S³awomir Proñczuk, Grzegorz ¯urek
Plant Breed ing and Ac cli ma ti za tion In sti tute, De part ment of Grasses, Le gumes and En ergy Plants, Radzików, 05-870 B³onie, Poland
THE RELATIONSHIP BETWEEN SOD STRENGTH AND TURF QUALITY OF COMMON GRASS CULTIVARS
ABSTRACT
The sod strength, root ing depth and turf qual ity (ex pressed by shoot den sity and vi sual merit) of ten turf grass cultivars were stud ied dur ing three years un der me dium in ten sive turf main te nance. Cultivars of smooth stalked meadow grass (SMG), pros trate meadow grass, tall fes cue (TF), red fes cue., tufted hair grass (TH) and pe ren nial ryegrass (PR) were ex am ined. Sim ple and fast eval u a tion ‘hand tool’ to de ter mine over all sod strength was used. Sea sonal vari a tion of traits for tested cultivars was de scribed. The high est val ues of sod strength were noted for SMG cultivars and the low est – for PR, TF and TH cultivars. Sod strength was not af -fected by root ing depth. Vi sual merit and shoot den sity were pos i tively cor re lated with sod strength only for few SMG cultivars. The method of test ing can be rec om mended for small turf plots or ex ist ing sport ar eas.
Key words: Poa pratensis, Poa supina, Deschampsia cespitosa, Lolium perenne, Fes tu ca rubra, root ing depth,
shoot den sity, vi sual merit
INTRODUCTION
The gen eral term ‘turf qual ity’ in volves many char ac ters. In ad di tion to traits af fect ing the aes thetic value of turf, also ‘func tional’ traits should be in cluded, es pe cially for sport or sod pro duc tion pur poses. One of ‘func tional’ traits of grasses is sod strength which is very im por tant for sod pro -duc tion, due to its im por tance for han dling with sod pieces dur ing cut ting, trans por ta tion and in stal la tion (Heckman et al. 2001). Sod strength is also im por tant for foot ball or other sports ar eas where di rect and strong im pact of play ers could sig nif i cantly af fect turf in teg rity. Here, it is claimed that if greater is the force re quired to tear the turf apart, the more able turf is to re -sist phys i cal dam age.
Many meth ods have been de vel oped so far to de ter mine turf strength or hard ness and all of them mea sure the phys i cal force needed to tear the turf (Beard, 1976; Sorochan et al. 1999 af ter Stier et al. 2000; Hurley and Skogley 1975; Burns and Futral, 1980; Haake, 1991; McNitt et al. 1997; Communicated by Andrzej Anio³
P L A N T B R E E D I N G A N D S E E D S C I E N C E
Volume 57 2008
Erusha et al. 1999). A de vice for sod strength test ing has been de scribed. This op er ated with a hy drau lic le ver pow ered by bat tery and re quire rather large sod pieces of ca. 1.5 × 0.5 m (Sorochan et al. 1999 af ter Stier et. al 2000). It is suit able while test ing for sod pro duc tion pur poses, but if some -one wants to mea sure turf sod strenght on ex ist ing foot ball or ath letic field or on ex per i men tal plots of 1 or 2 m2 such test ing unit is not suit able. There -fore, we de vel oped a sim ple, fast and easy eval u a tion method, pow ered only by hu man hand force for tear ing of small sod pieces (Proñczuk, 1993).
For many cool sea son turf grass spe cies rec om mended for sport ar eas, smooth stalked meadow grass (Poa pratensis L.) is one of the most pop u lar spe cies, due to its abil ity to form sod, even un der un fa vour able con di tions. It is a highly vari able spe cies, with cultivars which dif fer in color, tex ture, den sity, vigor, dis ease re sis tance and tol er ance to close mow ing. Blue grass is best adapted to well-drained, moist, fer tile soils with a pH be tween 6.0 and 7.0 (Wedin and Huff, 1996; Duble, 2004).
Other spe cies, widely used in turf pro duc tion are: pe ren nial ryegrass (Lolium perenne L.), red fes cue (Fes tu ca rubra L.) and tall fes cue (Fes tu ca arundinacea Schreb.). Ex am ples of spe cies that are not nor mally in cluded
in sod strength in ves ti ga tion are: pros trate meadow grass (Poa supina
Schrad.) and tufted hair grass (Deschampsia cespitosa L. P. Beauv.). The abil ity to pro duce rhi zomes or sto lons in the above spe cies could be ranked from tufted hair grass (no rhi zomes or sto lons) through pe ren nial ryegrass and tall fes cue (rhi zomes ab sent or only short) to red fes cue and smooth
stalked meadow grass (creep ing by sto lons or rhi zomes) and pros trate
meadow grass (veg e ta tive spread ing only by above ground sto lons) (Davy,
1980; Edmondson,1980; Markgraff-Dannenberg, 1980; Gib son and
Newman 2001).
The aim of the work was to eval u ate sod strength, root ing depth, sward den sity and vi sual merit for a se lec tion of com mon smooth stalked meadow grass cultivars in com par i son to cultivars of other turf grass spe cies and to de scribe re la tion ships be tween the traits.
MATERIALS AND METHODS
Ma te ri als used in ex per i ment were six com mon Eu ro pean turf cultivars (smooth stalked meadow grass: Conni, Lim ou sine, Balin, Baronie, pros trate
meadow grass Supranova, tall fes cue Asterix), three Pol ish cultivars
(smooth stalked meadow grass Bila, pe ren nial ryegrass Stadion and slen der creep ing red fes cue Nimba) and one breed ing strain (tufted hair grass Brok) rec og nized for turf po ten tial by Proñczuk (1994). Seed was sown on plots of
1m2 in April of 2001. Sow ing rates ranged from 10 g × m2 for tufted hair
-grass, smooth stalked and pros trate meadow grass cultivars, 15 g × m2 for
ar ranged in ran dom ized block de sign with three rep li ca tions, on silt sandy soil (pH 6.7) in cen tral Po land (Radzików, 52°12’N, 20°37’E). Af ter sow ing (in April 2001) plots were cov ered with ca. 0.5 cm of peat and white pro -pyl ene no-wo ven cover and wa tered daily un til seed lings emerged. Plots were fur ther wa tered dur ing drought pe ri ods, and few cuts were done us ing a ro tary mower with clip pings col lected. Her bi cide treat ment (fluroxypyr) against broad-leaf weeds was ap plied once be fore the sec ond cut. Dur ing three years (2002 – 2004) plots were cut 22 – 25 times per year at 3 cm height and fer til ized with: 180 kg of N per ha (5 doses per year), 67.2 kg of K per ha (2 doses) and 26.2 kg of P per ha (1 dose). No spe cial man age ment prac tices (i.e. aer a tion, roll ing, top dress ing etc.) were ap plied dur ing the eval u a tion pe riod.
Ob ser va tions and mea sure ments started in spring of 2002 and lasted for three con sec u tive years. Each year in the mid dle of spring, sum mer and au -tumn sod strength (SS), root ing depth (RD), shoot den sity (SD) and vi sual merit (VM) were de ter mined. VM and SD were eval u ated on a 19 scale rat -ing: 9 - ideal turf or of max i mum den sity and 1 - the poor est or dead. A rat ing of 5 was gen er ally con sid ered as the least ac cept able turf (Proñczuk, 1993).
SS and RD were de ter mined ac cord ing to the fol low ing meth od ol ogy. Turf cores (3 per plot) of 5.3 cm in di am e ter and 15 cm in depth were ob -tained by in sert ing a soil corer (metal tube), ver ti cally into soil. Root ing depth was mea sured as a length of the whole root sys tem with soil. No spe -cial treat ments were ap plied to sep a rate roots from soil. Fur ther to this, the up per part of turf core of 3 cm thick ness was cut off by knife and sod
Ta ble 1 Cli ma tic con di tions dur ing ex per i ment (ac cord ing to read ings from au to matic meteo sta tion
sit u ated at Radzików)
Year/Month
I II III IV V VI VII VIII IX X XI XII S Precipitation [mm] 2002 34.1 42.4 25.9 21.2 33.4 57.6 19.1 39.5 0.0 34.0 0.0 8.0 315.2 2003 8.2 0.0 6.2 7.5 21.0 25.4 61.9 35.3 4.3 14.8 15.4 27.1 227.1 2004 0.0 10.8 0.0 66.6 67.0 56.4 102.5 54.1 7.8 2.2 39.5 9.7 416.6 Normal (1955-2005) 23.9 21.7 24.5 34.8 52.7 66.6 77.3 56.6 41.8 31.4 35.5 32.4 499.1 Temperature [°C] Mean 2002 -0.1 4.5 5.3 10.2 19.4 19.4 23.0 22.8 13.7 7.2 4.1 -6.6 10.2 2003 -2.9 -4.9 1.9 7.3 15.7 18.0 20.2 18.7 13.8 15.4 4.9 0.9 9.1 2004 -5.1 0.0 3.5 8.7 12.0 15.8 17.9 19.0 13.5 10.0 3.7 1.8 8.4 Normal (1955-2005) -2.3 -1.4 2.3 8.1 14.0 17.1 18.7 18.1 13.4 8.8 3.2 -0.6 8.3
strength (SS) was eval u ated as the re sis tance of sod rings to tear ing in hands. The high est SS value was given 9 when it was not pos si ble to tear the sod, 7 – rel a tively high power nec es sary to tear sod ring, 5 – easy tear ing (light power), 3 – tear ing with out power (loose sod) and the low est SS value was 1 – no sod, no green cover.
Re sults were an a lyzed with SAS® sta tis ti cal pack age: three-way ANOVA was per formed and LSD val ues were cal cu lated us ing Fisher test with prob a -bil ity of 95% (SAS In sti tute, 2004 a, b).
Mean air tem per a ture and pre cip i ta tion dur ing the test ing pe riod (2002 – 2004) are shown in Ta ble 1.
RESULTS
Sig nif i cant dif fer ences be tween tested cultivars were noted for all traits (Ta ble 2). The high est vari a tion be tween tested cultivars was noted for SS, SD and the low est for VM and RD. Sig nif i cant in ter ac tions be tween all treat ments (years, sea sons and cultivars) were noted for SD and VM. Vari a tion of RD was mostly af fected by dif fer ent cli ma tic con di tions dur ing test -ing pe riod (Y × S).
Sod strength (SS) of smooth stalked meadow grass cultivars, ex clud ing Balin, was gen er ally higher than for other cultivars (Ta ble 3). It ranged from ‘un tear able’ (un break able) sod (Conni, Bila) to very loose, quite easy to tear (nonrhi zo ma tous cultivars)– Brok, Asterix and Stadion). Mi nor dif fer -ences be tween tested cultivars were ob served for RD, with very shal low root sys tem ob served for Supranova. The high est val ues of SD were noted for smooth stalked meadow grass Conni and Lim ou sine and for cultivars of
other spe cies: Supranova, Nimba, Asterix, Brok. Gen er ally, SD of sm ooth
stalked meadow grass cultivars was of me dium value (mean 6.7) and close Ta ble 2 Anal y sis of vari ance with mean squares and sig nif i cance of vari a tion com po nents
Variable Years (Y) Seasons(S) Cultivars(C) Y × S Y × C S × C Y×S×C Error mean square Turf strenght [1-9] 4.16 ** 4.29 ** 101.56 *** 0.18 ns 2.99 *** 2.10 *** 1.32 ** 0.73 Rooting depth [cm] 64.19 *** 79.06 *** 17.88 ***
3 el ba T )e c n a ne t ni a m f o sr ae y-3 m or f e g ar e v a( sr a vi tl uc de ts et f o sti ar t f o se ul a v n ae M si ce ps ,s u ne G yt ei ra v f o e ma N ] 9-1[ S S ] mc [ D R ] 9-1[ D S ] 9-1[ M V P S U S U A na e M P S U S U A na e M P S U S U A na e M P S U S U A na e M si s ne t ar p a o P * I N N O C 8 8. 8 8. 8 9. 8 a 8. 1 1 2. 8 7. 2 1 8. 0 1 ba 9. 8 0. 7 9. 7 9. 7 a 9. 7 8. 7 6. 7 3. 7 a 6. si s ne t ar p a o P A LI B 8 3. 8 4. 7 9. 8 b 2. 9 8. 9 6. 1 1 9. 0 1 ba 4. 6 7. 6 6. 5 4. 6 c 2. 6 7. 6 6. 5 3. 6 c 2. si s ne t ar p a o P E NI S U O MI L 8 1. 8 3. 7 8. 8 c b 1. 0 1 7. 0 1 8. 2 1 1. 1 1 ba 2. 8 1. 7 2. 8 0. 7 a 8. 8 0. 6 2. 6 7. 7 ba 0. si s ne t ar p a o P EI N O R A B 7 8. 7 7. 7 4. 7 dc 6. 1 1 1. 9 7. 2 1 4. 1 1 ba 0. 7 0. 5 9. 6 2. 6 b 4. 6 6. 5 0. 5 6. 5 c 7. ar b ur ac ut se F A B MI N 7 3. 8 0. 7 6. 7 dc 6. 0 1 5. 0 1 2. 3 1 7. 1 1 a 4. 7 9. 7 8. 7 9. 7 a 9. 7 2. 7 3. 7 6. 7 ba 4. a ni p us a o P A V O N A R P U S 7 7. 7 1. 7 4. 7 d 4. 8 3. 9 1. 8 9. 8 c 8. 7 9. 8 0. 8 0. 8 a 0. 8 0. 6 3. 6 4. 6 ba 9. si s ne t ar p a o P NI L A B 6 8. 4 9. 4 6. 5 e 4. 0 1 4. 8 8. 0 1 7. 0 1 c b 0. 4 9. 3 1. 3 6. 3 c 9. 4 1. 3 1. 3 9. 3 d 7. e n ne re p m uil o L N OI D A T S 5 1. 3 8. 4 6. 4 f 5. 0 1 7. 1 1 1. 2 1 1. 1 1 ba 3. 7 0. 6 3. 6 0. 6 b 4. 7 1. 6 6. 6 9. 6 ba 9. ae c a ni d n ur a ac ut se F XI R E T S A 4 4. 4 3. 4 6. 4 f 4. 0 1 3. 1 1 1. 2 1 4. 1 1 ba 3. 6 8. 8 1. 8 6. 7 a 8. 6 3. 5 7. 6 2. 6 c 1. as oti ps ec ai s p m a hc se D N K O R B 4 3. 3 6. 4 4. 4 f 1. 0 1 9. 1 1 4. 0 1 6. 1 1 ba 0. 7 6. 7 4. 7 4. 7 a 5. 7 2. 5 7. 5 7. 6 c 2. na e m l at o T 6 9. 6 5. 6 5. 6 6. 0 1 4. 0 1 0. 1 1 7. 0 1 7. 7 2. 6 8. 6 9. 7 0. 6 9. 6 0. 6 2. 6 4. ) % 5 9 < P( D S L 0 9. 1 0. 0 9. 0 5 5. n s. 1 6. 1 7. 1 4 4. 0 9. 0 8. 0 8. 0 1 5. 1 0. 0 9. 0 9. 0 9 5. :s n oi t a na l p x E e ul a v ht g ne rt s d os g n i sa er ce d ot e u d de k na r sr a vit l uc - * , yti s ne d t o o hs – D S , ti re m l a u s i v – M V , ht pe d g n it o or – D R , ht g ne rt s d os – S S n m u t ua – U A , re m m us – U S , g ni r ps – P S t n e re ffi d yll a c i t si t at s t o n er a sr e tt el e ma s hti w s na e m – f …a
to pe ren nial ryegrass (6.4). VM was high for Conni and Lim ou sine, as well as for a few other cultivars: Nimba, Supranova and Stadion. Mean value of
a) sod strength (SS) b) root ing depth (RD)
3 4 5 6 7 8 9
spring summer autumn
1 -9 sc al e 3 4 5 6 7 8 9
spring summer autumn
1 -9 sc a le 8 9 10 11 12 13 14
spring summer autumn
cm 3 4 5 6 7 8 9
spring summer autumn
1
-9
sc
a
le
c) shoot den sity (SD) d) vi sual merit (VM)
Solid lines and shaded sym bols – smooth stalked meadowgrass cultivars. Dashed lines and empty sym bols – cultivars from other species. Sym bols used for cultivars:
VM for smooth stalked meadow grass cultivars (6.2) was com pa ra ble to tufted hair grass and tall fes cue (6.2 and 6.1, re spec tively).
For some cultivars sea sonal vari a tion of SS was ob served (Fig. 1a). SS de cline from spring to sum mer and in crease from sum mer to au tumn was ob served for Brok, Stadion and Supranova. Sum mer in crease of SS was noted only for red fes cue Nimba. Rhi zo ma tous cultivars had high SS val ues, ex clud ing Balin where a rapid de crease of SS was ob served from spring to au tumn. In con trast to the above, all non-rhi zo ma tous cultivars showed low SS val ues dur ing all sea sons.
Root ing depth (RD) of ma jor ity of tested cultivars de creased dur ing sum mer and in creased in au tumn (Fig. 1b). For tall fes cue Asterix a con stant in -crease was ob served from spring to au tumn. Only for Supranova and Brok slightly higher val ues were ob served dur ing sum mer.
Sea sonal vari a tion of shoot den sity (SD) was ob served for Lim ou sine, Baronie and Balin (Fig. 1c). De crease in SD val ues across sea sons was ob -served for Bila and Stadion while in creases where noted for Asterix. For the other cultivars tested no sig nif i cant vari a tion among sea sons was ob served.
Vi sual merit (VM) in creased from spring to au tumn for Nimba and de -creased for Conni, Bila, Supranova and Brok (Fig. 1d). Sum mer de crease in VM was ob served for Lim ou sine, Baronie, Balin, Stadion and Asterix.
Ta ble 4 Cor re la tion co ef fi cients cal cu lated be tween sod strength (SS) and other traits eval u ated
Genus. species. variety RD SD VM
Festuca arundinacea - ASTERIX -0.10 0.30 0.35
Lolium perenne - STADION -0.25 0.25 0.17
Deschampsia cespitosa - BROK -0.32 0.02 0.31
Non-rhizomatous species (n=3) -0.20 0.12 0.28 **
Festuca rubra - NIMBA 0.09 0.35 -0.17
Poa supina - SUPRANOVA 0.20 -0.09 0.06
Poa pratensis - CONNI -0.06 0.51 ** 0.50 **
Poa pratensis - BALIN 0.19 0.39 ** 0.23
Poa pratensis - BARONIE 0.06 0.39 ** 0.39 **
Poa pratensis - BILA 0.08 0.47 ** 0.47 **
Poa pratensis - LIMOUSINE -0.36 0.064 0.062
Rhizomatous species (n=7) 0.11 0.58 *** 0.54 ***
Ex pla na tion: *** - sig nif i cance at level 0.001, ** - sig nif i cance at level 0.05
SS was sig nif i cantly re lated to SD for smooth stalked meadow grass cultivars, ex clud ing Lim ou sine (Ta ble 4). When cal cu lated for groups of cultivars (rhi zo ma tous and non rhi zo ma tous) sig nif i cant and pos i tive re la
-tion ships were noted be tween SS and VM. How ever, only for Conni,
Baronie and Bila sig nif i cant cor re la tions were found when cal cu lated sep a -rately for each cultivar.
DISCUSSION
Good sod strength for most of the smooth stalked meadow grass cultivars tested in our ex per i ment was no sur prise. It was un doubt edly due to the rhi -zomes, ap pear ing from the axils of leaves, the base of which may be above or just be low the sur face of the soil (Hurley and Skogley, 1975). More over, some shoots of smooth stalked meadow grass turn down ward and de velop into rhi zomes be neath the soil. Most rhi zomes, how ever, de velop be neath the soil sur face as branch shoots of other rhi zomes (Duble, 2004). Roots of smooth stalked meadow grass de velop from the un der ground nodes of rhi -zomes and from the basal nodes of above ground shoots. Roots also de velop at the ter mi nal nodes of rhi zomes that emerge above the soil as shoots. In es tab lished stands, the mix ture of roots and rhi zomes con cen trated in the up -per 6-8 cm of soil and form an ex tremely dense, re sis tant sod (DaCosta et al. 2004; Stew art et al. 2004). An ex cep tion to the high ranked smooth stalked meadow grass cultivars was Balin, which in fact is a for age va ri ety, how ever com monly used in turf mix tures due to its early spring green ness and good seed pro duc tion (Proñczuk, per sonal com mu ni ca tion). All ‘turf qual ity’ re -lated traits of Balin (SD and VM) were of the low est val ues.
Low sod strength val ues noted for non-rhi zo ma tous cultivars were mostly
due to dif fer ent sod struc ture. Plants from Stadion, Asterix and Brok
cultivars pro duce tus socks. Gen er ally, pe ren nial ryegrass and tall fes cue rarely pro duce rhi zomes and pros trate meadow grass is known to pro duce only above-ground sto lons (Falkowski, 1982). There fore, sod made from above spe cies con sists rather of sep a rate plants more or less loosely con -nected by roots rather than by rhi zomes.
Sod strength is one of many traits ex ten sively tested dur ing Na tional Turf Eval u a tion Pro gram (NTEP) in USA. Re sults from above pro gram were sim i lar to ours. Conni, Lim ou sine and Baronie ex hib ited high sod strength val ues but dif fer ences be tween them were not al ways sig nif i cant (NTEP, 1995, 2000, 2005). No dif fer ences be tween sod strength of smooth stalked meadow grass cultivars were re ported by Hurley and Skogley (1975). In for -ma tion is lim ited con cern ing sod strength of tufted hair grass, pros trate meadow grass or tall fes cue. As it has been re ported by Hurley and Skogley (1975) con cern ing red fes cues this spe cies it has not been widely used in sod
pro duc tion be cause of poor sod qual ity. Such state ment was not con firmed by our re sults con cern ing red fes cue Nimba (SS = 7.6).
CONCLUSIONS
It is pos si ble to rank tested cultivars due to sod strength val ues from strong sod of rhi zo ma tous spe cies to loose sod of non-rhi zo ma tous spe cies. Cultivars can dif fer sig nif i cantly.
The com mon use of pe ren nial ryegrass and tall fes cue on foot ball pitches was not sup ported by our re sults con sid er ing sod strength val ues.
Sim ple and fast method of test ing the over all sod strength can be rec -om mended.
The lack of sig nif i cant re la tion beetween sod strengt and root ing
deepth was found and for some cultivars re la tion be tween sod
strength and turf qual ity (sod den sity and vi sual merit) was noted. REFERENCES
Beard J.B. 1976. Suc cess ful turfgrass sod ding prac tices – part II. Cal i for nia Turfgrass Cul ture, vol.26, no. 4: 25 – 26.
Burns R.E., Futral G.J. 1980. Mea sur ing sod strength with an Instron Uni ver sal Test ing In stru ment. Agron -omy Journ. 72: 571 – 573.
DaCosta M., Wang Z., Huang B. 2004. Phys i o log i cal ad ap ta tion of Ken tucky blue grass to lo cal ized soil dry ing. Crop Sci. 44: 1307 – 1314.
Davy A. J. 1980. Deschampsia caespitosa (L.) Beauv. Bi o log i cal Flora of the Brit ish Isles, no.149. Jour nal of Ecol ogy, 68: 1075 – 1096.
Duble R. 2004. Kentycky blue grass http://plantanswers.tamu.edu/turf/publications/bluegrass.html Edmonson J. R. 1980. Poa L. In: Tutin T.G., Hey wood V.H., Burges N.A., Moore D.M., Val en tine D.H.,
Walters S.M., Webb D.A. (eds.) Flora Europea, vol 5. Cam bridge Uni ver sity Press, 159 – 167. Erusha K.S., Shearman R.C., Wit L.A. 1999. A de vice to mea sure turfgrass load bear ing ca pac ity un der
field con di tions. Crop Sci. 39: 1516 – 1517.
Falkowski M. 1982. Trawy polskie, PWRiL, Warszawa, pp. 565.
Gib son D. J., Newman J.A. 2001. Fes tu ca arundinacea Schreber (F.elatior L. ssp. arundinacea (Schreber) Hackel). Bi o log i cal Flora of Brit ish Isles, no. 217. Jour nal of Ecol ogy, 89: 304 – 324.
Haake S.J. 1991. The im pact of golf balls on nat u ral turf. I. Ap pa ra tus and test meth ods. Jour nal of the Sports Turf Re search In sti tute, vol. 67: 120 – 127.
Heckman N. L., Horst G. L., Gaussoin R. E., Frank W. K. 2001. Stor age and han dling char ac ter is tics of trinexapac-ethyl treated Smooth stalked meadow grass sod. HortScience 36(6): 1127 – 1130. Hurley R.H., Skogley C.R. 1975. Eval u a tion of Ken tucky blue grass and red fes cue cultivars for sod pro duc
-tion. Agron omy Journ. 67; 79 – 82.
MargrafDannenberg I. 1980. Fes tu ca L. in Tutin T.G., Hey wood V.H., Burges N.A., Moore D.M., Val en -tine D.H., Walters S.M., Webb D.A. (eds.) Flora Europea, vol 5. Cam bridge Uni ver sity Press, 125 – 153.
McNitt A.S., Middour R.O., Waddington D.V. 1997. De vel op ment and eval u a tion of method to mea sure trac tion on turfgrass. Jour nal of Test ing and Eval u a tion, vol. 25, (1): 1-9.
NTEP, 1995. Sod strength rat ings of Ken tucky blue grass cultivars grown un der high main te nance.1991 – 1995 data. http://www.ntep.org/data/kb90h/kb90h_96-11f/kb90_96-11f.pdf
NTEP, 2000. Sod strength rat ings of Ken tucky blue grass cultivars grown un der me dium/high in -put.1996-200 data. http://www.ntep.org/data/kb95h/kb95h_01-12f/kb95h01ft49.txt
NTEP, 2005. Sod stretch ing mea sure ments of Ken tucky blue grass cultivars. 2001-2005 data. http://www.ntep.org/data/kb00/kb00_06-11f/kb0006ft59.txt
Proñczuk S. 1993. Sys tem oceny traw gazonowych. Biul. IHAR, 186: 127 – 132.
Proñczuk S. 1994. Deschampsia cespitosa L. – pro posal for lawn in shade con di tions. In: Rognli O.A., Solberg E., Schjelderup I. (eds.). Breed ing fooder crops for mar ginal con di tions. Procc. of the 18th EUCARPIA Fod der Crops Sec tion Meet ing, Loen, Nor way, 25 – 28 Au gust 1993, Kluwer Acad. Publ. The Neth er lands: 8.
SAS In sti tute Inc. 2004 a. SAS 9.1 Com pan ion for Win dows. Cary, NC, USA, SAS Pub lish ing, SAS In sti -tute Inc.
SAS In sti tute Inc. 2004 b. SAS/STAT 9.1 User’s Guide. Cary, NC, USA, SAS Pub lish ing, SAS In sti tute Inc.
Stier J., Pearson S., Blair R. 2000. Ef fect of Primo on sod ten sile strength. www.hort.wisc.edu/uwturf/pdf/primsod.pdf
Stew art J. R., Kjelgren R., John son P. G., Kuhns M., R. 2004. Soilwa teruse char ac ter is tics of pre ci sionir -ri gated buffalograss and smooth stalked meadow grass. Ap plied Turfgrass Sci ence. Plant Man age ment Net work,
http://www.plantmanagementnetwork.org/ pub/ats/re search/2004/wa ter
Wedin W. F., Huff D.R. 1996. Bluegrasses. In: Moser L.E., Bux ton D.R., Casler M.D. (eds.) Cool-Sea son For age Grasses. ASA, CSSA, SSSA, Mad i son, USA, Agron omy Mono graph no.34: 665 – 690.
