016 \. .\\ ' \ .. , ,- , "- -...._?. " I' -- " - -- '- ... - ..:... ........ - - -\ ] '- ). -J' \ ' , . , ll!.-- EcH ....... , - "'" - The decrease in P solubility can be influenced by the form of P fertilizer added to highly calcareous soils, according to recent studies. The benefits of P supplied in fluid forms over conventional granular products in highly calcareous Australian soils have been demonstrated through field trials, x-ray, spectroscopic, and laboratory-based wet chemical analyses. The results suggest the use of fluid P fertilizer on the calcareous soils allows greater movement of P away from the point of application, thereby reducing the formation of Ca-P precipitates. These recent observations raise the question as to whether the observed behavior would extend to mild- moderately calcareous soils. One approach to investigate whether mobility and lability are improved by the use of fluid over granular P fertilizer in calcareous soil is the use of a lab-based incubation study. This allows for a close look at possible reaction products formed in and surrounding the granule. Useful measurements on the incubated soil from the study would include total Padded, a measurement of P mobility from the The Fluid Journal point of application, resin extractability of P, which measures lability of the P fertilizer type added to the soil. Also included could be more sophisticated spectroscopy-based techniques, such as scanning electron microscopy (SEM) and energy dispersive x-ray (EDS), allowing for a close-up view of potential changes in fertilizer granule structure as well as elemental mapping of the granule to analyze the P reaction products in the granules and surrounding soil. Lastly, x-ray absorption near edge of structure (XANES) analysis to lend direct evidence of changes in P adsorbed or precipitation P formation as a result of P treatment We hypothesize that there are differences in P diffusion and P reaction products in and around fertilizer granules and fluid fertilizer zones in mild to moderately calcareous soils, consequently resulting in differential plant-available P. We employed a combination of 1) wet chemical, 2) scanning electron microscopy combined with energy dispersive x-ray analysis, and 3) synchrotron-based x-ray techniques to identify chemical forms of APP-, 4