effect of biochar amendment on soil-silicon availability and rice uptake

2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.plant-soil.com

J. Plant Nutr. Soil Sci. 2014, 177, 91–96 DOI: 10.1002/jpln.201200582 91

Effect of biochar amendment on soil-silicon availability and rice uptakeXiaoyu Liu1, Lianqing Li1, Rongjun Bian1, De Chen1, Jingjing Qu1, Grace Wanjiru Kibue1, Genxing Pan1*,Xuhui Zhang1, Jinwei Zheng1, and Jufeng Zheng1

1 Institute of Resource, Ecosystem and Environment of Agriculture, and Center of Agricultural and Climate Change, Nanjing AgriculturalUniversity, 1 Weigang, Nanjing 210095, China

AbstractRice growth and its resistance to pests had been often constrained by soil-silicon (Si) availability.The purpose of this study was to assess the potential of biochar soil amendment (BSA) toimprove Si availability in paddy soils. A cross-site field trail with BSA was conducted in six loca-tions with different climatic and crop-production conditions across S China. Plant-available Sicontent before field-trials establishment and after rice harvest, as well as Si content in rice shootwere determined. Varying with site conditions, plant-available Si content of soil was observed toincrease significantly with BSA in most sites. Significant increase in rice shoot Si was detectedin four out of the six sites, which was well correlated to the concurrent increase in soil pH underBSA treatment. This study demonstrates an important role of BSA to improve Si availability anduptake by rice mainly through increasing soil pH of the acid and slightly acid rice soils.

Key words: biochar soil amendment / rice / silicon / field experiment / paddy soil

Accepted May 18, 2013

1 Introduction

Silicon (Si) had been considered as a necessary nutrient forrice (Ma et al., 2001) and adequate Si uptake promotes ricegrowth by increasing its tolerance to both abiotic and bioticstresses (Datnoff and Rodrigues, 2005; Liang et al., 2007;Guntzer et al., 2012). Soil Si could be potentially depletedunder intensified rice cropping systems (Savant et al., 1997)due to uptake by rice in a large amount up to 0.5 t ha–1 in asingle season (Ma et al., 2001; Makabe et al., 2009). Yet, Sideficiency in rice paddies could be further caused by soilacidification for plant availability of Si is affected by soil pH(Tavakkoli et al., 2011). Therefore, enhancing plant-availableSi pool of rice paddies would be important for sustaining riceproductivity in rice-growing regions of Asia. Recycling of ricestraw and/or Si fertilization had been recommended in rice-based agriculture to mitigate Si deficiency (Lucas et al.,1993). However, recycling via crop-straw return had beenincreasingly restricted due to technical and practical barriers(Khaliqet al., 2011), especially with pest control for the subse-quent crop (Li et al., 2013).

For the last decade, conversion of crop residues into biocharand its incorporation into agricultural soils had been encour-aged to improve soil fertility in the context of mitigating cli-mate change (Lehmann and Joseph, 2009). Field experi-ments with BSA had shown significant effects of biochar inreducing N2O emissions and increasing rice yield from ricepaddies (Asai et al., 2009; Zhang et al., 2010, 2012; Liu et al.,2012). The benefits for crop productivity of BSA had beenactively assessed (Jeffery et al., 2011; Biederman and Har-pole, 2013) and often attributed to the improvement of soilfertility by increasing soil pH, enhancing fertilizer-use effi-

ciency, and improving nutrient-retention capacity (Asai et al.,2009; Zhang et al., 2010; Haefele et al., 2011). Nevertheless,the potential role of biochar in improving Si nutrition to ricegrowth had not yet been addressed.

We hypothesized that BSA could increase soil available poolof silicon either by a supplementary supply from added bio-char or by increasing soil pH, a well-known liming effect bybiochar application to soil. Thus, the objective of this workwas to assess the effect of BSA on soil-Si availability andrice-plant Si uptake in rice soils using data from field experi-ments.

2 Materials and methods

2.1 Field Experiments

A cross-site field experiment was conducted in six siteslocated in five provinces of S China, representing themain rice-producing areas (DRS-SBS, 2007). The experi-mental sites in S China include GH (Guanghan County,Sichuan Province), CS and YY (Changsha and YueyangMunicipalities, Hunan Province), JX (Jinxian County, JiangxiProvince), GL (Guilin, Municipality of Guangxi AutonomousDistrict), and YY (Longyan Municipality, Fujian Province)(Fig. 1). All these sites are within a subtropical monsoon cli-mate with mean annual temperature in a range of16.0°C–19.3°C and mean annual precipitation in a range of921–1921mm. As shown in Tab. 1, soil properties vary in awide range with sites.

* Correspondence: G. Pan;e-mail: [email protected]; [email protected]

Field trials were established in 2010 (GH, CS, and JX) and2011 (YY, GL, and LY). Following a protocol described inZhang et al. (2010), biochar was broadcasted on soil surfaceand then mixed by plowing to a depth of about 12 cm beforerice transplanting. The biochar treatment was conducted at0 t ha–1 (C0), 20 t ha–1 (C20), and 40 t ha–1 (C40) in sites ofGH, CS, JX, and YY, and at 0 t ha–1 (C0) and 20 t ha–1 (C20)in sites of GL and LY, respectively. Each plot was 4 m × 5 min area with individual irrigation and drainage outlets, and

separated by a surrounding protection row of 0.8 m in width.All treatments in each site were replicated in triplicates andthe plots arranged in a randomized complete block design.

For crop-production management, chemical fertilizers (N, P,and K) were applied before rice transplanting and during theearly stage of rice tillering as dressing fertilization in all treat-ments. The total amounts of fertilizers for each site are shownin Tab. 2. The crop management and fertilization were per-


Figure 1: Site distribution of biochar field experiments in S China.

Table 1: Site climate condition and selected topsoil basic properties prior to experiment. MAP: mean annual precipitation; MAT: mean annualtemperature.

Site pH(H2O)

SOC/ g kg–1

TN/ g kg–1

Plant-available Si/ mg kg–1

Clay/ %

Silt/ %

Sand/ %

MAT/ °C

MAP/ mm

GH 6.0 20.1 1.8 94.0 16 32 52 16.0 921

CS 6.2 18.8 1.8 72.2 18 28 54 17.1 1546

YY 5.0 21.3 1.6 66.6 20 31 49 17.0 1302

JX 4.9 17.7 1.6 40.4 20 38 42 17.6 1624

GL 6.1 18.7 1.4 32.8 12 24 64 18.8 1921

LY 6.3 15.8 1.1 53.6 10 31 59 19.3 1564

92 Liu, Li, Bian, Chen, Qu, Kibue, Pan, Zhang, Zheng, Zheng J. Plant Nutr. Soil Sci. 2014, 177, 91–96

formed following the local farmers’ performance and consis-tent with the treatments in each site.

Commercial wheat-straw biochar was used for soil amend-ment consistently across the sites. The biochar was pro-duced via pyrolysis at temperature between 350°C and550°C in a vertical kiln at Sanli New Energy Company inHenan province, China (Zhang et al., 2010). The basic prop-erties of biochar used were: pH (H2O) 10.4, organic C467 g kg–1, total N 5.9 g kg–1, and citric acid–extractable Si718 mg kg–1.

2.2 Sample collection and analysis

Soil sampling to a depth of 0–15cm was done both beforeand after biochar treatment in each site. Three topsoil sam-ples of three random subsamples were collected from a fieldprior to treatment and at rice harvest in a plot under treat-ment, respectively. The samples were sealed in plastic bagsand shipped to laboratory within 1 week after sampling.

After removing roots and visible fragments, the soil sampleswere air-dried and ground to pass a 2-mm sieve prior to anal-ysis.

Rice-shoot samples from ten individual plants were collectedat rice harvest in each plot. After washing with distilled water,the shoot samples were oven-dried at 65°C to constantweight and then ground in a stainless-steel mill to passthrough a 0.84-mm mesh sieve.

Soil properties were determined following the protocol de-scribed by Lu (2000). Soil pH (H2O) was determined using a1: 2.5 soil-to-water ratio with a compound glass electrode(Seven Easy Mettler Toledo, China, 2008). A soil sample wasextracted with 0.025 M citric acid and Si in the digest wasdetermined using a silicomolybdous colorimetric method (vander Vorm, 1987). For rice-shoot Si determination, a shootsample of 200 mg was weighed into a nickel crucible, whichwas then heated in a muffle furnace at 300°C for 3 h and at550°C subsequently for 4 h. After cooling, the ash wasdigested with 50.0 mL of 0.08 M H2SO4 solution added, andthe digest was transferred to a plastic bottle added with 2 mLof 40% HF solution. Finally, Si concentration in the solutionwas determined with the above mentioned colorimetric meth-od.

2.3 Statistical analysis

Analysis of variance (ANOVA) was conducted to compare thedifference in both soil and plant silicon level between biochartreatments in a single site using Statistical Package for SocialScientists (SPSS 16.0). In case of significant difference, indi-vidual means were compared by least-significant-differencetest (LSD). For experiment with only two levels of biochartreatment, t-test was used to compare treatment effects. Thesignificance was defined at p < 0.05.

3 Results

3.1 Effect of BSA on soil pH

Figure 2 shows the change in soil pH (H2O) with BSA. BSAincreased soil pH in most of the sites, and this increase waspositively correlated with the application rates. The highestincrease in soil pH increase was observed by 0.6 and 1.3units, respectively, under C20 and C40 treatment at site YY.Whereas, soil pH in site LY was unexpectedly decreased by0.7 under C20 treatment over the control and soil pH undercontrol was 7.1 at rice harvest compared to 6.3 before ricetransplanting.

3.2 Effect of BSA on plant-available Si

Changes in soil plant-available Si contents with BSA treat-ments across sites are presented in Tab. 3. Clearly, the bio-char effect on soil-Si availability was site-specific and rate-dependent. BSA treatment of C40 significantly (2.2–4.2times) increased plant-available Si content in sites GH, CS,and YY though no change in site of JX. Under C20 treatment,however, plant-available Si content increased at YY and GLbut in other sites, whereas being coincident with the pHchange (Fig. 2), plant-available Si was reduced under BSAover control at site LY.

3.3 Shoot Si uptake

As shown in Tab. 3, shoot Si contents ranged from 23.5 g kg–1

to 46.35 g kg–1, varying in a much narrower range compared


Table 2: Rice cultivars and chemical-fertilizer-application rates.

Site Cultivar Fertilizer / kg ha–1 season–1

N P2O5 K2O

GH DYou202 240 150 75

CS Zhongjiazao17 150 90 90

YY Xiangwanxian12 170 – 95

JX Yougong98 300 220 150

GL Liangyou838 150 250 60

LY Fengyou559 170 225 140

Figure 2: Changes of soil pH with biochar amendment at rate of 0(C0), 20 (C20), and 40 (C40) t ha–1 across six sites. Error barsrepresent the standard deviations of the means.

J. Plant Nutr. Soil Sci. 2014, 177, 91–96 Biochar affects paddy soils Si availability 93

to the changes in plant-available Si of soil with treatmentsand sites. Shoot Si increased greatly under BSA at GH, CS,and YY, slightly but significantly at GL but insignificantly at JXand LY, whereas, there was no consistently significant differ-ence in shoot Si between C20 and C40 treatments in sites ofGH, CS, YY, and JX. However, statistical analysis demon-strated that the change in rice Si uptake with BSA was posi-tively correlated with the change in soil pH and plant-availableSi pool of soil (Fig. 3).

4 Discussion

In this study, plant-available Si pool of topsoil under controlwithout BSA was lower at harvest than before rice transplant-ing at all sites except JX and LY (Tabs, 1 and 3). Low plant-available Si pool had very often been observed in acid soils(Zang et al., 1982; Kraska and Breitenbeck, 2010). Thedecrease in soil pool of plant-available Si at harvest could beattributed to the decrease in soil pH after rice growing with N fer-tilization though it could also be resulted from the uptake by rice(Makabe et al., 2009). Nevertheless, compared to the thresh-old of plant-available pool of 65 mg kg–1 established (Zanget al., 1982) the lower plant-available Si pool under control inall sites reflected a Si deficiency already for rice cultivation.

In practice, silicate slag had been used to enhance Si avail-ability of paddy soils from Asian countries (He et al., 1980;Snyder at al., 1986). In this study, soil amendment withwheat-straw biochar showed a great increase in soil availablepool of Si in most sites. This was partly relevant to the inputof Si from added biochar (up to 700 mg [kg dry weight]–1) andrather could be attributed to the elevation of soil pH (Fig. 3)under BSA. Soil-Si availability had been well-known affectedby soil pH, clay content, weathering, and parent material(Tavakkoli et al., 2011). BSA treatment at 40 t ha–1 did notincrease Si availability at JX due to the very low initial soil pHand limited liming effect (Tab. 3). After rice harvest, the soilsunder BSA in most sites contained appreciable amounts ofplant-available Si, which was in contrast to the sharpdecrease under control (Tabs. 1 and 3). This demonstrated agreat potential of biochar amendment in increasing soil Sireservoir and supply.

Plant-available Si content generally represents the ability ofsoil to supply adequate Si for rice production. Similar to the

finding by Zang et al. (1982), rice-shoot Si content was signifi-cantly correlated with soil plant-available Si content (Fig. 3 A),and plant available Si content had been used as an indicatorfor Si supply of paddy soils (Kraska and Breitenbeck, 2010;Korndörfer et al., 2001). Content of rice-shoot Si under con-trol was in a range of 23.5–40.4 g kg–1 across sites, whichseemed significantly lower than a threshold value of 50 g kg–1

(Lian, 1976; DeDatta, 1981; Dobermann and Fairhurst,2000). Furthermore, about 40% of the rice-shoot samplesunder BSA treatments were still lower than a threshold of35 g kg–1 suggested for rice production in S China in the early1980s (Zang et al., 1982). This revealed an existing Si defi-ciency in the rice soils studied. Increase in shoot Si contentwith BSA treatment was observed at most sites. Theunchanged plant Si content in rice shoot at JX and LY wasattributed to the limited Si availability and/or a relatively high-er Si uptake at LY. Thus, with supplementing soil Si pool andincreasing soil pH, BSA could alleviate rice Si deficiencythough shoot Si uptake under BSA still beyond 50 g kg–1.

Although crop-straw return could be an option to recycle Siand reinforce soil Si pool in agro-ecosystems for sustainablerice production, it had been increasingly impractical due tothe cost of labor and pesticide control for the intensified cropproduction in China (Li et al., 2013). Consequently, conver-sion of straw into biochar via pyrolysis had been developedas a clean and economic technology in China for the last 5 y(Pan et al., 2011). This study further evidenced a great poten-tial of BSA to alleviate Si deficiency with acidic and slightlyacidic soils in S China. In these regions, rice was the majorcereal crop and had been cultivated for thousands of years.The improvement of Si deficiency could also be a supplemen-tary role of biochar in addition to its great effect on reducingN2O emissions (Liu et al., 2012).

5 Conclusions

In a cross-site field experiment, biochar exerted a significanteffect on improving plant-available Si pool and hence therice-shoot Si uptake. This could probably result from the bio-char-added Si input and the enhanced availability by in-creased soil pH. We conclude that biochar from crop strawcould be a practical option to alleviate Si deficiency existingwith continuous rice production in acidic rice paddy soils in SChina.


Table 3: Plant-available Si and rice-shoot Si contents (mean value ± standard deviation) under biochar-amendment experiment. C0, C20, andC40 represent the treatments with biochar-application rates of 0, 20, and 40 t ha–1, respectively. Different lowercase letters in the same row in asingle block indicate significant difference (LSD, p < 0.05).

Site Plant-available Si content / mg kg–1 Rice-shoot Si content / g kg–1

C0 C20 C40 C0 C20 C40

GH 60.9 ± 3.1 a 62.5 ± 4.6 a 139.1 ± 44.8b 29.8 ± 1.2a 41.9 ± 3.9b 42.8 ± 3.8b

CS 60.7 ± 3.4 a 73.3 ± 5.4 a 131.0 ± 41.0 b 36.6 ± 0.7 a 42.7 ± 3.8b 42.8 ± 1.6 b

YY 34.7 ± 6.7 a 92.8 ± 13.9 b 145.7 ± 23.4c 29.3 ± 3.1 a 44.3 ± 1.0 b 46.4 ± 2.1b

JX 42.6 ± 5.7 46.5 ± 2.9 50.3 ± 3.9 31.5 ± 2.6 31.7 ± 5.4 29.9 ± 6.9

GL 25.2 ± 1.1 a 27.4 ± 0.3 b – 23.5 ± 1.5 a 28.4 ± 2.7 b –

LY 63.9 ± 6.8 b 49.1 ± 8.4 a – 40.4 ± 5.3 36.5 ± 6.4 –


Acknowledgments

This work was partially funded by grants from the ChineseMinistry of Agriculture and the Ministry of Science and Tech-nology of China. The authors are grateful to Dr. Haiyan Zhao,Mr. Li Qian, and Ms. Li Li for their technical assistance in Sianalysis.

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