Micro station data logger

A digital pH meter was used to measure the soil pH in 1:5 soil/1 M KCl solutions (Mettler Toledo FE20/El20, Shanghai, China). The soil water content (SWC) was calculated by using the oven-drying method. Soil samples were oven dried for 48 h at 105°C. The SWC (%) was calculated by using the following formula:
where W1 is the weight of wet soil plus box, W2 represents the weight of dry soil plus box, and W3 represents box weight.
HOBO® Micro Station Data Loggers (H21-002) were installed to check the soil temperature (°C) and volumetric soil moisture content (m³/m³) during the study period. Soil moisture conditions were monitored using an automatic soil moisture smart sensor (HOBO Micro Station #H21-002 Data Logger; Onset Computer Corp., Bourne, MA, United States; #S-SMx-M005; Supplementary Figure 5). To measure the soil temperature, HOBO 12-bit temperature smart sensors (S-TMB-M0xx) were connected to HOBO Micro Station Data Loggers. Automatic measurements were obtained every 10 s (Supplementary Figures 6, 7). All measurements were recorded using the HOBO® Micro Station Data Logger.

Data on soil temperature at depths of 10 and 20 cm were recorded every minute and saved every five minutes, by an automated measuring system (Hobo Micro Station Data Logger, H21-002, USA). Climatic data in the form of daily precipitation and air temperature were obtained from the local meteorological station at National Hulunber Grassland Ecosystem Observation and Research Station.

The solar dryer was operated on the rooftop of the Sustainable Research Centre of Energy, Universitas Sumatera Utara. During the experimental period, solar radiation and ambient temperature were measured by a HOBO Micro Station Data Logger (version 3.7.12). Temperature, humidity, and mass of red chili inside the drying box or solar collector were measured using sensor DHT22, type J thermocouples, and a load cell weight system data logger with an Agilent type 3497A data acquisition system to record all the measurements. 1 kg of red chili for the experimental treatments was spread on each of the stainless steel trays inside a closed drying box of solar drying and on the stainless steel trays dried directly in the open sun for the natural convection solar drying. Red chili was dried starting at 9:00 AM until 6:00 PM. For the solar drying experiment using desiccant during nighttime, desiccant CaCl₂ was added inside the drying box, and the drying chamber was closed until the next morning. Drying time ended around three days when the dried chili from inside the solar drying box reached a constant weight, and then we ground all the dried chili into a powder.
The solar dryer details in this study are designed as follows (see Figure 1) with the solar collector specification as shown in Table 1.