Soil Structure of Putting GreensBy KENNETH WELTON

Read at tbe 6tb A11nual Educational Conference of tbe National Associatio11 of Greenkeepersof America, beld at New York City, January 19-22.

KENNETH WELTONMember of the staff of the U. S.G. A. Green Sectiolt, who bas11Iade alt exte1lSive study of soils

i1l relatiOIl to fine iurf.

IT SEEMS most appropriate thatthe subject, uSoil Texture of Put-ting Greens," be brought to yourattention at the commencement ofa conference during which theputting green will probably receivemajor consideration. In the studyof any subject it is always well tostart at the bottom and recognizethe fundamental facts concerningit before progressing to the manyphases which will develop later.Following this line of reasoning wewill commence far below the put-ting surface, with the fill or sub-soil.

The sub-soil is important to theturf on the green insofar as it in-fluences drainage and the rise ofwater from below by capillary at-traction. We require large quan-tities of sub-soil or fill in building putting greensand fortunately it does not matter a great dealwhat type of material we use since we can modifythe construction to suit the soil. When using finesoils, such as clays or silts, we should pay particularattention to procuring uniform drainage from thetop of the fill. In other words the fill should havegood surface drainage before the topsoil is put onit. No depressions or pockets should be left to col-lect water and toxic materials, and no sharp or highmounds should be left to shed water and dry outquickly.

For safety's sake tile underdrainage should be putin clay and silt sub-soils. Layers of various materials,such as cinders, sand, gravel and peat, should not belaid between the topsoil and the sub-soil. In thepast this was common practice but most greenswith such construction have had to be rebuilt. Suchlayers interfere with the natural rise and fall of soil

April, 1932

moisture. Porous layers drain thetopsoil too thoroughly and cut itoff from the reservoir of moistureand fertilizing elements which risefrom the soil below much as inkrises on blotting paper.

Lines of tile quickly carry awayexcess water and do not interferwith the rise of capillary moisturein the soil. Layers of clay or peatare sometimes pu t on sand fills topreserve moisture but these layersare as bad as layers of cinders orsand on clay fills. They preventna tural drainage and elimina tionof toxic materials from the topsoil.It is better to use the clay or humusto prepare a deeper topsoil on asand fill.

We now come to that importantpart of the putting green which

surrounds the roots of the turf and supplies theplants with food and water-the topsoil. Let usfirst consider the topsoil from the golfer's view-point. We all know how important modern golfarchitecture is in making the pitch shot. And weknow that by far the large majority of golfers usethat shot either from necessity or preference in theapproach to the putting green.

If the soil is as hard as concrete it is impossiblefor the average player to hold the green. Hence,when greens become in such a condition a great cryarises from the indignant players and the green-keeper is forced to soften the offending greens bypouring water upon them until the soil is saturatedand muddy. The players trample the greens whilein this condition and the soil become more packedor puddled and if allowed to dry it is harder. thanever. It is expensive to water greens frequently,but if that were the only disadvantage to keeping

19

20 The Nati011al Greenkee per APril,_ 1932

greens wet very few clubs would object.

The truth is, however, that such greens arealways going from one extreme to another. Theplayers cannot tell from day to day how differentputting greens will act. And more important stillis the fact that good turf cannot be kept for longon greens which require such treatment.

Now, let us consider the topsoil from the green-keeper's viewpoint. The greenkeeper knows thatthe soil is porous and that these pore spaces shouldbe filled with air since roots require an almost con-stant supply of oxygen. The greenkeeper alsoknows that the soil must be loose enough for theroots to grow and forage in search of moisture andplant food.

If the pore space in the soil is filled with freewater for too prolonged a period the roots areaffected and the plant sickens and dies. If the soilpuddles and packs while wet the soil becomes a solidmass and the pore space, and hence the oxygen inthe soil, is greatly restricted. If the soil becomes ashard as brick when dry the roots are sealed and can-not grow. Obviously a topsoil which exhibits theabove characteristics is unsuitable both from theplayers' and the greenkeeper's point of view, andwe must select or mix a soil which is suitable.

STUDY OF SOIL IS MOST INTERESTING

~EFORE speaking of topsoil preparation I wouldlike to remark that soil is not the commonplaceordinary material which some think it to be. Thestudy of soil is a most interesting one, and anyonewho follows the study to its ultimate conclusionswill find it as highly technical as desired. The morefamiliar greenkeepers become with soil phenomenathe more intelligently they will be able to attackthe many problems in plant growth.

The soil layer is a comparatively thin one cover-ing the solid part of the earth below. This layeroriginated from broken and weathered fragmentsof rock. At first simpler forms of vegetation grewon the pul verized rock, then more highly developedforms. Each tribe of plants has taken mineral mat-ter from the disintegrated rocks and carbon andoxygen from the air until the soil has accumulateda great store of organic 'matter and a teeming pop-ulation of n1icroscopic life.

The soil has three general phases: the physical,

which has to do with the size and shape of the parti-cles, the movemen t of air and wa ter in the soil andother physical aspects; the chemical, which dealswith the composition of the particles; and the bio-logical, which deals with the minute forms of lifewhich are of great importance in manufacturingfood for plants. The greenkeeper is concerned withall these phases but chiefly with the physical since hecan influence the other phases sufficiently with hiscultural practices providing he has the proper soiltexture and structure to start with.

Soil texture refers to the six of the soil particle.Soil is classified in to various types such as sand, siltand clay according to its texture-the sand beingthe large, coarse particles, silt finer particles andclay still finer. There are numerous classificationsor soil types depending upon the proportion ofparticles of various sizes. Loam soils are mixtures ofcoarse and finer particles along with more or lessorganic matter. Soil structure is the arrangementof the particles in the soil, and the arrangement maybe such that the soil is crumbly, open, and porous;or tight and compact.

Soil plasticity and cohesion have a great influenceon soil structure. Plasticity of soils enables it to bemolded into various forms without fracturingmuch as can be done with putty. Cohesion is closelyrelated to plasticity and is the tendency of theparticles to stick together and preserve the mass in-tact. Plasticity will allow soils to lose their crumblynature and become puddles when wet and cohesionwill hold the soil mass intact like rock or brick whenit is dry.

Soil structure is largely dependent upon plas-ticity and this in turn is largely dependent uponsoil texture since plasticity is most marked in thefiner particled soils such as silts and clays. In coarsesandy soils plasticity is nil.

Organic matter plays an important part in thefertili ty of the soil. It is necessary for the micro-scopic life in the soil, and has a marked effect onthe structure and water-holding capacity of thesoil. On account of the affinity of organic matterfor moisture, the moisture is held within the organicmatter and a certain amount of organic matter infiner soils increases the drainage and loss of freewater by keeping the finer particles from settlingtogether into a n10re or less compact mass. Soilswith sufficient organic matter do not dry so quickly

APril, 1932 The National Greenkee per 21

and hence they do not solidify by cohesion soreadily.

Due to its water-holding capacity comparativelylarge changes in volume occur in organic matterand such changes in the organic matter in the soilhave somewhat the same influence as freezing andthawing do on the soil and hence increase its gran-ular structure.

MUCK SOILS NOT SUITABLE

C['HERE are certain muck soils which, althoughthey may contain considerable organic matter, arenot suitable for improving soil structure. Somemucks have high mineral and colloidial contents andmay tend to increase rather than decrease soil plas-ticity and cohesion. Most commercial peat, humus,and peat moss on the market are suitable sourcesof organic materials for improving the structureof silt and clay soils.

It has been found that the addition of organicmatter to most clay and silt soils has more effect ondecreasing their plasticity and cohesion than hassand. But it is seldon1 advisable to add more thanone-third organic matter to putting green topsoilmixtures.

Since sand and some organic materials exhibitlittle plasticity and cohesion it seems probable thatthere are soils which contain sufficient of these ma-terials to make them suitable for putting green pur-poses. If such a soil cannot be readily procured sandand organic matter may be mixed with silt and claysoils in sufficient amounts to make ideal soils forputting green purposes. It is, however, very diffi-cult to describe a certain type of soil which, fromall sources would be suitable. Soil classification doesnot include the percentage of organic matter insoil, also there may be a considerable variation inthe amount of finer materials in soils of the sametype.

Two soils from different locations which areclassified as the same soil type may exhibit markeddifferences in their plasticity and cohesion andhence in their ultimate structure in the green. In ageneral way it is safe to state that soils classifying assandy loams and which contain sufficient organicmatter are suitable for putting green topsoil.

Soil experts would be able to judge more accu-rately how a soil would act under putting greenconditions by handling the soil than they could by

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being shown the results of a soil analyses alone.Some soils examined while under field conditionsmay appear open and friable and in excellent physi-cal condition, but that is no guarantee that this soilwill not become as hard as brick under puttinggreen conditions. Other soils are highly fertile anddesirable for agricultural or gardening purposes.

Fertility, however, is what a soil is capable ofproducing under best possible conditions and in theputting green these soils may lose the structurethey were maintained under in the field and in thegarden and become infertile in the green. It is,therefore, advisable for the golf course constructoror the greenkeeper to subject his putting green top-soil to some test calculated to show in a short timewhat structure it may be expected to exhibit in theputting green after it has been in use some time.The best method of doing this is to test its plasticityand cohesion. There are numerous reasons why it isdifficult for experimenters to arrive at exact nu-merical expressions of plasticity with soils. It ispossible, however, to arrive at the relative plasticityand cohesion of different soils even by simplemethods.

SIMPLE METHOD OF TESTING SOILS

EQUAL quantities of the various soils or mixturesshould be procured while dry enough to handle.They should then be wet and puddled in a uniformmanner. It is important that the samples be han-dled alike as difference in wetting and mixing mayconfuse the results. A practical manner of han-dling the samples alike is to pour a similar amount ofeach sample into a similar container. A quart ofsoil in a 12-quart bucket is easily handled. Thenadd water slowly while mixing and churning witha stick until the soil will absorb no more water. If

too much water has been given, a little more of thesame soil can be added to take up the superfluouswater. With a little practice it will be possible tobring each sample to such a condition with equalhandling that it will just flow from the pail whenagitated. No record need be kept of the amountof water added to the different samples, the pointis to add enough water to put each of them in thesame plastic condition.

The samples should then be poured into uniformmolds. Little troughs of equal size may be madefor this purpose or small flower pots or small boxesof the same capacity, shape and material may beused. The tops of these samples should then betrowled to smooth them and the samples set undercover to dry. After a few days the samples may beremoved from the containers and allowed to dryfurther. The time of drying of various samplesshould be noted. Samples containing too muchorganic matter will show up as they will take over-long to dry.

After the samples are thoroughly dry they maybe handled and it will at once become apparent ifsome samples are unfit for putting green purposes.Soils too high in sand or organic matter, or both,will not stand handling and may break while beingremoved from the UloId. Samples which exhibittoo much cohesion will be difficult to break. Sam-ples which took a reasonable time to dry, whichcould be removed from the mold withoutcrumbling and which could be broken down read-ily between the fingers and thumb, are at, or ap-proaching, the correct texture.

It will be found by this method that about onethird of clay or silt loam soils mixed with a thirdcoarse sand and a third organic matter such as cul-

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steady tramp, tramp, tramp of feet across its surface slowly, butsurely, packs it down until the condition of the soil area in whichthe grass roots are supposed to exist is no longer fit to sustainthem. Even the best of original soil preparation succumbs to thisarmy of heavy hoofs in time. If the original preparation hasn'tbeen so good and water is used too frequently to soften the turf,the packing process is hastened.

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not be soggy even an hour after a heavy rain andyet the soil will not dry out quickly, nor will it be-come too hard. It will have sufficient resiliency tohold properly-played pitch shots and will be ofproper structure for satisfactory plant growth.

tivated peat, humus or ground peat moss, will ap-proach the condition described.

This method of testing soils for putting greenpurposes may seem very simple but it is surprisinghow few golf course constructors will bother put-ting their soils to any plasticity test before usingthem on the putting green. This does seem negligi-ble when one considers that the putting green is notdug up or cultivated from year to year and hencethere is little opportunity to improve the soil oncethe green is in turf. Also, many greenkeepers kickabout the tendency of their putting greens to forma hard crust on the surface, but although they mixsoil for top-dressing purposes many times a yearthey never go to the trouble of testing the soilexcept by its feel when it is in that fine, floury con-dition just after it has been put through the screen.

Many greenkeepers realize that poor topsoil con-ditions are responsible for a good portion of theirputting green troubles, and I have tried to bringout the fact that one good reason for these condi-tions is that no adequate tests were made in select-ing the soil or soil mixture. If we use the right kindof topsoil in building and topdressing the puttinggreen it will drain well enough that the surface will