# Sustainable Management of Water Resources in Supplementary Irrigation Management
## 2 Materials and Methods
### Measuring Soil Water Content  
This section provides a short specification of each sensor used in this study. Sensor installation processes and operational procedures were carried out according to the manufacturer's recommendations and instructions for each sensor. Before sensor installation in the field, some undisturbed soil samples were taken for laboratory calibration in perforated cylindrical plastic columns. The laboratory testing was performed so that each sensor would be analyzed in the full range of moisture content (SAT to PWP) since the pea crop was grown in a non-irrigated condition. Soil samples were taken from the topsoil layer within 7 m diameter of sensors that were placed in the soil. For the calibration of Watermark sensors, soil samples were taken with 300 cc sample rings (Ejikelkamp, soil and water) hammered in the soil at the study site. Watermark sensors were placed in four sampling rings, and the excess soil was trimmed with the knife on top and the bottom of the sampling rings. After the sampling in the field, the sampling rings were taken in the laboratory and placed on a try with filter paper and filled with distilled water. Soil samples were watered until the Water Content (WC) was above FC. Sensors were then left for two days so that they could equilibrate with the matric potential of the soil water. At the same time, four sampling rings were filled only with soil (without the sensors), and those samples were oven-dried (105 \({}^{\circ}\)C for 24 h) and afterward weighted. As for field calibration, soil samples were taken along with each sensor measurement, at the same soil depth as the sensors were installed. After taking the soil samples, the sampling holes were immediately refilled with soil from the same location so that the mass flow of soil water would be reduced. Soil sample weight and sensor readings were taken a few times, averaged and recorded until the SWC was near the WP. For both field and laboratory testing, water content measured by the sensors was compared with corresponding values from gravimetric samples, and as a final result, a regression equation was created. As for the calibration of the tensiometer and TDR sensor, the protocol was similar to the one for GMS with the difference in soil sampling. For this testing, the disturber soil samples were taken, air-dried, passed through 2 mm sieve and packed in containers (10 L). Bulk Density (BD) of the soil samples was approximately the same as that in the field. Afterward, the sensors were inserted into the soil. The rest of the procedure was the same as for the GMS. Before being placed in the soil, GMS and tensiometer were soaked in water for 24 h.  
Figure 3: Rainfall (mm) and air temperatures (\({}^{\circ}\)C) (**a**), and groundwater level (**b**) during the January–July period. Tensiometers were filled with distilled water enriched by algaecide to prevent algae growth inside the tensiometer tube. The proper installation of GMS and tensiometer imply the good contact of a ceramic cup with the surrounding soil. For this reason, before setting the sensors in the soil, we prepared holes with an auger with a similar diameter as a tensiometer tube. Furthermore, we covered the porous ceramic cup and GMS with mud from the excavated site for better hydraulic connectivity with the surrounding soil. In this study, tensiometer 30 and 45 cm long rods were used, while the GMS was set up at 10 cm, 20 cm, 30 cm and 45 cm deep in the soil (Figure 4a). As for TDR, the 10 cm and 20 cm rods were used in this study, while the 30 cm long rods were excluded from the study, since it was impossible to insert the rods into the dry soil at their full length. Unlike tensiometer and GMS, there was no need to prepare the TDR device before usage. However, predrilling holes were made before the rods were inserted vertically into the soil to avoid the compaction caused around the holes by the rods, which can cause underestimation of SWC [27]. Sensors had 5 replications per measurement for each soil depth.