Phosphorus Leaching Through Intact Soil Columns From Fertilized and Manure Amended Plots with and without Incorporation.

Leaching of significant quantities of phosphorus (P) into groundwater from soils is an environmental concern with fertilized and manured soils. This study quantified and compared P leaching losses through intact soil columns four weeks after manure or fertilizer amendment with and without incorporation, and examined the relationships between quantities of P leached and alternative measures of soil test P (STP). Four fertility treatments (liquid swine manure (LSM), solid cattle manure (SCM), monoammonium phosphate fertilizer (MAP) and un-amended control) and two tillage treatments (incorporated with roto-tillage and unincorporated) were arranged in a split plot design with 4 replicates in a field with no recent history of manure application at Carman, Manitoba (Orthic Black Chernozem). Manure or fertilizer was surface applied at 80 kg P ha^-1 and immediately roto-tilled for incorporated treatments. A surface soil sample (0-15 cm depth) and an intact soil column were taken (15 cm soil depth) from each plot four weeks after fertilizer or manure application. Soil samples were analyzed for Olsen-P (OP), Mehlich 3-P (M3P) Modified Kelowna- P (KP) and water extractable P (WEP). Phosphorus leaching losses from intact soil columns were simulated in a laboratory by supplying water through a rain-drip system to the top of the columns. One pore volume of leachate was collected and analyzed for dissolved reactive phosphorus (DRP). The magnitude of STP increase and quantity of P leached from manured and fertilized plots followed the order of: MAP > LSM > SCM. Incorporation of manure or fertilizer did not have a significant influence on STP, but significantly reduced the quantity of P leached. Quantity of P leached in incorporated plots showed a significant but weak correlation with M3P only, whereas in unincorporated plots the quantity of P leached was significantly (P<0.05) correlated with all STP, with KP showing the strongest correlation (P<0.001).