Temporal Variability of the USLE Cover Management Factor (C) in Event Scale and Growth Stages of Rainfed Wheat

The C-factor of the Universal Soil Loss Equation (USLE) is used to reflect the effect of management practices on erosion rates. Information on its variations during the plant growth is important for determining the most susceptible stage in soil erosion. In this study, the temporal variability of the C-factor was determined during wheat growth period under two crop managements: row spacing (20 and 25 cm) and seed density (90 and 120 kg ha-1) in a rainfed land with slope of 10% in a semi-arid region. The C-factor was determined using the ratio of soil loss from plot cultivated with wheat to control plot with clean-tilled and continuous fallow conditions. A total of 18 plots (1.5 m × 5 m) were installed along the slope during 2015-2016. Out of 82 natural rainfall events, nine storms produced runoff and caused soil loss at the plots. Rainfall intensity varied from 2.2 to 4.5 mm h-1. The value of C-factor was varied for each storm during the growth period; so that the highest value was observed in the first storm for both row spacing (0.73) and seed density (0.72), while the lowest values for the two management factors were belong to the last storm; 0.140 and 0.145, respectively. The highest C-factors were occurred in October at the same time with the seedbed stage (0.47 and 0.48 for row space and seed density, respectively) and the lowest values found at May (0.14 and 0.14) according to the crop development stage. This study revealed that the seedbed stage is the most susceptible period for the C-factor in the two crop management methods. In conclusion, using 9-row spacing set with 25 cm row spacing along with maintaining crop residues is essential to conserve farm’s soil from water erosion and decline the C-factor in susceptible stages during wheat growth period.