Dataset on the influence of gas-to-liquid biosludge on arid soil properties and growth performance of alfalfa

The dataset presented here is related to our research article entitled “Effect of gas-to-liquid biosludge on soil properties and alfalfa yields in an arid soil” [1]. It relates to selected performance parameters of alfalfa grown in an arid soil amended with five different (0.75–12%) gas-to-liquid biosludge contents, and selected properties of the soil determined using several material characterization techniques. A detailed description of the raw data relating to figures on alfalfa performance parameters such as fresh biomass weight, plant height, the number of tillers, and biomass elemental content in the companion article is provided alongside additional data on the number of days to flowering. The underlying data for leachate from the soil and underlying spectra and diffractograms for the proton nuclear magnetic resonance (1H-NMR) and X-ray diffraction (XRD) data, respectively, shown in the companion article are presented. These show changes in the pore structure characteristics and the mineralogical composition of the soil, soil-fertilizer, soil-biosludge, and soil-compost mixtures tested over time. Additional data showing the effect of the amendments on the bulk and particle densities of the soil is presented. The dataset demonstrates the influence of the industrial biosludge on arid soil properties and alfalfa yields (Kogbara et al., [1]).

the soil is presented. The dataset demonstrates the influence of the industrial biosludge on arid soil properties and alfalfa yields (Kogbara et al., [1]). © 2019 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons. org/licenses/by/4.0/).

Data description
The raw data relating to figures on alfalfa performance parameters such as fresh biomass weight, plant height and the number of tillers in the companion article [1] are provided in Tables 1e3 respectively. These are presented for each of the three replicates in a given treatment. In contrast, Specifications Table   Subject Environmental Science Specific subject area Waste Management and Disposal Type of data Table, Image, Figure, Raw data How data were acquired Field measurements, Magritek 2 MHz nuclear magnetic resonance (NMR) rock core analyzer, Rigaku Ultima IV multipurpose X-ray diffractometer, standard test methods for determination of metals and anions in water samples, and standard test methods for laboratory determination of density of soil specimens.

Data format
Raw, analyzed and calculated Parameters for data collection Direct field measurements of plant performance parameters, NMR measurements of cumulative porosity, T 2 distribution and T 2 log-mean, XRD patterns collected at 2theta (2q) angle from 3 to 80 degrees with a step size of 0.01 degree and scanning speed of 0.5 /min.

Description of data collection
Alfalfa performance parameters such as aboveground fresh biomass weight was collected at about 5 cm above ground level during each cut. The plant height, the number of tillers and the number of days to flowering were determined by direct measurement, counting and field observation of the plants, respectively. Leachate characteristics and soil density parameters were determined using standard methods for water and soil analysis. Pore structure characteristics and mineralogical composition were determined using the aforementioned NMR and XRD instruments. Data source location Doha, Qatar.

Data accessibility
Data is within this article.  [1].

Value of the Data
The dataset is useful as it provides information on the effect of biosludge from the wastewater treatment plant of a gas-toliquid (GTL) plant on soil properties and growth performance of a forage crop, alfalfa, in a region with challenging soil and climatic conditions. The dataset provides insights, which can be used by researchers, agricultural scientists, civil/environmental engineers, and environmental management practitioners to understand how the amendment of arid soils with GTL biosludge influences soil properties and affect plant growth. The dataset can serve as a starting point for the planning of field trials related to the evaluation of the growth performance of different (forage or industrial) crops in biosludge-amended arid soils. Additionally, the data can assist young researchers in understanding how to employ the advanced material characterization equipment used here to determine soil properties such as pore structure characteristics and mineralogical composition.   these data were calculated and simply reported as the mean and standard deviation in the companion article [1]. Additional data not shown in the companion article on the number of days to flowering is provided in Table 4. Tables 5e7 show the raw data on the elemental content of the plant biomass at  each of the first, second and third cuts, which were summarily presented as the averages of the three cuts in the companion article [1]. Table 8 provides the underlying data for characteristics of the leachate from soils in each of the three replicate pots in a given treatment such as leachate volume, leachate pH, and concentration of selected metals, simply reported as mean and standard deviation in the companion article [1]. Further, the underlying spectra and diffractograms for the proton nuclear magnetic resonance ( 1 H-NMR) and X-ray diffraction (XRD) data, respectively, shown in figures and tables in the companion article are presented in Figs. 1e7. More specifically, the screenshots showing the NMR spectra contain information on the residuals (data-fit) and data error range, as well as the residual and data noise statistics, which indicate the accuracy of NMR measurements but is rarely published. These data show changes in the pore structure characteristics and mineralogical composition of the soil, soil-fertilizer, soil-biosludge, and soil-compost mixtures tested over time. Additional data on the evolution of the bulk and particle densities of the soil due to the amendments is shown in Fig. 8. It should be noted that the elemental composition of the soil in the different treatments is detailed in the companion article [1]. The dataset described here demonstrate the influence of the industrial biosludge on arid soil properties and alfalfa yields.
In this and all subsequent tables, the dashes (À) indicate the absence of data. Thus, all treatments except E1 did not indicate flowering by the first cut.

Experimental design, materials, and methods
The materials and experimental methodology employed in this work are detailed in the companion article [1]. However, pertinent information is presented here to provide a complete description of how the dataset in this article were acquired.

Experimental materials
Cylindrical pots, 92 cm long and 52 cm in diameter, with a valve connected at the bottom to permit leachate collection were employed for the experiment. Leachate collection from the bottom of the pot was facilitated by using gravel (>2 mm) and fine sand in the bottom layer, which served to avoid clogging and facilitate water movement. A slope of 6e7 was created at the bottom of the pot by filling it with glass-reinforced plastic at a slight tilt to enable the direction of the leachate to the water collection valve.
A typical soil available in farms in Qatar was used as control (C1) for the experiments. It was obtained from the research experimental farm of the Agricultural Department of Qatar Ministry of Municipality and Environment at Rawdat Al-Faras, Al Khor. A commercially available 20-20-20 NPK fertilizer was used together with Urea in the second control treatment (C2) as detailed in Table 1 in Kogbara et al., [1]. The fertilizer was applied in three doses at 2, 12 and 24 weeks after planting. A commercially available compost, which corresponds to the type usually used in the farm was employed for the third control (C3) treatment. GTL biosludge with 90e95% dry solids obtained from a GTL plant in Qatar was used in the experiments. The pots were filled with samples of soil, and   Table 1 in Kogbara et al., [1]. The inorganic fertilizer (C2) and compost (C3) controls were used for comparison with the biosludge treatments (E1 e E5) to assess soil fertility improvement caused by biosludge amendment in contrast to typical fertilizer and compost application levels on farmlands in Qatar. Each treatment had three replicate pots arranged in a completely randomized design containing alfalfa seedlings.

Seeding, irrigation and sampling
The pots were first irrigated to set the soil columns before sowing of alfalfa seeds at 1 cm depth at 10 locations for each pot. Irrigation was applied to each pot manually every three days during the winter and daily during the summer. The amount of water applied was based on the irrigation water requirements of alfalfa for different months, which has an annual average of 2.71 mm/day, the lowest being 1.3 mm/day in January and the highest 5.6 mm/day in July. This was conducted to be in line with the normal irrigation practice of the Qatar Ministry of Municipality and Environment.
Soil samples were collected from the pots for initial analysis before seed sowing and at the finalgrowth stage (12 months) using a tube sampler (auger). The samples were collected from the top (top 20 cm depth) and bottom (remaining depth) portions of the pots at the final-growth stage for evaluation of the spatial variability of selected parameters (for e.g., porosity and density). Plant samples were collected after each cut (harvest). All pots were checked simultaneously for leachate formation every 2e4 weeks. The entire leachate volume drainable via the collection valve of the pots was collected in clean glass bottles during each sampling whenever leachate formation occurred.  1. Screenshot of NMR T 2 relaxation analysis showing (from left to right in each image) the underlying spectra for the T 2 distribution (proxy for pore size distribution) and cumulative porosity data, residuals (data-fit) and data error range, and residual and data-noise statistics for the (a) Soil, (b) Soil þ 3% compost, (c) Soil þ 0.75% biosludge, and (d) Soil þ 1.5% biosludge mixtures before planting. Note: The Soil and Soil þ NPK þ Urea treatments are similar before planting. The green vertical dotted line in the T 2 distribution spectrum indicates the T 2 log-mean (proxy for mean pore size).

Fig. 2.
Screenshot of NMR T 2 relaxation analysis showing (from left to right in each image) the underlying spectra for the T 2 distribution (proxy for pore size distribution) and cumulative porosity data, residuals (data-fit) and data error range, and residual and data-noise statistics for the (a) Soil þ 3% biosludge, (b) Soil þ 6% biosludge, and (c) Soil þ 12% biosludge mixtures before planting. Note: The green vertical dotted line in the T 2 distribution spectrum indicates the T 2 log-mean (proxy for mean pore size).     The systematic change of mineral weight percentage with increasing biosludge content at the initial (before planting) stage is not apparent since all treatments contained various amounts of amorphous materials. Hence, the analysis at the final growth stage focused on selected treatments, namely, soil, and soil with 3, 6 and 12% biosludge contents.

Testing methods
The following is a description of the methods used for the analysis of the plant and leachate samples as well as the soil, soil-fertilizer, soil-biosludge, and soil-compost mixtures. For simplicity, mixtures of soil and other planting materials (fertilizer, compost, and biosludge) are referred to as soil in this section.
Aboveground fresh biomass weight: A stainless steel grass shear was used to collect samples for biomass determination from ten plants by snipping the plants at about 5 cm above ground level during each cut [2]. The fresh biomass weight was then taken. Three cuts were carried out on the plants at 3, 6 and 7 months after planting in line with the normal agronomic practice in Qatar.
Plant height, number of tillers and days to flowering: The plant height was determined by measuring the distance from the soil level to the terminal bud of the longest stem on that plant [3]. The number of main tillers/branches was determined by counting them from three randomly selected plants. The days to flowering was recorded as the number of days from the planting date to the opening of the first flower.
Plant elemental content: The elemental content of the plants was determined to evaluate the potential accumulation of elements from the biosludge in plant tissues. Biomass from plant cuts were dried and ground, and subjected to wet digestion with nitric acid. Thereafter, elemental content analysis was carried out using an iCAP 6000 Series ICP-OES (Thermo Scientific, USA).
Leachate characteristics: Leachates collected from the pots were filtered using 0.45-mm syringe cartridge filters to eliminate solid particles. A Mettler Toledo SevenMulti dual (conductivity/pH) meter was used to measure the pH of leachate samples. The leachate samples were subjected to ion chromatography (IC) following ASTM D 4327 [4] using an 850 Professional IC (Metrohm, Switzerland) for analysis of key anions (e.g. NO 3 À , PO 4 3À and SO 4 2À ). The aforementioned ICP-OES instrument was employed for analysis of metals in leachate samples after dilution with a 2% nitric acid solution following ASTM UOP714 [5]. The total nitrogen (Total N) content of the leachate samples was analyzed using a TOC-L series total organic carbon analyzer (Shimadzu, Japan) in line with the APHA Method 5310 [6]. Pore structure characteristics: Pore structure characteristics such as porosity and pore size distribution, which are among parameters that affect the flow of water through porous media [7], were characterized using a 2 MHz nuclear magnetic resonance (NMR) rock core analyzer with a 54 mm probe (Magritek, New Zealand). The equipment generates radio frequency signals or echoes from a saturated sample placed in a magnetic field. The initial amplitude of the signal indicates the total amount of fluid in the specimen, which in combination with a known volume of the saturation fluid is used to determine the cumulative or total porosity. The signal amplitude decays away with one or more Fig. 8. Density analysis of the different treatments at the initial (before planting) and final-growth stages in terms of (a) dry bulk density, and (b) particle density. Note: BS e Biosludge, C e Compost, Fert. e Fertilizer (NPK þ Urea). The dry bulk densities of biosludge and compost are 0.66 and 0.65 g/cm3, respectively. The particle densities of biosludge and compost are 1.64 and 1.72 g/cm3, respectively. relaxation times (T 2 ) that are characteristic of the fluid and its environment. The relaxation time distribution gives information about the environment of the fluid, such as the pore size distribution in the sample. The T 2 relaxation data was determined on a water-saturated soil sample placed in a 20-ml cylindrical plastic container. The Carr-Purcell-Meiboom-Gill (CPMG) sequence was used with 100 ms echo time, an inter-experimental delay time of 6500 ms and 200 scans. A Lawson and Hanson nonnegative least squares fit method was then employed to analyze the CPMG decay using Prospa software (Magritek, New Zealand). The software also outputs the T 2 log-mean, which is a proxy for the mean pore size. Details of the NMR technique are provided in Kogbara et al. [8].
Soil mineralogical composition: The mineralogical composition (crystalline minerals/phases) of the soil samples was monitored using X-ray diffraction (XRD) analysis. The analysis was conducted using a Rigaku Ultima IV multipurpose X-ray diffractometer (Rigaku Corporation, Tokyo, Japan). XRD pattern was collected at 2theta (2q) angle from 3 to 80 with a step size of 0.01 and scanning speed of 0.5 /min. The XRD pattern was analyzed using the integrated Rigaku PDXL2 powder diffraction software.
Dry bulk and particle densities: The bulk density is important as it affects water and solute movement in the soil, and soil aeration. The particle density indicates the relative amounts of organic matter and mineral particles in a soil sample. The dry bulk density was determined as the ratio of the oven-dry (105 C) weight of the soil to the total volume. The particle density was determined using the density bottle method as the ratio of the oven-dry soil weight to the volume of soil solids [9].