Soil acidity is one of the main limitations for optimal use of land resources for better crop production. And, long-term fertilization experiments found to be helpful in increasing the nutrient supply in these acidic soils. Keeping this in view, a field experiment on rice was carried out by applying biofertilizers and enriched compost in an acidic Inceptisol of Assam over 10 successive years (2006–15) to examine its effects on nutrient availability and soil enzymatic activity. This experiment had five treatments viz. absolute control (T₁), 100% recommended doses (RD) of inorganic NPK (T₂), 50% RD of inorganic NP + 100% K +biofertilizers (T₃), 50% RD of inorganic NP + 100% K +1 tonne enriched compost ha⁻¹ (T₄) and 25% RD of inorganic NP + 100% K +2 tonnes enriched compost ha⁻¹ (T₅) under randomized block design with four replications. After completing 10 years of experiment, it was observed that integrated use of enriched compost and biofertilizers with reduced doses of inorganic fertilizers enhanced the soil enzymatic activity as well as nutrient availability in rice grown in acidic clay loam soils of Assam. Application of biofertilizers and enriched compost had positive impact on plant accessible nitrogen, phosphorus and potassium in soil as compared to inorganic fertilizers. Also soil organic matter content increased considerably by these treatment. Integrated nutrient management practice in rice had also significantly enhanced the dehydrogenase, fluorescein diacetate and phospho-monoesterase activity in soil.

An in-depth knowledge on impact of integrated nutrient management (INM) practice on yield sustainability and soil quality is important to scale INM practice across regions. Therefore, field experiment was initiated in 2006, which consisted of five treatments: absolute control, 100% recommended doses of nitrogen (N), phosphorus (P) and potassium (K) (RDF), 50% recommended doses of NP + 100% K + biofertilizers, 50% recommended doses of NP + 100% K + 1 t ha⁻¹ enriched compost (ECM) and 25% recommended doses of NP + 100% K + 2 t ha⁻¹ ECM (25RDF + 2ECM). The use of 25RDF + 2ECM increased soil organic carbon by 32 and 24% over control and RDF, respectively, at 0–5 cm soil layer. It also increased soil microbial biomass carbon, microbial phosphorus and phenol oxidase activity by 13.7, 20.9 and 55.7% than RDF, respectively, at 0–5 cm layer. Notably, phenol oxidase activity, pH, DTPA-extractable iron, available K, mineral N and microbial biomass phosphorus came out as the key indicators of soil quality in acidic soil after 10 years. The study recommends that INM practice comprising ECM and reduced inorganic fertilizers could enhance soil quality and yield sustainability of rice in the long-run in acidic soil ecology.

Applications of enriched compost (ECM) with reduced doses of inorganic fertilizers over ten consecutive years reduced phytotoxic aluminium (Al) fractions, whereas, improved nutritional quality of rice in acid soil. The long-term field trial with integrated nutrient management (INM) practices was initiated in kharif–2006 at Instructional–cum–Research (ICR) farm under rice mono-cropping system. Treatments consisted of T₁; absolute control, T₂; 100% recommended doses of nitrogen (N), phosphorus (P) and potassium (K), T₃; 50% recommended doses of NP + 100% K + biofertilizer, T₄; 50% recommended doses of NP + 100% K + ECM at 1 tonne ha⁻¹ and T₅; 25% recommended doses of NP + 100% K + ECM at 2 tonne ha⁻¹. Exchangeable Al (~31%) and strongly organically bound and interlayer Al (~26%) fractions decreased with an increasing dose of ECM application at all soil depths. However, weakly organically bound Al (~25%), amorphous Al (~7.3%), and free Al (~13%) significantly increased over 100% NPK. Long-term use of ECM had a significant positive impact on micronutrient content in post-harvest soil. Micronutrient accumulation (Zn, Fe, Cu, Mn, and Ni) in rice increased with continuous application of manuring and fertilization, while the accumulation of Al decreased significantly.

The enriched compost (ECM) comprising rock phosphate and biofertilizer consortia (BC) is a cheap source of organic input. A long-term field trial was initiated in kharif–2011 with the following treatment combinations used for rice sole-cropping: T₁, absolute control; T₂, 3.5 kg ha⁻¹ biofertilizer consortia; T₃, 5.0 t ha⁻¹ compost (CM); T₄, 5.0 t ha⁻¹ CM + 3.5 kg ha⁻¹ BC; T₅, 2.5 t ha⁻¹ ECM; T₆, 5.0 t ha⁻¹ ECM; and T₇, 0.5 t ha⁻¹ Azolla + 3.5 kg ha⁻¹ BC. Owing to the usage of ECM for nine consecutive years, the organic carbon pools and biochemical properties of the soil were enhanced, and the nutritional quality of rice was enriched. Further, the potassium permanganate oxidizable carbon, total organic carbon, and microbial biomass carbon increased by 46%, 20%, and 15%, respectively, in the surface soil with T₆ relative to T₃. Such finding highlights the benefit of ECM application relative to CM and BC in enhancing rice nutritional quality and soil biochemical properties. Overall, the study suggests the use of 5 t ECM ha^–1 to improve the soil biochemical properties and nutritional quality of rice subjected to acidic inceptisol.