As a constructed wetland ecosystem, paddy field plays an irreplaceable role in flood storage and detention, groundwater replenishment, environmental protection, and ecological balance maintenance. New paddy field construction can give full play to the production and ecological functions of paddy field and can adjust the development structure of the agricultural industry effectively. The soil properties of shear strength and permeability, which provide a theoretical basis for engineering design, construction, and post-operation, are important indexes in the site selection of new paddy field. The shear strength and permeability properties of soils from different land use types (vegetable field, gentle slope dryland, corn field, grapery, and abandoned dryland) for engineering new paddy field construction were investigated in this study. The results showed that the soil water content had a significant effect on the soil shear strength, internal friction angle, and cohesion. The total pressure required for soil destruction decreased with increasing water content under the same vertical pressure, resulting in easier destruction of soils. The internal friction angle decreased with increasing soil water content, and the soil cohesion first increased and then decreased with increasing soil water content. Considering that paddy fields were flooded for a long time, the soil strength properties had certain water sensitivity. Effective measures must be taken to reduce the change in soil water content, so as to ensure the stability of the embankment foundation, roadside ditch foundation, and cutting slope. In addition, the influence of changing soil water content on the strength properties of paddy soils should be fully considered in engineering design and construction, and the soil bulk density at the plough pan should reach at least 1.5 g cm⁻³ or more to ensure better water retention and the anti-seepage function of paddy field. The study can provide construction technology for engineering new paddy field construction in a hilly mountainous region of southwestern China.

Ridge tillage is one of the essential tillage methods in China. It affects the soil structure by altering the soil-water environment. With the rapid development of agricultural mechanization, the mechanized ridge tillage technology that combines modern mechanized agriculture with conservation tillage has become a pertinent agricultural production technology in the hilly regions. However, to date, the effects of mechanized ridge tillage on soil structure have garnered little attention. In this study, a field plot experiment involving the following four treatments: conventional tillage with rice and winter fallow (CK1), conventional tillage with rice-rape rotation (CK2), wide ridge tillage with rice-rape rotation (BT), and narrow ridge tillage with rice-rape rotation (RT) was conducted to study the effects of mechanized ridge tillage with rice-rape rotation on soil aggregate stability and soil porosity. The results indicated that mechanized ridge tillage could reduce the porosity of pores > 30 μm in diameter and increase the porosity of pores < 0.5 μm. Furthermore, mechanized ridge tillage could increase soil aggregate stability; the order of average mass diameter and geometric average diameter was RT > BT > CK2 > CK1. The BT and RT treatments could increase the agglomeration degree of the soil particles, which followed the order of RT > BT > CK2 > CK1. Therefore, mechanized ridge tillage with rice-rape rotation is effective in enhancing soil structure.

High-intensity utilization of sloping farmland causes serious soil erosion and agricultural non-point source pollution (AGNSP) in the Three Gorges Reservoir Area (TGRA). Crop-mulberry systems are important agroforestry systems for controlling soil, water, and nutrient losses. However, there are many different mulberry hedgerow planting patterns in the TGRA. In this study, soil structure, nutrient buildup, and runoff nutrient loss were observed in field runoff plots with five configurations: P1 (two longitudinal mulberry hedgerows), P2 (two mulberry contour hedgerows), P3 (three mulberry contour hedgerows), P4 (mulberry hedgerow border), and P5 (mulberry hedgerow border and one mulberry contour hedgerow), as well as a control (CT; no mulberry hedgerows). P1 had the smallest percentage of aggregate destruction (18.8%) and largest mean weight diameter (4.48 mm). P5 led to the greatest accumulation of ammonium nitrogen (NH₄⁺–N) and total phosphorus (TP) (13.4 kg ha⁻¹ and 1444.5 kg ha⁻¹ on average, respectively), while P4 led to the greatest accumulation of available phosphorus (AP), nitrate nitrogen (NO₃⁻–N), and total nitrogen (TN) (114.0, 14.9, and 1694.1 kg ha⁻¹, respectively). P5 was best at preventing soil erosion, with the smallest average annual runoff and sediment loss of 112.2 m³ ha⁻¹ and 0.06 t ha⁻¹, respectively, which were over 72.4% and 87.4% lower than those in CT, respectively. P5 and P4 intercepted the most N in runoff, with average NH₄⁺–N, NO₃⁻–N, particulate N, and TN losses of approximately 0.09, 0.07, 0.41, and 0.58 kg ha⁻¹, respectively, which were 49.7%, 76.2%, 71.3%, and 69.9% lower than those in CT, respectively. P5 intercepted the most P in runoff, with average TP and total dissolved phosphorus (TDP) losses of 0.09 and 0.04 kg ha⁻¹, respectively, which were 77.5% and 70.4% lower than those in CT, respectively. Therefore, the pattern with one mulberry hedgerow border and one mulberry contour hedgerow (P5) best controlled AGNSP, followed by that with only a mulberry hedgerow border (P4).

It is of great significance to determine soil aggregate stability in predicting agricultural production conditions and soil erosion risk. However, the problem exposed in the process of evaluating soil aggregate stability cannot be ignored: Can the effects of different mechanisms on the degree of soil aggregate breakdown be distinguished by selecting ethanol and water as dispersion media? Based on this question, natural soils with a gradient in soil textures of silty loam to loamy clay were used as the test materials. Deionized water, ethanol and hexane were employed as soaking solutions to quantitatively analyze the extent to which the aggregates were dispersed in static disintegration experiments. The results suggested that the soil hydrophilicity (SH) of six soils with a texture gradient were >1 by comparing the aggregate breakdown index (ABI) of soils undergoing ethanol and hexane dispersion. This indicated that the hydrophilic group (-OH) contained in ethanol interacted with the hydrophilic surfaces of the soil particles. Therefore, the soil hydrophilicity (hydration) should be determined by comparing the ABI values undergoing hexane and water dispersion. From silty loam to loamy clay, the average contribution of hydration to aggregate fragmentation decreases, and the process of aggregate breakdown with different textures is characterized by size selectivity. When the soil aggregates were fragmented into 2–0.25 mm aggregate fractions, for silty loam and sandy clay loam, 0.002–0.02 mm and 0.002 mm particles were preferentially moved. When the soil aggregates were fragmented into <0.25 mm aggregate fractions for soils with different textures, the 0.002–0.02 mm and <0.002 mm particles all exhibited preferential migration characteristics. This work provides an idea for improving the methods of aggregate stability measurements in the future.