Introduction: Granulated straw incorporation is a novel approach designed to enhance straw decomposition and improve soil fertility. However, the effects of different straw incorporation amounts under deep tillage and rotary tillage on soil available nutrients, soil organic carbon (SOC) fractions, bacterial communities, and crop yield remain unclear.Methods: In a 3-year field experiment, three granulated maize straw amounts (G1, 2,250; G2, 4,500; and G3, 6,750 kg hm⁻²) and two tillage methods (T, deep tillage; and R, rotary tillage) were applied to evaluate their impacts on SOC fractions, available nutrients, bacterial communities, and flue-cured tobacco yield.Results and Discussion: Compared with conventional tillage (RG0), granulated straw incorporation significantly increased SOC content. Over the 3 years, the SOC content in the 0–20 and 20–40 cm soil layers increased by 4.40%–23.46% and 5.36%–39.21% (p < 0.05), respectively. Moreover, the incorporation of higher straw amounts significantly increased the content of dissolved organic carbon (DOC) and microbial biomass carbon (MBC). Specifically, the RG3 treatment significantly increased DOC content in both soil layers in 2016 and 2017, while TG3 showed the greatest increase in 2018. In addition, RG2 and RG3 consistently enhanced MBC content across both layers throughout the 3 years. During the tobacco growing period, soil ammonium nitrogen (NH₄⁺–N), nitrate nitrogen (NO₃⁻–N), and available potassium (AK) contents increased with higher straw amounts in both soil layers. The RG2 treatment notably enhanced the bacterial α diversity and increased the relative abundance of phyla Firmicutes and Gemmatimonadota in the 20–40-cm layer. Network analysis identified AK as a key nutrient influencing bacterial community structure under both tillage methods. Structural equation modeling further revealed that SOC fractions were primarily regulated by nutrient factors under rotary tillage, while under deep tillage, bacterial richness and AK played dominant roles. To improve soil quality and crop productivity, the incorporation of a medium amount of granulated straw combined with rotary tillage is recommended as a sustainable practice for flue-cured tobacco cultivation.

In China, increasing the quantity and quality of total carbon and nitrogen stocks in sandy soil used for crop production is an important research issue. Soil amendment with pelletized straw could improve both soil physical structure and fertility in sandy soils, but these aspects remain understudied. The present pot and field experiments examined the dynamic changes in sandy soil water holding capacity, soil bulk density, soil total carbon and nitrogen stocks, and the distribution of water-stable aggregates and soil total carbon stocks related to aggregates across the following treatments: no fertilization (i.e., study control (CK)), normal fertilizer rate (NM), soil amendment at 150 Mg ha⁻¹ (S150), manure amendment at 150 Mg ha⁻¹ (M150), pelletized straw amendment at 75 Mg ha⁻¹ (PS75), and pelletized straw amendment at 150 Mg ha⁻¹ (PS150). The results show that the pelletized straw incorporation significantly increased water holding capacity and decreased soil bulk density. PS150 notably increased the large macroaggregates (>2000 μm) proportion and decreased the ratio of <250 μm aggregate size fractions in comparison with CK, NM, S150, and M150 at 0–20 and 20–40 cm soil depths. Compared with the CK treatment, the bulk soil carbon and nitrogen stocks in the 0–20 cm layers under the PS150 treatment were significantly increased by 85.2% and 302.9%, and in the 20–40 cm layers those increased by 136.4% and 257.1%, respectively. The PS150 treatment resulted in higher soil organic carbon (SOC) and particulate organic carbon content than the CK and PS75 treatments, whereas the PS75 treatment achieved maximum soil inorganic carbon content. The pelletized straw treatment increased the large macroaggregate-associated soil total carbon content at 0–20 and 20–40 cm soil depths. The maximum soil total carbon stocks were in the small macroaggregates (250 < WSA < 2000 μm) rather than in the large macroaggregate and microaggregates under the PS75 and PS150 treatments. Additionally, the pelletized straw and manure amendments increased the yield of silage corn, which was dependent on the increase in soil total carbon and nitrogen content in the macroaggregates, whereas the soil and manure amendments did not facilitate sandy soil aggregation and soil total carbon stock increases. In conclusion, PS150 was found to be the optimal amendment for maintaining sandy soil profile physico-chemical properties through macroaggregate stabilization. These results will be beneficial for arid and semi-arid regions, thus contributing to soil carbon and nitrogen conservation.

An addition of straw interlayer in the 0.40 m soil depth could effectively reduce salt accumulation in the surface soils by regulating water fluxes, thus mitigating the salt stress to the crop growth and development. However, the positive effects of straw interlayer were weakened with straw decomposition, and whether we could use sand (an indecomposable substance) instead of straw for saline soil amelioration still needs further investigation. Therefore, a three-year field experiment was established with straw and sand interlayers, as well as with no interlayer as a control. Straw interlayer demonstrated an increase of 4.85~13.10% of water content, while the sand interlayer increased 12.41~16.48% of water content in the soil layer of 0–0.40 m depth comparing to the control. Salt contents were lowered by 10.69~17.01% in the same soil layer of the straw interlayer and lowered by 7.00~7.59% in the sand interlayer treatment after irrigation. Data also shows that irrigation significantly increased water content and lowered salt accumulation in the soil plough layer, thus increasing the sunflower emergence rate of 10.49~13.54% in the straw interlayer treatment and 12.53~14.78% in the sand interlayer treatment, respectively. Both the straw interlayer and sand interlayer treatments effectively reduced the evaporation of groundwater and established a beneficial plough layer with a lower salt accumulation throughout the sunflower growth period. At harvesting stage, the evaporation fluxes of salt in the straw interlayer and sand interlayer treatments were significantly lower than that in the control treatment. Lower salt accumulation conferred a beneficial promotion for the growth of sunflower, while the grain yields in the straw interlayer treatment were increased by 8.67% in 2018, 11.00% in 2019 and 17.37% in 2020 compared to the no-interlayer soil, respectively. However, the low water content in the soil layer of 0–0.40 m depth in the sand interlayer treatment inhibited the growth of sunflower, resulting in a significant decrease in the seed yields. It is worth noting that the precipitation effectively alleviated water stress on the sunflower at the middle and late growth stage in the sand interlayer treatment. This study suggests that a maize straw burial of 0.05 m thickness at a depth of 0.40 m soil layer could be used as an effective tillage practice that could improve the distribution of water and salt in saline soils.