Background Gully erosion damaging farmland is a key challenge for the conservation of black soil in China. Current research primarily focuses on the damage caused by permanent gullies, the quantitative understanding of farmland damage caused by ephemeral gullies is insufficient, and the relationship between such damage and the morphological characteristics of ephemeral gullies remains unclear, posing a significant challenge in gully erosion control. Therefore, this study selects two sub-watersheds, one managed and one unmanaged, in the Heilongjiang Nenjiang Hebei small watershed as the research area.

Methods Taking the erosion gullies in two sub-watersheds of Hebei as the research subjects. Utilizing high-resolution UAV imagery and precise field cross-section measurements from 2022 to 2023, combined with manual visual interpretation, the research quantitatively analyzed the relationship between the morphological characteristics of ephemeral gullies and the area of damaged farmland.

Results 1) The total area of farmland that is potentially affected by erosion gullies, as well as the specific area of farmland that has become so severely damaged that crops are unable to grow under these conditions, account for 32% and 0.258% of the total farmland area within the watershed, respectively. Notably, the area of farmland that is directly affected by ephemeral gullies constitutes 31% of the overall area affected by gully erosion. In watersheds where management interventions have been implemented, the area of farmland damaged by ephemeral gullies is reduced by 38% compared to those in non-managed watersheds. In 2022 and 2023, the area of farmland damaged by ephemeral gullies in plots planted with soybeans was 2.17 times and 2.03 times larger, respectively, than the corresponding areas in plots planted with corn. 2) From the perspective of ephemeral gully cross-sections, the width of farmland that is damaged by ephemeral gullies is on average 2.21 times the width of the ephemeral gullies themselves. Significant positive correlations were observed between the width, depth, cross-sectional area, and width-depth ratio of ephemeral gullies and the width of the damaged farmland (P < 0.05). Among these factors, the width of the ephemeral gullies exhibits the strongest linear relationship with the width of the damaged farmland. 3) From the overall perspective of ephemeral gullies, the interaction between the average width and length of the ephemeral gullies is identified as having the highest importance in determining the extent of damaged farmland, with a strong linear correlation between these variables.

Conclusions This study demonstrates that the farmland area damaged by ephemeral gullies is a significant component of gully-induced farmland loss in the black soil region of Northeast China and should not be overlooked, there exists a linear correlation between the morphological parameters of ephemeral gullies and the extent of farmland damage, and the findings from this research can significantly improve the accuracy of assessing areas affected by gully erosion, thereby supporting the national strategy for the conservation of black soil and ensuring food security.