Nitrogen fertilization impact on soil carbon pools and their stratification and lability in subtropical wheat-mungbean-rice agroecosystems

Abstract

Nitrogen (N) is the prime nutrient for crop production and carbon-based functions associated with soil quality. The objective of our study (2012 to 2019) was to evaluate the impact of variable rates of N fertilization on soil organic carbon (C) pools and their stocks, stratification, and lability in subtropical wheat (Triticum aestivum)—mungbean (Vigna radiata)—rice (Oryza sativa L) agroecosystems. The field experiment was conducted in a randomized complete block design (RCB) with N fertilization at 60, 80, 100, 120, and 140% of the recommended rates of wheat (100 kg/ha), mungbean (20 kg/ha), and rice (80 kg/ha), respectively. Composite soils were collected at 0–15 and 15–30 cm depths from each replicated plot and analyzed for microbial biomass (MBC), basal respiration (BR), total organic C (TOC), particulate organic C (POC), permanganate oxidizable C (POXC), carbon lability indices, and stratification. N fertilization (120 and 140%) significantly increased the POC at both depths; however, the effect was more pronounced in the surface layer. Moreover, N fertilization (at 120% and 140%) significantly increased the TOC and labile C pools when compared to the control (100%) and the lower rates (60 and 80%). N fertilization significantly increased MBC, C pool (CPI), lability (CLI), and management indices (CMI), indicating improved and efficient soil biological activities in such systems. The MBC and POC stocks were significantly higher with higher rates of N fertilization (120% and 140%) than the control. Likewise, higher rates of N fertilization significantly increased the stocks of labile C pools. Equally, the stratification values for POC, MBC, and POXC show evidence of improved soil quality because of optimum N fertilization (120–140%) to maintain and/or improve soil quality under rice-based systems in subtropical climates.

Biochar and Compost-Based Integrated Nutrient Management: Potential for Carbon and Microbial Enrichment in Degraded Acidic and Charland Soils

“…The fumigation extraction method (Vance et al, 1987;Wang et al, 2020;Begum et al, 2021;Jahangir et al, 2021b) served to calculate microbial biomass carbon (MBC) from the following relationship:…”

“…The SOC concentration was determined by following the standard wet oxidation method (Walkley and Black, 1934;Begum et al, 2021;Islam et al, 2021c). 1 g of ground, sieved, and oven-dried sample was placed into a 250 ml conical flask.…”

“…Following this, 2 ml of o-phenanthroline indicator were added to the content and titrated the solution with 0.5 M (NH 4 ) 2 Fe (SO 4 ) 2 .6H 2 O until a dark green colour appeared. Particulate organic carbon (POC) was determined according to the method utilized by Cambardella and Elliott, (1992) and Begum et al (2021). In short, 20 g of soil was dispersed in 100 ml of 5 g L −1 sodium hexametaphosphate solution by shaking for 15 h on an end-over-end shaker.…”

“…Organic carbon was measured in dried samples that were ground and analyzed. After mild oxidation of air-dried soil with a neutral KMnO 4 solution, the Permanganate oxidizable carbon (POXc) was quantified spectrophotometrically as a measure of chemically labile C pool (Weil et al, 2003;Begum , 2021). In brief, we used 20 ml of neutral KMnO 4 in water to react 1.0 g oven dry equivalent (ODE) of air-dried soil at concentrations of 0.005, 0.01, 0.0125, 0.025, 0.05, and 0.1 M. In screw-cap polycarbonate centrifuge tubes, the soil KMnO 4 suspensions were agitated at 200 rpm for 15 min at room temperature.…”

“…Using the measured SOC, MBC, POC, and POX C data, the CMI was calculated (Islam et al, 2021d;Begum et al, 2021;Franzluebbers, (2002)) as follows:…”