Cropping Systems for Phytoremediation of Phosphorus-Enriched Soils

Eutrophication of freshwater bodies is frequently attributed to elevated phosphorus (P) concentrations in surface runoff from P-enriched agricultural soils. Forage and grain-cropping systems were compared for their effectiveness at remediating P-enriched soils. At each of four locations, one of three forage systems (Forage I = cereal rye silage and corn silage annually; Forage II = alfalfa; Forage III = annual ryegrass and corn silage annually) and the grain system (corn, small grain, and soybean rotation) were maintained for 3 yr on soils with five distinct initial soil P concentrations that were established by using four annual applications (1994–1997) of five different rates (0, 100, 200, 300, and 400 kg total P ha⁻¹ y⁻¹) of poultry manure, dairy manure, or commercial fertilizer. Across all manure P treatments at all locations, the forage systems had greater removal of P than the grain system. Soil P concentration changes (2001–2004) did not reflect differences in crop P removal. Few significant reductions in soil P concentration were observed for either crop system. When reductions did occur, they were for the more highly enriched soil P treatments. No significant reductions in soil P concentration have occurred for the lowest manure P treatments. Considerable variability in crop P concentrations was observed among species at locations and among years produced. However, crop P concentrations did increase uniformly as soil P concentration increased, indicating that luxury consumption of P does occur in agronomic species produced on P-enriched soils.

KEY WORDS:

• phosphorus uptake
• cropping systems
• soil phosphorus

Notes

^a BL = broiler litter; DM = solid dairy manure; TSP = triplesuperphosphate fertilizer.

^a Forage I = cereal rye and corn harvested as silage annually; Forage II = alfalfa @ 4–5 harvests yr⁻¹; Forage III = annual ryegrass and corn harvested as silage annually.

^b Means for the 2yr for a crop system within a location and within a manure phosphorus treatment that have the same letter but different letter case are significantly different (P < 0.05).

^c Means for the two crop systems within the same location, the same year, and the same manure phosphorus treatment that have different letters that are either upper or lower case are significantly different (P < 0.05).

^d soil P concentration comparisons for WMREC are between 2002 (first year) and 2004.

^a NRC (2001).

^b NM-3 (Steinhilber et al., 2004).

^c Means with the same letter within a row are not significantly different (P = 0.05).

^a NRC (2001).

^b NM-3 (Steinhilber et al., 2004).

^c Means with the same letter within a row are not significantly different (P = 0.05).

^a NRC (2001).

^b NM-3 (Steinhilber et al., 2004).

^c Designates the number of location-years that a grain crop was produced during 2001–2003.

^d Means with the same letter within a row are not significantly different (P = 0.05).

^a NRC (2001).

^b NM-3 (Steinhilber et al., 2004).

^c Means with the same letter within a row are not significantly different (P = 0.05).