ering of a soil means the ability of thesoil to resist a change in pH. Bufferingcapacity is due to the cation exchangeability of the clays and humus whichwill be described in a latter article. Itmust be remembered, however, thatfields constructed on acid sands can be-come more acid relatively rapidly.

The effect of pH on grassWhy is the pH of the rooting zone

considered a problem? The hydrogenconcentration (pH) is not the directproblem as plants have been success-fully grown at pH 3.0 in solution culturewhen all the nutrients are controlled andprovided in a soluble form. The primaryproblem is that the pH of the soil has asignificant influence on the ability ofelements required for grass growth to bedissolved in the soil water. If, through achange in pH they become insoluble, orsoluble at rates less than that required tosupply the grass, a pH-derived, nutri-tional problem is created. If, on theother hand, they become too soluble, atoxicity problem is created.

Table 1 lists the pHat which the vari-ous nutrients required for grass growthare most soluble. With the exception ofiron and manganese a neutral pH wouldbe the most desirable.

UNDERSTANDING TURF MANAGEMENTThe eighth in a series byR.W. Sheard, Ph.D., P.Ag.

SOIL REACTION - pHMuch has been written about thesoil reaction or pH. Many sportsfield managers lose countless hours ofsleep worrying about the results of a labanalysis which indicated a high or a lowpH. Understanding what is meant bysoil reaction and its implications ingrass production can save many hoursof that lost sleep.

What does pH mean?pH is a measure of the relative acidity

or alkalinity of the soil and is measuredby a pH meter in negative logarithmicunits from 1 (very acid) to 14 (veryalkaline). In physical chemistry termspH is a measure of the hydrogen ionconcentration in the soil solution. Thelower the pH value the greater the con-centration of hydrogen ions, that is, themore acid the soil. A neutral soil is onethat has a pH of 7.0. Because the meas-uring system is logarithmic, a soil witha pH of 6.0 is 10 times as acid as onewith a pH of 7.0. Likewise a soil with apH of 5.0 is 100 times as acid as aneutral soil.

Soils in Canada, in their natural state,range in pH from 3.5 to 9.0. The acidsoils are primarily sands which havebeing growing coniferous forests forcenturies. Soils of pH 8.5 or greater areusually associated with the saline soilsin the prairie regions of Western Canadawhich contain relatively high amountsof soluble salts.

Most Ontario soils have developedfrom materials of limestone origin andhave a near neutral pH. Most WesternCanadian soils also tend to be neutral oralkaline in reaction whereas soils in theMaritime provinces tend to be acid.Therefore, in Ontario, most sports fieldsconstructed from local materials can beexpected to have a pH near 7.0. Analkaline reaction is also usually associ-ated with the sands used for construc-tion or topdressing if they are obtainedin Southern Ontario. Sands from theCanadian Shield, however, may be aciddue to the granites and other igneousrocks from which they were formed.

Table 1: The influence of pH on the solubility of the nutrients required forplant growth ..

With time, usually measured in dec-ades, all soils become more acid. Thereare five basic factors which contributeto this slow acidification of soils.• The formation of hydrogen ions dur-

ing root respiration and microbialbreakdown of organic matter.

• The conversion of ammonium nitro-gen to nitrate nitrogen when ammo-nium fertilizers are used.

• The addition of elemental sulphur toa soil.

• The breakdown of clay minerals inthe soil and the subsequent liberationof aluminum which reacts with waterto produce hydrogen. This break-down speeds up as the soil becomesmore acid.

• The leaching losses of calcium andmagnesium which have a neutralizingeffect on the hydrogen.

Obviously, the greater the biologicalactivity such as root growth, the greaterthe leaching (excess irrigation), themore ammonium fertilizers and ele-mental sulphur that is added to a sportsfield, the more quickly it will becomeacid. In sports fieldswhich contain sig-nificant amounts of clay and organicmatter, however, the acidification proc-ess is counteracted by a phenomenaknown as buffering capacity. The buff-

NutrientLeast SolublepH Range

Most SolublepH Range

NitrogenPhosphorusPotassiumCalciumMagnesiumSUlphurIronManganeseBoronZincCopper

6.5 - 8.06.5 -7.26.5 - 8.57.0 - 8.57.0 - 8.56.5 - 8.53.5 - 6.04.5 - 6.55.0 - 7.05.0 - 7.05.0 - 7.0

5.5 and lowerless than 6.5, over 7.26.5 and lower6.5 and lower6.5 and lower5.5 and lowergreater than 6.0greater than 6.0less than 5.0, over 7.5greater than 6.0greater than 6.0

The most widely discussed problem ofpH in soils and its effect on plant nutri-tion is phosphorus availability. Thesolubility of phosphorus reaches a maxi-mum between pH 6.5 and 7.2. Above7.2 the solubility decreases due to theformation of relatively insoluble com-pounds of calcium and magnesium; be-low 6.5 the solubility decreases due tothe formation of relatively insolublecompounds of iron, aluminium andmanganese. All forms of phosphorusfound in the soil have a low solubility inwater, however, it takes time, measuredin months or years for the phosphorus toreach the low solubility such as thatfound in the original phosphate mineral,apatite. The further the pH deviates fromthe optimum the less time required toform the very insoluble forms. There-fore, a program of regular phosphatefertilization, based on an approved soiltesting procedure, is a more realistic ap-proach to pH than an attempt to changethe pH.

The lower concentration of nitrogenand sulphur in the soil solution at a pHless than 5.5 is due to the decrease in theactivity of soil microbes that convert thevarious nitrogen and sulphur forms inthe soil to the forms which a grass rootcan absorb. Iron and manganese in-crease in solubility as the pH falls. Infact, one of the major reasons for liminga soil to increase the pH is to reduce thesolubility of manganese which can betoxic to grass roots at high concentra-tions.

The four minor elements, iron, manga-nese, zinc and copper decrease in solu-bility as the pH rises above 6.0, causingunnecessary concern for field managerswhose soils are testing 7.5. The concernis unnecessary in most cases becausethese are minor elements; elements re-quired in very small amounts for plant

growth. Only a few species, grass notbeing one of them, respond to applica-tions of these minor elements, even at apH greater than 8.0. If a response is tobe found, it will be on sands, very lowin organic matter. Grass species have avery low requirement for boron and ithas never been reported as a deficiencyproblem. However, in saline conditionsin arid regions on soils with a pH above8.0, boron may become soluble enoughto be toxic.

Changing the pHChanging the pH is not a simple pro-

cedure. If one wishes to increase the pHof an acid soil to the neutral range it isnecessary to add a liming material, gen-erally calcitic or dolomitic limestone.The dolomitic form of limestone is usedwhere a magnesium deficiency is knowto occur because it is a mixture of cal-cium carbonate and magnesium carbon-ate. Two other liming materials,quicklime and hydrated lime, may alsobe used but caution in their applicationmust be taken because they are causticto the eyes and skin.

Limestone is very slowly soluble inwater, thus it is necessary to use veryfinely ground material - 85% shouldpass a 10D-mesh screen. Because lime-stone is slowly soluble, it is best mixedwith the soil materials for the upper 15em of the rooting zone prior to construc-tion of a sports field. Application to an.existing field may require several yearsto show an affect below the first fewcentimetres. To speed up the penetrationof the liming materials applicationsshould be made during a coring opera-tion.

To determine the amount of limestoneto apply it is necessary to do a standardpH measurement. If the value is below

the desired target pH for the turf, i.e.,6.0, the a second pH measurementknown as the 'buffer pH' is made. Thebuffer pH reflects the difference in soilbuffering capacity of soils due to theirdifferent clay and humus contents. Forexample a high organic matter, clay soilwill require more limestone to changethe pH one unit than a sand. The amountof limestone required to raise the pH tothe target pH is shown in Table 2.

The turf species used in Canada dovery well at a target pH of 6.0, hence theaddition of limestone is seldom re-quired. Table 3 outlines the preferredpH range for these species.

Some turf managers want to lower thepH of a soil which reads 7.8 or greater.It has never been shown that there is anadvantage to doing so and the expenseis prohibitive. There may, however, belocalized horticultural situations wherelowering the pH is desirable, such as thegrowth of azaleas. The materials whichmay be used are elemental sulphur, alu-minum sulphate and sphagnum peat.Sphagnum peat generally has a pH be-tween 2.5 and 3.0

The amount of sulphur or aluminumsulphate required to adjust the pH of thetop 15 em of soil to pH 7.0 is recordedin Table 4.

Table 3: The preferred pH range forthe common turfgrass speciesgrown in Canada.

Species Preferred pH Range

Kentucky bluegrassColonial bentgrassCreeping bentgrassCreeping red fescueRyegrass

6.0 -7.66.0 - 7.06.0 - 7.05.5 - 6.56.0 -7.0

Table 2: The lime requirement to correct soil aciditybased on the target pH and the buffer pH.

Table 4: The amount of elemental sulphur or aluminumSUlphate required to lower the pH to 7.0.,

66.033.0

InitialpH

Elemental SulphurSand Loam Clay

Aluminum SUlphateSand Loam Clay

8.07.5

11.0 22.06.6 13.2

(kg/100m2)40.7 22.017.6 11.0

44.022.0

Buffer pH Target pH = 6.5 Target pH = 6.0(ton ne mate rial/hectare)

7.0 2 06.5 3 26.0 9 65.5 17 12~o ~ ~

In summary it must be emphasizedthat materials to directly alter the pHshould never be applied unless a pHdetermination has been made. Further-more the pH should seldom be aconcemfor the turf manager. If it becomes ex-cessively high (over pH 7.8) then bealerted to the possible requirement for ahigher phosphorus test to satisfy the re-quirements of the grass. If the pH fallsbelow 5.5 be prepared to apply somelimestone during coring. Inbetween en-joy a good night's sleep.

Composting for~~~....",mnm~

Athletic FieldsMichael J. BladonGrounds Dept., Univ. of Guelph

Benefits ofComposting

The principal benefit of compo stingis to recover or recycle biodegrad-able materials from agricultural,industrial and municipal waste streamsin an environmentally acceptable man-ner to produce a useful, marketableproduct.

A second benefit is that the end prod-uct (compost) is a safe material whichmay easily be transported using regularcommercial vehicles. The resulting ma-terial has many advantages and can beused in many ways.

For example, there is now evidencethat compost can be used to suppressplant diseases, stabilize soil pH and im-pede the movement and uptake by plantsof toxic metals such as cadmium andlead.

Furthermore, reclamation of stripmines, mine tailings and the rejuvena-tion of salt-damaged soil along road-ways may be aided. In addition,compost recycles the plant nutrients soless fertilizer is needed.

Finally, the use of compost on sportsfields for topdressing, construction orrenovation instead of peat moss is im-portant in two ways. It will help to pre-serve wetlands from which peat isharvested. Generally this harvest is airreversible process with the destructionof the wetlands. The destruction of wet-lands is now a serious environmentalissue, especially among the wildlifepeople.

Peat moss is very expensive - compostis a much more reasonable economicalternative, in fact some landscape ar-chitects are including compost in theirspecifications. In a survey conducted bythe lawn and landscape industry, therespondents categorized themselves as:• 71.3% being generators of lawn waste

(clippings, leaves, branches,

• 34.8% being collectors of lawn waste,and

• 33.0% being composters of lawnwaste.

Of those contractors that were sur-veyed who collected waste and gener-ated compost, 66% indicated they use itthemselves, 26.3% gave the materialaway, and 7.3% sold the compost.

Getting StartedFirst of all, depending on where you

live, obtain a copy of the ProvincialGovernment Guidelines for aerobiccomposting. It will be apparent fromreading these guidelines that in order togenerate good compost you need a rec-ipe which includes: air, moisture, cor-rect C:N ratio, temperature and pHbalance. Finally you will need at leastan acre of land for every 1,000 tonnes ofyard waste.Air: The bacteria which break downorganic matter are called aerobic be-cause they need oxygen. Lack ofaeration, because the pile is too wet,packed to tight, or is too large, can causeit to become anaerobic which can createodours objectionable to neighbours.Furthermore, anaerobic compostingdoes not create sufficient heat (min. of550 C) to kill weed seeds and variouspathogens. So turning, and hence aerat-ing, the pile during the compostingprocess will provide the oxygen neces-sary for the aerobic bacteria.