Performance of subsurface drip irrigation in pasture production

Performance of subsurface drip irrigation in pasture production under grazed conditions L. Finger 1, 5, Q. J. Wang 2, D. Chen 3, H. M. Malano 4 and A. Hussain 5 Department of Primary Industries, Future Farming Systems Research, Carlton 2 CSIRO Land Water, Highett 3 University of Melbourne, Melbourne School of Land Environment, Parkville 4 University of Melbourne, Department of Civil & Environmental Engineering, Parkville 5 Department of Primary Industries, Future Farming Systems Research, Tatura. Private Bag 1, Tatura, Victoria, 3616 1 Introduction Results Ongoing water shortages and projected long term reductions in water supply are focussing irrigator and water manager minds alike on the need to make best use of available water. Subsurface drip (SSD) irrigation delivers water to the plant rootzone through emitters and thus reduces potential evaporation, runoff and drainage losses. Adoption of SSD on dairy farms may also benefit regional water quality by altering water movement pathways off farm. However, dairy farmers will not invest in SSD irrigation until they are confident it can withstand cattle grazing and be economically viable. This project is testing the feasibility of SSD irrigation of pasture under grazed conditions on different soil types, using current knowledge of best practice. SSD has maintained pasture production under grazing throughout the 2006/07, 2007/08 and 2008/09 seasons without any pugging issues (Figure 1). If necessary a SSD system can be used to germinate pasture on a medium soil without excessive water loss (Figure 2), but SSD should not be used for pasture establishment on light soils. The performance of SSD in achieving uniform spread of water and hence pasture growth is strongly influenced by soil structure and hydraulic behaviour. On the medium soil, pasture production is unaffected by tape spacing or irrigation frequency, but on the light soil pasture production is decreased as tape spacing increases from 0. 6 to 1. 0 and 1. 4 m (see Figure 3). Figure 1: Cattle grazing subsurface drip irrigated pasture at the experiment sites, January 2007 Objectives • Assess practical & economic feasibility of SSD irrigation on dairy farms • Evaluate economic, environmental & social consequences of SSD irrigation on dairy farms, at farm and catchment scales • Produce information about SSD irrigation on dairy farms for irrigators, irrigation service providers, and irrigation extension and policy programs Methods The project is focussed around a field experiment located on two dairy farms in northern Victoria, testing how SSD performs on a ‘light’ and a ‘medium’ soil. Measurements will occur from October 2006 through to June 2010. The experiment will quantify SSD design (tape spacing) and management (irrigation frequency) effects for pasture production and the pathways of water and solute movement. Models will be used to extend the experimental results to other situations. This will identify the best combinations of system design and management for different soils to ensure the technology is used for maximum benefit. The implications for catchment level management of water and water quality will also be assessed. 0. 6 m 1. 0 m 1. 4 m Figure 2: Wetting patterns for the different tape spacings after 30 mm water was applied at the medium soil site, October 2006. Figure 3: Spatial variability in pasture production (t DM/ha) for the different tape spacings at (top) the light soil site and (bottom) the medium soil site, January 2009 For the medium soil, tape spacing does not influence any aspect of the water balance. For the light soil, tape spacing has affected drainage generation, with more drainage occurring on 1. 4 m spacing bays than 0. 6 m bays. Detailed water measurements during 2008/09 showed that for both soils, irrigation frequency has more impact on likely drainage loss than tape spacing. A desktop economic analysis commissioned by this project showed that SSD for pasture production could be profitable, provided that significant improvements in pasture production & consumption and water savings are achieved, with the grown pasture highly valued. The investment is not wise if water savings alone will be achieved. Conclusions The work to date has shown that while subsurface drip irrigation can maintain pasture production under grazed conditions, it will not be suitable for every dairy farm. From an economic viewpoint, significant gains in pasture production and water savings are required for it to be a wise investment. Its success will greatly depend on the soil characteristics of the site. If you are attempting to achieve uniform irrigation and pasture growth across the entire soil area, SSD will work best on duplex soils with a low permeability subsoil. On light soils it is difficult to overcome gravity driven downward movement of water, with implications for both pasture growth and drainage loss. Evaporation and runoff losses are minimal with this system, leaving drainage below the rootzone as the possible pathway for water loss. Published by the Department of Primary Industries, August 2009. © The State of Victoria, 2009. This publication is copyright. No part may be reproduced by any process except in accordance with the provisions of the Copyright Act 1968. Authorised by the Victorian Government, 1 Spring Street, Melbourne 3000. 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