Published in Soil Sci. Soc. Am. J. 68:558-561 (2004).
© 2004 Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
DIVISION S-5—PEDOLOGY
Recementation of Crushed Ortstein by Blueberry Leaf Extract
C. J. Bronick,
D. L. Mokma*,
H. Li and
S. A. Boyd
Dep. of Crop and Soil Sciences, Michigan State Univ., East Lansing, MI 48824-1325
* Corresponding author (mokma{at}msu.edu).
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ABSTRACT
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Cementing of sand grains by organo-Al and organo-Fe complexes is thought to be a gradual process and takes at least a few thousand years. The resulting ortstein inhibits root penetration. Blueberries (Vaccinium corymbosum L.) in isolated regions of blueberry fields in Michigan experience reduced growth that has been attributed to the presence of ortstein. Growers have used deep tillage to break up ortstein in these regions with only temporary benefits. This study was conducted to determine (i) if crushed ortstein would recement upon exposure to aqueous blueberry leaf extract, (ii) rate of recementation, (iii) the degree of recementation, (iv) the strength of recemented materials, and (v) the nature of the cementing agents. Crushed ortstein from Saugatuck sand (sandy, mixed, mesic, shallow, ortstein Typic Durorthod) was passed through a 2-mm sieve and used in column experiments to assess recementation. Aqueous blueberry leaf extracts were added daily to crushed ortstein columns for 1.5-, 3-, 6-, and 12-wk periods. Green and brown blueberry leaves were used to prepare extracts and compare the effect of leaf age on recementation. The degree and strength of aggregation were assessed by determining the amount of treated ortstein remaining on a 2-mm sieve, and by tensile strength analysis of aggregated material. Extensive recementation (96% aggregation) of crushed ortstein occurred after 1.5 wks. Cementation was highest in the upper layers and decreased with depth in the column. Degree and strength of cementation tended to increase with duration of the experiment. Green leaf extract caused more recementation of crushed ortstein than brown leaf extract. Recementation is thought to result from relocation of Al by organic compounds, originating from leaf extracts, to contact points between sand grains.
Abbreviations: DCP, direct current plasma emission spectroscopy • HPLC, high-pressure liquid chromatography • LMWOA, low molecular weight organic acids • OM, organic matter
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INTRODUCTION
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AS MORE organo-Al and organo-Fe complexes accumulate in Bhs and Bs horizons, the horizons tend to become cemented, forming ortstein. The time required to form ortstein and the degree of cementing varies considerably. In a Michigan chronosequence, only 20% of the Bh horizon of a 8000-yr-old pedon was weakly to strongly cemented, whereas the Bh horizon of a 10000-yr-old pedon was only weakly cemented (Franzmeier and Whiteside, 1963). In another Michigan chronosequence, the B horizons of the 4000, 10000, and 11000-yr-old pedons had strongly cemented chunks of ortstein that were 2, 20, and 30 cm in size, respectively (Barrett and Schaetzl, 1992). Moore (1976) reported that 5000 to 6000 yr were required for the formation of strong cementation in B horizons in northern Quebec, Canada. On the basis of these studies, it appears at least a few thousand years are required to cement Bhs or Bs horizons.
In Michigan, blueberries are grown primarily on Spodosols, some of which have ortstein. Ortstein, also referred to as hardpan, varies in occurrence and thickness within fields. Blueberry growers in southwest Michigan have experienced diminished growth in some blueberry plantings. This occurs in isolated regions of fields in which the remainder of the plants have reached full size and production. Ortstein has been reported to reduce blueberry growth (Lilly et al., 1975) by acting as a barrier to water percolation and root penetration. Growers have attempted to break up the ortstein with deep tillage before replanting blueberries. This was thought to be a permanent solution, but some growers now believe that the broken ortstein has recemented.
The objectives of this study were to determine (i) if crushed ortstein would recement, (ii) the rate of recementation, (iii) the degree of recementation, (iv) the strength of recemented materials, and (v) the nature of the cementing agents.
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MATERIALS AND METHODS
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Ortstein was collected from a blueberry field near West Olive, MI (86°08' W, 42°54' N). A trench was dug by hand in Saugatuck sand that has a Bhsm (ortstein) horizon that begins at about 20 to 50 cm and generally exceeds 25 cm in thickness. Cemented Bhsm horizon material was extracted from the sidewalls. The material was then air-dried, crushed, passed through a 2-mm sieve, and mixed thoroughly. This crushing process was more intensive than the breaking of the ortstein by growers during the deep tillage process. The original ortstein had a moist color of 2.5YR 2.5/3, 97% sand, a pH of 4.5, a tensile strength of 17.2 MPa, 3.3% organic matter (OM), 34 g kg–1 oxalate extractable Al, and 1.3 g kg–1 oxalate extractable Fe.
Effects of age and quality of leaves on recementation by leaf extract were assessed with fresh green leaves collected early in the growing season (June 2001) and brown decomposing leaves collected at the end of the season (November 2000). We collected green leaves from blueberry plants and dry, decomposing brown leaves from under blueberry plants. The plants were the same age. All leaves were stored at 5°C. After air-drying, leaves were placed in plastic bags and crushed by hand. Extract solutions were prepared by placing the crushed leaves in distilled water (1:10 mass ratio), and letting the mixture set for 24 h at 20°C. Each extract was filtered through a Buchner funnel without filter paper. Green leaf extracts were prepared and used the same day to minimize changes in composition during storage. Brown leaf extracts were prepared weekly and stored at 5°C.
The green leaf extract was designed to represent solution produced by precipitation flowing over live green leaves on blueberry plants, whereas the brown leaf extract was designed to represent solution produced by precipitation flowing over dead leaves on plants or on the ground. The pH of the green blueberry leaf extract was 3.5 and that of the brown blueberry leaf extract was 4.5. High-pressure liquid chromatography (HPLC) was used to identify and compare low molecular weight organic acids (LMWOA) present in the extracts. The HPLC analysis was achieved by absorbance detection at 280 nm. Compounds were eluted with a 1.0 mL min–1 flow rate and a mobile phase consisting of 5% acetonitrile mixed with 95% water containing 1% acetic acid (Vance et al., 1985).
Cylindrical, plexiglass tubes 30 cm in length and 11.5 cm inside diameter were mounted vertically. The bottom was covered with cheesecloth. Crushed ortstein material was placed in the columns. While adding crushed ortstein to columns, there was some segregation of particles and layering within the columns; mixing and sequential addition of material to columns reduced this effect. Triplicate columns were treated with green leaf extract for 1.5, 3, and 6 wk or with brown leaf extract for 1.5, 3, 6, and 12 wk at room temperature (about 20°C). Triplicate columns received water for 12 wks as a control. A 2-cm layer of crushed green or brown blueberry leaves was placed on the upper surface of the crushed ortstein to protect the surface, distribute the green or brown blueberry leaf extract, respectively, and reduce evaporation. A 2-cm layer of slow-decomposing pine-wood mulch was used on the surface of the control columns. Blueberry leaf extract or water (20 mL) was gently poured over the surface daily during a 1-min interval, attempting to evenly distribute the liquid. This amount corresponds to approximately twice the mean daily precipitation in the region.
At the end of the treatments (1.5, 3, 6, or 12 wk), the columns were allowed to air-dry and then separated into 3-cm-depth increments with a spatula. Materials from each 3-cm increment were sieved through a 2-mm sieve. The amount of aggregated material that remained on the sieve (>2-mm diam.) was determined gravimetrically. We focused on the upper 12 cm of each column. We expected the lower portion of each column to be at or near saturation before leachate would drip from the column, unlike in the blueberry field where the soil has a much longer column.
Aggregates were assessed for their structural tensile strength (in 3-cm increments) with a polar tensile strength press as modified (A.J.M. Smucker, 2001, personal communication) from Dexter and Kroesbergen (1985). Aggregates were placed in a mist chamber for 24 h, set in plastic bags for 24 h, and then gently broken along natural aggregate breaks and allowed to air-dry. Aggregates, 6.3 to 9.5 mm in diam. (A.J.M. Smucker, 2001, personal communication), were isolated by gently shaking soil samples from columns through a 9.5-mm sieve and collecting them on a 6.3-mm sieve. Smaller aggregates generally provide less useful data for identifying tensile strength differences among soils. Representative soil aggregates were randomly selected for quantifying tensile strengths of this aggregate size fraction (6.3–9.5 mm in diam.). Approximately 10 aggregates were tested for each replicate.
The polar tensile strength press consisted of two parallel plates. One plate was placed on a scale and the second, a moveable plate, was computer-controlled. An aggregate was placed between the two plates. The moveable plate incrementally moved downward, exerting pressure on the aggregate and scale. The pressure was measured on the scale and the computer recorded the pressure. The maximum force required to deform or break an aggregate was recorded. For aggregates that gradually deformed, the maximum stress required to initiate deformation was recorded. For aggregates that broke abruptly, the appropriate peak strength was recorded. The crushed aggregate was weighed, dried at 105°C for 24 h, and weighed again. These air-dried and oven-dried weights were used to calculate gravimetric water content of air-dried aggregates for tensile strength determination (Dexter and Kroesbergen, 1985; A.J.M. Smucker, 2001, personal communication).
To determine the nature of the cementing agents, Al and Fe concentrations were determined for loose (<6.3-mm) and aggregated (6.3–9.5 mm) materials in 3-cm column depth increments with ammonium oxalate extraction (Soil Survey Laboratory Staff, 1996) and direct current plasma emission spectroscopy (DCP) analysis. The DCP was rinsed regularly with dilute nitric acid to clean the DCP column. Organic matter was determined by the loss-on-ignition method (difference between 200 and 400°C) (Schulte, 1980).
Data from this study were analyzed by the Mixed model procedure (Proc mixed) with repeated statement in SAS statistical software (SAS Institute, 1989). The logarithmic transformation was applied to weight and strength data to provide the normality assumption for analysis. Differences between treatments were determined with least squared means differences in the (p < 0.05) significance level with the Tukey-Kramer adjustment.
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RESULTS AND DISCUSSION
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Green (fresh) blueberry leaf extract was light, yellow-brown, and clear, while brown (decomposing) blueberry leaf extract was dark and opaque. Green leaf extract had lower pH (pH = 3.5) compared with brown leaf extract (pH = 4.5). Green leaf extract contained higher concentrations of LMWOA, including protocatechuic acid, vanillic acid, p-hydroxybenzoic acid, and catechol, than brown leaf extract. The LMWOA with juxtaposed hydroxyl functional groups preferentially chelate with polyvalent ions such as Al3+ (Vance et al., 1986). Thus, green leaf extract was expected to be more effective in translocating Al. Leaf extracts contain a mixture of organic acids whose exact composition depends on age, season, and health of leaves.
Near the end of the 12-wk treatments with brown blueberry leaf extract, some columns had extract ponded on the surface. Ponding did not occur in the water–treated columns. This suggested that permeability of the extract-treated crushed ortstein had decreased across time. This may account for the high variability of data from these columns.
Aggregation
The top layers of the treated columns were highly aggregated. More than 95% of the crushed ortstein mass in the top 3 cm of columns treated with green leaf extract was aggregated (
2 mm) at the initial sampling time, 1.5 wk (Table 1). While separating the columns into 3-cm segments, some sand grains were broken from the aggregated material. Thus, the percentage of aggregation reported is slightly less than actual. Aggregation in the top 3-cm layer was not significantly different in the 1.5-, 3- and 6-wk green leaf extract treatments. Aggregation in columns treated with blueberry leaf extract was significantly greater than in columns treated with water.
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Table 1. Aggregation (percentage mass remaining on 2-mm sieve) with depth in columns treated with green or brown blueberry leaf extract or water.
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Brown leaf extract treatments resulted in less aggregation, 40%, in the top 0- to 3-cm layer than the green leaf extract treatments at the initial 1.5-wk sampling time (Table 1). Crushed ortstein from columns treated for 1.5 wks with green blueberry extract exhibited significantly (p < 0.05) more aggregation at all depths than the corresponding columns treated with brown leaf extract. Aggregation generally increased with treatment time at all depths in columns treated with brown blueberry leaf extract. A similar increase in aggregation with treatment time occurred at the lower depths in columns treated with green leaf extract. Overall, the greatest aggregation occurred in the top layers of columns treated with green leaf extract.
Tensile Strength of Aggregates
Aggregates from top layers displayed greater strength than those from lower layers. In the top layer (0–3 cm) of columns treated with green blueberry leaf extract, aggregate strength generally increased with duration of treatment (Table 2). Tensile strength of top-layer aggregates that received green leaf extract was greater than those that received brown leaf extract. Root pressure has been recorded at <1 MPa (Clark et al., 1999); most recemented materials exceeded this even after only 1.5 wks of treatment. More than 95% of the top layer aggregates (0–3 cm) exceeded 1 MPa after 1.5 wk of treatment with green blueberry leaf extract. Tensile strength of lower-layer (3–12 cm) aggregates was about 1 MPa. While this does not provide conclusive evidence that aggregated materials cannot be penetrated by roots, it suggests that the recemented materials may impede normal root growth.
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Table 2. Tensile strength of aggregated material (6.3–9.5 mm) in top layer (0–3 cm) of soil columns treated with green and brown blueberry leaf extract daily for various time intervals.
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Cementing Agents
Aggregates from the top layer of soil columns treated with green blueberry leaf extract had more OM than those from lower layers (Table 3). Aggregates in the top layer had more OM than loose materials; at depth there was little difference between loose and aggregated materials. Aluminum was generally higher in aggregated materials than in loose materials, but the differences were not significant (p < 0.05). Iron concentrations were low, <1.2 g kg–1, and not significantly different (p < 0.05) between loose and aggregated materials nor with depth in the columns, suggesting that Fe-containing compounds were not important in aggregating these crushed ortstein materials. The cementing agents were likely organic acids and Al.
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Table 3. Distribution of organic matter and oxalate extractable Al with depth in column for loose and aggregated materials treated with green blueberry leaf extracts or water.
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Recementation Process
The recementation process may be envisioned as follows. As a result of the initial crushing of ortstein, Al was exposed on the surfaces of sand grains. After filling the columns, most of the Al on the sand grains was not at the contact points between grains. The blueberry leaf extracts readily chelated the Al. The organo-Al complexes were moved to the contact points between sand grains. The accumulation of these organo-Al complexes at the contact points and subsequent drying caused recementation of the crushed ortstein. Green blueberry leaf extracts had more LMWOA than brown blueberry leaf extracts; therefore, green leaf extracts chelated more Al than brown leaf extracts. Recementation in the water-treated columns resulted from the Al at the contact points after filling the columns and drying.
Blueberry fields are more dynamic and complex than the laboratory column experiments described here. After deep tillage, ortstein in blueberry fields is less broken up than in this experiment. This would focus the flow of soil solutions containing organo-metallic complexes in preferential flow patterns, increasing the rate of recementation. In natural conditions, precipitation falling on green blueberry leaves or on brown leaves dissolve organic compounds and carries them into the soil where they act as complexing agents, translocating Al and contributing to the recementing of the broken ortstein. Irrigation water with varying pH would alter the natural system.
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CONCLUSIONS
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Recementation of crushed ortstein in columns began within 1.5 wks with aqueous blueberry leaf extract. Aggregation and aggregate strength tended to increase with time. Green (fresh) blueberry leaf extract increased the rate of aggregation and tensile strength of aggregates significantly more than brown (decomposing) blueberry leaf extract. This was apparent in the top layer (0–3 cm) and with depth across time. Green leaf extract had more LMWOA, higher OM, and lower pH than brown leaf extract. The tensile strength of some aggregated material exceeded the force some roots have been known to exert. Aggregated materials in the top layer had more OM compared with those deeper in the column. There was no significant difference in Al content in aggregated and loose materials. We propose that both green and brown blueberry leaf extracts were capable of moving exposed Al to contact points between sand grains, thereby causing recementation of the crushed ortstein. Green leaf extracts contain more LMWOA than brown leaf extracts and therefore were more effective in moving Al.
Received for publication August 22, 2002.
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REFERENCES
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ABSTRACT
INTRODUCTION
