###### Abstract  
Intercropping cover crops with trees enhance land productivity and improves the soil's physio-chemical properties while reducing the negative environmental impact. However, there is a lack of quantitative information on the relationships between fine root biomass and available soil nutrients, e.g., nitrogen (N), phosphorus (P), and potassium (K), especially in the rubber-_Flemingia macrophylla_ intercropping system. Therefore, this study was initiated to explore the seasonal variation in fine root biomass and available soil nutrients at different stand ages (12, 15, and 24 years) and management systems, i.e., rubber monoculture (mono) and rubber-_Flemingia macrophylla_ intercropping. In this study, we sampled 900 soil cores over five seasonal intervals, representing one year of biomass. The results showed that the total fine root biomass was greater in 12-year-old rubber monoculture; the same trend was observed in soil nutrients P and K. Furthermore, total fine root biomass had a significant positive correlation with available N (\(p<0.001\)) in rubber monoculture and intercropping systems. Thus, it suggests that fine root growth and accumulation is a function of available soil nutrients. Our results indicate that fine root biomass and soil nutrients (P and K) may be determined by the functional characteristics of dominant tree species rather than collective mixed-species intercropping and are closely linked to forest stand type, topographic and edaphic factors. However, further investigations are needed to understand interspecific and complementary interactions between intercrop species under the rubber-_Flemingia macrophylla_ intercropping system. fontsize=,xleftmargin=2 pt,rightmargin=2 pt,rightmargin=2 pt,rightmargin=2 pt,rightmargin=2 pt,topmargin=2 pt,bottommargin=2 pt,rightmargin=2 pt,topmargin=2 pt,rightmargin=2 pt,topmargin=2 pt,bottommargin=2 pt,rightmargin=2 pt,topmargin=2 pt,rightmargin=2 pt,topmargin=2 pt,topmargin=2 pt,topmargin=2 pt,rightmargin=2 pt,topmargin=2 pt,topmargin=2 pt,right  
acidification: changes in the composition and quantity of nutrients, forest degradation, and reduced vegetation biomass [3]. Such changes in above-ground vegetation will significantly affect the below-ground properties and soil biodiversity. Fine root systems have studied the competition between soil organisms [4]. Therefore, intercropping is seen as a sustainable farm management practice. In rubber plantations of Xishuangbanna and Southeast Asia, intercropping ensures resource sustainability [5]. Amongst roots of plants, fine roots (\(\leq\)2 mm, diameter) are essential as they play a crucial role in soil nutrient dynamics [6]. Hence, understanding whether intercropping can conserve soil resources and enhance productivity and ecosystem services is important. Hence, studying differences in the growth and production of fine root dynamics of rubber monoculture and rubber intercropping can help elucidate their role in soil nutrient biogeochemistry and overall ecosystem functions and services. Fine roots characterized by relatively short lifespan (a few months), faster growth, and rapid turnover and contribute 18 to 58% of total nitrogen to forest soil [7; 8]. Despite representing only, a small percentage of plant biomass, fine roots utilize about a third of annual global net primary productivity (NPP). Fine roots are a major source of soil carbon through root decomposition and rhizdeposition [9; 10]. More than 50% of the annual NPP is allocated to roots in many forests as they decompose relatively faster than the above-ground plant parts [11; 12]. Although fine roots represent only 5% of total tree biomass, they consume between 30 to 50% of annual gross primary production (GPP) [13]. As a part of below-ground processes, fine roots play a crucial role in tree growth, stand development, and the biogeochemical cycling of nutrients, primarily carbon (C), nitrogen (N), and water in forest ecosystems [14].