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TECHNICAL REPORT
Surface Water Quality

Controlled Drainage and Wetlands to Reduce Agricultural Pollution

A Lysimetric Study

Dipartimento di Agronomia Ambientale e Produzioni Vegetali, Università di Padova, Via Romea 16, 35020 Legnaro (Pd), Italy

* Corresponding author (maurizio.borin{at}unipd.it)

Received for publication August 14, 2000. Controlled drainage and wetlands could be very effective practices to control nitrogen pollution in the low-lying agricultural plains of northeast Italy, but they are not as popular as in other countries. An experiment on lysimeters was therefore carried out in 1996–1998, with the double aim of obtaining local information to encourage the implementation of these practices and to gain more knowledge on the effects involved. Controlled drainage + subirrigation and wetlands were all considered as natural systems where alternative water table management could ameliorate water quality, and were compared with a typical water management scheme for crops in the open field. Eight treatments were considered: free drainage on maize (Zea mays L.) and sugarbeet (Beta vulgaris L.), two treatments of controlled drainage on the same crops, and five wetland treatments using common reed [Phragmites australis (Cav.) Trin. ex Steud.], common cattail (Typha latifolia L.), and tufted sedge (Carex elata All.), with different water table or flooding levels. Lysimeters received about 130 g m^-2 of N with fertilization and irrigation water, with small differences among treatments. The effects of treatments were more evident for NO₃–N concentrations than for the other chemical parameters (total Kjeldahl nitrogen, pH, and electrical conductivity), with significantly different medians among free drainage (33 mg L^-1), controlled drainage (1.6 and 2.6 mg L^-1), and wetlands (0.5–0.7 mg L^-1). Referring to free drainage, NO₃–N losses were reduced by 46 to 63% in controlled drainage and 95% in the average of wetlands. Wetlands also reduced losses of total dissolved solids from 253 g m^-2 (average of crop treatments) to 175 g m^-2 (average of wetlands).

Abbreviations: C 0, treatment with a steady water table depth at soil level during the dormant season and fluctuating water table and possible flooding during the growing season on tufted sedge • EC_w, electrical conductivity • M/S 60, treatment with a steady 60-cm water table depth on maize and sugarbeet • M/S 60–100, treatment with a water table fluctuating between 60 and 100 cm depth on maize and sugarbeet • M/S_fd, treatment with free drainage on maize and sugarbeet • P 10, treatment with a steady 10-cm water table depth during the dormant season and a fluctuating water table and possible flooding during the growing season on common reed • P 30, treatment with a steady 30-cm water table depth during the dormant season and a fluctuating water table and possible flooding during the growing season on common reed • T 0, treatment with a steady water table depth at soil level during the dormant season and a fluctuating water table and possible flooding during the growing season on common cattail • T 20, treatment with a steady 20-cm water table depth during the dormant season and a fluctuating water table and possible flooding during the growing season on common cattail • TDS, total dissolved solids • TKN, total Kjeldahl nitrogen