View of Influence of sodium and potassium fertilization on the sodium concentration of timothy

Influence of sodium and potassium fertilization on

the sodium concentration of timothy

Tommi Peltovuori

DepartmentofApplied ChemistryandMicrobiology,POBox27,FIN-00014 UniversityofHelsinki, Finland, e-mail: tommi.peltovuori^@helsinki.fi

Markku Yli-Halla

Department ofApplied ChemistryandMicrobiology,FIN-00014 Universityof^Helsinki,Finland. Current address:

Instituteof^ResourceManagement, AgriculturalResearch Centreof^{Finland,FIN-31600Jokioinen.Finland}

Sodium(Na) concentration offoragecrops grown in Finland, particularlythat oftimothy, is much lower than is recommended inthe feed of cattle.Apotexperimentwas carried outonclay,loam and organogenicsoils to find out the effect of Naapplication^(0,200or400mg dm ³ofsoil,oneapplica- tion)onthe concentration ofNa, K,CaandMgoftimothyand the effect ofKfertilization (0, 100and 200mg dnr³for each three harvests)^ontheefficiencyof Naapplication.Added Na elevated the Na concentration inall harvestsonall soils. Themagnitudeof the effect(organogenic soilsloam>clay) wasoppositetotheK supplyingpower of the soil.Potassium fertilizationsuppressedthe effect of Na application substantially and Na concentration waselevatedremarkably onlywhen theK^concentra- tion of theplantsfell toorbelow thedeficiencylevel(approximately 15gkg^-1).Accordingtoa^cation exchange experiment, nearlyall added Na remained inthe soil solution. Still, the apparentutilization

of added Naremained^{below4% onallsoils,}demonstratingthenatrophobicnatureoftimothy. ^Sodi- umfertilization oftimothy seems^tobeanineffective way ofincreasing the Na content offorageat

leastonsoils ofagood K statusorwhenapplied withample Kfertilization.

Key words:calcium, cationexchange isotherms, magnesium, mineral composition offorage,potex- periment, selectivity incationexchange

Introduction

Sodium(Na)cansubstitute for potassium(K)in the biophysical functions of K in ^mostplants, e.g. in regulating osmotic pressure in vacuoles, andtoalimitedextentin biochemicalfunctions.

e.g. in activation of enzymes.However,the abil- ity of Na^to substitute for K varies greatly be- tweenplant species(Flowersand Läuchli 1983).

Most agronomically significant species like tim- othy, rye, corn and soybeanare natrophobic. In these species Na^cannoteffectively substitute for K and the Na concentration of plants tendstobe

©Agriculturaland FoodScience ⁱⁿFinland ManuscriptreceivedFebruary 1997

Voi 611997): 259-268.

low. The average Na concentration of timothy in Finland (mean 0.047 g kg'

1

^, Kähäri and Nissi- nen 1978) is of the_same order_asthat of the mi- cronutrients_Fe,Mn andZn,while in other grass- es like cocksfoot (0.3 g kg

1

^{,Rinne etal. 1974),}

and particularly in ryegrass ^(0.8 gkg

1

^{, Jansson}

1986),the Na concentration tends tobe higher.

The Na concentration of cereals is relatively unimportant but that ofpasture species affects the quality offodder used for animal production.

Sodium is anessential mineral element for ani- mals, and forage should contain Na 1.8-2g kg

1

of drymatter tosupply milking_cowswith suffi- cient Na (NJF 1975, Smith and Middleton 1978, Horn 1988).Thus, there is a big difference be- tween the requirement of cattle and the supply of Na from farm-produced fodder inFinland, and it hasto be compensated with mineral supple- ments.Another imbalance of mineral elements in fodder is brought about by heavy K fertiliza- tion of leys leading to excessive K concentra- tion and lower than optimum concentration of othercations, especially magnesium (Mg), in herbage (Smith and Middleton 1978, Leigh et al. 1988).The equivalent ratio K/(Ca+Mg) has been used as acriterion for forage grass quality;

values below2.2 aredesired(Ettalaand Kossila 1979). Substitution ofNa for K in plants has been showntoincrease their Mg concentration(Nowa- kowski et al. 1974, Smith 1974, Smith et al.

1980, Mundy 1983).Sodium application canthus improve the feeding quality of herbage by in- creasing the concentration of Na and Mg and possibly by lowering the concentration of K.

Elevated Na concentration of herbage may also increase the intake of fodder by cows (Horn 1988, Chiyetal. 1993),resulting inan increase in liveweight gain and in milk production (Chiy etal. 1993).

The purpose of this study was ^toexamine whether the Na concentration of timothy can be elevated by Na application and to find out the effects of Na application on the uptake of other cations on three different soils. The effect of K application on the efficiency of Na fertilization wasalso studied. The natrophobicnature of tim- othy and its poor response ^to added Na is evi-

dent from the literature. Nevertheless,itwas se- lectedasthe^testcropbecause,owing^to its win- terhardiness,it is by far themostcommon pas- turespecies in Finland. The fate of added Na in soilwas also investigated by determining cation exchange isotherms for the cation exchange pairs Na/K and Na/Ca.

Material and Methods

The effect of Na on the growth and chemical composition of timothy wasstudied in_{a pot ex-} periment. The experimental soils (silty clay, loam and organogenic soil.Table 1)weretaken from plough layers of cultivated fields in Southern Finland. In the^text,the silty clay will be referred to as clay. The high concentrations of Ca and Mg and the relatively high pH of the organogen- ic soil areprobably attributabletoliming.

The soilswereair-dried and ground^topass a 10-mm sieve. For chemical analyses,part of the soil was ground further topass _a 2-mm or a 0.6-mm sieve (C analysis). The carbonconcen- tration_wasdetermined usingaLECO CHN-900 analyser. The particle size distribution_was de- termined by apipette method. The pH was de- termined in a 0.01 M CaCl₂suspension at the

Table 1. Propertiesof theexperimentalsoils.

Clay Loam Organogenic soil Particle sizedistribution,^%

<0.002mm 44.1 8.0 29.9

0.002-0.02mm 24.5 19.4 39.4

0.02mm^< 31.5 72.6 30.7

OrganicC, ^% 3.9 2.8 26.6

SoilpH^(0.01 MCaCL,) 5.9 6.3 5.8

Exchangeable cations,mg dm³

Na 14.5 7.7 9.3

K 283 134 87

Ca 2207 1520 4530

Mg 196 81 225

Bulkdensity,gcm³ 0.77 0.90 0.34

solution-to-soil ratio of2.5:1 (v/v).The electri- cal conductivity of the soil wasdetermined in a water suspension atthe solution-to-soil ratio of

2.5:1.

Exchangeable cationswereextracted with four successive portions of1 M ammoniumace- tate,pH 7.0(Thomas 1982).The soil bulk den- sitywas determined for air-dry soil compressed asin the experimental pots.

Kick-Brauckmann pots with 7 dm³ of soil were used in the pot experiment. A small por- tion of soil (0.25 dm³⁾ wastaken from each pot tocoverthe seed and the_rest wasfertilized. The treatmentswere:

Sodiumas Na,SO-10H,O:_{2 4 2} PotassiumasKCI:

Abbre- Abbre-Abbre-

viation: mg dm*^{3 viation;} mg drtr³

Na₀ 0

K„

⁰

Na,

²⁰⁰

K,

¹⁰⁰

Na, ⁴⁰⁰ K, ²⁰⁰

All the nine combinations were made as 5 replicates for each soil. The_{pots were}fertilized also with other elements as analytical grade chemicals^atthe followingrates (mg dm*³): Nas

NH₄NO,^{(150), PasCa(H,P0}4)

2.H,0^{(150), Mg} as MgS0₄-7H₂0(80), S in sulfates of Mg, Cu, Mn,Fe and Zn (atleast 112), CuasCuS0₄-5H,0 (4), Mn as MnS0₄-H,O (4),Fe as

(2), Zn asZnS0₄-7H,0(3) and B as H,BO,^(2).

The seed of timothy (300 mg Phleum^pratense L. cv.Tuukka) was sown on the fertilized soil and covered with unfertilized soil. Three crops of timothy were harvested. The second and the third cropwerefertilized with solutions ofN and K atthe same rates as at the beginning of the experiment. Sodium wasapplied only _atthe be-

ginning. The plantswere grown outdoors under aglass roof from MaytoSeptember and watered with deionizedwater.The first crop wascut 59 days after planting, the second and the thirdone after 33 days’ growth. The plant material was dried at65°C and analyzed forCa, Mg, Na and K according to a dry combustion method by Helrich(1990). Potassium and Nawereanalyzed by flame photometry, Ca and Mg by atomic ab- sorptionspectroscopy. A known sample _was in-

eluded in every analysis series. The coefficients of variation (23 observations) for the analysis of the sample were: Na 17.0%, K 3.6%, Ca 2.9%

and Mg 1.1%.

Exchange isothermsweredetermined for Na/

Ca and Na/K exchangeon the three soils by a modified method of Levyetal. (1988). Isotherms were determined using 5 g of soil⁽²g of orga- nogenic soil) in duplicates. The soil samples were first equilibrated with 25 ml ofa mixture of solutions of NaCl and CaCI_2orNaCI and KCI.

Seven different cation equivalent ratios (0, 15, 30, 50, 70, 85 or 100^% ofNa) were used for both isotherms, and the chloride concentration of the first equilibration solutionwas 0.5 mol 11.I^{1 .} The suspensions were shaken for 20 min, cen- trifuged, and thesupernatant solution was dis- carded. This_wasrepeated threetimes,followed by three similarstepsusing 50 ml of 0.01 ^M so- lutions while maintaining the original Na/Caor Na/K ratios. The last0.01 M solutionswere fil- tered through Schleicher^&Schiill589³(bluerib- bon) filter paper and used to determine Na and K by flame photometry and Ca by atomic ab- sorptionspectroscopy.Theamountof equilibra- tion solution remaining in the soil samples after equilibration _was determined by weighing the centrifuge tubes containing the soil and theso- lution. Thereafter the exchangeable cations ad- sorbed_on the soil samples were determined by three repeated extractions with 30 ml of 1 M ammoniumacetate (20 min shaking, centrifug- ing and filtering through Schleicher ^& Schiill 589³ filter paper). The extracted cations were determinedasabove. The^amountof cations held in the soil by the remaining equilibration solu- tionwasdeducted from these results.

Results

The dry matter yields were notaffected by Na treatments.On the organogenicsoil,K fertiliza- tion elevated the yields of the second and third harvest by 10 and 51%, respectively (p<0.001) Vol.6(1997): 259-268.

Table2. Dry matteryields (g pot') atthe three levels of Kapplication.Treatments:K_n=omg dm³,K,=3x100^{mg dm’3,}

K₂=3x200mg dm3 .

Clay Loam Organogenicsoil

Harvest All Klevels All Klevels

K 0

^K,andK

2

I 15.4

II 31.5

111 24.2

Sum 71.1

16.5 23.2 23.4

30.0 32.9 18.2 27.4 71.4 83.7 30.0

23.8 70.3

(Table 2).Yet,therewere novisible K deficien- cysymptomsin any^treatmentof the experiment.

Without Na and K application (Na₀K₀^), the average Na concentration oftimothy (Table 3) was0.24 g kg

1

(range 0.17-0.30 g kg '),exclud- ing the plants grownon the clay in the first har- vest that had _a Na concentration (0.57 g kg ^') deviating from the other corresponding results.

When_noNa _wasapplied, K application seemed

toelevate the Na concentration but the effectwas notstatistically significant.

Application of Na increased the Na concen- tration of timothyonall soils and in all harvests (pccO.OOl). The effectwas greaterfor the loam and the organogenic soil than for the clay. The highest Na concentrations of timothy were reached without K and with the highestrate of Na(Na₂K₀⁾ in the third harvest: 6.9 gkg'on the loam and5.6 gkg ^'on the organogenic soil.

Sodium was much weaker than Ca or K in competition for cation exchange sites (Fig. 1).

In Na/K exchange, Na was least efficient_com- petitor for clay and somewhatmore efficient for the two lighter soils. In equimolar equilibrium solution(Na/K), Na occupied ^24, 33 and 38%

of the exchange siteson clay, loam and organo- genic soils, respectively. Sodium _{was even a} weaker competitor for exchange sites with Ca than with K. Inanequilibrium solution contain- ing 50% of both Na and Ca (expressed in mmol of charge dm’³⁾ therewas only 5, 4.5 and less

Table3.Sodiumandpotassiumconcentrations oftimothy inthe pot experiment (g kg

1

^drymatter). Treatments: Na|=200 mg dm ^',Na₂=400mg dm^’,K,=3xloo^{mg dm3,K}2=3x200mg dm^{3 .}

Clay Loam Organogenicsoil

Harvest

K 0

^K,

K 2 K 0

^K,

K 2 K 0

^{K, K}

2

Na() 0.6" ^{0.5a 0.7ah 0.3" 0.4"b 0.5ab 0.2" 0.4ab 0.5abc}

I

^{Na, 0.7ab 0.8ab 1.0fc I.l' 1.1» 1.0}

1

^{* \.s< 0.6}

1

^{* 0.6b-}

Na₂ 1.7^d 1.6^d 1.3'^d 2.3^d 1.9^d 2.2^f 1.1" o.B' Na₀ 0.2" 0.6"" 1.0""

1

^0.3" 0.5"" 0.5^ab 0.3" 0.4"^b 0.5"^b Na 11 Na, ^{0.6"b 0.7}

1

^{* \.0bcd 1.5'd 1.0b'd 0.9* 1.8J 0.6b 0.5»b}

Na₂ 1.2°" 1.2^d LO*" 3.5' 1.5°" 1.6^d 2.8' l.l^c 0.7^b Na0 0.3" 0.4" 0.5" 0.2" 0.4" 0.6" 0.2" 0.4" 0.5"

111 Na, ^{I.l* 0.7ab 0.6«b 3.2' 1.2"b 0.8" 4.2' 0.7" 0.6"}

Na₂ 2.6" 1.6' 1.2

1

^{* 6.9d 2.6* 2.4}

1

^{* 5.6d 1.5b 0.7'}

Na„ ^{45" 48"b 50"b 31" 43'} 48"" 20" 36' 47'

I

^{N3| 45. 47a 49.b 36ab 45cJc 49e 25b 40" 50'}

Na₂ 45" 48^ab 53^b 37^b 44'^d 49^d' 26^b 38'^d 50'

Na0 31" 42" 45^b 13^a 34' 41^d 10" 26" 40

1

K II Na, ^{32" 43b 44b 17b 35' 41d}

11'

^{29b 42'}

Na₂ 33" 42" 45^b 19^b 34' 45^e 10' 27^b 42'

Na0 21" 42' 50' 12" 35^b 47' 9" 31" 46'

111 Na, ^{23»" 45d 48' 13" 37" 47' 9" 32" 48'}

Na, 24^b 42' 49' 14* 36^b 46' 8' 31" 46'

Each soil and harvestwastested separately. Means with samesuperscriptsdo not differat p⁼0.05.

than 3% of exchange sites occupied by Na on clay, loam and organogenicsoils, respectively.

Application of K drastically depressed the effect of Na fertilization (p<0.001)eventhough added Kwas more likelytobe boundonthecat- ion exchange sites than Na. In the Na/K ex- change, K ^was least efficient competitoron the organogenic soil,and the effect ofKwas strong- eston this soil;K, application decreased the Na concentration of timothy at the Na₂ level in the third harvesttoone-eighth of that obtained with- out K application (Table 3). When plants were fertilized withK,the targeted^Naconcentration of2 g kg

1

^wasreached only with the higher Na level in the third harvest on the loam. The sodi- um concentration of timothy increased^mostef- fectively when the K concentration of the plants decreased toorbelow 15 g kg^'(Fig. 2). These concentrations, suggesting K deficiency, oc- curred in plants grown without K application in the second and third harveston the organogenic soil and in the third harvest on the loam.

Application of Na did notdecrease the con- centration of K in timothy atany K level. Fig- ure3 demonstrates the abundance of K compared

to other cations in the plants fertilized with the same amounts (mg dm³⁾ of Na and K. When expressed in mol dm ³, the plants received more Na than K. Despite the similaramounts added as fertilizer, the first harvest of timothy ^grown onmineral soils took50 times and timothy grown on the organogenic soil 80 timesmoreK than Na. A tenfold increase in Na concentration from the Na₀ level with an equivalent decrease in K concentration would theoretically lower the K concentration by only about4 g kg’

1

^atthemost.

Not_even this effect _seemstobe feasible.

Sodium application decreased the Caconcen- tration of timothy on all soils and for all har- vests (p<0.001). The mean Ca concentrations were8.5,7.2 and 6.6 g kg’

1

^{in thetreatmentsNa0,}

Na⁽ and Na₂^, respectively. In the third harvest on the organogenicsoil,the Ca concentration of timothy _{was as}muchas35% lower in the Na2K0

(10.7 g kg ^')than in the Na()K(|(16.5gkg ^')treat- ment. Sodium application did^notinfluence the Mg concentrationswhich, owingtoMg fertili-

zation, wererather high in the experiment. Po- tassium application strongly lowered the Mg concentration of timothy (pccO.OOl). The aver- ageMg concentrationwas4.6, 3.1 and 2.6 g kg'

1

in the treatmentsK_O,

K,

^{and K 2,}respectively.

One of the aims of Na fertilization has been todecrease the excessive concentration of K in herbage and thus to decrease the K/(Ca+Mg) ratio of fodder. In the^present study, Na fertili- zation, on the contrary, increased the ratio (p<0.001) because it decreased the Ca concen- tration but did notaffect the K and Mgconcen- Fig. 1.^Cationexchangeisotherms for the cationpairs Na/

Kand Na/Ca. Sodiumontheexchangesites andintheequi- librium solution expressedasafraction of total positive charge.

Vol.6(1997):259-268.

trations(Table 4). However, the K/(Ca+Mg) ra- tios remained below 2.5 in all treatments, and the unfavourable effect ofNa diminished towards the end of the experiment. Without K applica- tion(K₀⁾the K/(Ca+Mg) ratios decreased^tovery low values in the third harvest (range 0.2-0.8).

Potassium hada strong enhancing effect on the ratio (p«0.001) throughout the experiment.

Sodium fertilization lowered the K/Na ratios in

the plants (p«0.001) which is considered ^to improve the quality of fodder.

Inthe Na_nK₀pots, 22-34% of the nativeex- changeable Nawastaken up by plants while in the Na_QK₂pots, 52-71% was taken up. Howev- er,thereserves of exchangeable Nawerenotde- pleted during the experiment in clay while there was aconsistent decrease in the organogenic soil and inconsistent changes in the loam (Table 5).

Applied Na elevated the concentration ofex- changeable Na in the soiltovery high levels. At the end of thepotexperiment, Na extracted from the soils of the highest Na treatmentrepresent-

ed 11, 14 and 6% of all extracted cations (mol of charge dm³⁾ in clay, loam and organogenic soils,respectively. The heavy fertilization also elevated the electrical conductivities of the soils.

The maximum values atthe end of the experi- ment, measured in the Na₂K,pots, were0.8,0.6 and 1.0 dS nr

1

in clay, loam and organogenic soils,respectively.

In pots fertilized withK, the apparent utili- zation of added^Nawas less than4%onall soils and atthe K 2 level it remained below 0.8% for the clay and the organogenic soil. At the

K 0 lev-

el, the utilization of Na was somewhat higher Fig. ^2,Relationshipof theconcen- trations of Na and K oftimothy fertilized with two Na levels(Na,⁼ 200mg dm Na₂⁼400mg dm^{3 ).}

Fig.3. Na, K,Caand Mg concentrations of timothy (mmol ofcharge kg^')inthe first harvest. Theplantsreceived sim- ilar Na andKfertilization (200 mg dm¹,treatmentNa^,).

Table4. K/(Ca+Mg)ratios (mol ofcharge kg

l

^{) of timothy inthe pot} experiment. Treatments: Na,=2oo ^{mg dm \}

Na,=4oomg dm^-',K,=3xloo ^{mg dm-',K}2=3x200mg dm^-\

Clay Loam Organogenicsoil

Harvest

K 0

^K,

K 2 K 0

^{K, K, K„ K, K}

2

Na() 1.8" 2.0" 2.1"= 1.1" 1.6" L. 9" ^0.6» 1.4« ^2.1' I Na, ^{2.1bcd 2.2'd} 2.3"" 1.5» 2.0^d 2.1* 0.9" 1.7° 2.3' Na, 2.2'^d 2.3^d' 2.5' I.B' 2.3^cf 2.5' ^0.9b 1.8" 2.5*

Na(l 1.2" ^{2.1c 2.3d 0.4" 1.4'} 1.9' 0.2» 1.0" 2.0^d

II Na, ^{1.5b 2.3d 2.3d 0.6ab 1.6" 2.0' 0.3" 1.2' 2.3'}

Naj ^1.6b 2.2'^d 2.3^d 0.7^b 1.7^d 2.3' ^0.3a l.l^{ta 2.3'}

Na„ ^{0.6" 1.7b 2.2J 0.3" 1.2b 1.8d 0.2" I.l' 2.1'}

111 Na, ^{0.8" 2.0'd 2.2" 0.4»} 1.4^1* 1.8^d 0.2» l.2^b 2.4^d

Na₂ 0.8» 1.9^*

1

^{2.2" 0.4» 1.4' 2.1' 0.2» 1.2" 2.3d}

Each soil and harvestwastestedseparately.Means withsamesuperscriptsdo not differ atp=0.05.

(8-11%) for the loam and the organogenic soil but for the clay itwasbelow^4% in alltreatments.

By way of comparison, utilization of added K was 68-75% for the organogenic ^soil, 34-64%

for the loam and 21-45% for the clay. The re- serves of soil^K decreased ^atthe K()and

K,

^lev-

els for all thesoils, for the organogenic soil also atthe higher applicationrate (K₂⁾ (Table 5).The

Table5. ExchangeableNa andKconcentrations of theexperimentalsoils(mgdm^')before and after the pot experiment.

Original After theexperiment

JS>

^{!Sj K}

2

Na

Clay 15 Na,, ^{18 14 13}

Na, ^{208 174 191}

Na₂ 364 353 543

Loam 8 Na„ 4 10 14

Na, ^{189 211 253}

Na₂ 325 430 352

Organogenic 9 Na₀ 3 5 4

soil Na, ^{132 168 195}

Na₂ 276 325 353

K

Clay 283 Na„ ^{78 172 256}

Na, ^{78 152 310}

Na₂ 83 130 313

Loam 134 Na„ ^{32 58 163}

Na, ^{27 60 194}

Na₂ 27 45 240

Organogenic 87 Na₀ 19 33 66

soil Na, ^{19 32 55}

Na₂ 23 30 69

total uptake of K by plants (three harvests) at the K(| levelwas 325, 199 and 145 mg dm³ for clay, loam and organogenic soil, of which 120, 89 and 76 mg dm ³ was non-exchangeable K, respectively.

Discussion

The Na concentration of timothynot fertilized with Na wasupto 10 times higher in thepresent potexperiment than generally found in fieldcon- ditions in Finland (Kähäri and Nissinen 1978, Jansson 1986)eventhough the experimental soils hadanaverage Nastatusascomparedtothe soils of Finland (Sippola and Tares 1978).The high Na concentrationscan partly be explained by a high N fertilization rate (450 mg dm’³ corre- sponding to900 kg ha ^').In fieldconditions, N fertilization of600 kg ha

1

has increased the^Na concentration of mixed ley by afactor of6.7 as comparedtounfertilized ley (Rinneetal. 1974).

Duetothe high Na concentrations of timothy in thepresentpotexperiment, the results cannotbe applied quantitatively to field conditions, but they give qualitative information about the dif- ferent interactions between cations in the nutri- tion of timothy. ^Innormal cultivation the plants arebetter supplied with K than in the

K 0

^{pots of}

thepresentexperiment. Therefore,the response of timothy toNa fertilization in field conditions would mostlikely be closerto that observedat the

K,

^and

K 2 levels

and far from the higher re- sponses measured in the

K 0

^pots.

The increased Na concentration of timothy caused by the application of K at the Na₀level canbe explained by cation exchange. Added^K effectively displaces Na from the cation ex- change sites ofsoil, as was shown in the Na/K exchange studies. A higher Na concentration in the soil solution consequently promotes Na up- take by timothy. However,the observed increase of Na concentration brought about by K appli- cation is marginal. The slight increase in plant K concentration upon Na addition in the

K 0 treat-

ment on loam and organogenic soil reflects the exchange between added Na and soil K.

Calcium is the dominating exchangeable cat- ion in the ^soil, and the Na/Ca exchange equi- libriasuggest that added Na remained nearly completely in the soil solution. The particularly high selectivity for Ca of the organogenic soil is probably dueto the complexation of Ca with the functional groups of organic matter (Mcßride 1994). In spite of the lowest selectivity for Na overCa in the organogenic soil,the highest Na concentrationswereobtainedonthe loam. At the end of the experiment the percentage of Na of the sum of cations (in mol of charge dm³⁾ ex- tracted by ammoniumacetatewas highest in the loam,the Na activity of the soil solutionconse- quently being highest in this soil. The difference in Na activity in the soil solution may thus ex- plain the difference in the Na concentration of timothy grownon the mineral and the organo- genic soils. The high original Ca concentration of the organogenic soil may also have depressed the uptake of Na through cation antagonism. In K uptake the selectivity by plants seemedtodom- inate the selectivity in cation exchange. The dif- ference in Na concentrations between the min- eral soils is due tothe largerreserves of K in clay.

Indeed,the^mostpronounced phenomenon in thepresent studywasthe dependence of Na up- takeonthe K supply, either in the form of native oradded K. The effect of Na applicationon Na concentration of timothy for the three soils(or-

ganogenic wasatodds with the

K supplying power of the soils. The effect of the lower K supplying power of organogenic soils on the Na concentration of timothywasalsoev- ident in the study ofKähäri and Nissinen (1978).

They reported higher Na concentrations of tim- othy in the province of Lappi, dominated by or- ganogenic andcoarse mineral soils, than in the restof the _country.They also observed that tim- othy grown on Sphagnumpeat soils contained

122 mg Na kg^' incontrast tothe average around 50 mg kg ^'in timothy grownonothersoils,with-

outamarked difference in exchangeable Na in soil.

The increasing efficiency of Na fertilization towards the end of the experimentcan,besidesa decrease of thereserves of soil K upon K uptake by the plants, partly be caused by gradual filling ofstorage capacity for Na in^roots and conse- quent transport of Na to shoots. Distinctively natrophobic timothy stores as much as 90% of Na taken up in the^roots(Jarvis 1982).When this storage capacity is used up, the Na concentra- tion of the shoots starts to increase. It has in- deed been observed that the Na concentration of timothy increases when plants age (Jarvis 1982).

The same phenomenon, in a weakerform, has been observed with perennial ryegrass, meadow fescue and cocksfoot(Rinne etal. 1974, Smith etal. 1980).

The effect of Na fertilizationon the Cacon- centration and K/(Ca+Mg) ratio of timothy was oppositetothat observed with perennial ryegrass in field conditions (Chiy and Phillips 1993).

However, in Chiy and Phillips’ experiment,con- siderably natrophilic ryegrass wasgrownin sub- optimal K conditions: Na fertilization increased the Na concentration of herbage substantially, increased the yield and Ca concentration and even lowered the K concentration of herbage.

The apparentrecovery of Na by ryegrass in that field experimentwas 70%, which is considera- bly higher than in thepresent pot experiment.

The difference between timothy and ryegrass supplied adequately with K would probably be smaller than these results suggest.

Conclusions

Thepresent study shows that timothy has sucha preference for^K that even an excessive K con- centration in a plant _cannot be suppressed by ample Na additions. The strongreduction of Na uptake by native and added K makes it difficult toelevate the Na concentration of timothy sward by Na applications in practice. As longasK con- centration of timothy isata level sufficient for maximum growth or higher (luxury consump- tion), the Na concentration of shootscannot be effectively increased by Na application. It is possibletoelevate the Na concentration of tim- othy substantially only when plants arein K de- ficiency. However, adeficiency of K endangers the production of maximum yield and it may be unreasonabletoproduce grass high in Naatthe expense of the yield. If Na is applied totimothy in fieldconditions,the utilizationrate cannotbe expected to be high. Other grass species like cocksfoot and ryegrass utilize Namoreeffective- ly (Smith etal. 1980, Jarvis 1982).Cultivation of these less natrophobic species aspure stands or as mixtures with timothy is a morerealistic alternative toelevate the Nacontent of forage than Na fertilization of timothy.

Acknowledgement.The authors wish to thank KemiraAgro Oyfora^{grant forcarryingoutthisstudy.}

References

Chiy,^P.C.&Phillips, ^C.J.1993. Sodiumfertilizer applica- tion to pasture. 1.^Directandresidual effectsonpas- ture productionand composition. Grass and Forage

Science48: 189-202.

- ,Phillips, C.J. ^& Bello, M.R, 1993, Sodium fertilizer application to pasture. ^2,Effects on dairycow pro- duction and behaviour. Grass and Forage Science 48: 203-212.

Ettala, E. ^&Kossila,V. 1979.Mineral contentinheavily nitrogenfertilized grass and its silage. Annates Agri- culturae Fenniae 18: 252-262.

Flowers,T. J.^&Läuchli,A. 1983. Sodium versuspotassi-

um: Substitution and compartmentation.In:Läuchli,

A. ^& Bieleski, ^R, L. (eds.). Encyclopedia of Plant

Physiology,New SeriesVol. 15B:651-681,Berlin and NewYork,Springer-Verlag.

Helrich,K, 1990. Officialmethods of analysis. 15. ed.

Arlington, The Association of Official Analytical Chemists.639p.

Horn, G. 1988.Experienceswith ‘Magnesia-Kainit’ on grassland. Journal of the Science of Food and Agri-

culture43: 324.

Jansson, H. 1986. Sodium contentsof different plant species grown ^sideby side. Annales Agriculturae

Vol. 6(1997): 259-268.

Fenniae25: 273-277.

Jarvis,S.C. 1982.Sodium absorptionand distributionin foragegrasses of different potassium status. Annals of Botany (London)49: 199-206,

Kähäri,J.^&Nissinen, H. 1978.The mineral elementcon- tents of timothy ^(Phleumpratense L.) in Finland: t.

The elements calcium, magnesium, phosphorus, potassium,chromium, cobalt, iron, manganese, so- dium and zinc,Acta Agriculturae Scandinavica, Sup- plement20: 26-39.

Leigh,R.A., Gorham, J.^& Wyn Jones,R.G. 1988.The cellular and genetic basis for cation discrimination by plants.Journal of the Science of Food and Agri- culture43: 319-320.

Levy, G.J.,Watt, H. v.FI.^vander,Shainberg,I,^&Du Ples- sis, Fi.M. 1988.Potassium-calcium and sodium-cal- cium exchangeonkaolinite and kaolinitic soils. Soil Science Societyof America Journal52: 1259-1264, Mcßride, M.B. 1994. EnvironmentalChemistryof Soils.

NewYork,Oxford UniversityPress. ^{406 p.}

Mundy, G.N.1983.Effects of potassium^{and sodium}con- centrations on growth and cation accumulation in pasture species grownin sand culture. Australian Journal of Agricultural Research 34:469-481.

NJF. 1975.Förslagtillnormerför makro- och mikrominelarer till nötkreatur^ochsvin. Fodegoumalen3-4: 55-103.

Nowakowski, T.Z., Bolton,J.^&Byers, M. 1974.Effects of

replacing potassium bysodium^ongrowthand^onin- organicand organic composition of Italian ryegrass.

Journal of the Science of Food andAgriculture 25:

271-283.

Rinne,S.-L, Sillanpää, M., Huokuna, E.^&Hiivola, S.-L.

1974.Effects of heavy nitrogen fertilization on iron, manganese,sodium, zinc,copper, strontium,molyb- denum and cobalt contentsinleygrasses. Annates AgriculturaeFenniae 13: 109-118.

Sippola,J.^&Tares, T. ^1978,The soluble content ofmin- eral elementsin cultivated Finnish soils. ActaAgri-

culturaeScandinavica, Supplement20: 11-25.

Smith,F.W. 1974. ^Theeffect of sodium ^onpotassium nutrition and ionic relationsin Rhodes grass. Aus- tralian Journal of Agricultural Research 25: 407-414.

Smith, G.S. ^&Middleton, K.R. 1978.^Sodiumand potas- sium content of topdressed pasturesinNew Zealand

inrelation to plant and animal nutrition. New Zea- landJournal ofExperimental Agriculture6:217-225.

-

, Middleton, K.R. ^&Edmonds, A.S, 1980.Sodium nu- tritionof pasture plants. 11.Effect of sodium chloride ongrowth,chemical composition and reduction ofni- tratenitrogen. New Phytologist84: 613-622.

Thomas,G.W. 1982.Exchangeablecations.In:Page,A.L.

etal. (eds.). Methods of Soil Analysis.Madison,Wis- consin,American Society of Agronomy. Agronomy9, 2: 159-164.

SELOSTUS

Timotein natriumlannoitus

Tommi PeltovuorijaMarkku Yli-Halla

Helsingin yliopisto

Suomessa nurmikasvien natriumpitoisuus onpaljon pienempi kuinlypsykarjan rehun pitoisuudeksi suo- sitellaan. NurmirehunNa-pitoisuuden kohottaminen parantaisi senravitsemuksellista laatuajalisäisi joi- denkin tutkimuksien mukaan rehun maittavuutta.Eri- tyisenvähän natriumia^ontimoteissä. Astiakokeessa selvitettiin Na-lannoituksen (0, 200tai 400mg T1

kokeen alussa) vaikutusta timotein Na-, K-, Ca-ja Mg-pitoisuuteen jaK-lannoituksen (0, 100tai200mg 1

1

jokaiselle korjatulle sadolle) vaikutusta Na-lannoi- tuksen tehoon kolmella erimaalajilla.

Natriumlannoitus ei vaikuttanut timotein kuiva- ainesatoon,mutta sekohotti timoteinNa-pitoisuutta selvästi kaikilla maalajeilla jakaikissa korjatuissa sadoissa. Hieta-jaturvemailla vaikutus oli voimak-

kaampaakuin savimaalla, Kaliumlannoitus jamaan suuriK-pitoisuusheikensivät Na-lannoituksen tehoa erittäin voimakkaasti. Natriumlannoitus toimi tehok- kaimmin,kun timoteinK-pitoisuus laski lähelle puu- tostilaa (alle 15gkg^’)- Näinpieniin K-pitoisuuksiin päästiinvain ilman K-lannoitusta kasvaneissakoejä- senissä hieta- ja turvemailla. Natriumlannoituspie- nensijonkin verrantimoteinCa-pitoisuutta,mutta ei K- eikä Mg-pitoisuutta. Natriumlannoituksen näen- näinen hyväksikäyttöasteoli kaikilla mailla alle 4^%.

Natriumia timoteitä tehokkaammin ottavien nurmi- kasvilajien (koiranheinä, raiheinä) viljelysaattaaolla timotein Na-lannoitusta parempi keino nurmirehun Na-pitoisuudenkohottamiseksi.