Despite the well-documentation of the effects of straw returning on soil structural stability and fertility, its long-term in situ impacts on profile aggregate size composition and organic carbon (OC) fractions remain poorly investigated. To address this research gap, the present nine-year field trial explored the co-effects of straw returning and chemical fertilization on soil total OC (TOC), dissolved OC (DOC), resistant OC (ROC), easily oxidative OC (EOC), as well as soil aggregate size composition of different soil depths (0–15, 15–30, and 30–50 cm) in a paddy field, East China. To do so, four different treatments were set up, including no straw returning plus no fertilization (CK), conventional fertilization (F), straw returning plus conventional fertilization (SF), and straw returning plus 80 % conventional fertilization (SDF). Our findings revealed that the >2 mm aggregates were dominant in all treatments, particularly in SF and SDF 0–30 cm soil layers ranging from 62 to 70 % (P < 0.05). The highest TOC contents happened in SF topsoil 0.25–2 mm aggregates (0–30 cm; 21.4 g/kg), 44.4 and 21.1 % higher than the CK and F treatments, respectively (P < 0.05). Regardless of soil depth, the highest EOC contents occurred in SDF 0.25–2 mm aggregates varying from 2.36 ± 0.1 to 7.7 ± 0.57 g/kg (P < 0.05). Further, the highest ROC and DOC contents took place in SF 0.25–2 mm and SF > 2 mm aggregates, respectively, differing from 3.86 to 15.8 g/kg and 250–413 mg/kg, respectively (P < 0.05). It is also worth noting that SF had the highest crop productivity with the seasonal yields of 3.51 and 13.5 t ha⁻¹ for rapeseed and rice, respectively (P < 0.05). Altogether, our findings suggested that long-term straw returning coupled with conventional (SF) or 80 % conventional (SDF) fertilization are the most efficient schemes for the formation/stability of soil aggregates, as well as for the accumulation of different soil OC fractions and crop productivity in the Chaohu Lake agricultural soils of East China.

River water quality can be affected by a range of factors, including both point and non-point sources of pollution. Of these factors, changes in land use and land cover are particularly significant, as they can alter the structure of the landscape and consequently impact water quality in rivers. To investigate the relationship between patch shapes, a measure of landscape structure, and river water quality at the catchment scale, this study utilized spatial data from 39 catchments in the southern basin of the Caspian Sea. This study employed stepwise multivariate regression modeling to explore how changes in landscape structure, which can be measured by landscape metrics including the shape index, the contiguity index, the fractal dimension index, the perimeter–area ratio, and the related circumscribing circle, impact water quality variables. Four regression models—linear, exponential, logarithmic, and power models—were evaluated, and the most appropriate model for each water quality variable was determined using the Akaike information criterion. To validate the models, three groups of accuracy metrics were employed, and Monte Carlo simulation was utilized to analyze the models’ behavior. This study found that landscape structure metrics could explain up to 71% and 82% of the variations in the measures of TDS and Mg, respectively, and the shape index, the contiguity index, and fractal metric were particularly significant in predicting water quality. Moreover, this study verified the accuracy of the models and revealed that changes in landscape structure, such as a decline in patch continuity and an increase in patch complexity, can impact river water quality. The findings of this study suggest optimizing landscape structure metrics in land use planning to reduce river pollution and improve water quality.

Alternative fertilizers are essential to minimizing the deteriorating effects of chemical fertilizers on soil and water quality/health. Accordingly, the present work investigated the effects of combined organic–inorganic fertilization (COIF) on wheat and rice yields, soil nutrients, and soil Cd accumulation. Hence, seven different treatments were set up: control (CK); conventional fertilization (CF); adequate fertilization (OF); organic fertilizer replacing 25% (T1) and 50% (T2) of OF; and organic nitrogen (N) replacing 25% (M1) and 50% (M2) of OF-N. Overall, significant increases occurred in the yields of COIF crops. Compared with the CF, the highest wheat and rice yields happened in the M1 treatment (with a difference of approximately 18.5%) (p < 0.05). COIF slightly alleviated soil acidification, and improved the cation exchange capacity (CEC) of the study soils. Furthermore, COIF treatments significantly increased the contents of total phosphorus, total potassium, available phosphorus, and available potassium by 6.35 to 16.9%, 3.17 to 10.9%, 5.53 to 28.7%, and 2.6 to 12%, respectively (p < 0.05). Nevertheless, negligible increases took place in the Cd content of COIF soils compared with that of the CK. Altogether, our results concluded that 25% replacement of OF-N by organic N (M1) effectively improved the fertility/ecological sustainability of the study soils.

This study explored the effects and the associated processes of straw returning on soil organic carbon (SOC) and salinity in the Yalu River estuary region under river-sea mixed irrigation conditions. To do so, a field experiment was conducted via six different rates of rice straw returning: 0 kg/hm ² (CK), 2000 kg/hm ² (RF1), 4000 kg/hm ² (RF2), 6000 kg/hm ² (RF3), 8000 kg/hm ² (RF4), and 10000 kg/hm ² (RF5). The one-season experiment used rice cultivar Danjing 18. Soil samples (0–20 cm) were collected before sowing and after harvest on September 30, 2025. Overall, the results suggested that SOC and soil total nitrogen (TN) contents increased with increasing straw application rate. In particular, compared with the CK, RF5 significantly increased SOC by 13.5% (P < 0.05), while 8.3% increase in TN did not differ significantly from CK. Likewise, significant increases in soil cation exchange capacity (CEC) were observed with higher straw application rates (P < 0.05). In accordance, RF5 increased soil CEC by 19.4%, relative to the CK (P < 0.05). Meanwhile, significant increases in ion content occurred in straw-amended soils compared with the CK, with greater increases at the higher straw application rates (P< 0.05). For instance, compared with the CK, straw returning significantly increased K ⁺ (up to +83% in RF3), Ca ²⁺ (up to +> 110% in RF4), and Mg ²⁺ (up to +>100% in RF3) (P < 0.05). Significant positive correlations between SOC and TN, CEC, Ca ²⁺ , and major anions (P < 0.01) indicated that straw returning enhanced SOC accumulation by affecting salinity-related soil ion composition. Further, significant positive correlations between TN with HCO ₃ ^- and Cl ^- contents (P < 0.01), as well as with CEC and Ca ²⁺ contents (P < 0.05), suggested a close association between N dynamics and salinity-related ions. Overall, these results suggest that in situ rice straw returning enhances SOC and TN accumulation and helps regulate salinity-related ions in the Yalu River estuary, providing practical guidance for sustainable coastal paddy management.