Nutrient Leaching When Soil Is Part of Plant Growth Media

Soils can serve as sorbents for phosphorus (P), negating the need for artificial sorbents. The purpose of this study was to compare soils with different properties for their effect on nutrient levels in effluent. Four soils were mixed with sand and packed into columns 0.5 m long, with or without compost on the surface. Infiltration and effluent concentrations were measured before and after growing plants [Buffalograss (Buchloe dactyloides (Nutt.) Engelm.) and bluegrama 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 the final effluent nitrate concentrations post-harvest were significantly lower for columns with the compost blanket (59 vs. 86 mg L⁻¹). All of the nitrate concentrations were high (many >100 mg L⁻¹) due to mineralization and nitrogen fixation. The final effluent P concentrations before planting were significantly higher in the soil with the most sand (0.71 mg L⁻¹), and after harvest in the mixture that contained 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 soils often generated too much nitrate in effluent.