Phosphorus Leaching from Cow Manure Patches on Soil Columns

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Abstract
The loss of P in overland flow or leachate from manure patches can impair surface water quality. We studied leaching of P from 10‐cm‐high lysimeters filled with intact grassland soil or with acid‐washed sand. A manure patch was created on two grassland and two sand‐filled lysimeters, and an additional two grass lysimeters served as blanks. Lysimeters were leached in the laboratory during 234 d with a diluted salt solution, and column effluent was passed through a 0.45‐μm filter, analyzed for pH, dissolved reactive P (DRP), and total dissolved P (TDP). At the end of the experiment lysimeter soil was sampled and analyzed for pH, available P, and oxalate‐extractable P, Fe, and Al. The concentration of TDP in the effluent from the sand column increased to 25 mg L−1 during the first weeks and remained above 10 mg L−1 during the rest of the percolation. In effluent from grass + patch lysimeters TDP gradually increased to 4 mg L−1 Both in the manure and in the effluent of the sand lysimeter P was found mainly in the form of DRP, but in the effluent from the grass lysimeters was found mainly as dissolved unreactive P (DUP = TDP − DRP). Earthworm activity was responsible for decomposition of the manure patch on the grass lysimeters. Manure patches and their remains were found to be a long‐term source of high concentrations of P in leachates. Spreading of patches after a grazing period could reduce their possible negative impacts on the environment.

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