Depth Distribution of Bulk and Aggregate-Associated Manganese Oxides Mediated by Soil Chemical Properties in a Long-Term Fertilized Paddy Soil

Abstract

Fertilization regimes greatly influence how manganese (Mn) oxides are recycled. However, information on this subject is scarce in rice managed paddies. The objective of this study was to examine the distributions of Mn pools in bulk soil and aggregates under different chemical and organic fertilizer ratios at both surface (0-20 cm) and subsurface (20-40 cm) soil depths. Depth distributions of Mn pools in bulk soil and aggregates were extracted using Mehlich 3 (M3-Mn), dithionite (Mnd), oxalate (Mno), and pyrophosphate (Mnp) solutions under a long-term fertilization experiment in a double rice cropping system. Fertilizer treatments comprised unfertilized control (CK), mineral nitrogen, phosphorus, and potassium (NPK), 30% mineral NPK + 70% organic fertilizer (30F; pig manure + milk vetch), 50% mineral NPK + 50% organic fertilizer (50F), and 70% mineral NPK + 30% organic fertilizer (70F) under a randomly complete block design (RCBD) in paddy conditions. A pattern of 30F > 50F > 70F > NPK > CK was established with positive and significant correlations among total organic carbon (TOC), total nitrogen (TN), and pH. All pools of Mn were in higher concentrations at the subsurface compared to the surface layer, where all aggregate sizes contributed equally to the enrichment of the metal oxides except for Mno in the 0.25-2.0 mm sizes at the surface layer. Distribution of manganese oxides was equal among the different soil aggregates which could cause the microaggregates to transport Mn oxides and pollute both surface and underground water sources.

Fertilizer combination effects on aggregate stability and distribution of aluminum and iron oxides#

“…Arrows pointing nearly similar direction imply a significant and positive correlation, arrows intersecting at 90° indicate approximately no correlation, while arrows opposite to each other indicate significant negative correlations. Explanatory and response variables with long arrows are the most important in the analysis since the length of an arrow indicates the confidence associated with the correlation (Anthonio et al., 2020). Total organic C and GMD could explain 75.0% and 68.3%,and 80.4% and 73.0% ( p = 0.002; Supplementary Table 1 in the Supporting Information) variance in surface and subsurface layers, respectively.…”

“…With the exception of Al d , soil particle size was significant (p ≤ 0.05) in the distribution of all extractable Al and Fe oxides (Table 2). (Anthonio et al, 2020). Total organic C and GMD could explain 75.0% and 68.3%,and 80.4% and 73.0% (p = 0.002; Supplementary Table 1 in the Supporting Information) variance in surface and subsurface layers, respectively.…”