Using sap flow gauges to quantify water uptake by tree roots from beneath the crop rooting zone in agroforestry systems

Howard, S. B.; Ong, C. K.; Black, C. R.; Khan, A.A.H.

doi:10.1007/bf02345326

Cited by 40 publications

(17 citation statements)

References 9 publications

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“…Continuous sap flow measurements can be carried out with modern logging techniques (e.g., multiplexer and data logger), providing insight into the temporal dynamics of transpiration and how for instance RWU changes when SWP decreases over time. The use of sap flow measurements to validate theories of RWU was demonstrated for trees (Gong et al, 2006;Howard et al, 1996;Green and Clothier, 1998), but for crops, in particular wheat, such a validation has not yet been performed under field conditions.…”

Section: Introductionmentioning

confidence: 99%

Root growth, water uptake, and sap flow of winter wheat in response to different soil water conditions

Cai¹,

Vanderborght²,

Langensiepen

et al. 2018

Hydrol. Earth Syst. Sci.

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Abstract. How much water can be taken up by roots and how this depends on the root and water distributions in the root zone are important questions that need to be answered to describe water fluxes in the soil-plant-atmosphere system. Physically based root water uptake (RWU) models that relate RWU to transpiration, root density, and water potential distributions have been developed but used or tested far less. This study aims at evaluating the simulated RWU of winter wheat using the empirical Feddes-Jarvis (FJ) model and the physically based Couvreur (C) model for different soil water conditions and soil textures compared to sap flow measurements. Soil water content (SWC), water potential, and root development were monitored noninvasively at six soil depths in two rhizotron facilities that were constructed in two soil textures: stony vs. silty, with each of three water treatments: sheltered, rainfed, and irrigated. Soil and root parameters of the two models were derived from inverse modeling and simulated RWU was compared with sap flow measurements for validation. The different soil types and water treatments resulted in different crop biomass, root densities, and root distributions with depth. The two models simulated the lowest RWU in the sheltered plot of the stony soil where RWU was also lower than the potential RWU. In the silty soil, simulated RWU was equal to the potential uptake for all treatments. The variation of simulated RWU among the different plots agreed well with measured sap flow but the C model predicted the ratios of the transpiration fluxes in the two soil types slightly better than the FJ model. The root hydraulic parameters of the C model could be constrained by the field data but not the water stress parameters of the FJ model. This was attributed to differences in root densities between the different soils and treatments which are accounted for by the C model, whereas the FJ model only considers normalized root densities. The impact of differences in root density on RWU could be accounted for directly by the physically based RWU model but not by empirical models that use normalized root density functions.

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Section: Introductionmentioning

confidence: 99%

Root growth, water uptake, and sap flow of winter wheat in response to different soil water conditions

Cai¹,

Vanderborght²,

Langensiepen

et al. 2018

Hydrol. Earth Syst. Sci.

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show abstract

“…It is believed to be deep rooting and to possess few superficial lateral roots (Laycock and Wood, 1963;Mwihomeke, 1993). Recent sap flow studies in roots have shown that its root system is capable of extracting 80% of its water from below the crop rooting zone which suggests good potential for below-ground complementarity (Howard et al, 1997;Lott et al, 1996).…”

Section: Introductionmentioning

confidence: 99%

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et al. 2001

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and Gliricidia sepium (Jacq.) Walp. growing in association with maize (Zea mays L.) were examined in semiarid Kenya during the long rains of 1996 and 1997. Even although tree roots penetrated more deeply than maize roots, maximum root length densities for both tree species and maize occurred in the top 200 mm of the soil profile where soil moisture was frequently recharged by rains. Populations of roots in plots containing trees were dominated by tree roots at the beginning of the growing season but because tree roots died and maize root length increased during the cropping season, amounts of tree and maize roots were similar at the end of the season. Thus, there was evidence of temporal separation of root activity between species, but there was no spatial separation of the rooting zones of the trees and crops within that part of the soil profile occupied by crop roots. Tree root length density declined with increasing distances from rows of trees and with depth in the soil profile.Although Grevillea trees were largest, plots containing G. sepium trees always contained more tree roots than plots containing G. robusta trees and Gliricidia was more competitive with maize than Grevillea. Overall, Gliricidia reduced crop yield by about 50% andGrevillea by about 40% relative to crop yield in control plots lacking trees and reductions of crop yield were greatest close to trees. There was less soil moisture in plots containing trees than in control plots. Such difference between control plots and plots containing trees were maximal at the end of the dry season and there was always less soil moisture close to trees than elsewhere in the plots. Plots containing Gliricidia trees contained less soil water than plots containing Grevillea trees.

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“…Due to limitations of sensor installation on small and vulnerable crop stems, sap flow measurements on crops with small stem diameters of less than 5 mm are practically challenging. Senock et al (1996) (Gong et al, 2006;Howard et al, 1996;Green and Clothier, 1998), but for crops, in particular wheat, such a validation has not yet been performed under field conditions.…”

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confidence: 99%

Root growth, water uptake, and sap flow of winter wheat in response to different soil water availability

Cai

Vanderborght

Langensiepen

et al. 2017

Preprint

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Abstract. How much and where water is taken up by roots from the soil profile are important questions that need to be answered to close the soil water balance equation and to describe water fluxes in the soil-plant-atmosphere system. Physicallybased root water uptake (RWU) models that relate RWU to transpiration, root density, and water potential distributions have been developed but far less used or tested. This study aims at evaluating the simulated RWU of winter wheat by the empirical Feddes-Jarvis (FJ) model and the physically-based Couvreur (C) model for different soil water conditions and soil textures 5 against sap flow measurements. Soil water content (SWC), water potential, and root development were monitored noninvasively at six soil depths in two rhizotron facilities that were constructed in two soil textures: stony vs. silty with each three water treatments: sheltered, rainfed, and irrigated. Soil and root parameters of the two models were derived from inverse modeling and simulated RWU was compared with sap flow measurements for validation. The different soil types and water treatments resulted in different crop biomass, root densities and root distributions with depth. The two models simulated the 10 lowest RWU in the sheltered plot of the stony soil where RWU was also lower than the potential RWU. In the silty soil, simulated RWU was equal to the potential uptake for all treatments. The variation of simulated RWU among the different plots agreed well with measured sap flow but the C model predicted the ratios of the transpiration fluxes in the two soil types slightly better than the FJ model. The root hydraulic parameters of the C model could be constrained by the field data but not the water stress parameters of the FJ model. This was attributed to differences in root densities between the different soils and 15 treatments which are accounted for by the C model whereas the FJ model only considers normalized root densities. The impact of differences in root density on RWU could be accounted for directly by the physically-based RWU model but not by empirical models that use normalized root density functions.

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Using sap flow gauges to quantify water uptake by tree roots from beneath the crop rooting zone in agroforestry systems

Cited by 40 publications

References 9 publications

Root growth, water uptake, and sap flow of winter wheat in response to different soil water conditions

Root growth, water uptake, and sap flow of winter wheat in response to different soil water conditions

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Root growth, water uptake, and sap flow of winter wheat in response to different soil water availability

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