Research for standard of erosive rainfall on Quaternary Red Soil area in north of Jiangxi province in China

Abstract: Rainfall is regarded as one of the principal dynamic factors of soil erosion. The attainment of an erosive rainfall standard is acknowledged as the essential part in calculating rainfall erosivity. At present, results of research for an erosive rainfall standard are diverse in the red soil area. Hence, it deserves to be studied to a further extent. On the basis of the observation of runoff plots, the standard of erosive rainfall was comparatively analyzed under different soil and water conservation measures employing five types of underlying surface in the Quatenary red earth area of Northern Jiangxi province, including bare surface, citrus with cross-slope cultivation, citrus with clean cultivation, citrus with bahia grass covering, citrus with bench terrace with grass planted on the wall and mound before but ditch behind. Viewing it from the perspective of energy, this study sought for the standard amount of erosive rainfall with the indicator of EI30 and the standard intensity of erosive rainfall with the indicators of EI10、EI20、EI30、EI45、EI60 with reference to the rainfall amount and intensity of 1359 times during the period of 2001-2009 and the corresponding data of runoff and sediment observed on the condition of different soil and water conservation measures with five above-mentioned types of underlying surface. Compared with slope lands of bare surface and citrus with clean cultivation as a control, the study elaborated the feature of an erosive rainfall standard for citrus with soil and water conservation measures. The results of this study were intended to reveal the reduction mechanisms of runoff and sediment for red-soil slop lands under soil and water conservation measures, to provide a data basis for the enhancement of the local forecast accuracy for soil erosion and water loss and to supply scientific evidence for regional soil and water conservation planning at the same time. The conclusions of the study can be drawn as follows: 1) There were significant discrepancies in the length of the data sequence of different underlying surface when satisfying the proposed standard of erosive rainfall and the length of data sequence satisfying the proposed erosive rainfall standard is capable of revealing the time period which was required from the implementation of soil and water conservation measures to its production of stable benefits; 2) The underlying surface with soil and water conservation measures is effective enough to raise the amount standard of erosive rainfall, illustrating like the standard amount of erosive rainfall observed from the fifth plot employing citrus and bench terrace with grass planted on the wall and mound before but ditch behind was 16.2 mm, increasing 42.1% in comparison with the standard amount of erosive rainfall of 11.4 mm observed from the bare surface plot; 3) It is advisable to apply a standard intensity of erosive rainfall to the underlying surface with a high stability or without soil and water conservation measures, while with regard to those underlying surface with low stability, the standard amount of erosive rainfall is considered to be more suitable to employ. The results of this study may provide a reference for the planning of soil and water conservation in Quaternary Red soil area.