Residual effects of one-time manure, crop residue and fertilizer amendments on a desurfaced soil

Organic amendments are often used to mitigate the effects of soil degradation caused by erosion. In spring 1992, a desurfaced soil (∼15 cm depth mechanically removed to simulate erosion) received one-time applications of amendments (20 Mg ha -1 dry wt), and was subsequently seeded annually to spring wheat (Triticum aestivum L.). By 2009, six treatments (fresh and old cattle manure, hog and poultry manure, alfalfa (Medicago sativa L.) hay and straw+200 kg P ha 1) had cumulative yields which were not significantly different (-6.5 to -19.5%) from the topsoil check treatment (no topsoil removed, no amendment). Most (8 of 13) amendment treatments showed significant power function relationships between cumulative grain yield (expressed as a percent of topsoil check) and time while two (hog and poultry manure) were quadratic. Soil organic carbon (SOC) accrued on all treatments over time, increasing significantly from an average of 12.2 g kg -1 in 1992 to 13.2 g kg -1 (0-15 cm depth) in 2003. Residual amendment effects on total nitrogen (N) and phosphorus (P) were apparent 11.5 yr after application. Results demonstrated that while drastically disturbed soils may recover productivity in the absence of organic amendments (e.g., eroded check treatment), organic amendments play a residual role in their ongoing maintenance.