PertanikaJ. Trap. Agric. Sci. 18(3): 149-157(1995) ISSN: 0126-6128© Universiti Pertanian Malaysia Press

Ammonium (NH4+): Nitrate (N0

3-) Ratio and its Relation to the Changes

in Solution pH, Growth, Mineral Nutrition and Yield of Tomatoes Grownin Nutrient Film Technique

MOHD. RAZI ISMAIL and ABD. AZIZ OTHMANDepartment of Agronomy and Horticulture

Faculty of AgricultureUniversiti Pertanian Malaysia

43400 UPM Serdang, Selangor, Malaysia

Keywords: NH4+: NO;- ratio: growth, pH, water uptake, yield, blossom-end rot, mineral nutrition

ABSTRAKPengaruh nisbah NH/,NO;- terhadap pertumbuhan, pengambilan air, pH larutan, pemakanan tanaman danhasil tanaman tomato telah dikaji menggunakan teknik nutrien cetek. Enam perlakuan rawatan nisbahNH/:NO;- telah diberikan kepada tanaman: 0:100 dengan dan tanpa kawalan pH; 12.5:87.5, 25:75,37.5:62.5 dan 50:50 tanpa kawalan pH. Kajian mendapati pH didalam larutan meningkat apabila beradadi dalam NH/:NO;- dengan nisbah 0:100 dan 12.5:87.5, tetapi menurun pada nisbah 50:50. NisbahNH/:NO;- yang tinggi mengurangkan pertumbuhan daun dan akar tanaman. Pengurangan ini mungkin disebabkan oleh pengurangan pengambilan air. Berat basah buah juga dikurangkan dan peratus kejadian rcputhujung buah meningkat apabila tanaman didedahkan pada nisbah NH/:NO;- yang tinggi. Nisbah NH/:NO;­yang tinggi meningkatkan kandungan N dan mengurangkan kandungan Ca dalam bahagian tisu tanaman.Kandungan P, K dan Mg menurun didalam tisu daun dengan peningkatan nisbah NH/: NO;-.

ABSTRACTThe effects ofNH/:NO;- ratio on growth, water uptake, solution pH, mineral nutrition and yield of tomatoes wereinvestigated using the nutrient film technique. There were six NH/:NO;- ratios: 0:100 with and without pHcontrol; 12.5:87.5, 25:75, 37.5:62.5 and 50:50 without pH control. There was an increase in pH ofthe nutrientsolution with 0:100 and 12.5:87.5 ratios, but the pH decreased with 50:50 ratio. Higher NH/:NO;- ratioreduced leaf and root growth. The reduction in leaf and root growth could be attributed to reduction ofplant wateruptake. Fruit fresh weight was reduced and the percentage of blossom-end rot increased with higher ratio ofNH/:NO;- in the solution. Increased ratio of NH/:NO;- increased N content and decreased Ca content in allthe plant tissues. P, K and Mg content decreased in leaf tissue with increasing NH~+:NO;- ratio.

INTRODUCTION

Cultivation of tomatoes by conventionalmethods on soil in lowland areas of Malaysia islimited due to the unfavourable weather andoccurrence of soil-borne pathogens. Toovercome these limitations, the technology ofsoilless crop production has been developedand has proved advantageous (Lim 1985).Nutrient film technique (NIT) is one of thesoilless culture systems used for cultivation ofhorticultural crops.

One factor that may contribute to theeffectiveness of mineral nutrition in NIT systemis the form of nitrogen added to the nutrientformulation. In common with conventionalmethods, nitrogen is supplied to the plants inthe form of ammonium ion (NH

4+) and/or

nitrate ion (NOs-)' Cooper (1979), Iwata (1983)and Ikeda and Yamada (1984) reported thatgrowth and plant development are enhanced bythe use of NOs- in the fertilizer formulation.However, there are also reports indicating better

MOHD. RAZI ISMAIL AND ABD. AZIZ OTHMAN

growth if both NH4+and N0

3- are used as the N

source (Cox and Reisenauer 1973; Follett andDoaglas 1987). Costellane et ai. (1987) reportedmaximum growth of tomatoes when 25% NH/was used in the liquid feed. Similarly, Monneratet aL (1982) reported that NHtN03' ratio of60:40 resulted in increased dry weightaccumulation. NH

4+salts are cheaper sources of

nitrogen than N03- salts. Furthermore, uptake

of NH4+ is usually coupled with H+ enrichment

in the nutrient solution which consequentlyminimises the rise in solution pH.

This study was undertaken to investigategrowth, water uptake, changes in solution pH,mineral nutrition and yield of tomatoes grownin NIT-trough system.

MATERIALS AND METHODS

The experiment was conducted at theHydroponic Unit, Universiti Pertanian Malaysia.The plants were grown under glasshouseconditions with air temperatures ranging from27-35°C and relative humidity of 65-80%.

Four-week-old uniform-sized tomato(Lyropersicon esculentum Mill) plants var. SweetChelsea were transplanted into the NIT-troughsystem. The plants were grown in therecirculating water for one week and thensubjected to treatments of six H 4+:N0 3­

treatments (Table 1)The NH/:N0

3- ratio was calculated based

on the concentration of salts used in the nutrientformulation. Cooper formulation full strengthsolution (Cooper 1979) was modified so that thedesired H

4+:N0

3- ratio was achieved while the

N level was maintained. Chloride and sulphatesalts were used to replace specific cations andanions and to maintain a constant solutionconductivity. The treatments were arranged in arandomized design with four replicates. Sevenplants spaced 40 cm apart in a trough

represented a replicate. Each trough had its owncatchment tank supplying nutrient solution tothe plants (Jarret and Charter 1981). Troughswere spaced 55 cm apart.

As the relative concentration of salts was notcontinuously monitored, the nutrient solutionin the catchment tank was replenishedfortnightly. When new nutrient solution wasprepared, pH was adjusted to 6.0 using sulphuricacid, after which it was not readjusted. Changesin pH were monitored daily.

Mter 14 weeks, plants were sampled for leaf,root and stem dry weight by oven drying at 80°Cfor 48 hours. Leaf area was determined using anautomatic leaf area meter (Delta-T Devices).Leaf area index (lAI) was recorded in week 7using a 'Plant Canopy Analyser' (LiCor 2000).

Plant water uptake was recorded over 24hours by measuring water loss from thecatchment tank. Accumulation of radiantenergy was also recorded concurrently withwater loss from the catchment tank usingsolarimeters attached to a microvolt integrator(MV2, Delta-T Qevices).

Flower number was recorded to determinefruit set in the various treatments. Fruits wereharvested at the orange to red stage and thenumber of fruits and their fresh weight wererecorded. Fruit physical characters were alsorecorded. Fruit diameter was recorded using avernier caliper. Total soluble solids weredetermined from 2-3 drops of expressed fruitjuice using a hand refractometer. Fruit dryweight was determined after 72 hours ovendrying at 80°C.

Nutrient analysis was performed on drysamples of plant parts according to the standardprocedure described by Mohd. Haniff et ai.(1990). Plant parts were sampled in week 5 and12 for mineral nutrition determination. Total N,P and K were determined using an autoanalyser

150

TABLE INHt N0

3- ratios of fertiliser used in nutrient film technique experiments on tomato

Treatment NH; NO; pH

TI 0 100.0 maintained at 6.0T2 12.5 87.5 not controlledT3 25.0 75.0 not controlledT4 37.5 62.5 not controlledT5 50.0 50.0 not controlledT6 0 100.0 not controlled

PERTANIKAJ. TRap. AGRIC. SCI. VOL. 18 0.3, 1995

AMMONIUM (NH,'): NITRATE (NO;) RATIO AND PlANT DEVELOPMENT

(Technicon Auto Analyser). Ca and Mg weredetermined using an atomic absorptionspectrophotometer.

RESULTS AND DISCUSSION

pH of Nutrient Solution

The pH fluctuated within a narrow range In

weeks 3 and 4 (Fig. la). At this stage, plantswere probably capable of absorbing thenutrients actively, which would result in lessimbalance of nutrients in the catchment tank.By weeks 5 and 6, pH of 100% NO~ in T6,showed a marked increase (Fig. 1b). On theother hand, nutrient solution containing NH/ratio of more than 37.5% resulted in a declinein the pH level, but did not fall below pH 5.5.In weeks 7 and 8, the pH for T6 exceeded 7.3(Fig. 1c). In contrast, when the proportion ofNH

4' was 50% (T5) the pH in the nutrient

solution did fall below 5.5. The changes in pHdetermined in weeks 10 and 11 followed asimilar trend as weeks 5 and 6 (Fig. 1d). Thehigher pH values obtained with higherproportions of NOg- agree with those observedby Ikeda and Osawa (1981). In contrast, higherproportions of NH

4' (T4, T5) resulted in

decreased pH in the nutrient solution, whichis attributable to acidification of the nutrientsolution due to the release of H+ in the activetransport of nutrients, a phenomenon reportedby other investigators (Maynard and Barker1969; Qasem and Hill 1993).

Plant Vegetative Growth

Table 1 illustrates leaf, stem and root growth asinfluenced by different NH/:N03' ratios. Leafarea and dry weight were significantly reducedwith NH

4+ higher than 37.5% in the nutrient

solution. For leaf area, increasing the proportionof NH/to 37.5 and 50% caused a 17% and 20%reduction in leaf area compared with the 100%NOg- treatment.

Treatments with higher proportions of NH/reduced plant dry weight, the reduction beinggreatest in the roots, followed by stems andleaves. The NH

4+ ions hasten breakdown of

carbohydrates (Barker et al. 1965), uncouplephotosynthetic phosphorylation (Gibbs andColo 1959) and playa significant role in thedisruption of chloroplast membrane (Purichand Barker 1967).

The present study did not attempt to confirmthe above-mentioned role of NH/, but itprovided evidence that there may be a possibleeffect on plant-water relations which causedreductions in leaf area and dry weight. Fig. 2illustrates the of influence NHtN03- ratio onplant water uptake. Water uptake was reducedwith higher proportions of NH

4+; the effect was

particularly obvious with increasing irradiance.The role of water relations in influencing growthwhen plants are subjected to increasing NH/ inthe nutrient solution agrees with reports by Pilland Lambeth (1977) and Pill et al. (1978).Quebedeaux and Ozbun (1973) suggested NH/N alters the physiological mechanisms involvedin uptake and movement of water. The inhibitoryeffect of NH/ on water uptake may involve twomechanisms: NH

4+ may directly interfere with

water uptake, and NH/ may cause an anatomicaland physiological change requi~ing a longerperiod for recovery.

Yield

The effect of NHtNOg- ratios on fruit freshweight is consistent with fruit yield being reducedas NH4' ratio increases. Increasing the proportionof NH/ to 25, 37.5 and 50% resulted inreductions in fruit fresh weight compared with100% N03- (Table 2). This reduction in fruitfresh weight may result from reduced assimilatebeing translocated due to reduced leaf areawhen the proportion of NH/ is higher.Increasing the proportion of NH

4+to more than

25% significantly increased the percentage offruits with blossom-end rot (BER) (Table 3). Itis well known that this disorder in tomatoes isassociated with reduced Ca++ translocation to thegrowing region of the fruit (Cerda et al. 1979;Ehret and Ho 1986). Moreover, the partitioningof Ca++ concentration in different regions ofleaves and fruit shows a clear involvement ofNH

4+in suppressing the translocation of Ca++ to

growing region (Fig. 3). Ca++ concentration inthe root did not differ indicating that Ca++ uptakeat the root surface was not inhibited by thepresence of NH

4+at early stages of plant growth,

but deficiency in Ca++ may arise fromtranslocation to the actively growing regions.The NH/:NOg- ratio did not produce anappreciable effect on fruit size, total solublesolids and percentage of fruit dry matter.

PERTANlKAJ. TROP. AGRIC. SCI. VOL. 18 NO.3, 1995 151

MOHO. RAZI ISMAlL ANO ABO. AZIZ OTHMAN

co..-<...,:l.....o.,...,cOJ

..-<t....,:lC

.....o

(a~ 7':

7.e

5..5 \

r,b) 7.5

7.0

5..5

6.0

5.5

'"c.

(e) 75

c0

..-< 70...,:l

(3., Go...,cOJ

..-< SOt....,:lC

..... ~.~

0

'"c. 5.0

o s

8

10

to

12 14

14

Cd)

5.0'0

o

2

4

10

10

12

12

14

Fig. 1: Changes of pH in the nutrient solution influenced lJy NH;:NO; ratio at various durationsa) weeks 3-4 b) weeks 5-6 c) weeks 7-8 d) weeks 9-10

Fig. 3: Distribution of Ca in leaves, fruits and roots atweek 5

600

500'0c"'~

400E<II~

!9~ 300:::l...~

"' 1:i-i4 ::it 3.... 200 0: 100C.!l! 25: 75~ 50: 50

lsdO•05

100 II 0: 10025: 75

0 2 3 4 5 6 7 8 9 10 50: 50lsdO. 05

Fig. 2: Plant water uptake (ml/plant) as influenced lJyaccumulated radiant energy at different NH;:NOJ'

ratios. 0=0.100; -=25:75 and .1= 50:50. Meas·urement of radiant energy was done conecurrentl)with the plant water uptake throughout the daytherefore radiant energy is not replicated

r:-:~: 1:03

[:in

0:100 o. :1~25: 75 0.31050: 50 0.214

15(0.05 n.5

II 0:100 0.37425: 75 0.37050: 50 0.249

lsdO. 05 n.s

III 0: 100 0.32325: 75 0.302

I50: 50 0.035

lsdO• 050.114

w. 4':m3Hin

0: 100 O. :5525: 75 0.55E50: 50 0.555

lsdO•05 n.s

152 PERTANIKAJ. TROP. ACRIC. SCI. VOL. 18 NO.3, 1995

AMMONIUM (NH:>: NITRATE (NO;) RATIO AND PLANT DEVELOPMENT

TABLE 2Leaf area, leaf, root and stem dry weight of tomato plants subjected to different NH::N03' ratios. Tl=0:100

(pH adjusted to 6.0), T2=12.5:87.5, T3=25:75, T4=37.5:62.5, T5=50:50, T6=0:100; T2-T6 (pH not adjusted)

Dry weight (g/plant)Treatment Leaf area (cm2) Leaf Stem Root

Tl 6309.30 40.2 32.6 21.7T2 5933.00 38.8 31.1 20.0T3 6061.30 38.6 28.9 20.1T4 5252.50 36.6 29.3 18.5

T5 5110.30 38.1 29.7 20.6

LSDo.o5 761.20 1.9 ns 2.1

TABLE 3Effects of NH::N0

3' ratio in the nutrient solution on fresh weight production of tomatoes

Treatment Flower Fruit Fresh weight % of BER Fruit % dry Totalnumber number (g/plant) diameter matter soluble

(unit) (unit) (mm) solids(%)

Tl 62 36 915.55 0 35.27 5.51 4.90T2 62 34 886.35 2.57 34.15 5.37 4.97T3 64 34 688.67 17.97 34.27 5.53 5.00T4 60 33 623.91 24.37 34.65 5.48 5.05

T5 62 34 533.72 37.75 34.70 5.42 5.07T6 61 36 857.42 2.72 34.70 5.30 4.72

LSDO.05 ns ns 118.12 4.35 ns ns ns

Means of 4 replication; NH::N03' ratio of; Tl & T6=0:100 (with and without pH controlled); T2=12.5:87.5;

T3=25:75, T4=37.5:62.5 and T5=50:50; T2-T5 (without pH controlled)

Mineral Nutrition

Fig. 4-8 illustrate the partitioning of total N, P,K, Ca and Mg in different parts of the plant. Inweek 5, N concentration in young leaves andfruits generally increased with the concentrationof NH

4+ in the solution (Fig. 4). Similarly, by

week 12, increase in N ratio significantlyincreased N in all parts of the plant except inthe stem. The percentage of P in the youngleaves at both harvest dates increased withincrease of NH

4+ in the N ratio (Fig. 5).

Changes in the percentage of Pareassociated with the mechanism of active uptakewhere anions such as P are present in higherconcentration when NH

4+ is used as nitrogen

source (Costellane et al. 1987). Similarmechanisms also apply when referring to Klevel (Fig. 6) in the plant parts where inorganic

cations such as K+ is depressed with increasingNH

4+ (Mengel and Kirkby 1982).The effect of increasing the proportion of

NH4+ on Ca++ at both harvest dates is illustrated

in Fig. 7. Increasing the proportion of NH4+ to

more than 35% significantly reduced thepercentage of Ca++ in the young leaves at bothharvest dates and in mature leaves, stems, rootsand fruits at week 12. Pill et aL (1978) indicatedthat NH

4+ uptake must be accompanied by either

inorganic anion uptake and/or higher organicanion production, or reduced uptake orinorganic cations. Furthermore, higher solublesalt concentration of substrate under NH +

4

nutrition may render divalent ions less availablethan monovalent ions. Our results showed thatthere were no significant differences (P>O.05)between treatments on Ca++ level in roots when

PERTANIKAJ. TROP. AGRIC. SCI. VOL. 18 NO.3, 1995 153

MOHD. RAZI ISMAIL AND ABD. AZIZ OTHMAN

FruitsRootsStemsYoungLeaves

FruitsRootsStemsMatureLeaves

YoungLeaves

5

3

0 11""'.""

Fig. 4: Effects of NH/:NO; ratio on the N content in various parts of the planta) week 5 b) week 12.

FruitsRootsStemsMature.Leaves

YoungLeaves

FruitsRootsStemsMatureleaves

Youngleavt;!:s

.. p2.5 .S.5

32

2.5

1.5

1.5

Fig. 5: Effects of NH/.NOJ- ratio on the P content in various parts of the planta) week 5 b) week 12.

FruitsRootsStemsMatureLeaves

YoungLeaves

.. K7~-----------""'------"'I

FruitsRootsStemsMatureLeaves

YoungLeaves

Fig. 6: Effects of NH;:NOJ• ratio on the K content in various parts of the planta) week 5 b) week 12.

154 PERTANlKAJ. TROP. AGRIC. SCI. VOL. 18 NO.3, 1995

AMMO IUM ( H;): NITRATE ( 0;) RATIO AND PlANT DEVELOPMENT

FruitsRootsStemsMatureLeaves

YoungLeaves

2

o

, ca3r---;:------------------,

2.5

0.5

FruitsRootsstemsMatureLeaves

YoungLeaves

Fig. 7: Effects of NH;:NO)' ratio on the Ca content in various parts of the planta) week 5 b) week 12.

,Mg0.25r----------------------,

0.3

0.2

0.1

YoungLeaves

MatureLeaves

Stems Roots

0.2

0.15

0.1

0.05

oYoung Mature Stem Roots Fruits

Fig. 8. Effects of NH;:NO)' ratio on Mg content in various parts of the planta) week 5 b) week 12

sampling was done in week 5. Evans and Troxler(1953) suggested that higher rates of organicacid synthesis as a result ofNH4+may immobilizeCa++ within the roots. However, sampling in week12 saw Ca++ levels significantly reduced withincreased proportion of NH4+.

The effect of the NH/:NO~+ ratio on thepercentage of MgH was not pronouncedexcept for mature leaves when sampled inweek 12 (Fig. 8). Leaf MgH decreased at thehighest NH/:NO~- ratios. The mechanism ofthis reduction may be similar to those of Caand K.

CONCLUSION

The reduction in plant growth with increase inthe H4+:NO~- ratio could be due to theimbalance of nutrient uptake resulting fromchanges in the plant-water relationship. Therewas a clear increase in fruits with BER withincrease of NH4+in the nutrient solution. Sincethe occurrence of BER is related to Ca++concentration, it may be necessary to increaseapplication of Ca when fertilizer containing ahigh proportion of NH4+ is used in order toreduce the severity of NH/ related BER.Although NH4+is useful in controlling pH level

PERTANlKAJ. TROP. AGRIC. SCI. VOL. 18 NO.3, 1995 155

MOHD. RAZI ISMAIL AND ABD. AZIZ OTHMAN

in the nutrient solution, our results suggestthat this advantage is offset by the lower yieldsobtained at higher NH/:NOgo ratios. Therelationship between NH

4+and changes in plant

water needs to be explored in detail. The properNH

4+:Ca++ ratio in the nutrient solution needs

to be determined under conditions where theN form is NH

4+.

ACKNOWLEDGEMENT

This research project was funded by IRPAHydroponic Research Grant (50307) of theFaculty of Agriculture, Universiti PertanianMalaysia.

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AMMONIUM (NH:>: NITRATE (NO;) RATIO AND PlANT DEVELOPMENT

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(Received 29 November 1993)

(Accepted 11 December 1995)

PERTANlKAJ. TROP. AGRIC. SCI. VOL. 18 NO.3, 1995 157