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International Journal of Agronomy
Volume 2017, Article ID 3158207, 12 pages
https://doi.org/10.1155/2017/3158207
Research Article

The Effects of Biochar and Its Combination with Compost on Lettuce (Lactuca sativa L.) Growth, Soil Properties, and Soil Microbial Activity and Abundance

1Dipartimento di Bioscienze e Territorio, Università degli Studi del Molise, 86090 Pesche, Italy
2Istituto di Biometeorologia-Consiglio Nazionale delle Ricerche (IBIMET-CNR), 50145 Firenze, Italy

Correspondence should be addressed to Dalila Trupiano; ti.lominu@onaipurt.alilad

Received 16 December 2016; Revised 6 March 2017; Accepted 19 March 2017; Published 5 April 2017

Academic Editor: Ibrokhim Y. Abdurakhmonov

Copyright © 2017 Dalila Trupiano et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Impacts of biochar application in combination with organic fertilizer, such as compost, are not fully understood. In this study, we tested the effects of biochar amendment, compost addition, and their combination on lettuce plants grown in a soil poor in nutrients; soil microbiological, chemical, and physical characteristics were analyzed, together with plant growth and physiology. An initial screening was also done to evaluate the effect of biochar and compost toxicity, using cress plants and earthworms. Results showed that compost amendment had clear and positive effects on plant growth and yield and on soil chemical characteristics. However, we demonstrated that also the biochar alone stimulated lettuce leaves number and total biomass, improving soil total nitrogen and phosphorus contents, as well as total carbon, and enhancing related microbial communities. Nevertheless, combining biochar and compost, no positive synergic and summative effects were observed. Our results thus demonstrate that in a soil poor in nutrients the biochar alone could be effectively used to enhance soil fertility and plant growth and biomass yield. However, we can speculate that the combination of compost and biochar may enhance and sustain soil biophysical and chemical characteristics and improve crop productivity over time.

1. Introduction

Soil fertility degradation, caused by erosion and depletion or imbalance of organic matter/nutrients, is affecting world agricultural productivity [1]. Inorganic fertilizers have played a significant role in increasing crop production since the “green revolution” [2]; however, they are not a sustainable solution for maintenance of crop yields [3]. Long-term overuse of mineral fertilizers may accelerate soil acidification, affecting both the soil biota and biogeochemical processes, thus posing an environmental risk and decreasing crop production [4]. Organic amendments, such as compost and biochar, could therefore be useful tools to sustainably maintain or increase soil organic matter, preserving and improving soil fertility and crop yield.

Biochar is a carbon-rich material obtained from thermochemical conversion (slow, intermediate, and fast pyrolysis or gasification) of biomass in an oxygen-limited environment. It can be produced from a range of feedstock, including forest and agriculture residues, such as straw, nut shells, rice hulls, wood chips/pellets, tree bark, and switch grass [5]. Biochar has been described as a possible tool for soil fertility improvement, potential toxic element adsorption, and climate change mitigation [68].

Indeed, several studies have shown that biochar application to soil can (i) improve soil physical and chemical properties [9, 10], (ii) enhance plant nutrient availability and correlated growth and yield [11, 12], (iii) increase microbial population and activities [1315], and (iv) reduce greenhouse gas emissions through C sequestration [16].

The beneficial effects of biochar on plant productivity and soil microbial population are related to the improvement of specific surface area, cation exchange capacity, bulk density, pH, water, and nutrients within the soil matrix [17]. Beside the generally positive plant growth responses to biochar amendment, especially in acidic coarse texture soil, negligible or negative effects also occur due to types of feedstock and pyrolysis process, biochar application rate, plant species, and soil characteristics [18, 19]. Furthermore, in most cases, biochar does not provide high amounts of nutrients [20, 21].

Some recent studies have indicated that combined applications of biochar with organic or inorganic fertilizers could lead to enhanced soil physical, chemical, and biological properties, as well as plant growth. In particular, several composted materials represent a sustainable source of available nutrients that could enhance plant growth, ameliorating soil physicochemical characteristics and microbiological properties [2226]. Liu et al. [26] showed that the combined application of compost and biochar had a positive synergistic effect on soil nutrient contents and water-holding capacity under field conditions. In addition, the combination of biochar with compost has proved to be suitable, allowing the reduction of fertilizer inputs, stabilizing the soil structure, and improving its nutrient content and water retention capacity [27, 28]. Again, these studies underline that compost and biochar combination could enhance compost properties, leading to a higher added value and a much better carbon sequestration potential due to the long-term stability of biochar [24, 25].

However, the literature shows that compost effects, as also reported above for biochar, can differ on soil biophysical-chemical properties and plant growth and yield on the basis of feedstock types, methods of producing, and application [29]. The objectives of this study were thus to determine the effect of biochar application alone, obtained from orchard pruning biomass by slow pyrolysis (550°C), or combined with compost, obtained from olive mill residues, on (i) plant growth, physiology, and yield, (ii) soil chemical characteristics, and (iii) soil microbiological abundance and enzyme activities. For this purpose, a short-term potting experiment was performed, using Lactuca sativa L. as reference plants and a soil poor in nutrients as growing substrate, to test the following hypotheses: biochar addition together with compost improves (1) soil chemical and (2) microbiological properties and enhances (3) plant growth and physiology more than compost and biochar alone.

2. Materials and Methods

2.1. Biochar, Compost, and Toxicity Test

The biochar used was a commercial charcoal (provided by Romagna Carbone s.n.c., Italy), obtained from orchard pruning biomass through a slow pyrolysis process at a temperature of 500°C in a transportable ring kiln 2.2 m in diameter that holds around 2 t of feedstock.

An olive waste compost was used, prepared in a specific experimental composting process, following Alfano et al. [30]. Briefly, compost was prepared mixing humid olive husks, from a two-phase extraction plant, with olive leaves (8% w/w); one-year-old, humid, composted husks (25% w/w) were then added to this mixture. Biochar and compost characteristics are summarized in Table 1 and analytical methods are provided in Amendola et al. [31] and Alfano et al. [30].

Table 1: Biochar and compost characteristics. The complete biochar and compost characterization and related methods are detailed in Amendola et al. [31] and Alfano et al. [30], respectively. All concentrations refer to dry matter and represent the means of three replicates ± standard error.

Biochar and compost phytotoxicity was assessed through the germination index (GI%) of cress plants (Lepidium sativum L.) [26]. Three different solutions were used to evaluate the biochar and compost toxicity on seed germination: sterile deionized water as control solution and solutions containing 50% and 75% extract of biochar or compost. Solutions were added to Petri dishes containing 10 sterile seeds of L. sativum. Germination percentage and plant root length were recorded after incubation for 42 h at 27°C in the dark (according to Vitullo et al. [32]). Seeds were scored as germinated if the radicle exceeded the length of the longest seed coat dimension. The seed germination percentage was assessed according to the formula: GI% = ()/() × 100, where and are seed germination and root elongation (mm) for the samples and and the corresponding values for controls. The test was repeated in triplicate. The GI% was obtained by means of GI50% and GI75% values. Potential toxicity of biochar was also tested on earthworms (Lumbricus terrestris L). For the earthworm avoidance test, equal amounts of unfertilized soil with and without biochar (65 g kg−1 of dry soil) were placed in two halves of a pot (50 × 30 cm). Forty earthworms were released between the two substrates. After 48 hours, the pot was examined to determine the soil selected by earthworms [33].

2.2. Experimental Design

One-month-old lettuce (Lactuca sativa L. var. longifolia) seedlings (Vivaio Mignogna, Ripamolisana, Molise, Italy) were transplanted into plastic pots (3.5 l) prepared with four different substrates: (i) unfertilized soil (PS); (ii) unfertilized soil plus compost (PSC); (iii) unfertilized soil plus biochar (PSB); and (iv) unfertilized soil plus compost and biochar (PSCB). Plants were then grown until maturity (9 weeks) in a screened greenhouse (University of Molise, Pesche, Italy; Lat 41°37′00′′N; Long. 14°17′00′′E; 510 m a.s.l.) under a controlled water regime, temperatures ranging between 12 and 25°C, and natural day length corresponding to spring-summer season (May–July). Soil was collected from an uncultivated pasture area, located in Pesche, with a floral composition predominantly of graminoid grasses, not under a rotation system and that includes hedges. This area is mainly used for grazing, but the fodder is harvested mechanically. The preplanting physicochemical properties of the soil are given in Supporting Information (Table S1 in Supplementary Material available online at https://doi.org/10.1155/2017/3158207). Briefly, the soil was moderately subalkaline (0–30 cm) with a clay texture according to United States Department of Agriculture classification [34]; it was characterized by low electrical conductivity (EC), cation exchange capacity (CEC), and nitrogen and carbon content; it is unlikely that this soil already contained charcoal as there had been no tradition of crop residue or other burning on the land. For the experiment, soil was air-dried for 72 h, weighed and finely crushed, and then mixed thoroughly before packing lightly in the pots on top of 100 g of pebbles placed on the base to improve drainage. The weight of each filled pot was 3000 g.

Biochar and compost application rates were set up on the basis of previous lettuce pot and field researches [12, 3539]. In detail, data reported by Carter et al. [35] showed that 50 and 150 g kg−1 rice-husk biochar application rate led to a highly positive effect on lettuce growth in compost fertilized and unfertilized soils, respectively. Based on this finding, in the present study, biochar and compost were supplied at an application rate of 65 g and 50 g per kg of dry soil, respectively. After mixing, the pots were filled in order to ensure the same soil bulk density. There were ten pots (one plant per pot) for each treatment arranged in a complete randomized block design and rotated each day to a different position within the block for the duration of the trial. The pots were fully irrigated to prevent water stress (twice a day, as required) and a suspended shade cover net was used to reduce exposure to sunlight.

2.3. Soil Analyses

Soils were sampled at the end of the experiment and air-dried for 72 h. The moisture content was calculated according to the Black method [40] as the difference in sample weight before and after oven drying to constant weight at 105°C. The pH was measured by potentiometry (pH meter Eutech Instruments) in H2O and 0.01 M CaCl2 using a 1 : 2.5 soil weight : extract-volume ratio. Alkalinity of samples with a pH value greater than 7.0 was determined by titrimetry according to the Higginson and Rayment method [41, 42]. Electrical conductivity (EC) was determined by a conductivity meter (Cond 510, XS Instruments) on a 1 : 5 soil : water suspension [41, 42]. Ash content was determined by igniting an oven-dried sample in a muffle furnace at 440 ± 40°C, according to the American Society for Testing and Materials [43]. Cation exchange capacity (CEC) was assessed according Mehlich [44] using the BaCl2. For total nitrogen () determination a modified Kjeldahl procedure was used with Devarda’s alloy pretreatment, important to recover both -N and -N [45]. Total phosphorus () was detected by spectrophotometry (UV-1601 Shimadzu) according to the test method described by Bowman [46]. Available phosphorus () was extracted by a NaHCO3 solution at pH 8.5 and evaluated by spectrophotometry according to the Olsen test method [47]. Total carbon () content was determined using a CHN autoanalyzer (CHN 1500, Carlo Erba) [48].

2.4. Plant Analysis

Plant morphological analyses were performed weekly by measuring the main leaf parameters: number (LN); area (LA); length (LL); width (LW); and perimeter (LP). The Image J 1.41 (https://rsb.info.nih.gov/ij/) software was used for analysis. In addition, at the end of the experiment, leaf and root biomass allocation was determined before (fresh weight, FW) and after (dry weight, DW) two days of drying in an oven at 60°C. The measurements were performed on six plants.

Leaf water potential (ψ) was measured using a pressure chamber (PMS, Instrumentation Co., Corvallis, OR, USA). Leaf gas exchange measurements were performed using a portable gas exchange system (CIRAS-1, PP Systems, Hertz, Hitchin, UK). Leaf gas exchanges and ψ were measured on the fourth fully expanded and sun exposed leaf on a cloud-free day (after 3 months of growth). These measurements were taken on five plants (one leaf per plant) per treatment around midday (between 11.30 a.m. and 1.30 p.m.).

Chlorophyll content was also measured. For this, chlorophylls (Chl) and (Chl) were extracted from three randomly sampled leaf discs (10 mm) with N,N dimethylformamide (DMF). Extraction was performed for 48 h at 4°C in the dark at a ratio of 1 : 20 (plant material : solvent, w : v) [49]. The extinction coefficients proposed by Inskeep and Bloom [50] were used for the quantification by spectrophotometric analysis. The following formulas were used: Chl a = 12.70  −  2.79; Chl b = 20.70  −  4.62; Chl = 17.90 + 8.08, where A is absorbance in 1.00 cm cuvettes and Chl is mg per l. The leaf area Chl content was then calculated (mg cm−2) together with the Chl a/Chl b ratio by dividing the Chl a content by the Chl b content.

2.5. Microbiological Analyses

Cellular cultivability was assessed by plate-counting. Cultivable aerobic bacteria in soil samples were analyzed on standard plate count agar (Difco Bekton Dikson, Milan, Italy), at 28 and 55°C for 48 h; actinomycetes on actinomyces agar (Difco), at 28°C and 55°C for 48–72 h; eumycetes on malt agar (Difco) + rose bengal 33 mg l−1 and tetracycline 100 ml l−1, at 28°C for 72 h, following the method described by Alfano et al. [30]. Cellular counts were done in triplicate by performing quantitative determinations on the basis of colony forming units (CFU) in agarized media, according to Alfano et al. [30]. All results are expressed as log CFU/g DW, after drying aliquots of the samples at 105°C for 48 h.

Soil enzymatic activities were determined by the API-ZYM system (bio-Mérieux Italia, Rome, Italy). With the API-ZYM system, semiquantitative evaluation of the activities of 19 hydrolytic enzymes [alkaline phosphatase, esterase (C4), esterase-lipase (C8), lipase (C14), leucine arylamidase, valine arylamidase, cystine arylamidase, trypsin, α-chymotrypsin, acid phosphatase, phosphoamidase, α-galactosidase, β-galactosidase, β-glucuronidase, α-glucosidase, β-glucosidase, N-acetyl-β-glucosaminidase, α-mannosidase, and α-fucosidase] was determined [51, 52]. Using a sterile Pasteur pipette, each gallery was inoculated with two drops of 10−1 or 10−2 suspensions of 20 g of soil in 180 mL of sterile saline solution (0.9% NaCl, w/v). The color that developed in each enzymatic reaction was assigned according to the color chart (range 0–5) supplied with the system, and this, in accordance with reported procedures, provided the conversion evaluation of the hydrolyzed substrates in nanomoles [51]. The samples were analyzed in triplicate and the average data were used. Results were expressed as enzyme relative activity/g of DW of substrate; data were corrected by the dilution factor.

2.6. Statistical Analysis

Analysis of variance (ANOVA) was applied in order to evaluate the effect of each treatment on soil proprieties, chlorophyll, ecophysiology, and microbiological data (one-way ANOVA) and the effect of day, treatments, and their interaction (two-way ANOVA) for plant morphological data. To assess the differences in the measured parameters among treatments, a postmeans comparison was performed using the Fisher least significant difference (LSD) test at the 0.05 significance level. Statistical analysis was conducted with OriginPro version 8.5.1 (OriginLab, Northampton, MA, USA).

3. Results

3.1. Biochar and Compost Characteristics

Biochar and compost used for the experiment were previously analyzed by Amendola et al. [31] and Alfano et al. [30], respectively. Main biochar and compost characteristics are summarized in Table 1. Briefly, as in the majority of biochar, the pH value was within the range of alkalinity. The and contents of biochar were 77.8% and 0.9%, respectively, according to Class 1 of the Guidelines for Certification of the International Biochar Initiative (IBI, http://www.european-biochar.org/en/ebc-ibi). The compost was mature, showing stable chemical and microbiological characteristics, with the potential to be used as an agricultural substrate or soil conditioner.

The results showed that biochar was not toxic for soil biotic communities, L. sativum seeds, or earthworms. Indeed, the phytotoxicity test with Lepidium showed no effects of biochar and compost on the germination index (82 ± 4 and 95 ± 4%, resp.) compared to the control (water; 100 ± 2%) (data not shown), while the avoidance test showed that L. terrestris preferred the biochar-amended soil (Figure 1).

Figure 1: Earthworms avoidance test. Number of earthworms (Lumbricus terrestris L.) recovered in unfertilized (PS) versus unfertilized plus biochar (PSB) soil compartments after 48 h. Vertical bars represent the standard error of the mean of three replicates of 40 earthworms each. Asterisks indicate significant differences ().
3.2. Soil Characterization

Soil chemical analysis showed that the addition of biochar induced a significant increase of pH values from 6.9 (PS) to 8.0 and from 7.5 (PSC) to 7.7 in PSB and PSCB, respectively. On the contrary, the alkalinity value did not change in PSB and PSCB compared to PS and PSC, respectively (Table 2).

Table 2: Soil chemical properties. Data represent the mean () ± standard error. Mean values marked with the same letter are not statistically different. One-way ANOVA was applied to weigh the effects of different treatments ().

An increase of total N content from 0.8 (PS) to 1.2 was observed in PSB. Conversely, the EC increased about 1.4 and 1.1 fold in PSB and PSCB, respectively, while moisture decreased 0.8-fold in PSCB. Ash content slightly decreased in PSB and PSCB. The was increased about 1.5-fold in PSB, whereas no alteration was observed in PSBC. On the contrary, the was 2-fold greater in PSCB than PSC. The content was significantly increased in PSB (5-fold) and PSCB (2-fold) compared to the relative controls (PS and PSC). The CEC value was also slightly increased in PSB and PSCB compared to PS and PSC, respectively. All the above parameters were increased in PSCB compared to PSB, except for pH, moisture, and ash that decreased.

3.3. Plant Growth

Significant differences in growth parameters were recorded between treatments (Figure 2). In detail, lettuce plants showed higher leaf number in PSB than PS while leaf length, width, area, and perimeter were unchanged. Plants grown in PSCB showed lower leaf length, width, area, and perimeter compared to PSC while leaf number was unchanged. Furthermore, all leaf parameters were increased in PSC compared to PS and also in PSCB compared to PSB, although they were almost unchanged at the end of treatment (after 9 weeks).

Figure 2: Morphological analysis. The main leaf parameters were analyzed: LN = leaf number; LL = leaf length; LW = leaf width; LA = leaf area; LP = leaf perimeter. Data represent the mean () ± standard error. Mean values marked with asterisks are statistically different at , at , and at . Two-way ANOVA was applied to weigh the effects of day, treatment, and their interactions on plant growth parameters ( and level values are reported). PS = lettuce plants grown in unfertilized soil; PSB = lettuce plants grown in unfertilized soil plus biochar; PSC = lettuce plants grown in unfertilized soil plus compost; and PSCB = lettuce plants grown in unfertilized soil plus compost and biochar.

Total plant dry weight, considering leaf and root biomass, increased in PSB compared to PS; on the contrary, leaf biomass decreased in PSCB and root biomass was unchanged compared to PSC and PSB (Figure 3). Chlorophyll content did not show significant changes between treatments (data not shown).

Figure 3: Effects of biochar and/or compost on leaf and root biomass (g of dry tissue weight). Data represent the mean () ± standard error. Mean values marked with the same letter are not statistically different. One-way ANOVA was applied to weigh the effects of different treatments (). PS = lettuce plants grown in unfertilized soil; PSB = lettuce plants grown in unfertilized soil plus biochar; PSC = lettuce plants grown in unfertilized soil plus compost; and PSCB = lettuce plants grown in unfertilized soil plus compost and biochar.

The leaf water potential was more negative in plants grown in PS than those grown in other substrates, followed by PSB and PSC and PSCB (Figure 4).

Figure 4: Leaf water potential at midday of plants grown in different substrates. Values are means () ± standard error; significant differences between the means (at least , according to ANOVA) appear with different letters. PS = lettuce plants grown in unfertilized soil; PSB = lettuce plants grown in unfertilized soil plus biochar; PSC = lettuce plants grown in unfertilized soil plus compost; and PSCB = lettuce plants grown in unfertilized soil plus compost and biochar.

Stomatal conductance showed no significant differences between control and treated plants (Figure 5), while transpiration rate was slightly increased in PSCB and unchanged in PSC and PSB compared to PS (Figure 5). Assimilation rate was not altered by treatment with biochar (PSB) and biochar-compost (PSCB). In particular, plants showed the highest assimilation rate and water use efficiency in PSC (Figure 5).

Figure 5: Transpiration rate, stomatal conductance, assimilation, and water use efficiency (WUE) of plants grown in different soils. Values are means () ± standard error; significant differences between the means (at least , according to ANOVA) appear with different letters. PS = lettuce plants grown in unfertilized soil; PSB = lettuce plants grown in unfertilized soil plus biochar; PSC = lettuce plants grown in unfertilized soil plus compost; and PSCB = lettuce plants grown in unfertilized soil plus compost and biochar.
3.4. Cultivable Microorganisms

The analysis of cultivable microorganisms showed that in PSB the cultivable aerobic bacteria, actinomycetes, and eumycetes decreased () compared to PS while they were unchanged in PSBC compared to PSC (Table 3). Furthermore, the abundance of cultivable aerobic bacteria and eumycetes was higher in PSC than PS while actinomycetes were unchanged; all cultivable microorganisms increased in PSCB compared to PSB (Table 3).

Table 3: Soil microbiological characteristics. Values are expressed as dry weight (DW). Data represent the mean () ± standard error. Mean values marked with the same letter are not statistically different. One-way ANOVA was applied to weigh the effects of different treatments (). PS = unfertilized soil; PSB = unfertilized soil plus biochar; PSC = unfertilized soil plus compost; and PSCB = unfertilized soil plus compost and biochar.
3.5. Soil Enzyme Activities

Enzymatic profile analysis revealed that all enzymatic activities were increased in PSC compared to PS, except lipase-esterase and esterase that were unchanged. Biochar treatment alone or in combination with compost induced specific enzymatic variations. In detail, in PSB, compared to PS, the activities of alkaline phosphatase, acid phosphatase, chymotrypsin, trypsin, phosphohydrolase, lipase-esterase, and esterase were increased, while lipase was unchanged (Table 4). In PSBC, compared to PSC, alkaline phosphatase, acid phosphatase, lipase-esterase, and esterase strongly increased (), whereas chymotrypsin and trypsin activities decreased () and phosphohydrolase and lipase activities were lost (Table 4). In PSCB, compared to PSB, we recorded that alkaline phosphatase and acid phosphatase increased and trypsin, phosphohydrolase, and esterase decreased, while chymotrypsin, lipase-esterase, and lipase were unchanged ().

Table 4: Soil enzymatic activities. Soil enzymatic activities were determined by the API-ZYM system (bio-Mérieux Italia). Results are expressed as nanomoles/g of dry weight of substrate; the data have been corrected by the dilution factor. PS = unfertilized soil; PSB = unfertilized soil plus biochar; PSC = unfertilized soil plus compost; and PSCB = unfertilized soil plus compost and biochar.

4. Discussion

The study showed that both biochar amendment and compost addition to a soil poor in nutrients induced a positive effect on lettuce plant growth and physiology and on soil chemical and microbiological characteristics; however, no positive synergic or summative effects exerted by compost and biochar in combination were observed.

In detail, the biochar alone induced a positive lettuce yield response, although transpiration, stomatal conductance, and assimilation rate did not show relevant variations. Positive yield responses to biochar addition have been reported for a wide variety of crops. For example, it is reported that maize yield increased by 98–150% as a result of manure biochar addition [53], lettuce and Arabidopsis plant biomass increased by 111% after poplar wood chips biochar addition [54], and wheat grain yield increased by 18% with the use of oil mallee biochar [55].

A possible explanation is that the biochar, increasing the pH, CEC, , , , and water content, could enhance available nutrients for plants and, consequently, biomass accumulation [22, 56]. In fact, the increase in CEC value could be driven by the presence of cation exchange sites on the biochar surface [10, 57], and, as also reported in Vaccari et al. [58], this could contribute to retaining , leading to improved N nutrition in biochar-amended soils [5961]. This would confirm a direct biochar role in the nutrient supply to plants [20, 62]. The increased pH in biochar treated soil could also be indirectly related to growth stimulation in lettuce. Indeed, Beesley and Dickinson [63] hypothesized that soil alkalization caused by biochar addition might positively influence earthworms, as also observed in our study, with a subsequent positive effect on dissolved organic carbon content. The pH value has also been found to influence the soil microbial population and enzymatic activities; indeed, a high pH might enhance bacteria abundance, whereas it did not change fungi total biomass or dramatically reduce their growth [64, 65]. The activity of alkaline phosphatase, aminopeptidase, and N-acetylglucosaminidase enzymes has also been reported to increase after biochar applications [66, 67]. In accordance with this evidence, our results showed that the biochar alone decreased cultivable microorganisms abundance, while it enhanced the activity of enzymes involved in phosphorus, nitrogen, and carbon cycling (alkaline phosphatase, acid phosphatase, phosphohydrolase, lipase-esterase, esterase, chymotrypsin, and trypsin). These results could indicate that although the bacteria abundance could be reduced by biochar soil alkalization, the microbial communities related to nitrogen, phosphorus, and carbon cycling could be stimulated by biochar-induced increasing of soil , , and availability [68, 69].

Nevertheless, the compost alone amendment showed the best clear and positive effects on plant growth and yield and on soil chemical characteristics. Indeed, according to data reported in the literature [70, 71], in compost amended soil lettuce plants showed the maximum total biomass accumulation, assimilation rate, and water use efficiency, probably due to the high soil nutrients availability (soil , , , and content was increased). This high soil nutrient status could also have enhanced the activity of enzymes involved in phosphorus and nitrogen cycling (phosphohydrolase, chymotrypsin, and trypsin), which increased compared to those in the unamended soils; on the other hand, the slight pH increase could be responsible for the decrease of cultivable bacteria.

No synergic or positive effects exerted by compost and biochar combination were observed here compared to the compost alone treatment. Indeed, we showed that lettuce growth changes were negligible combining compost and biochar amendment, although, as shown above, the amount of compost applied and the nutrients supplied were adequate to produce the highest plant benefits in the compost alone treatment. Furthermore, compared to the addition of compost alone, the compost and biochar combination did not improve soil chemical characteristics, except for an increase in C and P content. These increases could be related to biochar capacity to enhance C accumulation and sequestration and to retain and exchange phosphate ions by its positively charged surface sites [59, 60]. Additionally, in compost and biochar-amended soil, microorganism abundance was unchanged while the activity of enzymes involved in N and P mineralization (chymotrypsin, trypsin, and phosphohydrolase) was reduced or completely lost compared to those in the compost alone treatment.

It is reported that biochar can have significant effects on microbially mediated transformation of nutrients by its surface interaction with substrate and soil microbial enzymes [72, 73] or by inducing soil alkalization [74]. Indeed, we hypothesized that soil microbial abundance and activities were shaped by nutrient availability and pH, which in turn could be balanced by biochar-compost combination. However, the biochar benefits could be amplified over time through surface oxidation and bioactivation with soil microbes and fungi [75, 76]. In addition, given that the beneficial effects of biochar were found to increase more in sandy than in loamy substrates [25], we hypothesized that, in PSCB, the high nutrient status, due to the compost, could have masked biochar effects [77].

In summary, our short-term potting experiment clearly demonstrated that compost addition provided the best solution regarding soil quality and fertility, which were also reflected in best plant growth and biomass yield.

Furthermore, taking into account that the soil used in this study had low nutrient status, suboptimal for plant growth without additions of organic and/or inorganic amendments, these results demonstrate that the application of biochar alone could also be effectively used to enhance soil fertility and plant growth and biomass yield. This may have important implications for sustainable low-input agriculture, with economic and environmental benefits for both marginal and productive cropland.

Nevertheless, unexpectedly, combined application of biochar and compost did not outperform compost amendment in terms of biomass yield and soil fertility. However, it may enhance and sustain soil biophysical and chemical characteristics over time, given that most of compost will disappear through mineralization within 5 years after application whereas most of the biochar will stay in the soil for decades [20, 78].

Further long-term and large-scale field experiments are required to analyze differences over time and in particular to quantify the amount of recalcitrant carbon supplied and sequestered in the soil by both biochar alone and the combination of biochar and compost. Their benefits and effects in terms of improving and sustaining soil fertility, crop productivity, and economic returns to users should be also evaluated over time.

Conflicts of Interest

The authors declare that there are no conflicts of interest regarding the publication of this paper.

Authors’ Contributions

Gabriella Stefania Scippa coordinated the project. Gabriella Stefania Scippa, Dalila Trupiano, Claudia Cocozza, and Roberto Tognetti conceived and designed the experiments. Dalila Trupiano, Carla Amendola, Claudia Cocozza, Francesca Fantasma, Silvia Baronti, Sara Di Lonardo, and Giuseppe Lustrato performed the experiments. Dalila Trupiano, Carla Amendola, Claudia Cocozza, Silvia Baronti, Sara Di Lonardo, and Giuseppe Lustrato analyzed data. Gabriella Stefania Scippa contributed reagents/materials/analysis tools. Dalila Trupiano wrote the manuscript. Claudia Cocozza, Roberto Tognetti, Silvia Baronti, and Francesco Primo Vaccari revised the manuscript. All authors approved the manuscript.

Acknowledgments

The authors thank Dr. Luisa Andrenelli and Dr. Adriano Baglio (University of Florence), Italian Biochar Association (ICHAR http://www.ichar.org), and Federica Oliva (University of Molise) for their technical support during laboratory measurements. Research was supported by grants from Molise Region (PSR Molise 2007/2013-Misura 124) through the ProSEEAA Project (CUP: D95F14000030007) and it contributes to the EuroCHAR Project (FP7-ENV-2010 ID-265179).

References

  1. J. A. Foley, R. DeFries, G. P. Asner et al., “Global consequences of land use,” Science, vol. 309, no. 5734, pp. 570–574, 2005. View at Publisher · View at Google Scholar · View at Scopus
  2. E. Liu, C. Yan, X. Mei et al., “Long-term effect of chemical fertilizer, straw, and manure on soil chemical and biological properties in northwest China,” Geoderma, vol. 158, no. 3-4, pp. 173–180, 2010. View at Publisher · View at Google Scholar · View at Scopus
  3. B. Vanlauwe, A. Bationo, J. Chianu et al., “Integrated soil fertility management: operational definition and consequences for implementation and dissemination,” Outlook on Agriculture, vol. 39, no. 1, pp. 17–24, 2010. View at Publisher · View at Google Scholar · View at Scopus
  4. J. C. Aciego Pietri and P. C. Brookes, “Relationships between soil pH and microbial properties in a UK arable soil,” Soil Biology and Biochemistry, vol. 40, no. 7, pp. 1856–1861, 2008. View at Publisher · View at Google Scholar · View at Scopus
  5. S. Sohi, E. Lopez-Capel, E. Krull, and R. Bol, “Biochar, climate change and soil: a review to guide future research,” CSIRO Land and Water Science Report 05/09, 2009. View at Google Scholar
  6. C. J. Ennis, A. G. Evans, M. Islam, T. K. Ralebitso-Senior, and E. Senior, “Biochar: carbon sequestration, land remediation, and impacts on soil microbiology,” Critical Reviews in Environmental Science and Technology, vol. 42, no. 22, pp. 2311–2364, 2012. View at Publisher · View at Google Scholar · View at Scopus
  7. S. Malghani, G. Gleixner, and S. E. Trumbore, “Chars produced by slow pyrolysis and hydrothermal carbonization vary in carbon sequestration potential and greenhouse gases emissions,” Soil Biology and Biochemistry, vol. 62, pp. 137–146, 2013. View at Publisher · View at Google Scholar · View at Scopus
  8. C. E. Stewart, J. Zheng, J. Botte, and M. F. Cotrufo, “Co-generated fast pyrolysis biochar mitigates green-house gas emissions and increases carbon sequestration in temperate soils,” GCB Bioenergy, vol. 5, no. 2, pp. 153–164, 2013. View at Publisher · View at Google Scholar · View at Scopus
  9. A. Mukherjee and R. Lal, “Biochar impacts on soil physical properties and greenhouse gas emissions,” Agronomy, vol. 3, pp. 313–339, 2013. View at Google Scholar
  10. S. P. Sohi, E. Krull, E. Lopez-Capel, and R. Bol, “A review of biochar and its use and function in soil,” Advances in Agronomy, vol. 105, no. 1, pp. 47–82, 2010. View at Publisher · View at Google Scholar · View at Scopus
  11. L. A. Biederman and W. Stanley Harpole, “Biochar and its effects on plant productivity and nutrient cycling: a meta-analysis,” GCB Bioenergy, vol. 5, no. 2, pp. 202–214, 2013. View at Publisher · View at Google Scholar · View at Scopus
  12. S. Jeffery, F. G. A. Verheijen, M. van der Velde, and A. C. Bastos, “A quantitative review of the effects of biochar application to soils on crop productivity using meta-analysis,” Agriculture, Ecosystems and Environment, vol. 144, no. 1, pp. 175–187, 2011. View at Publisher · View at Google Scholar · View at Scopus
  13. N. M. Jaafar, P. L. Clode, and L. K. Abbott, “Microscopy observations of habitable space in biochar for colonization by fungal hyphae from soil,” Journal of Integrative Agriculture, vol. 13, no. 3, pp. 483–490, 2014. View at Publisher · View at Google Scholar · View at Scopus
  14. R. S. Quilliam, H. C. Glanville, S. C. Wade, and D. L. Jones, “Life in the ‘charosphere’—does biochar in agricultural soil provide a significant habitat for microorganisms?” Soil Biology and Biochemistry, vol. 65, pp. 287–293, 2013. View at Publisher · View at Google Scholar · View at Scopus
  15. J. Lehmann, M. C. Rillig, J. Thies, C. A. Masiello, W. C. Hockaday, and D. Crowley, “Biochar effects on soil biota—a review,” Soil Biology and Biochemistry, vol. 43, no. 9, pp. 1812–1836, 2011. View at Publisher · View at Google Scholar · View at Scopus
  16. K. Crombie, O. Mašek, A. Cross, and S. Sohi, “Biochar—synergies and trade-offs between soil enhancing properties and C sequestration potential,” GCB Bioenergy, vol. 7, no. 5, pp. 1161–1175, 2015. View at Publisher · View at Google Scholar · View at Scopus
  17. J. Thies and M. C. Rillig, “Characteristics of biochar: biological properties,” in Biochar for Environmental Management: Science and Technology, J. Lehmann and S. Josep, Eds., Earthscan, London, UK, 2009. View at Google Scholar
  18. K. A. Spokas, K. B. Cantrell, J. M. Novak et al., “Biochar: a synthesis of its agronomic impact beyond carbon sequestration,” Journal of Environmental Quality, vol. 41, no. 4, pp. 973–989, 2012. View at Publisher · View at Google Scholar · View at Scopus
  19. R. D. Lentz and J. A. Ippolito, “Biochar and manure affect calcareous soil and corn silage nutrient concentrations and uptake,” Journal of Environmental Quality, vol. 41, pp. 1033–1043, 2012. View at Google Scholar
  20. B. Glaser, J. Lehmann, and W. Zech, “Ameliorating physical and chemical properties of highly weathered soils in the tropics with charcoal—a review,” Biology and Fertility of Soils, vol. 35, no. 4, pp. 219–230, 2002. View at Publisher · View at Google Scholar · View at Scopus
  21. B. Glaser and J. J. Birk, “State of the scientific knowledge on properties and genesis of Anthropogenic Dark Earths in Central Amazonia (terra preta de índio),” Geochimica et Cosmochimica Acta, vol. 82, pp. 39–51, 2012. View at Publisher · View at Google Scholar · View at Scopus
  22. R. Scotti, G. Bonanomi, R. Scelza, A. Zoina, and M. A. Rao, “Organic amendments as sustainable tool to recovery fertility in intensive agricultural systems,” Journal of Soil Science and Plant Nutrition, vol. 15, no. 2, pp. 333–352, 2015. View at Google Scholar · View at Scopus
  23. K. S. Khan and R. G. Joergensen, “Compost and phosphorus amendments for stimulating microorganisms and growth of ryegrass in a Ferralsol and a Luvisol,” Journal of Plant Nutrition and Soil Science, vol. 175, no. 1, pp. 108–114, 2012. View at Publisher · View at Google Scholar · View at Scopus
  24. D. Fischer and B. Glaser, “Synergisms between compost and biochar for sustainable soil amelioration,” in Management of Organic Waste, S. Kumar and A. Bharti, Eds., pp. 167–198, InTech, 2012. View at Google Scholar
  25. H. Schulz and B. Glaser, “Effects of biochar compared to organic and inorganic fertilizers on soil quality and plant growth in a greenhouse experiment,” Journal of Plant Nutrition and Soil Science, vol. 175, no. 3, pp. 410–422, 2012. View at Publisher · View at Google Scholar · View at Scopus
  26. J. Liu, H. Schulz, S. Brandl, H. Miehtke, B. Huwe, and B. Glaser, “Short-term effect of biochar and compost on soil fertility and water status of a Dystric Cambisol in NE Germany under field conditions,” Journal of Plant Nutrition and Soil Science, vol. 175, no. 5, pp. 698–707, 2012. View at Publisher · View at Google Scholar · View at Scopus
  27. G. Agegnehu, M. I. Bird, P. N. Nelson, and A. M. Bass, “The ameliorating effects of biochar and compost on soil quality and plant growth on a Ferralsol,” Soil Research, vol. 53, no. 1, pp. 1–12, 2015. View at Publisher · View at Google Scholar · View at Scopus
  28. H. P. Schmidt, C. Kammann, C. Niggli, M. W. H. Evangelou, K. A. Mackie, and S. Abiven, “Biochar and biochar-compost as soil amendments to a vineyard soil: influences on plant growth, nutrient uptake, plant health and grape quality,” Agriculture, Ecosystems & Environment, vol. 191, pp. 117–123, 2014. View at Google Scholar
  29. M. P. Bernal, J. A. Alburquerque, and R. Moral, “Composting of animal manures and chemical criteria for compost maturity assessment. A review,” Bioresource Technology, vol. 100, no. 22, pp. 5444–5453, 2009. View at Publisher · View at Google Scholar · View at Scopus
  30. G. Alfano, G. Lustrato, G. Lima, D. Vitullo, and G. Ranalli, “Characterization of composted olive mill wastes to predict potential plant disease suppressiveness,” Biological Control, vol. 58, no. 3, pp. 199–207, 2011. View at Publisher · View at Google Scholar · View at Scopus
  31. C. Amendola, A. Montagnoli, M. Terzaghi et al., “Short-term effects of biochar on grapevine fine root dynamics and arbuscular mycorrhizae production,” Agriculture, Ecosystems & Environment, vol. 239, pp. 236–245, 2017. View at Publisher · View at Google Scholar
  32. D. Vitullo, R. Altieri, A. Esposito et al., “Suppressive biomasses and antagonist bacteria for an eco-compatible control of Verticillium dahliae on nursery-grown olive plants,” International Journal of Environmental Science and Technology, vol. 10, no. 2, pp. 209–220, 2013. View at Publisher · View at Google Scholar · View at Scopus
  33. ISO, “Soil quality—avoidance test for determining the quality of soils and effects of chemicals on behaviour - part 1: test with earthworms (Eisenia fetida and Eisenia andrei),” ISO 17512-1, 2008. View at Google Scholar
  34. USDA, United States Department of Agriculture, Natural Resources Conservation Service, National Soil Survey Handbook, 2005, http://www.nrcs.usda.gov/wps/portal/nrcs/detail/national/home/?cid=nrcs142p2_054241.
  35. S. Carter, S. Shackley, S. Sohi, T. B. Suy, and S. Haefele, “The impact of biochar application on soil properties and plant growth of pot grown lettuce (Lactuca sativa) and cabbage (Brassica chinensis),” Agronomy, vol. 3, no. 2, pp. 404–418, 2013. View at Publisher · View at Google Scholar
  36. H. Sokchea, K. Borin, and T. R. Preston, “Effect of biochar from rice husks (combusted in a downdraft gasifier or a paddy rice dryer) on production of rice fertilized with biodigester effluent or urea,” Livestock Research for Rural Development, vol. 25, no. 1, 2013. View at Google Scholar · View at Scopus
  37. A. Fabrizio, F. Tambone, and P. Genevini, “Effect of compost application rate on carbon degradation and retention in soils,” Waste Management, vol. 29, no. 1, pp. 174–179, 2009. View at Publisher · View at Google Scholar · View at Scopus
  38. M. Reis, L. Coelho, J. Beltrao, I. Domingos, and M. Moura, “Comparative response of lettuce (Lactuca sativa) to inorganic and organic compost fertilization,” in Recent Advances in Energy, Environment, Economics and Technological Innovation, pp. 61–68, 2008. View at Google Scholar
  39. J. Lehmann, J. Gaunt, and M. Rondon, “Bio-char sequestration in terrestrial ecosystems—a review,” Mitigation and Adaptation Strategies for Global Change, vol. 11, no. 2, pp. 403–427, 2006. View at Publisher · View at Google Scholar · View at Scopus
  40. C. A. Black, Methods of Soil Analysis: Part I Physical and Mineralogical Properties, American Society of Agronomy, Madison, Wis, USA, 1965.
  41. F. R. Higginson and G. E. Rayment, Australian Laboratory Handbook of Soil and Water Chemical Methods, Inkata Press, 1992.
  42. Y. P. Kalra and Soil & Plant Analysis Council, Handbook on Reference Methods for Soil Analysis, Soil & Plant Analysis Council, 1992.
  43. ASTM, “Standard test methods for moisture, ash, and organic matter of peat and other organic soils,” ASTM D2974-00, ASTM International, West Conshohocken, Pa, USA, 2000. View at Google Scholar
  44. A. Mehlich, “Use of triethanolamine acetate-barium hydroxide buffer for the determination of some base exchange properties and lime requirement of soil,” Soil Science Society of America Proceedings, vol. 29, pp. 374–378, 1938. View at Google Scholar
  45. C. F. H. Liao, “Devarda's alloy method for total nitrogen determination,” Soil Science Society of America Journal, vol. 45, no. 5, pp. 852–855, 1981. View at Publisher · View at Google Scholar
  46. R. A. Bowman, “A rapid method to determine total phosphorus in soils,” Soil Science Society of America Journal, vol. 52, no. 5, pp. 1301–1304, 1988. View at Publisher · View at Google Scholar · View at Scopus
  47. S. R. Olsen, C. V. Cole, F. S. Watanabe, and L. A. Dean, Estimation of available phosphorus in soils by extraction with sodium bicarbonate, Circular 939, USDA, Washington, DC, USA, 1954.
  48. J. B. A. Dumas, “Procedes de l'analyse organique,” Annales de Chimie et de Physique, vol. 247, pp. 198–213, 1831. View at Google Scholar
  49. R. Moran and D. Porath, “Chlorophyll determination in intact tissues using N,N-dimethylformamide,” Plant Physiology, vol. 65, no. 3, pp. 478–479, 1980. View at Publisher · View at Google Scholar
  50. W. P. Inskeep and P. R. Bloom, “Extinction coefficients of chlorophyll a and b in n,n-dimethylformamide and 80% acetone,” Plant Physiology, vol. 77, no. 2, pp. 483–485, 1985. View at Publisher · View at Google Scholar
  51. C. Viti, A. Mini, G. Ranalli, G. Lustrato, and L. Giovannetti, “Response of microbial communities to different doses of chromate in soil microcosms,” Applied Soil Ecology, vol. 34, no. 2-3, pp. 125–139, 2006. View at Publisher · View at Google Scholar · View at Scopus
  52. S. M. Tiquia, “Evolution of extracellular enzyme activities during manure composting,” Journal of Applied Microbiology, vol. 92, no. 4, pp. 764–775, 2002. View at Publisher · View at Google Scholar · View at Scopus
  53. K. C. Uzoma, M. Inoue, H. Andry, H. Fujimaki, A. Zahoor, and E. Nishihara, “Effect of cow manure biochar on maize productivity under sandy soil condition,” Soil Use and Management, vol. 27, no. 2, pp. 205–212, 2011. View at Publisher · View at Google Scholar · View at Scopus
  54. M. Viger, R. D. Hancock, F. Miglietta, and G. Taylor, “More plant growth but less plant defence? First global gene expression data for plants grown in soil amended with biochar,” GCB Bioenergy, vol. 7, no. 4, pp. 658–672, 2015. View at Publisher · View at Google Scholar · View at Scopus
  55. Z. M. Solaiman, P. Blackwell, L. K. Abbott, and P. Storer, “Direct and residual effect of biochar application on mycorrhizal root colonisation, growth and nutrition of wheat,” Australian Journal of Soil Research, vol. 48, no. 6-7, pp. 546–554, 2010. View at Publisher · View at Google Scholar · View at Scopus
  56. M. Ros, M. T. Hernandez, and C. García, “Soil microbial activity after restoration of a semiarid soil by organic amendments,” Soil Biology and Biochemistry, vol. 35, no. 3, pp. 463–469, 2003. View at Publisher · View at Google Scholar · View at Scopus
  57. D. L. Jones, J. Rousk, G. Edwards-Jones, T. H. DeLuca, and D. V. Murphy, “Biochar-mediated changes in soil quality and plant growth in a three year field trial,” Soil Biology and Biochemistry, vol. 45, pp. 113–124, 2012. View at Publisher · View at Google Scholar · View at Scopus
  58. F. P. Vaccari, A. Maienza, F. Miglietta et al., “Biochar stimulates plant growth but not fruit yield of processing tomato in a fertile soil,” Agriculture, Ecosystems and Environment, vol. 207, pp. 163–170, 2015. View at Publisher · View at Google Scholar · View at Scopus
  59. T. H. De Luca, M. D. MacKenzie, and M. J. Gundale, “Biochar effects on soil nutrient transformations,” in Biochar for Environmental Management: Science and Technology, J. Lehmann and S. Joseph, Eds., pp. 251–270, Earthscan Publications, London, UK, 2009. View at Google Scholar
  60. J. Major, C. Steiner, A. Downie, and J. Lehmann, “Biochar effects on nutrient leaching,” in Biochar for Environmental Management: Science and Technology, J. Lehmann and S. Joseph, Eds., pp. 271–287, Earthscan, London, UK, 2009. View at Google Scholar
  61. C. C. Hollister, J. J. Bisogni, and J. Lehmann, “Ammonium, nitrate, and phosphate sorption to and solute leaching from biochars prepared from corn stover (Zea mays L.) and oak wood (Quercus spp.),” Journal of Environmental Quality, vol. 42, no. 1, pp. 137–144, 2013. View at Publisher · View at Google Scholar · View at Scopus
  62. T. J. Clough and L. M. Condron, “Biochar and the nitrogen cycle: introduction,” Journal of Environmental Quality, vol. 39, no. 4, pp. 1218–1223, 2010. View at Publisher · View at Google Scholar · View at Scopus
  63. L. Beesley and N. Dickinson, “Carbon and trace element fluxes in the pore water of an urban soil following greenwaste compost, woody and biochar amendments, inoculated with the earthworm Lumbricus terrestris,” Soil Biology and Biochemistry, vol. 43, no. 1, pp. 188–196, 2011. View at Publisher · View at Google Scholar · View at Scopus
  64. J. Prommer, W. Wanek, F. Hofhansl et al., “Biochar decelerates soil organic nitrogen cycling but stimulates soil nitrification in a temperate arable field trial,” PLoS ONE, vol. 9, no. 1, Article ID e86388, 2014. View at Publisher · View at Google Scholar · View at Scopus
  65. C. R. Anderson, L. M. Condron, T. J. Clough et al., “Biochar induced soil microbial community change: implications for biogeochemical cycling of carbon, nitrogen and phosphorus,” Pedobiologia, vol. 54, no. 5-6, pp. 309–320, 2011. View at Publisher · View at Google Scholar · View at Scopus
  66. J. Rousk, P. C. Brookes, and E. Bååth, “Contrasting soil pH effects on fungal and bacterial growth suggest functional redundancy in carbon mineralization,” Applied and Environmental Microbiology, vol. 75, no. 6, pp. 1589–1596, 2009. View at Publisher · View at Google Scholar · View at Scopus
  67. J. Rousk, P. C. Brookes, and E. Bååth, “Investigating the mechanisms for the opposing pH relationships of fungal and bacterial growth in soil,” Soil Biology and Biochemistry, vol. 42, no. 6, pp. 926–934, 2010. View at Publisher · View at Google Scholar · View at Scopus
  68. V. L. Bailey, S. J. Fansler, J. L. Smith, and H. Bolton Jr., “Reconciling apparent variability in effects of biochar amendment on soil enzyme activities by assay optimization,” Soil Biology and Biochemistry, vol. 43, no. 2, pp. 296–301, 2011. View at Publisher · View at Google Scholar · View at Scopus
  69. H. Jin, Characterization of microbial life colonizing biochar and biochar amended soils [Ph.D. thesis], Cornell University, Ithaca, NY, USA, 2010.
  70. F. Amlinger, S. Peyr, J. Geszti, P. Dreher, W. Karlheinz, and S. Nortcliff, Beneficial Effects of Compost Application on Fertility and Productivity of Soils, Federal Ministry for Agricultural and Forestry, Environment and Water Management, Lebensministerium, Vienna, Austria, 2007.
  71. M. Diacono and F. Montemurro, “Long-term effects of organic amendments on soil fertility,” Journal of Sustainable Agriculture, vol. 2, pp. 761–786, 2011. View at Google Scholar
  72. V. L. Bailey, S. J. Fansler, J. L. Smith, and H. Bolton, “Reconciling apparent variability in effects of biochar amendment on soil enzyme activities by assay optimization,” Soil Biology and Biochemistry, vol. 43, no. 2, pp. 296–301, 2011. View at Publisher · View at Google Scholar · View at Scopus
  73. C. Lammirato, A. Miltner, and M. Kaestner, “Effects of wood char and activated carbon on the hydrolysis of cellobiose by β-glucosidase from Aspergillus niger,” Soil Biology and Biochemistry, vol. 43, no. 9, pp. 1936–1942, 2011. View at Publisher · View at Google Scholar · View at Scopus
  74. Y. Yao, B. Gao, M. Inyang et al., “Biochar derived from anaerobically digested sugar beet tailings: characterization and phosphate removal potential,” Bioresource Technology, vol. 102, no. 10, pp. 6273–6278, 2011. View at Publisher · View at Google Scholar · View at Scopus
  75. H.-J. Xu, X.-H. Wang, H. Li, H.-Y. Yao, J.-Q. Su, and Y.-G. Zhu, “Biochar impacts soil microbial community composition and nitrogen cycling in an acidic soil planted with rape,” Environmental Science and Technology, vol. 48, no. 16, pp. 9391–9399, 2014. View at Publisher · View at Google Scholar · View at Scopus
  76. W.-C. Ding, X.-L. Zeng, Y.-F. Wang, Y. Du, and Q.-X. Zhu, “Characteristics and performances of biofilm carrier prepared from agro-based biochar,” China Environmental Science, vol. 31, no. 9, pp. 1451–1455, 2011. View at Google Scholar · View at Scopus
  77. B. T. Nguyen, J. Lehmann, W. C. Hockaday, S. Joseph, and C. A. Masiello, “Temperature sensitivity of black carbon decomposition and oxidation,” Environmental Science and Technology, vol. 44, no. 9, pp. 3324–3331, 2010. View at Publisher · View at Google Scholar · View at Scopus
  78. Y. Kuzyakov, I. Subbotina, H. Chen, I. Bogomolova, and X. Xu, “Black carbon decomposition and incorporation into soil microbial biomass estimated by 14C labeling,” Soil Biology and Biochemistry, vol. 41, no. 2, pp. 210–219, 2009. View at Publisher · View at Google Scholar · View at Scopus