February 2007

RESEARCH SUPPORTS USE OF OLSEN SOIL TEST FOR PREDICTING PHOSPHORUS IN RUNOFF

February 9, 2007 - FOR IMMEDIATE RELEASE

A commonly used agronomic soil test shows promise for predicting a soil’s environmental risk of losing phosphorus, according to the early results of an ARDI-funded research project to be released this afternoon at the 50^th Annual Manitoba Soil Science Society Meetings in Winnipeg.

Clay Sawka and Dr. Don Flaten, Professor at the University of Manitoba’s Department of Soil Science, conducted the project to better understand how a variety of agronomic and environmental soil tests could predict the risk of phosphorus in runoff from Manitoba soils. 

The $120,000 project, jointly funded by ARDI and the Canadian Fertilizer Institute, involved collecting different types of soil from across agricultural Manitoba with varying concentrations of phosphorus. Duplicate samples of 41 soils were packed into separate boxes and placed under simulated rainfall. The runoff water was then collected and analyzed for various forms of phosphorus, as well as nitrogen and carbon.

“Soils don’t have an infinite capacity to retain phosphorus,” explains Dr. Flaten. “We set out to test the ability of several different soil tests to predict phosphorus loss from the soil, as part of our efforts to develop an objective approach for reducing phosphorus loss to surface water.”

The results showed that an agronomic soil test known as the Olsen or sodium bicarbonate P test is a very good predictor of phosphorus loss across a range of Manitoba soil types. The Olsen P test performed particularly well with clay and clay loam soils, especially in the first 30 minutes of simulated rainfall. Since these types of soil are prone to having the most runoff, this finding is significant.

“The information from this research will help to provide an objective, scientifically sound base for recommending beneficial management practices for farmers,” said Dr. Flaten. “We have shown that the Olsen P test, a commonly available agronomic test, is a good indicator of the potential for phosphorus loss from Manitoba soil. This study also supports the Government of Manitoba's selection of the Olsen test as the basis for regulating applications of manure P in this province.”

Phosphorus loss from agricultural land is a concern because phosphorus in lakes can stimulate high concentrations of nitrogen-fixing algae. These algae create aesthetic problems, produce nerve and liver toxins and, during their decomposition, deplete the oxygen from lakes, causing fish kills.

Most of the phosphorus found in Manitoba waterways, including Lake Winnipeg, is not from local agriculture. According to Manitoba Water Stewardship, only 15 per cent of phosphorus loading into Lake Winnipeg is as a result of present day agricultural activities in the province. However, the U of M study shows how farmers in Manitoba can do their share to reduce P loss by minimizing or avoiding application of manure or fertilizer phosphorus onto “high soil test P” soils, especially if those soils are prone to generating runoff.

"These results help us to select the right type of test for predicting environmental risk; however, these laboratory rainfall simulation studies cannot be used to predict exactly what will occur in the real world," cautions Dr. Flaten. "For that, we need to use this knowledge to investigate phosphorus losses in the snowmelt-dominated runoff from fields in Manitoba watersheds."

ARDI is a research and development granting program of Agriculture and Agri-Food Canada and Manitoba Agriculture, Food and Rural Initiatives. It is funded through the Agricultural Policy Framework, a federal-provincial-territorial long-term action plan for agriculture.

ARDI program information, applications and application guidelines can be found at www.gov.mb.ca/agriculture/research/ardi/.

Research results will be presented at 3:30 p.m. on Friday, Feb. 9 at the 50^th Annual Manitoba Soil Science Society Meetings, taking place at the Holiday Inn Winnipeg-South (1330 Pembina Highway).

For more information, please contact:

David Gislason, ARDI Council Chair

(204) 376-5578

Dr. Don Flaten, Professor, Department of Soil Science

(204) 474-6257

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