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Highlights • Heavy rainfalls are major causes for severe soil erosion and nutrient losses. • Soil management measures can reduce runoff, sediment and associated nutrient losses. • TN and TP were mainly transported by sediment particles <0.05 mm fractions. • Straw mulch is most efficient soil and water conservation measure. Abstract Heavy rainfall becomes more variable and erratic in the subtropical areas, increasing unpredictable risks of soil erosion and nutrient losses on the sloping farmland. Soil management practice also plays an important role in soil erosion. However, the effects of management practices on soil erosion and nutrient losses in response to heavy rainfall remain uncertain. A field study was carried out under natural rainfalls, including five treatments: bare land as control (CK), downslope tillage (DT), hedgerows with downslope tillage (DT + HG), contour ridge tillage (CT) and straw mulch (SM). The effects of management measures on runoff depth, sediment yield and nutrient losses were evaluated during peanut growth. The results indicated that heavy rainfalls caused severer soil erosion and nutrient losses. Significantly reduced runoff and sediment loss were found in all the conservation measures (p < 0.05). Compared with CK, the runoff depths under DT, DT + HG, CT and SM were reduced by 10%, 37%, 49% and 81% respectively under heavy rainfalls. In addition, sediment loss under DT, DT+HG, CT and SM were 30.81, 7.42, 1.83 and 1.34 Mg ha−1, respectively. These values were 42%, 86%, 97% and 97% lower than that for CK, respectively. TN and TP losses were mainly controlled by sediment yield. The majority of nutrient losses occurred in the particulate fraction (93% of TN and 99% of TP). Generally, much of the TN and TP were transported by the particles <0.05 mm. Over 51% of TN was transported by fractions of <0.05 mm in CK and DT sediments under heavy rainfalls; in CT and SM, this percentage increased to 61% and 74%, respectively. The findings indicated that straw mulch is the most cost-effective management measure to control soil and nutrient losses in sloping farmland of southern China. [ABSTRACT FROM AUTHOR]

Abstract: Suspended sediment transport into Laguna Lake (Philippines) due to soil erosion from agricultural activities in the Pagsanjan–Lumban catchment is of great concern because of its impacts on water quality. The Pagsanjan–Lumban catchment contributes about 18–20% of the total freshwater inflows to the lake but represents only 10% of the catchment area. In this study the suspended sediment transport model, SedNet, was used to assess the relative impacts of changes in land use within the catchment on the quantities of suspended sediment discharged to the lake. The SedNet model predicted the total suspended sediment supply from the Pagsanjan–Lumban catchment (280km2) to be 231.2kt/y of which almost 70% was predicted to come from Balanac River, 23% from Bombongan River and the remaining 7% from the catchment downstream of these two river systems. Overall, the suspended sediment supply was predicted to decrease by 8% for every 20% of intercropped coconut plantations converted to forest. A greater reduction in the total suspended sediment yield discharging to the lake was predicted when reforestation was targeted at the steep slopes (<6.6°) than when reforestation was untargeted (20% reduction compared with approximately 7%). The major limitation with the application of the SedNet model for this work was the limited availability of input data such as more detailed land use classifications (i.e. differentiating plantation into various kinds of crops, as well as different types of grass covers) and information about gullies throughout the catchment. This improved data input would provide greater accuracy and confidence in the modelling. However, the model was very useful for giving a preliminary assessment of the sources of suspended sediment transported from the catchment, and for targeting reforestation for reducing suspended sediment accessions to the lake. [Copyright &y& Elsevier]

Abstract: The application of polymer for controlling erosion and the associated nutrient transport has been well documented. However, comparatively less information is available on the effect of polymer application together with soil amendments. In this study, the effect of polyacrylamide (PAM) in combination with surface application of gypsum and Milorganite™ (MILwaukee ORGAnic NITtrogEn) biosolid for reducing sediment and phosphorus transport under laboratory rainfall simulations was investigated. The treatments considered were bare soil, gypsum, Milorganite™, gypsum+Milorganite™, PAM-coated gypsum and PAM-coated Milorganite™. Application rates for gypsum and Milorganite™ were 392kgha−1 (350lb/acre) and 726kgha−1 (650lb/acre), respectively. The PAM was coated on gypsum and Milorganite™ at an application rate of 11.2kgha−1 (10lb/acre) and 22.4kgha−1 (20lb/acre), respectively. Rain simulation experiments were conducted using a rainfall intensity of 6.0cmh−1 for 1h on a 10% slope. Surface runoff was collected continuously from each soil box over 10min intervals and leachate was collected continuously over the 60min simulation. The reduction in runoff or in leachate for all treatments was not significantly different from the bare soil control. The sediment loss for PAM coated Milorganite™ was reduced by 77%, when compared to bare soil. However, the sediment loss was not significantly reduced for any other treatment compared to bare soil. The PAM-coated gypsum was not effective for erosion control in our study, and there appears to be a correlation between effectiveness and prill size. However, the gypsum (coated and uncoated) contributed about half of the dissolved reactive phosphorus (DRP) export (in the runoff) compared to bare soil. The PAM-coated Milorgante™ reduced the DRP and total phosphorus (TP) export to 0.3–0.5 times that of Milorganite™ and to levels similar to bare soil. The decreased sediment and phosphorus export for the PAM-coated Milorganite™ treatment is a signal for a potential management practice for controlling erosion and nutrient transport in fertilized agricultural landscapes. [Copyright &y& Elsevier]

Earthworms are ecological engineers that play an important role in hydrological processes and soil erosion by their burrowing and casting activities. Little is known, however, about the ecological function of the activities of an anecic species (Metaphire guillelmi) from the Loess Plateau in China where the soil is severely eroded. We conducted rain-simulation experiments on artificial slopes (mesocosms) filled with soil from Loess Plateau. Two rain intensities (90 and 120 mm h−1) and slope gradients (5° and 15°) were used to investigate the influences of earthworm activity on runoff and soil loss under multiple conditions. Data from 15 d of earthworm activity and 1 h of rain indicated that earthworm activity significantly reduced runoff but aggravated soil erosion. Runoff initiation time increased 2.7–3.1-fold, contributing to the promotion of water infiltration, and the amounts and rates of runoff were 35.8–61.6% and 35.1–60.8% lower under earthworm activity than the controls, respectively. Earthworms greatly influenced the physical and chemical properties of the soil, and these properties were strongly correlated with runoff initiation time and cumulative runoff. The surface casts produced by the earthworms on the soil surface were completely dispersed, increasing the cumulative sediment by a maximum of 169%. Both rain intensity and slope gradient greatly influence runoff and soil detachment, but with earthworm activity, slope gradient was more influential due to its superior contribution to sediment transport. This study quantified the effects of M. guillelmi on runoff and soil erosion and provides basic data for developing a more integrated control of soil erosion on the Loess Plateau. • The increase in infiltration related to earthworm activities decreases runoff. • Soil erosion is aggravated by the low stability of surface cast under intense rainfall. • Earthworm impact on soil loss is larger at lower rain intensity and steeper slope. [ABSTRACT FROM AUTHOR]