By the experiments of simulated rainfall

the effects of straw mulching on nitrogen and phosphorus loss and runoff shear force were studied. Soil plots (1.5 m length × 0.5 m width × 0.3 m height) and rainfall intensity (2.0 mm/min) and slope gradient (20°) were established. Latosolic red soil was selected. The results showed that: (1) Straw mulching significantly decreased sediment yield and runoff volume

the benefit was 69.3% in sediment yield

and 99.2% in runoff volume. The infiltration rate of soil was improved at 32%

so straw mulching could conserve soil and water significantly. (2) Straw mulching significantly decreased the loss of runoff-associated total nitrogen

particulate nitrogen

dissolved nitrogen and total phosphorus

dissolved phosphorus

particulate phosphorus

and the loss benefits were more than 74% in nitrogen more than78% in phosphorus. The runoff-associated dissolved nitrogen and phosphorus loss were greater than the particulate nitrogen and phosphorus loss. Straw mulching reduced the runoff-associated phosphorus loss greater than that of nitrogen. (3) Cubic equations were established between runoff shear force per unit area per unit time and runoff-associated nitrogen and phosphorus loss rates and sediment yield rates

and the preliminary inference indicated that runoff shear force was the main dynamic factor of soil erosion. (4) The critical starting runoff shear force was 2.8 N m-2 under straw mulching

and 1.5 N m-2 under non-straw mulching.