Effects of co-composted maize, sewage sludge, and biochar mixtures on hydrological and physical qualities of sandy soil

Effects of co-composted maize, sewage sludge, and biochar mixtures on hydrological and physical qualities of sandy soil

Geoderma 315 (2018) 27–35 Contents lists available at ScienceDirect Geoderma journal homepage: www.elsevier.com/locate/geoderma Effects of co-compos...

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Geoderma 315 (2018) 27–35

Contents lists available at ScienceDirect

Geoderma journal homepage: www.elsevier.com/locate/geoderma

Effects of co-composted maize, sewage sludge, and biochar mixtures on hydrological and physical qualities of sandy soil

T



Tomasz Głąba, , Andrzej Żabińskia, Urszula Sadowskaa, Krzysztof Gondekb, Michał Kopećb, Monika Mierzwa–Hersztekb, Sylwester Taborc a

Institute of Machinery Exploitation, Ergonomics and Production Processes, University of Agriculture in Krakow, Poland Department of Agricultural and Environmental Chemistry, University of Agriculture in Krakow, Poland c Institute of Agricultural Engineering and Informatics, University of Agriculture in Krakow, Poland b

A R T I C L E I N F O

A B S T R A C T

Editor: Morgan Cristine L.S.

The agronomic utilization of compost has some benefits to soil. Compost increase soil nutrients, and soil organic matter content; thus, it has a positive effect on biological, physical, and chemical properties of the soil. During the composting process, different feedstocks such as plant wastes, sewage sludge, and biochar are used. Biochar has great potential to improve the quality of compost. This paper reports the effects of different compost rates and feedstock types of biochar on water retention characteristics of sandy soil in a standard natural turfgrass root zone. Using soil with the texture of loamy sand, a pot experiment was established. The following mixtures of feedstocks were used in this study: compost of maize straw (MS), compost with sewage sludge (MS + SS), and compost of mixture of maize straw, sewage sludge, and biochar (MS + SS + BC). Mixtures of compost additives and soil were prepared at 0.5% (R05), 1% (R1), 2% (R2), and 4% (R4). Compared to untreated soil, the physical properties of the sandy soil were significantly improved with the application of compost. The basic physical parameters of the soil, such as bulk density and total porosity, depended mainly on the rate of the biochar additive. The differential porosity of the soil was affected by both compost rate and feedstock type. For compost with sewage sludge, the highest content of large pores with diameters above 500 μm was observed, and this was achieved with biochar addition. Addition of the compost also significantly increased the volume of pores with diameters below 50 μm compared to the untreated control soil. The water retention properties of the soil were improved with the compost application and were dependent on the rate of compost and the type of feedstock. The lowest value of available water content (AWC) was obtained for soil with maize straw compost. The addition of sewage sludge or biochar during the composting process resulted in an increase in AWC in the soil. The best combination of compost rates and feedstock types is maize compost with both sewage sludge and biochar at a rate of 4%.

Keywords: Compost Sewage sludge Biochar Sandy soil Soil quality Soil water retention

1. Introduction Composting organic bio-wastes and applying them as organic fertilizers has become increasingly popular in Europe. The agronomic utilization of compost has some benefits to soil. Compost increase soil nutrients, and soil organic matter content; thus, compost application has a positive effect on biological, physical, and chemical properties of the soil (Aggelides and Londra, 2000; Hargreaves et al., 2008). Because of the high macronutrient (e.g., nitrogen, phosphorus, calcium, and sulfur), micronutrient (e.g., copper and zinc) and organic matter contents, municipal sewage sludge (SS) is recognized as a source of valuable fertilizer. However, SS also contains contaminants such as



heavy metals, organic pollutants or pathogens, which may lead to environmental or health risks (Bartl et al., 2002; Mosquera–Losada et al., 2010), and this can limit the direct application of sewage sludge to soil fertilization. Therefore, SS should be composted before its application. Composting is one of the more acceptable and economically feasible technologies for recycling SS (Villasenor et al., 2011). Composting SS helps with waste management, and it appears to be an appropriate soil conditioner due to a high content of stable, humified organic matter (He et al., 2011; Sevilla–Perea and Mingorance, 2015; Yuan et al., 2016). However, because of a high moisture content that affects the

Corresponding author at: University of Agriculture in Krakow, ul. Balicka 116B, 31–149 Krakow, Poland. E-mail address: [email protected] (T. Głąb).

https://doi.org/10.1016/j.geoderma.2017.11.034 Received 27 February 2017; Received in revised form 9 November 2017; Accepted 23 November 2017 0016-7061/ © 2017 Elsevier B.V. All rights reserved.

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the rootzone, thus permitting longer intervals between irrigations (Shao-Hua et al., 2012; Andry et al., 2012). However, reports on the effects 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. A risk exists that the organic substances in the soil and their biodegrading products may induce water repellency (Scott, 2000; McKissock et al., 2000). We hypothesize that a compost of maize straw and sewage sludge with a biochar additive influences the soil pore system, but this influence can be modified by adjusting compost components and application rate. The objective of this study was to determine the effect of different compost rates and feedstock types of compost on sandy soil water retention characteristics in a standard natural turfgrass rootzone.

dynamics of the composting process, SS is composted alone. Furthermore, a low C/N ratio is not beneficial to the progress of composting because it causes volatilization of a large amount of ammonia (Li et al., 2013; Wang et al., 2014; Kulikowska, 2016). During composting, small particles of SS cause poor gas permeability (Zhao et al., 2016). Thus, SS should be mixed with dry organic material in order to adjust the moisture content and C/N ratio (e.g., straw or wood chips), as well as to improve the gas permeability and reduce the nitrogen losses (Awasthi et al., 2016; Meng et al., 2017). The co-composting of SS reduces the contamination with pathogenic microorganisms, improves stability, and contributes to a lowering of the availability of metals in amended soils (Smith, 2009; Alvarenga et al., 2015). However, researchers are constantly searching for other soil additives to improve both the process and the final compost quality. Biochar, the solid product of biomass pyrolysis, seems to be a very promising soil amendment and compost component. During the past decade, biochar has been considered a valuable product that results in soil improvement and carbon sequestration that may mitigate climate change (Peake et al., 2014). Biochars are described as produced from organic feedstocks heterogeneous materials that vary in their chemical and physical properties. This variability depends not only on the parameters involved in pyrolysis but also on the materials used to produce biochar (Gundale and DeLuca, 2006; Atkinson et al., 2010). As a soil additive, biochar has been shown to affect the physical, chemical, and biological properties of the soil (Lehmann et al., 2011; Mukherjee and Lal, 2013; Herath et al., 2013). Nutrient availability (N and P) in the soil may be enhanced by adding biochar because of a higher cation adsorption (Liang et al., 2006) or because of an increased pH in acidic 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, these effects depend on biochar characteristics, doses, and soil properties (Jha et al., 2010). Głąb et al. (2016) in a previous study reported that biochar improved the physical properties of sandy soil. By adding biochar, the macroporosity and mesoporosity of the soil were significantly increased, thus improving aeration and water availability for plant roots (Herath et al., 2013). This characteristic of biochar is ascribed to its highly porous structure and large surface area (Atkinson et al., 2010). However, other studies have reported no impact. Jeffery et al. (2015) found no significant effects of biochar application on sandy soil water retention. Hardie et al. (2014) observed similar results with no improvement in soil moisture or water retention characteristics. Some advantages of biochar application have also been recognized during the composting process. Biochar reduces gaseous emissions including ammonia, carbon dioxide, and other greenhouse gasses (Malińska et al., 2014; Steiner et al., 2011). It improves the quality of composts by reducing nitrogen losses and by reducing the mobility of heavy metals (Dias et al., 2010; Chen et al., 2010; Jindo et al., 2012; Zhang et al., 2014). Biochar has an impact on composting dynamics by causing a faster decomposition of organic matter, and by increasing the porosity and the water holding capacity (Czekała et al., 2016). In coarse-textured soils, the application of organic fertilizers, especially compost, is particularly important. Sandy soil is widely used at sport facilities with natural turfgrass. A typical soil profile under sport turfgrass contains a sand-enriched rootzone on top of a coarse-textured sand or gravel. The principal motivation of using a high sand-content rootzone is to improve the mechanical properties of the turf surface and to resist soil compaction from frequent foot traffic. This contradicts the main function of the rootzone, which is to store water and nutrients (McCoy and McCoy, 2009). Coarse-structured 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). One of the solutions is to increase the soil organic matter content by adding organic materials such as sphagnum peat moss or compost, including composted sewage sludge (Rawls et al., 2003; Bigelow et al., 2004; Cheng et al., 2007). This increases the amount of available moisture in

2. Materials and methods 2.1. Sample preparation In this experiment, the following three feedstocks were used to produce compost: maize straw (MS), sewage sludge (SS), and biochar (BC). SS used in this study came from a municipal wastewater treatment plant (mechanical and biological system) located in the Małopolska Province (southern Poland). Before the sampling, sewage sludge was subjected to oxygen stabilization in separate open chambers in which continuous aeration was performed at ambient temperature. The aeration process lasted for 5 days. Then, sewage sludge was dewatered using a settling centrifuge. Biochar was produced from willow (Salix viminalis L.). The plant material was pyrolyzed in an electrical laboratory furnace at a temperature of 350 °C for 15 min with limited air access (International Biochar Initiative, 2014). Time and temperature were set according to Lu et al. (2013), Mendez et al. (2013) and Domene et al. (2015). The rate of the furnace heating was 10 °C min− 1. Then, the biochar was removed from the furnace and cooled in a desiccator. The following mixtures of feedstocks were used in this study: maize straw (MS), maize straw with sewage sludge (MS + SS) and maize straw, sewage sludge and biochar (MS + SS + BC). The proportions of the components used in individual treatments were (by weight of dry matter): MS:SS – 1:0.15; MS:SS:BC – 1:0.15:0.1. These proportions of feedstock in the mixtures correspond to a C/N ratio of 30. The feedstock was composted for 140 days from May to the end of September 2015. The process was carried out in 1.2 × 1.0 × 0.8 m bioreactors with perforated bottoms to allow active aeration. The moisture of the composted material was equilibrated to 60% by weight. Aeration of the biomass was performed in cycles 6 times a day; air was flown through the bioreactor at a rate of 15 dm3 per min for 60 min. The biomass was manually shifted every 10 days. Laboratory bioreactors were sheltered against precipitation, but they were exposed to outside temperatures and sunlight. The basic chemical characteristics of the composts are presented in Table 1. According to the ASTM F2396–04 and DIN 18035–4 standards, soil Table 1 Chemical properties of tested composts made of maize straw (MS), sewage sludge (SS) and biochar (BC). Standard deviations in parentheses. Parameter Dry matter Ash pH H2O Electrical conductivity C N P K Ca Mg

28

Units −1

g kg g kg− 1 μS cm− 1 g kg− 1 g kg− 1 g kg− 1 g kg− 1 g kg− 1 g kg− 1

MS

MS + SS

MS + SS + BC

705 (9) 209 (2) 7.89 (0.79) 6.78 (0.70) 406 (3) 31.8 (0.7) 11.2 (0.7) 35.9 (2.3) 11.4 (0.6) 6.10 (0.33)

745 (10) 296 (3) 7.96 (0.80) 4.86 (0.49) 365 (4) 39.4 (1.9) 18.1 (0.4) 28.3 (1.0) 26.0 (0.5) 7.85 (0.23)

642 (7) 288 (4) 7.60 (0.76) 4.64 (0.46) 382 (32) 33.2 (2.8) 14.4 (0.3) 22.0 (0.2) 28.3 (2.1) 6.60 (0.15)

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Table 2 Results from a two-factor ANOVA testing for the effects of feedstock and compost rates on soil physical parameters. Factors

df

Parametersa TP

Feedstock Rates T×R

2 3 6

BD

FC

PWP

AWC

S

RFC

WDPT

F

p

F

p

F

p

F

p

F

F

F

p

F

p

F

p

2.9 66.5 3.1

0.058 < 0.001 0.006

2.9 66.5 3.1

0.058 < 0.001 0.006

15.9 278.1 2.0

< 0.001 < 0.001 0.070

152.0 686.5 31.7

< 0.001 < 0.001 < 0.001

9.1 9.1 2.5

< 0.001 < 0.001 0.022

2.2 31.5 0.3

0.078 < 0.001 0.692

15.9 278.1 2.0

< 0.001 < 0.001 0.070

35.3 104.3 12.0

< 0.001 < 0.001 < 0.001

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.

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. Soil wettability was classified according to Dekker and Jungerius (1990) who described the following repellency classes: non-water repellent (WDPT < 5 s), slightly water repellent (WDPT 5–60 s), strongly water repellent (WDPT 60–600 s), severely water repellent (WDPT 600–3600 s), and water repellent (WDPT > 3600 s).

with a texture of loamy sand (81% sand, 14% silt, and 5% clay) was used. Mixtures of organic amendments and soil were prepared in March 2016 with the following four rates (which equal organic amendment mass as a percentage of the whole sample mass): 0.5% (R05), 1% (R1), 2% (R2), and 4% (R4). The control was prepared without any addition of amendments (CT). The prepared samples were stored in 0.03 m3 pots for three months with periodic watering to avoid drying. In June 2016, the soil samples were collected for laboratory measurements using steel cylinders with a capacity of 100 cm3 in twelve replications for every treatment. To achieve a comparable and replicable compaction of samples, they were subjected to a consolidation cycle under a static load of 600 g, based on the method described by Stock and Downes (2008).

2.3. Statistics Using the statistical software package Statistica v. 10.0 (StatSoft Inc., Tulsa, OK, USA), an analysis of variance for a randomized block design was performed to evaluate the significance of different organic amendment mixtures and their rates on the physical parameters of the soil (Table 2). Using Shapiro-Wilk test, the data were checked for the normality of the distribution. The homogeneity of variance was checked using Levene's test. Means were compared using a Bonferroni test with a level of significance of P < 0.05. A regression analysis was carried out to describe the relationship between water retention and treatments.

2.2. Measurements According to Richards' method (Klute and Dirksen, 1986), the soil water retention curve (SWRC) was determined using pressure plates (Soil Moisture Equipment Corp., Santa Barbara CA, USA). 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). The SWRC models were fitted to the experimental water retention data using a nonlinear least-squares procedure in the statistical software package Statistica v. 10.0 (StatSoft Inc., Tulsa, OK, USA). Then, the soil quality parameters were calculated as follows: field capacity (FC; defined as the equilibrium volumetric soil water content at −10 kPa matric potential, Marshall et al., 1996), permanent wilting point (PWP; volumetric soil water content at −1500 kPa matric potential, Marshall et al., 1996), relative field capacity (RFC; defined by Reynolds et al., 2008 as proportion between FC and total porosity (TP)), the available water content (AWC; calculated as the difference between the FC and PWP), and the slope (S) at the inflection point of the SWRC (according to the Stheory by Dexter, 2004). The value of S indicates the extent to which the soil porosity is concentrated into a narrow range of pore sizes. The S parameter is mostly due to microstructural porosity, and, therefore, S directly governs many of the principal soil physical properties. A large value of S indicates the presence of structural pores and is a characteristic indicating good soil quality (Dexter, 2004). 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 (< 0.005 μm), residual pores (0.005–0.5 μm), storage pores (0.5–50 μm), transmission pores (50–500 μm), and fissures (> 500 μm). To determine the bulk density (BD), the samples were weighed and dried at a temperature of 105 °C. TP was calculated from the soil particle density and dry BD of the samples. Using the pycnometer method, the soil particle density was determined. Water repellency was determined based on water drop penetration

3. Results 3.1. Soil pore characteristics The BD of sandy soil without biochar was 1.798 g cm− 3. The application of all amendments resulted in a decrease in BD (Table 3). The BD for all treated soil samples was 1.637 g cm− 3, approximately 9% lower than CT. However, the type of compost showed an interaction with the rate of application. A lower BD was observed for all soil mixtures (i.e., MS, MS + SS and MS + SS + BC) treated with the highest compost rates (R4), with an average of 1.583 g cm− 3. When lower compost rates were applied, this resulted in an increase in BD (1.659 g cm− 3 on average), except in the MS/R2 treatment where the BD was significantly lower at 1.626 g cm− 3. In general, the compost rates substantially affected the BD of sandy soil, from 1.583 g cm− 3 at the R4 rate to 1.672 g cm− 3 at the R05. An inverse effect was observed for TP when compared to the data acquired for BD, which is a result of the way TP was calculated. The TP of the CT was 0.322 cm3 cm− 3, and it increased when different compost treatments were applied. Changes in the TP and BD were strictly due to differential soil porosity. The most frequent pore fraction for all treatments was a diameter above 500 μm (Table 4). This corresponds to pore fractions classified by Greenland (1981) as fissures. These pores are involved in water movement and root growth, but they have no role in water retention capability. The fissures' capacity in the CT group was 0.2296 cm3 cm− 3, and it increased when compost was added. The highest fissure content was in the MS + SS and MS + SS + BC treatments (0.2638 cm3 cm− 3 on average), whereas this value for the MS was significantly lower at 0.2497 cm3 cm− 3. Compost rates also affected the capacity of large pores. However, the difference was only 29

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

Fertilizer rates (% m/m)

TP (cm3 cm− 3)

BD (g cm− 3)

FC (cm3 cm− 3)

PWP (cm3 cm− 3)

AWC (cm3 cm− 3)

S

RFC

WDPT (s)

MS

0.5 1 2 4 0.5 1 2 4 0.5 1 2 4

0.366d 0.375c,d 0.386b,c 0.414a 0.371c,d 0.375c,d 0.378c,d 0.397b 0.370d 0.376cd 0.378cd 0.397b 0.322⁎⁎

1.681a 1.656a,b 1.626b,c 1.554c 1.666a,b 1.657a,b 1.644a,b 1.597c 1.668a 1.654a,b 1.648a,b 1.598c 1.798⁎⁎

0.051 0.062 0.087 0.122 0.049 0.057 0.073 0.106 0.050 0.057 0.073 0.100 0.044⁎⁎

0.0233f,g 0.0325d,e 0.0551c 0.0902a 0.0211g 0.0282d,f 0.0375e 0.0624b 0.0211g 0.0251f,g 0.0351e 0.0551c 0.0116⁎⁎

0.0282c 0.0292c 0.0316c 0.0318c 0.0275c 0.0290c 0.0358b,c 0.0434a,b 0.0289c 0.0323b,c 0.0381a,b,c 0.0445a 0.0318⁎

0.0515 0.0455 0.0322 0.0253 0.0445 0.0398 0.0375 0.0345 0.0444 0.0443 0.0407 0.0363 0.0482⁎

0.141 0.165 0.225 0.296 0.131 0.153 0.194 0.267 0.135 0.153 0.194 0.253 0.136⁎⁎

32e 255c,d 644c,d 1645b 47e 244c,d,e 1347b 2519a 30e 62d,e 481c,d,e 685c 1⁎⁎

0.385 0.380 0.380

1.629 1.641 1.642

0.080a 0.071b 0.070b

0.0502a 0.0373b 0.0340c

0.0302b 0.0339a 0.0359a

0.0391 0.0386 0.0414

0.207a 0.186b 0.184b

644b 1039a 315c

0.369c 0.375b,c 0.381b 0.403a

1.672a 1.655a,b 1.639b 1.583c

0.050d 0.059c 0.078b 0.109a

0.0218d 0.0286c 0.0426b 0.0692a

0.0282b 0.0302b 0.0352a,b 0.0399a

0.0468a 0.0432a 0.0368b 0.0320b

0.136d 0.157c 0.204b 0.272a

36c 187c 824b 1616a

MS + SS

MS + SS + BC

CT Means for treatments MS MS + SS MS + SS + BC Means for rates 0.5 1 2 4

For each column, mean values with different letters are significantly different (P < 0.05); Bonferroni post-hoc test; superscripts used only for significant differences according to ANOVA (Table 2). Asterisks denotes a significant difference between the control soil without amendments and treated soil; ⁎P < 0.05, ⁎⁎P < 0.01, nsnon-significant.

observed between the R4 rate (0.2438 cm3 cm− 3) and all other rates from R05 to R2 (0.2642 cm3 cm− 3 on average). The pore diameters ranging from 50 to 500 μm were not affected by any compost treatments. Pores with a diameter below 50 μm showed a reaction when the organic amendments were applied. However, this effect was different for the pores with diameters above 500 μm. When compared with the CT, the volume of these pores significantly increased when compost was added. No differences were found between soils with MS compost, with sewage sludge, and with MS + SS. Only the application of compost with biochar, MS + SS + BC, resulted in significantly lower volumes of all pore fractions with diameters below 50 μm. Higher rates of compost

resulted in an increase in the pore capacity.

3.2. Soil water retention Changes in the soil porosity were reflected in the water retention properties of the investigated soil. The water retention curves are presented in Fig. 1. The differences between the SWRC of the treated soil appeared not only within a high matric potential range but also in a low range below 1500 kPa. When compared with the CT, compost application improved the water retention properties of the soil. However, the scale of this effect

Table 4 Pore size distribution of the soil for the investigated soil/compost mixtures. Treatments

Fertilizer rates (% m/m)

Volume of pores (cm3 cm− 3) for diameter classes < 0.005 μm

MS

MS + SS

MS + SS + BC

0.5 1 2 4 0.5 1 2 4 0.5 1 2 4

CT Means for treatments MS MS + SS MS + SS + BC Means for rates 0.5 1 2 4

0.005–0.5 μm

50–500 μm

> 500 μm

0.0558 0.0546a,b,c,d 0.0439a,b,c,d,e 0.0484a,b,c,d,e 0.0380d,e 0.0384c,d,e 0.0441a,b,c,d,e 0.0563a,b 0.0360e 0.0407b,c,d,e 0.0490a,b,c,d,e 0.0591a 0.0351⁎⁎

0.0477 0.0415 0.0290 0.0266 0.0335 0.0294 0.0335 0.0369 0.0301 0.0344 0.0387 0.0416 0.0412ns

0.2411 0.2486 0.2593 0.2496 0.2770 0.2783 0.2615 0.2421 0.2833 0.2745 0.2541 0.2397 0.2296⁎⁎

0.0202a 0.0184a,b 0.0178b

0.0507b 0.0442a,b 0.0462a

0.0362 0.0333 0.0362

0.2497b 0.2647a 0.2629a

0.0129b 0.0158b 0.0201a,b 0.0264a

0.0433b 0.0446b 0.0456b 0.0546a

0.0371 0.0351 0.0338 0.0351

0.2672a 0.2671a 0.2583a 0.2438b

e

b,c

0.0071 0.0127c,d 0.0319b 0.0618a 0.0099d,e 0.0138c,d 0.0203c 0.0351b 0.0089e 0.0114d 0.0174c,d 0.0314b 0.0046⁎⁎

0.0139 0.0178b 0.0222a,b 0.0271a 0.0128c 0.0148b,c 0.0191b 0.0270a 0.0122c 0.0149b,c 0.0189b 0.0250a 0.0105⁎⁎

0.0284a 0.0198a 0.0173b 0.0086c 0.0127b,c 0.0232b 0.0428a

0.5–50 μm a,b,c

For each column, mean values with different letters are significantly different (P < 0.05); Bonferroni post-hoc test; superscripts used only for significant differences according to ANOVA (Table 2). Asterisks denotes a significant difference between the control soil without amendments and treated soil; ⁎P < 0.05, ⁎⁎P < 0.01, nsnon-significant.

30

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Fig. 1. The soil water retention curves based on van Genuchten equation for the investigated soil/compost mixtures. Vertical bars represent standard deviations (n = 12).

as S-slope and RFC (Table 3). The S-index depended only on the compost rates. Higher rates decreased the S value. The RFC was affected not only by the rates but also by the feedstock type. The highest RFC value was obtained for the soil with MS compost (0.207). The RFC for the other treatments with sewage sludge, MS + SS and MS + SS + BC, was significantly lower (0.185 on average).

depended on the compost rate and feedstock type (Table 3). The highest value of FC was observed in the MS treatment (0.080 cm3 cm− 3). When compost with sewage sludge was applied, it reduced the FC value to 0.071 cm3 cm− 3. Biochar additive did not change the FC. The field capacity was strongly influenced by the compost rate. Higher rates resulted in higher FC values, from 0.050 cm3 cm− 3 at the R05 rate to 0.109 cm3 cm− 3 at the R4 rate. A similar relationship was observed for the PWP. The highest value was determined for the MS compost, and it was significantly lower for MS + SS and MS + SS + BC treatments. Compost rates increased the PWP values. The changes in FC and PWP were reflected in the AWC. The AWC was affected by the interaction of feedstock type and compost rate. The lowest AWC value was obtained for the soil with MS compost (0.0413 cm3 cm− 3 on average), regardless of the compost rate. When sewage sludge or biochar was added during the composting process, it resulted in an increase in the AWC value of soil. The highest AWC was obtained for the MS + SS + BC/R4 treatment (0.050 cm3 cm− 3). The regression models for the relationship between compost rates and AWC are presented in Fig. 2. Correlation coefficients, r, were calculated first. When r was significant, then the regression model was determined. The r was significant (P < 0.05) for the MS + SS and MS + SS + BC treatments at 0.481 and 0.549, respectively. The relationship between compost rates and AWC for MS was not statistically significant. For both composts with sewage sludge, the soil AWC increased when higher rates of compost were used. The compost application also affected the soil quality indices, such

3.3. Water repellency Compost application significantly increased the water repellency of the tested soil (Table 3). The WDPT depended on both feedstock type and compost rate. The WDPT for the CT object was only 1 s, which means that this soil was not water repellent, whereas it was much higher (666 s on average) for any other soil samples amended with compost. The MS application resulted in a strong increase in the WDPT, up to 644 s. However, for the soil treated with the MS + SS (1039 s), the highest WDPT was obtained. This soil was classified as severely water repellent. When sandy soil was treated with compost produced with maize straw and sewage sludge, but complemented with biochar (MS + SS + BC), it resulted in a decrease of water repellency to the value below that of the MS treatment (315 s). The relationship between WDPT and compost rates was strongly significant. Higher rates resulted in higher water repellency, from 36 s for R05 to 1616 s for soil with the R4 rates. The regression models for the relationship between compost rates and WDPT are presented in Fig. 3. 31

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other studies for fine-textured soils (Celik et al., 2004) and coursetextured soils (Turner et al., 1994). These changes in the soil porosity improved its hydraulic properties. According to Curtis and Claassen (2005), compost incorporation at a rate of 24% resulted in a greater than twofold increase in AWC. In this study, water retention increased in direct proportion to the compost rate. These results confirm those found by Aggelides and Londra (2000) who reported that retention capacity was higher in soils amended with high compost rates than in soils receiving low rates. In contrast, Mamo et al. (2000) observed that the addition of municipal composts did not significantly affect available water. However, they ascribed this effect to the salt loading, as the investigated composts were relatively high in salinity. The application of composted sewage sludge showed a very similar effect to that of the composted plant wastes, with regard to basic physical parameters. MS + SS improved the physical parameters of the soil. These positive effects on the quality of the soil were also confirmed by Madejón et al. (2003) for water sludge compost. According to Epstein et al. (1976), sludge and compost increase the water content and the water retention of a silt loam soil. Ramulu (2002) also observed that organic matter added to the soil as sewage sludge composts improved soil properties such as bulk density, porosity, and water-holding capacity. Ojeda et al. (2003) reported that a higher organic matter proportion in sludge not only decreased the bulk density but also increased the aggregate stability. MS + SS increased the volume of large pores in sandy soils but reduced the volume of pores with diameters below 50 μm when compared with the MS treatment without the addition of sewage sludge. These improvements in the physical properties of the soil increased the water-holding capacity by promoting higher water retention in sludgeamended soils (Ojeda et al., 2003). This relationship is evident in sandy soil. However, this effect was less pronounced in soils with higher clay content, where adding sludge to the soil reduced hydraulic conductivity in an experimental column due to the blockage of soil pores caused by the proliferation of bacteria (Metzger and Yaron, 1987). Hydrophobic effects, which are common in a variety of dry organic amendments including dry sludge, may reduce the infiltration rate in the soil amended with sludge (Bachmann et al., 2008). This effect may persist for a long period of time after the sludge has been applied (Agassi et al., 1998; Ojeda et al., 2003). Our study confirmed this effect; the WDPT increased when MS was applied and was much greater after MS + SS application. González and Cooperband's (2002) findings also showed that the effects of compost on the physical properties of the soil differed among feedstocks. They used duck manure-sawdust, potato cull-sawdust-dairy manure, and paper mill sludge-bark composts on a silt loam soil. These differences were ascribed to different soil carbon contents. Bulk density decreased with increasing total carbon content. Lynch et al. (2005) also obtained similar results. Cheng et al. (2007) noticed that the BD of sandy soil decreased with an increase in the composted sewage sludge rate due to the lower density of the compost material. Water retention of the substrates also improved with the composted sewage sludge content, which is beneficial for turfgrass growth. This type of compost can be recommended as a soil amendment for turfgrass production on sandy loam soil. The MS + SS + BC significantly improved the physical quality of the soil in relation to the control soil. The decrease in bulk density of the biochar-amended soils could be ascribed to the changes in soil structure and the alteration of soil aggregate sizes (Tejada and Gonzalez, 2008; Jien and Wang, 2013). However, this effect was mainly observed for soils with higher clay content, organic matter, and with higher aggregate stability (González and Cooperband, 2002; Kimetu and Lehmann, 2010). Biochar also affected the water retention properties of the soil. The addition of pure biochar leads to an increase in water content at the permanent wilting point. An increase in AWC was observed for all sandy substrates, except for highly humic sand (Abel et al., 2013). According to Xu et al. (2012), improvements in soil water

Fig. 2. The relationship between rate of composts and available water content (AWC) (n = 12).

4. Discussion The results obtained in this experiment indicate that compost application significantly affects the physical properties of sandy soil. These changes can be ascribed to the effect of mixing the soil with less dense material, which is evident immediately after application in compacted, fine-textured soils (Celik et al., 2004), and in coarse-textured soils (Głąb, 2014; Głąb et al., 2016). Hargreaves et al.'s (2008) review confirmed these relationships between compost application and physical properties of the soil. Similar effects were also reported by Głąb (2014) in a laboratory-scale experiment. It was confirmed that an improved physical quality of the compost-amended soil correlated with compost rates. In the current study, the basic physical parameters of the soil, such as BD and TP, were also affected by compost rates. The higher the biochar rates, the lower the BD and higher the TP. This relationship between the compost rate and the basic physical properties of the soil confirmed the results obtained by Aggelides and Londra (2000) and Pagliai et al. (2004). Changes in BD were reflected in the differential porosity of the soil. In comparison with the control group, the application of compost increased the volume of all fractions of pores. A similar effect was observed by Larney and Angers (2012) who noted that soil microporosity and macroporosity increased with the application of livestock manure or compost. Positive effects of compost additives were also identified in

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Fig. 3. The relationship between rate of organic fertilizers and soil water repellency (WDPT) (n = 5).

untreated soil. The basic physical parameters of the soil, such as BD and TP, were mainly dependent on the rate of the biochar. The lowest BD values were observed when the highest compost rates were applied. The differential porosity of the soil was affected by both compost rate and feedstock. The highest large (diameters above 500 μm) pore content was observed for compost with sewage sludge and with biochar additives. The pores with diameters ranging from 50 to 500 μm were not affected by any compost treatments. Pores with a diameter below 50 μm showed the highest reaction when the organic amendments were applied. In comparison with the control untreated soil, the volume of these pores significantly increased when compost was added. No differences were observed between soil with maize straw compost and with sewage sludge addition. However, when biochar was added, it resulted in a significantly lower volume of all pore fractions with a diameter below 50 μm. Higher rates of compost resulted in an increase in these pores' capacity. The compost application improved the water retention properties of the soil depending on the compost rate and feedstock type. The AWC was affected by the interaction of feedstock type and compost rate. The lowest AWC was obtained for the soil with maize straw compost. When sewage sludge or biochar was added during the composting process, it resulted in an increase in the soil AWC value. The maize straw compost

retention by biochar additions are mainly restricted to coarse-textured soils. Spokas et al. (2016) explain these changes as being due to alterations in soil particle packing. Alterations in pore geometry, such as the blocking of larger macropores by the amendment, could explain this behaviour. Thus, the alterations of the hydraulic properties of an amended soil were primarily a function of the particle size of the material, regardless of the feedstock material converted to biochar. Bass et al. (2016), with research on compost, biochar, and their mixture, concluded that the largest improvements were recorded in treatments where biochar was present. They suggested that the presence of biochar has a potentially greater impact than that of compost alone. In this study, the addition of biochar to the sewage sludge compost did not significantly influence the basic physical parameters of the soil, such as BD, TP, and AWC, when compared with MS and MS + SS. However, the volume of macropores was significantly affected by the addition of biochar to the MS + SS treatment. This was also reflected in PWP but did not influence AWC.

5. Conclusion The results presented in this study indicate that compost application significantly improved the physical properties of sandy soil relative to 33

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application resulted in a strong increase in the water repellency. The soil became severely water repellent when the soil was treated with sewage sludge compost. The addition of biochar resulted in a decrease of water repellency to the value below that obtained in the maize straw compost treatment. The best combination of the compost rates and the type of feedstock is maize compost with sewage sludge and biochar addition at a rate of 4%. Sandy soil amended with this compost is characterized by high water retention and by severe water repellency. To reduce water repellency, it is recommended that the rate of compost is decreased. From this point of view, the compost produced from the mixture of maize straw, sewage sludge and biochar still has the best hydraulic parameters.

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