Eastern China coastal mudflats: Salt-soil amendment with sewage sludge

The mudflats developed along the east coast of China can be important alternative land sources for agricultural purpose after amending with organic fertilizers in large amounts. Abundant in quality organic matter and other plant nutrients, municipal sewage sludge has great potential to be used in mudflat amendment. However, the conflict between agricultural benefits from soil fertility elevation and environmental risks from hazard substances existing in sewage sludge is the critical issue to be resolved before large-scale application of sewage suldge into salt-affected degradaed mudflats. In compliance with the national standard for land application in China, raw sewage sludge and its compost can be used to amend mudflat salt-soil by one-time or multiple-time application. One-time input of sewage sludge followed by planting and tilling green manure has proved to be an optimal way for rapidly improving salt-affected soil degradation with sustaining fertility benefits and minimal environmental risks. In salt-soil amended with sludge, soil organic matter content was significantly elevated, and soil physicochemical properties were subsequently improved due to the increase of soil porosity, available nitrogen and phosphorus, and the decrease in bulk density, salinity, and pH in salt-soil. Application of sewage sludge to mudflat soils increases soil total and bioavailable heavy metals derived from sludge application and thus increases risk of metal uptake by plants grown in mudflat salt-soil. Environmental risks still represent a major issue in mudflat salt-soil amendment by sewage sludge. Future holistic environmental risk assessment is warranted before using sewage sludge to amend mudflat salt-affected degradated soil in China.