Understanding water losses from irrigated pastures on loess-derived hillslopes

  • Stephanie Langer Plant & Food Research
  • Rogerio Cichota Plant & Food Research
  • Steve Thomas Plant & Food Research
  • Dirk Wallace Plant & Food Research
  • Gina van der Klei Plant & Food Research
  • Mike George Plant & Food Research
  • Tom Johns ECan
  • Peter Almond Lincoln University
  • Shane Maley Plant & Food Research
  • Nathan Arnold
  • Wei Hu Plant & Food Research
  • MS Srinivasan NIWA
  • Channa Rajanayaka NIWA
  • Matt Dodson ECan
  • Roderick Hayman Springbank Farm
  • Chandra Ghimire AgResearch
Keywords: runoff, irrigation, water balance, fragipan, pasture

Abstract

Irrigation is likely to increase water losses from hillslopes, particularly on loess-derived soils with impeded drainage. This is important as irrigation of these soils in New Zealand is increasing. A field site was established to measure runoff from a pasture hillslope irrigated by a centre-pivot in South Canterbury. Between November and March, 161 and 199 mm of irrigation was applied, with 23% more at the bottom of the slope. Runoff varied with position in the hillslope, with 3.5 times from the bottom plot (52 mm) compared to the top. Over the length of the slope (40 m) this represents a potential loss of 9% of precipitation, or 21% of the irrigation. Evidence for saturation excess and infiltration excess runoff was observed, with antecedent soil moisture conditions being a key factor. Pasture production and water use efficiency (WUE) also varied with slope, the least (4.6 t DM/ha or 12 kg DM/ha/mm) observed at middle and most at the top of the slope (10.1 t DM/ha or 23 kg DM/ha/mm). This was likely due to a combination of differences in radiation and soil conditions. There was indication that pasture growth was limited by water availability at the top and potentially excess at the bottom of the slope. Our results indicate potential for improving irrigation practices.

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Published
2020-09-29
Section
Research article