Responsive of aggregate stability of meadow black soil to different tillage practices and carbon-based fertilizers

The stability and size distribution of soil aggregates is profoundly affected by tillage and fertilizers, but the influencing mechanisms of tillage and fertilizers on meadow black soil are not clear. A study was carried out to investigate and attempted to interpret the effects of short-term tillage and fertilizers on soil aggregates from types of tillage and soil properties in soil samples and size fractions of soil aggregates. Soil samples were taken from 6 treatments under deep plow (DCF) and shallow plow (SCF) with organic fertilizers (M) and biochar (C), including: DCF, DCF+M, DCF+B, SCF, SCF+M and SCF+B. The wet-sieving and dry- sieving method was used to obtain 6 size fractions of soil aggregates: >5, 5-2, >2-1, >1-0.5, >0.5-0.25, and <0.25 mm. The stability and size distribution of soil aggregates was measured as mean weight diameter (MWD), the percentage of water-stable aggregate (WSA) and percent of soil aggregate destruction (PAD), geometric mean diameter (GMD) of water-stable aggregate. The quantities of soil organic carbon (SOC), humic substances, dithionite-citrate-bicarbonate (DCB) and oxalate extractable iron (Fe) and aluminum (Al) oxides were also measured. The results showed under the MWD values of different tillage methods were significantly different, showing that shallow > deep tillage, the content range of water stable aggregates (WSA) was 80.0% to 93.5%. Compared with DCF, DCF+M, SCF, SCF+M and SCF+B, DCF+B treatment was significant lower, while the differences between the other treatments were not significant. The content of iron and aluminum oxides in different forms was 0.10-2.45 g/kg. The content of free crystalline iron and aluminum oxides was significantly higher than that of amorphous iron and aluminum oxides. The content of free crystalline iron and aluminum oxides were significantly higher than that of amorphous iron and aluminum oxides, and the trend was FeDCB＞AlDCB＞Aloxa＞Feoxa . Except FeDCB, the content of iron-aluminum oxide in DCF treatment was higher than that in DCF+B treatment. The content of Aloxa in SCF treatment was significantly higher than that in SCF+M and SCF+B, 19.35% and 12.12% respectively. The humus component (HF, HA, FA) of DCF+M in each treatment had the highest carbon content, which was 6.9, 3.9 and 3.0 g/kg, respectively, and it was significantly different from other treatments. According to RDA and partial redundancy analysis, the correlation between amorphous iron oxide and the percentage content of >0.25 mm aggregates and water-stable aggregates was higher than that of other influencing factors, and the contribution rate of amorphous iron to variation interpretation was 61.3%. Soil organic carbon content was negatively correlated with <0.25 mm, and positively correlated with the formation of large aggregates, with a contribution rate of 33.0%. Both free and amorphous aluminum oxides were positively correlated with the formation of large aggregates, and their contribution rate was 9.3%. The changes of Fe and Al oxides and organic carbon could jointly explain 74.9% of the stability and distribution of soil aggregates, 7.9% of Fe and Al oxides and 9.2% of organic carbon components, respectively. Therefore, the comprehensive analysis showed that short-term farming and charcoal fertilizer application have a significant impact on the stability of the soil structure. SCF + M and DCF + B are ideal farming models and have certain application values in the improvement of meadows black soil.