Technologie-Transfer Service und Beratung in Sachen

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Sheltered plot (P1). Rain-fed plot (P2). ➢ Spatial and temporal distributions of soil water status and root development dependent on weather and treatment.
Effects of soil water availability on water fluxes in winter wheat Gaochao

1 Cai ,

Jan

1Agrosphere,

1 Vanderborght ,

Matthias

2 Langensiepen ,

and Harry

1 Vereecken

Institute of Bio- and Geosciences (IBG-3), Forschungszentrum Jülich, Germany 2Faculty of Agriculture, University of Bonn, Germany [email protected]

Introduction

Results

 Quantifying soil water availability in water-limited ecosystems continues to be a practical problem in agronomy;  Transpiration (T) which represents crop water demand is closely related to root water uptake (RWU) in the root zone and sap flow (SF) in plant stems;  Few studies concentrated on combining sap flow measurements in crops with measurements of root development and root zone soil water potential. Objectives:  Monitor sap flow, root development, root zone water potential in winter wheat (Triticum aestivum) for different water treatments;  Simulate root water uptake and plant transpiration for different water treatments using a new water stress function.

Materials and Methods

 Observations P1

P1

P1

P2

P2

P2

Fig. 3 Variations of soil water content at 6 depths in the two plots

 Rhizotron construction

Fig. 4 Variations of soil water potential at 6 depths in the two plots

Fig.5 Root length density distribution along the soil profile of the two plots

 Simulations: first results Sheltered time

10 cm

20 cm

10 cm

0.5 1.0

0.5 1.0

40 cm

60 cm

40 cm

60 cm

80 cm

120 cm

80 cm

120 cm

P1

Germany

Excavation

Backfill

Sheltered plot (P1)

Rain-fed plot (P2)

P2 Fig.6 Variations of hourly root water uptake rate, Sap flow velocity, and potential crop transpiration in the two plots

 Rhizotron setup

Soil water status Soil water content (SWC): TDR*4 Soil water potential (SWP): Tensiometers, MPS-2

Fig.7 Comparisons of simulated and observed soil water content at 6 depths in the sheltered plot (r2=0.80, RMSE=0.014)

a

b

a

Horizontal transparent tubes (rhizotube*3) at 10, 20, 40, 60, 80, 120 cm An accessible camera connected with a laptop Sensors installation

b

Wproot: effective root zone water potential Rrwu: root water uptake/Potential transpiration Rsf: sap flow/potential transpiration

Inside of the facility

Simulation of water fluxes  SWC calibration, water retention curve

Mitglied der Helmholtz-Gemeinschaft

Fig.8 Comparisons of simulated and observed soil water content at 6 depths in the rain-fed plot (r2=0.74, RMSE=0.017)

 Relations and effects

Root development

Hydrus 1D adapted version with a new RWU function ∗ 𝑅𝑊𝑈𝑧 =𝐾𝑟𝑠 𝑁𝑅𝐿𝐷𝑖 (ψ𝑒 -ψ𝑙𝑒𝑎𝑓 )+𝐾𝑐𝑜𝑚𝑝 𝑁𝑅𝐿𝐷𝑖 (ψ𝑖 -ψ𝑒 ) 𝐾𝑟𝑠 (ψ𝑒 -ψ𝑙𝑒𝑎𝑓 )=𝑇𝑝 when ψ𝑙𝑒𝑎𝑓 >ψ𝑙𝑒𝑎𝑓 _Crit 𝐾𝑟𝑠 (ψ𝑒 -ψ𝑙𝑒𝑎𝑓_𝐶𝑟𝑖𝑡 )=𝑇𝑎 else

Fig.9 Relation between simulated root water uptake and sap flow in the sheltered plot (a, r2 = 0.70) and rain-fed plot (b, r2 = 0.68)

a

b

Fig. 1 SWC was calibrated in the lab by Topp and CRIM model with dielectric permittivity. a. Relation between dielectric permittivity and SWC calculated by Topp, CRIM model; b. Conversion of SWC from Topp to CRIM.

b

ψ𝑒 =

𝑁 𝑖=1 ψ𝑖 𝑁𝑅𝐿𝐷𝑖 ∆𝑧𝑖 𝑁 𝑁𝑅𝐿𝐷 ∆𝑧 𝑖 𝑖 𝑖=1

𝐾𝑟𝑠 : the equivalent conductance of the root system (L3 P−1 T−1) 𝑁𝑅𝐿𝐷𝑖 : normalized root length density of the ith soil layer (-) ψ𝑒 : effective root zone water potential (L) ψ𝑙𝑒𝑎𝑓 : leaf water potential (L) ψ𝑙𝑒𝑎𝑓 _Crit : a constant for plants (L) 𝐾𝑐𝑜𝑚𝑝 : the compensatory RWU conductance of the plant (L3 P−1 T−1) ψ𝑖 : the SWP in ith soil layer (L) N: the number of soil layers (-) 𝑧𝑖 : the thick of the ith soil layer (L) 𝑇𝑝 : potential transpiration(LT-1), 𝑇𝑝 = 𝐸𝑇𝑝 * (1-𝑒 −𝑘𝐿𝐴𝐼 ) 𝐸𝑇𝑝 : potential evapotranspiration (LT-1) k: a coefficient representing the extinction coefficient per unit leaf area 𝑇𝑎 : actural transpiration(LT-1)

Sap flow: an improved heat-balance approach** Fig. 2 Water retention curves of the top- (a) and subsoil (b) under dry and wet conditions

Fig.10 a. Differences of effective root zone water potential in the two plots; b. Relation between measured root zone soil water potential and simulated, measured relative transpiration in the two plots

Conclusions

while

a

20 cm

 Spatial and temporal distributions of soil water status and root development dependent on weather and treatment.  Simulated RWU matched well with measured sap flow though the values were underestimated by 1.3% and 6% in two different treatments, respectively.

Ongoing work  Long time (e.g. from vegetation to maturity) effect of different soil water conditions, such as irrigated, sheltered and normal status, on water fluxes in terms of RWU and sap flow.  Dynamic root distribution and hydraulic architecture. References and acknowledgements *Couvreur V, Vanderborght J, Javaux M. A simple three-dimensional macroscopic root water uptake model based on the hydraulic architecture approach[J]. Hydrology and Earth System Sciences Discussions, 2012, 9(4): 4943-4987. **Langensiepen, M., Kupisch, M., Graf, A., Schmidt, M. and Ewert, F., 2014. Improving the stem heat balance method for determining sap-flow in wheat. Agricultural and Forest Meteorology, 186: 34-42 The research gratefully acknowledge the financial support from Deutsche Forschugsgemeinschaft [CRC:TR32] and colleagues in IBG-3, Valentin Couvreur and Jirka Simunek for providing the new version of Hydrus.