Soil water status mapping and two variable-rate irrigation scenarios |
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| Authors: | Carolyn B Hedley Ian J Yule |
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| Institution: | (1) New Zealand Centre for Precision Agriculture, Massey University, Palmerston North, New Zealand;(2) Landcare Research, Massey University Campus, Palmerston North, New Zealand |
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| Abstract: | Irrigation is the major user of allocated global freshwaters, and scarcity of freshwater threatens to limit global food supply
and ecosystem function—hence the need for decision tools to optimize use of irrigation water. This research shows that variable
alluvial soil ideally requires variable placement of water to make the best use of irrigation water during crop growth. Further
savings can be made by withholding irrigation during certain growth stages. The spatial variation of soil water supplied to
(1) pasture and (2) a maize crop was modelled and mapped by relating high resolution apparent electrical conductivity maps
to soil available water holding capacity (AWC) at two contrasting field sites. One field site, a 156-ha pastoral farm, has
soil with wide ranging AWCs (116–230 mm m−1); the second field site, a 53-ha maize field, has soil with similar AWCs (161–164 mm m−1). The derived AWC maps were adjusted on a daily basis using a soil water balance prediction model. In addition, real-time
hourly logging of soil moisture in the maize field showed a zone where poorly drained soil remained wetter than predicted.
Variable-rate irrigation (VRI) scenarios are presented and compared with uniform-rate irrigation scenarios for 3 years of
climate data at these two sites. The results show that implementation of VRI would enable significant potential mean annual
water saving (21.8% at Site 1; 26.3% at Site 2). Daily soil water status mapping could be used to control a variable rate
irrigator. |
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| Keywords: | (ECa) mapping Soil water Irrigation |
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