# Assessing Water Infiltration and Soil Water Repellency in Brazilian Atlantic Forest Soils
## 2 Materials and Methods
### Unsaturated and Saturated Soil Hydraulic Conductivity Measurements  
Unsaturated soil hydraulic conductivity was measured using the Mini-Disc Infiltrometer (MDI) [28]. A total of 108 MDI experiments were carried out in the study sites. At each plot, we randomly selected six points with a minimum distance between measurements of 2 m. At the same sampling point, we used three different water pressure head values, \(h\), in the ascending sequences \(-20\), \(-5\), and \(0\) mm, in order to sample several subdomains of the pore size distribution. Unsaturated soil hydraulic conductivity was calculated according to the method proposed by [PERSON] [29]. Before the MDI tests started, we removed the litter and leaves, and the sampled soil surface was gently levelled and smoothed. We used a thin layer of fine sand to ensure the contact between the inflitrometer and the soil (Figure 1). The thickness of the layer of sand was negligible and did not modify the imposed pressure head of the MDI. Visual readings of the water level were taken every 30 s until steady infiltration was nearly reached. For further descriptions of the MDI, details of measurements and calculations of hydraulic conductivity see Decagon Devices Inc. (Washington, DC, USA) [28].  
The saturated soil hydraulic conductivity, \(K_{\delta}\) (mm h\({}^{-1}\)), was measured with ponding infiltration experiments of the Beerkan type [13]. At each plot, we performed seven Beerkan tests, for a total of 126 experiments. We used a steel ring with an inner diameter of 16 cm inserted to a depth of about 1 cm into the soil surface (Figure 1). In each infiltration point, a known volume of water (150 mL) was repeatedly poured into the cylinder at a small height above soil surface (i.e., a few cm) and the energy of the water was dissipated with the hand fingers to minimize the soil disturbance. Then, the time needed for each poured volume to complete infiltration was logged. This procedure was repeated until the difference in infiltration time between three consecutives trials became negligible.  
Figure 1: Picture in the forest site showing the mini-disk inflitrometer and the steel ring used for the Beerkan infiltration test.  
The equilibration time, \(t_{s}\) (s), namely the duration of the transient phase of the infiltration process, was estimated according to the suggested criterion by [PERSON] et al. (2018) for analyzing cumulative infiltration data. More specifically, the \(t_{s}\) value was determined as the first value for which:  
\[\hat{E}=\left|\frac{I(t)-I_{reg}(t)}{I(t)}\right|\leq E \tag{1}\]  
where \(I_{reg}(t)\) is estimated from regression analysis considering the last points, and \(E\) defines a given threshold to check linearity. Equation (1) is applied from the end of the experiment until finding the first data point that fits the condition \(\hat{E}\leq E\)([PERSON] et al., 2018; [PERSON] et al., 2018). An illustrative example of \(t_{s}\) estimation using the commonly used value of \(E=2\%\)([PERSON] et al., 2018) is shown in Figure 2a. Transient infiltration conditions therefore occur from time 0 until time \(t_{s}\) (i.e., when \(\hat{E}>2\)), while steady-state conditions establishes for all data points measured after time \(t_{s}\) (i.e., when \(\hat{E}\leq 2\)).  
At the end of each infiltration test, we collected a disturbed soil sample within the infiltration surface to determine the saturated gravimetric water content, and thus the saturated volumetric water content, \(\theta_{s}\) (cm\({}^{3}\) cm\({}^{-3}\)), considering the values of dry bulk density, \(\rho_{b}\), previously determined.