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Author(s): Goss, M.J., P.D. Zwart and R.G. Kachanoski
Publication Date: January 1, 1996
Reference: In Managing Manure for Dairy and Swine - Towards Developing a Decision Support System. Edited by M.J. Goss, D.P. Stonehouse and J.C. Giraldez. Chapter 7.
Country: Canada

Summary:

This chapter, the factors that can have an impact on water quality are reviewed particularly for contamination of ground and surface water by nitrate, phosphorus and disease organisms. The focus is made on potential contamination as a result of manure application on land. The first step is to present the unbalanced nutrients ratio N:P:K of the swine and dairy manure (2:1:1,5 and 4:1:3 respectively) compared to the need of heavy yielding corn (7:1:7) for example. This would suggest not to use N as the limiting factor but rather to use P and supplement for the other nutrients. However the availability of nutrients is difficult to assess particularly for N as many losses can occur depending on the climatic conditions and also on the spreading method as NH3 can be emitted directly as gas, nitrification can occur and nitrate can be lost by leaching and denitrification can also occur resulting in N2O and N2 as gaseous emissions. N deposition can also come from the atmosphere, quantity which is difficult to evaluate. The survival of different pathogenic bacteria depends on different factors for example: soil pH, soil water and organic matter contents, soil texture, temperature and others. It is thus difficult to predict the bacteria becoming as a general trend. The transport of the contaminant is dependent of their concentration in the soil and also on the water flow available to move them. The application rate of the manure and also the number of years of repeated manure applications have a direct effect on the nitrate potentially available for leaching. So the higher are the rates and the more years the manure is applied, the higher are the risks for leaching contaminants in water. Manure spreading the closer to the crop growing period lower also the risk for nitrate leaching. Injection rather than surface application lower the risk of leaching. Some paths are given for further research particularly on the availability of nitrogen and other nutrients in the manure, the transport of those nutrients that can become contaminants under certain circumstances and the more information on disease organisms and the factors affecting their transport.

Many elements are presented in this review. Some conclusions can be drawn from this information and they are that specific factors increase the risks for leaching of contaminants and degradation of water quality and they are: high application rate; application done a long time before the growing season; manure applied directly on soil rather than injected particularly during rainy periods.

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