Mudflat soil amendment by sewage sludge: Soil physicochemical properties, perennial ryegrass growth, and metal uptake

Abstract

The fast pace of cropland loss in China is causing alarm over food security and China's ability to remain selfreliant in crop production. Mudflats after organic amendment can be an important alternative cropland in China. Land application of sewage sludge has become a popular organic amendment to croplands in many countries. Nevertheless, the land application of sludge to mudflats has received little attention. Therefore, the objective of the present work was to investigate the impact of sewage sludge amendment (SSA) at 0, 30, 75, 150 and 300 t ha −1 rates on soil physicochemical properties, perennial ryegrass (Lolium perenne L.) growth and heavy metal accumulation in mudflat soil. The results showed that the application of sewage sludge increased organic matter (OM) content by 3.5-fold while reducing salinity by 76.3% at the 300 t ha −1 rate as compared to unamended soil. The SSA reduced pH, electric conductivity (EC) and bulk density in mudflat soil, increased porosity, cation exchange capacity (CEC) and contents of nitrogen (N), phosphorus (P), exchangeable potassium ions (K + ), sodium ions (Na + ), calcium ions (Ca 2+ ) and magnesium ions (Mg 2+ ) in comparison to unamended soil. There were 98.0, 146.6, 291.4 and 429.2% increases in fresh weight and 92.5, 132.4, 258.6 and 418.9% increases in dry weight of perennial ryegrass at 30, 75, 150, and 300 t ha −1 , respectively, relative to unamended soil. The SSA increased metal concentrations of aboveground and root parts of perennial ryegrass (p < 0.05). The metal concentrations in perennial ryegrass were Zn > Cr > Mn > Cu > Cd > Ni, and the metal concentrations in roots were significantly higher than aboveground parts. The metal accumulation in perennial ryegrass correlated positively with sludge application rates and available metal concentrations in mudflat soil. Land application of sewage sludge was proved to be an effective soil amendment that improved soil fertility and promoted perennial ryegrass growth in mudflat soil. However, heavy metal accumulation in plants may cause food safety concern.

Sewage Sludge Amendment Combined with Green Manuring to a Coastal Mudflat Salt-Soil in Eastern China: Effects on Soil Physicochemical Properties and Maize Yield

“…The pH in mudflat salt-soil decreased with increasing SSA rates, which was similar to our previous studies [9,20,21]. Other authors have also found lowering of pH with SSA [50][51][52].…”

“…The result in the reduction in bulk density by the amendments was not only due to the addition of less dense organic material, but also due to the increase in soil aggregate stability [40] (Figure 6(b)). Previous studies have shown that the application of sewage sludge increased organic carbon in saline and salinized soil [41,42], subsequently increased aggregate stability in saline-sodic and salinized soil [ 42,43], and decreased bulk density in salt-soil and salinized soil [9,42]. Topsoil salinity in mudflat salt-soil decreased as a result of increasing soil aggregate stability and decreasing bulk density.…”

“…Agricultural application of sewage sludge is an effective waste disposal and soil amendment technique that can improve the chemical, physical, and biological characteristics of soils [16][17][18][19]. Sewage sludge is rich in organic matter and other nutrients and can be used for mudflat salt-soil amendment [9,20,21].…”

“…However, the application of sewage sludge combined with green manuring to amend mudflat salt-soils has received no attention. The impacts of applying sewage sludge alone to reclaimed mudflat soil on fertility development, growth of ryegrass, Sesbania, and maize and on heavy metals behaviors including their accumulation and fraction in soil and uptake by plants were investigated and evaluated in our previous studies [9,20,21,35]. This study was one of pioneering studies to investigate and evaluate the sustaining effects of sewage sludge amendment combined with green manuring on the soil aggregates, organic carbon, salinity, pH, and N and P of mudflat salt-soil, as well as yield of maize (Zea mays L.) in mudflats salt-soil in a rain-fed agroecosystem.…”

“…In the area rich in freshwater resources, soil salinity reduction is often accomplished through freshwater irrigation [7]. However, faced with the scarcity of freshwater resources, organic matter amendment is an effective alternative to decrease soil salinity by forming soil aggregates and breaking capillary rise in saltsoil reclaimed from coastal mudflats in the eastern area of China [8,9].…”