张华 王一淳 李德颖

摘要：土壤盐渍化是草坪管理中危害草坪草健康的严重问题。 盐渍化是由于灌溉用的再生水等非传统水源常含有较高的盐分。在土壤可交换钠累积高的情况下，用雨水或者清水灌溉会导致土壤颗粒分散，降低土壤水分入渗与渗透。试验目的为：研究灌溉用水中的盐分组成对高尔夫果岭根层基质及根基系统的饱和导水率 （Ksat） 的影响。试验对粘土（Fargo，North Dakota，USA），粘壤土 （Garick Corp.，Cleveland，OH）和泥炭/砂混合物 （Dakota Peat，North Dakota，USA） （90/10 v/v），其在3种根层的基质建筑系统40 cm深自然型果岭，USGA标准的泥炭/砂基果岭的30 cm根层和10 cm砾石层和加利福尼亚标准果岭的40 cm深泥炭/砂根层进行了测定。材料经过5个钠吸附率水平 （SARw） （0，2.5，5.0，15.0，and ∞）溶液的淋洗预处理或灌溉后测定了饱和导水率。除SARw 0外，所有溶液的导电度（ECw） 都为11.0 dS/m。结果表明：使用SARw >5的溶液灌溉淋洗易导致粘土和粘壤土发生较严重的土壤颗粒分散。实验室测定虽然可以估测土壤分散的严重程度，但还需进一步的研究来量化土壤有机物含量和粘土矿物组成对其影响。总之，用于加利福尼亚和USGA 标准果岭根层的泥炭/砂混合物不易产生由含盐灌溉水源导致的土壤结构分散及饱和导水率降低。

关键词：高尔夫场；果岭；根层基质；导水率；土壤淋洗

中图分类号：G 849.3；S 155 文献标识码：A 文章编号：1009-5500（2013）05-0072-07

收稿日期：2013-08-17； 修回日期：2013-10-09

作者简介：张华（1972-），男，广西柳州人。

E-mail：zhanghua887@oa.szpt.edu.cn

Hydraulic conductivity of golf course putting green

root zones affected by sodium adsorption

ratio of leaching water

ZHANG Hua WANG Yi-chun LI De-ying

（1.School of Applied Chemistry and Biological Technology，Shenzhen Polytechnic，Shenzhen

518055，China；2.Department of Plant Sciences，North Dakota

State University，Fargo，ND 58108，USA）

Abstract：Soil salinization is a major problem threatening turfgrass management.Alternative water sources such as recycled water （RW） usually have elevated salt content.With high exchangeable sodium in soil，rain or irrigation with fresh water can cause soil dispersion，and thus reduce water infiltration and permeability.The objective of this study was to determine the effect of salt composition in irrigation water on saturated water conductivity （Ksat） of putting green root zone materials and constructions.Three root zone materials，clay （Fargo，North Dakota，USA），clay loam （Garick Corp.，Cleveland，OH），and sand/peat mixture （Dakota Peat，North Dakota，USA） （90/10 v/v） were tested alone，as well as tested in different root zone construction，i.e.soil pushup green （40 cm deep），sand/peat mixtures in USGA-putting green style （30 cm of root zone over 10 cm gravel） and California putting green style （40 cm deep）.Saturated water conductivity was determined after the root zone materials and construction were leached with water of five levels of SARw （0，2.5，5.0，15.0，and ∞）.All except the SARw 0 had an ECw of 11.0 dS/m.The results showed severe soil dispersion may happen when SARw of leaching water is greater 5 for clay and clay loam.A laboratory test may predict the severity of dispersion but further study is needed to quantify the effect of soil organic matter （OM） and clay mineralogy.Generally，sand/peat mixtures used in root zones of either California or USGA putting green style is not vulnerable to dispersion by salt in irrigation water.

Key words： golf course；putting green；root zone；saturated water conductivity；salinity；leaching.

INTRODUCTION

Soil salinization is a major problem threatening crop production in arid and semi arid areas.Compared to agriculture turfgrass management is facing a greater challenge because turfgrass irrigation is often viewed as a low priority when water shortage happens.Recycled water （RW） is a practical alternative for turfgrass irrigation as it is the only water source with increasing availability （Harivandi，2007；Qian and Harivandi，2008）.The National Golf Course Owners Association reported that 12% of the golf courses have adopted RW solely or partially for irrigation （NGCOA，2005）.Recycled water usually contains significant amounts of salt，and repeated use for turfgrass irrigation may result in soil salinization （Mancino and Pepper，1992；Thomas et al.，2006）.Excessive salts adversely impact turfgrass growth by inducing osmotic stress and toxicity （Munns and Tester，2008）.Leaching is an important means of removing excess salts out of the root zones.Once exchangeable sodium in soil is too high，rain or irrigation with fresh water can cause soil dispersion，surface crusting and compaction，and thus reduce water infiltration and permeability （Carrow and Duncan，1998）.The efficiency of leaching practice is affected by many factors，such as water quality，soil types，irrigation，and climate.For non-sodic saline soils，leaching can be achieved using water with electrical conductivity （EC） below the targeted soil EC.Nevertheless，larger leaching fractions （LF） are required as EC of leaching water increases.Once soil becomes sodic，leaching will not be effective because soil hydraulic conductivity decreases with decreasing electrolyte concentration and increasing sodium adsorption ratio （SARw） of the leaching water，especially for soils high in 2∶1 layer-silicates （McNeal and Coleman，1966；McNeal et al.，1966）.

The widely used guidelines of SAR and EC thresholds for water infiltration in salt management were established by Ayers and Westcot （1985） based on the research by Oster and Schroer （1979） and Rhoades （1977）.A more recent guideline was developed to include soil texture information （Steppuhn and Curtin，1993）.An evaluation of those guidelines using different soils and leaching water was conducted by Buckland et al.（2002） and the results indicated that soil texture is important in the selection of leaching water.

Currently，LF in turfgrass management is mostly based on the measurement of water EC and soil EC （Carrow and Duncan，1998；Rhoades and Loveday，1990）.However，different leaching strategies are recommended for sand and soil root zones.On sand-based systems，large amounts of water can be applied at one time，while for soils with lower infiltration rates，a leaching fraction slightly above the evapotranspiration （ET） can be applied （Soldat，2007）.Water permeability （infiltration and percolation） through different turfgrass root zones such as the United States Golf Association （USGA） style and California style is usually different （Aragao，et al.，1997；McCoy and McCoy，2006）.A small amount of silt and clay fraction is allowed in the USGA specifications （USGA Green Section Staff，1993），whether such a small amount has any influence on leaching practice in salinity management of sand-based root zones is not well understood.

The objective of this study was to determine the effect of salt composition in irrigation water on saturated water conductivity （Ksat） of four putting green root zone materials.The result will provide better understanding of interactions between root zone media and water quality and quantity in leaching process so that turfgrass managers can make decisions accordingly.

MATERIAL AND METHODS

Three root zone materials，clay （Fargo series，fine，smectitic，frigid Typic Epiaquerts），clay loam （topsoil，Garick Corp.，Cleveland，OH），and sand/peat mixture （Reed sedge peat，Dakota Peat，North Dakota，USA） （90/10，v/v） were packed into brass cylinders （6 cm diam. 5.4 cm i.d.） with two layers of cheese cloth attached at the bottom.Compaction was kept consistent by 5 drops of a 1.36 kg hammer from a 305 mm height （USGA Green Section Staff，1993）.Each soil type had four replicates.The compacted soil cores were treated in a laboratory for 10 saturation/drying cycles with salt solutions at five levels of SARw.Saturation was achieved by introducing the salt solutions from the bottom of the samples and drying process was conducted at room temperatures.The five levels of SARw were 0，2.5，5.0，15.0，and ∞，all except the SARw 0 had an EC of 11.0 dS/m.The EC for SARw 0 was 0.2 dS m^-1 from distilled water.A target SARw level was achieved by mixing appropriate amounts of NaCl，CaCl2·2H2O，and MgCl2·6H2O，respectively，with Ca²+ and Mg²+ in 1∶1 ratio where they were needed，following the equation of SARw = [Na⁺]/（Ca²++Mg²+）/2，with concentration expressed in meq/L.After the wet/dry cycles，Ksat of those samples were measured using distilled water by a constant head method following Klute and Dirksen （1986）.Organic matter content was tested by the loss on ignition method （Nelson and Sommers，1996）.Soil EC was determined following the method of Whitney （1998） with miner modifications.Briefly，to a 10 g of soil sample deionized water was added in 1∶5 soil to water gravimetrical ratio and agitated on a shaker （Model 6010；Eberbach Corp.，Ann Arbor，MI） at 180 osc/min for 10 min.Then，following a 15-min equilibration，the EC from the supernatant was measured with an EC meter （model 1054；VWR Scientific，Phoenix，AZ）.Soil pH was determined with a pH meter （model 420；Thermo Fisher Scientific Inc.，Waltham，MA） following the method of Watson and Brown （1998） using a 1∶1 soil to water gravimetric ratio.Cation exchange capacity was measured using ammonium acetate extraction method at pH = 7 （Hendershot et al.，1993）.The chemical properties of soil materials used in the study are shown in Table 1.

The three root zone materials also were used to fill in clear polyethylene tubes （5.4 cm diam.，40 cm height） to simulate root zones.Clay and clay loam were packed to 40 cm depth.Sand/peat mixtures were packed in USGA putting green style （30 cm of root zone over 10 cm gravel） and California putting green style，respectively.Therefore，four different root zones were created.Each tube was supported within a 7.5 cm diameter opaque polyvinyl chloride （PVC） pipe capped on the bottom.Holes were drilled on PVC cap and plastic tubing to allow for drainage.Sea-

Table 1 Properties of three soil materials used in the construction of putting green root zones

prior to the leaching experiment with different levels of sodium adsorption ratio （SARw）

1：Electrical conductivity measured in a 1：5 soil to water gravimetric ratio.²：Cation exchange capacity.³：Organic matter. side II' creeping bentgrass was seeded at a rate of 49 kg/ha in the four root zone mixtures.

Irrigation was applied with an automated mist system to maintain moisture during germination and then hand watered every other day four weeks after germination.Milorganite （5.0 N-0.9 P-0.0 K） was applied at 24.5 kg N/ha at the time of seeding and 13.0 N-0.0 P-22.0 K was applied every two weeks at 49 kg N/ha in the following two months.The grass was hand cut at 2 cm height twice a week following the germination.Average day/night air temperature was 28/18 ℃ and supplemental light with metal halite lamps were provided to have a minimum PAR of 375 mol/m·s and photo period of 12 h/d.

The experiment was set up as a split-plot with root zone mixtures being the whole-plot factor arranged in a randomized complete block design with three replicates.The sub-plots were assigned to a combination of five SARw levels as used above.A micronutrient fertilizer （0.84% B，1.80% Cu，15.25 % Fe，5.55% Mn，0.09% Mo，5.25% Zn，and 8.45% S） （EnP Inc.，Mendota，IL） was applied at 91.5 kg product per ha when the leaching treatments were initiated to avoid potential micronutrient deficiency.

Six months after the initiation of the study，all soil profiles were removed from the plastic tubes and air dried prior to crushing into particles and aggregates smaller than 3 mm.The soil samples from the top 0 to 10 cm depth were repacked into brass cylinders （5.4 cm diam.，6 cm height） and their Ksat values were determined using same methods described above.

Data were subjected to analysis of variance （ANOVA） using the general linear model procedure with the Ksat data transformed with the natural logarithm prior to the ANOVA analysis （SAS Institute Inc，2008）.Means of soil Ksat were compared using the Duncan's multiple range tests at 0.05 probability level.

RESULTS AND DISCUSSION

There was significant soil type，SARw level，and interaction effects on Ksat after the saturation/dry cycles （Table 2）.Saturated water conductivity of clay and clay loam was affected by SARw level in the salt solutions，whereas sand/peat mixture was not.For clay soil，significant reduction of Ksat from the control occurred as SARw became higher than 2.5，with the lowest Ksat occurred in the treatment that had no CaCl2

Table 2 Analysis of variance for the saturated water conductivity of the root zone materials （clay，clay loam，

sand/peat） after 10 cycles of saturation/drying cycles using salt solutions with

SARw at 0，2.5，5.0，15.0，and ∞. added （SARw = ∞） （Fig.1）.For the clay loam soil，significant reduction of Ksat from the control occurred only in salt solution without CaCl2 addition （SARw = ∞）.Therefore，the clay soil was more prone to dispersion than clay loam as a result of exposure to salt solutions with high SARw values.Sand/peat mixtures were most labile in response to different EC and SARw in irrigation water followed by leaching with distilled water.

Fig.1 Saturated water conductivity of root zone materials affected by 10 cycles of saturation/drying using salt solutions with sodium adsorption ratio （SARw） at 0，2.5，5.0，15.0，and ∞.Bars with a same letter are not significantly different at the 0.05 probability level.

Results from the greenhouse study were similar to that from the laboratory，with significant root zone material/construction effects，SARw effects and interactions （Table 3）.The Ksat of sand/peat mixtures was not affected by different levels of SARw in leaching water when used in California and USGA root zones （Fig.2）.There were no differences between California and USGA root zones despite the higher water holding potential in the USGA style root zone （Li et al.，2005）.All salt solutions resulted in reduction of Ksat from the control in clay soil，with the most reduction occurred in the treatment that had no addition of CaCl2 （SARw = ∞） （Fig.2）.A 25% reduction of Ksat occurred when SARw was greater than 2.5 with no difference for SARw levels of 2.5 to 15.For clay loam，significant reduction of Ksat showed as SARw was higher than 2.5，with the lowest Ksat occurred in the treatment that had no addition of CaCl2 （SARw = ∞） （Fig.2）.A 25% reduction of Ksat occurred when SARw was greater than 5 but there was Ksat difference between SARw levels of 5 and 15.

Table 3 Analysis of variance of saturated water conductivity affected by four root zone constructions and materials （clay

pushup，clay loam pushup，sand/peat California，sand/peat USGA） after 6 months of irrigation using sodium

adsorption ratio （SARw） levels at 0，2.5，5.0，15.0，and ∞

Results from this study are in agreement with McNeal and Coleman （1966） in that hydraulic conductivity decreases with decreasing electrical conductivity and increasing SARw of the leaching solution and the responses vary with different clay mineralogy，with montmorillonite being most sensitive.This study also supports the maximum SARw of 5 as the guideline for leaching fine textured soil as reported by Steppuhn and Curtin （1993）.In addition to the clay content，soil samples used in this study had a great difference in OM content （Table 1）.Therefore，OM content may also influence the levels of soil dispersion caused by high SARw in the leaching water.

In conclusion，a severe soil dispersion hazard may happen when irrigating with salt water with SARw value greater than 5 as shown in the reduction of Ksat.A laboratory test could be used to predict the severity of dispersion but further study is needed to quantify the effect of soil OM and clay mineralogy.Generally，sand/peat mixtures used in either California or USGA style root zones are not vulnerable to dispersion from the salt in irrigation water，although the threshold of clay or OM content in sand-based root zones requires further investigation for saline water irrigation.

Fig.2 Saturated water conductivity of four root zone constructions and materials （clay pushup，clay loam pushup，sand/peat California，sand/peat USGA） affected by 6 months of irrigation with different sodium adsorption ratio （SARw） levels in the water.Bars with a same letter are not significantly different at the 0.05 probability level.

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