An in situ mini lysimeter with a removable ion exchange resin trap for measuring nutrient losses by leaching from grazed pastures

Abstract

This study describes the construction, installation and evaluation of an in situ mini-lysimeter with a removable ion exchange resin trap for measuring nutrient losses by leaching from grazed pastures. The resin trap efficiently removed solutes from simulated drainage water at a flow rate of 14 mm h-1. Over 88% of each of the solutes was removed from synthetic nutrient solution containing 1.65 mM nitrate-N, 1.65 mM ammonium-N, 0.25 mM sulfate-S (SO2-4-S) and 0.6 mM potassium. In a further test of the system, sulfate leached in simulated rainstorm events from two undisturbed soil cores, taken from legume based pastures of contrasting superphosphate (SSP) fertilizer history following 495 mm of simulated rainfall, was all recovered using the resin trap. Seven times more SO2-4 (21.2 kg S ha-1) was leached and recovered from the resin trap of the core collected from the high fertility (HF, 375 kg SSP ha-1 year-1) site than from the low fertility (LF, 125 kg SSP ha-1 year-1) site (3.1 kg S ha-1). As part of the field evaluation of the technique, lysimeters with resin traps were placed in the field at four sites (8 lysimeters/site) contrasting in fertilizer history, landslope, and dung and urine return. Two additional lysimeters with drainage collection reservoirs (vessels) and eight soil solution samplers were placed on each site to collect drainage water and soil solution. The amount of SO2-4 present in drainage water was more closely related (1:1, R2 = 0.861) to the amount of SO2-4 collected by the resin traps over a period of 9 months than estimates made using soil solution samplers (1:1, R2 = 0.829). The advantages of the resin trap technique over alternative methods for estimating SO4-S leaching losses from field soils are discussed, as are applications of the technique for studying nutrient losses and cycling in grazed pastures.