S-index and soybean root growth in different soil textural classes

Oliveira, Pedro D. de; Sato, Michel K.; Rodrigues, Sueli; Lima, Herdjania V. de

doi:10.1590/1807-1929/agriambi.v20n4p329-336

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SOIL, WATER AND PLANT MANAGEMENT • Rev. bras. eng. agríc. ambient. 20 (4) • Apr 2016 • https://doi.org/10.1590/1807-1929/agriambi.v20n4p329-336 copy

S-index and soybean root growth in different soil textural classes

Índice S e crescimento radicular da soja em diferentes classes texturais

Authorship SCIMAGO INSTITUTIONS RANKINGS

ABSTRACT

This study tested the hypothesis that the limiting values of S-index, proposed in the literature can not be used to determine the degradation condition of soils under soybean cultivation in the state of Pará, Brazil. The objective was to determine limiting values of S-index using soil physical attributes and validate it with soybean root growth, in soils with different textural classes. For the experimental design, the following treatments were established: five compaction levels for sandy loam and sandy clay loam soils and three levels for clayey and very clayey soils. The following physical parameters were analysed: particle-size distribution, soil bulk density, critical soil bulk density, degree of compaction, soil-water retention curve, S-index and relative root length of soybean. The limiting values of S-index varied according to soil textural class and were equal to 0.037, 0.020 and 0.056 for sandy loam, sandy clay loam and clay, respectively. The S-index does not apply to soils with clay content > 71%, because it does not vary with the degree of compaction of the soil or the root growth of the evaluated crop.

Key words:
degree of compaction; critical soil bulk density; relative root length

Area	Latitude	Longitude	Municipality	Sand^* * Sand = 2-0.05 mm; Silt = 0.05-0.002 mm; Clay = < 0.002 mm; OM = Organic matter; N = 3 replicates	Silt	Clay	OM	Textural class
Area	Latitude	Longitude	Municipality	(g kg^-1)				Textural class
1	1º 44' 42"	47º 03' 54"	Capitão Poço	756.2	68.6	175.2	25.8	Sandy loam
2	2º 59' 42"	47º 21' 10"	Paragominas	663.3	129.9	206.8	37.1	Sandy clay loam
3	1º 44' 42"	47º 03' 54"	Capitão Poço	396.4	165.3	438.3	27.3	Clay
4	2º 59' 42"	47º 21' 10"	Paragominas	53.2	237.0	709.8	43.4	Clay

Soil (Textural class)	Equation	R²	Bd_max (Mg m^-3)
Sandy loam	Bd = -27.03 θg² + 5.93 θg + 1.470	0.94	1.80
Sandy clay loam	Bd = -30.88 θg² + 14.9 θg - 0.303	0.96	1.77
Clay	Bd = -24.77 θg² + 15.7 θg - 1.161	0.98	1.52
Clay	Bd = -23.15 θg² + 5.21 θg + 1.477	0.96	1.31

DC (%)	Number of samples	θs (kg kg^-1)	θr (kg kg^-1)	α (hPa^-1)	n -	S-index
Sandy loam
75	8	0.3247 a ± 0.005	0.0812 a ± 0.002	0.0108 a ± 0.000	2.3177 a ± 0.037	0.115 a
78	8	0.2849 b ± 0.003	0.0757 a ± 0.002	0.0090 ab ± 0.000	2.4398 a ± 0.077	0.105 a
83	8	0.2737 b ± 0.005	0.0875 a ± 0.004	0.0079 b ± 0.000	2.4845 a ± 0.179	0.094 a
89	6	0.2387 c ± 0.008	0.0904 a ± 0.008	0.0076 b ± 0.000	2.3956 a ± 0.216	0.070 b
95	3	0.2017 d ± 0.016	0.0965 a ± 0.003	0.0068 b ± 0.000	2.7363 a ± 0.217	0.063 b
Sandy clay loam
77	8	0.3496 a ± 0.011	0.1217 a ± 0.005	0.0169 a ± 0.001	2.5728 a ± 0.120	0.121 a
81	6	0.3218 a ± 0.007	0.1126 a ± 0.003	0.0148 a ± 0.000	2.3500 ab ± 0.080	0.100 a
85	8	0.2809 b ± 0.010	0.1106 a ± 0.010	0.0132 a ± 0.000	2.2503 ab ± 0.088	0.076 b
91	3	0.2090 c ± 0.011	0.1209 a ± 0.012	0.0078 b ± 0.002	2.0567 ab ± 0.110	0.035 c
96	3	0.1891 c ± 0.003	0.1006 a ± 0.013	0.0107 a ± 0.000	1.7512 b ± 0.213	0.027 c
Clayey
89	5	0.3644 a ± 0.016	0.2158 a ± 0.007	0.0169 a ± 0.002	2.3852 a ± 0.131	0.072 a
93	3	0.3496 a ± 0.018	0.2267 a ± 0.011	0.0183 a ± 0.000	2.2859 a ± 0.294	0.055 a
97	3	0.3295 a ± 0.019	0.2129 a ± 0.010	0.0147 a ± 0.009	2.2805 a ± 0.106	0.053 a
Very clayey
88	6	0.3816 b ± 0.000	0.2250 a ± 0.002	0.0011 a ± 0.000	1.7948 a ± 0.064	0.051 a
94	7	0.4207 a ± 0.005	0.2236 a ± 0.014	0.0040 a ± 0.001	1.5339 b± 0.026	0.049 a
97	6	0.3982 b ± 0.007	0.2011 a ± 0.005	0.0023 a ± 0.000	1.4661 b ± 0.044	0.043 a

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[1] herdjania@pq.cnpq.br (Corresponding author)