Effect of Tile Drain Depth, Spacing and Drain Water Management on PhosphorusLosses in Corn and Soybean Rotation

摘要

Phosphorus (P) losses from tile drained agricultural lands may differ with tile depth and spacing. Studies were conducted on clay loam soils using large field plots equipped with automatic flow volume measurement and sampling systems over a 4-year period to evaluate tile depth (0.65 m vs. 0.85 m) and spacing (4.2 m vs. 7.5 m) on P losses under two drainage water management systems (regular free drainage, RFD, vs. controlled drainage/sub-irrigation, CDS) with a corn-soybean rotation. Under RFD with 4.2m tile spacing, soil P losses with the tile depth of 0.65 m were 0.021 kg ha"1 for dissolved reactive P (DRP) and 0.275 kg ha"1 for total P (TP) in surface runoff, and 0.382 kg ha"1 for DRP and 5.43 kg ha"1 for TP in sub-surface drainage. Increased tiledepth to 0.85 m, soil P losses increased by 92 folds for DRP and 28 folds for TP in surface runoff and by 8.8 folds for DRP and by 1.5 folds for TP in sub-surface drainage, because of the increased both water flow discharge and flow weighted mean DRP and TP concentrations. Effects of tile depth on soil DRP and TP losses under CDS followed the similar patterns to those under RFD in surface runoff, except for the greater increases, while in sub-surface drainage there were slight increases in DRP and decreases on TP with increased tile depth, due to the redirection of water discharge from subsurface to surface. Regardless of water management, increased tile depth increased soil DRP loss in both surface runoff and sub-surface drainage at the similar extent. However, CDS reduced soil TP loss in combined surface runoff and sub-surface drainage by 15.7 %, relative to RFD. Effects of tile spacing on soil TP loss were less profound than those of tile depth. With tile depth of 0.65 m, increased tile spacing from 4.2 m to 7.5 m increased soil TP loss in surface runoff at a similar extent for both RFD and CDS. In contrast, increased tile spacing decreased TP loss in sub-surface drainage under both RFD and CDS. Consequently, increased tile spacing increased soilTP loss in combined surface and sub-surface drainage, regardless of water management. There appeared greater effects of tile depth than tile spacing on both DRP and TP losses, of which the effects were predominately attributed to the redirection of field water discharge, followed by the changes in P concentration. Managing tile depth can be an efficient practice to mitigate soil P loss from tile drained agricultural lands.