Effects of tillage measures on soil loss
Both Hr and Cm could alleviate soil erosion, mainly by improving the microtopography to increase soil surface roughness (Rodríguez-Caballero et al., 2012; Vermang et al., 2015), and improve soil physico-chemical properties. Moreover, Vr should be circumvented as it augments both soil loss rate and amount (Kader et al., 2017; Mulumba & Lal, 2008).
When there was no ridge rupture during the rainfall, Hr effectively reduced sediment yield and soil loss rate, as shown in previous studies (García-Orenes et al., 2012). However, after ridge rupture, the impacts on sediment loss were much more severe than on runoff, e.g., the runoff rate was amplified 22.6 times compared to its neighboring point, while the sediment loss rate was amplified 94.7 times after ridge rupture occurred in Hr under a rainfall intensity of 100 mm h-1. This outcome may have occurred because the broken ridges, which were normally big soil blocks, were prone to being directly swept and, thus, lost via runoff (Xu et al., 2018). The residual ridge remaining to be washed continuously by runoff would also increase the sediment concentration in runoff after the ridge rupture, leading to a higher soil loss rate. Soil loss would be further amplified if ridge rupture occurred in the top section of the plot and thus likely triggered successive ruptures.
Our study found that Cm was more reliable than Hr in controlling soil loss (Kader et al., 2017; Prosdocimi et al., 2016b), as it could restrict both the sediment yield and soil loss rate to very low levels (García-Orenes et al., 2012). The reason might be that the flow could accumulate sufficient power to detach and transport particles with mulching (Mannering & Meyer, 1963; Poesen & Lavee, 1991). In addition, Cm could postpone the soil loss rate that increasingly responded to rainfall intensity enhancement, which is an important effect on soil erosion because rainfall has a short duration but high intensity during the maize seeding stage in Northeastern China (Sun et al., 2000; Zhang et al., 2010). This postponing effect would counteract or even eliminate the instantaneous serious destruction due to torrential rain. Hence, Hr+Cm significantly prevented soil loss, especially under light rainfall intensity conditions, and thus, in practice, should be suggested to reduce soil erosion.