Effects of straw and biochar amendments on aggregate stability, soil organic carbon, and enzyme activities in the Loess Plateau, China

Abstract

Soil from the Loess Plateau of China is typically low in organic carbon and generally has poor aggregate stability. Application of organic amendments to these soils could help to increase and sustain soil organic matter levels and thus to enhance soil aggregate stability. A field experiment was carried out to evaluate the effect of the application of wheat straw and wheat straw-derived biochar (pyrolyzed at 350-550 °C) amendments on soil aggregate stability, soil organic carbon (SOC), and enzyme activities in a representative Chinese Loess soil during summer maize and winter wheat growing season from 2013 to 2015. Five treatments were set up as follows: no fertilization (CK), application of inorganic fertilizer (N), wheat straw applied at 8 t ha with inorganic fertilizer (S8), and wheat straw-derived biochar applied at 8 t ha (B8) and 16 t ha (B16) with inorganic fertilizer, respectively. Compared to the N treatment, straw and straw-derived biochar amendments significantly increased SOC (by 33.7-79.6%), microbial biomass carbon (by 18.9-46.5%), and microbial biomass nitrogen (by 8.3-38.2%), while total nitrogen (TN) only increased significantly in the B16 plot (by 24.1%). The 8 t ha straw and biochar applications had no significant effects on soil aggregation, but a significant increase in soil macro-aggregates (>2 mm) (by 105.8%) was observed in the B16 treatment. The concentrations of aggregate-associated SOC increased by 40.4-105.8% in macro-aggregates (>2 mm) under straw and biochar amendments relative to the N treatment. No significant differences in invertase and alkaline phosphatase activity were detected among different treatments. However, urease activity was greater in the biochar treatment than the straw treatment, indicating that biochar amendment improved the transformation of nitrogen in the soil. The carbon pool index and carbon management index were increased with straw and biochar amendments, especially in the B16 treatment. In conclusion, application of carbonized crop residue as biochar, especially at a rate of 16 t ha, could be a potential solution to recover the depleted SOC and enhance the formation of macro-aggregates in Loess Plateau soils of China.

Soil quality indicators under management systems in a Quilombola community in the Brazilian Cerrado

“…The EEG content exhibited a behavior similar to the carbon content in micro and macro-aggregates of the soil (Figure 3E and F), which reinforces the concept that EEG is an important source of soil organic carbon (Zhang et al, 2017). The highest EEG levels were found in the AC system, differing between the depths evaluated only in the EEG-MAC (p < 0.05), and the systems with the least EEG were the MA and PA ( Figure 3E).…”

“…A higher ASI was expected in the sys- tem with greater species diversity (AC), including the reference area (CR), since both could promote a greater diversity of root exudates of different compositions, guaranteeing greater carbon source diversity in the soil system (Silva et al, 2016a). In addition to the biological diversity of natural systems that improves the stability of soil aggregates, another controversial aspect refers to spontaneous burning in the Cerrado that may or may not promote an increase in the stability of these aggregates (Thomaz, 2017;Hobley et al, 2017;Zhang et al, 2017). Despite this, the ASI value found for the management systems lies within the range commonly found for tropical soils (82 ± 6 %) (Thomaz, 2017).…”

Three‐Year Field Observation of Biochar‐Mediated Changes in Soil Organic Carbon and Microbial Activity

“…1a, the fraction of <0.05 mm was the dominant aggregate size, accounting for ∼70% of the total weight. Study of Zhang et al (2017) demonstrated that the greatest proportion of soil aggregates were in smaller size classes. Incorporation of straw and biochar decreased the proportion of >0.25‐mm size fractions (>1‐mm and 0.25‐ to 1‐mm fractions) but increased the amount of <0.25‐mm size fractions (0.05‐ to 0.25‐mm and <0.05‐mm fractions) in this soil.…”

“…Studies showed that SOC can be stabilized by both the soil silt-clay fractions (<0.053 mm) and microaggregates (0.053-0.25 mm), which significantly influence the accumulation and bioavailability of SOC (Six and Paustian, 2014). Although a positive effect of both straw and derived biochar on SOC content and soil aggregation has been reported (Zhang et al, 2017), debate continues on the influence of biochar amendment on soil aggregate distributions and associated SOC contents (Pituello et al, 2018). Studies found an increase in SOC content among different aggregate fractions after biochar amendment, whereas others obtained a decreasing tendency (Pituello et al, 2018).…”

“…Despite the SOC distribution, biochar amendment to soil influenced soil microbial biomass, activity, and community structure (Luo et al, 2017; Zhang et al, 2017). Biochar can act as an energy source for microorganisms (Farrell et al, 2013; Gomez et al, 2014), and also as a habitat for microorganisms from grazers (Luo et al, 2013).…”