Growth characteristics, nutrient uptake, and metal accumulation of ryegrass (Lolium perenne L.) in sludge-amended mudflats

The objective of this study was to investigate the impact of sewage sludge amendment (SSA), with the rates of 0, 30, 75, 150, and 300 t ha(1), on soil chemical properties and biomass, aboveground and root growth, and nitrogen and phosphorus uptake of ryegrass (Lolium perenne L.) seedling grown on a mudflat soil. Results showed that SSA modified the chemical properties of mudflat soil by decreasing soil salinity and pH, increasing soil organic matter, total and available N and P, and heavy metals. The biomass of root and aboveground parts of ryegrass showed increments with increasing SSA rates. Maximum increases of 5.6- and 1.3-fold in fresh weight of aboveground parts and root of ryegrass were observed at 300 t ha(1) rate. Root grown at all SSA rates showed positive response to higher nutrient availability in the mudflat soil with increasing root average diameter and volume. The root length and surface area at 30 t ha(1) SSA rate was significantly higher than those in other treatments. The sewage sludge amendment increased N and P content in both aboveground and root parts of ryegrass. Cd, Cr, Cu, Mn, Ni, and Zn accumulation in ryegrass was positively correlated with SSA rates. However, heavy metal concentrations in ryegrass did not exceed the safety standard for feed in China (GB 13078-1999), except for Cd at 300 t ha(1) SSA rate. The study suggests that sewage sludge can be applied for mudflat soil amendment, which provides an innovative solution pertaining to new arable land resources and solid waste disposal. The optimum SSA rate is 150 t ha(1) with maximum plant yield yet permissible metal accumulation.