**1. Introduction**

Infiltration is the process of water entering soil from the soil surface [1,2]. This process is one of the most important components in the hydrological cycle and is related to many environmental problems and soil erosion [3]. It is influenced by many internal and external factors, such as rainfall characteristics, slope gradients, soil hydraulic properties, soil properties, and surface sealing, which makes infiltration hard to quantify [4].

Numerous models have been proposed for vertically homogeneous soils with constant initial soil water content and flow over horizontal surfaces for infiltration estimations [5,6], including physically-based models and empirical models [7–14]. However, these models have limited applicability under complex initial factors. Many studies have been conducted to modify the applications of these models under various scenarios and assumptions. The Green–Ampt model is one of the most widely used hydrological and erosion models, as it involves simple expression, uses few parameters, and has a specific physical meaning. The model was initially developed to simulate infiltration under ponding conditions in homogeneous soil [15]. Modifications have continuously been proposed to expand the scope of the model's application so that infiltration can be simulated under steady rainfall events [16], layered soil [17], or unsaturated soil with different slopes [18–20], as well as other conditions. The aforementioned models should be modified and improved based on a variety of scenarios to obtain the most accurate infiltration estimations.

Black soil, classified as a Haplic-Ustic sohumosol in the Chinese Soil Taxonomy and Udic Argiboroll in the U.S. Soil Taxonomy [21], is mainly distributed in Northeastern China. As this soil is rich in organic matter (OM) and appears black, it is referred to as "black soil" and the "black soil region" by local people and researchers alike [22]. The parent material of the soil contains mostly loess clay loam deposits. Due to the fine soil texture, black soil is poor in terms of permeability and is easily eroded. Coupled with the effect of seasonal variation in the region, i.e., freeze–thaw erosion in the winter and spring and rainstorm erosion in the flood season, black soil is impacted by severe runoff erosion. Erosion diminishes the OM content and soil thickness, and even induces decreasing soil productivity and environmental deterioration. It is essential to study black soil infiltration processes to prevent soil erosion.

Leaving field residues on the top of soil is a practical conservation tillage in the black soil region since there is a large annual production of crop residues. It was demonstrated that residue cover had a positive effect on soil infiltration, which increased infiltration into the soil and reduced surface runoff [19]. Although, researchers have paid much attention to the benefits of residue cover in terms of preserving soil and water and maintaining soil productivity, they have so far neglected infiltration estimation under residue cover [22,23]. Moreover, infiltration models have been mostly used for bare soils without the effects of residue cover. It is therefore necessary to modify the existing infiltration models to take into account the effects of residue cover for infiltration estimations of black soil on farmland.

In this study, the infiltration process of black soil under various rainfall intensities and residue coverages was studied with simulated rainfall. The objectives of the paper are:

