Data on the thermal properties of soil and its moisture content

The dataset contains thermal properties of soil such as thermal conductivity, thermal diffusivity, temperature and specific heat capacity in an agricultural farm within the University of Ibadan, Ibadan, Nigeria. The data were acquired in forty (40) sampling points using thermal analyzer called KD-2 Pro. Soil samples taken at these sampling points were analyzed in the laboratory for their moisture content following the standard reference of American Association of State Highway and Transport Officials (AASHTO) T265. The data were acquired within the first and second weeks in the month of April, 2012. Statistical analyses were performed on the data set to understand the data. The data is made available publicly because thermal properties of soils have significant role in understanding the water retention capacity of soil and could be helpful for proper irrigation water management.


a b s t r a c t
The dataset contains thermal properties of soil such as thermal conductivity, thermal diffusivity, temperature and specific heat capacity in an agricultural farm within the University of Ibadan, Ibadan, Nigeria. The data were acquired in forty (40) sampling points using thermal analyzer called KD-2 Pro. Soil samples taken at these sampling points were analyzed in the laboratory for their moisture content following the standard reference of American Association of State Highway and Transport Officials (AASHTO) T265. The data were acquired within the first and second weeks in the month of April, 2012. Statistical analyses were performed on the data set to understand the data. The data is made available publicly because thermal properties of soils have significant role in understanding the water retention capacity of soil and could be helpful for proper irrigation water management. &

Subject area
Earth, Environment and Planetary science More specific subject area

Thermal Physics
Type of data Tables and figures How data was acquired KD-2 Pro thermal Analyzer using SH-1 thermal sensor was used to determine the thermal properties at each sampling point, moisture contents of soil samples were equally determined in the laboratory.

Data format
Raw and Analyzed Experimental factors The top of the ground was scooped before measuring thermal properties to mitigate the effect of top layer. The thermal sensor was calibrated using a twohole Delrin block, the thermal sensor was then correctly placed into the soil and the dual needle was maintained parallel to each other during insertion into the ground.

Experimental features
Thermal properties including thermal conductivity and diffusivity, and specific heat of soil were measured. Moisture contents were also measured in the laboratory Data source location Agricultural farm in University of Ibadan, Ibadan, Nigeria. The study area for the data acquisition is within latitude 7°26′.8020′′ -7°26′.9320′′ and longitude 3°5 3′.7230′′ -3°54′.0000′′

Data accessibility
The Data are available within this article

Value of the data
The dataset can be used to monitor soil moisture content. The knowledge of the dataset can help to improve irrigation scheduling in the area. The knowledge of the irrigation scheduling would help to optimize water usage for improved crop productivity.

Data
The dataset contains thermal properties of soil and their moisture contain in an agricultural farm within University of Ibadan, Ibadan, Nigeria. These thermal properties include thermal conductivity, thermal diffusivity, temperature and specific heat capacity. The data also contain moisture contents that were measured in the laboratory following the standard reference of American Association of State Highway and Transport Officials (AASHTO) T265 [14] and are shown in Table 1. The understanding of these properties would help in proper irrigation planning for water management which in turn would help to optimize water usage in improving crop productivity. The statistical analyses to further understand the statistical distribution of the data are shown in Table 2.

Experimental design, materials and methods
The understanding of the thermal properties of soil is very important in agricultural science. This is because there is exchange of heat at the soil surface. The availability of the dataset on soil thermal properties would help in the improvements of wider applications of the heat of soil and modelling of the water transport in the soil. The availability of these dataset would also help in the understanding of seed germination and crop yield. Several works have been carried out on the various applications of thermal properties of soil [15][16][17][18][19].

Field survey and laboratory analysis
The location of study is an agricultural farm land within the University of Ibadan campus. It is situated between latitude 7°26′.8020′′ -7°26′.9320′′ and longitude 3°53′.7230′′ -3°54′.0000′′, southwestern Nigeria (Fig. 1). The distribution of the sampling points is also presented in Fig. 1. The thermal properties were acquired using a thermal analyzer termed KD-2 Pro (Fig. 2). The KD2 Pro is a fully portable field and laboratory thermal properties analyzer. This probe makes use of transient line heat source technique in the determination of thermal properties of materials. A small dual-needles sensor called SH-1 was used for the measurements. The sensor measures the thermal conductivity, thermal diffusivity, volumetric specific heat and temperature of materials. This sensor uses the heat pulse methodology to generate dependable soil thermal conductivity and thermal diffusivity values. It also estimates the volumetric specific heat using a nonlinear least square procedure. SH-1 sensor is 30 mm long and 1.28 mm in diameter, and the spacing between the two needles is 6 mm. Field sampling design was conducted prior to the data acquisition on the field and random sampling technique was adopted. The surface of the ground was scooped before measurements to remove the effects of top soil on the acquired data. The thermal sensor was calibrated using a white plastic cylinder (a two-hole Delrin block). This was done with a view to test the functionality of the sensor [17,20] in order to ascertain that the sensor is operating according to the prescribed specifications. The Delrin block has two pre-drilled holes where the sensor was inserted. We then allowed it to calibrate for about 15 min before taking measurements. In order to measure thermal properties    using the KD-2 Pro, SH-1 sensor was connected to the KD-2 Pro and was turned on. As part of the percussion for effective data acquisition, the sensor was placed into the soil correctly, maintaining the dual needle sensor to be parallel to each other while inserting the sensor into the soil. The probe was turned on and the thermal properties (conductivity, diffusivity and specific heat) measurements were conducted. Also, after taking the first measurement, the probe was then allowed to rest for more than 15 min before taking subsequent readings. This time is called measurement interval, which allows thermal gradients to dissipate (i.e. for equilibration between readings). Forty sample points were considered for thermal properties measurements while soil samples were collected at these points to determine their moisture contents in the laboratory. These soil samples were put in polythene bags and stored in a cool dry place after which necessary laboratory analyses were carried out on them. Moisture contents were determined in the laboratory following the standard reference of AASHTO T265 [14].

Descriptive statistics
The detailed descriptive statistics which provide basic statistical information about the measured thermal properties and moisture contents are presented in Table 2. The histogram plots indicate the statistical distribution of each measured properties as shown in Fig. 3.