Maximising the value of irrigation
The MBIE Programme ‘Maximising the Value of Irrigation’ is undertaking research to support industry develop irrigation control systems that improve productivity, minimise wasted water, and reduce negative environmental impacts such as ponding and nitrate leaching.
The programme is led by Landcare Research with Plant & Food Research, and also includes researchers from FAR, Lincoln AgriTech, Massey University, and the University of Southern Queensland. The Programme is also financially supported by the Vegetable Research and Innovation Board, Hawke’s Bay Regional Council, ECan, and IrrigationNZ.
The Programme, now half-way through its 6-year duration, has gathered a wide range of soil data for modelling over two irrigation seasons from commercial farms (arable, mixed arable/pastoral, process vegetables, high-value seed crops, and fresh vegetable crops) and research trial plots (Massey, Lincoln, Chertsey). These data are being used for scenario modelling with APSIM software (Agricultural Production Systems Simulation model, www.apsim.info) to investigate (i) potential benefits of precision irrigation for different levels of soil variability, and (ii) soil management effects on irrigation water use efficiency (including mulching, cultivation, hydrophobicity). The model uses a specially developed spatial framework for sub-paddock scale modelling (Fig. 1) with a web processing service created to generate APSIM soil libraries from the S-map database.
An APSIM modelling exercise has been completed for one focus farm, where a 470-m centre pivot, with variable rate control, is used to irrigate a range of crops at any one time. The modelling was undertaken by Landcare Research scientist, Joseph Pollacco, for a 10-year period. Recent alluvial soils and older Brown and Gley soils are mapped for this site by pedologist Andrew Manderson and the modelling exercise compared the three alluvial soils (Fig. 2). The results showed that variable rate irrigation would reduce drainage and run-off by about 14% through reducing irrigation-related drainage events, and that these water savings vary from year to year depending on patterns of rainfall during the irrigation season. The modelling exercise also found that water savings for a shallow rooting crop (peas) was 11% and for a deeper rooting crop (maize) was 8%.
Modelling exercises are being validated by in-field soil moisture monitoring, using wireless soil moisture sensor network technologies, developed within this programme, by Jagath Ekanayake. Jagath has also developed a smart phone app, which is being developed and shared with participating farmers, to investigate how effectively real-time soil moisture monitoring can be used to improve irrigation scheduling decisions (see Apps for Irrigation Control).
CAROLYN HEDLEY, PIERRE ROUDIER AND JAGATH EKANAYAKE – LANDCARE RESEARCH
Figure 1 Soil maps are converted into (a) management zone maps for potential upload to precision irrigation control software, and for Spatial-APSIM modelling exercises. A digital elevation map (b) is used to derive a relative wetness index (c) for each cell, and potential water run-off pathways (d).
Figure 2: Farm-scale map overlaid onto EM map indicates the pattern of soils occurring under the centre pivot (soil map: A Manderson).
