The Importance of Slope Properties Analysis in Undulating Farmland for Sustainable Agricultural Utilization in Bompon Sub-Watershed, Central Java – Indonesia

Abstract

Tropical zones generally get evenly distributed solar radiation throughout the year. However, the slope properties in hilly areas can influence the solar radiation intensity and potentially change the tropical soil characteristics. This study aimed to measure the difference in the solar radiation intensity received by undulating slopes and to analyze its effect on the Soil Organic Carbon (SOC) stocks and Total Nitrogen (TN). The solar radiation intensity in each slope orientation was calculated using Geographic Information System (GIS) modelling and field survey. In addition, soil samples were collected from each different slope orientation at a depth of 20 cm and analyzed its characteristics associated with SOC and TN. This study found that on the east-facing slopes of the Bompon Sub-watershed, the radiation intensity was 213 minutes longer than on the west-facing slopes. The longer solar radiation intensity causes the soil on the east-facing slope tend to be drier and higher clay content as a sign of a more intensive weathering process. However, the rapid decomposition rate in warmer microclimate edaphic, such as in east-facing slopes, does not always result in low SOC and C due to farmers' organic matter input. Although the high clay content can help soils in the study area to store SOC stocks and absorb C, adding organic carbon is needed to avoid land degradation due to erosion, especially on slopes with longer solar radiation and areas lacking cover crops. These findings confirm the urgency of considering slope properties to overcome land degradation issues in tropical zones.