TEMPORAL AND SPATIAL CHARACTERISTICS OF PHOSPHORUSFRACTIONS UNDER LONG-TERM WASTEWATER IRRIGATION IN TONGLIAO CITY, CHINA

摘要

The irrigation reuse of municipal and industrial effluents conserves freshwater resources and avoids direct nutrient discharges to surface waters. The sustainability of agricultural reuse programs, however, may be challenged by changes in phosphorus (P) availability. To understand the characteristics of P fractions, 130 soil samples were collected around an irrigation drain in May 2009, at the beginning of the growing season. In the study area, total phosphorus (TP) varied from 302.32 to 716.30 mg/kg, residual P varied from18.21 to 126.08 mg/kg, and Olsen P varied from 0.71 to 90.04 mg/kg. The relative abundance detected for nearly every P fraction followed the order Ca-P>residual P>NaOH-Po≈NaOH-Pi>KCl-P. Although NaOH-Pi and most of the Ca-P fractions contributed markedly to P availability, NaOH-Po and Ca-P contributed more to residual P when different phosphate sources were added to the soil. However, the available P in the studied soils represented only 5.5% of the TP, which was inadequate for the growth and development of crops. The influence of wastewater irrigation differs significantly at different depths. Wastewater irrigation is favorable to the transformation of stable P (NaOH-Po and Ca-P) into available P (NaOH-Pi), and cancause an increase in residual P in the shallow layer (0- 60 cm), as well as an increase in TP in the middle layer (60- 110 cm). However, wastewater and groundwater irrigation is beneficial to the increase in soil P concentration in the deep layer (110-170 cm). These effects may depend on soil properties, water cycles and biological processes, among other factors.