Ratio of C[O.sub.2] and [O.sub.2] as index for categorising soil biological activity in sugarcane areas under contrasting straw management regimes.
Measurements of oxygen flux (F[O.sub.2]) in soils are related to the metabolic status of microorganisms and carbon accumulation or loss, especially in environments where these processes are driven by aerobic microbial activity (Stern et al. 1999), considering F[O.sub.2] as a reflection of carbon dioxide flux (FC[O.sub.2]) in the global carbon cycle (Keeling and Shertz 1992; Dilly 2003).
The FC[O.sub.2] is considered to be the result of biochemical processes in soil, and is directly related to the respiration of roots and decomposition of organic matter through microbial activity (Lai 2009). It is estimated that for a mixed hardwood forest ecosystem, root respiration accounts for 14--21% of FC[O.sub.2], with the remaining fraction due to the biological activity of soil microorganisms (Melillo et al. 2002). It is noteworthy that FC[O.sub.2] can also result from chemical activities in soil (calcareous and urea reaction; Angert et al. 2015), and processes of degassing of the soil solution and C[O.sub.2] desorption from the solid phase can produce soil C[O.sub.2] efflux (Smagin et al. 2016).
The relationship between FC[O.sub.2] and F[O.sub.2], known and described by Angert et al. (2015) as apparent respiratory quotient (ARQ), is an alternative means of describing and categorising soil activities (chemical, physical and biological), where there is a strong relationship between C[O.sub.2] production and [O.sub.2] consumption. Values of ARQ that are higher or lower than 1 can be interpreted as an imbalance between C[O.sub.2] production and [O.sub.2] consumption as a response to chemical and physical activities in soil (Linn and Doran 1984).
The soil pore network characteristics and soil texture directly influence FC[O.sub.2] and F[O.sub.2] exchange between soil and the atmosphere, through the presence of empty spaces between soil particles and aggregates (Chen et al. 2011). Furthermore, water and nutrient availability (Almeida et al. 2015), and tillage management (Bicalho et al. 2014), can also influence C[O.sub.2] production and transport, as well as [O.sub.2] consumption in soil.
Sugarcane can mechanically harvested with removal or burning of the straw or with maintenance of straw on soil without burning (De Figueiredo and La Scala 2011). Brazil is currently the largest sugarcane producer globally, with an average of 74.1 Mg [ha.sup.-1] biomass yield annually (Conab 2014), and 20 Mg [ha.sup.-1] of resulting residues are retained on the soil surface following harvest (Urquiaga et al. 1991; Oliveira et al. 1999).
The study aimed to (i) examine the profile and relationship between FC[O.sub.2] and F[O.sub.2] in a sugarcane area under contrasting management regimes (mechanical harvesting with straw burning versus mechanical harvesting with maintenance of straw), considering soil moisture; (ii) and suggest the use of ARQ as an index for categorising biological activity in soil.
Material and methods
Characterisation of the study area
The study was conducted in an area under sugarcane (Saccharum spp.) cultivation located in the state of Mato Grosso do Sul, near the municipality of Aparecida do Taboado (20[degrees]19'S and 51[degrees]13'W), Brazil, during 4-14 July 2014. The soil was classified as a dystrophic Red-Yellow Latossolo (Embrapa 2014) and Oxisol (Soil Survey Staff 2014), with a sandy clay loam texture across the 0-0.2 m depth layer (Table 1).
The region has a tropical humid climate classified as Aw (Peel et al. 2007), characterised by a rainy summer (September-June) and a dry winter (June-August), with an average annual rainfall of 1595 mm. During the field measurements, there were two precipitation events on 13 and 14 July with a daily rainfall of 6.1 and 1.5 mm, respectively (Climate Channel at UNESP Ilha Solteira, http://clima.feis.unesp.br).
The effect of residue management was evaluated in two sections of the production field under contrasting straw management regimes (Sections): Section 1, mechanical harvesting with straw burning (BH) and Section 2, mechanical harvesting with maintenance of straw (GH). Normally, GH adds an average of 20 Mg [ha.sup.-1] of crop residue; however, the quantity depends on the variety and the harvest stage (Correia and Durigan 2004; Tofoli et al. 2009; Almeida et al. 2014). Both sections had a sugarcane productivity of 63 and 46 Mg [ha.sup.-1] in 2013 and 2014, respectively.
The study area was 21.77 ha cultivated with the CTC variety of sugarcane, at a population density of 60 000 [ha.sup.-1]. This area has been used for sugarcane production for 20+ years. The soil was prepared and sugarcane planted using the conventional system (soil disturbance) in 2012.
Fertilisation was performed along the furrow and involved the distribution of 250 kg [ha.sup.-1] of mono-ammonium phosphate, equivalent to 120 kg [ha.sup.-1] of [P.sub.2][O.sub.5] and 27 kg [ha.sup.-1] of N-N[H.sub.4.sup.+]. Subsequently, topdressing was done using a liquid formula 05-00-13 + 0.3% Zn + 0.3% B, in the amount of 1000 L [ha.sup.-1], equivalent to 50 kg [ha.sup.-1] N, 130 kg [ha.sup.-1] of [K.sub.2]O, 3 kg [ha.sup.-1] of Zn and B, respectively. After the first cutting, ratoon fertilisation was performed using the best management practices of applying 90kg [ha.sup.-1] N, 30kg [ha.sup.-1] of [P.sub.2][O.sub.5] and 110kg [ha.sup.-1] of[K.sub.2]O.
For the BH, sugarcane was harvested mechanically, with burning; for the GH, the harvest was also mechanical but without burning. At sampling time, the sugarcane plants were ~20 cm tall at 2 weeks after their second cutting (harvest). Therefore, the area did not include plants that displayed higher growth stages.
Field sampling was done by selecting 10 points that had at least 5 m spacing from within each management treatment, and within the four central lines of each plot. The results of soil testing from the two sections (0-0.2 m layer), including soil physical (sand, silt and clay) and chemical properties (pH, soil organic matter, phosphorus, sulfur, calcium, potassium, magnesium, aluminium and cation exchange capacity), as well as the soil porosity (macroporosity, microporosity and total porosity), are shown in Table 1. These measures were determined using methodology from Embrapa (1997).
Water-filled porosity (WFP) was calculated using Eqn 1 described by Linn and Doran (1984). Where, soil moisture was the volumetric water content (%) and the total soil porosity (TP, %) was calculated by TP-(1 - PB/PP) x 100, where the soil particle density (PP) is assumed to be 2.65 Mg [m.sup.-3] and soil bulk density (PB) is in Mg [m.sup.-3].
%WFP = (soil moisture/TP) x 100 (1)
PVC rings (10 cm in diameter and 8.5 cm in height) were previously installed and fixed at the sample points. After 24 h, FC[O.sub.2] and F[O.sub.2] were collected along with data describing soil moisture and temperature for six separate measurement days (4, 6, 8, 10, 12 and 14 July). We used this period because we wanted to observe the relationship between these variables and the soil without the confounding contribution from crop growth at later stages. Soil measurements were made during 07:00-08:00 hours.
To collect FC[O.sub.2] we used an IRGA (LI-COR Inc, Lincoln, NE, USA) with a closed circulation system, an internal volume of 854 mL and a soil contact area of 84 c[m.sup.2]. The IRGA had an infrared (IR) system that measured the C[O.sub.2] concentration using optical-IR absorption spectroscopy. The soil temperature was monitored using a temperature probe that was integrated into the IRGA system.
The soil moisture was measured using a portable Time Domain Reflectometry system (Hydrosense[TM]; Campbell Scientific, Garbutt, Australia) that determined the soil moisture according to the dielectric constant of the travel time for an electromagnetic pulse across the space separating the two end points (two rods, 12 cm high) inserted into the soil adjacent to the PVC ring (0-10 cm).
The soil F[O.sub.2] was monitored using an [O.sub.2] sensor (CM-021; C[O.sub.2] Meter Inc., Ormond Beach, FL, USA) with a full-scale span of 0-25% (v/v). This sensor was portable and utilised ultraviolet light fluorescence to assess the [O.sub.2] concentration. The sensor result was read using Gaslab software to calculate the soil [O.sub.2] uptake rate. With the C[O.sub.2] and [O.sub.2] results, we calculated the ARQ (mol [mol.sup.-1]) according to Wolinska et al. (2011), where the ARQ is a ratio of the C[O.sub.2] emission and [O.sub.2] uptake.
Estimation of soil F[O.sub.2]
Soil F[O.sub.2] rate (d[O.sub.2]/dt) was calculated by a linear interpolation of the concentration values as a function of time, taking into account the atmospheric pressure, temperature and volume of the gas trapped in the chamber, using Eqn 2 as described by Smagin et al. (2016) and Smagin (2006):
F[O.sub.2](g x [m.sup.-2][s.sup.-1]) d[O.sub.2][10.sup.-6]PM/dt RT H (2)
where, d[O.sub.2]/d/ is the amount of [O.sub.2] (ppm) measured at time t (s); P is atmospheric pressure (Pa); M is [O.sub.2] molar mass (g [m.sup.-3]); R is the universal gas constant (8.31 J [mol.sup.-1] [k.sup.-1]); T is absolute temperature (K) and H= V/A: for volume (V)=0.00066 [m.sup.3] and cross-sectional area (A) = 0.008 [m.sup.2] of the camera above the ground (soil surface).
Data processing and statistical analysis
Soil moisture, [O.sub.2] uptake (F[O.sub.2]), C[O.sub.2] emission (FC[O.sub.2]) and the daily mean of ARQ were calculated using an N (number) of 10 replicates per day, compared using Student's t-test (P [less than or equal to] 0.05) per each management sector. Consequently, FC[O.sub.2], F[O.sub.2] and total ARQ were calculated using all days observed, with N= 60 per treatment. An integration of the area under the FC[O.sub.2] and F[O.sub.2] curves was calculated. Thereafter, the treatment results were compared using Student's t-test (P [less than or equal to] 0.05).
The relationships of F[O.sub.2] and FC[O.sub.2] with soil moisture were calculated using Pearson's correlation for both management regimes. The analysis of presuppositions was conducted using analysis of residuals, identifying the outliers and influent values using leverage statistics. The normality of residuals was verified by the Shapiro-Wilk test (P [less than or equal to] 0.05) and homogeneity of variance was assessed using the Bartlett test (P [less than or equal to] 0.05).
Daily results of soil variables
Soil C[O.sub.2] emission on 4, 6, 8 and 10 July were similar, with means of 0.04, 0.06, 0.03 and 0.04 mg [m.sup.-2] [s.sup.-1] for GH and 0.07, 0.07, 0.06 and 0.07 mg [m.sup.-2] [s.sup.-1] for BH respectively (Fig. Id). Both treatments, presented lower and relatively constant C[O.sub.2] emission when the soil moisture varied within 6.44-8.60% (BH) and 6.0-7.4% (GH), (Fig. 1b). However, after 10 July, C[O.sub.2] emission and soil moisture increased by means of 0.07 and 0.14 mg [m.sup.-2] [s.sup.-1] and 14.11 and 14.33% respectively for GH and BH (Fig. 1 d, b), following a precipitation event of 6.1mm (Fig. 1a).
The BH provided higher C[O.sub.2] emission across all days observed, and significantly differed from those of GH on the 4, 8, 10, 12 and 14 July. The highest BH difference was on 12 July with a C[O.sub.2] emission increase of 53.68% compared with GH (Fig. 1 d).
The temporal variability in soil [O.sub.2] uptake was inverse compared with C[O.sub.2] emission the estimates of [O.sub.2] uptake revealed variation of 0.22-0.46 and 0.20-0.40 mg [m.sup.-2] [s.sup.-1] on the first days (4 and 10 July), and following the precipitation event the [O.sub.2] uptake decreased (without a significant difference between the days and treatments) (Fig. 1c).
The ARQ profile was very similar to the estimates of C[O.sub.2] emission, soil moisture and precipitation (Fig. 1). In other words, ARQ was constant, lower than 1 and mean variation range of 0.27-0.90 (GH) and 0.17-0.31 (BH) during 4-10 July. Contrastingly, following the precipitation event (12 July) ARQ was higher than 1, with the greatest values for ARQ in BH (1.38 [+ or -] 0.46 mol [mol.sup.-1]) and lower than 1 in GH (0.77 [+ or -] 0.46 mol [mol.sup.-1]).
Accumulated FC[O.sub.2], F[O.sub.2] and ARQ
Accumulated F[O.sub.2] revealed means of 202.52 [+ or -] 49.62 and 267.41 [+ or -] 73.6 g [O.sub.2] [m.sup.-2] for the GH and BH regimes respectively (Fig. 2a). Comparison by t-test showed no differences in the F[O.sub.2] uptake between harvesting techniques (P>0.05). However, BH demonstrated higher cumulative C[O.sub.2] emission (87.07 [+ or -] 19.45 g C[O.sub.2] [m.sup.-2]), which was 50.0% higher but not significantly different compared with GH (52.31 [+ or -] 15.41 g C[O.sub.2] [m.sup.-2]) (Fig. 2a).
The cumulative ratio of FC[O.sub.2] and F[O.sub.2], represented by ARQ, was below 1 in both treatments, having means of 0.23 [+ or -] 0.18 and 0.18 [+ or -] 0.07 for BH and GH respectively (Fig. 2b). The ARQs for both treatments did not significantly differ according to t-test.
Relationships of soil C[O.sub.2] emission and [O.sub.2] uptake with soil moisture
The C[O.sub.2] emission and soil moisture were positively and significant correlated for both treatments (Fig. 3a, c), although higher for BH (r=0.74) than for GH (r=0.50). The higher r for BH suggests a greater sensitivity of burned residue management. The soil moisture was negatively correlated with [O.sub.2] uptake in BH (r=-0.43) and GH (r = -0.42) (Fig. 3b, d). The C[O.sub.2] and [O.sub.2] were negatively correlated for BH (r=-0.41), but not correlated for GH (Fig. 4). We also noted that GH had a higher microporosity (31.6%) and lower macroporosity (11.1%) and WFP (18.73%) compared with BH (Table 1).
C[O.sub.2] and [O.sub.2] results
The consistent magnitude of FC[O.sub.2] across 4-10 July for GH and BH suggests a corresponding stability in soil microbial activity. Typically, low and stable FC[O.sub.2] occurs after the soil carbon mineralisation of soil organic matter (Cunha et al. 2011; Badia et al. 2013; Knicker et al. 2013) leading to lower emissions and microbial activity (Luo et al. 2006).
Higher C[O.sub.2] emission for BH compared with GH has been observed in other studies by Panosso et al. (2009) and Corradi et al. (2013), who examined a similar Oxisol and soil management regimes in Sao Paulo. This difference could be explained by higher nutrient availability in the BH treatment due to burning (Marques et al. 2009; Panosso et al. 2011). However, in our experiment we did not observe a significant difference in soil nutrient availability between BH and GH. This is likely to be driven by the fact the burning occurred once, and that changes to organic nutrient availability through this process depend upon the intensity and duration of burning.
Contrastingly, the BH had higher macroporosity and total porosity, and lower microporosity, compared with GH. The high porosity for BH may have resulted from burning of sugarcane residue and an increase in empty spaces in soil, causing the opening of potentially charred root channels or plugging of smaller micropores by ash deposits. It should be kept in mind that both the BH and GH treatments had the same degree of mechanical harvesting traffic and soil preparation.
The relationship between soil porosity and C[O.sub.2] has been previously reported (Xu and Qi 2001; Epron et al. 2006; Panosso etal. 2011; Bicalho etal. 2014). Soil porosity is responsible for soil gaseous transport (Xu and Qi 2001; Epron et al. 2006) and the movement of organic and inorganic solutions throughout the soil, which supports the natural habitat for microbial communities (Ranjard and Richaume 2001). Therefore, soil porosity can help to explain the degree of soil C[O.sub.2] emission (Wick etal. 2012).
Additionally, the lower FC[O.sub.2] estimates for GH were likely the result of sugarcane residues on the soil surface, which have been shown to present a high carbon/nitrogen ratio (Almeida et al. 2015), lignin (Costa et al. 2013) and cellulose contents (Almeida et al. 2009), and a lower crude protein concentration (Pereira et al. 2000). These characteristics are important parameters in nutrient dynamics (Lai 2004) and can consequently reduce FC[O.sub.2] because of slow residue decomposition (Almeida et al 2014).
Relationships between soil C[O.sub.2] and [O.sub.2]
The temporal variability in soil [O.sub.2] was inverse compared with C[O.sub.2], reflected by a decrease in [O.sub.2] and an increase in C[O.sub.2] for both treatments, following precipitation. Consequently, these results confirm that soil moisture can change the soil C[O.sub.2] and [O.sub.2] profile. According to Gardini et al. (1991) and Howard and Howard (1993), soil moisture is a key abiotic factor affecting the C[O.sub.2] emission and [O.sub.2] uptake processes (Gardini et al. 1991), as well as soil temperature (Kyaw Tha Paw et al. 2006).
The positive correlation between C[O.sub.2] and soil moisture was also observed by Lai (2009) and Wei et al. (2014), and can be described as linear response with respect to soil moisture (variations of 38-47%) at clay soil (Corradi et al. 2013). Soil moisture can promote increases in FC[O.sub.2] of up to 80% (Chen et al. 2011) as result of higher microorganism and root activity (Lai and Kimble 1997). According to Doran et al. (1990) and Chen et al. (2011) the highest soil respiration rates occur for WFP of 40-70% for the majority of soils. In our experiment, there was WFP <70% for all treatments and days observed.
Additionally, the high correlation between FC[O.sub.2] and soil moisture for BH can be explained by higher macroporosity and lower microporosity, which has been shown to govern C[O.sub.2] transport rates and water infiltration in soil aggregations (Silva et al. 2005), and is typically faster in soils with higher macroporosity than microporosity (Ceddia et al. 1999).
Decreases in [O.sub.2] following precipitation events were also observed by Linn and Doran (1984) and Gardini et al. (1991), and have been explained by a reduction in the amount of [O.sub.2] in soil pores with water infiltration (Cook et al. 2007), which limits the [O.sub.2] exchange between soil and atmosphere (Armstrong and Drew 2002; Elberling et al. 2011). This suggests that water in soil pores limits [O.sub.2] uptake, but may increase C[O.sub.2] release for WFP <70%.
Relationships between soil C[O.sub.2] emission and [O.sub.2] uptake
The FC[O.sub.2] and F[O.sub.2] were negatively correlated for the BH treatment. However, we did not observe a relationship between these factors for the GH treatment. Kyaw Tha Paw et al. (2006) also found a negative relationship between FC[O.sub.2] and F[O.sub.2] in soil (at 15 cm in depth) with vegetation of ~3cm high, as consequence of respiration by roots and microorganisms and the simultaneous increase of FC[O.sub.2] concentration and [O.sub.2] depletion. We further observed that F[O.sub.2] was higher than FC[O.sub.2] for both treatments and, similarly, Angert et al. (2015) found higher F[O.sub.2] compared with C[O.sub.2] in a study of temperate and alpine forest ecosystems.
To understand ARQ as an index for categorising soil activity, it must first be understood that ARQ values close to 1 are considered a reflection of aerobic activity with ARQ balance-the result of production of 1 mol C[O.sub.2] and consumption of 1 mol of [O.sub.2]. However, ARQ values higher or lower than 1 indicate an imbalance between FC[O.sub.2] and F[O.sub.2]. The ARQ index has similarly been used as a criterion for soil microbial activity across different WFP conditions (Stotzky 1960; Alef 1995; Dilly 2003), as a means of elucidating the relationship between FC[O.sub.2] and F[O.sub.2].
The ARQ was below 1 before the rainfall event for BH and GH, but shifted closer to 1 after precipitation (12 July) with soil moisture in the range of 6.4-14.5% and WFP <32.0%. According to Linn and Doran (1984), an increase in ARQ values of 1.3-1.7 can occur with an increase in soil water content and WFP >70% and indicates a shift towards anaerobic metabolism. However, in our experiment the WFP value was not >70% on 12 July. Franzluebbers (1999) highlighted that the maximum respiratory activity of soil microbial biomass at WFP levels in the range of 27-68% was due to higher availability of [O.sub.2]. Under this WFP condition, it is likely that there was a predominance of aerobic compared with anaerobic respiration, soil chemical reactions (presence of calcareous materials and urea fertilisation) and the degassing process. According to Smagin et al. (2016), processes of degassing of the soil solution and C[O.sub.2] desorption from the solid phase can produce soil C[O.sub.2] efflux. Therefore, these processes can produce C[O.sub.2] with no direct
relationship to [O.sub.2] consumption, thus changing the soil C[O.sub.2] and [O.sub.2] balance.
Our results show that soil moisture affected the [O.sub.2] uptake and C[O.sub.2] emission profile of soil by limiting [O.sub.2] uptake and increasing the release of C[O.sub.2] for conditions of WFP < 70%. The high level of soil macroporosity and low degree of soil microporosity increased C[O.sub.2] emission.
The correlation between [O.sub.2] uptake and C[O.sub.2] emission profiles depends on crop residue management and soil pore network characteristics. The BH management regime provided higher cumulative C[O.sub.2] emission with a 50.0% increase compared with GH, which added sugarcane residue to the superficial soil layers and so helped prevent soil erosion.
The ARQ can be used as an index to categorise biological activity in soil, with ARQ values close to 1 considered a reflection of aerobic activity with balance between C[O.sub.2] production and [O.sub.2] consumption.
Conflicts of interest
The authors declare no conflicts of interest.
The authors would like to thank the following Brazilian institutions for their financial support: Brazilian Federal Agency for Support and Evaluation of Graduate Education (CAPES) and Brazilian National Council for Scientific and Technological Development (CNPQ). Many thanks to the Exact Sciences Department (Universidade Estadual Paulista), and to the Soil, Water and Climate Department (University of Minnesota) for the opportunity to develop this paper.
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Risely Ferraz de Almeida (A,E), Daniel de Bortoli Teixeira (B), Rafael Montanari (C), Antonio Cesar Bolonhez (C), Edson Belisario Teixeira (C), Mara Regina Moitinho (A), Alan Rodrigo Panosso (A), Kurt A. Spokas (D), and Newton La Scala Junior (A)
(A) Sao Paulo State University (FCAV/UNESP), Jaboticabal, Sao Paulo, Brazil.
(B) University of Marilia (Unimar), Marflia, Sao Paulo, Brazil.
(C) Sao Paulo State University (FEIS/UNESP), llha Solteira, Sao Paulo, Brazil.
(D) ARS, USDA, Soil and Water Res Management Unit, St Paul, MN, 55108, USA.
(E) Corresponding author. Email: email@example.com
Received 7 December 2016, accepted 27 December 2017, published online 20 April 2018
Caption: Fig. 1. (a) Precipitation, (b) soil moisture, (e) [O.sub.2] uptake, (d) C[O.sub.2] emission and (e) apparent respiratory quotient (ARQ) of soil under contrasting sugarcane management regimes of mechanised harvesting with straw (GH) and burned straw (BH). Note: days marked with different lower-case letters differ according to t-test (P [less than or equal to] 0.05). The [O.sub.2] uptake and ARQ show no significant difference for days according to t-test (P [less than or equal to] 0.05).
Caption: Fig. 2. (a) Soil cumulative C[O.sub.2] emission and soil cumulative [O.sub.2] uptake and (b) apparent repiratory quotient (Total ARQ) of soil under contrasting sugarcane management regimes of mechanized harvesting with straw (GH) And burned straw (BH). Note: bars identified with different upper-case letters differ according to t-test (P [less than or equal to] 0.05).
Caption: Fig. 3. Relationship of soil moisture (%) with (a, c) [O.sub.2] uptake and (b, d) C[O.sub.2] emission, within a sugarcane area under contrasting sugarcane management regimes of mechanised harvesting with straw (GH) and burned straw (BH).
Caption: Fig. 4. Relationship between soil C[O.sub.2] emission and soil [O.sub.2] uptake within a sugarcane soil under contrasting sugarcane management regimes of mechanised harvesting (a) with burned straw (BH) and (b) straw (GH).
Table 1. Physical and chemical attributes of a Red-Yellow Latosol under contrasting sugarcane management regimes involving mechanised harvesting with the presence of straw (GH) and with straw burning (BH) pH in 0.1 KC1, soil organic matter (SOM), phosphorus (P), sulfar (S), calcium ([Ca.sup.2+]), potassium ([K.sup.+]), magnesium ([Mg.sup.2+]), aluminium ([Al.sup.3+]), cation exchange capacity (CEC), macroporosity (Macro), microporosity (Micro), total porosity (TP) and water-filled porosity (WFP) Soil chemical attributes Straw PH SOM P management -- (g [dm.sup.-3]) (mg [dm.sup.-3]) BH 5.11 [+ or -] 16.30 [+ or -] 8.0 [+ or -] 0.04 0.58 0.26 GH 5.18 [+ or -] 15.90 [+ or -] 8.2 [+ or -] 0.08 0.23 0.29 Soil chemical attributes Straw S [Ca.sup.2+] [K.sup.+] management (mg [dm.sup.-3]) ([mmol.sub.c] [dm.sup.-3]) BH 5.5 [+ or -] 19.7 [+ or -] 1.36 [+ or -] 0.22 1.1 0.09 GH 5.3 [+ or -] 22.0 [+ or -] 1.26 [+ or -] 0.26 0.86 0.13 Soil chemical attributes Straw [Mg.sup.2+] [Al.sup.3+] CEC management ([mmol.sub.c] [dm.sup.-3]) BH 9.1 [+ or -] 0 8 [+ or -] 55 06 [+ or -] 0.81 0.2 1.95 GH 8.7 [+ or -] 0.9 [+ or -] 53.46 [+ or -] 0.58 0.31 0.72 Soil physical attributes Straw Sand Silt Clay management (g [kg.sup.-1]) BH 613 [+ or -] 101.0 [+ or -] 286.0 [+ or -] 1.0 1.0 0.0 GH 602 [+ or -] 111.5 [+ or -] 286.0 [+ or -] 0.35 0.35 0.0 Soil physical attributes Straw Macro Micro management BH 14.6 [+ or -] 29.01 [+ or -] 2.01 0.60 GH 11.1 [+ or -] 31.58 [+ or -] 1.37 1.05 Soil physical attributes Straw TP WFP management (%) BH 43.69 [+ or -] 18.73 [+ or -] 1.66 5.6 GH 42.75 [+ or -] 18.49 [+ or -] 1.07 6.4
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|Author:||de Almeida, Risely Ferraz; de Bortoli Teixeira, Daniel; Montanari, Rafael; Bolonhez, Antonio Cesar;|
|Date:||Jul 1, 2018|
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