Leaching losses of nitrate from undisturbed soil lysimeters under continuous and intermittent rainfall : A dissertation submitted in partial fulfilment of the requirement for the degree of Bachelor of Agricultural Science (Honours) at Lincoln College

Abstract

The amounts of NO₃⁻₋N leached from small undisturbed soil lysimeters (180mm diameter x 200-210mm deep) were compared under continuous and intermittent simulated rainfall conditions. Examination of breakthrough curves from both treatments indicated extensive preferential flow of solute had occurred through macropores such as earthworm burrows, plant root channels, natural structural cracks and large inter-aggregate spaces. Trends indicated that leaching of nitrate was initially less efficient under intermittent versus continuous rainfall. It was suggested that this was due to solute diffusion into intra-aggregate pores during the interval between intermittent rainfall events slowing down leaching losses. This mechanism also delayed the peak leachate NO₃⁻₋N concentrations by approximately 0 . 1 pore volume under intermittent versus continuous rainfall. Leaching losses under continuous and intermittent rain-fall of up to respectively were calculated to occur from NO₃⁻₋N fertiliser applied to the lysimeters offer 100 mm rainfall. It was suggested that fertiliser N losses would be less when several small rainfall or irrigation events immediately followed fertiliser application rather than one large rainfall/irrigation event.