DOI: 10.5061/dryad.b5mkkwh9n
title: Soil physical-hydric attributes under no-tillage crop in the savannah of the Southwest region of the Piaui State, Brazil

description: The soils of the savannah region, Piaui State, Brazil, are favorable to
 agriculture; however, intensive use combined with inadequate management
 has caused soil degradation in the region. For this reason, studies
 focused on the use of alternative production systems as a no-till system
 (SPD), have become essential. Thus, the objective was to evaluate the
 changes in the physical-hydric attributes and organic matter in Oxisols
 under different times of no-tillage crop under straw in savannah areas of
 the Southwest region of the Piaui State, Brazil. Field data collection was
 carried out on commercial farms in the municipalities of Baixa Grande do
 Ribeiro (07° 48'10” S, 45° 00'60" W and altitude of 600 m),
 Uruçuí (08º14'07" S, 44º38'09" W and altitude of 550
 m) and Bom Jesus (09º10'35" S, 44º50'36" W and
 altitude of 600 m), Piaui State, Brazil. The areas had different times of
 no-tillage crop under straw: SPD2 - 2 years, SPD3 - 3 years, SPD6 - 6
 years, SPD10 - 10 years, SPD12 - 12 years, SPD15 - 15 years and SPD18 - 18
 years old, as well as areas of native forest (control), in which the
 physical-water attributes were evaluated (distribution of granulometric
 fractions, soil density, total porosity, macro and microporosity,
 available water and field capacity), organic matter and the humid
 fraction. The database is organized as follows: identification of sampling
 sites, characterization of no-tillage systems under straw, soil
 physical-hydric attributes by layers and figures with the location of the
 farms and points sampling.
description: <strong>2.1. Data
 collection sites</strong> The study was carried out on farms
 representing grain production systems, in three municipalities in the
 savannah region of the southwest of the Piauí State, Brazil: Baixa Grande
 do Ribeiro (07°48'10” S, 45°00'60" W and altitude of 600 m)
 , Uruçuí (08º14'07" S, 44º38'09" W and altitude of 550
 m) and Bom Jesus (09º10'35" S, 44º50'36" W and
 altitude of 600 m) (Figure 1). The region's climate is
 tropical savannah Aw, according to the Köppen classification, with a
 predominance of the rainy season between October and April and an average
 annual rainfall of 1,200 mm. Soils of the typical dystrophic Yellow
 Latosol class predominate, with a clay-sand-sandy texture (Embrapa, 2018),
 with the remaining vegetation of the savannah (Pragana et al.,
 2012). <strong>2.2. Evaluated
 systems, history of use and soil sampling</strong> Seven managed areas and one native
 forest were evaluated, used as a reference ecosystem to compare the
 original soil conditions, totaling eight areas (Table 1). The managed
 areas were arranged in a chrono sequence according to the time of
 no-tillage system crop (SPD) (Sá et al., 2004), in: SPD2 - 2 years
 (initial phase), SPD3 - 3 years (initial phase), SPD6 - 6 years (
 transition phase) SPD10– 10 years (transition phase), SPD12 - 12 years
 (consolidation phase), SPD15 - 15 years (consolidation phase) and SPD18 -
 18 years (consolidation phase). Details of the plots and location of the
 sampled areas on each farm used in the study are shown in Figure 2 and
 Table 1. For the
 collection of soil data, in each farm, two sampling points were
 determined, one at the top of the slope and the other at the middle. At
 these points, mini trenches were opened in the soil, to allow the
 collection of samples with deformed structure and with undeformed
 structure, in the layers: 0.0-0.1; 0.1–0.2; 0.2–0.3 and 0.3-0.5
 m. At each
 sampling point and depth evaluated, an unformed sample with a volumetric
 cylindric of 100 cm³ (5 cm in height and diameter) and a deformed sample
 (300g) were collected. The granulometry, soil density, total porosity,
 soil water retention curve, granulometric fraction content (clay, sand and
 silt), volume of macro, micro and total porosity, moisture in the field
 capacity and permanent wilt, and total availability of water, organic
 matter and humine fraction were measured. <strong>2.3. Analysis of
 physical-hydric attributes of soil and organic
 matter</strong> To determine the granulometry,
 which aims to quantify the participation of each granulometric fraction in
 the soil sample, the deformed sample was used with the application of the
 total dispersion methodology described by Teixeira et al. (2017). The soil
 density, which corresponds to the relationship between the sample's
 soil mass and the volume occupied by the sample, samples collected with
 100 cm³ volumetric rings at different depths were used. For these
 determinations, the methodology proposed by Teixeira et al.
 (2017). The soil
 water retention curves, which demonstrate the relationship between the
 matrix potential and soil moisture, were constructed using undisturbed
 samples with the following stress points: saturation, 2, 4, 6, 10, 30, 300
 and 1500 kPa, combining the methodologies of the tension table (for
 tensions of 2, 4 and 6 kPa) and the Richards chamber (for tensions of 10,
 30, 300 and 1500 kPa) described by Teixeira et al. (2017) and Richards
 & Fireman (1943). To determine the total porosity
 (TP) obtained by the difference between the saturated soil mass and the
 dry soil mass in an oven at 105ºC for 24 h, the method proposed by
 Teixeira et al. (2017). The micro, macro and total porosity of the soil
 was determined by the tension table method according to the methodology
 proposed by Teixeira et al. (2017). The determination of moisture in
 the field capacity (θCC) was obtained at a tension of 10 kPa (Cassel
 & Nielsen, 1986; Reichardt, 1988), which corresponds to the soil
 moisture when it is retaining the largest possible amount of water in the
 soil. The point of permanent wilt (θPMP), which is equivalent to the lower
 limit of soil moisture capable of being absorbed by the plants, was
 obtained at the tension of 1500 kPa, in the Richards chamber (Klein,
 1999). The soil
 organic matter content was obtained by applying the correction factor of
 1.724 to the soil carbon values, as recommended by Pribyl (2010), commonly
 used to estimate the organic matter (OM) content in soils, based on the
 total organic carbon (TOC) which was determined by the Walkly Black
 method, by hot oxidation with potassium dichromate (K2Cr2O7) and titration
 with ferrous sulfate (FeSO4) (Teixeira et al., 2017). For the
 determination of the humine fraction, chemical fractionation was carried
 out using the methodology that is based on solubility in alkaline or
 acidic medium and subsequent determination of the fraction carbon, which
 in the present study was used humine (C-HU) (Teixeira et al.,
 2017).
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