Aggregation rate as a function of soil organic matter in heavy clayey Ferralsols

Melo, Thadeu Rodrigues de; Pereira, Marcos Gervasio; Shimizu, Gabriel Danilo; Barbosa, Graziela Moraes de Cesare; Tavares Filho, João

doi:10.36783/18069657rbcs20220035

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Division – Soil Processes and Properties • Rev. Bras. Ciênc. Solo 46 • 2022 • https://doi.org/10.36783/18069657rbcs20220035 linkcopy

Aggregation rate as a function of soil organic matter in heavy clayey Ferralsols

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Heavy clayey Ferralsols are known for their high capacity to form water-stable macroaggregates. However, little is known about how different size classes of macroaggregates exchange mass with increasing organic matter content. This study aimed to characterize and detail aggregation dynamics with increasing organic matter content in these soils. Profiles of three heavy clayey Ferralsols were sampled to isolate the role of organic matter on the stability of aggregates. In this sampling scenario, a conceptual model was established to calculate the aggregation rate of different size classes of water-stable aggregates. This approach allowed the establishment of a critical value for classifying microaggregates in the studied soils (≤0.50 mm) based on their behavior as “building blocks” for macroaggregates when organic matter content is increased. In surface soil layers, where organic matter is higher, most dynamics are expected to happen between macroaggregates classes because free microaggregates are scarce. Consequently, it is important to subdivide macroaggregates into different size classes when evaluating their stability. Quantifying macroaggregates as a single class (e.g., >0.25 or >0.50 mm) was insufficient in representing the macroaggregation dynamics in heavy clayey Ferralsols.

Oxisol; macroaggregate; microaggregate; soil aggregate stability; soil structure

Variable/soil property	Unit	Site
Variable/soil property	Unit	Guarapuava	Londrina	Rondon
Elevation	m	1043	566	250
Temperature⁽¹⁾	°C	17.2	21.1	20.1
Precipitation⁽²⁾	mm year^-1	1938	1641	1656
Sampling layer⁽³⁾	m	0.00–0.60	0.00–1.00	0.00–0.60
Clay⁽⁴⁾	g kg^-1	715	750	719
Silt⁽⁴⁾	g kg^-1	211	117	148
Sand⁽⁴⁾	g kg^-1	74	133	133
pH⁽⁴⁾	-log[H⁺]	4.55	4.97	4.95
CEC⁽⁴⁾	cmol_c kg^-1	12.62	11.35	11.55
Al³⁺⁽⁴⁾	cmol_c kg^-1	0.33	0.05	0.31
Ca²⁺⁽⁴⁾	cmol_c kg^-1	3.35	4.38	4.31
Mg²⁺⁽⁴⁾	cmol_c kg^-1	1.23	0.99	2.06
K⁺⁽⁴⁾	cmol_c kg^-1	0.22	0.82	0.16
Na⁺⁽⁴⁾	cmol_c kg^-1	0.00	0.00	0.00
Fe_Dit⁽⁵⁾	g kg^-1	174	319	239

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Sociedade Brasileira de Ciência do Solo Sociedade Brasileira de Ciência do Solo, Departamento de Solos - Edifício Silvio Brandão, s/n, Caixa Postal 231 - Campus da UFV, CEP 36570-900 - Viçosa-MG, Tel.: (31) 3612-4542 - Viçosa - MG - Brazil
E-mail: sbcs@sbcs.org.br

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[TFN1] ⁽¹⁾ Average annual temperature. ⁽²⁾ Average total annual precipitation. ⁽³⁾ Sampling layers: Guarapuava and Rondon (0.00-0.05, 0.05-0.10, 0.10-0.15, 0.15-0.20, 0.20-0.25, 0.25-0.30, 0.30-0.35, 0.35-0.40, 0.40-0.50, 0.50-0.60 m); Londrina (0.00-0.10, 0.10-0.20, 0.20-0.30, 0.30-0.40, 0.40-0.50, 0.50-0.60, 0.60-0.70, 0.70-0.80, 0.80-0.90, 0.90-1.00 m). ⁽⁴⁾ Average values across all layers. ⁽⁵⁾ Dithionite-extractable iron; measurement performed at the 0.40-0.60 m layer (top of B horizon).