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TECHNICAL REPORTS

Surface Water Quality

Treatment of Drainage Water with Industrial By-Products to Prevent Phosphorus Loss from Tile-Drained Land

^a AgResearch, Invermay Agricultural Centre, Private Bag 50034, Mosgiel, New Zealand
^b Dep. of Crop, Soil, and Environmental Sciences, 115 Plant Sciences Bldg., Univ. of Arkansas, Fayetteville, AR 72701, USA
^c SteelServ, Glenbrook, South Auckland, New Zealand

^* Corresponding author (richard.mcdowell{at}agresearch.co.nz).

Received for publication August 24, 2007. Tile drained land with phosphorus (P)-rich topsoil is prone to P loss, which can impair surface water quality via eutrophication. We used by-products from steel and energy industries to mitigate P loss from tile drains. For each by-product, P sorption maximum (P_max) and strength (k) were determined, while a fluvarium trial assessed P uptake with flow rate. Although two ash materials (fly ash and bottom ash) had high P_max and k values, heavy metal concentrations negated their use in the field. The fluvarium experiment determined that P uptake with by-products was best at low flow, but decreased at higher flow in proportion to k. A mixture of melter slag (<10 mm) and basic slag (high P_max, 7250 mg kg^–1; and k, 0.508 L mg P^–1) was installed as backfill in eight drains on a dairy farm. Four drains with greywacke as backfill were constructed for controls. The site (10 ha) had P-rich topsoil (Olsen P of 64 mg kg^–1) and yielded a mean dissolved reactive P (DRP) and total P (TP) concentration from greywacke backfilled drains of 0.33 and 1.20 mg L^–1, respectively. In contrast, slag backfilled drains had DRP and TP concentrations of 0.09 and 0.36 mg L^–1, respectively. Loads of DRP and TP in greywacke drains (0.45 and 1.92, respectively) were significantly greater (P < 0.05) than those from slag drains (0.18 and 0.85, respectively). Data from a farm where melter slag was used as a backfill suggested that slag would have a life expectancy of about 25 yr. Thus, backfilling tile drains with melter slag and a small proportion of basic slag is recommended as an effective means of decreasing P loss from high P soils.

Abbreviations: DRP, dissolved reactive phosphorus • DURP, dissolved unreactive phosphorus • PP, particulate phosphorus • SS, suspended sediment • TDP, total dissolved reactive phosphorus • TP, total phosphorus