Effects of biochar application rate on sandy desert soil ...

Catena 135 (2015) 313–320

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Effects of biochar application rate on sandy desert soil properties and sorghum growth Mahmood Laghari a,b, Muhammad Saffar Mirjat b, Zhiquan Hu a,⁎, Saima Fazal a, Bo Xiao a, Mian Hu a, Zhihua Chen a, Dabin Guo a a b

School of Environmental Science and Engineering, Huazhong University of Science and Technology, Wuhan 430073, Hubei, PR China Faculty of Agricultural Engineering, Sindh Agriculture University, Tandojam 70060, Sindh, Pakistan

a r t i c l e

i n f o

Article history: Received 25 March 2015 Received in revised form 17 August 2015 Accepted 20 August 2015 Available online xxxx Keywords: Sandy desert soils Fast pyrolysis Hydraulic properties Plant growth Soil fertility

a b s t r a c t The addition of biochar (BC) has been suggested to increase the soil fertility and crop productivity of agricultural lands. This study evaluated the effect of different levels of BC on properties of sandy desert soils and its ultimate impact on plant growth. The samples of desert sand were taken from the Kubuqi of Inner Mongolia, China and the Thar Desert, Pakistan. The sands were treated with a BC made from the fast pyrolysis of pine sawdust at 400 °C. Four BC application rates i.e. 0, 15, 22 and 45 t ha−1 were used in this study. Effects of BC addition on the water consumption and plant growth of sorghum were monitored for eight weeks in a pot experiment. The hydraulic and chemical properties of soil were analyzed to discern the effect of BC on the fertility of sandy desert soils. The results showed that BC amendment significantly improved soil hydraulic and chemical properties. The BC applied at the rate of 22 t ha−1 provided the best results as compared to all other treatments. Compared with the control group, the soil water-holding capacity (WHC) increased by 11% and 14%, water-retention capacity (WRC) increased by 28% and 32% and hydraulic conductivity decreased by 32% and 7% under the Kubuqi and the Thar Desert soils, respectively when BC was applied at 22 t ha−1. Similarly, total C increased by 11% and 7%, total K increased by 37% and 42%, total P increased by 70% and 68% and total Ca increased by 69% and 75% while soil pH significantly reduced by 0.67 and 0.79 units, in the Kubuqi and the Thar Desert soils, respectively. The sorghum dry matter yield (DMY) was also significantly improved by 18% and 22% under the Kubuqi and the Thar Desert soils, respectively. The higher sorghum DMY consequently improved water-use efficiency (WUE) by 40% and 41% under the Kubuqi and the Thar Desert soils, respectively. In contrast, the plant growth and DMY declined at higher application rate (45 t ha−1) of BC. The BC made from fast pyrolysis of pine sawdust at a temperature of 400 °C showed great potential in improving the quality of sandy desert soils. Hence, it can be used for sandy desert soil management. © 2015 Elsevier B.V. All rights reserved.

1. Introduction The world's population is expected to increase by 65% up to year 2050. The additional food required to feed future generations will put further pressure on soil and water resources (Yu et al., 2013). At present, about 22% of world's total population lives in China and it will continue to increase with the same magnitude. It is anticipated that China will be facing the challenges of food shortages in the years to come (Peng et al., 2011). To meet food requirements of ever increasing population in China and elsewhere, additional soil resources need to be exploited and utilized. Dry lands contribute about 47.2% of the world's total land area (Lal, 2004). Most soils in dry regions are considered marginal for agriculture due to coarse-texture (Sun et al., 1998), low water and nutrient retention capacity (van Asperen et al., 2013) and low in soil organic C (Lal, 2004). For sustainable soil quality, the aggregate structure of soil ⁎ Corresponding author. E-mail addresses: [email protected], [email protected] (Z. Hu).

http://dx.doi.org/10.1016/j.catena.2015.08.013 0341-8162/© 2015 Elsevier B.V. All rights reserved.

plays an important role and the addition of organic C can improve soil aggregation and its physical and chemical properties (Fallahzade and Hajabbasi, 2012). Sandy deserts cover a significant portion of land and occur all over the world. China is no exception and occupies about 7% of the world's total arable land. If the soil quality of Chinese sandy deserts was improved, then this would be useful for desert restoration throughout the world. Desert lands in China could be used as an additional source for cultivation in order to enhance food production to meet future needs of increasing population (Fallahzade and Hajabbasi, 2012). BC is a C rich organic material which is produced by thermal decomposition of plant-derived biomass in partial or total absence of oxygen (Sohi et al., 2010). The stability of BC in soil environment has been reported up to 1000 years (Sohi et al., 2010). Recently, BC has been used in arable soils for improving soil physical properties and plant growth (Liu et al., 2014; Lu et al., 2014). The use of BC in sandy soils increases soil organic C (Busscher et al., 2010), water-holding capacity (Kinney et al., 2012), and nutrient retention (Shafie et al., 2012) and improves

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aggregate stability and water content at permanent wilting point (Abel et al., 2013). It has been reported that BC amendment in sandy soil increased maize yield up to 150% (Uzoma et al., 2011b), radish yield by 96% (Chan et al., 2008), cherry tomato yield by 64% (Hossain et al., 2010) and also improved tomato yield by 13% under deficit irrigation (Akhtar et al., 2014). BC has been mostly applied in conventional arable soils (Laird et al., 2010; Major et al., 2012; Peng et al., 2011); few studies have focused on the use of BC in dry lands (Laghari et al., 2015; Mulcahy et al., 2013; Uzoma et al., 2011a; van Asperen et al., 2013). To our knowledge, there is little information on the effect of BC on plant growth and soil response in sandy desert soils. This study was undertaken with three specific objectives: (i) to evaluate physicochemical properties of BC derived from the fast pyrolysis of pine sawdust, (ii) to quantify the impact of BC amendment on plant growth and dry matter yield (DMY) of sorghum in sandy desert soils collected from the Kubuqi and the Thar Desert, and (iii) to determine the effects of BC amendment on hydraulic characteristics and chemical properties of both sandy desert soils. We hypothesize that (i) the BC made from fast pyrolysis of pine sawdust at low reactor temperature (400 °C) will be acidic when used as a soil amendment, so it will decrease soil pH, increase total soil C and plant nutrient content, (ii) amending sandy desert soils with fast pyrolysis BC will improve soil hydraulic properties, and (iii) appropriate application rate of the BC will enhance plant growth and improve water-use efficiency in sandy desert soils.

2. Materials and methods 2.1. Biomass feedstock The pine sawdust was collected from a furniture factory of Huazhong University of Science and Technology (HUST), Wuhan, China. The particle size distribution by mass of the pine sawdust was as follows: 55% below 1.5 mm, 36% from 1.5 to 1.8 mm, 7% from 1.8 to 2.5 mm, and 2% from 2.5 to 3.0 mm. The proximate and ultimate analyses of the feedstock are shown in Table 1.

Table 1 Physicochemical properties of feedstock and produced biochar. Elements

Pine sawdust

Biochar

Yield (%) pH EC (dS m−1) CEC (cmol+ kg−1)

– – – –

51.0 4.2 0.5 21.5

Proximate analysis (%) MC VM Ash Fixed carbon

4.5 82.0 1.3 12.1

3.5 29.2 3.2 64.1

Ultimate analysis (%) C N C/N ratio

36.2 0.19 222.7

51.7 0.86 70.0

Plant nutrients (g kg−1) Ca P K S Al BET (m2 g−1) Pore volume (m3 g−1) Average pore size (nm) WHC (g g−1)

– – – – – – – – –

270.4 17.8 78.1 31.0 19.0 6.2 0.011 53.2 4.0

EC, electrical conductivity; CEC, cation exchange capacity; MC, moisture content; VM, volatile matter, BET, Brunauer–Emmett–Teller surface area; WHC, water-holding capacity; ND, not detected.

2.2. BC preparation The BC was made using a lab-scale screw-type continuous-feed fast pyrolysis reactor (Fig. 1) at Bioenergy Laboratory, School of Environmental Science and Engineering, HUST, China. The setup comprised a stainless steel tube reactor (ID 81 mm, OD 89 mm, and height 114 mm) that was externally heated with an electric furnace. The temperature of the reactor was controlled homogeneously by a thermocouple with an accuracy of ± 5 °C. Pyrolytic runs were performed to produce BC at 400 °C under limited O2 condition in triplicate. For BC production, the reactor was first allowed to heat up to the desired pyrolysis temperature, then the feedstock was loaded into the hopper, and the feed screw motors were switched on at 30 rpm at the feed rate of 0.18 kg h−1, while the biomass particle pyrolysis time was kept constant at 3 s. After pyrolysis, the reactor was switched off and allowed to cool to ambient temperature. The BC was collected from the ash bucket, weighed, and stored in airtight containers for characterization and further experimentation. 2.3. BC characterization The BC yield was calculated on wet basis. For chemical analyses, oven-dried BC samples were grounded in a ceramic pot and sieved through a 0.15-mm sieve. Chemical analyses were conducted in triplicate. The proximate analysis was conducted following ASTM D 3176 (ASTM, 2006). The elemental compositions of BC such as C, H, N, S and O were determined by the dry combustion method using a CHNS/O analyzer (Vario Micro Cube; Elementar, Germany). Total oxides of different elements such as Mg, Al, P, K, and Ca in the BC were determined by X-ray fluorescence (EDAX, Mahwah, NJ, USA). The pH and electrical conductivity (EC) were measured in 1:10 (w v− 1) BC to deionized water after shaking the samples on a mechanical shaker at 200 RPM for 1 h. A PHS-3C digital glass electrode precision pH meter and a DDS-307 digital glass electrode conductivity meter (Analytical Instruments Co., Ltd., Shanghai, China) were used to test the pH and EC, respectively. The cation exchange capacity (CEC) of the BC was measured using the 1 M ammonium acetate (pH 7) method described by Wu et al. (2012). Details have been provided in the Supplementary information (SI). The Brunauer–Emmett–Teller (BET) surface area of the BC was determined using an accelerated surface area porosimetry system (ASAP2010; Micrometrics, Norcross, GA, USA). The X-ray diffraction (XRD; X'Pert PRO; PANalytical B.V., Almelo, Netherlands) analysis was carried out to identify the crystallographic structure of the BC. The Fourier transformation infrared (FTIR) analyses of the BC were carried out using a VERTEX 70 FTIR Spectrometer (Bruker, Ettlingen, Germany). The BC samples were scanned at the mid-infrared electromagnetic spectrum range of 4000 to 400 cm−1 wave numbers. To analyze the surface morphology of the BC, scanning electron microscope (SEM) (EMINI 1530; Oberkochen, Germany) imaging analyses of the BC samples were conducted. The WHC of the BC was measured gravimetrically according to the procedures described by Kinney et al. (2012) with slight modification. Simply, we soaked a 10-g oven-dried BC sample without further size reduction in distilled water in a glass beaker at 40 °C. After 1 h, we transferred the suspension in a clamped ceramic Buchner funnel wrinkled with cellulose filter paper (Whatman No. 1). The sample was allowed to drain freely for 1 h, and WHC was calculated as mass of water retained by the mass of dry BC while water absorbed by the filter paper was adjusted. The physicochemical properties of the BC are given in Table 1. 2.4. Soil sampling Two different desert soils were used for experiments. First bulk samples were taken from an uncultivated area of Kubuqi desert (the 7th largest desert of China with an area of 16,600 km2) located in southern section of Inner-Mongolia, China (39.588°N, 109.588°E). The second

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Fig. 1. Illustration of fast pyrolysis reactor: 1. feed hopper, 2. screw feeder, 3. cooling water, 4. fixed-bed reactor, 5. biochar tank, 6. cyclone, 7. filter, 8 and 9. condenser,10. bio-oil container, 11. gas wool filter, 12. mist filter, 13. chiller, 14. gas compressor, 15. pre-heater, 16. gas flow meter, 17. gas sampling point, 18. gas burning stack.

bulk soil samples were taken from a rain-fed research field of Arid Zone Research Institute (AZRI), Umerkot, Sindh, Pakistan (25°21′N, 69°44′E). The field is located in the Thar Desert also called Great Indian Desert which is the world's 9th largest subtropical desert with an area of 200,000 km2. On both sites, ten sampling plots (1 m × 1 m each) were randomly set about 20 m apart from each other. From each plot, the soils at the depths of 0–100 mm, 100–200 mm and 200–300 mm were separately sampled with soil auger. The soil samples were packed in air tight plastic bags and shipped to our laboratory at HUST for experiments. In the laboratory, soil samples were air dried, mixed well, and sieved through a 2-mm sieve before soil analyses and pot experiment. The soils collected from both deserts were sandy in texture. The Kubuqi desert soil contained 80.0% sand (2000–50 μm), 16.1% silt (50–2 μm) and 3.8% clay (b2 μm). Whereas, the Thar Desert soil had 84.2% sand, 10.3% silt and 5.4% clay particles. The main crystalline component in both sandy desert soils was quartz that was observed in the form of silicon dioxide (SiO2) with iron oxide impurities. The physicochemical properties of both desert soils are given in Tables 2 and 3. 2.5. Pot experiment The BC was crushed manually in a ceramic pot and passed through a 0.125-mm sieve until it had the same particle size as that of the sandy soils used in the experiment. The BC was thoroughly mixed in both desert soils with four application rates i.e. 0, 15, 22 and 45 t ha−1 (0%, 0.6%, 1.0% and 2.0% by mass, respectively). The BC mixing rates were calculated considering the soil depth and bulk density values to be 150 mm

Table 2 Effect of biochar amendment on soil water-holding capacity and hydraulic conductivity. Treatments

Water-holding capacity (g g−1)

Hydraulic conductivity (mm h−1)

KB-0 KB-15 KB-22 KB-45 TR-0 TR-15 TR-22 TR-45

0.21 0.24NS 0.26NS 0.28a 0.19 0.20NS 0.21NS 0.24a

216.0 216.0NS 151.2a 136.8a 32.4 31.3NS 30.2NS 27.3NS

In the same column, a is significant at P b 0.05; b is significant at P b 0.01; c is significant at P b 0.001and NS is not significant from the control (KB-0 or TR-0).

and 1.5 g cm− 3, respectively. The treatments with four BC mixing rates of 0, 15, 22 and 45 t ha−1 in the Kubuqi desert soil were abbreviated as KB-0, KB-15, KB-22 and KB-45, respectively. Meanwhile, the treatments with the same mixing rates of BC in the Thar Desert soil were referred as TR-0, TR-15, TR-22 and TR-45. Specially designed open-top glass containers (S.I. Fig. 1) having 200 mm height and 60 mm diameter with 0.50-mm holes at the bottom were used for plant growth experiment. A 15-mm layer of quartz sand (particle size 1.0–2.0 mm) was placed in the bottom of each container to facilitate the drainage of excess irrigation water. The soil was manually compacted in containers up to a density of 1.5 g cm−3 while providing a freeboard of 40 mm for irrigation. Four BC application rates and two different desert soils gave a total of twenty four treatments in triplicate. The containers were placed outside the laboratory under sunlight at 17 to 30 °C and 82% relative humidity, except rainy days. The containers were irrigated from the top using distilled water to the field water capacity (100% WHC). Five seeds of sorghum were sown in each container. After one week of emergence, weak plants were thinned, and only one healthy plant in each container was grown for eight weeks. Plants were grown at 100% WHC, moisture loss was measured by weighing the containers, and the weight of the containers was adjusted by adding water on a daily basis. Commercially available NPK fertilizer with total 45% NPK content and the NPK ratio of 1:4:7 was applied at a dose of 100 g m−2 after one week of germination (Bird et al., 2012). The plant height was recorded on 20, 30, 45 and 60 days after germination. During weeks 7 and 8, drought conditions were imposed by keeping the soil MC at less than 50% of WHC in order to assess the plant's tolerance level in the BC-amended soil to drought. After eight weeks of emergence, the plants were cut from the nodes of the roots, washed with distilled water, and oven-dried in paper envelopes at 60 °C for 72 h. The DMY was computed and it was divided by the quantity of total irrigation water consumed during the plant growth to determine the WUE (DMY L−1 of irrigation water) of sorghum.

2.6. Effect of BC on sandy desert soil properties After plant growth experiment, the soil was removed from the containers, air-dried, thoroughly mixed, and sieved in a 2-mm sieve. The samples were analyzed in triplicate to assess the effect of BC amendment on the hydraulic and chemical properties of the soil.

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Table 3 Effect of biochar on soil properties after pot experiment. Elements

KB-0

KB-15

KB-22

KB-45

pH EC (dS m−1) CEC (cmolc kg−1) SOM (g kg−1) Total C (g kg−1) Total N (g kg−1) C/N ratio Minerals (g kg−1) Total Al Total Si Total K Total P Total Ca Total Fe Total Mn Total Cu Total Ti

8.47 0.29 2.7 25.7 6.3 0.50 12.6

8.14a 0.35a 2.8a 30.8c 6.8a 0.40NS 15.0

7.80b 0.45c 2.8b 44.3c 7.0a 0.40NS 17.2a

7.55c 0.47c 2.9c 73.2c 7.9c 0.29NS 27.0c

91.7 401.0 5.6 1.6 27.7 6.6 ND ND ND

95.0NS 368.0NS 7.0NS 2.2a 40.8NS 6.0NS ND ND ND

96.0 376.0NS 7.7NS 2.7b 46.9a 5.6NS ND ND ND

131.0a 404.8NS 9.8NS 3.5c 71.0b 4.7a ND ND ND

TR-0 8.06 0.23 2.2 9.6 5.4 0.60 9.0 40.3 307.1 6.4 3.4 32.1 14.3 8.9 0.3 5.8

TR-15 7.68b 0.41c 2.3a 11.4c 5.7 0.40NS 13.9 42.3 NS 303.4NS 8.4NS 4.4b 50.2a 13.9NS 7.9NS 0.6a 5.2a

TR-22 7.27c 0.47c 2.4a 18.5b 5.8 0.40NS 14.1a 42.9 309.5NS 9.0a 5.8c 56.1a 5.9a 8.3NS 0.4NS 6.3NS

TR-45 7.11c 0.48c 2.6a 24.0c 6.5b 0.26NS 25.0c 62.1a 324.2a 11.1b 5.9c 63.6b 4.8a 7.7NS 0.1NS 1.9a

In the same row, a is significant at P b 0.05; b is significant at P b 0.01; c is significant at P b 0.001and NS is not significant from the control (KB-0 or TR-0); EC, electrical conductivity; CEC, cation exchange capacity; SOM, soil organic matter; ND, not detected.

2.6.1. Soil hydraulic properties The influence of BC on the WHC of sandy desert soils was tested gravimetrically as follows. A known amount of soil was filled in specially designed equipment (S.I. Fig. 2) to a density of 1.65 g cm−3. The soil was then thoroughly saturated with a known amount of water. The soil was left to drain freely in a graduated cylinder until the last drop of water had drained. The WHC was calculated by comparing the amount of water absorbed per unit volume of soil. The WRC of the soil was determined gravimetrically. Simply, 100-g soil samples pre-saturated at 100% WHC were placed in open-top plastic containers (height, 65 mm; width, 45 mm; length, 95 mm) and then oven-dried at a wide range of temperature (i.e. 20, 25, 30, 35, 40, 45, and 50 °C) for different time periods, and the average moisture loss percentage was calculated by weighing the containers. The effect of BC on depth-wise depletion of MC in the soil columns was determined as follows. The soil samples were re-packed in the containers in which they had been packed for plant growth. The soil containers were saturated at 100% WHC and then ovendried at 105 °C for 1, 2, and 3 h. The soil samples from each container were carefully taken from the top 0–2-cm, middle 6.5–8.5-cm, and bottom 14–16-cm depths. The MC of the samples was determined gravimetrically. Soil hydraulic conductivity (K) was measured by the constant-head method in triplicate using a soil-permeability tester (Model-TST-55; Nanjing T-Bota, Ltd., Jiangsu, China) having 61.8-mm diameter and 40.0-mm height. A constant head of water (670 mm) was fixed during the test as demonstrated in (S.I. Fig. 6). The test duration was kept constant at 5 min for each sample test.

2.6.2. Soil chemical properties Soil pH was determined using 1:2.5 (w v−1) soil:deionized water. The soil total C was measured by elemental analysis. The soil total N, plant nutrients, and CEC were determined using the procedures described above for the BC analyses.

2.7. Statistical analysis Statistical differences between the means of control and BCamended soils were determined using a one-way analysis of variance (ANOVA) with P b 0.05, P b 0.01 and P b 0.001 significance levels. We used Origin software (Origin Lab., Northampton, MA, USA) for analyses.

3. Results 3.1. BC characterization The yield and properties of produced BC are shown in Table 1. The average yield of BC recovered by mass was about 50% of the biomass used. The BC had a relatively low BET surface area and pore volume. The BC was rich in C as revealed by elemental analysis (Table 1). The C/N ratio of the BC was reduced by 66% compared to the C/N ratio of the feedstock. The produced BC had less ash content and it had acidic pH and a moderate CEC (Table 1). The content of essential plant nutrients such as Ca, P and K increased in BC as compared to the biomass used (Table 1). The SEM images (S.I. Fig. 3) revealed that the BC had a porous structure with high WHC. The O–H hydroxyl and –CO Carboxyl functional groups were present in the BC as revealed by FTIR Spectra of BC (S.I. Fig. 4). Aromatic C–H stretching vibration was not observed while phenolic O–H functional groups were also present in the BC. XRD spectrum of the BC (S.I. Fig. 5) showed a broad peak at 2θ 22.5 (d = 3.9 Å) probably due to the presence of whewellite (calcium oxalate, Ca (C2O4)·H2O), while a peak at 2θ 35.2 (d = 1.3 Å) indicated the sylvite. 3.2. Effect of BC on hydraulic characteristics of sandy desert soils Results of the effect of BC amendment on WHC of both soils are presented in Table 2. As shown in Table 2, soil WHC increased in all BC treatments. BC treatment with mixing rate of 45 t ha−1 caused a significant increase in the WHC of both soils (P b 0.05). The BC treatment reduced soil hydraulic conductivity under different treatments as demonstrated in Table 2. The soil K values significantly decreased by 37% under KB-45 as compared to KB-0 (P b 0.05).The distribution of soil MC at different depths in soil containers is shown in Fig. 2. It is clearly shown that BC amendment increased soil MC of both sandy desert soils at different depths. As compared to the control, plant available moisture significantly increased by 47% and 100% in KB-45 and TR-45 treatments, respectively at a soil depth of 14–16 cm (P b 0.05). The WRC of both sandy desert soils was improved in all BC treatments as shown in Fig. 3. The average loss of soil moisture at 20 °C from the Kubuqi and the Thar Desert soils, at a BC level of 45 t ha−1 was 81% and 84% lower than the control soils, respectively (P b 0.05, Fig. 3). 3.3. Effect of BC on chemical properties of sandy desert soils The effect of different application rates of BC on chemical properties of both sandy desert soils is shown in Table 3. The soil organic matter

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and 5). After 60 days of germination, the plant height was significantly higher by 15% and 24% in KB-22 and TR-22, respectively as compared to the control. As shown in Fig. 5, sorghum DMY was significantly increased in the Kubuqi desert soil at a 22 t ha−1 BC application rate. In contrast, negative effect of BC on sorghum growth and DMY was experienced under both desert soils at higher mixing level (45 t ha−1). The plant height was significantly reduced by 23% and 24% in the Kubuqi and the Thar Desert soils, respectively with a BC mixing level of 45 t ha− 1. The sorghum DMY was also significantly reduced by 24% and 27% due to BC amendment at 45 t ha−1. The results of sorghum WUE under the control and different treatments are presented in Table 4. The sorghum WUE improved under both sandy desert soils at 15 and 22 t ha−1 BC application rate. Meanwhile, the WUE was reduced under both soils at higher dose of BC (45 t ha−1). 4. Discussion 4.1. BC characterization Fig. 2. Effect of biochar on depth-wise moisture content in soil root zone after oven drying the containers at 105 °C for different time periods i.e. 1, 2 and 3 h. Error bars show standard deviations of the means of different treatments.

(SOM) significantly increased under both soils at a BC application rate of 45 t ha−1 (P b 0.001). As compared to the control, the total soil C significantly increased by 25% and 20% in KB-45 and TR-45, respectively (P b 0.001, P b 0.01, Table 3). Soil total N decreased in all BC treatments. However, the effect was not statistically significant (P N 0.05, Table 3). BC amendment increased soil C/N ratio in all treatments; however, BC with application rate of 45 t ha−1 caused a significant increase in soil C/N ratio (P b 0.05, Table 3). Soil pH decreased in all BC amended treatments as shown in Table 3. Soil pH significantly decreased by 0.92 and 0.95 units in the Kubuqi and the Thar Desert soils, respectively at 45 t ha−1 BC level (P b 0.001). The CEC of soil slightly increased by 8% and 20% in KB-45 and TR-45 as compared to the control. BC amendment also increased soil total P and K contents. However, total K content significantly increased under the Thar Desert soil with a BC application rate of 45 t ha−1 (P b 0.01, Table 3). Meanwhile, soil total P content significantly improved in all BC treated soils. The total Ca content of both sandy desert soils also significantly increased with a BC application rate of 45 t ha−1 (P b 0.01). BC amendment also caused a significant increase in the total Al content of both soils with a 45 t ha−1 mixing rate of BC (P b 0.05, Table 3). 3.4. Effect of BC on sorghum growth and DMY BC amendment increased sorghum growth and DMY under both sandy desert soils at the application rates of 15 and 22 t ha−1 (Figs. 4

Fig. 3. Effect of biochar on water-retention capacity of desert soils.

BC characteristics varied with the production conditions and the biomass used. Total C, fixed C and ash content of the BC is more dependent upon the feedstock than the pyrolysis temperature, while volatile matter and yield are sensitive to pyrolysis temperature (Zhao et al., 2013). The BC yield recovered in this study (51%) was consistent with that reported by Novak et al. (2009b) who reported a BC yield between 40% and 57% at a pyrolysis temperature of 350–400 °C. But, DeSisto et al. (2010) and Kim et al. (2012) reported about 20% and 33.5% yield of BC made from pine sawdust through a fast pyrolysis at 400 °C. Demirbas (2004) reported that BC yield variance is due to the difference of particle size and quality of biomass. Ash content of the BC found in this study was much lower than that reported previously (Kim et al., 2012) for pine wood BC. But, it was similar to that reported by Mukome et al. (2013), who observed 2.6% ash content for softwood BC made at 410 °C. However, lower ash content (0.5%) for pine wood-derived BC made at 400 °C was also reported by Mukherjee et al. (2011). Zhao et al. (2013) have reported that wood-derived BCs had lower ash content compared with the manure derived BCs possibly due to lower mineral contents in woody feedstock. The BC had a low surface area (6.2 m2 g− 1) which is consistent with the findings of Mukome et al. (2013) and Kim et al. (2012), who reported a surface area of 2.20 and 8.80 m2 g−1 for pine wood BC was produced at 400 °C. Meanwhile, Zhao et al. (2013) reported a higher surface area (203 m2 g−1) of sawdust BC made at 500 °C. Further increase in temperature (N 500 °C) may increase the volatilities of organic compounds and create more pores which contribute to larger surface area (Shaaban et al., 2013). Higher

Fig. 4. Effect of BC on plant height. Error bars show standard deviations of the means of different treatments.

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Fig. 5. Effect of biochar on sorghum dry matter yield. Error bars show standard deviations of the means of different treatments.

surface area of BC provides more adsorption space for water and nutrient retention in soil (Peng et al., 2011). The BC demonstrated a WHC of 4.0 g g− 1, while Kinney et al. (2012) reported much higher WHC (7.68 g g−1) of apple wood BC made at 400 °C. In contrast, Yu et al. (2013) pointed lower WHC (0.27 g g− 1) of yellow pine-derived BC made at 400 °C. The O–H hydroxyl and –CO carboxyl functional groups were present in our BC. The results of surface functional groups of the BC were consistent with the findings of the past studies reported by AlWabel et al. (2013) and Zhao et al. (2013). The BC made in this study had acidic pH (4.21), which is in strong contrast with other BCs, which were quite alkaline (pH 7.5 to 9.4) (Al-Wabel et al., 2013; Novak et al., 2009a). While, some BCs made from pine wood at lower pyrolysis temperature (400–500 °C) demonstrated acidic pH ranging from 4 to 5 (Mukherjee et al., 2011; Nelissen et al., 2014). Softwood BC was obtained through fast pyrolysis (400–500 °C) also had acidic pH (4.2). However, acidic pH of wood-derived BC was attributed to the presence of acidic functional groups such as aliphatic carboxylic acids (Mukherjee et al., 2011). 4.2. Effect of BC on hydraulic characteristics of sandy desert soils Low WHC of both sandy desert soils used in this experiment was probably due to less soil organic matter and coarse texture. Both sandy desert soils had more than 80% (by mass) coarse particles (2000–50 μm). On the other hand, the average particle size of the BC was around 50 nm. After the BC amendment in sandy desert soils, the fine particles of the BC probably filled the pore spaces of the soils. Hence, the BC addition significantly increased the WHC of the Kubuqi and the Thar Desert soils by 30% and 27%, respectively as compared to the control. Briggs et al. (2012) reported a rise in WHC of soil up to

Table 4 Effect of biochar amendment on sorghum water-use efficiency. Treatments

Irrigation water used per pot (mL)

DMY (mg pot−1)

Water-use efficiency (mg L−1)

KB-0 KB-15 KB-22 KB-45 TR-0 TR-15 TR-22 TR-45

610 567a 521c 491c 561 540NS 501a 563c

67 78NS 80b 51c 81 96a 99c 59c

109 137b 153b 103a 139 177b 197b 127a

In the same column, a is significant at P b 0.05; b is significant at P b 0.01; c is significant at P b 0.001and NS is not significant from the control (KB-0 or TR-0).

6.9% by applying approximately 5% (w w−1) BC. In contrast, the BC obtained from flash pyrolysis of soft wood did not increase the WHC of sandy soil at 1.5% (w w−1) mixing rate (Borchard et al., 2014). However, comparable results were recorded by Abel et al. (2013), where the WHC of a sandy soil was improved by 16.3% by adding 5% (w w−1) BC. In the current study, BC amendment improved the WHC of sandy desert soils which ultimately resulted in higher amount of water to plants. Meanwhile, the BC reduced soil K and also improved WRC of soil; hence, it resulted in savings of irrigation water under BC-amended soils. Due to savings of irrigation water and higher crop yields, the sorghum WUE increased under BC-treated soils. In a previous study, BC increased WUE of maize under a sandy soil up to 91% (Uzoma et al., 2011a). Singh et al. (2010) suggested that the addition of BC in soils may increase WRC owing to high porosity of BC. Shafie et al. (2012) observed the improvement in WRC of a sandy soil due to the addition of BC derived from slow pyrolysis of empty fruit bunches at 350–450 °C. But, there was no effect on WRC of a sandy soil after addition of 11 t ha−1 different temperature BCs (Brewer et al., 2012), suggesting that BC effects varied with soil properties. The BC amendment also significantly reduced the depletion of moisture at different depths in the root zone. This effect was consistent with BC application rate. Results demonstrated that BC-amended soil held more water against gravity and evaporation that increased water availability in the root zone under both sandy desert soils. A previous study by Busscher et al. (2010) suggested that soils having more SOM can hold more water. The decrease in the hydraulic conductivity of BC-amended soil is attributed to the large surface area and a significant number of soil pores occupied by the BC. The fine particles of BC filled the pores that reduced permeability and increased water retention in the BC-amended soil (Uzoma et al., 2011b; Busscher et al., 2010).

4.3. The effect of BC on chemical properties of sandy desert soils BC significantly changed some soil chemical properties. However, the effect varied with BC application rate. The BC amendment decreased soil pH and increased CEC and EC which are in agreement with previous reports (Hossain et al., 2010; Peng et al., 2011; Uzoma et al., 2011a). Peng et al. (2011) reported that the increase in soil CEC can be ascribed to the high surface area and charge density of the BC. In addition, Hossain et al. (2010) reported a 16% increase in the CEC of a chromosol soil after applying a 10 t ha−1 BC, and it was attributed to the improved availability of P, N and major cations. In contrast, the BC did not increase the CEC of sandy soil when it was applied at 5% w w−1 application rate (Schulz and Glaser, 2012). Similarly, Novak et al. (2009a) did not find any increase in the CEC of a Norkfolk soil when the BC was applied at 2% w w− 1, and it was attributed to the high C/N ratio of the soil. Uzoma et al. (2011a, 2011b) noted increase in the pH of a sandy soil by 1.6 units due to the addition of a cow manure-derived BC made at 500 °C with a 20 t ha−1 application rate. Hossain et al. (2010) reported a change in pH of a sandy soil by 0.2 units only at a 10 t ha−1 sludgederived BC. The BC amendment also increased the CEC of both sandy desert soils, which might be attributed to the presence of KCL (Kloss et al., 2012). The addition of pine sawdust-derived BC, improved SOM and total C. In a past study, 5 g kg−1 BC amendment increased soil total C by 68% (Laird et al., 2010). Even higher improvements up to 526% in soil total C of sandy soils have been reported due to the application of 20 t ha− 1 manure-derived BC (Uzoma et al. 2011a, 2011b). We also found that, the BC amendment increased total N content of both sandy desert soils lesser than that of total C which is consistent with previous reports (Chan et al., 2008; Uzoma et al., 2011a). The BC also increased plant essential nutrients in the soil which is in agreement with past studies (Hossain et al., 2010; Novak et al., 2009a; Uzoma et al., 2011a). Higher dose of BC caused the reduction in some micro plant nutrients such as Cu, Fe and Mn in both sandy desert soils. These micro nutrients were probably absorbed by the charred C of the BC in higher concentrations, which were unavailable to plant roots.

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4.4. Effect of BC on sorghum growth and DMY The use of BC increases soil fertility and agricultural production, improves soil WHC and nutrient retention, and reduces the greenhouse gas (GHG) emission (Mukome et al., 2013). This study indicated the potential of sawdust-derived BC to improve crop yield up to 22% under two different sandy desert soils. Our results are in agreement with the findings of previous reports (Chan et al., 2008; Hossain et al., 2010; Uzoma et al., 2011a). In this study, sorghum growth and yield were significantly improved under both desert soils at BC application rate of 15–22 t ha−1. Possible explanation of improved crop yield under BCamended soils could be that it improved soil hydraulic characters (Figs. 2 and 3) and also increased plant nutrients in soil (Table 3). BC was rich in C and other plant nutrients; hence, it increased plant nutrients in soil (Alburquerque et al., 2014). Uzoma et al. (2011a, 2011b) used BC made from cow manure at 500 °C in a sandy soil under greenhouse experiment. Under their experiment, maize yield increased from 8% to 150% at 10 to 15 t ha−1 BC application rate, respectively. The authors attributed this to the higher content of essential plant nutrients in BC which increased plant nutrients in soil; hence, improved crop yield. Poultry litter BC made at 450 °C was mixed in a chromosol soil, the radish yield compared with the control augmented from 42% at 10 t ha− 1 to 96% at 50 t ha− 1 of BC application rate (Chan et al., 2008). The improvement in radish yield was correlated to the ability of BC to increase N availability to plants. Hossain et al. (2010) observed that a 64% increase in cherry tomato yield due to BC amendment at 10 t ha−1 was attributed to the increased soil P and N as well as improved soil properties. In a past study, addition of BC in sandy soils slightly increased plant growth, but statistically significant positive effects on plant growth were observed when BC was combined with organic fertilizer, and it was attributed to the higher nutrient retention capacity of the BC (Schulz and Glaser, 2012). In a previous study, BC improved crop yield up to 324% at an application rate of 133 t ha−1 (Glaser et al., 2002). But under a loamy soil, BC amendment did not increase corn yield at an application rate of 18 t ha−1; however, there was no any negative effect of BC on the soil or crop (Unger and Killorn, 2011). In contrast, BC with 7.5% to 15% w w− 1 mixing rate reduced wheat growth and biomass under an alluvial loess soil with a silt loam texture due to deficiency of N (van Asperen et al., 2013). Therefore, it can be concluded that agronomic benefits of BC vary with BC and soil types. Results on sorghum DMY (Fig. 5) confirmed the hypothesis that the BC may enhance sorghum yield under desert soils. But sorghum DMY decreased by 21% and 28% compared to the control under the Kubuqi and the Thar Desert soils, respectively at higher application rate of BC (45 t ha− 1). This is in agreement with previous reports (Borchard et al., 2014; Kloss et al., 2014; Uzoma et al., 2011a). Due to high C/N ratio of BC, the C/N ratio significantly increased in both sandy desert soils treated with 45 t ha−1 BC (Table 3), which caused N-deficiency to plants (Kloss et al., 2012; Uzoma et al., 2011a). Other possible reason of depressed plant growth and yield could be the aluminum toxicity, as Al content increased under both soils at 45 t ha−1 BC mixing rate (Table 3). This is in agreement with other reports (Emmanuel and Peter, 1995; Rout et al., 2001). We observed Al toxicity symptoms in plants under KB-45 and TR-45 that the lateral roots were thickened and turned brown (Rout et al., 2001). Another possible reason of reduced crop yield under higher dose of BC could be the presence of phytotoxic compounds in the BC; however, our data is insufficient to prove that. Borchard et al. (2014) reported the reduction in maize growth and yield under a sandy soil after applying a fast pyrolysis BC obtained from pine wood due to the presence of soluble organic phytotoxic compounds. In addition, reduced DMY can be accompanied with the decrease of some micro plant nutrients such as Cu and Fe (Table 3). Kloss et al. (2014) noted a 68% decrease in crop yield due to 90 t ha−1 BC amendment, and it was attributed to the decrease in plant nutrients in soil such as Fe, Cu, Zn and Mn. Uzoma et al. (2011a, 2011b) also observed a 34% decrease in maize yield with increased rate of BC from

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15 to 20 t ha−1. The reduction in maize yield with increasing application rate of BC was attributed to the increase in soil C/N ratio hence lower N availability to plants. 5. Conclusions An acidic BC derived from fast pyrolysis of pine sawdust improved sorghum growth and yield in two different sandy desert soils under pot experiment. The BC improved hydraulic characteristics of both sandy desert soils such as WHC, WRC and hydraulic conductivity. In addition, the BC amendment increased soil total organic C and essential plant nutrient contents such as P and K. The BC amendment altered soil pH and improved soil CEC. Due to the improvement in soil hydraulic and chemical properties, sorghum growth and yield significantly increased under BC-amended soils. Highest yield of sorghum was achieved at the application rate of 22 t ha−1 BC, while it significantly declined at higher application rate (45 t ha−1) of BC. The suppression of crop growth at higher application rate of BC is mainly due to the increase in soil C/N ratio and loss of some micro plant nutrients such as Cu, Fe and Mn. It is also possible that BC application (BC can be also referred to as pyrogenic carbon) may improve rainfall as a result of land's albedo change produced. It can be concluded that BC derived from fast pyrolysis of pine sawdust can be used to improve the quality of sandy desert soils for sustainable development. Acknowledgments This research was partially funded by Wuhan International Science and Technology Cooperation Project (No. 2015030809020369) and Strengthening and Development of Sindh Agriculture University Tandojam Project. We thank the Analytical and Testing Center of HUST., Wuhan, P.R. China for carrying out the analyses on BC. Appendix A. Supplementary data Supplementary data to this article can be found online at http://dx. doi.org/10.1016/j.catena.2015.08.013. References Abel, S., Peters, A., Trinks, S., Schonsky, H., Facklam, M., Wessolek, G., 2013. Impact of biochar and hydrochar addition on water retention and water repellency of sandy soil. Geoderma 202-203, 183–191. Akhtar, S.S., Li, G., Andersen, M.N., Liu, F., 2014. Biochar enhances yield and quality of tomato under reduced irrigation. Agric. Water Manag. 138, 37–44. Al-Wabel, M.I., Al-Omran, A., El-Naggar, A.H., Nadeem, M., Usman, A.R., 2013. Pyrolysis temperature induced changes in characteristics and chemical composition of biochar produced from conocarpus wastes. Bioresour. Technol. 131, 374–379. Alburquerque, J.A., Calero, J.M., Barrón, V., Torrent, J., delCampillo, M.C., Gallardo, A., Villar, R., 2014. Effects of biochars produced from different feedstocks on soil properties and sunflower growth. J. Plant Nutr. Soil Sci. 177, 16–25. ASTM, 2006. Refractories, Activated C; Advanced Ceramics. American Society for Testing Materials, West Conshohocken, PA. Bird, M.I., Wurster, C.M., Silva, P.H.D., Paul, N.A., de Nys, R., 2012. Algal biochar: effects and applications. Global Change Biology Bioenergy 4, 61–69. Borchard, N., Siemens, J., Ladd, B., Möller, A., Amelung, W., 2014. Application of biochars to sandy and silty soil failed to increase maize yield under common agricultural practice. Soil Tillage Res. 144, 184–194. Brewer, C.E., Hu, Y.Y., Schmidt-Rohr, K., Loynachan, T.E., Laird, D.A., Brown, R.C., 2012. Extent of pyrolysis impacts on fast pyrolysis biochar properties. J. Environ. Qual. 41, 1115–1122. Briggs, C., Breiner, J.M., Graham, R.C., 2012. Physical and chemical properties of Pinus ponderosa charcoal: implications for soil modification. Soil Sci. 177, 263–268. Busscher, W.J., Novak, J.M., Evans, D.E., Watts, D.W., Niandou, M.A.S., Ahmedna, M., 2010. Influence of pecan biochar on physical properties of a Norfolk loamy sand. Soil Sci. 175, 10–14. Chan, K.Y., Zwieten, L.V., Meszaros, I., Downie, A., D, S.J., 2008. Using poultry litter biochars as soil amendments. Aust. J. Soil Res. 46, 437–444. Demirbas, A., 2004. Effects of temperature and particle size on biochar yield from pyrolysis of agricultural residues. J. Anal. Appl. Pyrol. 72 (2), 243–248. DeSisto, W.J., Hill, N., Beis, S.H., Mukkamala, S., Joseph, J., Baker, C., Ong, T.-H., Stemmler, E.A., Wheeler, M.C., Frederick, B.G., van Heiningen, A., 2010. Fast pyrolysis of pine sawdust in a fluidized-bed reactor. Energy Fuel 24, 2642–2651.

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