Sustainable Cropping Strategies Restor Soil Microbial Fertility in Sloped Agricultural Land in Karo Indonesia

Abstract The agricultural landscape in Merek District, Karo Regency, is dominated by sloping lands from flat to steep, cultivated with vegetables, particulary potatoes. Intensive land use and excessive chemical inputs have soil degradation and declining fertility. This study sustainable land management based on biophysical soil characteristics, focusing on nitrogen- fixing (N-fixing) microorganisms as indicators of soil fertility. A survey combining remote sensing interpretation, GIS-based land unit analysis, and microbial population assessment was employed. Soil samples were collected from the rhizosphere at a depth of 0-20 cm using a composite sampling approach across representative land- map units with uniform slopes and elevations. Microbial analysis involved the use of Jensen’s medium for total N-fixing bacteria, and Ashby’s medium for Azotobacter enumeration. Data were analyzed descriptively to interpret these biological conditions. Results showed that the crop rotation pattern (legume-potato) supported the highest abundance of N -fixing microbes (216CFU/ml) and Azotobacter (121CFU/ml), followed by intercropping (legume-potato) atwith 189CFU/ml and 78CFU/ml, respectively. Crop rotation system also maintained a higher soil pH (5.06) favorable for microbial activity. Interestingly, the intercropping system exhibited a higher proportion of gram-negative bacteria (40%), which wais associated with a lower soil pH (4.86). These findings suggest that legume-based cropping systems, particularly crop rotation, soil biological fertility by increasing beneficial nitrogen N-fixing microbes. Such practices are a promising strategy for restoring soil health and promoting sustainable potato production ion sloped agricultural lands.