## 2 Materials and Methods
### Monitoring Equipment: Soil Moisture and Temperature Sensors  
The volumetric soil water content is measured at four depths using Campbell CS616 soil water reflectometers (FDRs). Each FDR sensor consists of two stainless steel rods (300 mm long, 3.2 mm diameter, 32 mm spacing) connected to a printed circuit board. A shielded four-conductor cable is connected to the circuit board to supply power, enable the probe, and monitor the pulse output. The circuit board is encapsulated in epoxy. High-speed electronic components on the circuit board are configured as a bistable multivibrator. The output of the multivibrator is connected to the probe rods which act as a wave guide. The travel time of the signal on the probe rods depends on the dielectric permittivity of the material surrounding the rods and the dielectric permittivity depends on the water content [20]. Digital circuitry scales the multivibrator output to an appropriate frequency for measurement with a datalogger (in our case a Campbell Scientific CR1000). The sensor output is essentially a 0.7 V square wave with frequency dependent on water content. The probe output period average (_PA_) ranges from about 14 microseconds with rods in air to about 42 us with the rods completely immersed in tap water. A calibration function, which needs to be monotonically increasing, converts output period (_PA_) to volumetric water content (\(\theta_{FDR}\)) predicted by the sensor. The probe output period (_PA_) was measured by a special CS616 data logger instruction and stored in the loggers' memory as raw data. Campbell Ltd. [20] provides standard manufacturers' calibration functions, valid for all soils with a bulk electrical conductivity < 500 uS/cm and a soil bulk density < 1550 kg m\({}^{-3}\):  
\[\text{Linear model }\theta_{FDR}=-0.4677+0.0283\textit{PA} \tag{1}\]  
\[\text{Quadratic model }\theta_{FDR}=-0.0663-0.0063\textit{PA}+0.0007\textit{PA}^{2} \tag{2}\]  
where \(\theta_{FDR}\) being the measured volumetric water content expressed as a fraction (m\({}^{3}\) m\({}^{-3}\)), _PA_ the period average (in us) as uncorrected sensor output. The manufacturer reports an error in measured \(\theta_{FDR}\) caused by the temperature dependency of the CS616 sensor, and provides the following correction equation to be applied to the uncorrected sensor output:  
\[\text{PA}_{\text{c}}=\textit{PA}+(20-ST)*(0.526-(0.052\textit{PA})+(0.00136 \textit{PA}^{2})) \tag{3}\]  
where PA\({}_{\text{c}}\) is the temperature corrected period (in us), _ST_ the soil temperature (\({}^{\circ}\)C) at the time and depth of the _PA_ measurement. The coefficients of the standard linear (LM) and quadratic model (QM) given in (1) and (2) are also applied when PA\({}_{\text{c}}\) instead of _PA_. Soil temperature was measured using BetaTherm 100K6A Thermistor (model T107, Campbell) with a measurement range between \(-\)35 \({}^{\circ}\)C and +50 \({}^{\circ}\)C and with an interchangeability error of \(<\)\(\pm\)0.2 \({}^{\circ}\)C within the 0-60 \({}^{\circ}\)C range. According to the manufacturer and in a \"worst case\" situation, all errors add to an accuracy of \(\pm\)0.4 \({}^{\circ}\)C within the range \(-\)24 \({}^{\circ}\)C to 48 \({}^{\circ}\)C and maximally \(\pm\)0.9 \({}^{\circ}\)C within the range \(-\)38 \({}^{\circ}\)C to 53 \({}^{\circ}\)C.  
Three dedicated profile pits were dug in spring 2010 and soil material was layerwise temporarily on-site stored till the pit was ready to be closed again, layerwise with exactly the same soil material. Prior to installation of the sensors, a soil profile description of the pedogenetic horizons was performed and soil core samples were taken at the fixed depth intervals 0-10, 10-20, 20-40 and 40-80 cm, yielding the data in Table 2.  
CS616 sensors were carefully introduced horizontally in the wall of these soil pits (Figure 1). A fork hole with a dummy and level was applied to assure good contact of the rods with the soil following the guidelines of [13].