The temporal variation of farmland soil surface roughness with various initial surface states under natural rainfall conditions

Soil surface roughness not only affects the hydrological and erosive behavior of soils, but also influences their spectral reflectivity in the optical and microwave bands. Field measurement of soil surface roughness is time-consuming, laborious, costly, and, for vegetated areas, impractical. We attempt to find a method to predict the dynamics of soil surface roughness for various soil surface states for black soils in Northeast China. In this study, four soil surfaces with different roughness were designed, and three kinds of roughness parameters, root-mean-square height (rmsh), correlation length (cl) and rmsh/cl, of each soil surface were measured. The results of soil surface roughness were as follows: (1) a decrease over time was observed for rmsh and rmsh/cl as well as an increase in cl over time; (2) an exponential relationship was confirmed between roughness parameters (rmsh, cl, and rmsh/cl) and cumulative rainfall (CR) for soil plots without ridge, as well as for the relative change (RC) of roughness parameters and CR; (3) a significant difference in change of soil surface roughness with CR existed for soil surfaces with ridge and without ridge, and a Gaussian function was more suitable for describing the dependence of soil roughness evolution on CR than an exponential function. These results indicate that the temporal change of soil surface roughness in the black soil of Northeast China could be predicted by CR based on the empirical relationship achieved in this study regardless of whether soil surface has a ridge and of different initial roughness.