Assessing of the influence of organic and inorganic amendments on the physical-chemical properties of a red soil (Ultisol) quality

Catena 183 (2019) 104231

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Assessing of the influence of organic and inorganic amendments on the physical-chemical properties of a red soil (Ultisol) quality

T

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Yangbo He , Feng Gu, Cheng Xu, Yao Wang Key Laboratory of Arable Land Conservation, Ministry of Agriculture and Rural Affairs, Huazhong Agricultural University, Wuhan, Hubei, China

A R T I C LE I N FO

A B S T R A C T

Keywords: Soil aggregates Plant available water Fe/Al oxides pH Amendments

Many highly weathered soils in subtropical environments have low organic matter contents that limit the aggregation, plant available water (PAW) and have acidity issues, increasing the risk of erosion and limiting plant growth. The objective of this study was to determine the influence of gypsum, lime, fused calcium-magnesium phosphate (fertilizer) (CaMgP), and biochar on soil physical and chemical properties in two types of red soil (Ultisol). In a laboratory study, two types of red soil aggregate stability, PAW, the saturated hydraulic conductivity (Ksat), pH, and Fe/Al oxides were measured after 21, 60, 180, and 365 days application. The soil amendments increased soil pH and the amount of amorphous Fe/Al oxides for two soils. The clayey red soil amorphous Fe/Al oxides (ammonium oxalate extracted oxides) were significantly (P < 0.05) positively correlated with the small macroaggregate fraction (0.25–2 mm) and hence increased the mean weight diameter (MWD). Consistent with the increased clayey red soil aggregation stability compared to control, the PAW was significantly increased after amendments where CaCO3 and CaMgP resulted in greater PAW than biochar followed by CaSO4. Ksat was not obviously changed after all amendments except for biochar. However, for granite red soil, the oxides and aggregates exhibited no change overtime under each amendment except for Al oxides compared to clayey red soil, resulting in a slight increase in PAW but a significant increase in Ksat. Application time for two red soils was also significant (P < 0.05), displaying substantial change 60 days after application. These findings suggest that amendments are helpful to red soil quality through their positive increase in aggregate stability, PAW and Ksat over time as influenced by the pH and soil amorphous oxides, probably beneficial for future crop yields.

1. Introduction

quality, limiting crop yields and soil resilience to erosion (Chen et al., 2010; Li et al., 2014). Soil quality is defined as “the capacity of a specific kind of soil to function, within natural or managed ecosystem boundaries, to sustain plant and animal productivity, maintain or enhance water and air quality, and support human health and habitation” (Karlen et al., 1997). Therefore, exploring different amendments to improve soil quality (including physical-chemical properties) of red soil will be necessary. Building the macroaggregate fraction and stability of red soils can increase the amount of PAW, and improve the root penetration and crop yield (He et al., 2017; Shi et al., 2017). When soil aggregate size distribution changes, the soil water properties are affected by the change in the distribution and connectivity of soil pores (Verheijen et al., 2010). The soil aggregate evolution is controlled by the content in organic matter, soil oxides, and water (Algayer et al., 2014). Gradual increase in soil organic carbon (SOC) over a 25 year period in South Dakota USA increased the soil aggregation, PAW and crop yields,

Strongly leached red soils (Ultisol) in subtropical climate have relative low native fertility and organic matter contents (Zhao et al., 2000) which result in poor physical properties such as low saturated hydraulic conductivities (Ksat) and low plant available water (PAW) (Lal, 2000; Chen et al., 2004; Liu et al., 2013). For example, the amount of PAW in the surface 100 cm of a silty clay red soil ranged from 9 to 12 cm (Liu et al., 2013). For comparative purposes, a silt loam soil in temperate regions contains between 10.8 and 21.8 cm of water per meter of soil (Clay and Trooien, 2017).The low Ksat and PAW are generally attributed to poor soil pore architecture determined by poor microaggregation of Ultisols (Yang et al., 2013). In addition, the red soils are subjected to a more serious acidity problem indicated by a sharp decline in pH about 0.5 in unit due to large inputs of chemical fertilizers from the 1980s to 2000s in major Chinese croplands (Guo et al., 2010). Due to these reasons, many red soils exhibited poor soil

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Corresponding author. E-mail address: [email protected] (Y. He).

https://doi.org/10.1016/j.catena.2019.104231 Received 11 January 2018; Received in revised form 16 August 2019; Accepted 20 August 2019 0341-8162/ © 2019 Elsevier B.V. All rights reserved.

Catena 183 (2019) 104231

yielding a 1 billion dollars (U.S.) return on investment (Clay et al., 2014). The crystallization of soil oxides was thought to be the dominant cementing agent in the aggregates of southern-China Ultisols which can be influenced by the content of SOC and pH (Duiker et al., 2003; Jiang et al., 2010; Peng et al., 2015). All these properties can be affected by the use of soil amendments. Chemical amendments such as liming, gypsum, and by-products from agro-industries including crop residuals, manures and biochar have been proposed as reliable approaches for enhancing soil structure and soil fertility recovery (Lin and Chen, 2015; Raboin et al., 2016; Cesarano et al., 2017). However, different amendment types, rates and application techniques and soils caused different soil aggregation, water retention, and chemical properties. Liming (5 Mg ha−1) had positive effect on reducing the soil acidity, increasing the total soil porosity and hence Ksat of an Ultisol (Anikwe et al., 2016). Liming also generated microaggregates as a consequence of ionic calcium bridges, and resulted in great improvement in the soil water retention including the field capacity (FC) and PAW (Barthes et al., 2008). Perez-de-losReyes et al. (2011) had similar results and reported that PAW was increased when sugar foam (dominated by CaCO3) was applied (20–40 ha−1 y−1) to Ultisols in Spain. However, in different soils, Perez-de-los-Reyes et al. (2015) reported that sugar foam to a depth of 40 cm did not increase the PAW. The differences in liming effect on the aforementioned soil water retention may be attributed to the different change of aggregate and other chemical agents after long-term. Phosphogypsum long-term application was also beneficial for SOC increase, but had residual effect on the accumulation of sulfate in subsoil after five years (Martins da Costa and Costa Crusciol, 2016). Other amendments have had some success in increasing the aggregates and PAW. For example, Biochar+ NPK addition increased the PAW (Ma et al., 2016), probably through change of aggregation induced by SOC and soil Fe oxides crystallization (Andruschkewitsch et al., 2014; Yin et al., 2016). But, biochar caused a decline in macroaggregates yields in 50–70% even though macroaggregate-associated OC was increased in a silty loam soil (Grunwald et al., 2018). Biochar also had unique properties to reduce nitrous oxide and CO2 emissions (Chang et al., 2016). Gas reductions may be as consequences of changes in C sequestration induced by soil physical properties such as aggregation, and soil water holding capacity, and chemical properties of soil pH after biochar application. In general, the inorganic and organic amendments may result in different soil physical and chemical properties and therefore influence crop growth (Thangarajan et al., 2018). However, functions of different chemical and organic amendments on red soil quality are not clear. Which is the best amendment? Therefore, we hypothesize that the application of chemical materials and biochar will improve the soil aggregate, the water retention, and change chemical properties of red soils. The objectives of our study were to determine the effect of different amendments (lime, gypsum, CaMgP and biochar) at successive times on soil quality through their impact on soil physical properties (specifically, aggregate, Ksat and PAW), and chemical properties (soil oxides and pH). SOC indicates the soil organic carbon. CEC indicates the cation exchange capacity.

2. Materials and methods 2.1. Study area and soil samples Two types of red soils are sampled from two fields in Xianning County, which lies in the southeast of Hubei province, China. The annual average temperature in the region is approximately 16.8 °C. Annual average precipitation is approximately 1300 mm, > 50% of annual rainfall occurs from March to July, and < 20% occurs from August to October. The first clayey red soil (Ultisol) that is developed from Quaternary red clay parent material is located in the field (N. 114.3663°, E. 30.0167° N), which has a relatively thin A horizon (0–30 cm) and thick B horizon (30–150 cm) through the field investigation. The bulk density increases with depth from 1.44 g cm−3 at

b

a

6.33 4.47 Granite red soil

7.71

67.0

4.81

78.8

16.2

5.0

Mica:30%, Kaolinite:69% Transitional minerals (1.4 nm): 1% Mica: 19%, Kaolinite: 27% Transitional minerals (1.4 nm): 54% 50.7 44.5 4.8 4.46 214.9 19.86 19.89 11.54 Clay red soil

CEC (cmol kg−1)b Soil organic matter (g kg−1) SOC (g kg−1)a Soil name

Table 1 Basic soil physical and chemical properties of the two soils.

EC1:1 (μS cm−1)

pH1:1

Sand (2–0.05 mm) (%)

Silt (0.05–0.002 mm) (%)

Clay (< 0.002 mm) (%)

Dominant clay minerals

Y. He, et al.

2

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surface to 1.59 g cm−3 in the subsurface (> 30 cm). The second granite red soils (Ultisol) that is developed from granite weathered detritus are located in the site (N. 113.7717°, E. 29.3347°) which has thin soil A and B horizons. All samples in this study were collected from about 0–30 cm. After collection, the soils were air-dried, broken apart along the natural break points, and were passed through a 5 mm sieve to collect aggregates for following laboratory test. The soil particle size distribution (< 2 mm) was determined by the Robinson's pipetting method. Soil cation exchange capacity (CEC) was determined by 1 M NH4OAc extraction. Soil organic carbon (SOC) was tested by the oxidation with potassium dichromate and soil organic matter value was corrected by an oxidation coefficient of 1.33 based on SOC (Bao, 1999). Soil pH1:1 was also tested in 1:1 soil: water solution. Soil clay minerals were determined by the Xray diffraction, where the clay particles (< 2 μm) were firstly treated by citrate-biocarbonate-dithionite for removal of irons. Then Mg-glycerol and K-saturated oriented samples were prepared and scanned by X-ray diffraction using Cu Kα radiation, followed by being quantified using MID Jade6.0. All the basic properties are shown in Table 1.

et al., 2008). After each centrifugal step, the samples were weighed and returned to the centrifuge to undergo the next higher rotation speed until the last water potential (1500 kPa). The samples were finally oven-dried at 105 °C for 24 h to obtain the soil dry mass. The difference between the water content at the FC (33 kPa) and permanent wilting point (PWP) (1500 kPa) was taken as the PAW. The soil Ksat was determined by the constant head method. Soil aggregate were mainly measured on the clayey red soil type and aggregation on the granite red soils was very low due to high sand percentage. Air-dried soil subsamples were sieved on the assembled sieves: 5.00, 2.00, 1.00, 0.50, 0.25, and 0.10 mm for dry aggregate size analysis. Then the clayey red soil aggregates between 2 and 5 mm during dry sieving were collected and then oven-dried at 40 °C for about 24 h prior to the water stable aggregate determination. The water stable aggregate stability was determined by the modified slow wetting (SW) and fast wetting (FW) methods in Le Bissonnais (1996). For SW method, 5 g of aggregates were placed on the filter paper and subjected to tension of 33 kpa for 30 min, and then the aggregates were transferred to a 50 μm sieve, submerged into ethanol to be gently shaking for 20 times (with 2 cm in the amplitude). The aggregates remaining on the 50 μm sieve were collected, and dried for at least 48 h at 40 °C, followed by being passed through the sieves assembled as 2.00, 1.00, 0.50, 0.25, and 0.10 mm. For the FW method, 10 g of aggregates were generally submerged in the distilled water for 10 min. The subsequent sieving procedure in the FW repeated as that in the SW. The aggregate determination was repeated for five times for each treatment. The aggregate mean weight diameter (MWD) was determined as in Eq. 1, the percentage of aggregate destruction (PAD) was defined as Eq. 2.

2.2. Soil amendments and laboratory treatments For the lab experiment, the following four types of amendments were applied to both soils. The amendments included lime (CaCO3), a fused calcium-magnesium phosphate fertilizer (CaMgP: the dominant components are Ca3(PO4)2, CaSiO3, and MgSiO3), gypsum (CaSO4.2H2O), and a commercial biochar (produced from rice bran and animal manures at temperature of 550 °C, with C/N = 13). Each amendment was applied to soils at two rates of 2 and 8 g [kg soil]−1 (about 5 and 20 Mg ha−1). The soil without any amendment was used as control. So, nine treatments were set up: (1) Control; (2) CaCO3 at 2 g kg−1; (3) CaCO3 at 8 g kg−1; (4) CaMgP at 2 g kg−1; (5) CaMgP at 8 g kg−1; (6) CaSO4 at 2 g kg−1; (7) CaSO4 at 8 g kg−1; (8) biochar at 2 g kg−1; (9) biochar at 8 g kg−1. All the treated soils were maintained in laboratory for four different times after application (21, 60, 180 and 365 days) and replicated for three times for each soil as below. A mixture of soils and above amendment (< 5 mm, to keep the original soil aggregates) were mixed thoroughly and added in each plastic PVC pot (diameter = 11 cm; height = 10 cm) to a bulk density about 1.3 and 1.5 g cm−3 for the clayey red soil and granite red soil, respectively. The soils in pot were then slowly wetted to approximately 70% of its FC (about 0.24 and 0.15 cm3 cm−3 for clayey red soil and granite red soil, respectively). After that, soils in pots were allowed to equilibrate overnight at the room temperature followed by being covered with the plastic film (with small holes). Subsequently, samples in the pots were placed into incubation chambers to keep for time periods of 21, 60, 180, and 365 days. All the samples were maintained in the chamber at 25 °C and moisture of 70%. During the incubation, the weight of PVC pot with soils was weighted by every 10 days, averagely about 15 g of water was added to maintain the desired water content. When the required application time was reached, soil core was taken using the cutting ring (diameter = 2.5 cm, height = 5.1 cm) in each PVC pot for the later soil water retention measurement. The remaining subsamples of soils in each PVC pot were kept to analyze the soil aggregate, oxides content, pH, ion content, and organic carbon.

MWD =

n+1

∑1

ri − 1 + ri × mi 2

(1)

where, r = aperture of the ith mesh (mm), r0 = r1, and rn = rn+1; mi = mass fraction of aggregates remaining on ith sieve; n = number of the sieves.

PAD =

Wa − Wb × 100% Wa

(2)

where, Wa and Wb are the dry and wet fraction of aggregate in certain size (e.g., 0.25–2 mm), respectively. 2.4. Soil chemical properties measurement Soil chemical analyses were conducted on the < 2 mm soil fraction. The electrical conductivity (EC) and pH were determined from 1:1 soil to water solution. The “free” Fe (Fed) and Al (Ald) oxides of all soil samples were extracted with the citrate-biocarbonate-dithionite, “chelated” Fe (Fep) and Al (Alp) oxides were extracted with the sodium pyrophosphate, and the “amorphous” Fe (Feo) and Al (Alo) oxides were extracted by the ammonium oxalate according to the Bao (1999). The Ca2+ ions of soils were extracted by shaking 1 g of soil with 20 mL of 1 M NH4OAc, followed by a centrifugation for 5 min. The Fe, Al, and Ca in above extraction were determined by the atomic absorption spectrophotometry (Agilent Technologies 200 Series AA, Santa Clara, CA, USA). The total organic carbon in the biochar treatments was tested by the Total Elemental Carbon (Vario Pyro Cube, Germany).

2.3. Plant available water, Ksat, and soil aggregate stability 2.5. Statistical analysis The soil water retention properties of the two soils were determined by using the core soil samples through the centrifuge methods (Russel and Richards, 1938), which can indirectly reflect the soil pore size situation. A centrifuge (GR21G, Hitachi, Japan) with an outer radius of 9.8 cm (re) was used to hold four soil samples. Prior to the experiment, a preliminary test was conducted to determine the rotation speed and period to reach the specific soil water potential equilibrium (0, 33, 50, 500, and 1500 kPa) corresponding to a given centrifugal force (Reatto

Soil aggregate MWD and PAW within the four application times under the major different types of amendments (CaCO3, CaSO4, CaMgP, biochar, and Control) was tested by General Linear Model-Repeated Measures using SPSS 17.0. Under this analysis, the Mauchly's test of Sphericity was first conducted to test the effects of incubation time. If the results did not fulfill a sphericity assumption, the Multivariate tests was conducted to evaluate the Within-Subjects-Effects (incubation 3

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Fig. 1. Comparisons of amendments' effect on aggregate size fractions for 21, 60, 180, and 365 days for fast wetting (FW) and slow wetting (SW) methods of the clayey red soil. The lower-case letters indicate significant difference of aggregate size portion among the amendments types at the same aggregate size (P < 0.05).

over the application time. The large macroaggregate fraction after amendments was not significantly different from control under application time except for 21 and 60 days. However, with application time going, the small macroaggregate fraction (0.25–2 mm) under amendments was significantly increased compared to control and the most remarkable increase was on 60 days (Fig. 1). At the FW method, the soils were dominated by the small macroaggregates and the fraction differences among amendments mainly occurred on 21 and 60 days. The above differences in aggregate size fraction under SW and FW methods reflected different stability of red soil subjected to water which can be indicated by PAD. The PAD > 2mm and PAD0.25–2 mm for clayey red soil in Fig. 2 showed a decline trend with time under each type of treatment for FW method, for example. For PAD > 2mm, a substantial lower PAD > 2mm under biochar happened for 21 and 60 days compared to control, while slightly lower PAD > 2mm under biochar happed for longer times. This may be due to the significantly greater formation of large macroaggregate in biochar for 21 and 60 days compared to control at FW in Fig. 1. But for PAD0.25–2 mm, the control had PAD values between 9.8% and 21.7% while the amendments additions significantly reduced this value which followed an order of CaMgP < CaCO3 < biochar < CaSO4 < control (Fig. 2). This indicated the newly-formed small macroaggregate (0.25–2 mm) after amendments was stable. The different PAD among amendments with time demonstrated that the new-formed aggregates had different resilience to water. The above aggregate size distribution and PAD differences among amendments overtime were also reflected in aggregate MWD for clayey

time) and Between-Subjects-Effects (types of amendments) on soil MWD and PAW. The aggregate fraction and the PAW after different treatments were also tested for significant differences using the Fisher's least significant difference test (P < 0.05). The plots of aggregates, soil water retention, Ksat, and the soil oxides under the treatments were all determined by Origin 8.0 (One Roundhouse Plaza, Northampton, MA, USA). Finally, Pearson correlation coefficients (r) were calculated using all the soil parameters in study by SPSS 17.0. 3. Results 3.1. Change of soil aggregates The clayey red soil aggregates size distribution was displayed among the five types of amendments under the application time for SW and FW methods (Fig. 1). However, for granite red soil, the change of aggregate size distribution and MWD was not obvious due to do high sand percentage during the study period, so no aggregation data was reported here. Below aggregation variation overtime was reported all for the clayey red soil. At the SW method, the clayey red soils were dominated by the large macroaggregates (> 2 mm) followed by the small macroaggregate fraction (0.25–2 mm) and the fractions of each size were different among the amendments at a rate of 8 g kg−1(Fig. 1). The control had the large macroaggregate fraction from 31.4% to 59.8%, whereas in the amendments the average fraction of large macroaggregates ranged from 46.3 to 67.2%, 38.5 to 61.8%, 33.4 to 53.2%, and 37.3 to 59.4% for biochar, CaMgP, CaCO3, and CaSO4, respectively 4

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Fig. 2. The percentage aggregate destruction (PAD > 2mm, PAD0.25–2 method.

mm)

variation over the application time for all amendments of clayey red soil under the FW

red soil (Fig. 3). The change in MWD after amendments had similar evolution overtime compared to control except for CaCO3 and biochar. Generally, at the SW and FW method, the MWD started to significantly increase after 60 days, indicating that the first 60 days being important in aggregate formation after amendments (Fig. 3). The highest MWD value generally reached after 180 and 365 days for SW and FW method, respectively. For example, MWDsw under biochar increased from 1.58 to 1.92 mm from 21 to 365 days (35% increase vs 17% increase for control). Statistical analysis in Table 2 also confirmed that application time and types of amendments had significant effect on soil MWD. For example, the MWDfw at FW method among amendments at the same day after application was significantly different through multivariate analysis: tests of between-subjects effects (Table 2). 3.2. Variation of soil water retention and saturated hydraulic conductivity Due to the change of soil aggregate size and MWD over time, the clayey red soil water retention properties (PAW and FC) were changed differently overtime among amendments (Fig. 4). The Table 2 also demonstrated the significant effect of amendment type on soil PAW. All the amendments improved the soil PAW compared to that in control under each application time (Fig. 4). But the PAW among amendments types was significantly different only under the specific time of 21, 60 and 365 days by tests of between-subjects effects in Table 2. The PAW improvement followed the order of CaMgP > CaCO3 > biochar > CaSO4 > control (Fig. 4). For example, at 8 g kg−1, the control had PAW between 0.12 and 0.13 cm3 cm−3, whereas the CaMgP, CaCO3, and biochar had the PAW ranging from 0.13 to 0.16, 0.12 to 0.18, and 0.12 to 0.15 cm3 cm−3, respectively (Fig. 4). The amendments influence on the PAW overtime was consistent with their effect on building of soil aggregate, with PAW reaching the highest values at 60 and 180 days for 8 and 2 g kg−1, respectively. However, for granite red soil, even though the PAW was also improved after amendments compared to control, the magnitude of increase was small and not significant (e.g., 0.15 vs 0.16 cm3 cm−3 for control vs. CaCO3 at 60 d) (Fig. 5), consist with their no obvious change

Fig. 3. Variation of the clayey red soil MWD within the application time under each type of amendment at the rate of 8 g kg−1 at fast wetting (FW) and slow wetting (SW) methods. Different lower-case letters denote significant differences in the MWD over the time under each type of amendment (P < 0.05).

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Table 2 Statistical analysis of clayey red soil aggregate MWD at FW method and plant available water (PAW) under different types of amendment by General Linear ModelRepeated Measures and Multivariate Analysis with application time at rate of 8 g kg−1. \Source

Test method/incubation time

Type III sum of squares

df

Mean square

F

Sig.

MWD GLM repeated measures: tests of within-subjects effects Application time Greenhouse-Geisser Application time * Greenhouse-Geisser Amendment Error Greenhouse-Geisser GLM multivariate analysis: tests of between-subjects effects Intercept 21 day 60 day 180 day 365 day Amendment 21 day 60 day 180 day 365 day Error 21 day 60 day 180 day 365 day Total 21 day 60 day 180 day 365 day

Type III sum of squares

df

Mean square

F

Sig.

PAW

2.84 1.70

2.25 9.01

1.26 0.19

0.20

101

0.00

14.53 20.50 24.03 37.66 0.32 0.75 0.17 1.39 0.04 0.04 0.06 0.13 14.88 21.29 24.25 39.17

1 1 1 1 4 4 4 4 45 45 45 45 50 50 50 50

14.53 20.50 24.03 37.66 0.08 0.19 0.04 0.35 0.00 0.00 0.00 0.00

642 96

17,607 21,262 19,807 13,468 97 193 35 124

0.00 0.00

0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

0.01 0.00

1.78 7.13

0.00 0.00

0.01

17.83

0.00

0.29 0.35 0.31 0.23 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.30 0.36 0.32 0.24

1 1 1 1 4 4 4 4 10 10 10 10 15 15 15 15

0.29 0.35 0.31 0.23 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

6.27 1.19

0.01 0.36

1785 800 612 7200 3.74 2.66 1.72 9.71

0.00 0.00 0.00 0.00 0.04 0.01 0.22 0.00

Fig. 5. Dynamics of granite red soil plant available water over the application time for each type of amendment.

Fig. 4. Dynamics of clayey red soil plant available water (PAW) and the field capacity (FC) over the application time for each type of amendment.

6

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red soil: 0.045 vs. 0.23 cmol(+) kg−1for control vs. CaCO3 at 180 d). Additionally, soil oxides content also varied (Figs. 7 and 8). For clayey red soil, Fig. 7 showed that the soil oxides transformed from the free Fed/Ald oxides to the chelated and amorphous oxides overtime. The transformation was indicated by the decline trend in free oxides, and increase trend in the chelated and amorphous oxides compared to control overtime (Fig. 7). Compared to the control, amendments significantly improved the amount of soil amorphous Al/Fe oxides and activity of Fe-oxides (Feo/Fed, by 34% for CaCO3) over time. For granite red soil, similar trend was displayed in Fig. 8 for free and chelated Al oxides overtime but Fe-oxides were not stated due to close to 0 values for amorphous state. For clayey red soil, chelated soil oxides were negatively correlated with aggregate fraction of 0.25–2 mm, but amorphous oxides were positively correlated with this aggregate fraction (e.g., r = 0.54 and 0.33 for Alo vs. aggregate 0.25-2 mm and Fo vs. aggregate 0.25-2 mm). So the increase of amorphous Feo/Alo oxides compared to control overtime was a dominant factor for controlling soil small macroaggregate (0.25–2 mm) formation. This helped to explain Fig. 1 that the aggregates were either dominated or high in small macroaggregate. Amorphous Fe/Al oxides also influenced the soil water retention through their effect on aggregate. However, for granite red soil, the chelated Al oxides and Ca2+ hydration might be proposed as important factors determining soil water retention instead of aggregation. 4. Discussion 4.1. Improvement of soil aggregates and plant available water due to amendments addition Amendments addition improved the soil MWDsw (slow wetting) of clayey red soil from the medium stable level to stable level in our study, where stable level was classified as MWD 1.3–2 mm according to the criteria in Kemper and Chepil (1965). The MWD of clayey red soil gradually increased in a subsequent time was probably attributed to the gradual formation in soil small macroaggregate fraction (0.25–2 mm), slight increase in large macroaggregate (> 2 mm) and reduction in microaggregate fraction (< 0.25 mm) compared to control (Fig. 1). This trend suggested that the microaggregates were bound into small macroaggregates through temporary binding agents such as organic matter or oxides. Andruschkewitsch et al. (2014) also demonstrated that > 50% of rebuilt of macroaggregtes in a Luvisol were formed by binding microaggregates after wheat straw addition in a 28-d incubation experiment. However, among all the amendments, aggregate MWD was not significantly different, except for the biochar resulting in relatively greater macroaggregate fraction and MWD and lower PAD than others (Figs. 1 and 2). The amendment beneficial effect was probably attributed to the formation of P-Al complex in red soils (Martins da Costa and Costa Crusciol, 2016), and accumulation in total OC and Feoxides (Perez-de-los-Reyes et al., 2011; Briedis et al., 2012), acting as the bridge between aggregates. Due to the increase in the fraction of small macroaggregates and MWD, the soil water retention was often found to be improved (Perezde-los-Reyes et al., 2011; Ma et al., 2016). The soil water retention was determined by the size distribution and connectivity of soil pores which were largely regulated by the soil aggregate size distribution (Verheijen et al., 2010). Even though not directly determined, soil pore architecture can be indirectly indicated from Ksat properties of two soils, where the clayey red soil probably had poor soil pore connectivity indicated by low Ksat, while granite red soil might exhibit better pore connectivity indicated by significant increase in Ksat after amendments. This might be helpful to explain different degrees of improvement in PAW for two soils. Additionally, change in PAW was probably also supported by different degree of aggregation after different amendments. For clayey red soil, the P source in CaMgP was accessible to form a complexation of Fe/Al oxides to bridge the aggregates particles for

Fig. 6. Comparison of saturated hydraulic conductivity among amendments within the same days after application for granite red soil. Different lower-case letters denote significant differences in Ksat among amendments within the same application time.

in soil aggregation. Even though all the amendments enhanced soil water retention properties, amendments generated no change in Ksat except for biochar compared to control for the clayey red soil. For example, the Ksat changed from 0.91 to 1.76 cm h−1 for the biochar at the rate of 8 g kg−1 overtime (control with Ksat around 0.81 cm h−1, data not shown). However, for granite red soil, Ksat was significantly increased after amendments compared to control (Fig. 6), where biochar and CaMgP especially resulted in averagely 6.5 and 2 times increase in Ksat at 8 g kg−1. Generally, for two types of soils, the most pronounced effect of biochar on Ksat was consistent with its beneficial effect on the cementing of soils particles overtime, which was probably as consequences of organic carbon (0.67%–0.82%) and soil Fe/Al oxides. 3.3. Change of soil pH and soil oxides and their effects on aggregates and PAW The amendments also changed the soil chemical properties by significantly increasing soil pH (Supplemental Table S1) and changing the dynamics of soil oxides for the two soils (Figs. 7 and 8). Firstly, soil pH was significantly increased after all amendments except for CaSO4 (P < 0.05). For example, for clayey red soil, pH significantly increased from 4.95 of control to an average of 7.5 after 180 days of application of CaMgP (8 g kg−1), and it also increased the pH from 6.3 of control to 7.6 for CaMgP of the granite red soil. The change in pH was explained by high concentration of Ca2+ in the extracted soil solution (e.g., clayey 7

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Fig. 7. Clayey red soil change of the type of soil oxides (Ald/Fed, Alp/Fep, and Alo/Feo) within the application time for each type of amendment at the applied rate of 8 g kg−1.

dominant impact of oxides on aggregates fraction (0.25–2 mm). Similar effects were also stated in Duiker et al. (2003) and Wang et al. (2013) that the amorphous Fe-oxides were reported to be more efficient than free Fe-oxides in stabilizing soil macroaggregates (> 0.25 mm). Above amorphous and chelated oxides effect on stabilization of soil aggregates was as consequences of oxides at the edge of clay particles enabling aggregate formation (Yin et al., 2016). In addition, the clay minerals surface charge was important in soil particles binding (Goldberg and Glaubig, 1987). The kaolinite (dominant mineral in red soils) can have positive charges in acid condition through the protonation of Al-octahedron in Kaolin (Igwe et al., 2010), influencing particles aggregation. Aggregation differences resulted from Fe/Al oxides also depended on types of amendments. Firstly, the biochar enabled the highest formation of amorphous Fe oxides and Al oxides, which reacted with the SOC (from 0.67% to 0.82% overtime) to form a complex OM-chelated oxide (Inda et al., 2013; Barbieri et al., 2014), favoring aggregate formation. Although the accumulation in total OC was thought to help develop macroaggregates in the long-term (Filho et al., 2016), in our soils, the significant change in oxides played more important roles than OC on aggregates in the short term after biochar. The results agreed with the findings that the oxides were the dominant factor controlling the aggregate stability in Southern China Ultisols (Peng et al., 2015). Secondly, the CaCO3 and CaMgP treatments resulted in medium-high amorphous oxides even though not significantly different in Fe oxides compared to biochar, enabling stabilization of aggregate (Fig. 7). The CaMgP provided extra P to retain the soil oxides (Martins da Costa and Costa Crusciol, 2016; Maranguit et al., 2017) to offset the Fe/Al oxides precipitation, beneficial for binding of aggregates. Finally, the CaSO4 treatment displayed little change in amorphous oxides and resulted in no aggregate change compared to others. Therefore, the results indicated that above amendments' effect on oxides transition was a gradual process and Feo/Alo gradually increased overtime could help to explain why MWD had peak values overtime. In turns, amended-soil

macro-pores in arable soils (Bonini and Alves, 2011; Jiang et al., 2015). The CaCO3 generated similar increase in the aggregation as CaMgP. Biochar caused greater fraction of > 2 mm aggregates than others, probably producing high macro-pores fraction difficult to maintain high PAW retention as expectation (Glaser et al., 2004), but biochar still maintained a greater PAW than control due to its greater absorption area (Mukherjee et al., 2014). However, for granite red soil, the slight PAW change after treatments might not be due to the aggregation but more is associated with the Al-oxides and Ca2+ ions hydration (Khorshidi and Lu, 2016). Both the change in soil aggregate size and improvement in soil PAW were beneficial to soil quality. The improvement in soil small macroaggregate fraction (0.25–2 mm) and decline in PAD compared to control (Fig. 2) made the clayey red soil resistant to erosion in rains (Yang et al., 2013). Possible greater intra-aggregate porosity (Briedis et al., 2012) and hydration of minerals ions enabled the increase in PAW. The increase in PAW was important to plants when drought induced the water stress, especially during the “seasonal drought time” (from the late Aug. to late Oct.) when large areas of rape (Brassica napus L.) still grew in the field (Chen et al., 2010). Also, change of soil water holding capacity including PAW was responsible for reducing gas emissions (N2O and CO2) (Chang et al., 2016). 4.2. Relationships between the Fe/Al oxides, soil aggregates and PAW The soil macroaggregates were generally regulated by the high contents of Fe, Al and silicon oxides in tropical soils (Jiang et al., 2010; Liu et al., 2013; Peng et al., 2015). Perez-de-los-Reyes et al. (2015) also found that the aggregate was more related to the content of oxides instead of SOC because the SOC was low in the B horizon of the Red soil in Spain. In our study, the positive correlation between particles (0.25–2 mm) and the content of amorphous Fe/Al oxides in clayey red soil and chelated Al oxides in granite red soil further confirmed the 8

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improved PAW similarly as that in clayey red soil but in a smaller magnitude and significantly improved soil Ksat. The improvement in above physical properties after amendments was attributed to the change in soil pH and Fe/Al oxides. The amendments promoted the transition of Fe/Al oxides due to increase in soil pH and specifically amorphous oxides were positively correlated with soil small macroaggregate fraction and PAW. But for granite red soil, oxides resulted in no obvious aggregate change. All these properties change could be helpful for red soil quality to improve soil resistance to erosion and crop yields. But their long-term effects on red soils may need to be further investigated. Supplementary data to this article can be found online at https:// doi.org/10.1016/j.catena.2019.104231. Acknowledgements This work was supported by the National Natural Science Foundation of China (41601219, 2016); the Fundamental Research Funds for the Central Universities (2662015BQ030, 2015). The authors were grateful to the writting comments from Dr. David Clay in South Dakota State University. References Algayer, B., Le Bissonnais, Y., Darboux, F., 2014. Short-term dynamics of soil aggregate stability in the field. Soil Sci. Soc. Am. J. 78, 1168–1176. Andruschkewitsch, R., Geisseler, D., Dultz, S., Joergensen, R.G., Ludwig, B., 2014. Rate of soil-aggregate formation under different organic matter amendments—a short-term incubation experiment. J. Plant Nutr. Soil Sci. 177, 297–306. Anikwe, M.A.N., Eze, J.C., Ibudialo, A.N., 2016. Influence of lime and gypsum application on soil properties and yield of cassava (Manihot esculenta Crantz.) in a degraded Ultisol in Agbani, Enugu southeastern Nigeria. Soil Till. Res. 158, 32–38. Bao, S.D., 1999. Soil and Agricultural Chemistry Analysis. China Agriculture Press, Beijing, China. Barbieri, D.M., Júnior, J.M., Siqueira, D.S., Teixeira, D.D.B., Panosso, A.R., Pereira, G.T., Junior, N.L.S., 2014. Iron oxides and quality of organic matter in sugarcane harvesting systems. Revista Brasileira de Ciencia so Solo 38, 1143–1152. Barthes, B.G., Kouakoua, E., Larre-Larrouy, M., Razafimbelo, T.M., de Luca, E.F., Azontonde, A., Neves, C.S.V.J., de Freitas, P.L., Feller, C.L., 2008. Texture and sesquioxide effects on water-stable aggregates and organic matter in some tropical soils. Geoderma 143, 14–25. Bonini, B. dos Santos C., Alves, M.C., 2011. Aggregate stability of a degraded oxisols in recovery with green manure, lime and gypsum. Revista Brasileira De Ciencia Do Solo 35, 1263–1270. Briedis, C., de Moraes Sa, J.C., Caires, E.F., Navarro, J.D.F., Inagaki, T.M., Boer, A., Neto, C.Q., Ferreira, A.D.O., Canalli, L.B., dos Santos, J.B., 2012. Soil organic matter pools and carbon-protection mechanisms in aggregate classes influenced by surface liming in a no-till system. Geoderma 170, 80–88. Cesarano, G., De Filippis, F., La Storia, A., Scala, F., Bonanomi, G., 2017. 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American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Madison, WI. USA. https://doi.org/10.2134/practicalmath2016.0025. Clay, D.E., Clay, S.A., Reitsma, K.D., Dunn, B.H., Smart, A.J., Carlson, C.G., Horvath, D., Stone, J.L., 2014. Does the conversion of grasslands to row crop production in semiarid areas threaten global food security? Global Food Security 3, 22–30. Duiker, S.W., Rhoton, F.E., Torrent, J., Smeck, N.E., Lal, R., 2003. Iron (hydr)oxide crystallinity effects on soil aggregation. Soil Sci. Soc. Am. J. 67, 606–611. Filho, A.C.A.C., Crusciol, C.A.C., Calonego, J.C., 2016. Impact of amendments on the physical properties of soil under tropical long-term no till conditions. PLoS One. https://doi.org/10.1371/journal.pone.0167564. Glaser, B., Guggenberger, G., Zech, W., 2004. Identifying the pre-Columbian anthropogenic input on present soil properties of Amazonian Dark Earths (Terra Preta). In: Glaser, B., Woods, W.I. (Eds.), Amazonian Dark Earths: Explorations in Space and Time. Springer, Berlin, Heidelberg, New York, pp. 145–158. Goldberg, S., Glaubig, R.A., 1987. Effect of saturating cation, pH, and alunimum and iron oxide on the flocculation of kaolinite and montmorillonite. Clay Clay Miner. 35, 220–227.

Fig. 8. Granite red soil change of the type of soil oxides (Ald and Alp) within the application time for each type of amendment at the applied rate of 8 g kg−1.

oxides interaction with clay minerals was influential on water retention. Generally, in our study, the physical properties including aggregation of clayey red soil (small macroaggregate fraction and MWD), Ksat of granite red soil and PAW of two soils were significantly improved after amendments, but Ksat for clayey red soil barely changed except for biochar. For chemical properties, soil pH was increased to alleviate the acidity problem, which also enhanced the transformation of soil Fe/ Al oxides for two red soils. Especially, the increase in soil amorphous Fe/Al oxides was beneficial to the improvement of above soil physical properties. The amendment beneficial effects generally started to occur after 60 days. The further improvement in red soil physical-chemical quality after amendments application may compensate the water erosion under high precipitation, with more effective effect on clayey red soils than poorly developed granite red soils. 5. Conclusions Application of CaCO3, gypsum, CaMgP fertilizer and biochar were beneficial for red soil quality across the time. For clayey red soil, amendments improved soil small macroaggregate fraction (0.25–2 mm) indicated by decline in PAD0.25–2 mm compared to control. The improvement in soil aggregate stability resulted in high water retention especially the PAW compared to control after amendments. CaCO3 and CaMgP resulted in greater PAW than biochar, followed by CaSO4 even though the aggregation was higher in biochar. This was probably associated with the macro-pores formation indicated by high Ksat in biochar. The amendment application time was also significant (P < 0.05) in influencing soil MWD and PAW and generally resulting in a highest value after 60 days. For granite red soil, the amendments 9

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