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TURFGRASS

Recent Mechanical Cultivation of Lawns Enhances Lime Application Efficacy

^a Dep. of Crop & Soil Sci., The Pennsylvania State Univ., 116 ASI Bldg., University Park, PA 16802
^b Dep. of Crop & Soil Sci., Univ. of Georgia Agric. Exp. Stn., 119 Redding Bldg., Experiment, GA 30212
^c Rutgers, The State Univ. of New Jersey, Dep. of Plant Biology and Pathology, 59 Dudley Rd., New Brunswick, NJ 08901

^* Corresponding author (mjs38{at}psu.edu).

	ABSTRACT

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
While the relationship between soil acidity and thatch accumulation in maintained lawns has been reported, interacting effects of cultivation and surface lime applications on soil acidity have not. The experimental objective was to determine how antecedent mechanical cultivation of mature turfgrasses interacts with surface application of liming agents to neutralize soil acidity within the upper and lower depth segments of a hectare furrow slice (2.24 x 10⁶ kg soil). Various liming agents were applied to three lawn systems, each afflicted with soil acidity and thatch accumulations, at rates from 0 to 200% of soil test lime recommendations (LR). In Experiment 1, resulting active acidity (pHw) was measured in the 0 to 5 (thatch excluded) and 5 to 10 cm soil depths over 23 mo. In Experiments 2 and 3, described lime applications followed mechanical cultivation treatments; core aeration, vertical mowing, or none. Resulting pHw and exchangeable acidity (pH_KCl) were measured in 0 to 6 (thatch excluded) and 6 to 12 cm soil depths after 1 or 2 yr. Application of the prescribed LR (100%) to uncultivated surfaces did not increase 5 to 10 or 6 to 12 cm pHw levels above unlimed plot levels. One or 2 yr following either lime application rate, statistically higher pH_KCl values corresponded to either cultivation treatment in the 6 to 12 cm soil depth. Mechanical cultivation, conducted before surface application of the LR, accelerated the rate of acid neutralization throughout the 0 to 12 cm soil depths of mature lawn systems.

Abbreviations: CCE, calcium carbonate (CaCO₃) equivalency • CEC, cation exchange capacity • ECs, electrolytic conductivity soil:water suspension (1:1) • LR, lime recommendation • pH_KCl, soil:1 M KCl pH (1:1) • pHw, soil:water pH (1:1) • PSU-AASL, Penn State University Agricultural Analytical Services Laboratory • SMP, Shoemaker, McLean, and Pratt lime recommendation • SOM, soil organic matter

	NOTES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher.

Received for publication July 25, 2007.

	INTRODUCTION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
SOIL ACIDITY can limit root development, thatch decomposition, and nutrient procurement, thus significantly influencing turfgrass vigor and stress tolerance (Carrow et al., 2001; Musser, 1962). Acid soil toxicity manifests through a complex of contributing factors, including plant species sensitivity, clay mineralogy, characteristics and quantities of soil organic matter (SOM), salinity, and metal solubility (e.g., Al⁺³ and Mn⁺²) in soil solution. Acid soil complex often reduces uptake of water and nutrients by plants, particularly in base–cation–depleted subsurface horizons where acidity may persist despite systematic application of liming agents to the soil surface (Sumner and Yamada, 2002; Carrow et al., 2001).

Aluminum toxicity, a naturally-occurring and significant limitation to plant root health, is exacerbated in severely acid soils (pH < 5.0). This toxicity, resulting from activity of monomeric Al in the rhizosphere, restricts root elongation, branching, and function in all but the most Al–tolerant turfgrass species (Carrow et al., 2001). Furthermore, saprophytic processes are often substantially reduced at suboptimal soil pH levels (Smith, 1979; Potter et al., 1985). Several long-term studies report acidic soil pH levels (4–6) promote accumulation of thatch (a loose intermingled organic layer of dead and living shoots, stems, and roots that develops between turfgrass verdure and the soil surface) in managed Kentucky bluegrass (Poa pratensis L.) swards (Edmond and Coles, 1958; Smiley and Craven, 1978; Murray and Juska, 1977). Likewise, turfgrass-availability of soil P, K, Mg, S, and Mo is decreased at suboptimal soil pH levels (Carrow et al., 2001). In soil demonstrating a severe degree of active acidity (pHw = 4.4), P uptake by annual bluegrass (Poa annua L.) more than doubled in response to lime incorporation treatment over a 5- to 7-wk period following establishment (Kuo, 1993).

Numerous agricultural liming agents are available to turfgrass managers, varying primarily by calcium carbonate equivalency (CCE), nutrient concentration, and particle size. Considering incorporation of liming agents is the most rapid and effective method of neutralizing rootzone acidity (Barber, 1984; Woodhouse, 1956), the best opportunity for ameliorating soil acidity is before turfgrass establishment (Carrow et al., 2001). This obstacle is certainly not unique to turfgrass; it has historically limited yield of leguminous and/or grassland pastures (Sumner and Yamada, 2002), and more recently no-till agronomic production (Godsey et al., 2007; Edwards and Beegle, 1988). However, an additional turfgrass liming efficacy constraint is the accumulation of thatch associated with rapid shoot initiation and turnover rates demonstrated by improved cultivars of Poa and Cynodon genera.

The foremost justifications for disruptive and laborious turfgrass cultivation procedures are thatch removal and short-term enhancement of soil/air interfacial area. Core aeration, a process of removing cylindrical soil cores from the upper 5- to 10-cm of the soil profile, is an effective method of removing thatch while improving air and water exchange between the atmosphere and soil of mature turfgrass systems (Dunn et al., 1981). Moreover, evaluations on the effects of antecedent core aeration and fertilizer and/or amendment broadcast application have shown enhanced efficacy (Murphy and Zaurov, 1994) and delayed runoff from sloped turfgrass sites (Moss et al., 2007). Vertical mowing, or verticutting, is a turfgrass cultivation practice that employs vertically-oriented blades to penetrate the canopy and/or soil surface to a desired depth (Beard, 1973). Vertical mowing mature turfgrass systems to a depth wholly-penetrating the thatch layer is an effective technique for reducing this accumulation (Landreth et al., 2008; Landry, 2002).

Soil testing is an inexpensive and accurate tool used by managers to identify and optimize chemical properties of managed turfgrass systems. Soil testing labs measure the exchangeable acidity of soil having a pH level below the optima of the designated turfgrass species. This procedure explicitly provides the lime application rate necessary to optimize the base saturation/pH level in the upper hectare furrow slice (2.24 x 10⁶ kg soil), and is referred to as the LR. In soils having bulk densities of 1.6 g cm^–3, the LR comprises the mass CCE necessary to neutralize all plant-health-limiting exchangeable acidity within the upper 14 cm of soil. Lime recommendations for turfgrass systems typically do not account for thatch layers, or the fact that lime applications in maintenance scenarios are not incorporated. The suitability of surface applications of lime (0.0153 g CaCO₃ L^–1 aqueous solubility at 25°C) as a rapid ameliorant of acidity in typically root accessible subsurface soil depths ( >7 cm), has not been comprehensively validated in mature turfgrass systems.

While the influence of soil pH on organic matter decomposition has been reported (Carrow et al., 2001; Engel and Aldefer, 1967; Murray and Juska, 1977), interacting effects of antecedent mechanical cultivation/thatch removal and surface lime application on acidity in managed turfgrass swards have not. Considering thatch accumulation is associated with both mature and acidic turfgrass systems, an evaluation of thatch layer influence on liming practice is of fundamental interest. Thus, our experimental objective was to determine how recent mechanical cultivation procedures interact with surface application of liming agents to neutralize acidity throughout the upper and lower depth segments of the hectare furrow slice within mature turfgrass systems.

	MATERIALS AND METHODS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
Experiment 1: Efficacy of Lime Rates and Agents Surface-Applied to a Heavily-Thatched Lawn
A 2-yr lime efficacy study was initiated in early 2000 on a stand of Kentucky bluegrass (cultivar unknown) maintained within the Joseph Valentine Turfgrass Research Center, University Park, PA. This "home lawn" system, situated on a level Hagerstown silt loam (fine, mixed, semiactive, mesic, Typic Hapludalf), had been managed under a perfunctory degree of culture since its establishment (ca. 1980). While records show applications of pre-emergence herbicide and N and K fertilizers were made annually, the lawn had been neither cultivated nor limed in 10 yr. Samples from the upper 5-cm of soil, excluding thatch (visually estimated to be 3–5 cm thick), were submitted to the Penn State Univ. Agricultural Analytical Services Laboratory (PSU-AASL; University Park, PA) for routine soil analysis (Shoemaker et al., 1961; Eckert and Sims, 1995; Wolf and Beegle, 1995). Results are shown in Table 1 .

Experiment 2: Efficacy of Cultivation and Subsequent Surface-Application of Various Lime Rates and Agents to a Heavily-Thatched Lawn
This 2-yr lime efficacy study was initiated in 2002 on a level, 0.4-ha lawn bordering the Valentine Turfgrass Research Center. Established to a Hagerstown silt loam in 1968, the mixture present at experiment initiation contained unknown cultivars of Kentucky bluegrass, tall fescue (Festuca arundinacea Schreb.), and quackgrass [Agropyron repens (L.) Beauvois]; in a respective area-based ratio of approximately 3:6:1. This cool-season grass mixture is a typical composition of home lawns in the Mid-Atlantic region of the United States, particularly those receiving few irrigation and lime inputs.

Four spatially-distinct 27 m² areas (9 by 3 m), similar in their above-described turfgrass mixture composition, were established as the experimental blocks of a randomized complete strip-plot design. On 20 Oct. 2002, 54 soil cores (18 x 5.1 cm i.d.) were randomly sampled from every other plot. The thatch layer (visually estimated to be 4–6 cm thick) was manually recovered from each core surface, dried to constant mass (as described), and combusted (440°C) to provide area-based mean thatch mass (Mg ha^–1)(Waddington, 1992). Each remaining soil core was segmented by 0 to 6 or 6 to 12 cm depth, oven dried, ground, and passed through a 1-mm sieve. Exchangeable acidity (pH_KCl) of depth-segments was determined by measuring H⁺ activity within equilibrated 1:1 slurries of soil and 1 M KCl (Thomas, 1996), using a temperature-adjusted, hydrogen-specific potentiometer (Omega Eng. Inc., Stamford, CT). Depth segments of the sieved soils were submitted for SOM content (Schulte, 1995) and routine analysis by PSU-AASL (as described). Results are shown in Table 1.

On 5 Nov. 2002, mechanical thatch removal treatments were made to the 9 by 1 m main-plots in each block. Mechanical verticutting (i.e., thatch removal) was conducted using a self-propelled Ryan Mataway 2000 (Cushman Inc., Lincoln, NE) vertical mower, set to penetrate the upper 4 cm of the soil profile with 3.2-mm-wide, vertically-oriented blades on 2.6-cm spacing. Vibration-induced "drift" or inadvertent shifting of the vertical mower penetration depth was assessed following each of three passes (per block) and reset as necessary.

On that same date, thatch removal procedures within a second main-plot were facilitated by a self-propelled greens aerator (The Toro Co., Bloomington, MN). This unit cored to a 7-cm depth using 1.6-cm i.d. hardened-steel tines on 5.1-cm centers. A single 61-cm-wide pass was first made along the 9-m length of one main plot border in each block. Next, 5 of the 12 tines were removed from one side of the coring block, and a second coring pass was made parallel and immediately adjacent to the first pass. This allowed uniform coring of one 9 by 1-m main-plot in each block, minimizing the irregular thatch removal patterns that can persist where coring passes overlap. Organic residue and/or soil cores generated from the above-described main-plot treatments were hand raked and discarded. The third main plot in each block served as a control, where no mechanical thatch removal procedure was conducted.

Eight treatments were prepared at 100 or 200% of the CCE recommended (4.4 Mg ha^–1) to reach a target pH of 6.8 (Shoemaker et al., 1961), and included commercially-available hydrated lime, dolomitic or calcitic limestone, or a calcium silicate liming agent (Table 2). On 9 Nov. 2002, liming agent treatments were surface-applied using shaker jars to 3 by 1 m plots in the randomized complete strip-block design described above. A control plot in each block was left untreated. Over a 48-h period beginning 10 Nov., 4-cm precipitation activated the lime treatments.

Cultural inputs over the 2003 and 2004 seasons were minimal, as plots were rotary-mowed semimonthly at a height of 7 cm (clippings returned), and a single annual N application (46–0–0; 98 kg ha^–1) was made each September. In July 2003, two 5.1-cm diam. core samples were collected from the upper 9 cm of each plot. Area-based mean thatch mass (Mg ha^–1) was again quantified to evaluate the comparative effectiveness of mechanical cultivation procedures conducted 8-mo previously. Duplicate soil cores (18 by 5.1 cm diam.) were collected from each plot in Nov. 2004, and identifiable thatch layers manually discarded before segmenting by 0 to 6 or 6 to 12 cm soil depths. Core segments were dried to constant mass in a forced-air oven (70°C).

Oven-dried soil from each segment was ground to pass a 1-mm sieve and split to determine 1:1 deionized water electrolytic conductivity (ECs)(Shirokova et al., 2000) or pHw by a four-cell conductivity probe or hydrogen-specific potentiometer, respectively. Additional duplicate samples from each experimental unit depth segment were used to measure soil pH_KCl. Each replicate pH value (1:1 DI H₂O or KCl) was converted to its respective hydrogen activity value (mol L^–1) and averaged before ANOVA by the linear mixed model of SAS/STAT (ver. 8.2, SAS Institute, Inc., Cary, NC). Significance of both cultivation and lime treatment sources were tested by their respective block interaction terms, while significance of the cultivation by lime treatment interaction was tested using the mean square error term (Gomez and Gomez, 1984).

Experiment 3: Efficacy of Cultivation and Subsequent Surface-Application of Various Lime Rates and Agents to a Moderately-Thatched Lawn
This 1-yr lime efficacy study was initiated in Sept. 2003 on a sloped (3%), 0.3-ha bermudagrass lawn [Cynodon dactylon (L.) Pers. ‘Princess 77’] maintained within the University of Georgia Agric. Exp. Stn. (Experiment, GA). A 2-cm i.d. steel probe was used to collect 18-cm deep soil cores across the Cecil sandy clay loam (fine, kaolinitic, thermic, Typic Kanhapludult). The thatch layer (visually estimated to be 2–3 cm thick) was methodically recovered from the surface before segmenting cores by 0 to 6 or 6 to 12 cm depths. Mean area-based thatch mass (Mg ha^–1) was determined as described in Exp. 2. Depth segments of soil cores were composited by area quadrant, dried, and sieved. Soil pH_KCl was determined by depth, in duplicate, as previously described. Remaining composite soil samples were submitted for SOM content and routine analysis by PSU-AASL (Table 1).

Four spatially-distinct 60 m² areas (10 by 6 m) were established as the experimental blocks of a randomized complete strip-plot design. On 23 Sept. 2003, cultivation treatments were made to 10 by 2 m main-plots in each block. Mechanical thatch removal treatments similar to those described for Exp. 2 were applied using either a self-propelled Ryan Greensaire core aerifier (Cushman Inc., Lincoln, NE), or a self-propelled Ryan Mataway 2000 (Cushman Inc., Lincoln, NE) vertical mower. These machines were configured identically to those described in Exp. 2 (tines, blades, spacings, etc.), yet penetration of the clayey Cecil soil surface by the core aeration procedure was limited to a 4- to 5-cm depth. Organic residue and/or soil cores generated from the above-described main-plot treatments were hand raked and discarded. The third main plot in each block served as a control, where no mechanical thatch removal procedure was conducted.

Once cultivation treatment application and clean up was complete, six treatments were prepared at 100 or 200% of the LR recommended (3.6 Mg ha^–1) to reach a target pH of 6.8 (Shoemaker et al., 1961), and included commercially-available calcitic or dolomitic limestone, or a calcium silicate soil amendment (Table 2). Shaker jars were used to surface-apply liming agents to all 6 by 1 m strip plots except one unlimed control plot in each block. One hour following lime applications, the plots were irrigated (3 cm) using potable water.

Plots were mowed weekly (4 cm) and clippings returned throughout the remainder of 2003 and 2004 seasons (April–October). Between May and Aug. 2004, granular ammonium nitrate (35–0–0) was used to N fertilize plots monthly (49 kg ha^–1). On 20 Sept. 2004, duplicate soil cores (18 by 3.8 cm diam.) were collected from each plot and identifiable thatch layers were manually discarded, and remaining soil segmented by 0 to 6 or 6 to 12 cm depth before drying to constant mass in a forced-air oven (70°C). Oven dried soils were ground to pass a 1-mm sieve and split for soil ECs or pHw analysis. Exchangeable acidity of each experimental unit depth segment was measured in duplicate and averaged as previously described. Dependent variable transformations and statistical analyses were conducted identically to those described in Exp. 2.

	RESULTS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
Experiment 1
Lime treatment significantly decreased active soil acidity (pHw) in the 0 to 5 cm soil depth, but not the 5 to10 cm soil depth of this Kentucky bluegrass lawn, over the 23-mo study (Fig. 1 ). In the 0 to 5 cm soil depth, orthogonal contrasts (not shown) indicated the linear lime application rate to account for 62% of the significant lime treatment main effect (Type III SS). With respect to soil pHw, no differences between any liming agents were observed at either soil depth. The main effect of time elapsed from treatment applications also significantly influenced soil pHw (Table 3 ) in the upper (0–5 cm) and lower (5–10 cm) soil profiles. Twenty-three mo following lime applications, mean pHw in the treated 0 to 5 cm soil depths exceeded initial and 6-mo mean pHw levels by 0.3 and 0.2 units, respectively (data not shown). Though statistically significant, this linear time effect on pHw in the 5 to 10 cm soil depth did not exceed 0.1 units (data not shown).

View larger version (24K): [in this window] [in a new window]   Fig. 1. Experiment 1 mean soil:water pH (1:1) (pHw) values (soil pH of 1:1 H2O:soil suspension) at 0 to 5 or 5 to 10 cm soil depths as affected by CaCO3 application rate. Predicted linear response to application rate is shown for the 0 to 5 cm (solid) or 5 to 10 cm (dashed) soil depths. Each symbol represents the mean of three repeated measures (taken 6, 12, or 23 mo after treatment).

Two years following surface applications, the main effect of lime treatment significantly influenced soil pHw, pH_KCl, and ECs levels in the 0 to 6 cm soil depth, but not in the 6 to 12 cm soil depth of the Exp. 2 plots (Table 3). Within the 0 to 6 cm soil depth, increased pHw and pH_KCl levels corresponded to LR application rates of 0 to 100 to 200% of the LR (Fig. 2A and 2B, respectively). Furthermore, specific liming agent type was observed to significantly affect both acidity measures as well as soil ECs in the 0 to 6 cm soil depth (Table 3). Applications of dolomitic limestone, the only pelletized treatment applied in Exp. 2 (Table 2), was less effective at increasing soil pHw and pH_KCl levels in the 0 to 6 cm depths than all other materials except calcium silicate (data not shown). Compared to other liming agents at any rate, the hydrated lime treatment significantly raised soil ECs in the 0 to 6 cm soil depth, but corresponding salinity hazards (ECs > 0.5 dS m^–1) were not observed.

View larger version (30K): [in this window] [in a new window]   Fig. 2. Experiment 2 mean 0 to 6 cm soil depth (A) pHw values (soil pH of 1:1 H2O:soil suspension) and (B) pHKCl values (soil pH of 1:1 1 M KCl:soil suspension), or 6 to 12 cm soil depth (C) pHw, and (D) pHKCl values by CaCO3 application rate and antecedent cultivation procedure; 2 yr following treatment. For each graph pane (A–D), significant differences do not exist between means having overlapping error bars (Fisher's least significant difference, = 0.05).

Experiment 3
One year following surface applications, the main effect of lime treatment significantly influenced pHw and pH_KCl levels in both the 0 to 6 and 6 to 12 cm soil depths of the Exp. 3 plots (Table 3). Application of the LR significantly decreased active (Fig. 3A ) and exchangeable acidity (Fig. 3B) within the 0 to 6 cm soil depth compared to no lime application. Compared to the 100% LR application rate, no significant increase in 0 to 6 cm soil depth pH_KCl values corresponded to the 200% LR applications (Fig. 3B). Specific liming agent type significantly affected both acidity measures in the upper furrow slice (data not shown). At either application rate, the coarse-textured calcium silicate liming agent (Table 2) resulted in statistically lower 0 to 6 cm soil depth pHw and pH_KCl values than either the dolomitic or calcitic liming agent.

View larger version (30K): [in this window] [in a new window]   Fig. 3. Experiement 3 mean 0 to 6 cm soil depth (A) pHw values (soil pH of 1:1 H2O:soil suspension) and (B) pHKCl values (soil pH of 1:1 1 M KCl:soil suspension), or 6 to 12 cm soil depth (C) pHw, and (D) pHKCl values by CaCO3 application rate and antecedent cultivation procedure; 1 yr following treatment. For each graph pane (A–D), significant differences do not exist between means having overlapping error bars (Fisher's least significant difference, = 0.05).

One year following treatment applications, pH_KCl levels in the 6 to12 cm soil depth of uncultivated 100% LR treatment plots remained statistically equal to plots receiving no lime treatment, and were lower than the 100% LR treated plots cultivated by either procedure (Fig. 3D). Although both cultivation procedures neutralized more exchangeable acidity in the deeper soil depth at the 100% LR rate than no cultivation treatment, vertical mowing proved more effective than coring (Fig. 3D). In the uncultivated main plots, the 200% LR treatment resulted in significantly greater pH_KCl levels in the 6 to12 cm depth relative to the unlimed soil. Meanwhile, any combination of cultivation and 200% LR application rate resulted in 6 to12 cm depth soil pH_KCl values significantly exceeding levels observed in uncultivated lawns treated with lime (Fig. 3D).

	DISCUSSION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
The most notable features of the three turfgrass systems evaluated in this study were acidity, maturity, and degree of thatch accumulation. Experiments 1 and 2 were conducted on soils weathered from calcareous alluvium, yet acidified over the last 25+ yr by frequent fertilizer applications, subsequent microbial transformations, and/or turfgrass nutrient uptake processes (Table 1). In these Alfisols, soil pH levels increase with soil depth. At the Experiment 3 site, the residual Ultisol was comprised of a subsurface horizon of amorphous sesquioxides with greater affinity for acid cations than the shallow epipedon above (Table 1). This profile shows decreasing pH levels with soil depth, typical of upland sola in the southern U.S. Piedmont region.

Despite varying climate, predominate turfgrass composition, and severity and distribution of acidity by depth across the experimental sites; specific LR rates broadcast across uncultivated surfaces did not increase pHw of the 0 to 5 cm soil depth (Fig. 1) or 0 to 6 cm soil depth (Fig. 2 and 3) to the desired level (6.8) 1 to 2 yr following treatment applications. Over the same time frame, application of specific LR rates to uncultivated surfaces failed to increase subsurface pHw (5–10 or 6–12 cm) above levels initially measured or observed in unlimed plots (Table 1; Fig. 1, 2C, and 3C). However, where cultivation treatments were performed immediately before surface applications of the prescribed lime rate 2 yr earlier (100% LR); exchangeable acidity was significantly reduced throughout the entire upper 12 cm soil, compared to an uncultivated treatment (Fig. 2B and 2D). In 1 or 2 yr time, 200% LR application rates made to the surface of recently-cultivated home lawn systems increased pH_KCl levels within the 6 to12 cm soil depth compared to uncultivated lawns receiving equal lime rates (Fig. 2D and 3D). In agreement with a recent lime study (Godsey et al., 2007), our results showed soil acid neutralization to be more highly influenced by CCE-based application rate than liming agent type.

Fundamentals of associated soil chemical mechanisms are often useful resources in interpreting experimental results. An integral yet frequently overlooked component of the liming reaction (i.e., neutralization of two 2 H⁺ ions by a single CaCO₃ or MgCO₃ molecule) is the prerequisite of dissolution. In the presence of lime, acid cations will neither be displaced from soil exchange sites nor neutralized by CO₃^–2 or HCO₃^–, until each occupies a common aqueous solution. Equally important aspects of liming practice are the low solubility of CaCO₃ and MgCO₃ and their notoriously-limited vertical mobility in soils. Therefore, placement of liming agents where both supraoptimal exchangeable acidity and soil moisture coexist will expedite an increase in soil pH to the desired level.

A uniform thatch layer may restrict soil penetration of surface-applied insoluble amendments. Thatch layers provide less volumetric water holding capacity than soil, and layer thickness is negatively-correlated to the efficacy of urea and plant protectant applications (Waddington, 1992). Furthermore, its intermediate position in the water potential gradient connecting air to soil causes thatch to desiccate more rapidly than underlying soils. Thus, thatch layer interception of surface-applied amendments delays the onset of processes essential to the liming reaction; namely the sustained hydration of lime in proximity to excessive exchangeable acid concentrations.

	CONCLUSIONS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
The described experimental results support the conclusion that antecedent mechanical cultivation enhanced short-term efficacy of lime applications broadcast to the surface of maintained turfgrass swards at laboratory recommended rates. Enhancement of soil to air interfacial surface, facilitated by recent mechanical thatch removal procedures, contributes to reduced exchangeable acidity throughout the hectare furrow slice following application of the LR. While the ultimate goal of the lime recommendation is to neutralize all supraoptimal acidity in the hectare furrow slice, significant progress observed over the experimental periods indicate antecedent core aeration or vertical mowing can expedite the process throughout the upper 12 cm of soil. Despite the results collected over these short-duration studies, the authors cannot recommend arbitrary doubling of soil laboratory-recommended lime application rates for neutralization of acidity in the hectare furrow slice. Rather, thatch accumulation should be assessed, necessary cultivation procedures conducted, recommended lime rate applied, and soil sampled and analyzed annually thereafter. The preceding steps can then be repeated as necessary until the target pH is achieved in the effective turfgrass root zone.

	ACKNOWLEDGMENTS

 
The authors thank the Pennsylvania Turfgrass Council and the Georgia Turfgrass Assn. for their financial support of this research. Likewise, we thankfully recognize the prompt and insightful review of the original manuscript by Drs. Donald Waddington, Micah Woods, and the three anonymous volunteers. Lastly, we appreciate the technical assistance provided by Matt Cloud, Bob Perry, Jonathon Bohn, Jerome Alsdorf, Andy Billing, Tom Vosters, Mike Schmalzer, Chad Rightmeyer, P. Joshua Cook, Terrence Reeves, Matthew Dachowski, Erik MacPherson, and William Green.

All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher.

	REFERENCES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 

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