Grantee Research Project Results

Final Report: Phosphorus Control in Soils with Legacy Phosphorus Using RhizoSorb® Technology

EPA Contract Number: 68HERC25C0032
Title: Phosphorus Control in Soils with Legacy Phosphorus Using RhizoSorb® Technology
Investigators: Maruvada, Sriramakrishna
Small Business: Phospholutions, Inc.
EPA Contact: Richards, April
Phase: I
Project Period: December 16, 2024 through June 15, 2025
Project Amount: $100,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2025) RFA Text |  Recipients Lists
Research Category: Small Business Innovation Research (SBIR)

Description:

Executive Summary

This report documents the work performed thanks to a 2025 SBIR Phase I grant awarded by EPA to Phospholutions, Inc. The purpose of this research has been to develop an affordable technology that can help to reduce the environmental impact of phosphorus (P) while maintaining or increasing agricultural crop yields. Fertilizers are routinely applied on farmlands to maximize crop yield. However, much of the applied P becomes immobilized in soils in forms unavailable to crops. Cumulative P applications at rates exceeding crop demands therefore lead to soils high in legacy P and to P runoff into nearby water bodies. As a result, farmers must balance the conflicting requirements of maximizing crop yields while protecting the environment.

Phospholutions proposed addressing these issues through an innovative application of RhizoSorb^® technology. RhizoSorb technology comprises a mixture of activated metal oxides that effectively manages the adsorption of excess P and its subsequent controlled release based on concentration gradients. The effectiveness of RhizoSorb as an enhanced efficiency fertilizer (EEF) has been demonstrated through extensive laboratory studies, including batch sorption isotherms and column studies, which show its high efficiency in adsorbing and desorbing phosphorus. Additionally, the technology has been tested in pot studies where its slow release of phosphorus for plant uptake and control of phosphorus in leachate have been demonstrated. Adapting this technology to address the specific challenges posed by legacy phosphorous soils has been the focus of this project.

Summary/Accomplishments (Outputs/Outcomes):

The primary objective of this EPA SBIR multi-phase project is to optimize and validate RhizoSorb technology as an effective tool for controlling phosphorus levels in soils with legacy phosphorus. Phase I of the project focused on optimizing the phosphorus sorption capacity of RhizoSorb, assessing its impact on phosphorus desorption kinetics, and evaluating its effectiveness in reducing phosphorus losses in runoff. The specific objectives were to: (a) identify a RhizoSorb grade with maximal P adsorption capacity; (b) assess the effect of RhizoSorb on P desorption kinetics; and (c) evaluate the impact of RhizoSorb on P losses in runoff. We hypothesized that:

1. Optimizing the selection of RhizoSorb will significantly enhance its phosphorus adsorption capacity, making it more effective in soils with high legacy P levels;
2. RhizoSorb will control the desorption of phosphorus from soils, providing a slow and sustained release of bioavailable phosphorus that benefits plant growth while minimizing environmental losses; and
3. The use of RhizoSorb in soils will result in a significant reduction in phosphorus leaching and runoff compared to untreated soils, thereby decreasing the potential for waterway contamination.

Research conducted to confirm the technical feasibility of our hypothesis included a three-stage approach: (a) identifying and down-selecting a RhizoSorb grade with suitable P sorption properties and favorable economics; (b) carrying out batch sorption studies to determine the optimum RhizoSorb concentration to maximize the initial capture of P associated with a high P soil (with high P being defined as a soil with measured total P content of ≥ 500 ppm); and (c) performing dynamic column studies to evaluate the ability of the down-selected RhizoSorb grade to minimize P runoff at simulated rain elution conditions. Key results stemming from this research include the following:

1. We identified a RhizoSorb grade (herein labeled grade A) with material properties that maximize its ability to adsorb phosphorus from soil solution and reduce its environmental impact by preventing its runoff and leaching into waterways. These included relatively high surface area and high resistance to weight loss upon heating.
2. We established the RhizoSorb dosage that provides the optimal balance between performance and economics, with performance defined as the delivery of bio-available phosphorus in a controlled release manner. Working with high P soils (and manure-soil proxies) we demonstrated a consistent increase in P capture with increasing RhizoSorb dosage. For a high P soil with 524 ppm P, batch sorption experiments confirmed that increasing the RhizoSorb/(High P Soil) weight ratio to ≥ 1 successfully captures > 90% of the P released to solution.
3. We performed dynamic column experiments designed in accordance with standard column leaching test method OECD/OCDE 312 (OEDC, 2004), with water feed rates mimicking an equivalent target rainfall of 0.27 cm/h, which can be deemed as moderate by OECD guidelines. Dynamic column tests of the high P soil with 524 ppm P, with and without RhizoSorb application, indicated that, in agreement with batch sorption tests, that RhizoSorb can successfully capture P released from high P soil into solution.

Conclusions:

Initial actions to assess the commercial viability of the proposed technology included closely interacting with a nearby farm 33-acre farm to procure high P legacy soil samples, supply them with two tons of RhizoSorb control material, and set up ongoing control trials for corn growth evaluation. In addition, based on their independent research, Foresight Science and Technology insight, innovation and commercialization consultants provided a Commercialization Readiness Assessment Report [1] which clearly favored the commercialization potential of RhizoSorb for this innovative application. Furthermore, Foresight outlined the commercialization strategy most likely to yield a successful implementation of RhizoSorb technology in Ag markets for the benefit of farmers having to deal with the need to increase crop yields while minimizing nutrient losses and environmental impacts.

Having also assessed the lifecycle of RhizoSorb technology by considering its inception, use, disposal and recycling aspects, Phospholutions is confident that RhizoSorb represents an innovative and next-generation EEF that can successfully meet the technical and commercial needs of its target market. Achieving this overall goal will require additional support through the project’s continuation via EPA SBIR Phase II as the next step.