Minimising surface water pollution resulting from farm-dairy effluent application to mole-pipe drained soils. I. An evaluation of the deferred irrigation system for sustainable land treatment in the Manawatu

• Published in: New Zealand journal of agricultural research Vol. 47; no. 4; pp. 405 - 415
• Main Authors: Houlbrooke, D. J., Horne, D. J., Hedley, M. J., Hanly, J. A., Scotter, D. R., Snow, V. O.
• Format: Journal Article
• Language: English
• Published: Taylor & Francis Group 01.12.2004
• Subjects: farm-dairy effluent; mole drainage; nutrient loss; pipe drainage; preferential flow; soil water balance; spray irrigation; New Zealand
• ISSN: 0028-8233; 1175-8775
• DOI: 10.1080/00288233.2004.9513609

There is little information available on the magnitude of nutrient losses to surface water from the two-pond and daily irrigation treatment systems for farm-dairy effluent (FDE). A research site has been established on a mole-pipe drained Tokomaru silt loam at Massey University's No. 4 Dairy Farm (475 cows) to investigate some of these issues. The site consists of four plots (40 × 40 m) that have been instrumented to allow the continuous monitoring of drainage and surface runoff. The research was conducted over three lactation seasons (2000/01-2002/03). Based on data collected at the study farm it was calculated that in the past 1500 kg N yr −1 and 250 kg P yr −1 were potentially discharged from the two-pond system directly to a stream. A simulation exercise suggests that approximately 108 kg N yr −1 and 18 kg P yr −1 would be lost to surface waters if daily irrigation was practised at the farm. The problems of daily irrigation, particularly those related to surface runoff, were further quantified in an experiment in which a single 25-mm FDE irrigation was applied to a soil near field capacity. Approximately 40% of the applied effluent left the soil profile as mole and pipe drainage and 30% as surface runoff. These losses equated to 12 kg N ha −1 and 2 kg P ha −1 . To minimise nutrient losses from land application of FDE, a system called "deferred irrigation" was designed. Deferred irrigation involves storing effluent in a two-pond treatment system and then applying it strategically when there is a suitable soil water deficit, i.e., the irrigation volume does not exceed the potential soil-water storage. The evaluation of deferred irrigation over three lactation seasons showed that direct losses of nutrients to surface waters were almost eliminated and resulted in the drainage of only approximately 1% of the total effluent nutrients applied. The successful adoption of the deferred irrigation system would require only the capability to store effluent and model or measure soil moisture status within the active root zone.