Enhancing soil ecosystem services through sustainable integrated nutrient management in double rice-cropping system of North-East India

The wetland cultivation of rice is subjected to anaerobic and aerobic soil conditions causing substantial changes in the soil system. However, how long-term supplementation of organics with reduced chemical fertilizers affects microbial composition, their activities, and enzymatic activities in acid soil has not been sufficiently investigated. This research is focused on a rice-rice system after an ongoing field experiment set-up in 1977–78 at Assam Agricultural University, Jorhat, India, where 7 alternative nutrient management have been investigated to: (1) assess the effects on soil organic carbon (SOC), microbial biomass carbon, and enzymatic activity in acid soil; (2) identify and discuss the most suitable treatment combinations of organic and chemical fertilizers to enhance soil ecosystem services (SES). Accordingly, we analysed the soil microbiological properties as affected by the 32 years of continuous integrated nutrient management (INM) practices and also evaluated the INM treatments in terms of SES. Results revealed that the soil microbial biomass carbon significantly varied across the treatments from 129.4 to 412.1 µg g−1 which comprises 2.4 to 4.4% of the SOC. The highest bacterial count (8.95 log cfu g−1 soil) was recorded in RDF + Azolla treatment, whereas fungal count was the maximum (7.47 log cfu g−1 soil) in RDF + FYM treatment. All the enzymatic activities responded significantly to the INM practices, but the trend of response was different for different enzymes. The highest dehydrogenase (223.6 µg TTF g−1 soil 24 h−1) and urease (4.1 μg NH4-N g−1 soil 2 h−1) activities were recorded in RDF + Azolla, while phosphomonoeaterase (337.4 μg p-nitrophenol g−1 soil h−1) and fluorescein diacetate hydrolysis (10.0 μg fluorescein g−1 soil h−1) activities were found to be the maximum in RDF + FYM. The microbial and enzymatic activities decreased significantly in the control after 32 cycles of rice-rice cropping. In this study, a significant positive statistical correlation of all the microbiological properties with soil pH, soil organic carbon and grain yield of crops were recorded. Finally, the different soil properties under the different nutrient treatments have been discussed in terms of SES provision, highlighting that the most sustainable treatments have resulted in RDF + FYM, RDF + RS and RDF + Azolla.