Impacts of humic acid on soil microbial diversity and productivity in tea cultivation toward sustainable agriculture

Abstract

Tea is an important perennial plantation crop whose prolonged monoculture practice and continuous usage of inorganic fertilizers often result in soil degradation, depletion of organic matter, and reduced nutrient use efficiency (NUE). In this context, this study evaluated the application of humic acid, a sustainable soil amendment with beneficial effects on soil health across agro-ecosystems, in combination with inorganic fertilizers on soil health, nutrient uptake, and crop productivity under high elevation conditions. A long-term field experiment consisting of eight treatments with three replications in a Randomized Block Design (RBD) was conducted during the year 2021 to 2025. The treatments comprised humic acid at the rate of 20 and 40 kg ha-1, along with reduced inputs of NPK application ranging from 100%, 75%, and 50%. Soil samples were collected annually to assess soil properties and microbial dynamics and green leaf yield during each plucking round was recorded. Results revealed that the humic acid application at 40 kg ha-1 integrated with reduced 75% NPK, helped in achieving relatively higher productivity of 21.1%. This also significantly improved soil nutrients and microbial activity besides the crop yield when compared to untreated control. Thus, the present study confirmed that the integration of humic acid with inorganic NPK fertilizers improves soil health and tea productivity while reducing dependence on synthetic fertilizers up to 25% in high elevation tea growing regions of South India.