Detection of nitrate leaching through bypass flow using pan lysimeter, suction cup, and resin capsule

Abstract

We compared the use of mixed-bed ion exchange resin capsules (RC), suction cups (SC), pan lysimeters (PL), and subsurface drainage (DR) for the detection of nitrate movement through a clayey soil where onion (Allium cepa L.) had been cultivated over a period of seven months. At the topsoil level, solutions collected with SC showed higher concentrations of NO₃ ⁻ than the PL-collected samples. At 80-cm depth, however, the concentrations of NO₃ ⁻ were higher for the DR and PL samples than for the SC samples, suggesting that bypass or macropore flow was the primary mechanism of NO₃ ⁻ transport to subsurface drainage or groundwater, while solutions collected by SC mostly represented solutions inside soil aggregates. The use of the resin capsule method resulted in higher values of NO₃ ⁻ at 15- than at 50-cm depth initially but the trend was reversed after sufficient leaching and plant uptake. High and significant correlations were obtained between the amount of NO₃ ⁻ adsorbed on RC at 15-cm depth and the mean concentration of NO₃ ⁻ in the DR samples during the RC installation period and between the NO₃ ⁻ adsorbed on RC at 50-cm depth and the mean NO₃ ⁻ concentration of PL samples at 80-cm depth. Such results indicate that the RC method which enables the detection of nitrate transport via macropore flow is a promising technique for nitrate leaching measurements.

Key Words:

• bypass flow
• nitrate transport
• pan lysimeter
• resin capsule
• suction cup