The Influence of Root Zone Temperature on Phosphorus Nutrition of Sugarbeet Seedlings

KONSTANlINOS M. SIPITANOS AND .\LBJ,;RT ULRICH'

Received for imblieation October 8, f970

Introduction

Among the major factors influencing nutrient absorption, and thereby plant composition , are the nutrient supplies of the soil and soil temperature (12)2 . Soil temperature has been rec­ognized for a long time as a factor influencing sugarbeet com­position and growth (20). Sailsbery ei al. (17) found a striking visible respome of sugar1)eets to P-fertilization early in the sea­son in five fields when (he NaHCO] soluble soil-P levels had a range of 4.5 to 8.4 ppm. By mid-]\'Tay leaf analysis showed that nonfertilized plants were taking up sufficient phosphorus for maximum growth. It was concluded, therefore, that the period of P-deficiency occurred very early in the growth period of the plants. This conc!u~ion was also supported by their finding that by midseason the visible differences in top growth had largely disappeared. They also reported that in one trial where the soil-P level was 22 Pf"n there was no visual response to phos­phorus, even early in the season.

The response of sugarbeet seedlings to P-fertilization in soils low to incermediate in NaHCO. soluble-P may therefore be attricuted to the low soil temperatures prevailing at the seedling stage of development in contrast to the higher soil temperatures preva iling when sugzrbeet plants are large. It is the purpose of the present study to determine the influence of soil tempera­twe and of P-fertilization on plant growth and on the concen­trations of soluble-P and NO,,- ]\; of tissues of sugarbeet -seedlings from early to very late thinning stages of development.

Materials and Methods Plant cultuTe

An Imperial silty clay soil at the 0-30 cm depth from the Imnerial Valley Field Station, Meloland, California, was used in the pot experiment. The soil had a pH of 7.95 (1 to 2.5, soil to water suspension) and a NaHCO:)-soluble P concentration of 8.8 ppm. Soil temperatures during the experiment were main­tained at 5, 10, 15, 20, 25, and 30' C by means of thermostatical­

1 Instructor, Lahoratory of AgriclIllIIral Chemistry, University of Thessaloniki , Thessa­Ioniki , Greece, and Plant PhYSiologist, U ni versity of Ca lifo rnia , Berkeley.

"N umbers in paren th eses refer to literature cit ed.

VOL. 16, No.5, AP RIl. 1971 <l09

ly controlled water baths. Ammonium nitiate, C.P., was applied to the soil for all treatments at the rate of 336 kg- of N per hec­tare (300 Ibs of ::--J per acre). Phosphorus was applied to the soil in the form of C.P. monocalcium phosphate monohydrate [Ca(HZP04)2 0HzOJ at the rate of Po = control (without P addi­tion), P, = 16.8 kg- of P per ha (15 Ibs PI A), Pz = 33.6 kg of P per ha (30 Ibs P / A), and P 4 = 67.2 kg of P per h a (60 1bs PIA). The four phosphorus treatments were replicated six times and arranged in a randomized complete block design in each of the six temperature baths, but there was no replication of temperature. The one-gallol1 cans, without holes, used to hold the soil, were painted on the inside and outside with non-toxic plastic (Amercoat ~o. 33).

Four hundred grams of washed salld was spread to a depth of 1.5 cm over the bottom of each ca n . /\ glass tube, one cen­timeter inside diameter, was next inserted to the bottom of the can so that an excess of soil moisture, as soil extract, could be detected immediately after each watering and removed by suc­tion and returned to the pot at the nf'xt watering. In this way soil moisture was maintained near field capacity throughoLlt the experiment by w;;,tering the pots as required from the sur­face 'w ith distilled water. Three k ilograms of air-dri ed soil were then added to each container. Appropriate volumes of phos­phorus and nitrogen in solution were made to 500 ml with dis­tilled water and then poured uniformly over the soil surface one day before the seeds were sown. /\dditions of N or P were based on a hectare of soil weighing 2,240,000 kg, which is equivalent to 2,000,000 Ibs per acre of soi l. Thus an applica­tion of 112 kg of N or P per hectare is equivalent to 100 Ibs of :'\ or P per acre of 0.150 gar N or P to 3,000 g of soil.

Sugarbeet seeds (Beta v lllgaris) var. F 58554 H " i.e., F, H y­brid) treated with Phygon XL at a 1% rate, were planted on April 23, 1968. Two seeds were placed in e:>ch of twel~ equally spaced positions, 3 cm away from the wall of (he can . The seeds were then pressed gently to the surface level of the soil. The seeds and soil were covered uniformly wi"h 35 ,grams of dry vermiculite (1.5 cm in depth) and then watere.::l with 200 ml of distilled water. The layer of vermiculite leduced the :lea t transfer between the soil and the atmosphere, decreased mois ture losses, and provided a good, hon10geneous surface for seed emJ­gence. Immediately after planting, the 1o~s were placed in the water baths below the vermicu lite level. In t~ i s way the seeds and later the roots of the seedlings were oal ta inec( at th e de­sired temperature during the experimen t. The aerial tempf'ra­ture in the smog-free clear-glass greenhouse did not exceed 30 °C during the day and did not fall below 17°C during the night.

410 JOVRl" ,\L Of THE A. S. S. B. T.

Thinning) harvesting, preparation of samples and chemical analy­StS

The seedl ings were thinned for the first thinning to 12 peT pot at the mid 2-leaf stage. This is abou t the normal time of thin­ning under field conditions. The date of thinning, however, de­pended on the soil temperature (15); it was on 6/ 19, 5/ 21 and 5/ 15/ 68, for 5, 10, and 15°C, respectively and on 3/~/68 for 20, 25, and 30C. The second thinning was made at about the mid 3-leaf stage of development for the temperatures of 5, 10, and lSoC, on 6/28/68, 5/ 27168, and 5/21/68, respectively, and for 20, 25, and 30"C, on 5/ 14/ 68; and for the third thinning at about the mid 4-leaf stage for 5, 10, and 15°C on 7/ 3/ 68 , 6/ 3/ 68, and 5/ 24/ 68, respectively, and for 20, 25, and 30°C, on 5/ 20/ 68 .

Harvesting at the first thinning consisted of taking the tops of all thinned seedlings; at the second thinning, the tops of every other plant, and at the third thinning the tops of the re­maining six plants. The seedlings were cut at ground level, weighed and separated into a) cotyledons and b) first pair of leaves formed. The leaves were then separated into blades and petioles. The cotyledons, blades, and petioles for each pot were weighed separately, placed into separate paper bags and dried at 70 to 80 C in a forced draft oven to constant weight. The dried plant material was ground in an oscillatory ball mill made of plastic (vVig-L-Bug amalgamator, Crescent Dental Mfg. Co. , Chicago, Illinois) and then stored in plastic vials for chemical analysis.

The plant samples were analyud: a) for phosphorus soluble in 2% acetic acid by the ammonium molyhdate-stannous chloride method (2), and b) for nitrate-nitrogen by the phenoldisulfonic acid method, after removing chlorine (2).

Results and Discussion Seedling emergence

The first seedlings in the experiment emerged at 30°C in all pots on April 26, 1968, only 3 days after planting. Those at 25, 20, 15, and 10'C emerged on 4/27 / 68, 4/28/68, 4/ 29/68, and 5/ 1/ 68, respectively. Finally, at 5°C the first seedlings emerged in the Po treatment on 5/ 5/ 68, in the P 1 and Pz-treat­ment, 5/ 6/ 68, and in the P ,-treatment on 5/7/ 68 .

The time in days for the emergence of at least 50% of the seeds planted for the various phosphorus treatments and soil temperatures are given in Table 1. The results indicate that emergence takes place in 6 days at 25 and 30°C, 7 days at 20 'C, in about 9 days at 15°C, in 11.5 days at lOoC and in about 23 days at 5 °C. Apparently the optimum temperature for emer­gence lies in the region of 25 to 30°C.

VOL. 16, No.5, A PRIL 1971

Table I.-Time in da),s for 50% emergence of sug'arbeet seeds as affected by phos­phorus treatment and root zone temperature.

Root zone tenlpera tu re Phosphorus treatment*

°C Po p , p, P.

5 22.8dD 23.0dD 23.3eD 23.5dD

IO 11.7cC 11.3cC 11.5dC 13.0cC

15 8.7hB 9.2bB 9.2cB 8.8bB

20 7.0aA 7.0aA 7.0hA 7.0aA

25 6.0aA 6.0aA 6.0aA 6.0aA

30 6.0aA 5.8aA 5.7aA 6.0aA

It All values are means of six replications. :Means ·within a column followed by a common sma)1 or large letter do not dfEfer at the 5% or I % level of sig'nificance, respectively, as shown by Duncan's i'vlultipl e Range T es t. P, = 15 Ibs PIA or 16.8 kg' P/ha or 0.0225 g P/pot.

A better estimate of the optimum temperature for germina­tion can be made from the seedling top dry weights presented in Tahle 2 for the first thinning for the soil temperatures of 20, 25, and 30 J C. These values vvere obtained for seedlings harvested on the same day, May 8, 1968, and indicate that the highest seedling dry weight was obtained at 25 'C for all phos­phorus treatments. Leach (5) also found that the emergence of sugarbeets was most rapid at soil temperatures of 25 and 30°C, with the highest total emergence at 23°C.

Phosphorus fertilization had no effect on emergence of sugar­beet seeds, using the criterion of least time required for the appearance of the first or last of the seedlings (15), except in the case of 5°C soil tern perature, where the seedlings in the un­fertilized pots appeared first and those in the P 1-treatment ap­peared two days later. Also, phosphorus had no effec;t on the rate of emergence as measured by the seed-day method (14).

Visual symptoms of P-deficiency Plants at root zone temperatures of 20, 25, and 30°C did not

show any visual P-deficiency symptoms during their growing period, whereas those at 5, 10, and 15°C showed all the char­acteristics of visual P-deficiency symptoms (18) from the time of emergence to harvest, These symptoms became more severe with time at 5'C than at 15 L C, and at lower P-treatments than at higher ones. In addition, these plants showed symptoms similar to iron deficiency on the first pair of leaves. The symp­toms became less severe with time, but were more severe at 5 and less at 15°C. 'Cnfortunately the plants have not been an­alyzed for iron to verify the deficiency,

Table 2 . - Effects of phosphorus treatment and root zone temperature on dry weigh t of tops at the first, second and third th innings. *" ~

Ory tops, mg per plant *

Phos­phorus 5° C 10° C ISo·C 20°C 25°C 30°C treat ­mentH

570** 660 7ID 280 340 4ID 220 280 3ID ISO 2ID 270 ISO 2ID 270 ISO 210 270

M2L L2L L2L M2L L2L M3L M2L E3L M3L M2L M3L M4L M2L M3L M4L M2L .M3L M4L

Po 26a 44aA 6 1aA l7a 34aA 82aA 12aA 66aA 15 1aA 12a 79aA 279aA 16a 97aA 256aA 12a 70aA nOaA

293++ 30a 74bcA 163bB 15a 47aA 132bA 12aA 87bA 198bA 12a Ill bB 396bB 18a 11 2aA 466 bB 14a 78aA PI

32a 66bA 234eB 19a 6 1 bAB 233eB I7 bA 104cA 274cB 12A 11 7 bB 52 1cC 16. 13 1bA 432bB 13. 90abA 36S bBP2 '-< oc:

35a 133 dB 32 1dC 15a 73b B 296dC 20bA 149dB 31 7dB 14a 143cC 577cC 19a 16 1eB 53 1bB 15a 96 bA 344bB P4 "z ;,. r o "1 ...,

* All va lues are mea ns o f six rep lica tio ns except when less than six as indica ted by ++. Means within a co lumn followed by a common small or large letter do not ~ differ at the 5% or 1% level of sig nificance , respectively, as shown by Duncan's Mult iple Range Test. ~

Y>

* * D = days; ~2L = mid 2-leaf stage ; M3L = mid 3-leof stage ; M4 L = mid 4-leaf stage ; L2 L = late 2-leof stage; E3 L =ea rl y 3-lea f stage. Y>

~

11 PI = 15 Ibs PIA or 16.8 kg Pl ha or 0 .0225 g Plpo t. >-l

VOL. 16, No.5, APRIL 1971 413

Seedling top dry weight Sugarbeet seedlings grew less as root zone temperature was

lowered from 20 to SoC. Similar results have been reported for corn (3) and tomato (6) seedlings, for tomatoes (7,1), corn and bromegrass tops (8), clover (16), corn (4), sugarbeets (10,20) and piper sudangrass (19). The effects of soil temperature on plant growth have been reviewed up to 1952 by Richards et al. (IS) and up to 1966 by Nielsen and Humphries (9). Radke and Bauer (13) have reported that there is no information available on the growth rate of sugarheets as influenced by soil tempera­ture after the seedlings have emerged.

The dry weight of the seedling-s for the first thinning- was not influenced by phosphorus treatment (Table 2), except at 15"C, where a significant increase in top growth was observed for the P2 and P ! treatments. The response to phosphorus at l S' C was correlated with a phosphorus deficiency of the un­trea ted plants (Table 4) and with the extra growth made by the phosphorus treated plants (Table 2). Apparently, a phos­phorus respo -:se requires three events to take place: (a) the untreated pIa ts must become deficient in phosphorus, (b) the treated plants must absorb and translocate the phosphorus ap­plied, and (c) a sufficient time period must elapse for the re­sponse to take place. Thus, at the first thinning, the untreated plants at 15°C were deficient in phosphorus, whereas the treat­ed plants absorbed some of the applied phosphorus and there was sufficient time for a response to be observed and measured . At 5'C the seedlings were deficient in phosphorus (Table 4), but phosphorus was not ahsorbed and therefore no response took place. At lOoC the seedlings were also deficient in phosphorus (Table 4) and phosphorus was absorbed in the p . treatment only, but insu£ficen~ t ime elapsed for a growth response to be ob­served at thinning. At the higher soil temperatures, 20, 2S , and 30"C, all seedlings at the first thinning were much higher in phosphorus concentration Cfable 4) and no yield response for the first thinning was expected and none was observed (Table 2).

Responses to phosphorus, however, were observed at the sec­ond and third thinnings (Table 2). At the second thinning-, phosphorus increased the yields significantly at 20 and 25°C and only slightly at 30°C (Table 2). If 1,000 ppm in the petiole is taken as the approximate critical soluble phosphorus concen­tration, then the observed increase in yield at 20°C is unexpect­ed but the increases at 2S and 30°C would have been somewhat expected, although some fungal root damage is a complicating factor at 30"C. If, however, the critical soluble phosphorus con­centration is taken as 1,500 ppm for petioles of the first pair of

>l>­->l>­Table 3. · Effects of phospho ru s treatment and root zone tem pe rature on percentage dry matter of tops at first , second and third thinnings.

Dry tops, percent*

Phos· SoC 10°C lSoe 20°C 2SoC 30°C phorus trea t·

S7D 66D 710 28D 34D 4ID 22D 28D 31D lSD 2ID 270 15D 2ID 27D 15D 2ID 27Dment

M2L L2L L2L M2L L2L M3L M2L E3L M3L M2L M3L M4L M2L M3L M4L M2L M3L M4L

Po I S.6cB 16.8cC 15 AcB 11.8cB 12.0cC 11.1 a 8.2cB 7.3bB 7.8bA 7. 8a 7.1 a · 7.0a 6.8a 6.8a 6.9a 6.0a 7.1a 8.3a

'-;PI 14.0bAB 14.9bB 14.2bAB l1.3cB 12.0cC IIAa 7.7bAB 6.6aA 6.7aA 8. 1a 7. 1a 7. 1a 6.8a 7. la 7.3a 6.2a 7.2a 8A++ 0

c ;<l z

12.SaA 13.3aA 13.6bA 10.7bB 10. 7bB 10. 9a 7.7bAB 6.6aA 6.9aA 7.9a 7.1 a 7.2a 6.6a 7.3a 7.9 a 5.8a 6.9a 8.4a :>­P2 t"

0 "1

12.2aA 12.6aA 12.6aA 9.1aA 9.8aA I 1.3a 7.2aA 7.2bB 7.0aA 7. 1a 7.3a 7.2a 6.2a 7 .2a 7.7a S.9a 7.Sa 8.SaP4 >-I ::r: ~

?> ~

~

~* See Table 2 for footnotes and definitions of symbols.

:J

<: Table 4. - Effects of phosphorus treatment and root zone tempe rature on 2% acetic acid soluble phosphorus (P0 4-P) concentration of the co tyledons at the first o

r" thinning, and of the petioles at the second and third thinnings.

~

9'

L: o

Ph os­phorus trea t­ment S7D

sDe

66D 7ID 28D

loDe

34D 41D.

Soluble phosphorus concentration in ppm (dry basis)*

Is0e 20De

22D 28D 3ID ISD 2ID 27D ISD

2sDe

2ID 27D ISD

30De

21D 27 D

Y', ;;0

r ~

to "-l

M2L L2L L2L M2L L2L M3L M2L E3L M3L M2L M3L M4L M2L M3L M4L M2L M3L M4L

Po 230aA 280aA 240a S50aA 520++ 590a 640<i 1010aA 730aA 1I I0aA l 260aA 640aA 1400aA 1080aA 710a 1530a 980++ 640.

PI 270aA 310aA 220a 580++ 510aA 590a 89 0ab 1410bB 920bA 1370aA 1680bB 740aA 15 30aA 1290bA 620. 1580a 11 30a 790++

Pz 430++ 430bA 230a 66 0aA 590aA 55 0a 840a 1780ce 990bA 1540bA 2250cC 920bA 1820bA 1560cB 760. ' 1550a 1250a 740a

P4 440bB 340aA 240a 960bA 870bB 470a 1070b 1150aA 840aA 2050cC 2070cC 860abA 1840bA 168 0cB 800a 1720a l440b 730a

*" * See Table 2 for footnotes and definitions of symbols. -""

416 JOURNAL 010 THE A. S. S. B. T.

leaves, OP, (18) then the response to phosphorus at 20 0 e (Table 2) would also be expected. At the third thinning all plants were below 1,000 ppm P04-P (Table 4), indicating that demand had exceeded phosphorus supply, and accordingly these plants were deficient in phosphorus. The growth responses observed in Table 2 are therefore associated with the phosphorus values or the plants at the second and third thinnings (Table 4).

Relative phosphorus response At the second thinning the seedling top dry weight increased

significantly with P-treatment for all root zo e temperatures. In terms of percentage change, the Pi plants increased over the comparable unfertilized plants by 202%, 11.5%, 126%, 81 %, 66%, and 37% for the 5, 10, 20 , 25, and 30"e root zone tem­perature plants, respectively.

At the third thinning the comparable increases in seedling top dry weight with the P , treatment are 426 %, 261 %, 110%, 107 %, 107 %, and 56%, respectively. It is obvious that in both the second and third thinnings the plants at the 10'wer tempera­tures have been infl uenced more by phosphorus treatment than plants at the higher temperatures. These results are in accord with those of unpublished data of Beadle, Jenny and L'lrich for a pot experiment with sugarbeets in soil in which a response to phosphorus at 10, 15, and 20 0 e was observed but not at 5, 25 , and 30 oe. They reported that at 5 G C the soil was too cold for the plants to grow appreciably, regardless of P-treatment. At soil temperatures of 25 and 30 ' e the plants absorbed ample amounts of phosphorus for growth, even from the unphosphated soil. In the present experiment there was no response to rhos­phorus fertilization at the first thinning, but at the second and third thinnings, top yields increased relativel y more with P­treatment at the lower soil temperatures. These increases were also gTeater at the third thinning, from which one may con­clude that plant age is a factor in considering sugarbeei: seedling response to P-fertilization. Similarly, Power et al. (11) r eported that by increasing the availabl e P-supply with either increased soil or fertilizer P the soil temperature range over which a nearly maximum growth for barley occurred vvas widened.

Seedling dry matter jJeTcentage The dry matter percentages of the tops for the first thinning

(Table 3) decreased with phosphorus treatment for the root zone temperatures of 5, 10, and 15°C. In the second thinning decreases in percent dry matter took place with phosphorus treatment at 5 and lO o e and at the third thinning at 5c- e only. :Major increases in percent dry m atter of the tops took place in the Po treatment a t lODe and again at Jo e , with the values of

<o r -Table 5. Effects

blades a t trealmen! and root

second thinning for 5 and temperature on nitrate~nitrogcn concentration of the

I he petioles for the second and third thinnings at ?'

z (J

.:n Nitrate-nitrogen concentration in ppm (dry basis) * »

'tl

C r

Phos- SoC 10°C J SoC loDe 2Soc 30°C <0­-1

ment 570 66D 71D l8D 34D 4lD 22D 28D 31D 15D 21D 27D 15D 210 27D ISO 21D 27D

M2L L2L L2L M2L L2L M3L M2L E3L M3L M2L M3L M4L M2L M3L M4L M2L M3L M4L

Po 1210cB 590. 1370B 2770a 570aA 3190++ 5390.A 21700aA 22000a 5910. 27500. 10000a 31900aA 28800aA 29000.

PI 810bA 850. 480A 3310++ JOOOaA 4870++ 6200bA 24900bB 24800. 6160. 29500++ ]0300. 33200bA 31000. 29900aA 29800++

P2 410++ 1350a 430++ 3340a 1590bAB 8300. 5700aA 26500l>B 24300. 6460. 30500bB 600a 10300. 34800cAB 31300a 1l700++31800bAB 32100.

P4 SIDaA 320++ 200++ 3110++ 2210bB 11200. 6300bA 25600bB 6910. 30500bB 30800. 10400a 35900cB 31400. 11300. 31600.bAB

• See Table 2 for footnotes and definitions of symbols.

>!>­

...;}

418 JOURNAL OF THE :\. S. S. B. T.

15.4 to 16.8% at 5°C more than double those of 6.0 to 8.3% at 15 to 30°C. These results agTee with those found earlier (18i.

Seedling tissue soluble phosphoru.s The effects of root zone temperature and phosphorus treat­

ment on acetic acid soluble phosphorus of the cotyledons for the first thinning and for the petioles of the first pair of leaves for the second and third thinnings are presented in 'fable 4. These values have been discussed in an earlier section on growth in this paper and therefore a discussion of these aspects will not be repeated. In general, low soil temperatures are condu­cive to low phosphorus in plant tissues, followed by poor growth from phosphorus deficiency. .'\t higher soil temperatures plant tissue phosphorus increases and better plant growth takes place. But in time, however, plants at higher soil temperatures and with phosphorus fertilization may even become P deficient, as in the third thinning when growth was rapid and the phosphorus supplying power of the soil was inadequate to meet the needs of the plants at all root zone temperatures even with fertilization (Table 4).

Seedling tissue nitrate nitrogen concentration The N 0 3-N concentration of the cotyledons at the first thin­

ning, the blades of the first pair of leaves at the second thinning for 5 and 10G C and the petioles of the first pair of leaves for the second and third thinnings for all other root temperatures are given in Table 5.

At the first thinning the N 0 3-N concentration of the cotyle­dons for the plants at the root zone temperature at 5°C de­creased significantly with Psupply up to the Prtreatment, fol­lowed by no change at p.. The plants at root temperatures of 10, 15, 20, 25 , and 30 ' C did not change significantly in N0 3-N with phosphorus treatment, but the N O ,-N values did increase appreciably with root zone temperature up to 15°C and again at 25°C and only slightly from 25 to 30°C.

At the second thinning, except in the 5°C plants, an i.ncrease in concentration of tissue N03-N took place with P-supply. This effect was more pronounced at IO ~ C than at the other tempera­tures.

At the third thinning a significant decrease in the concen­tration of tissue N 0 3-:\ took place with P-treatment at 5°C, but in the 10C plants phosphorus caused a major increase in N03-N, although at root zone temperatures of 15, 20, 25, and 30"C no significant differences due to phosphorus treatment were observed.

419 VOL. 16, No.5, APRIL 1971

Summary and Conclusions Sugarbeet seedlings were grown in the greenhouse at soil

temperatures of 5, 10 , 15, 20, 25, and 30°C in pots containing Imperial silty clay, a soil with a pH of 7.95 and testing inter­mediate in phosphorus, with a NaHCO j soluble-P of 8.8 ppm. Soil temperature greatly influenced the emergence of sugar­beet seeds, the growth of seedlings and the response to P-fertiliza­tion. The optimum soil temperature for seed emergence and seedling growth was about 25 °C. Phosphorus fertilization had no effect on emergence except at 5"C, where the P-treatments delayed emergence. Visual symptoms of P-deficiency appeared on all plants at 5, 10, and 15'C and became more pronounced with age at the low P-treatments. These plants at the early two-leaf stage showed symptoms resembling those of iron de­ficiency, which became less severe with time and progressively less pronounced from 5 to 15"C.

The relative dry-matter response to P at the second and third thinnings decreased gradually with increased root temperature over the range of 5 to 30°C. The relative increase in dry matter of tops from phosphorus fertilization was also higher at the third thinning in comparison with the same root zone tempera­ture at the second thinning. Therefore, there seems to be a plant age factor in considering sugarbeet seedling response to P-fertilization. At all harvests the percentage dry matter of the tops at 5, 10, and 15~C root zone temperature seedlings decreas­ed with increased temperature and with P-treatment. Tissue sol u bIe P concen trations tended to increase with: a) an increase in root zone temperature up to 30 c C at the first thinning, up to 20°C at the second thinning and up to 15~C at the third thin­ning, for the same P-treatment and b) with P-treatment for the same root zone temperature. It may also be concluded that for satisfactory growth of sugarbeet seedlings, growing in low or intermediate P-soils, P-fertilization is needed, since the soil tem­peratures at seedling time usually are low. In terms of growth, seedlings with petioles from the first pair of leaves with less than 1,000 ppm of phosphorus soluble in 2% acetic acid are definite­ly deficient in phosphorus a t the time of sampling, and those between 1,000 and 1,500 ppm are less likely to be deficient in phosphorus when sampled.

]OCRNAL OF THE A. S. S. B. T.

Lil~rature Cited

(1 ) DAVIS, R. IVI. anu j. C. LINGLE. 1961. Basis of shoo t response to root temperature in tomato . P lant 1'1lys. 36 : 153-1 62.

(2) J OHNSON, C. M., and A. l ·LRICH. 1959. Analytical methods for usc in plant analysis. C~lif. Agr. Expt. Sta. Bull. 766: 25-78.

(3) KETCIIFSON, J. \1\-. 1957. Some effects of soil temperature on phos­phorus req u irements of you ng corn plants in the green house. Can. J. So il Sci. 37: 41-47.

(4) KNOLL, H. A., D . J. L ATI-lWF LL, and N. C . BRADY. 1964. The influ­ence of root zone tempera ture on the growth and contents of phos­phorus and anthocyanin of corn. Soil Sci. Soc. Am. Proe. 28: '100­403

(5) LEACH, L. D. 1947 . Growth rates of host and pathogen as factors determin ing the severity of prccmergence damping-off. J. ,\gr. Research. 7S: 161-179.

(6) LINGLE, J. C., and R. i\[. DAVI~. 1959. Th e influence of soil tem­perature and phosphorus fert ili z<lLion on the growth and mineral abso rption of toma ro seedlings. Proe. Am. Soc. Hort. Sci . 73: 312·322.

(7) LOCASCIO, S. J., and G. F. ''''ARRF.N. 1960. Interaction o f soil tempera­ture and phosphorus on growth of tomatoes. Proe. Am. Soc. H ort. Sci. 75: 601-610 .

(8) NIELSEN, K. F., R. L. H ALSTEAD, ,\. J. MACLEAN, S. J. BOURGET, and R . M. Houu:s. 1961. The in tlucnce of soil temperature on the growth and mineral composition of corn, bromegrass and potatoes. So il Sc i. Soe. Am. Proc. 25: 369-372.

(S) NlELSF'i, K. F., and E. C. HD'lPHRIES. 1966. Effects of root tem­perature on plant growtll. So ils and Fert. 29: 1-7.

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