Sen Dou

TL;DR: Straw returning to the field has become a common way to utilize crop residues as mentioned in this paper, which does not only solve the problem of rational utilization of straw but also improves soil organic ca...

TL;DR: In this paper, different corn straw returning modes affect the contents of labile organic carbon (SOC) and its labile fractions, as well as soil aggregates and organic carbon associated with water-stable aggregates.

Abstract: Studying changes in soil humus composition and humic acid (HA) structural characteristics caused by agronomic practices provide insights into the pathways of soil organic carbon (C) stabilisation dynamics. This five-year field study evaluated the effects of straw returning modes on humus composition and HA structure. Treatments included (i) corn straw returned on the soil surface (NTS), (ii) corn straw incorporated into soil within 0–10 cm (MTS), (iii) corn straw incorporated into soil within 0–20 cm (CTS) and (iv) no corn straw applied (CT). Soil HA was characterised by Fourier transform infrared (FTIR) and fluorescence spectroscopies. The results demonstrated that corn straw returning improved humus C fractions in this order NTS > MTS > CTS > CT in 0–20 cm depth. The FTIR and fluorescence results demonstrated that corn straw returning enhanced aliphatic, hydroxyl, methoxyl and carboxyl groups and simplified HA molecular structure, indicating regenerated and newly formed HA. Among all treatments, NTS was more conducive in simplifying HA molecular structure and enhancing aliphatic and hydrophobic C. Hydrophobicity in aliphatic C is the driving force in the stabilisation of soil C, which is important for sustainable agriculture. Therefore, we conclude that NTS is the better practice to turn arable lands into a sink for C.

TL;DR: Among the four straw returning modes, Ss is the most beneficial for reducing the oxidation degree and increasing the aromatization and humification degree of subsoil HA and it was established that IR spectroscopy can estimate the complication and oxidation degree of soil HA and also evaluate its aliphaticity and aromaticity.