Chen, et al (2024) Changes in aggregate-associated carbon pools and chemical composition of topsoil organic matter following crop residue amendment in forms of straw, manure and biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More in a paddy soil. Geoderma. https://doi.org/10.1016/j.geoderma.2024.116967

In agricultural systems, incorporating crop residues is a common practice aimed at enhancing soil organic matter (SOM) and soil fertility. However, the effects of different forms of crop residue amendments—such as straw, manure, and biochar—on soil organic carbon (SOC) pools and SOM composition are not fully understood. A recent study conducted over a short-term period (2015-2019) in paddy soil investigated these effects using maize residue in three forms: air-dried straw (CS), cattle manure (CM), and biochar (CB), with a control (CK) receiving no amendments.

The study employed 13C isotopic tracing, biomarker analysis, and solid-state 13C nuclear magnetic resonance spectroscopy to assess changes in SOC and SOM. Results indicated that, after four cropping cycles, SOC content remained unchanged under CS and CM treatments but increased by 24% under CB. The particulate organic matter (POM) to mineral-associated organic matter (MAOM) ratio significantly increased under all residue amendments compared to the control. Specifically, maize-derived organic carbon was best preserved in POM within macroaggregates, especially under CB.

Chemical analyses revealed that all residue amendments led to an increased ratio of plant- to microbe-derived lipids, with plant-derived lipids mainly concentrated in macroaggregates, while microbial lipids were more abundant in silt-clay fractions. Biochar amendment particularly enriched plant-derived carbon due to its stable char content, which promoted macro-aggregation and preserved the carbon input.

Nuclear magnetic resonance (NMR) spectroscopy showed that biochar had higher aromaticity and alkyl to O-alkyl ratios compared to straw and manure. These differences in chemical composition indicate that biochar amendments enhance SOC accumulation by stabilizing plant-derived carbon.

The study further showed that soil amendments with crop residues in different forms altered the distribution of SOC pools and the chemical composition of SOM. For instance, while straw and manure increased microbial activity and soil fertility, biochar significantly improved SOC storage through enhanced preservation of plant-derived carbon. This highlights the potential of biochar as a more effective amendment for long-term carbon sequestration in paddy soils.

The findings suggest that the form in which crop residues are returned to the soil plays a crucial role in determining their impact on SOC dynamics and SOM composition. The increased diversity of biomarker groups following amendments indicated significant shifts in SOM composition, with biochar showing the most pronounced effects.

Overall, the study provides valuable insights into how different crop residue amendments affect SOM composition and SOC pools in paddy soils. This knowledge can guide the selection of residue management practices to optimize soil health and carbon sequestration in agricultural systems.

These results underscore the importance of considering the form of crop residues when aiming to enhance soil organic carbon storage and soil fertility. Biochar, in particular, emerges as a superior amendment for promoting SOC accumulation and stability in paddy soils, making it a promising strategy for sustainable soil management.