Abstract
A three-year field experiment was conducted to analyze the effects of straw enrichment and deep incorporation on the humus composition and the structure of humic acid (HA) in black soil. The differences in the HA structure between different straw returning methods were detected by three-dimensional fluorescence spectroscopy and 13C NMR technology. The purpose of this paper is to provide a theoretical basis and data support for improving the straw returning system. Four different treatments, including no straw applied (CK), straw mulching (SCR), straw deep ploughing (MBR), and straw enrichment and deep incorporation (SEDI: harvested the corn straw from four rows together with a finger-plate rake and then crushed and buried them in one row in the 20∼40 cm deep level in the subsoil with a wind-driven input cylindrical plough), were used in this study. Our results showed that compared to CK treatment, SEDI significantly increased the contents of organic carbon (SOC), soil humic acid carbon (HAC), fulvic acid carbon (FAC), and humin C content (HM-C) in the subsurface soil layer by 27.47%, 34.33%, 19.66%, and 31.49%, respectively. Among all the straw returning treatments, SEDI treatment had the most significant effect in increasing the contents of HEC, HAC, and FAC. Straw returning not only reduced the degree of condensation and oxidation of the HA structure but also increased the proportion of alkyl C and enhanced the hydrophobicity of the HA structure in subsurface soil. Moreover, SEDI treatment significantly increased the proportion of aliphatic C/aromatic C of the HA structure in subsurface soil and improved the aliphatic property of HA, which had a significant effect on the HA structure compared to other treatments.
Highlights
In recent years, due to long-term intensive agricultural production and soil erosion, the soil organic content and humus quality of black soil have decreased significantly in Northeast China, resulting in shallower soil layers [1] and poor cultivability of land
A new straw returning method had been developed, namely, straw enrichment and deep incorporation (SEDI), consisting in (1) raking the corn stalk in the field together into rows at a ratio of 4 : 1 with a International Journal of Analytical Chemistry finger-plate rake; (2) crushing the corn straw and burying it into subsoil, 20∼40 cm deep along designated strips with a wind-driven input cylindrical plough; (3) sowing seeds into the strips with no straw buried in between the strips with straw buried in a normal way with a nontillage seeder, to realize separation of the seeded strips from the strips with straw buried in a wide-andnarrow row alternating cultivation mode
CK: no straw was applied; SCR: corn straw was evenly placed on the soil surface; MBR: corn straw was evenly placed on the soil surface, and straw deep turning and returning to the field to 25–30 cm soil layer; SEDI: the corn straw was harvested from four rows together with a fingerplate rake and crushed and buried them in one row in the 20∼40 cm deep level in the subsoil with a wind-driven input cylindrical plough. e corn straw was mechanically crushed in all three corn straw treatments. e experiment selected field planting; each treatment area was 1334 m2
Summary
Due to long-term intensive agricultural production and soil erosion, the soil organic content and humus quality of black soil have decreased significantly in Northeast China, resulting in shallower soil layers [1] and poor cultivability of land. Corn straw incorporation was effective in increasing soil organic carbon [2] and humus C content [3], deepening the degree of soil humification [4], and improving the HA structure. Returning straw to the field can improve soil fertility and increase the content of soil organic matter. Straw deep incorporation can significantly increase the content of soil subsurface active organic carbon [13], deepen the degree of soil humification [14], reduce the degree of HA structure condensation and oxidation, and increase the content of aliphatic chain hydrocarbons and aromatic carbon. Zhang et al have shown that straw deep incorporation accumulates soil organic carbon and humus component carbon content in different soil layers and improved the aromaticity and hydrophobicity of HA molecules [15]. Chen Xi et al showed that straw returning could increase the relative content of alkoxy carbon in soil organic carbon through 13C NMR research [17]
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