The impact of chemical amendment of dairy cattle slurry before land application on soil phosphorus dynamics
Brennan, Raymond B.
Healy, Mark G.
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Brennan, R.B., Wall, D., Fenton, O., Grant, J., Sharpley, A.N., Healy, M.G. (2014) 'The impact of chemical amendment of dairy cattle slurry before land application on soil phosphorus dynamics'. Communications In Soil Science And Plant Analysis, 45 (16):2215-2233.
Application of dairy cattle slurry to agricultural soils, particularly those with high phosphorus (P) status or vulnerability to runoff, can increase P loss to waterbodies, which may accelerate eutrophication. While the effectiveness of P stabilizing amendments added to slurry or soil for reducing incidental P losses is well established, their effectiveness in reducing chronic (long-term) P losses is not as well known. Five soils (4 mineral and 1 organic) were selected to represent the range of chemical and physical properties typically found in agricultural soils in Ireland, and a 9-mo incubation study was conducted to investigate the effectiveness of amending dairy cattle slurry with either alum, lime, poly-aluminum chloride (PAC), or ferric chloride (FeCl3), in reducing water extractable P (WEP) levels in the soils. Alum, lime, and PAC were the most effective amendments in decreasing WEP (compared to a slurry-control) for the four mineral soils (up to 97% 1 mo after application and by an average of 47% at the end the 9-mo incubation period). In comparison, FeCl3 increased WEP (compared to the slurry-control) by an average of 35% at the end the study. None of the amendments examined effectively reduced WEP of the organic soil. No amendment reduced soil test P (Morgan s P (Pm) and Mehlich-3 P (M3P)) compared to the soil-only treatment. Therefore, amendment of dairy cattle slurry with alum, lime, and PAC can reduce the risk of chronic P loss in mineral soils without decreasing plant available P. Alum maintained the highest levels of M3P across the 4 mineral soils with the least risk of P loss to overlying water. With the exception of the soil-only treatment, there were significant positive relationships (p<0.05) between M3P and WEP for each treatment. Further work across a wider range of soil types and drainage regimes is required before recommendations can be made to farmers or catchment managers.