Soil hydraulic properties, mineralogical alteration and pore formation in Regosols from southern Brazil

Pedron, Fabrício de Araújo; Deobald, Gabriel Antônio; Gubiani, Paulo Ivonir; Santos, Luís Antônio Coutrim dos; Azevedo, Antônio Carlos de; Reichert, José Miguel; Dambroz, Alice Prates Bisso

doi:10.36783/18069657rbcs20240013

Fabrício de Araújo Pedron ^** Corresponding author: E-mail: fapedron@ufsm.br

Conceptualization (lead)

Data curation (lead)

Formal analysis (equal)

Investigation (equal)

Methodology (equal)

Project administration (lead)

Writing – original draft (lead)

Writing – review & editing (equal)

Universidade Federal de Santa Maria, Departamento de Solos, Santa Maria, Rio Grande do Sul, Brasil.

https://orcid.org/0000-0002-5756-0688

Gabriel Antônio Deobald

Conceptualization (equal)

Formal analysis (equal)

Investigation (equal)

Methodology (equal)

Writing – original draft (equal)

Writing – review & editing (equal)

Empresa de Pesquisa Agropecuária e Extensão Rural de Santa Catarina, Florianópolis, Santa Catarina, Brasil.

https://orcid.org/0009-0003-3460-6051

Paulo Ivonir Gubiani

Investigation (equal)

Methodology (equal)

Writing – original draft (equal)

Writing – review & editing (equal)

Universidade Federal de Santa Maria, Departamento de Solos, Santa Maria, Rio Grande do Sul, Brasil.

https://orcid.org/0000-0002-8840-3976

Luís Antônio Coutrim dos Santos

Formal analysis (equal)

Investigation (equal)

Methodology (equal)

Writing – original draft (equal)

Writing – review & editing (equal)

Universidade do Estado do Amazonas, Itacoatiara, Amazonas, Brasil.

https://orcid.org/0000-0002-0824-0901

Antônio Carlos de Azevedo

Investigation (equal)

Writing – original draft (equal)

Writing – review & editing (equal)

Universidade de São Paulo, Departamento de Ciência do Solo, Piracicaba, São Paulo, Brasil.

https://orcid.org/0000-0002-1681-3212

José Miguel Reichert

Investigation (equal)

Writing – original draft (equal)

Writing – review & editing (equal)

Universidade Federal de Santa Maria, Departamento de Solos, Santa Maria, Rio Grande do Sul, Brasil.

https://orcid.org/0000-0001-9943-2898

Alice Prates Bisso Dambroz

Formal analysis (equal)

Investigation (equal)

Writing – original draft (equal)

Writing – review & editing (equal)

Universidade Federal de Santa Maria, Departamento de Solos, Santa Maria, Rio Grande do Sul, Brasil.

https://orcid.org/0000-0003-0921-1034

* Corresponding author: E-mail: fapedron@ufsm.br

Editors: Reinaldo Bertola Cantarutti https://orcid.org/0000-0002-4360-0247 and João Tavares Filho https://orcid.org/0000-0002-6005-6335.

Profiles/	Horizon	Layers	SG/U⁽¹⁾ (1) Slope gradient {SG: (GS: gently sloping, U: undulating, SS: strongly sloping)}/Land use {U: (NP: native pasture; BF: bushy field; CP: cultivated pasture; AG: annual grain crop; FL: florest)};	FT⁽²⁾ (2) fractures thickness (FT);	DF⁽³⁾ (3) distance between fractures (DF);	WC⁽⁴⁾ (4) weathering classes (WC) – I2: rock slightly weathered, I3: rock moderately weathered, I4: saprolite slightly weathered, I5: saprolite moderately weathered, I6: saprolite very weathered;	PRPR⁽⁵⁾ (5) penetration resistance (PR). All saprolite samples (Cr, CrR, RCr) showed fractures filled with soil and roots. nd: not determined.	Roots	Altitude
		m		mm	cm		kPa		m
P1	A	0.00-0.10	SS/ BF	nd	nd	nd	nd	Common	284
	Cr1	0.10-0.50		2	20	I6	4.90	Few
	Cr2	0.50-0.90⁺		2	20	I5	3.24	Very few
P2	A	0.00-0.10	SS/ FL	nd	nd	nd	nd	Many	235
	Cr1	0.10-0.30		2	5	I5	5.29	Common
	Cr2	0.30-0.60		2	5	I5	8.04	Common
	RCr	0.60-1.50⁺		2	5	I3	12.65	Few
P3	A	0.00-0.23	GS/ NP	nd	nd	nd	nd	Many	228
	Cr1	0.23-0.43		5	20	I5	7.75	Common
	Cr2	0.43-1.20		5	20	I5	6.37	Few
	RCr	1.20-1.40⁺		5	20	I3	13.53	Very few
P4	A	0.00-0.30	GS/ NP	nd	nd	nd	nd	Many	218
	Cr	0.30-1.15		5	8	I5	6.37	Few
	RCr	1.15-1.50⁺		5	8	I2	15.39	Very few
P5	A	0.00-0.14	U/ BF	nd	nd	nd	nd	Common	452
	Cr/A	0.14-0.53		1	5	I6	3.14	Few
	Cr	0.53-1.40		1	5	I5	6.18	Very few
	RCr	1.40-2.40⁺		1	5	I2	21.48	Very few
P6	A	0.00-0.28	U/ CP	nd	nd	nd	nd	Common	467
	CrR	0.28-0.70		2	8	I3	12.06	Few
	Cr	0.70-1.00⁺		2	8	I5	3.43	Very few
P7	A	0.00-0.12	GS/ AG	nd	nd	nd	nd	Many	490
	Cr1	0.12-0.85		1	2	I6	6.47	Few
	Cr2	0.85-1.40⁺		1	2	I5	7.85	Very few
P8	A	0.00-0.25	GS/ NP	nd	nd	nd	nd	Common	458
	Cr/A	0.25-0.75		3	10	I5	4.22	Few
	RCr1	0.75-1.05		3	10	I3	20.79	Very few
	RCr2	1.05-1.20⁺		3	10	nd	nd	Very few

Profiles	Horizons	Total sample		Fine earth			SOC⁽¹⁾	Fed⁽²⁾	Kt⁽³⁾	Parent material
Profiles	Horizons	>2 mm	<2 mm	Clay	Sand	Silt	SOC⁽¹⁾	Fed⁽²⁾	Kt⁽³⁾	Parent material
		––––––––––––– g kg^-1–––––––––––––							%	% SiO₂
P1	A	507	493	120	465	416	14.2	25.03	43	Basic 50.9
	Cr1	666	334	99	262	639	2.7	22.71	39
	Cr2	980	20	108	279	613	2.6	12.39	37
P2	A	748	252	234	273	492	55.3	23.05	45	Basic 55.5
	Cr1	881	119	247	269	484	29.8	20.94	38
	Cr2	982	18	272	330	398	15.1	10.52	37
P3	A	410	590	296	278	426	18.5	61.11	49	Basic 50.4
	Cr1	748	252	55	442	503	3.0	42.37	39
	Cr2	980	20	53	552	395	2.5	23.32	37
P4	A	331	669	251	377	372	19.0	45.62	40	Basic 50.4
P4	Cr	975	25	60	575	365	2.3	24.46	38	Basic 50.4
P5	A	746	254	298	212	491	28.8	11.75	37	Acidic 68.6
	Cr/A	647	353	228	267	504	10.9	9.57	32
	Cr	960	40	283	267	450	8.9	10.36	30
P6	A	263	737	348	210	442	23.8	17.64	35	Acidic 70.5
	CrR	729	371	429	196	374	13.6	12.15	30
	Cr	957	43	nd	nd	nd	8.2	11.24	31
P7	A	345	655	211	396	393	12.0	21.02	34	Acidic 71.0
	Cr1	963	37	84	579	338	1.3	9.00	30
	Cr2	990	10	73	500	428	1.8	10.53	32
P8	A	138	862	280	143	577	19.3	30.37	43	Acidic 68.6
P8	Cr/A	687	313	221	196	583	5.4	71.57	33	Acidic 68.6

Profiles	Horizons	BD	θ_sat	θ₁₀	θ₁₅₀₀	AW	K_sat
		Mg m^-3	m³m^-3				cm h^-1
P1	A	1.29 a	0.55 a	0.40 b	0.21 b	0.19 a	0.20 ab
	Cr1	1.18 a	0.57 a	0.44 ab	0.32 a	0.12 a	0.71 a
	Cr2	1.22 a	0.57 a	0.48 a	0.25 ab	0.23 a	0.04 b
P2	A	0.87 b	0.74 a	0.43 a	0.21 ab	0.22 a	4.79 ab
	Cr1	1.12 ab	0.60 ab	0.44 a	0.20 a	0.24 a	6.40 a
	Cr2	1.28 a	0.55 b	0.47 a	0.29 b	0.18 a	1.17 b
P3	A	1.02 b	0.67 a	0.39 ab	0.19 a	0.20 b	3.19 a
	Cr1	1.25 a	0.55 b	0.38 b	0.18 a	0.20 b	0.40 ab
	Cr2	1.04 b	0.58 ab	0.43 a	0.18 a	0.25 a	0.16 b
P4	A	1.23 a	0.54 a	0.34 b	0.21 a	0.12 b	nd
P4	Cr	1.24 a	0.53 a	0.43 a	0.17 b	0.26 a	nd
P5	A	1.01 a	0.64 a	0.45 b	0.28 a	0.17 a	2.01 a
	Cr/A	0.94 a	0.61 a	0.46 ab	0.22 b	0.24 a	0.18 ab
	Cr	1.00 a	0.61 a	0.52 a	0.26 ab	0.26 a	0.05 b
P6	A	1.36 a	0.50 b	0.42 b	0.22 ab	0.19 b	0.25 a
	Cr	1.15 b	0.57 a	0.53 a	0.30 a	0.23 ab	0.00 b
	CrR	1.16 b	0.57 a	0.51 ab	0.22 b	0.30 a	0.02 ab
P7	A	1.30 b	0.51 a	0.42 a	0.21 b	0.21 a	0.32 a
	Cr1	1.39 ab	0.47 ab	0.40 ab	0.27 a	0.13 b	0.01 b
	Cr2	1.43 a	0.46 b	0.36 b	0.21 b	0.15 ab	0.01 ab
P8	A	1.48 a	0.44 b	0.39 b	0.26 a	0.13 b	0.22 a
	Cr/A	1.26 ab	0.51 ab	0.46 ab	0.27 a	0.19 ab	0.18 a
	Cr	1.18 b	0.56 a	0.51 a	0.27 a	0.24 a	0.47 a

Profiles⁽¹⁾ (1) P7 was not analyzed.	Pethographic description
P1	Aphanitic rock without visible microphenocrysts and with pronounced and filled amygdaloid structures. Microgranular with microphenocrystals in the form of elongated slats of plagioclase-type feldspars, determined by the unclear presence of twins, immersed in a matrix consisting of plagioclase and mafics (pyroxenes/amphiboles). Presence of magnetite. Iron oxide is found filling fracture and cleavage planes, especially in feldspar crystals, also found in fractures of mafic minerals. High degree of alteration of the feldspars and mafics evidenced by the significant loss of the optical characteristics of the feldspars and by the release of red inks (iron oxide) by the mafics, which, together with the hazy aspect resulting from the alteration of the feldspars, prevents a precise classification of the rock. However, due to the absence of quartz, the macroscopic color, and the structures present, it can be inferred it is a basic rock.
P2	Aphanitic rock with rare microphenocrysts of feldspars and without visible structures, consisting of few elongated laths of feldspars - plagioclase type, pyroxenes and some crystals of alkaline feldspar and rare quartz, in a feldspars/pyroxenes ratio of 3:2. High amount of opaque represented by magnetite occurs. Plagioclase was recognized as being labradorite, which corresponds to a percentage of anorthite (An) between 50-70 %, showing it to be a more calcic term in the plagioclase series. Pyroxene is the augite recognized by the relief, the absence of pleochroism and the quadratic aspect established by the crossing of cleavages in section (001). Magnetite is recognized for its cubic and octahedral crystals. The degree of alteration of the rock is not accentuated, where the pyroxene shows up a little more than the feldspar, which releases reddish inks that lend a cloudy appearance to the blade. The rock is classified as a basalt-type volcanic rock.
P3	Coarse aphanitic rock, without phenocrysts, massive appearance and no visible structure. Consisting of labradorite plagioclase-type feldspar (An+50 % and -70 %) and hypersthene-type pyroxene (Mg, Fe) SiO₃in a ratio of practically 1:1. Opaques are frequent, possibly represented by ilmenite (FeTiO₃), subordinately by magnetite. Quartz and biotite crystals are rare. The chemical alteration is already present, but even so, it allowed the optical recognition of the pyroxene and the type of plagioclase. Due to its petrographic characteristics, it is a volcanic rock of the tholeiitic basalt type, although texturally, it may resemble a diabase (a shallow rock, mineralogically similar to basalt).
P4	Rock with slightly more developed and strongly altered feldspar crystals, which imposes a speckled appearance, without visible structures. Consisting of plagioclase-type feldspar, varying between andesin and labradorite (Close to 50 %) and hypersthene-type pyroxene, in a ratio of 3:2. The presence of opaques, especially magnetite is greater than 5 %. Quartz presence is rare. The degree of alteration of both pyroxenes and feldspars is already significant. Along the cleavage and fracture planes of pyroxenes, oxide precipitation, possibly iron, is common. Based on its petrographic characteristics, it can be said it is a volcanic rock classified between andesite and basalt. The texture of the material suggests it is a diabase.
P5	Very fine aphanitic rock, almost glassy, without phenocrysts, presenting a vesicular/amygdaloid structure. Microscopically, the mineralogical constitution is difficult to recognize due to the fine texture and the high degree of alteration, although some blades (slats) of feldspars can be observed. In these, no twins are observed, which makes it difficult to recognize the type of feldspar, limiting the petrographic classification. The very fine texture and the vesicular/amygdaloid structure suggest this is a volcanic rock corresponding to the top of the flow.
P6 and P8	Microgranular aphanitic rock with a large amount of elongated feldspar microslats, with a layered structure and some tonsils, which indicates the position in the flow profile. Microscopically, feldspars show a rough texture in natural light when, in fact, they should be colorless, which indicates the degree of significant weathering of the rock. It is constituted by plagioclase-type feldspar identified by the unclear presence of twins, by mafics (pyroxene/amphibole) already heavily destroyed, and by magnetite, the latter recognized by its cubic and octahedral sections. The degree of alteration is significant, especially of the mafics that release reddish inks (iron oxide), which, associated with the cloudy appearance of the feldspars, makes it difficult to accurately identify the mineral constituents, consequently making it difficult to classify the rock.

Elements	P1	P3	P4	P7	P6/P8
	––––––––– % –––––––––
SiO₂	50.87	50.37	48.19	71.03	70.61
Al₂O₃	19.11	20.89	19.70	15.04	14.81
Fe₂O₃	17.62	10.91	8.81	5.53	6.09
CaO	4.45	10.33	9.86	1.61	0.64
K₂O	2.35	1.14	0.79	5.01	4.75
MgO	1.59	2.91	8.81	0.66	0.62
Na₂O	1.05	1.93	1.00	0.00	0.00
TiO₂	1.35	0.63	0.53	0.73	0.83
P₂O₅	0.38	0.59	1.27	0.12	1.04
MnO	0.24	0.16	0.15	0.05	0.06
Total	99.01	99.85	99.11	99.77	99.45

[1] * Corresponding author: E-mail: fapedron@ufsm.br

Brasil

Brasil

Soil hydraulic properties, mineralogical alteration and pore formation in Regosols from southern Brazil

ABSTRACT