Effect of Organic Amendments on Soil Health in Wetland Rice Growing Soils of Southern Kerala, India

Abstract

Enhancing soil health is vital for nutrient cycling and sustainability in wetland rice based ecosystems. The objectives of this study were to evaluate the impact of organic amendments on soil biological activities, physical properties and nutrient availability in wetland soils of southern Kerala. The field experiment was conducted during the rabi season of 2024 at Integrated Farming System Research Station, Karamana, Kerala Agricultural University, using the rice variety Uma. The experiment was laid out in a randomized block design with eight treatments and replicated thrice. The organic amendments applied include farmyard manure, vermicompost, thermochemical organic fertilizer, green leaf manure, coconut husk biochar and neem cake. Soil test based recommended dose of nutrients (STBRDN) were compared along with adhoc fertilizer recommendation and organic farming practices. Microbial biomass carbon (MBC) was measured by fumigation extraction, dehydrogenase activity (DHA) by triphenyl tetrazolium chloride reduction and acid phosphatase activity (APA) by p- nitrophenyl phosphate hydrolysis, while soil physical properties and nutrient availability were assessed using standard procedures. Results revealed that coconut husk biochar @ 5 t ha−1 + STBRDN produced the highest MBC (456.00 mg kg−1), whereas vermicompost @ 2.5 t ha−1 + STBRDN significantly enhanced DHA (76.03 μg TPF g−1 24 h−1) and APA (37.73 μg p-nitrophenol g−1 soil h−1). Vermicompost and biochar also improved soil bulk density, water holding capacity and nutrient availability by approximately 40% and 45% for N, P2O5 between 365 and 42% and K2O, compared to inorganic fertilizer alone and the control. The findings highlight the role of vermicompost and biochar as climate-smart strategies for sustaining soil health and productivity in rice based ecosystems.