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Irrigation – Does Variability Matter? Ian McIndoe Fraser Scales Background • With irrigation, we have to get SMARTer! – Production – Drainage (due to irrigation AND rainfall) – Allocation limits/ water use – Other factors, e.g. energy • We need irrigation to be well-designed and well-managed • Design sets the platform for high performance The challenge • We live in an imperfect world • Variability is a fact of life • Variability has to be accommodated in both design and management • Optimum solutions are site specific What variability? • Climatic – rainfall, wind, humidity, temperature • Agronomic – crop, stage, physical composition, actual water use • Soils – PAW, infiltration, depth to pans, surface storage • Topographical – shape, slope, infrastructure, natural features What variability? • Water supply – reliability, quantity, quality • Irrigation system – components, pressure, flow, uniformity, application intensity • Management – timing, depth applied • Given this, how can we deal with variability to deliver SMART irrigation? Climate • Generally, good historical data is available – useful for determining design specs and overall need • For rainfall, need to make full use of local data Wind speed Wind speed Temperature Agronomic • Currently, mostly standard values used to determine crop water need • Improved data is being produced – e.g. grazed pasture crop factors • Need for irrigation systems to be designed to better match crop needs Soils • Currently, soil maps often used (e.g. S Map) • Need better information on soil properties and variability of soils on farm – PAW and its variability – Depth to pans/ lower hydraulic conductivity horizons • How much does PAW variability matter? Soil PAW variability Soil PAW variability Topography • Slope matters more than you might think • Very few paddocks are actually flat • Surface redistribution is very common • Need to tailor design and management to maximise benefits • Land levelling under spray irrigation? Application uniformity • Is about how evenly water is being applied to the ground surface • Easily checked using bucket tests • Low uniformity usually leads to low efficiency Spray irrigation bucket test Application uniformity Application uniformity Ponding and surface redistribution • Probably the biggest contributor to low irrigation performance • Can generally be observed • Driven by application intensity and depth applied • Particularly an issue on slopes • Needs full consideration in irrigation design and management. Ponding under pivot Ponding Application intensity Application intensity Supply reliability • Impacts on irrigation mind set – just in case versus just in time • Impacts on production, water use, drainage • Need to have high reliability to achieve high performance Irrigation system • Irrigation method • Pressure variability - tradeoffs • Flow variability – issue with VRI, corner arms, multiple pumps • Voltage variability • INZ Codes of practice – design, installation Performance – 60 mm PAW Performance – 60 mm PAW Performance – 120 mm PAW Performance – 120 mm PAW Irrigation management strategies • Depth of water applied • Return interval • Seasonal limits • Where and how irrigation is scheduled • A lot of work has been done and is being done in this area. • Weather forecasting will be critical! Effect of scheduling location Conclusions • We need to become SMARTer irrigators • Variability does matter in some areas • We need to focus on production, water use and drainage • Better engineering will be required – in the factory: new or improved irrigation methods – in the design shop • We need to target application uniformity • We need to target surface redistribution Priorities • What is easy and cost-effective to implement? – Some things are well understood – Some things need to be better communicated to end users – Some things require further investigation • We can achieve our targets, but its not going to be easy. Questions Temperature Centre-pivot