ABSTRACT
In view of the current situation of black soil degradation, straw return as an important conservation tillage measure has been extensively promoted. Based on 15N tracing technology, this paper carried out experiments of different straw returning modes, including CK (conventional fertilizing tillage with straw-free returning), straw mulching (i.e., M), straw mixed with topsoil (i.e., T), and straw deep incorporation (i.e., D), to explore the influence of straw returning on the distribution and stability, and the carbon and nitrogen content of water-stable aggregates in black soil, and to analyze the distribution and stability of aggregates on the carbon and nitrogen content of aggregates. The results showed that the macroaggregate content, mean weight diameter (MWD) and geometric mean diameter (GMD) of the returned soil layers were 16.53-84.65%, 16.73-128.73% and 23.47-97.14% higher than those in CK, respectively. The contents of organic carbon, total nitrogen and 15N accumulation of aggregates in the straw-returning soil layer were 6.38-23.55%, 8.65-31.19% and 13.52-150.19% higher than those in CK, respectively. Pearson correlation analysis and redundancy analysis showed that the content of macroaggregates and stability of aggregates were positively correlated with the carbon and nitrogen contents. In conclusion, straw return significantly improved soil structure characteristics and carbon and nitrogen content. The results of this study provided a theoretical basis and technical guidance for farmland soil improvement in black soil areas, and selected an appropriate straw returning mode according to local soil conditions to maximize the effect of straw returning.
Key words
returning modes; 15N; redundancy analysis; C/N
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CK: conventional fertilization and cultivation without straw return; M: corn straw mulching; T: corn straw mixed with topsoil; D: corn straw deep incorporation.
*Columns represent means (n = 3) and bars represent the standard deviation; means with the same letter within groups are not significantly different at P < 0.05. Different lowercase letters indicate that the difference among treatments of each grain size at each depth reaches a significant level (P < 0.05), and different capital letters indicate that the difference among depths of each grain size at each treatment reaches a significant level (P < 0.05); CK: conventional fertilization and cultivation without straw return; M: corn straw mulching; T: corn straw mixed with topsoil; D: corn straw deep incorporation.
RDA: redundancy analysis; *> 2: > 2 mm aggregate content; 2-0.25: 2-0.25-mm aggregate content; 0.25-0.053: 0.25-0.053-mm aggregate content; < 0.053: < 0.053-mm aggregate content; > 0.25: > 0.25-mm aggregate content; MWD: mean weight diameter; GMD: geometric mean diameter; AOC: aggregate organic carbon; AOCS: aggregate organic carbon stock; TN: total nitrogen content of aggregates; 15N: 15N accumulation of aggregates.