- Department of Soil and Environment, Swedish University of Agricultural Sciences
Liu, Jian; Aronsson, Helena; Blombäck, Karin; Persson, Kristian; Bergström, Lars
Long-term repeated applications of animal manure at high rates contribute to buildup of soil P status, which poses a risk of P losses by leaching. However, contrary phenomenon may present in soils with abundant P sorption capacities, which brings difficulties in assessing the risk of P leaching. Phosphorus leaching was studied in a long-term experimental field with a sandy soil in southwest Sweden. Field measurements, model simulations, and laboratory lysimeter experiments, were used to assess the risk of P leaching associated with pig slurry applications. The plots in the field received different P applications, i.e. high rate of P (58 kg P ha-1 yr-1) with pig slurry, low rate of P (37 kg P ha-1 yr-1) with pig slurry, and mineral P (24 kg P ha-1 yr-1) without N applications, since the experiment started in 1983. These treatments resulted in average annual surpluses of P from 16 kg ha-1 to 37 kg ha-1. Mean annual total-P leaching and total-P concentration measured at a drain depth of 90 cm ranged respectively from 0.14 kg ha-1 and 0.06 mg L-1 at the high rate of slurry application to 0.20 kg ha-1 and 0.08 mg L-1 in the mineral P treatment. These observations were in general low in a Swedish context and pig slurry application did not elevate P concentrations in drainage water. One explanation was that the abundant P sorption capacity due to considerable Fe, Al, and Ca present in the soil overshadowed the effects of soil P status and fertilization. It was confirmed by the simulations with the ICECREAM model, where the role of the soil P pool for leaching was tested. The model produced 5 to 9 times higher P leaching than measured when no special attention was paid to the high sorption capacity. Laboratory lysimeter studies showed high potential of P leaching from the topsoils in this field, which was resulted from long-term pig slurry applications even long before the field experiment started. This was consistent with the results with model simulations with the low P sorption capacity. On one hand, although high amount of P leaching has not been observed, this field has a high risk of P leaching if pig slurry application continues to saturate the soil P sorption capacity; on the other hand, it indicated that the subsoil played a crucial role in sorbing P moving through the soil profile and reducing P concentrations in drainage. One main conclusion from the study was that soil P sorption capacity should also be considered, besides soil P status and fertilization, when identifying hotspots and designing P mitigation strategies.
2011, Volume: 7, number: 8, pages: 30-33
NJF seminar 443: Utilization of Manure and Other Residues as Fertilizers