Amendment of crop residue in different forms shifted micro-pore system structure and potential functionality of macroaggregates while changed their mass proportion and carbon storage of paddy topsoil

Abstract

Soil organic carbon (SOC) sequestration in croplands was well known through physical protection of particulae organic carbon (POC) in macroaggregates, particularly with crop residue amendment. How different forms of crop residue could affect development of macroaggregates and their micro-pore system remained unclear. In a field experiment, a rice paddy was amended respectively with fresh (CS), manured (CM) and pyrolyzed (CB) maize residue at 10 t ha−1 in carbon equivalent, in comparison to no residue amendment (CK). In 3 years following amendment, undisturbed topsoil (0–15 cm) cores were collected under the treatments respectively. Following size fractionation of water-stable aggregates and SOC pool analysis, macroaggregate (MAC) samples were characterized with SR-µCT tomography. Compared to CK, bulk SOC storage increased by 13.9 % and 31.3 %, POC storage by 32.6 % and 63.3 % while MAC mass proportion by 7.4% and 24.5%, under CM and CB, respectively. Coincidently, total micro-porosity of MAC was increased by ca 30 % but porosity ratio of connected pores to isolated pores increased almost 1-fold though fractal dimension (FD) increased slightly, both under CM and CB. However, indices of pore throats were seen higher under CB than other treatments though micro-pore networking promoted under both CM and CB. In addition, micro-porosity and pore structure as well as POC were all observed similar between fresh residue and no residue treatments. Thus, crop residue amendment in different forms shifted micro-pore structure and potential functionality of MAC while changed their mass proportion and carbon storage of the paddy topsoil. Overall, crop residue recycled as biochar to paddy could ensure SOC sequestration through enhanced physical protection of POC in MAC, which could further potentially contribute to soil function improvement. How the short-term changes in macroaggregation and the pore system could contribute to the soil fertility and functioning deserve further studies.