The Influence of Topographic Factors and Ridge Tillage Methods on Soil Nutrients and Fertility Index of Sloping Arable Land in the Black Soil Region

This study aimed to investigate the impact of different topographic factors (such as slope position and slope gradient) and ridge tillage methods (such as transverse ridge tillage and longitudinal ridge tillage) on soil nutrient content and fertility indexes of sloping arable land, which would provide a scientific basis for selecting the ridge tillage method and maintaining soil fertility of sloping arable land in this region.

The study was conducted on a typical long, gentle slope arable land in Hongxing Farm, Bei’an City, Heilongjiang Province. Grid-based sampling was conducted in plots with two different ridge tillage methods (transverse ridge tillage plot, 18 points; longitudinal ridge tillage plot, 11 points). Comparative analysis was carried out to assess the effects of slope position and slope gradient on soil nutrient contents and the Soil Fertility Index (SFI) under the two ridge tillage methods. Analysis of variance (ANOVA) was used to test the impact of topographic factors, ridge tillage methods, and their interactions on the differences in soil nutrient spatial distribution between the two plots. Finally, variance partitioning analysis (VPA) was used to quantify the contribution of each factor to the explanatory degrees of SFI.

The differences in soil nutrient content and fertility index between the two plots were significant. The mean values of soil organic matter, total nitrogen, total phosphorus, total potassium, effective phosphorus, and available potassium were all significantly higher in the transverse ridge tillage plot compared with the longitudinal ridge tillage plot. However, the pH value was significantly lower in the transverse plot than that in the longitudinal plot. Consequently, the SFI of the two plots was ranked as follows: transverse ridge tillage>longitudinal ridge tillage (P<0.05). Slope position and slope gradient significantly influenced the spatial distribution of soil nutrients in plots with different ridge tillage methods, resulting in significant differences in the explanatory degree of each influencing factors on SFI variation between the two plots. In the transverse ridge tillage plot, the slope gradient differences caused by the micro-terrain (explanatory degrees, 32.62%) were the main drivers of soil nutrient differentiation. In this plot, soil total and effective phosphorus decreased as the slope increasing. In the longitudinal ridge tillage plot, soil organic matter, total nitrogen, and total phosphorus were the highest at the middle slope, and soil organic matter, total nitrogen, total potassium, effective phosphorus, and available potassium initially decreased and then increased with rising slope. In this plot, the slope position (explanatory degrees, 6.81%) and slope gradient (explanatory degrees, 7.22%) influence the distribution of soil nutrients. A comprehensive analysis of the SFI across the entire slope surface revealed that ridge tillage method had the highest explanatory degrees for the spatial variation of SFI (15.46%), followed by slope position (9.54%). The combined explanatory degree of the interaction between ridge tillage method and the two topographic factors, slope gradient and slope position, was 9.49%.

Topographic factors played a key role in soil nutrient migration in sloping arable land, and the impact of each factor (slope gradient and slope position) varied significantly under different ridge tillage methods. In transverse ridge tillage, slope differences caused by internal micro-terrain helped retain soil nutrients, while in longitudinal ridge tillage, slope gradient and slope position influenced the spatial differentiation of soil nutrients. Across the entire slope surface, the contribution of ridge tillage method to the spatial variation in soil fertility was greater than that of topographic factors. Therefore, the management of black soil sloping farmland needed to consider the combined effects of ridge tillage methods and topography.