J Soils Sediments DOI 10.1007/s11368-016-1447-9
BIOCHAR FOR A SUSTAINABLE ENVIRONMENT
Combined biochar and nitrogen fertilizer reduces soil acidity and promotes nutrient use efficiency by soybean crop Lu Yu 1,2 & Xing Lu 3 & Yan He 1,2 & Philip C. Brookes 1,2 & Hong Liao 4 & Jianming Xu 1,2
Received: 24 December 2015 / Accepted: 10 May 2016 # Springer-Verlag Berlin Heidelberg 2016
Abstract Purpose Soil acidification is universal in soybean-growing fields. The aim of our research was to evaluate the effects of soil additives (N fertilizers and biochar) on crop performance and soil quality with specific emphasis on ameliorating soil acidity. Materials and methods Four nitrogen treatments were applied as follows: no nitrogen (N0), urea (N1), potassium nitrate (N2), and ammonium sulfate (N3), each providing 30 kg N ha−1. Half plot area of the N1, N2, and N3 treatments was also treated with biochar (19.5 t ha−1) to form N-biochar treatments (N1C, N2C, N3C). Both bulk and rhizosphere soils were sampled separately for the following analyses: pH, exchangeable base cations (EBC), exchangeable acidity (EA), total inorganic N (IN), total N (TN), and microbial phospholipid fatty acids (PLFAs). Soybean biomass and nutrient contents were also determined. Correlation analysis was applied
Responsible editor: Yong Sik Ok * Hong Liao
[email protected] * Jianming Xu
[email protected] 1
Institute of Soil and Water Resources and Environmental Science, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou 310058, China
to analyze the relationships between soil chemical properties and soybean plant parameters. Results and discussion With N-biochar additions (N1C, N2C, N3C), soil chemical properties changed as follows: pH increased by 0.6–1.2 units, EBC, IN, and TN increased by 175–419, 38.5–54.7, and 136–452 mg kg−1, respectively, and PLFAs increased by 23.6–40.9 nmol g−1 compared to the N0 in the rhizosphere. Microbial PLFAs had positive correlations with soil pH; EBC; exchangeable K, Ca, Na, and Mg; TN; IN; NH4+; and NO3− (r = 0.66–0.84, p < 0.01). There were negative correlations between PLFAs and EA or exchangeable Al (r = −0.64, −0.66, p < 0.01), which indicated that the additives increased microbial biomass by providing a suitable environment with less acid stress and more nutrients. The additives increased soil NH4+ and NO3− by promoting soil organic N mineralization and reducing NH4+ and NO3− leaching. Moreover, the soybean seed biomass and the nutrient contents in seeds increased with N-biochar additions, especially in the N3C treatment. Conclusions N-biochar additions were effective in ameliorating soil acidity, which improved the microenvironment for more microbial survival. N-biochars influenced N transformations at the plant–soil interface by increasing organic N mineralization, reducing N leaching, and promoting N uptake by soybeans. The soil additive ammonium and biochar (N3C) were best in promoting soybean growth. Keywords Bulk soils . N-biochar additives . Nitrogen transformation . Rhizosphere . Soil acidity . Soybean growth
2
Zhejiang Provincial Key Laboratory of Agricultural Resources and Environment, Hangzhou 310058, China
3
Root Biology Center, South China Agricultural University, Guangzhou 510642, China
1 Introduction
4
Haixia Institute of Science and Technology, Root Biology Center, Fujian Agriculture and Forestry University, Fuzhou 350002, China
Soil acidification has become a worldwide concern, as it significantly affects agricultural sustainability (Xiao et al. 2013;
J Soils Sediments
Guo et al. 2010). Approximately 50 % of the world’s potentially arable land area consists of acid soils (pH ≤ 5.5) (Kochian et al. 2015). The major causes of acidification in farming systems are the removal of alkalinity in farm products and the release of protons during N2 fixation and nitrate leaching (Tang et al. 2013). It is possible that the growth of legumes, which are fixing atmospheric N2, involves the excess uptake of nutrient cations over anions from soil solution, which results in the net efflux of H+ ions from plant roots in the rhizosphere (Haynes 1983). A fraction of the H+ ions generated within the legume roots may come from the dissociation of the carboxyl groups of amino acids (Bolan et al. 1991). The acidity generated by legume fixation of N2 is equivalent to the excess uptake of cations over anions by the plant and may vary from 0.2 to 0.7 mol H+ per mole of fixed N (Jarvis and Robson 1983; Liu et al. 1989). When no ionic N is taken up by the plant, basic cations are imported into the legume in exchange for H+ ions generated during carbon assimilation. To maintain a pH balance, these H+ ions must be exported from the roots (Bolan et al. 1991). Various methods have been studied to determine their effectiveness in ameliorating soil acidity, including applications of lime, gypsum, industrial by-products and organic materials such as plant residues, and growing acid-tolerant crops (Xu et al. 2006; Li et al. 2010; Tang et al. 2013). However, in view of comprehensive benefits such as soil acidity reduction, efficient waste disposal, and nutrient supply, biochar can be an effective and long-lasting amendment to ameliorate the soil environment (Abiven et al. 2014). Soil pH increases with biochar addition, probably due to carbonates and organic anions in the biochars, which contribute to their alkalinity (Yuan et al. 2011b; Dai et al. 2014). The liming effect also depends on the types of biochar feedstocks and pyrolysis conditions, i.e., residence time, temperature, heating rate, and soil initial pH (Ok et al. 2015; Rajapaksha et al. 2016). Biochars with high alkalinity (e.g., swine manure, fruit peel, and leaf biochars) resulted in larger soil pH increases than biochars with low alkalinity (e.g., wetland plant biochars) (Dai et al. 2013, 2014). The liming effect of biochars was greater in acid soils with a low initial pH (Yuan and Xu 2011; Yuan et al. 2011a; Hass et al. 2012). Biochar, with its properties such as high organic C concentration, a porous structure, high pH, and high adsorption capacity (Singh et al. 2010; Spokas 2010; Tan et al. 2015), has been considered as an effective way to improve soil quality (Dai et al. 2013; Mohan et al. 2014). Biochar can reduce N2O emissions from soils (Lehmann 2007; Mathews 2008; Taghizadeh-Toosi et al. 2011), improve plant growth (Graber et al. 2010), reduce nutrient leaching losses (Lehmann et al. 2003; Mohan et al. 2014), ameliorate soil acidity (Yuan and Xu 2011), and stimulate soil microbial activity (Smith et al. 2010; Jones et al. 2011; Lehmann et al. 2011). However, biochar application in field trials gave conflicting results. Jones et al. (2012) considered that biochar availability and,
particularly, economic cost were the greatest barriers when considered for use by regional farmers. Other negative and practical consequences (e.g., wind erosion during spreading and risk of human inhalation) also exist (Jones et al. 2012). There is no practical way to remove biochar from soil following its application (Lehmann 2007). Finally, it is not possible to extrapolate laboratory results to the field situation, and many of the short-term effects of biochar on plant growth and soil properties reported from laboratory studies are not observed in the field. For example, Vaccari et al. (2015)) reported controversial effects on soil–plant interactions and on crop yield response. Biochar can affect chemical and biological N reactions in soils. For example, biochar appears to increase nitrogen use efficiency (Gathorne-Hardy et al. 2009), influence nitrification rates and adsorption of ammonia, and increase NH4+ accumulation by enhancing cation exchange capacity in soils (Clough and Condron 2010). However, a field trial is required to verify biochar’s agricultural functions together with nitrogen fertilizer as well as to understand its mechanisms. The aim of our research was to evaluate the effects of biochar with added N fertilizers (N-biochars) on crop performance and soil quality with specific emphasis on ameliorating soil acidity. Firstly, we compared soybean biomass production and basic chemical properties of different N-biochar additives to soil. Secondly, we contrasted the integrated effects of Nbiochars on soil pH, exchangeable base cations (EBC), IN, and microbial PLFAs in the rhizosphere with bulk soils. Thirdly, we discussed important issues like N transformations influenced by external additives in plant–soil interface. In addition, a correlation analysis was conducted to understand the relationships between soil chemical properties and soybean plant parameters to illustrate the mechanisms. We hypothesized that N-biochar amendments would increase soil pH and exchangeable base cations to ameliorate soil acidity as well as to promote soybean biomass. This effect would be expected to be more strongly expressed in the rhizosphere. The N transformations in the plant–soil interface are also probably influenced by N-biochars.
2 Materials and methods 2.1 Field site and soils The field site was located at the experimental station of South China Agricultural University in the Guangdong Province of China in 2013 at Boluo (E 114.28°, N 23.18°). It was previously used for growing soybeans. This site has an acidic red soil of pH 5.78 and an organic C concentration of 13.6 g kg−1. The total nitrogen (N), available phosphorus (P), and available potassium (K) were 547, 26.1, and 55.3 mg kg −1 soil, respectively.
J Soils Sediments
2.2 Biochar characterization The biochar used in the field experiment was generated from pyrolyzing wheat straw under O2-limited conditions, produced by N2 purging (Sanli Company, Shandong Province). The pyrolysis temperature was raised at a rate of 26 °C min−1 to 450 °C and held for 2 h. After cooling (3 °C min−1 cooling rate), the biochar samples were ground and sieved
