Effect of applying hong kong biosolids and lime on nutrient availability and plant growth in an acidic loamy soil

A greenhouse experiment was conducted to evaluate the growth of Brassica chinensis L. in an acidic loamy soil amended with municipal biosolids with or without Ume treatment (750 mg kg^-1). The soil was amended with one of two municipal biosolids from Tai Po (TP) or Yuen Long (YL) wastewater treatment plants at application rates of 0, 5, 10, 25 and 50% (v/v). Initial NH₄⁺-N and PO₄^3--P concentrations in the amended soil increased with an increase in municipal biosolids loading rates and those with biosolids from TP had a greater increase in nutrients than those from YL. However, initial NO₃^--N contents in both municipal biosolids amended soils decreased with an increase in biosolids loading rates, particularly for the soil amended with YL. Soluble K Mg, Na and Ca concentration in the soil increased with application rates. Municipal biosolids amended soil without lime treatment had higher NH₄⁺-N, NO₃^--N and major cation contents than those with lime. Addition of Tai Po municipal biosolids and lime significantly increased the dry weight yields of B. chinensis L., while YL municipal biosolids increased yields only at the 5% rate with lime amendment. The maximum growth was obtained at municipal biosolids application rates of 5 and 10% for TP and 5% for YL for limed soil. Addition of municipal biosolids increased the total N, P, Zn, Cr and major cation concentrations in the shoot tissue, while lime treatment reduced Zn and Cr contents. The high salt and metal concentrations would likely be factors inhibiting plant growth at high application rates, especially for YL biosolids. Further studies to determine the long-term effects of biosolid application on soil and crop quality are warranted.