Soil Effects on Nutrient Leaching When Part of Engineered Plant Media.

Soils can serve as sorbents for phosphorus (P) within engineered plant growth media, instead of artificial sorbents. The purpose of this study was to compare soils with different properties, as part of plant growth media, for their effect on nutrient levels in effluent from the plant growth media. Four soils were mixed with sand, with or without a compost blanket. Infiltration  and effluent concentrations were measured before and after growing plants [Buffalo (Buchloe dactyloides (Nutt.) Engelm.) and blue grama grasses (Bouteloua gracilis H.B.K.) and red clover (Trifolium pratense L.)]. The growth media with compost at the surface had higher nutrient levels than the media without the compost, but column effluent nutrient levels were not significantly increased. The final nitrate concentration after harvest was significantly lower for columns with the compost blanket (59 vs. 86 mg L^-1). All of the nitrate concentrations were high (> 10 mg L^-1, many > 100 mg L^-1). The final P concentrations before planting were significantly higher in the soil with the most sand (0.71 mg L^-1), and after harvest in the soil with the high soil P levels (0.58 mg L^-1). Some soils (high in aluminum or calcium) were adequate sorbents for P without additions of other sorbents, but the soils might generate too much nitrate in leachate.