Acidity, water retention, and mechanical physical quality of a strongly acidic Ultisol amended with biochars derived from different feedstocks
Strongly acidic Ultisols in tropical and subtropical regions of China present one of the most important degraded soils. The improvement of soil quality for these soils is a key goal for sustainable agriculture. The purpose of this study is to evaluate the beneficial effects of biochar amendments on the soil acidity, plant available nutrient contents, and physical properties of a strongly acidic Ultisol.
Materials and methods
A Typic Plinthudult with low soil fertility and poor physical properties was amended by three biochars made from straw (SB), woodchips (WCB), and wastewater sludge (WSB) at the rate of 0, 2, 4, and 6 % biochar, respectively. After 180 days of incubation, the chemical, nutrient contents, water retention, consistency, tensile strength, and shear strength of biochar-amended soils were determined.
Results and discussion
Experimental results indicate that biochars significantly (p < 0.05) increase the pH of the soil and decrease the contents of exchangeable H+ and Al3+. The WCB treatment results in higher pH values than the SB and WSB treatments. The biochars significantly increase total C, available P, K, and exchangeable K, Ca, and Mg contents. Biochar applications significantly enhance water-holding capacity of soil, while not increasing the available water content (AWC) of the soil. Biochar application significantly (p < 0.05) increases the liquid limit (LL) and plastic index (PI) of the soil. The effectiveness of biochar on LL and PL is more pronounced in the SB-amended soils. With application of biochar, the tensile strength (TS) of Ultisol decreases from original 466 kPa to 233, 164, and 175 kPa for 6 % WCB-, SB-, and WSB-amended soils, respectively. Direct shear tests indicate WCB significantly reduces the cohesion (c) of the soils, while biochars do not alter the internal friction angle (φ) of soil. Analyses of scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS) reveal that soil mineral particles are inserted inside the pores of biochar and attached on the surface of biochar, indicating that biochar greatly changes the microstructure and pore system of soil.
It is suggested that biochar amendment generally improves the quality of degraded Ultisols with strong acidity, low fertility, and poor physical properties. The physical dilution effect and microstructure change caused by the porous and less dense biochar are identified to be the main mechanism for the biochar to improve the physical properties of strongly acidic Ultisols.
KeywordsAcidity Biochar Mechanical strength Soil consistency Ultisol Water retention capacity
- Gee GW, Bauder JW (1986) Particle-size analysis. In: Klute A (ed) Methods of soil analysis, vol 9, Agronomy Monograph. ASA and SSSA, Madison, USA, pp 383–411Google Scholar
- He YQ, Sun B (2008) Evolution and regulation of red soil quality (in Chinese). Science Press, Beijing, p 375Google Scholar
- Hseu ZY, Jien SH, Chien WH, Liou RC (2014) Impacts of biochar on physical properties and erosion potential of a mudstone slopeland soil. The Scientific World Journal ID 602197, http://dx.doi.org/10.1155/2014/602197
- Lal R, Shukla MR (2004) Principles of soil physics. Marcel Dekker, New YorkGoogle Scholar
- Nelson DW, Sommers LE (1982) Total carbon, organic carbon, and organic matter. In: Page AL, Klute A (eds) Methods of soil analysis: part 2. Chemical and microbiological methods, agronomy monograph, vol 9. ASA and SSSA, Madison, pp pp. 539–pp. 579Google Scholar
- Soil Survey Staff (2010) Keys to soil taxonomy (11th ed.). USDA-NRCS, Washington, DC, p 336Google Scholar
- State Standard of the People’s Republic of China (SSPRC) (1999) Standard for Soil Test Method (GB/T50123-1999) (in Chinese). People’s Republic of China Ministry of Construction, pp 41–46, 107–114Google Scholar
- Thomas GW (1982) Exchangeable cation. In: Page AL, Miller RH, Keeney DR (eds) Methods of soil analysis: part 2. Chemical and microbiological methods, vol 9, Agronomy Monograph. ASA and SSSA, Madison, pp 159–165Google Scholar
- Zhang GL, Gong ZT (2012) Soil survey laboratory methods (in Chinese). Science Press, Beijing, pp 58–60Google Scholar
- Zhejiang Province Soil Survey Office (1994) Soils of Zhejiang Province (in Chinese). Zhejiang Science & Technology Press, Hangzhou, pp 103–128Google Scholar