Tile Drainage Phosphorus Losses From Agricultural Soils: Case Studies in Canada.

Artificial tile drainage, that is both agronomically and economically beneficial, has been increasingly implemented by farmers in Canada and the world. Adoption of tile drainage alters the fate of soil phosphorus (P) and the pathways of its losses, which can be a function of agricultural management practices, in addition to soil indigenous properties and topographies. This presentation attempts to summarize the results from long-term studies (up to 45 years) in Canada that were consistently maintained and meanwhile equipped with automatic monitoring and sampling systems for continuous flow volume recording and determination of P contents to evaluate the inherent effects of a range of crop, soil, and water management practices on soil P loss in tile drainage water (SPLTD). Of the annual total soil P loss, from 36 to 97% was attributed to tile drainage discharge. Effects of cropping system on SPLTD followed the order of continuous sod > rotation corn > continuous corn. Dissolved reactive P predominated SPLTD for continuous sod with fertilization, accounting for 72%, while particulate P predominated SPLTD, accounting for 62 to 74%, for continuous corn and rotation corn with and without fertilization, and continuous sod without fertilization. Dry matter based compost application resulted in substantially greater P loss with swine manure compost than with chemical fertilizer and yard waste compost, due to both of its high P content and high P loss potential. No-tillage increased dissolved reactive P loss in tile drainage when surface soil P levels were high, relative to conventional tillage. Compared with regular drainage, controlled drainage with sub-irrigation reduced SPLTD through the reduction of tile drainage flow volume and particular P content. Contribution of each management practice to SPLTD varies, and some of the current BMPs may need to be re-evaluated, if SPLTD is incorporated into the risk assessment of soil P.