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[Display omitted] • Proposed concept of an equivalent exchange layer (EEL). • Equivalent exchange model (EEM) developed for nutrient migration. • EEM accurately forecasts K+ and NH 4 +-N concentrations and amounts. • Raindrop-induced transfer rate and depth of EEL are primary variables controlling nutrient loss. • Raindrop splashing is the primary nutrient transfer pathway in the EEM. Nutrient loss from the topsoil reduces agricultural productivity and contributes to the eutrophication of water bodies like rivers and lakes. To reduce agricultural non-point source pollution, ongoing efforts must be made to develop mathematical models that can accurately forecast the process of nutrient loss and provide a theoretical foundation for developing prevention and control strategies. In this study, the concept of an 'equivalent exchange layer, EEL', which consists of an 'equivalent runoff layer' and an 'equivalent infiltration layer', was proposed. The equivalent exchange model (EEM), which describes nutrient migration from upper soil to runoff, was developed on this basis. The EEM was validated, and its parameters were calibrated using 12 sets of K+ loss data on bare slopes and 30 sets of NH 4 +-N loss data on six vegetation growths. Overall, EEM exhibited good accuracy in forecasting the process by which the of K+ and NH 4 +-N concentrations changed and as the total amount of K+ and NH 4 +-N in the runoff (R2 ≥ 0.713,RMSE ≤ 2.373 mg/L, NSE ≥ 0.701). Compared to the model developed by Shao et al. (2021) , EEM outperformed in terms of simulation performance when predicting the total amount of nutrient loss (R2 ≥ 0.963, NSE ≥ 0.911), effectively resolving the problem that the total amount of nutrient loss is overestimated. A single parameter perturbation simulation and a global sensitivity analysis revealed that the raindrop-induced nutrient transfer rate e r and the depth of the equivalent exchange layer EED were the primary variables controlling nutrient loss, while the initial ratio of the depth of the equivalent infiltration layer to the equivalent exchange layer α 0 and index m were the secondary variables accurately predicting nutrient content in the stable runoff stage. This research contributes to understanding the mechanisms underlying nutrient transfer on slopes. [ABSTRACT FROM AUTHOR]

Nearly one-half of New Zealand’s ruminant livestock graze on hill country pastures where spatial differences in soil conditions are highly variable and excretal deposition is influenced by pasture production, animal grazing and resting behaviour that impact the nitrous oxide (N 2 O) emission factor from excreta (EF 3 ). New Zealand currently uses country-specific EF 3 values for urine and dung of 0.01 and 0.0025, respectively, to estimate direct N 2 O emissions from excreta. These values have largely been developed from trials on flat pastoral land. The use of the same EF 3 for hill pasture with medium and steep slopes has been recognised as a possible source of overestimation of N 2 O emissions in New Zealand. The objectives of this study were to develop and describe an approach that takes into account the effects of slope in estimating hill country N 2 O emissions from the dung and urine of ruminant animals (sheep, beef cattle, and deer) across different slope classes, and then compare these estimates with current New Zealand inventory estimates. We use New Zealand as a case study to determine the direct N 2 O emissions between 1990 and 2012 from sheep, beef cattle and deer excreta using updated estimates of EF 3 for sloping land, the area of land in different slope classes by region and farm type, and a nutrient transfer model to allocate excretal-N to the different slope classes, and compare the changes between these hill pastures-specific and current inventory estimates. Our findings are significant – the proposed new methodology using New Zealand specific EFs calculated from a national series of hill country experiments resulted in 52% lower N 2 O estimates relative to using current inventory emission factors, for the period between 1990 and 2012 and reduces New Zealand’s total national agricultural N 2 O greenhouse inventory estimates by 16%. The improved methodology is transparent, and complete, and has improved accuracy of emission estimates. On this basis, the improved methodology of estimating N 2 O emission is recommended for adoption where hill land grasslands are grazed by sheep, beef cattle and deer. [ABSTRACT FROM AUTHOR]

• Proposed an efficient method for controlling soil erosion and nutrient loss. • Improved the application effect of biochar by nanotechnology. • Nano-biochar and vegetation cover have better soil amendment effect. The effects of biochar on soil erosion and nutrient loss on the Chinese Loess Plateau have been well reported, but the huge required application rate of biochar limits the biochar use. The specific nano-treatment can improve the distribution and properties of biochar (e.g., increase the specific surface area). To investigate the migration processes of runoff, sediment and nutrients on the nano-biochar (NB) applied sloping land during rainfall events, different mass content of NB (0.0%, 0.1%, 0.5%, 0.7%, and 1.0%) were used on the three types of vegetation covered sloping land (bare, caragana, and maize). The effects of NB and vegetation on runoff volume, sediment yield, and nitrate loss were studied under simulated rainfall in the northeastern region of the Loess Plateau. The main results were as follows: the application of NB effectively reduced runoff (39.7–74.4%), sediment yield (8.9–41.8%), and nitrate loss (13.6–59.8%) in all treatments. Losses of nitrate in runoff and sediment were negatively correlated with increased content of NB (when NB application rate was 1.0%, the maximum nitrate loss in runoff and sediment were 27.43 and 6.25 mg, respectively). The equivalent model of convection was more suitable for analyzing the nutrient transfer process with the application of NB. The effective mixing depth decreased with NB content and could be well described by a power function. NB might promote the nitrate migrate to deep soil and reduce nitrate loss in runoff and sediment. With NB application, the peak value of nitrate distribution in the profile moved downward, and the maximum value was obtained at 10–15 cm. Moreover, the most effective NB content for reducing nitrate loss were 1.0%. Comparing with bare and maize, caragana had the most significant effect on reducing runoff, sediment and nutrient loss. In addition, Synergistic effect of NB and caragana showed the great potential on soil and water loss control. The findings in this study provide an efficient and economic method for controlling soil erosion and nutrient loss on the Chinese Loess Plateau. [ABSTRACT FROM AUTHOR]