Vol. 10, Special Issue 12 (2021)

Author(s):
Rajaram Choudhary, RK Naresh, Mohd Shah Alam, Manisha, Himanshu Tiwari and K Lokeshwar

Abstract:
Soil microbial biomass plays a significant role in soils, and it is often used as an early indicator of change in soil quality. Soil microbial biomass is affected by different fertilization management practices. Therefore, the impact of different long-term fertilization management practices on the soil organic carbon (SOC) content, soil microbial biomass carbon (SMBC), and soil microbial biomass nitrogen (SMBN), as well as the soil microbial quotient (SMQ) in the tilled layer (0.00-0.20 m) were included in the review study. Organic Carbon content was highest in 0.25–1mm aggregate (6.9–9.6 g kg⁻¹) prior to incubation, followed by >2mm aggregates (2.2–5.8 g kg⁻¹), 1–2mm aggregates (2.4–4.6 g kg⁻¹), and <0.25 mm aggregates (3.3–4.5 g kg⁻¹). After 360-day incubation with straw incorporation, organic C content was 2.3–4.5 g kg⁻¹,2.9–5.0 g kg⁻¹,7.2–11 g kg⁻¹ and 1.8–3.0 g kg⁻¹ in >2, 1–2, 0.25–1, and < 0.25mm aggregates, respectively, with the highest in the IFMS treatment. Straw-derived C content was 0.02–0.05 g kg⁻¹, 0.03–0.04 g kg⁻¹, 0.11–0.13 g kg⁻¹, and 0.05–0.10 g kg⁻¹ in >2, 1–2, 0.25–1, and < 0.25 mm aggregates, respectively. The relative distribution of straw-derived C was highest (40–49%) in 0.25–1 mm aggregate, followed by <0.25mm aggregates (21–31%), 1–2mm aggregates (13–15%), and > 2 mm aggregates (9.4–16%). Transition from conventional tillage to no-tillage may alter the depth distribution of soil organic carbon (SOC) and its chemical composition. Aggregate stability, as indicated with the mean weight diameter, was higher for NTS and CTS than that for CT. SOC occluded in the >1 mm fraction was higher under NTS and CTS than under CT. Both NTS and CTS had more aliphatic carbon than CT did, and CT contained more aromatic carbon in the 0–20 cm layer. Chemical fractionation showed long-term MNPK fertilization strongly increased the SOC storage in both soil layers (0-20 cm = 1492.4 g C m (2) and 20-40 cm = 1770.6 g C m (2)) because of enhanced recalcitrant C (RC) and labile C (LC). Overall, application of N and NPK fertilizers cannot significantly increase the SOC storage but enhanced C in mSOM of aggregates, whereas MNPK fertilizer resulted in the greatest amount of SOC storage (about 5221.5 g C m (2)) because of the enhanced SOC in LF, iPOM and mSOM of each aggregate. The SNPK fertilizer increased SOC storage in >250 μm aggregates but reduced SOC storage in <250 μm aggregates due to SOC changes in LF and iPOM.