Abstract
Tree rooting strategies are driven by external and internal factors such as climate conditions (rain frequency, wind direction), soil structure and crop type. In order to ensure water efficiency for irrigated crops, it is essential to know how each crop adapts its rooting strategy. We couple Mise-a-la-masse (MALM) with Electrical Resistivity Tomography (ERT) for investigating orange tree roots undergoing different irrigation strategies (Partial Root-zone Drying – or PRD - versus Full Irrigation). This is a totally novel approach giving an overall picture of roots structure and functioning in the subsoil. Our results show clear differences of rooting extent between different irrigation strategies, and identify privileged direction of root development due to distinct RWU patterns. These results are corroborated also by seasonal monitoring of evapotranspiration (ET) and soil water content (SWC), which exhibit very large differences in the soil water distribution in space and time for the trees undergoing different irrigation schedules.
Highlights
Soil is never homogeneously explored by roots
root water uptake (RWU) is controlled by fine structures that are in connection with the woody roots, but their distribution varies as a function of depth, soil heterogeneity, and plant cover and as a function of time, with major seasonal changes[6]
Different Deficit Irrigation (DI) strategies have been applied at this orange orchard ([Citrus sinensis (L.) Osbeck] cv “Tarocco Sciara” C1882 grafted on Carrizo citrange rootstock [Poncirus trifoliata (L.) Raf. × C. sinensis (L.) Osbeck]) since 2010
Summary
Soil is never homogeneously explored by roots. during drought or the application of deficit irrigation (DI) regimes, soil is dried in a highly heterogeneous manner[1] with strong variations at the decimetre scale - in dependence of the soil capillary and hydraulic properties, and of the root water uptake (RWU) processes. Shao et al.[10] report that water stress decreased the root length (in Acacia, Eucaliptus, groundnut), while for orange trees, Hutton et al.[11] observed by soil moisture monitoring that rooting depth was very similar for both control and PRD treatment (confined in first 30–40 cm of soil profile). Cai et al.[23] reported an example of the application of a 3-D macroscopic RWU model considering a dynamic root distribution Another way to improve RWU or root zone water quality models is the application of data assimilation schemes using soil moisture data[24] or ERT25 data. For non-irrigated plants and/or specific growth conditions such as in semi-arid areas or tropical soils, the soil sampling strategy has to be adapted since root length density profiles may be very different, with much larger rooting depth. The results showed that the main depth of RWU ranged from 0 to 60 cm depth during the growing season, with the main contribution occurring in the 0–40 cm depth range
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