View of The influence of soil water potential and soil temperature on the seedling emergence of wheat and barley

MaataloustieteellinenAikakauskirja Vol. 58: 185—190, 1986

The influence of soil water potential and soil temperature on the

seedling

MARKKU TENHOVUORI

Helsinki University

of

of

and Water Resources Engineering SF-02150ESPOO, Finland

Abstract. Thetime for⁵⁰Vo^emergenceof wheat and barley increases linearly^with de- creasingmatric potential. This increase actually begins at matricpressuresabove pF2.7.The riseintemperaturemakesemergencefaster within the^rangeof minimumtemperature(3.l°C for wheat and I.9°C for barley) and thetemperaturewhere growth begins to slow down (about 31°C for wheat and 27°C for barley). The optimumrangefor50Voemergencewasobtained atamatricpressure rangeof pF 1.3—2.7^or—5.0 0.20m (water column) ata tempera- tureof 10°C, which quite well corresponds to the situation inFinland during the emergence periodinspring.Aclear increasecanbe observedinthe required heat sumfor wheat and bar- leywhen the soil water potential reaches acritical point whichwaspF2.8 or—6.3m for^wheat and pF2.7^or—5.0m for barley. The total^emergenceas a function of matric potential for wheat and barleywas determined over aperiod of30days at 10°C.In thewet side,pF ^1,0 canbe considereda limit,_{the total}emergencedecreasingwith lower values.Inthe dryside, acorrespondingdecreasecanbe noticedintotalemergenceat pFabove3.0.The water uptake byseeds speededupwith increasingtemperaturefrom 10to25°C.Radicles of wheat and barley began toappearwhen the water uptake by^theseedwasapproximately50—60^%of the initial weightof the seed. The initial water uptake caused by the moistening of the pericarp due to capillaritywasabout 3Vo for wheat and 5Vo for barley at^asoil water potential of pF 1.2.

Index words: seedling ^emergence,soil water potential, soiltemperature

Introduction

The two major factors affecting seedling emergencearethe moisture and thetempera- tureof the seed bed. InFinland, temperature is the minimum factor for seedling emergence of cereals. Inversely, in arid and semi-arid

regions the factor restricting emergence is generally the low moisture content of soil.

Because of the short growingseasonin Fin- land, early sowing in spring and fast emer- genceareveryimportantaspectsin obtaining a good yield.

Thetermsoil matric potential is preferable

JOURNAL OFAGRICULTURAL SCIENCEIN FINLAND

tosoil moisture whenwateruptake by plants isdiscussed,because indifferentsoils the the water uptake by plants is ^{dependent on the}

amountof energy neededto detachwater for theuseof plants. In different soils the plants haveto exertasimilar suctional power toward water despite the fact ^{that the} water content of clay for example is many times higher^com- paredto that of sand.

Thepresent paper isdealing with the effect of soil matric potential and soiltemperature onthe seedling emergence of wheat and bar- ley.

Material and methods

The grain size of the sand used in theex- perimentsas seed bed was0.1 —0.6 mm. The waterretentioncurveof the sand is presented in Figure 1.

Four methodswereusedtodetermine the points of thewaterretention_curvefor^{the soil} used_asseed bed. The matric potential values

—l5O 10 m (water column) were ob- tained osmotically using asemi-permeable cel- luloseacetatemembrane, pore size 5^nm,im- mersed in polyethylene glycol solution (PEG,

Table 1. The correspondence ofPEG solution and ma- tric potential.

PEG (20 000)g/100gsolution Matric potential m

7.2 ^- 10

- 30 14.0

- 50 17.4

- 70 20.0

-100 22.9

-130 25.4

-150 27.0

molecular weight about 20.000). Table 1 shows the correspondence of the PEG solu- tion and the matric potential. The points —1

m and —5min thewaterretentioncurve were determined by a method developed in the course of the experiments. The sandwas put into a small closed plastic vessel and moist- enedto saturation.Thereafter, pressurewas appliedtothe sandto removeanyextra water through the holes under the vessel. The points mentioned above_werechecked usingawater retention curve determination device. The fourth method was used to determine the points —0.25 0 m in the water retention curve. The arrangement was based ^{on the} capillaryrise of sand. The vessel ^containing sand was laid in another vessel containing water. This allowed the soiltotake up water, and matric potential values of —0.25 0 m were determined according to the different heights of sand columns. This method didnot allowtodetermine matric pressure values be- low—0.25m,because the capillary rise of the sand _{was no} higher.

The seedling emergence experiments were made with spring wheat (Tähti) and barley (Pokko). The investigationswerecarried out using three different methods. The first meth- od _was used _toregulate themoisture of the sand osmotically in the cellulose acetate membrane which allowed capillary rise of water in the funnel where the seeds were im- mersed into the depth of about 1.5cm. Each funnel contained 20 seeds. By the second method the effect of low soil moisture on emergence _was investigated using the first method described above for determinationof

Fig. I. Water retention curvefor the sand used^asseed bed in the experiments.

thewaterretention curve. The matricpoten- tialranged from —IOOto—lO m and 10 seeds wereimmersedintothe depth of about 1.5cm.

The third method which_was the same as the one described in connection with the water retention curvedetermination by thefourth methodwas used to determinethe effect^of high soil moistureonemergence. Observations wererecorded daily. Germination_wasdefined as a seedling of 0.5cmemerging from the soil surface. After the experiments the moisture of the seed bed _was measured.

In addition to theabove, water uptake by seeds was studied by immersing 5 seeds of wheat and barley in the soil at a depth of about 1.5cmfor differentperiods of timeat pF 1.2. Themoisture ^{was maintained}at the desired level bymeans of the fourth method as wasdone in the determination of the water retention curve. The seeds were thereafter dried and weighed to determine theamount ofwaterimbibed. The seedswerereimmersed in the seed bed and the experimentcontinued.

Also the number and length ofradicles ^aswell as the length of shoot were measured.

The experimentsweremade_atthe tempera- ture of 10, ^15, 20 and 25°C.

The minimum temperatures for germina- tion were determinedata soil water content of 10—30 ^% (vol. ^%)or—0.20 0.10 m.

The reciprocal of time for 50 ^% emergence wascalculated andaregression linewas drawn (Feddes 1972). The minimumtemperatures obtainedwere3.l°C for wheat and I.9°C for barley. The corresponding heat sums(slopes of the lines)were70 degree days for wheat and 73 degree days for barley.

Results and discussion

Figure 2 shows the effect of matric poten- tial andtemperature on 50 ^% emergence for wheat and barley, the time for emergence in- creasing linearly with decreasing matric pres- surefrom less than —0.15 0.10. Infact, the actual increase in the emergence time be- gins at matric potential approximately below

—5 m. A similar linear increase has beenno- ticed e.g. by Aura (1975) for 75 ^% emer- gence of sugar beetin fine sand soilatamatric pressure range of about —l3O 15 m. The gradual decrease in time for emergence with decreasing matric pressure has been reported by several investigators. Figure 2 shows the effectoftemperature ontime for emergence, the increase intemperature accelerating emer- gence. This temperature-related acceleration is a common feature of growth at a range from minimum temperature to the point where growth begins toslow down. For corn the growth of radicle and shoot begantoslow downattemperatures exceeding 32°C inaver- age (Blacklow 1972). The maximum tem- perature where^growthstops is30 43°C for wheat and30—40°C for barley. For wheat the optimum temperature is 15—31°C and for barley 19—27°C(Mayer ^& Poljakoff-May- ber 1975). The emergence of barley is in average faster than that of wheat(Fig. 2). The equations (matric potentials considered posi- tive) presented in Figure 2 are as follows:

WHEAT ⁼ 11,22 ^{+ 0,27 (r = 0,945) (1)}

tJo

150 ⁼ 4,45 ⁺0,11 ^{i(r = 0,988) (3)} BARLEY

tjQ

tJJ

tjjJ

Fig. 2. 50 ^%emergence ofwheat and barleyasthe func- tion of matric potential and temperature.

Figure 3 shows the dependence of soilwater potential on the 50 ^% emergence rate for wheat and barley at a temperature of 10°C which produced the most reliable results.

Feddes (1971) observed slowing down in the emergencerate at pF values above2.7 which canalso be consideredalimittothat of wheat and barley. In the^wet side, however, ^Feddes reported of the limit for slowing down in the emergencerate of different vegetables tobe about pF 2.0or —1 m, whenthiswas about pF 1,^{3 or}—0.20 m in thepresent study. Ac- cordingtoFigure 3,the optimum emergence rate is achieved at about pF 1.3—2.7 or

—5.0 0.20 m. It is, however, possible that although the waterpotential of —0.20 m still produces fast emergence, it may be too highortoo wetfor _anormal development of seedlings. Feddes observed the pF range 1.0—1.5toproduce toopoorseedlings despite otherwise normal germination. These experi- mentswere,^{however, made}onradish and the results differed also in other respects from those of the cereals mentioned above, spe- cifically in thewet side.

In Southern Finland the average tempera- ture in the latter half of May when theemer- gence ofspring cereals is taking place is about

10°C. Thus Figure 3 gives an idea of the de-

pendence of the emergencerate of cerealson the soil water tension in Southern Finland when sowing is carriedoutnormallyin^about mid-May. During the emergence period, lack ofwater doesnotusually restrict emergence.

Thus the optimumareain Figure 3canbecon- sidered normal in regard to onset of _emer- gence. Itis, however,possible that the soil_sur- face where the emergence takes placecan in clay, silt andpeat soils become too dry as a result of evaporation, emergence slowing down because of lack of water.

The effect of matric pressure on the heat sumrequired for 50 ^% emergence ispresented in Figure 4. The heatsum wascalculated using the following equation:

F=(T T_{min )}t (7)

where

T ⁼ averagetemperature °C T_min ⁼ minimum temperature for

emergence °C t ⁼ time d

F ⁼ heat sum as degree days °C d Figure 4 shows a clear increase in there- quired heat sum for wheat and barley when the matric pressure reaches a critical point which ^{was pF 2.8 or} —6.3 m for wheat and pF 2.7 or—5.0 m for barley which wellcor- respond to the critical value pF 2.7 obtained by Feddes (1971) for four vegetable crops.

Fig. 3. Effect of soil water potential^onthe rate of^50% emergence of wheat and barley at 10°C.

Fig. 4. Developmentof heat sumfor^{wheat and}barley as the function of matric potential for 50 ^% emergence.

It isnotpossibleon the basis of the experi- ments to determine the lowest and highest matric pressures whereno moreemergenceoc- curs. But withina certain period of time the

emergencepercentage for totalemergence can be determined. Figure 5 shows the dependence of total emergence during 30 days on the matric potential of wheat and barleyatatem- perature of 10°C. In bothcases, one point clearly differing from the other observations has been excluded. For barley the curve has been drawn directly through theobservations, whereas for wheat the curve is partly drawn approximately. The results donotdiffer much from those obtained by Aura (1975) with sugarbeet, although the experimentsarenot entirely comparable.

Figure 6 shows the imbibition by wheat and barley atthetemperatures of 10,20 and 25°C atasoilwaterpotential of about pF 1.2. Com- pared tothe imbibition bycorn(Seneca Gol- den)at 24°C, forinstance, ^thecurveis fairly similartothat for wheatat25°C with the dif- ference that therise ofthe imbibition ^curve of _corn is to start with slightly steeper

(Blacklow 1972). The imbibition results for wheat and barley donot showas clearly the point where the exponential phase becomes linear as presented by Blacklow for corn (UH 108) at 16°C and 24°C. Thereare con- siderable differences between plants and varie- ties. The matric potential of the seed bed greatly affects also the imbibition by different seeds (Hadas 1970). The course of the imbi- bition by wheat in thepresent studywas sim- ilar to that described by Chino (1972) for wheat during 30 hours. Chino reported ofan imbibition slightly faster in average, but this can be ascribed to an initially greater water uptake. The initialwateruptake, definedac- cordingtoBecker (1960) asthewateruptake caused by the moistening of the pericarp be- cause of capillarity occurring during 1 min, wasin thepresentstudy about 3 ^% for wheat and 5 ^% for barley. Blacklow reported an

initialwater uptake of 6 ^% by corn.

In conclusion, in Finnish conditions it is essential for efficient seedling emergence of

Fig. 5. Total^emergencefor wheat and barley occurring during30daysas thefunction ofmatric poten- tial at 10°C.

Fig. 6. The imbibition of wheat and barley^asthe func- tion of time indifferent temperatures.

wheatand barley in spring that the soil ma- tric potential is withinthe optimum range, i.e.

about pF 1.3 2.7 or—5.0 0.20 m. It is,^however, possible that pF ^1,3is still slightly too wet for normal seedling tooccur despite otherwise fast germination. Already a small rise in soil temperature greatly affects the rateof emergence inconditionslike those pre- vailing in Finland. With efficient drainage it

is possibletoaffect the soiltemperature in the emergenceperiod, thereby shortening for in- stancethe^ripening ofwheat and barley by 10 days. Which is ofgreatimportance in Finland because of the short growing season. Also by meansof irrigation seedling emergence could be promoted in Finland during ^some years mainly in silt,^{clay and}peat soils because of the possible drying of^top soil.

References

Aura, E. 1975.Effects of soil moistureonthe germina- tion and emergenceof sugarbeet (Beta vulgaris L.).

J. Scient. Agric. Soc. Finl. 47. 70^p.

Blacklow, W.M. 1972.Mathematical description of the influence oftemperatureand seed qualityon imbibi- tion by seeds ofcorn (Zea maysL.). Crop Sci. 12:

643—646.

Blacklow, W.M. 1972. Influence of temperatureon germination and elongation of the radicle and shoot of corn (ZeamaysL.). Crop Sci. 12: 647—650.

Chino,T.M. 1972.Metabolism of germinating seeds.In:

Seed Biology, 2: 103—218.New York.

Feddes,R.A. 1971. Water,heat andcropgrowth.184 p.

Wageningen.

Feddes, R.A. 1972.Effects of water and heatonseedling emergence. J. Hydrology ^16;341 —359.

Hadas, A. 1970. Factors affecting seed germination under soil moisture stress. Israel J. Agric. Res. 20:

3—14.

Mayer, A.M.^&Poljakoff-Mayber, A. 1975.The ger- mination of seeds. 192p. Oxford.

Tenhovuori, M. 1986.Kuivatuksen ja kastelun vaikutus viljakasvien itämiseen. Thesis86p. Otaniemi.

Msreceived September ^{10, 1986}

SELOSTUS

Maaveden potentiaalin ja maaperän lämpötilan vaikutus vehnän ja ohran itämiseen

Markku Tenhovuori

Teknillinen korkeakoulu Vesitalouden laboratorio 02150Espoo

Kokeissa tutkittiin kevätvehnän (Tähti) ja ohran (Pok- ko) itämisen riippuvuutta maaveden potentiaalista ja maan lämpötilasta.

Kasvualustana käytetyn hiekan raekoko vaihteli välil- lä0,1 —0,6mm. Hiekan vedenpidätyskäyrän määrittämi- sessäkäytettiin neljäämenetelmää,joistakahta sovellet- tiin myös varsinaisiin itämiskokeisiin. Matrikpotentiaa- linarvot—l5O 10mv.p. saatiinosmoottisesti,kun hiekka pantiin puoliläpäisevän selluloosa-asetaattikalvon sisään. Systeemi upotettiin polyetylenglykoliliuokseen (PEG), jonka molekyylipainooli noin 20 000.Tällöin eri

liuosväkevyyksilläsaatiin kasvualustassa aikaan halutun- lainen matrikpotentiaalinarvo.Varsinaisissa itämiskokeis- sa käytettiin tällä menetelmällä potentiaalin arvoja

—IOO 10mv.p.Vedenpidätyskäyrän pisteet—1m ja—5m määritettiin kokeiden yhteydessä kehitetylläme- netelmällä,jossahiekka pantiin pieneen suljettuunmuo- viastiaan ja saatettiin paineenalaiseksi, jolloin ylimää- räinen vesi pääsi pois astian alapuolelle olevista rei’istä.

Tätäennenhiekka oli ollut vedellä kyllästetyssä tilassa.

Varsinaisella pF-käyrän määrityslaitteella saatiin vielä pis- teiden 1mv.p. ja5mv.p.paikkansapitävyystarkistet-

lua. Neljännellämenetelmällä määritettiin vedenpidätys- käyrän pisteet—0,25 0mv.p. Tämä perustui veden kapillaariseen nousuun maassa. Erikorkuisilla hiekka- patsaillasaatiin haluttu potentiaali. Tätä järjestelyäkäy- tettiin myös itämiskokeissa ja siemenen vedenottoa sel- vittävissä kokeissa. Itämiskokeissa käytettiin 1,5cm:nkyl- vösyvyyttä jakymmentä siementä kutakin potentiaaliar- voakohti. Itämisen katsottiin tapahtuneen, kun n.0,5 cmtaimesta oli tullut esiin. Flavainnot tehtiin päivittäin jakokeen jälkeen mitattiin kylvöalustan kosteus. Sieme- nenvedenottoa tutkittaessa5vehnän ja ohran siementä upotettiin 1,5cm syvyyteeneri pituisiksi ajoiksi pF-arvon ollessa 1,2.Siemenetnostettiin maasta,kuivattiin,pun- nittiin ja pantiin takaisinmaahan,jonka jälkeenkoetta jatkettiin. Tässä yhteydessä laskettiin myös alkeisjuurten lukumäärä ja pituus sekäversonpituus.Edellä mainitut kokeet tehtiin lämpötiloissa 10, 15,20ja 25°C.

Itämisen minimilämpötila määritettiin kosteuspitoi- suuksissa 10 30til. ^%eli matrikpotentiaalin arvoilla

—0,20 0,10 mv.p. siten, että laskettiin erilaisilla lämpötila-arvoilla50 Vo itäraisajan käänteisarvo ja näi- den kautta piirrettiin regressiosuora, jonkakulmakerroin ilmaisee lämpösumman astepäivinä.

Vehnän ja ohran itämisaika pitenee suoraviivaisesti matrikpotentiaalin pienentyessä n.—5mv.p.pienemmis- täarvoista lähtien. Lämpötilannousu saaaikaan oras- tumisen nopeutumisen orastumisen minimilämpötilasta siihenasti,kunnes saavutetaan lämpötila, jossa kasvual- kaa hidastua. Minimilämpötiloina käytettiin laskelmissa koetuloksista saatuja arvoja 3,l°C^vehnälleja I,9°C oh- ralle. Vastaavat lämpösummat ovat 70astepäivää veh- nälle ja73astepäivääohralle. Lämpötila, jonka jälkeen kasvu alkaa hidastuaonn.31°Cvehnälle ja n. 27°C oh- ralle.

Suomenolosuhteita itämisjakson aikana keväisinmelko

hyvin vastaavassa 10°C lämpötilassasaatiin optimialu- eeksi50^%itämisnopeudellenoin pF-alue 1,3 2,7eli

—5,0 0,20m v.p. Vehnä ja ohra vaativat selvästi suuremman lämpösumman^kunmaaveden jännityssaa- vuttaa tietynns.kriittisen arvon.Vehnän kriittiseksiar- voksi saatiin aineiston perusteella pF2,8eli n. 6,3mv.p.

ja^ohranpF2,7 eli n.5,0 mv.p.

Lämpötilassa 10°Cmääritettiin30päivänkuluessa ta- pahtuvavehnän ja ohran kokonaisitäminen raatrikpoten- tiaalin funktiona. Märällä puolella voidaan pF-arvoa 1,0 pitää arvona, jotasuuremmissa kosteuksissa kokonais- itäminen alkoi vähentyä. Kuivalla puolella voidaanvas- taavasti havaita kokonaisitämisen vähenemistä senjälkeen kun pF-arvo noin 3,0on ylittynyt.

Siemenenvedenotonnopeuskasvoi kokeiden perusteel- la lämpötilan kohotessa 10°C:sta 25°C:een. Alkeisjuuri ilmaantui^vehnäänjaohraanvaiheessa,^missä siemenen vedenotto oli n. 50—60Vo siemenen alkuperäisestä pai- nosta.Siemenenseinämän kostumisesta kapillaarisuuden johdosta tapahtuvasiemenen vedenotto alussa oli veh- nällä n. 3 ^%jaohralla n. 5^%maaveden potentiaalin ollessa n. pF 1,2siemenen vedenottoa selvittävissä ko- keissa.

Käytännössäonoleellista tehokasta itämistä ajatellen pyrkiä pitämäänvehnän ja ohran kohdalla matrikpoten- tiaali Suomen olosuhteissa keväällä optimialueella, joka onn. pF 1,3 2,7. Jopienimaanlämpötilankohoami- nenvaikuttaa positiivisesti itämisnopeuteen Suomen olois- sa.Tehokkaalla kuivatuksella voidaan vaikuttaa sopivan kosteuspitoisuuden ylläpidon lisäksi maaperän lämpöti- laan siten,ettäviljakasvittuleentuvatnopeammin,millä on tärkeämerkitys Suomen lyhyestäkasvukaudesta joh- tuen. Myöskastelulla olisi mahdollista joinakin vuosina edistää itämistä Suomenkin oloissa pääasiassa joillakin hiesu-, savi- ja turvemailla.

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