Effect of biochar application on soil hydrological ...

Geoderma 281 (2016) 11–20

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Effect of biochar application on soil hydrological properties and physical quality of sandy soil Tomasz Głąb a,⁎, Joanna Palmowska a, Tomasz Zaleski b, Krzysztof Gondek c a b c

Institute of Machinery Exploitation, Ergonomics and Production Processes, University of Agriculture in Krakow, Poland Department of Soil Science and Soil Protection, University of Agriculture in Krakow, Poland Department of Agricultural and Environmental Chemistry, University of Agriculture in Krakow, Poland

a r t i c l e

i n f o

Article history: Received 30 August 2015 Received in revised form 21 June 2016 Accepted 24 June 2016 Available online xxxx Keywords: Biochar Winter wheat Miscanthus Sandy soil Soil porosity Soil water retention

a b s t r a c t Biochar is a valuable soil amendment and is recognized to have a positive effect on the crop yield, soil quality, nutrient cycling, and carbon sequestration. However, the effect depends on biochar characteristics, doses, and soil properties. This paper reports the study on determination of the effect of different rates of biochar based on their size fractions on water retention characteristic of sand-based rootzone mixture characteristic for natural turfgrass rootzone. The pot experiment was established using a soil with the texture of loamy sand. Mixtures of biochar and soil were prepared in March 2014. Biochar was produced using the straw of two species, namely miscanthus and winter wheat, by pyrolysis process at a temperature of 300 °C for 15 min with limited air access. Then, biochar particles were separated into three size fractions as follows: 0–500 μm, 500–1000 μm, and 1000–2000 μm. The following four biochar rates were used in this experiment: 0.5%, 1%, 2%, and 4%. The results indicated that biochar application significantly improved the physical properties of the tested sandy soil. The basic soil physical parameters, such as bulk density and total porosity, were not only dependent on the rate but also on the size of the biochar. Small particles of biochar reduced the volume of soil pores in diameter below 0.5 μm but increased the volume of larger pores with a diameter 0.5–500 μm. Biochar application increased the available water content (AWC), especially when the finest fraction was used (0.064 cm3 cm−3). Biochar made of miscanthus was characterized by higher AWC (0.056 cm3 cm−3) than that made of winter wheat (0.050 cm3 cm−3). In the present study, the soil water repellency was increased by biochar application, but it was still classified as non-repellent. © 2016 Elsevier B.V. All rights reserved.

1. Introduction Sandy soil is widely used at sport facilities with natural turfgrass. Two national standards are commonly used in the construction of natural turf sport field: ASTM (American Society for Testing and Materials) standard F2396-04 (Standard Guide for Construction of High Performance Sand-Based Rootzones for Sports Fields) and DIN 18035-4 (German National Standard, Sports Grounds, Sports Turf Areas). According to these standards, a typical soil profile under sport turfgrass contains a sand-enriched rootzone laying on a coarse-textured sand or gravel. A high-quality turf is related to grass cultivars, climate conditions, and management practices and these factors are strictly connected to proper rootzone layer construction. The principal motivation of using high sand-content rootzone is to improve the mechanical properties of the turf surface and to resist soil compaction from frequent foot traffic. This is in contradiction with the main function of rootzone, which is to ⁎ Corresponding author at: ul. Balicka 116B, 31-149 Krakow, Poland. E-mail address: [email protected] (T. Głąb).

http://dx.doi.org/10.1016/j.geoderma.2016.06.028 0016-7061/© 2016 Elsevier B.V. All rights reserved.

store water and nutrients (McCoy and McCoy, 2009). The coarsestructured soil with low clay content is characterized by a lack of water retention and nutrient-holding capacity necessary for healthy turf growth (Nasta et al., 2009). The following two types of soil amendments are commonly used together with sand to make up the rootzone material: peat or soil, or both. The first is commonly known as an inorganic amendment with silt and clay texture modifying water retention (Li et al., 2000). The second is to increase the soil organic matter content, which improves water retention. According to Rawls et al. (2003), the soil water content at high water potential is affected more strongly by the organic carbon compared to that at low water potential. Water retention of coarsetextured soil is substantially more sensitive to the amount of organic carbon compared to fine-textured soils. In addition water retention of the soil mixture at the sport turfgrass can be improved by adding more organic materials such as sphagnum peat moss (Bigelow et al., 2004) or composted sewage sludge (Cheng et al., 2007). Some inorganic amendments have also been suggested for the use in these sandy soils, in order to increase plant available water including calcined clay,

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T. Głąb et al. / Geoderma 281 (2016) 11–20

diatomite or zeolite (Li et al., 2000). A combination of these options allows to retain additional water, increasing the amount of available moisture in the root zone, and thus permitting longer intervals between irrigations (Shao-Hua et al., 2012; Andry et al., 2012). However, reports on the positive effect of organic matter on soil hydraulic properties are sometimes contradictory. Danalatos et al. (1994) did not find any effect of organic matter content on water retention. There is also risk that the organic substances content in soil and their biodegradation products may induce water repellency, particularly in coarse textured soils (Scott, 2000; McKissock et al., 2000). Thus new methods and materials for improving water retention are still being sought. Biochar, the solid product of biomass pyrolysis, seems to be a very promising soil amendment. During the past decade, biochar has been considered as a valuable product that gives opportunities for soil improvement and carbon sequestration, in order to mitigate climate change (Peake et al., 2014). Biochar amendment has been shown to influence physical, chemical, and biological properties of soil (Mukherjee and Lal, 2013; Herath et al., 2013; Lehmann et al., 2011). This characteristic of biochar is mainly ascribed to its physical feature such as its highly porous structure and large surface area (Atkinson et al., 2010). The biochars are usually described as a heterogeneous material that varies in its chemical and physical properties. This variability depends not only on the parameters involved in pyrolysis but also on the materials used to produce biochar (Atkinson et al., 2010; Gundale and DeLuca, 2006). Nutrient availability (N and P) in soil may be enhanced by the addition of biochar due to a higher cation adsorption (Liang et al., 2006) or by increased pH in acid soils (Van Zwieten et al., 2010). Lehmann et al. (2011) reported that the application of biochar affects the activity of soil fauna and microorganisms. However, the effect depends on biochar characteristics, doses, and soil properties (Jha et al., 2010). According to Mahmood et al. (2003), the incorporation of biochar appears to have a positive impact on mycorrhizal fungi and also influences basic soil properties such as soil bulk density, texture, and particle size distribution. By adding biochar, soil macroporosity and mesoporosity were significantly increased and thus improved the aeration and water availability for plant roots (Herath et al., 2013). On the contrary, in their experiment on sandy soil, Jeffery et al. (2015) found no significant effects of biochar application on soil water retention. Similar results were observed by Hardie et al. (2014) with no improvement in soil moisture and water retention characteristics. Based on these results, the following question arises: What are the predominant factors that prevent improvement of soil quality by the addition of biochar? We hypothesize that the biochar application has a positive effect on the soil pore system but this effect is modified by factors connected with biochar properties. The objective of this study was to determine the effect of different rates, size fractions, and feedstock type of biochar on water retention characteristics of sandy soil in a standard of natural turfgrass rootzone. The knowledge of the relationship between soil water retention properties and biochar amendments can be useful in turfgrass management particularly when concerned with irrigation. 2. Material and methods 2.1. Sample preparation Biochar was produced from the biomass of the following two species: miscanthus (Miscanthus × giganteus) and winter wheat (Triticum aestivum L.). The straw of miscanthus and winter wheat was left to dry at ambient air temperature, ground to fine particles (b4 mm), and mixed to ensure homogeneity. The plant material was pyrolyzed in an electrical laboratory furnace equipped with a temperature controller at a temperature of 300 °C for 15 min with limited air access (International Biochar Initiative, 2014). The speed of the furnace heating was 10 °C min−1. The time and temperature were set according to the research of Lu et al. (2013), Mendez et al. (2013), Gondek et al. (2014) and Domene et al. (2015).

The biochar was then removed from the furnace and cooled in a desiccator. It was then passed through sieves with a mesh size of 500, 1000 and 2000 μm, which resulted in three biochar classes of the following size fractions: 0–500 μm, 500–1000 μm, and 1000–2000 μm. All particles with a diameter above 2000 μm were removed from the samples. The basic chemical characteristics of the biochar are presented in Table 1. The dry weight content was determined in materials which had been shredded and sifted through a sieve with a mesh size 1 mm, and then dried at temperature of 105 °C for 12 h (Jindo et al., 2012). Content of total forms of carbon and nitrogen was determined on the vario MAX cube CNS analyzer (Elementar Analysensysteme GmbH, Hanau, Germany). The total contents of other macroelements and trace elements were determined after incinerating the sample in a chamber furnace at 450 °C for 12 h and mineralization of the residue in a mixture of concentrated nitric and perchloric acid (3:2 v/v) (Gondek et al., 2016). Concentration of the studied elements in the obtained solutions was determined by inductively coupled plasma optical emission spectrometry Optima 7300 DV ICP-OES (Perkin Elmer, Waltham, Massachusetts, USA). Soil with a texture of loamy sand (81% sand, 14% silt, and 5% clay) was used, according to the ASTM F2396-04 and DIN 18035-4 standards. Mixtures of biochar and soil were prepared in March 2014 with the following biochar rates (which equal biochar mass as a percentage of the whole sample mass): 0.5% biochar (B05), 1% biochar (B1), 2% biochar (B2), and 4% biochar (B4). The control object without biochar addition (B0) was also tested. The prepared samples were stored in 0.03 m3 pots for three months with periodic watering to avoid drying. In June 2014, the soil samples were collected for laboratory measurements using steel cylinders with a capacity of 100 cm3 (5.02 cm diameter and 5.05 cm height) in six replications for every treatment. To achieve a comparable and replicable compaction of samples, they were subjected to consolidation cycle under a static load of 600 g, based on to the method described by Stock and Downes (2008). These samples were used to determine soil water retention characteristics and bulk density (BD). 2.2. Measurements The soil water retention curve (SWRC) was determined using pressure plates (Soil Moisture Equipment Corp., Santa Barbara CA, USA) according to Richards' method (Klute and Dirksen, 1986a). The soil samples were saturated with water for 24 h. After saturation, suction was successively applied to establish seven matric potentials, namely, −4, −10, −33, −100, −200, −500, and −1500 kPa. Van Genuchten (1980) parameters were fitted to the SWRC experimental data with the Mualem constraint (Mualem, 1986) (Eq. (1)): θs −θr θ ¼ θr þ 1 n 1−n 1 þ ðαhÞ

ð1Þ

where θ is the soil water content (cm3 cm−3), h represents the matric potential (kPa), θs is the saturated water content (assuming equivalence with total porosity (TP)), θr is the residual soil water content, while α and n represent the model parameters. θr is associated with the immobile water present within a dry soil (at h = ∞). It was found that the value of the residual soil water content does not appear to greatly affect the goodness of fit of the SWRC (Fayer and Simmons, 1995; Leij et al., 2005; Haverkamp et al., 2005); therefore, in this study, θr = 0 was set. The SWRC models (Eq. (1)) were fitted to the experimental water retention data using the method of nonlinear least-squares procedure in the statistical software package Statistica v. 10.0 (StatSoft Inc., Tulsa OK, USA). Based on this method, the following soil quality parameters were calculated: (i) Field capacity (FC), defined as the equilibrium volumetric soil water content at −10 kPa matric potential


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Table 1 Chemical properties of feedstock and biochar obtained from winter wheat and miscanthus. Standard deviations in parentheses. Feedstock (dry matter)

Biochar

Biochar characteristics

Units

Triticum aestivum L.

Miscanthus × giganteus

Triticum aestivum L.


Dry matter C N P K Mg Na Ca Cd Cr Cu Fe Mn Ni Pb Zn

g kg−1 g kg−1 g kg−1 g kg−1 g kg−1 g kg−1 g kg−1 g kg−1 mg kg−1 mg kg−1 mg kg−1 mg kg−1 mg kg−1 mg kg−1 mg kg−1 mg kg−1

903.3 (3.7) 439.6 (0.96) 7.18 (0.78) 1.29 (0.32) 5.83 (0.39) 0.89 (0.17) 0.17 (0.07) 3.99 (1.17) 0.62 (0.02) 7.59 (0.34) 2.28 (0.16) 492.1 (21.2) 65.12 (3.65) 4.17 (0.44) 1.78 (0.11) 50.10 (0.84)

887.2 (14.4) 452.7 (0.34) 3.86 (0.08) 0.62 (0.02) 2.53 (0.07) 0.52 (0.00) 0.09 (0.00) 1.90 (0.11) 0.24 (0.01) 3.63 (0.40) 2.34 (0.28) 350.3 (14.2) 49.16 (1.30) 2.74 (0.05) 1.91 (0.05) 19.93 (0.29)

988.9 (3.5) 632.9 (1.0) 11.98 (0.24) 2.61 (0.313) 12.55 (0.319) 1.69 (0.150) 0.191 (0.054) 7.41 (0.722) 0.99 (0.02) 13.43 (0.53) 4.23 (0.03) 867 (8.67) 117 (1.13) 6.34 (0.55) 2.84 (0.21) 82.8 (1.02)

991.2 (2.7) 658.5 (2.0) 7.53 (0.056) 1.38 (0.039) 5.40 (0.284) 1.01 (0.038) 0.122 (0.011) 4.01 (0.183) 0.41 (0.05) 5.91 (0.74) 5.02 (0.67) 702 (5.47) 103 (4.91) 3.92 (0.16) 3.14 (0.32) 40.4 (1.64)

(ii) Permanent wilting point (PWP), volumetric soil water content at −1500 kPa matric potential (iii) Relative field capacity (RFC), defined by Reynolds et al. (2008) as proportion between FC and θs (iv) The slope (S) at the inflection point of the SWRC according to the S-theory by Dexter (2004), with the Mualem constraint. The large value of S indicates the presence of structural pores and is characteristic for good soil quality. (v) The available water content (AWC), calculated as the difference between the FC and PWP.

After Dekker and Jungerius (1990) described the following repellency classes: non-water repellent (WDPT b 5 s), slightly water repellent (WDPT 5–60 s), strongly water repellent (WDPT 60–600 s), severely water repellent (WDPT 600–3600 s), and extremely water repellent (WDPT N 3600 s). 2.3. Statistics The analysis of variance for a randomized block design was performed in order to evaluate the significance of biochar rates and size of particles on soil physical parameters using the statistical software package Statistica v. 10.0 (StatSoft Inc., Tulsa OK, USA) (Table 2). The data were checked for the normality of the distribution using Shapiro– Wilk test and for homogeneity of variance using Levene's test. Means were compared using Tukey's test with a level of significance of P b 0.05. Regression analysis was carried out, in order to describe the relationship between water retention and biochar treatments.

The SWRC models were also used to estimate the pore size distribution (Ahuja et al., 1998). The volume of different pore categories was determined according to the pore classification developed by Greenland (1981), which characterizes pores as a bonding space (b0.005 μm), residual pores (0.005–0.5 μm), storage pores (0.5–50 μm), transmission pores (50–500 μm), and fissures (N500 μm). The samples were weighed and dried at a temperature of 105 °C to determine BD. TP was calculated from the soil particle density and dry BD of the samples. The soil particle density was determined using the pycnometer method. Hydraulic conductivity in the saturated zone (Ks) was determined by constant head method in soil samples with a volume of 100 cm3 in a laboratory permeameter (Eijkelkamp Agrisearch Equipments, Giesbeek, The Netherlands), (Klute and Dirksen, 1986b). For the determination of water drop penetration time (WDPT) (Van't Woudt, 1959), 10 small drops (0.04 ml) of distilled water from a laboratory pipette were placed on a smoothed, dried soil surface and the time taken for a water drop to infiltrate into the soil was recorded as the WDPT.

3. Results 3.1. Soil pore characteristics The BD of sandy soil without biochar was 1.80 g cm−3. Biochar application showed a decrease in BD (Table 3). This relationship between biochar and BD can be described by the linear function y = −0.0856 × + 1.6559 (where y is BD and x represents the percentage of biochar in biochar/sandy soil mixture, R2 = 0.903). An inverse effect was observed for TP when compared to the data acquired for BD. The highest value of TP was noticed for the B4 treatment (0.489 cm3 cm−3).

Table 2 Results from a three-factor ANOVA testing for the effects of species, biochar size class and biochar rates on soil physical parameters. Parametersa TP Factors

df F

Species Size classes Rates S × SC S×R SC × R S × SC × R

1 2 3 2 3 6 6

BD P

0.024 0.876 9.430 b0.001

F

FC P

0.024 0.877 9.434 b0.001

F

PWP P

7.763 3.020

F

AWC P

F

S F

RFC

F

P

F

0.008 0.101 0.752 4.883 0.032 2.541 0.089 0.058 27.574 b0.001 15.117 b0.001 32.652 b0.001

37.037 b0.001 44.212 b0.001 99.094 b0.001 72.051 b0.001 21.608 b0.001 2.038 0.141 2.039 0.141 1.865 0.166 0.249 0.781 0.327 0.723 0.194 0.900 0.193 0.900 0.451 0.717 0.058 0.982 0.266 0.850 0.541 0.774 0.530 0.782 2.639 0.027 3.960 0.003 8.378 b0.001 0.375 0.891 0.372 0.893 0.288 0.940 0.149 0.988 0.315 0.926

1.265 0.248 0.087 1.982 0.854

WDPT P

3.029 3.009

F 0.088 0.059

Ks P

1.965 7.666

F 0.162 0.001

0.254 21.915 b0.001 27.647 b0.001 0.795 0.217 0.806 0.873 0.419 0.896 0.075 0.973 0.995 0.396 0.096 1.979 0.087 3.655 0.002 0.091 0.091 0.997 2.038 0.0619

P

0.095 0.759 1.077 0.349 1.036 0.017 0.306 0.262 0.464

0.385 0.983 0.821 0.952 0.831

a TP: total porosity; BD: bulk density; FC: field capacity; PWP: permanent wilting point; AWC: available water content; S: slope at the inflection point of the soil water retention curve; RFC: relative field capacity; WDPT: water drop penetration time; Ks: hydraulic conductivity.

14


Table 3 Soil physical quality parameters of the investigated soil/biochar mixtures.

Plant species Triticum aestivum L.


Size classes

Biochar rates (% m/m)

0–500

0.5 1 2 4 500–1000 0.5 1 2 4 1000–2000 0.5 1 2 4 0–500 0.5 1 2 4 500–1000 0.5 1 2 4 1000–2000 0.5 1 2 4 Control without biochar

Means for biochar particle size and biochar rates interaction 0–500 0.5 1 2 4 500–1000 0.5 1 2 4 1000–2000 0.5 1 2 4

TP (cm3 cm−3)

BD (g cm−3)

FC (cm3 cm−3)

PWP (cm3 cm−3)

AWC (cm3 cm−3)

S

RFC

WDPT (s)

Ks (cm day−1)

0.373 0.399 0.410 0.449 0.403 0.411 0.459 0.505 0.418 0.427 0.450 0.525 0.390 0.404 0.421 0.470 0.403 0.419 0.461 0.504 0.386 0.423 0.451 0.483 0.322⁎⁎

1.66 1.58 1.55 1.44 1.58 1.56 1.42 1.29 1.54 1.51 1.44 1.24 1.61 1.57 1.52 1.38 1.58 1.53 1.42 1.29 1.62 1.52 1.44 1.35 1.80⁎⁎

0.047 0.054 0.078 0.109 0.048 0.056 0.068 0.095 0.057 0.059 0.070 0.104 0.054 0.060 0.083 0.115 0.053 0.059 0.070 0.090 0.057 0.062 0.067 0.096 0.044⁎

0.0095 0.0102 0.0118 0.0159 0.0121 0.0161 0.0219 0.0307 0.0162 0.0218 0.0283 0.0489 0.0061 0.0078 0.0084 0.0118 0.0097 0.0113 0.0169 0.0255 0.0109 0.0169 0.0222 0.0373 0.0116⁎

0.0373 0.0438 0.0655 0.0925 0.0352 0.0393 0.0457 0.0641 0.0405 0.0367 0.0415 0.0545 0.0479 0.0518 0.0742 0.1018 0.0426 0.0471 0.0532 0.0639 0.0455 0.0446 0.0443 0.0586 0.0318⁎

0.0639 0.0709 0.0790 0.0878 0.0620 0.0589 0.0616 0.0679 0.0606 0.0520 0.0514 0.0521 0.0834 0.0821 0.0930 0.1030 0.0719 0.0735 0.0731 0.0731 0.0678 0.0626 0.0595 0.0570 0.0482⁎

0.126 0.136 0.190 0.243 0.118 0.136 0.148 0.189 0.136 0.138 0.156 0.198 0.140 0.149 0.198 0.244 0.131 0.140 0.153 0.178 0.147 0.146 0.148 0.200 0.136⁎

1.00 1.10 1.40 2.00 1.00 1.00 1.10 2.10 1.10 1.00 1.00 1.10 1.00 1.00 1.20 1.80 1.00 1.10 1.20 1.40 1.00 1.00 1.00 1.30 1.00⁎

110.8 129.4 151.5 138.1 93.9 203.1 181.2 114.0 217.1 176.1 190.2 179.1 117.4 154.0 130.8 121.7 100.5 149.6 174.4 115.1 133.7 103.4 177.4 74.5 115.0 ns

0.381 0.402 0.415 0.459 0.403 0.415 0.460 0.504 0.402 0.425 0.451 0.504

1.636 1.579 1.536 1.408 1.578 1.544 1.420 1.291 1.581 1.518 1.443 1.293

0.051 f 0.057 ef 0.081 c 0.112 a 0.050 f 0.057 ef 0.069 d 0.093 b 0.057 ef 0.060 e 0.068 de 0.100 b

0.008 d 0.009 d 0.010 d 0.014 cd 0.011 d 0.014 cd 0.019 c 0.028 b 0.014 cd 0.019 c 0.025 b 0.043 a

0.043 de 0.048 d 0.070 b 0.097 a 0.039 e 0.043 de 0.049 cd 0.064 b 0.043 de 0.041 de 0.043 de 0.057 c

0.074 0.077 0.086 0.095 0.067 0.066 0.067 0.070 0.064 0.057 0.055 0.055

0.133 0.142 0.194 0.244 0.124 0.138 0.151 0.184 0.142 0.142 0.152 0.199

1.00 c 1.05 c 1.30 b 1.90 a 1.00 c 1.05 c 1.15 bc 1.75 a 1.05 c 1.00 c 1.00 c 1.20 bc

114.1 141.7 141.1 129.9 97.2 176.3 177.8 114.5 175.4 139.8 183.8 126.8

0.436 0.434

1.484 1.487

0.070 b 0.072 a

0.020 0.015

0.050 b 0.056 a

0.064 0.075

0.159 0.164

1.17 1.24

157.0 129.4

0.414 b 0.445 a 0.445 a

1.540 a 1.458 b 1.459 b

0.075 0.067 0.071

0.010 c 0.018 b 0.025 a

0.064 a 0.049 b 0.046 b

0.083 a 0.068 ab 0.058 b

0.178 0.149 0.159

1.31 1.24 1.06 b

131.7 141.5 156.4

0.395 d 0.414 c 0.442 b 0.489 a

1.599 a 1.547 b 1.466 c 1.330 d

0.053 b 0.058 ab 0.073 ab 0.102 a

0.011 c 0.014 bc 0.018 b 0.028 a

0.042 c 0.044 c 0.054 b 0.073 a

0.068 0.067 0.070 0.073

0.133 c 0.141 c 0.165 b 0.209 a

1.02 b 1.03 b 1.15 b 1.62 a

128.9 152.6 167.6 123.8

Means for plant species Triticum aestivum L. Miscanthus × giganteus Means for biochar size classes 0–500 500–1000 1000–2000 Means for biochar rates 0.5 1 2 4

For each column, mean values with different superscripts are significantly different (P b 0.05); Tukey post hoc test; superscripts used only for significant differences according to ANOVA (Table 2). Asterisks denotes a significant difference between the control soil without biochar addition and soil with biochar; ns non significant. ⁎ P b 0.05. ⁎⁎ P b 0.01.

The BD depended not only on the biochar percentage in soil but also on the size of biochar particles; the smaller the particles, the higher the BD. The feedstock type of biochar, winter wheat or miscanthus, did not significantly modify both BD and TP. Changes in the TP were strictly due to differential soil porosity. The pore size distribution of soil in over a wide range of pore diameters, from below 0.005 to above 500 μm, was determined using the water retention characteristics. The most frequent pore fraction for all treatments was a diameter above 500 μm (Table 4). It corresponds to pores' fraction classified by Greenland (1981) as fissures. These pores are involved in water movement and root growth but have no role in water retention capability.

Biochar addition increased volume of small pores (b50 μm in diameter), decreased volume of pores 50 500 μm and had no impact on pores larger than 500 μm. Biochar particle size significantly affected all pore fractions (Table 4). Smaller particles of biochar, 0–500 μm in diameter, reduced the volume of small pores (b0.5 μm) and fissures (N500 μm) but increased the volume of pores in a diameter range from 0.5 to 500 μm. Higher rates of biochar increased the volume of all pores with diameter b 500 μm. Only the bonding space was species dependent. The biochar made of winter wheat resulted in a higher volume of pores whose diameter was b0.005 μm (0.0092 cm 3 cm − 3 ), whereas for miscanthus, it was only 0.0059 cm3 cm− 3 (P b 0.05).


15

Table 4 Pore size distribution of the investigated biochar/soil mixtures. Volume of pores (cm3 cm−3) for diameter classes Plant species Triticum aestivum L.


b0.005 μm

0.005–0.5 μm

0.5–50 μm

50–500 μm

N500 μm

0.0031 0.0031 0.0031 0.0041 0.0047 0.0068 0.0099 0.0139 0.0067 0.0109 0.0150 0.0289 0.0013 0.0019 0.0017 0.0024 0.0030 0.0036 0.0062 0.0106 0.0034 0.0068 0.0103 0.0192 0.0046⁎

0.0099 0.0110 0.0139 0.0190 0.0112 0.0138 0.0174 0.0244 0.0140 0.0156 0.0188 0.0277 0.0080 0.0098 0.0115 0.0161 0.0106 0.0120 0.0161 0.0221 0.0116 0.0150 0.0173 0.0257 0.0105⁎

0.0427 0.0507 0.0778 0.1103 0.0390 0.0429 0.0491 0.0689 0.0443 0.0387 0.0432 0.0555 0.0591 0.0627 0.0926 0.1265 0.0494 0.0542 0.0595 0.0699 0.0524 0.0490 0.0474 0.0614 0.0351⁎

0.0590 0.0733 0.1229 0.1656 0.0471 0.0478 0.0512 0.0719 0.0500 0.0369 0.0391 0.0455 0.1123 0.1097 0.1687 0.2062 0.0721 0.0772 0.0744 0.0787 0.0746 0.0566 0.0486 0.0571 0.0412⁎⁎

0.2579 0.2613 0.1920 0.1498 0,2911 0.2994 0.3310 0.3256 0.3028 0.3244 0.3339 0.3668 0.2090 0.2200 0.1468 0.1188 0.2680 0.2718 0.3043 0.3227 0.2442 0.2953 0.3276 0.3191 0.2296 ns

0.0022 0.0025 0.0024 0.0033 0.0038 0.0052 0.0081 0.0122 0.0051 0.0089 0.0126 0.0241

0.0090 0.0104 0.0127 0.0176 0.0109 0.0129 0.0168 0.0232 0.0128 0.0153 0.0180 0.0267

0.0509 0.0567 0.0852 0.1184 0.0442 0.0485 0.0543 0.0694 0.0484 0.0438 0.0453 0.0585

0.0857 0.0915 0.1458 0.1859 0.0596 0.0625 0.0628 0.0753 0.0623 0.0468 0.0439 0.0513

0.2335 0.2406 0.1694 0.1343 0.2795 0.2856 0.3176 0.3241 0.2735 0.3099 0.3308 0.3430

Triticum aestivum L. Miscanthus × giganteus

0.0092 a 0.0059 b

0.0164 0.0146

0.0552 0.0653

0.0675 0.0947

0.2863 0.2540

0–500 500–1000 1000–2000

0.0026 c 0.0073 b 0.0127 a

0.0124 b 0.0159 ab 0.0182 a

0.0778 a 0.0541 b 0.0490 b

0.1272 a 0.0651 b 0.0511 c

0.1945 b 0.3017 a 0.3143 a

0.5 1 2 4

0.0037 c 0.0055 c 0.0077 b 0.0132 a

0.0109 b 0.0129 b 0.0158 ab 0.0225 a

0.0478 b 0.0497 b 0.0616 ab 0.0821 a

0.0692 c 0.0669 c 0.0842 b 0.1042 a

Size classes

Biochar rates (% m/m)

0–500


Means for biochar particle size and biochar rates interaction 0–500 0.5 1 2 4 500–1000 0.5 1 2 4 1000–2000 0.5 1 2 4 Means for plant species

Means for biochar size classes

Means for biochar rates 0,2622 0.2787 0.2726 0.2671

For each column, mean values with different superscripts are significantly different (P b 0.05); Tukey post hoc test; superscripts used only for significant differences according to ANOVA. Asterisks denotes a significant difference between the control soil without biochar addition and soil with biochar, ns non significant. ⁎ P b 0.05. ⁎⁎ P b 0.01.

3.2. Soil water retention The changes in the soil porosity were reflected in the water retention properties of the investigated soil. Figs. 1 and 2 present the water retention curves. Table 5 shows the estimated parameters (θs, α, and n) of the van Genuchten model and coefficients of determination. The differences between the SWRC of treated soil appeared not only within a high matric potential range but also in a low range below 1500 kPa. The biochar application improved water retention properties of soil when compared with the B0 control. However the scale of this effect depended on biochar particle size, its rate, and feedstock type (Table 3). The difference between the FC value of biochar produced from miscanthus and winter wheat was only 0.002 cm3 cm−3 with

P = 0.008. The FC value of soil increased with an increase in biochar rate. Finer fractions increased the FC values. As a result, the higher FC value was recorded for B4 treatments with the finest particles whose diameter is in the range 0–500 μm (0.112 cm3 cm−3). A different relationship was observed for the PWP. Higher values were noted for B4 treatment. However, finer biochar particles resulted in lower PWP values. This effect was opposite to that noted for the FC. The changes in FC and PWP were reflected in AWC. The lowest value of the AWC was obtained for B05 with biochar particles in the range 500–1000 μm in diameter (Table 3). The AWC increased when higher rates of biochars were applied. The highest AWC was observed for B4 treatment with the fine biochar particle size in the range 0–500 μm (0.097 cm3 cm−3). Biochar made of miscanthus showed a slightly higher AWC than that made

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of winter wheat. Fig. 3 presents the regression model for the relationship between biochar rates, size of particles, and AWC. According to this regression equation the highest value of AWC was calculated for sand/biochar mixture with 4% of biochar and biochar particle size is close to zero (0.0829 cm3 cm−3). The lowest value of AWC was determined for the mixture with 0.5% of biochar and biochar particle size of 800 μm in diameter (0.0306 cm3 cm−3). The biochar application affected the soil quality indexes, such as Sslope and RFC (Table 3). The S-index depended only on the size of the biochar particles. Coarser particles resulted in higher values of the Sslope. Unlike the S-index, the RFC was affected only by biochar rates. Higher rates increased the RFC from 0.133 for B05 treatment to 0.209 for the B4. 3.3. Water permeability and repellency The biochar application significantly increased the water repellency of tested soil (Table 3). The WDPT depended on both biochar rates and biochar particle size. At all biochar size fractions, there was no difference between B05 and B1 rates (Table 3). When higher rates of biochar were applied, WDPT increased. No such effect was observed for the coarsest biochar particles where the WDPT was not significantly affected by any biochar rates. However, all biochar treatments were classified as non-water repellent because the WDPT was below 5 s. Different biochar treatments did not lead to statistically significant differences in water permeability (Table 3). There was also no difference between biochar treated samples and control B0·The mean value of Ks in all the treated samples was 143.2 cm day−1. 4. Discussion The results obtained in this experiment indicated that biochar application significantly affected the physical properties of the sandy soil. Biochar application showed lower BD values. TP was increased by the biochar amendment. These relationships between biochar application and physical properties of soil ware also observed by Herath et al. (2013) for silt loam soil and similar effects were reported by Mukherjee and Lal (2013) in laboratory and field-scale experiments. They confirmed that improved physical quality of biochar-amended soil is correlated with biochar rates. The basic soil physical parameters, such as BD and TP, were affected by biochar rates. Higher the biochar rates, the lower the BD and higher the TP. These changes in the soil physical properties can be ascribed to the mixing of soil with less dense material, which is clearly evident immediately after the application in compacted, fine-textured soils (Celik et al., 2004), and in coarse-textured soils (Głąb, 2014). The decrease in bulk density of the biochar-amended soils could be also ascribed to changes in soil structure and alteration of soil aggregate sizes (Tejada and Gonzalez, 2007; Jien and Wang, 2013). However, this effect was mainly observed for soils with higher clay content, existing organic matter in soil and with higher aggregates stability (Kimetu and Lehmann, 2010). A more detailed analysis of the soil pore system showed that some pore fractions were dependent not only on the rate of the biochar but also on its particle size. Small particles of biochar reduced the volume of soil pores whose diameter is below 0.5 μm but increased the volume of larger pores with a diameter range of 0.5–500 μm. Thus, this study suggests that the soil water retention characteristics also depended on biochar particle size. The AWC is resultant of FC and PWP characteristics of tested soil mixtures. Practically, AWC plays the most important role in the irrigation systems used at the turfgrass sport facilities. The application of biochar significantly increased AWC, especially when the finest fraction Fig. 1. The soil water retention curves based on van Genuchten equation for the investigated biochar/soil mixtures. Biochar prepared from winter wheat (Triticum aestivum L.).


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was used. It may reduce the irrigation frequency and/or the amount of irrigation water. This positive effect of biochar application on water retention ability was also reported in some research (Karhu et al., 2011; Baronti et al., 2014; Herath et al., 2013). However, there are some factors that determine this effect such as, soil texture, aggregation, and soil organic matter content (Verheijen et al., 2010). The soil texture is considered to be the most important. According to Mukherjee and Lal (2013), the application of biochar increased AWC in sandy soil, but this effect decreased in soil with higher clay content. Also Verheijen et al. (2010) stated that improvements in soil water retention by biochar additions can be observed in coarse-textured soils or soils with large amounts of macropores. According to Peake et al. (2014) soils that are low in silt are likely to be more hydrologically responsive to biochar application. Properties such as specific surface area (SSA) and intraparticle porosity were attributed as the most important factors that increased AWC (Crabbe, 2009; Uzoma et al., 2011). It was reported that AWC increased even by 170% after biochar application compared to control treatment. The increase was significantly higher for high biochar rates and higher pyrolysis temperatures, and generally higher for sands compared to loamy sands (Kinney et al., 2012; Peake et al., 2014; Uzoma et al., 2011). Abel et al. (2013) found that the increase in AWC in sandy soils was due to the addition of biochar, primarily occurring in the drier range of the AWC (from −30 to −1500 kPa). According to Eibisch et al. (2015), the increase in AWC was due to the changes in water content only in the low-pressure range (from −6 to −30 kPa), whereas AWC was found to be decreased in the high-pressure range (from − 30 to −1500 kPa). The impact of biochar on soil water retention characteristics is attributed to its highly porous structure (Ogawa et al., 2006). According to Graber et al. (2012), the SSA of biochar can reach values up to 500 m2 g−1 which is important when mixed with a sandy soil of very low SSA, i.e. below 10 m2 g−1 (Herbrich et al., 2015). On the contrary, Jeffery et al. (2015) and Hardie et al. (2014) in their research reported no significant effects of biochar application on water retention of soil with a high sand content. The results obtained in this study suggest that such lack of changes in hydraulic properties of soil might be due to large particle size of biochar used in the above mentioned studies. Hardie et al. (2014) proposed the following three mechanisms by which biochar application might increase soil porosity: (i) pore contribution from the high-porosity biochar material, (ii) modification of pore system by creating packing or accommodation pores, and (iii) improved aggregate stability. However, all these mechanisms might lead to different outcomes in different soil–climate–management combinations (Verheijen et al., 2010). It could be expected that biochar amendment should affect the water permeability of the examined sandy mixture because it significantly increased total porosity and large pores (50 500 μm) responsible for gravitational water movement in soil. However, in the presented study, biochar application did not change the value of KS of the examined sandy mixture. The impact of biochar on the soil hydraulic properties is an interaction of soil and biochar physical properties. Some studies have reported that the biochar application increased the KS in fine texture soils (Novak et al., 2016; Barnes et al., 2014). The increase in KS agrees with the increase in the overall porosity of these soils. Uzoma et al. (2011) reported higher KS values for a sandy soil after biochar amendment. Conversely, Brockhoff et al. (2010) reported that KS of the turfgrass root zones decreased as biochar concentrations increased. Barnes et al. (2014) proposed two hydrologic mechanisms that are potentially responsible for this behavior: one through the interstitial biochar-sand space and a second through pores within the biochar grains themselves. Therefore, the addition of biochar can increase or decrease soil drainage, and any potential improvement of water delivery to plants is dependent on soil texture, biochar rate, and biochar properties. Fig. 2. The soil water retention curves based on van Genuchten equation for the investigated biochar/soil mixtures. Biochar prepared from miscanthus (Miscanthus × giganteus).

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Table 5 Parameters values (θs, α and n) of the van Genuchten model fitted for the different biochar/soil mixtures.

Plant species Triticum aestivum L.


Biochar rates Size classes (% m/m) 0–500


θs (cm3 cm−3)

α (kPa−1) n

R2a

0.373 0.399 0.410 0.449 0.403 0.411 0.459 0.505 0.418 0.427 0.450 0.525 0.390 0.404 0.421 0.470 0.403 0.419 0.461 0.504 0.386 0.423 0.451 0.483 0.321

71.85 42.19 8.70 4.15 280.50 358.75 530.14 176.28 309.61 2596.39 3354.55 5702.62 9.61 11.60 3.63 2.34 45.25 42.53 78.82 105.03 36.65 186.89 663.03 557.61 210.53

0.913 0.889 0.909 0.929 0.868 0.861 0.865 0.875 0.764 0.822 0.803 0.769 0.734 0.852 0.810 0.823 0.754 0.779 0.819 0.810 0.725 0.816 0.712 0.686 0.825

1.32 1.33 1.37 1.38 1.27 1.24 1.22 1.22 1.25 1.20 1.18 1.15 1.43 1.40 1.45 1.45 1.33 1.33 1.28 1.25 1.33 1.26 1.22 1.19 1.26

a Coefficient of determination between measured and fitted θ(h) data for estimation of α and n.

When biochar is applied as a soil amendment, there is a threat that it may promote water repellency and counteract the positive effect of the water retention capabilities. Water repellency and delayed wetting commonly contribute to higher volume of entrapped air and thus decreasing the fraction of saturated soil pores, thereby reducing both AWC and hydraulic conductivity (Kinney et al., 2012; Eibisch et al., 2015). In this study, soil water repellency was slightly increased by biochar application, but it was still classified as non-repellent. The highest biochar dose was 4%, and so the observed WDPT values were not very high. Biochar application was reported to increase the water repellency

Fig. 3. The relationship between the available water content (AWC), biochar rates and particle size. Mean values for both feedstock types, wheat and miscanthus biochar.

of soil (Eibisch et al., 2015; Kinney et al., 2012). According to the results obtained by Kinney et al. (2012), water repellency increased significantly when higher rates, that is, above 5% of biochar were applied. On the other hand, Briggs et al. (2012) observed an extremely hydrophobic characteristic (water drop penetration time N 2 h) for a Pinus ponderosa biochar. However, they observed that older carbon under forest floor layers was less water repellent. Baronti et al. (2014) did not confirm a significant increase in soil hydrophobicity in the field trial with biochar produced from orchard wastes. Also Abel et al. (2013) concluded that biochar produced from maize feedstock and pyrolyzed at 750 °C had no effect on soil water repellency. Kinney et al. (2012) found that biochars from three different feedstocks followed the same trend: pyrolysis at 300 °C produced very hydrophobic biochar, but hydrophobicity decreased with an increase in the temperature. The explanation for that phenomenon was proposed by Hallin et al. (2015). They found that biochar produced at lower temperatures b 500 °C retained organic functional groups from the feedstock, and therefore it is usually water repellent. However, pyrolysis at temperature above 500 °C volatilized the organic groups linked to hydrophobicity, making the biochar more hydrophilic. Novak et al. (2012) also suggested that reduced biochar repellency in higher temperature were due to changes in the proportions of hydrophobic and hydrophilic functional groups. It is thought that the hydraulic properties of biochar depend largely on the biomass feedstock used and pyrolysis conditions. Moreover, it is also stated that hydrophobicity of biochar changes over the time. Briggs et al. (2012) observed high water repellency for a freshly produced wooden biochar, but older carbon under forest condition was less water repellent. To explain the mechanism of soil water repellency after biochar amendment, Verheijen et al. (2010) proposed an analogy between the impact of biochar addition and the result of wildfire when water repellency was observed in forest soils. According to Doerr et al. (2000), this mechanism is ascribed to the reorientation of amphiphilic molecules by heat from a fire. This does not affect the soil but could affect the biochar during pyrolysis process. Yet this hypothesis of the mechanism of the soil hydrophobicity after biochar application is still not fully understood. To sum up, biochar application improves soil water retention. From this point of view, biochar can be recommended as a valuable amendment which improves hydraulic properties of turfgrass rootzone. As the addition if biochar increases the volume of stored water in soil it may allow a reduction in the frequency of irrigation (McCready and Dukes, 2011). This feature of biochar amendment is particularly important for soil sensor based irrigation systems. However, the size of the water retention effect depends on a number of factors, including the dose, feedstock type and the biochar particle size. Sand-based turfgrass root-zones should provide high infiltration and drainage rates. At the same time, sand-based root-zones must retain enough water and nutrients to support turfgrass health. Some of these functions contradict each other. The organic or inorganic amendments are incorporated to soil to promote water and nutrient retention should not adversely affect infiltration and drainage ability. However, these practices usually change the particle-size distribution of soil and affect soil mechanical properties such as penetration resistance, impact hardness, shear resistance and energy absorption (ASTM, 2000). The mechanical behavior of turfgrass root-zone is quantified because of aspects of surface performance: ball–surface interaction and the performance and safety of players (Guisasola et al., 2009; Caple et al., 2012). If we consider the possibilities of using biochar in sport facilities, not only water but also mechanical properties are very important. Verheijen et al. (2010) reported that biochar was characterized by low elasticity, which is defined as the ratio of the BD of the test material under stress to the BD after the stress has been removed. These mechanical properties combined with hydraulic properties seem very promising in the application of biochar as a substrate in sport facilities with natural turfgrass. However, the mechanical behavior of biochar particles in the soil under compaction has received very little attention so far, with a poor understanding of the mechanisms (Verheijen et al., 2010).


5. Conclusions The results obtained in this experiment indicated that biochar application significantly improved the physical properties of the sandy soil. The basic soil physical parameters, such as BD and TP, were dependent not only on the rate of the biochar but also on the size. Small particles of biochar reduced the volume of soil pores with diameter below 0.5 μm but increased the volume of larger pores with diameter ranging 0.5–500 μm. Biochar application improved the soil water characteristics by increasing the AWC, especially when the finest fraction was used. Biochar made of miscanthus slightly increased AWC than that made of winter wheat. In this study, soil water repellency was slightly increased by biochar application, but it was still classified as non-repellent. Biochar application has a great potential in the improvement of soil water retention. This material can be recommended for natural turfgrass fields as a soil amendment which improved sandy soil quality. The biochar can be applied with rates of 4% m/m but it should be rather in small grain size, below 500 μm as this significantly increased the beneficial effect of biochar application. Further investigations are recommended to recognize the influence of biochar amendment on soil and turf mechanical properties used on sport objects. Acknowledgments Financial support for this study was provided by the Ministry of Science and Higher Education in Poland, statutory funds no. DS-3615/ WIPiE/2014; Institute of Machinery Exploitation, Ergonomics and Production Processes, University of Agriculture in Krakow, no. DS 3138/ WRE/2015; Department of Soil Science and Soil Protection, University of Agriculture in Krakow and no. DS-3139/WRE/2014; Department of Agricultural and Environmental Chemistry, University of Agriculture in Krakow. References Abel, S., Peters, A., Trinks, S., Schonsky, H., Facklam, M., Wessolek, G., 2013. Impact of biochar and hydrochar addition on water retention and water repellency of sandy soil. Geoderma 202−203, 183–191. Ahuja, L.R., Fiedler, F., Dunn, G.H., Benjamin, J.G., Garrison, A., 1998. Changes in soil water retention curves due to tillage and natural reconsolidation. Soil Sci. Soc. Am. J. 62, 1228–1233. American Society for Testing and Materials, 2000. Annual Book of ASTM Standards. Vol. 15.07. End Use Products. Standard Test for Shock Attenuation Characteristics of Natural Playing Surface Systems Using Lightweight Portable Apparatus. F1702-96. ASTM, West Conshohocken. Andry, H., Yamamoto, T., Irie, T., Moritani, S., Inoue, M., Fujiyama, H., 2012. Water retention, hydraulic conductivity of hydrophilic polymers in sandy soil as affected by temperature and water quality. Acta Ecol. Sin. 32, 26–32. Atkinson, C.J., Fitzgerald, J.D., Hipps, N.A., 2010. Potential mechanisms for achieving agricultural benefits from biochar application to temperate soils: a review. Plant Soil 337 (1–2), 1–18. Barnes, R.T., Gallagher, M.E., Masiello, C.A., Liu, Z., Dugan, B., 2014. Biochar-induced changes in soil hydraulic conductivity and dissolved nutrient fluxes constrained by laboratory experiments. PLoS One 9 (9), e108340. Baronti, S., Vaccari, F.P., Miglietta, F., Calzolari, C., Lugato, E., Orlandini, S., Pini, R., Zulian, C., Genesio, L., 2014. Impact of biochar application on plant water relations in Vitis vinifera (L.). Eur. J. Agron. 53, 38–44. Bigelow, C.A., Bowman, D.C., Cassel, D.K., 2004. Physical properties of three sand size classes amended with inorganic materials or sphagnum peat moss for putting green rootzones. Crop Sci. 44, 900–907. Briggs, C., Breiner, J., Graham, R., 2012. Physical and chemical properties of Pinus ponderosa charcoal: implications for soil modification. Soil Sci. 177 (4), 263–268. Brockhoff, S.R., Christians, N.E., Killorn, R.J., Horton, R., Davis, D.D., 2010. Physical and mineral-nutrition properties of sand-based turfgrass root zones amended with biochar. Agron. J. 102 (6), 1627–1631. Caple, M., James, I., Bartlett, M., 2012. Mechanical behaviour of natural turf sports pitches across a season. Sports Eng. 15 (3), 129–141. Celik, I., Ortas, I., Kilic, S., 2004. Effects of compost, mycorrhiza, manure and fertiliser on some physical properties of a Chromoxerert soil. Soil Tillage Res. 78 (1), 59–67. Cheng, H., Xu, W., Liu, J., Zhao, Q., He, Y., Chen, G., 2007. Application of composted sewage sludge (CSS) as a soil amendment for turfgrass growth. Ecol. Eng. 29, 96–104. Crabbe, M.J.C., 2009. Modelling effects of geoengineering options in response to climate change and global warming: implications for coral reefs. Comput. Biol. Chem. 33 (6), 415–420.

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