Phosphorus Mobility Study

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 Methods and equipment | Preliminary results | Conclusions
Livestock manure is a valuable resource. It provides crop nutrients and improves the soil. However, when allowed to enter surface or ground water, phosphorus (P) and other components of manure can become harmful pollutants. Increased levels of phosphorus (P) entering water bodies cause excessive growth of algae and weeds. High levels of algae increase water turbidity, block sunlight, and disrupt normal biological activity. When the algae die and decay, they use up available oxygen and release toxins. This results in poor water quality for recreation and other uses, and will reduce desirable aquatic plants and fish populations.

Research recently completed in Alberta has shown that phosphorus levels in surface water are too high in many areas, especially areas with moderate or high agricultural intensity Assessing Alberta's Water Quality . The CAESA Water Quality Study did not evaluate specific agricultural activities which caused the buildup of phosphorus in surface water, but livestock operations and manure application were identified as contributing to total phosphorus. One of the recommendations made was to develop research projects which will give a better understanding of the sources of contaminants and the way they move in surface and ground water.

Surface runoff carries phosphorus from the soil

Changes are presently being made to the regulations for livestock operations in Alberta. Projected growth estimates led to concerns that existing regulations and guidelines needed to be improved to protect the environment, and support a sustainable livestock industry. The Alberta Government requested input from the public, and created a stakeholders advisory group to identify the issues and develop standards and regulations. Because phosphorus levels are critical to water quality in Alberta, future manure application rates will be based on phosphorus. More information specific to Alberta soils, climate, and crops is needed to determine the amount of phosphorus that can be safely applied.

A research project currently underway at Alberta Agriculture is addressing these phosphorus questions. The livestock industry supports the project through funding provided by the Canada-Alberta Beef Industry Development Fund (CABIDF), and the Canada- Alberta Hog Industry Development Fund (CAHIDF). The project is a cooperative effort between the Conservation and Development Branch and the Agronomy Unit, directed by project leaders Dan Heaney and Douwe Vanderwel. Other members of the research team are: scientists Ralph Wright, Dr. Mohammed Amrani, Dr. Mingchu Zhang, Engineer Andy Jedrych, and Technologists Syd Abday, Martin Blank, and Wilson Mallorca and administrative support, Michele Dannish.

The bulk of the research is being done in the Alberta Agriculture soil and hydrology labs, located in Edmonton, with a field component conducted throughout the province. The project will utilize various methods to define and measure the movement of phosphorus in manured soils. The goal of the project is to document the movement of P from manured soils to surface water, and develop soil tests which can be used to assess and predict that movement. The project will provide the following information:
  • An evaluation of different soil phosphorus tests for use in predicting potential for P losses from the landscape.
    An accurate soil test is necessary to predict P movement and develop site specific manure loading rates.
  • Improved understanding of the fate and chemistry of manure applied phosphorus.
    It is necessary to know what portion of phosphorus is used by crops , remains in the soil, or is available to be moved by water.
  • An understanding of the relationship between P mobility and P movement, and the effect of slope on P movement.
    It is necessary to document the actual movement of P which has the potential to move (mobility) when the right conditions exist. One of the most important factors influencing the movement of water and the transport of soil components is slope.
  • A comparison of the results of lab experiments with similar work done in the field, and with data collected from farm field scale watersheds.
    Lab results must be validated by comparing them to events taking place under natural field conditions. This comparison will allow a relationship to be documented and used to predict P movement under field conditions.
Methods and Equipment

Samples of manured soils are being taken from research plots and farm fields throughout the province. These soils were selected to give a wide range of soil characteristics and manure treatments. The soils are analyzed in the lab to determine soil characteristics and define P content and mobility. Different soil test methods will be compared to determine which are best for predicting P mobility. Soils with different rates of manure application over a number of years will be compared to soils which have had no manure application. Manure will be added to the soils, and the changes in organic and inorganic P fractions will be monitored at intervals during the experiment. This will provide information on the changes in P over time on manured land.

Soil and water samples are analyzed in the lab

One series of experiments uses rainfall simulation equipment which has been constructed at the hydrology lab. The simulator uses precision nozzles which closely imitate natural rainfall and deliver a consistent intensity and spray pattern . A water softener is used to ensure a consistent supply of mineral free water. Soil frames are placed on stands which can be adjusted for different slopes.

The hydrology lab rainfall simulator

The simulator uses two nozzles and can accommodate four soil frames for each test. Soils with a wide range of characteristics and different rates of manure loading are being tested at various slope angles. All soils are first screened to ensure uniformity, and then placed in a 100x50 cm. steel frame at a depth of 10 cm. The frames have a mesh bottom lined with a permeable membrane. This allows water to pass through the soil to be collected and analyzed. The permeable membrane also allows the soil to be pre-wet from the bottom of the frame through capillary rise.

Field rainfall simulator

All soils are pre-wet to near field capacity. The simulator is run until inter flow and surface runoff rates reach a point of steady equilibrium. If equilibrium is reached, a test is completed in 90 minutes. If not, the run time is extended until equilibrium is reached. Samples of runoff are taken 8 times during a 90 minute run, inter-flow samples are taken at 30 minute intervals. Soil samples are taken for analysis before and after simulation.

A portable rainfall simulator has been constructed for use at field sites . To ensure uniform soil characteristics, these are the same sites from which soils for lab testing were taken. The field simulator uses the same nozzles as the lab unit, and delivers the same rainfall intensity. Portable steel frames are inserted into the soil to define a uniform test area.

The soils are uniformly pre-wet using a precision calibrated sprinkler system. Each field simulation comprises four repetitions, using paired frames for each run. Runoff samples are taken at intervals during the test which continues until runoff equilibrium is reached.

Field watershed research site

Two watersheds on manured fields have been selected for study. The study sites are instrumented with a complete climate station to collect climate data. 2 foot H flumes equipped with water level recorders are being used to measure runoff volume.

Automated water sampling systems collect runoff and snowmelt samples for analysis. Climate and water level data are stored in data loggers equipped with telephone modems which allows remote site monitoring and data collection.

The portable simulator has also been used at the field sites, and soil from the sites has been taken to the lab for testing. Comparison of the results will help define a relationship between field and lab data.

Preliminary Results

  • Dissolved P delivery increased as manure
    loading rates increased.
  • Sediment P delivery did not increase with
    increased manure loading rates.
  • Sediment concentration decreased
    with manure additions.

  • Not all soils showed the same increases in
    soil test P with similar P additions.
    For example, for soil #4 soil test, P levels
    increased slightly with P additions.
    By contrast, when the same amount of P
    was added to soil #2 soil test, P increased more.
  • The amount of added P that a soil can hold (absorb) is dependent on the soil type.
    For example, soil #14 could safely handle higher manure loading rates than soil #1.

Adding manure to soils greatly increased the amount of dissolved P exported in runoff. In contrast, manure additions did not lead to increases in sediment P export. Since dissolved P poses the greatest threat to surface waters, manure management strategies are necessary to help prevent surface water contamination. This research shows that soils vary in their ability to hold P. In addition, increases in soil test P with similar manure additions are not always the same for different soils. Therefore, maximum recommended levels for soil test P need to be soil specific. Future work will examine the effect of climate, management, and landscape characteristics on runoff generation and P export. This will lead to flexible manure management guidelines that are soil and site specific.

This information is provided by Syd Abday , Resource Sciences Branch, Alberta Agriculture and Rural Development
For more information about the content of this document, contact Ralph Wright.
This document is maintained by Deb Sutton.
This information published to the web on October 11, 2001.
Last Reviewed/Revised on August 28, 2008.