Influence of Nutrient Concentration and Composition on the Growth, UptakePatterns of Nutrient Elements and Fruit Coloring Disorder for TomatoesGrown in Extremely Low-volume Substrate

Yiting Zhang1, Yoshikazu Kiriiwa1,2* and Akira Nukaya1,2

1United Graduate School of Agricultural Science, Gifu University, Gifu 501-1193, Japan2Graduate School of Agriculture Science, Shizuoka University, Shizuoka 422-8529, Japan

In order to modify nutrient solution for tomatoes grown in extremely low-volume substrate (ELVS) combinedwith low-node-order pinching and high-density planting (LN&HD), the effects of nutrient solutionconcentration and supplemented K and P were investigated. Plant growth, nutrient uptake, and fruit yellow-shoulder disorder were measured in two experiments. Treatments included three nutrient solutionconcentration levels (0.6, 0.9, and 1.2 dS·m−1 EC) in Experiment 1 and added K or P (EC 0.9+K, EC 0.9+P)and P+K (EC 0.9+P+K) on the basis of Enshi nutrient solution at EC 0.9 dS·m−1 in Experiment 2. Tomatoes‘CF Momotaro York’ were grown in a 250 mL pot filled with granular rockwool combined with LN&HD. Ahigh-frequency and small-volume fertigation system was used based on the integrated solar radiation amount.In Experiment 1, mineral elemental uptake rate, plant growth and fruit yield increased with increasingnutrient solution concentration, and fruit yellow-shoulder disorder decreased. In Experiment 2, Psupplementation treatments of EC 0.9+P and EC 0.9+P+K largely enhanced fruit yield, shoot weight and allnutrient uptake rates. In contrast, yield improvement was not observed at EC 0.9+K, and only K uptake waspromoted in K-supplemented treatment. The fruit yellow-shoulder incidence and index tended to decrease inthe following order: EC 0.9 > EC 0.9+P > EC 0.9+K > EC 0.9+P+K. In conclusion, it was effective to increase Pand K concentrations of nutrient solution on the basis of Enshi nutrient solution formula (EC 0.9 dS·m−1), tomaintain optimal tomato vegetative growth, achieve higher yield comparable to that with EC 1.2 dS·m−1, andproduce fewer P- and K-deficiency symptoms in the case of ELVS combined with LN&HD culture by a high-frequency and small-volume application method.

Key Words: EC, extremely low-volume substrate, high-density planting, low-node-order pinching, yellow-shoulder.

Introduction

Tomato (Solanum lycopersicum L.) is one of themost important horticultural crops in Japan and its year-round supply is desired by consumers. However, it isextremely difficult to produce normal tomatoes insummer due to high-temperature conditions. Recently,plant factories using sunlight were installed in manycountries. In Japan, research on fully monitored andcontrolled culture systems integrated into natural-light‑using plant factories for year-round plant produc-tion has also been conducted (Hashimoto, 2013;Masuda et al., 2013; Noguchi, 2012; Saito et al., 2008;

Received; May 2, 2014. Accepted; October 20, 2014.Published Online in J-STAGE.* Corresponding author (E-mail: akykiri@ipc.shizuoka.ac.jp).

Toma et al., 2013).One of the culture systems applied in plant factories

is the extremely low-volume substrate (ELVS) cultiva-tion system that is known as the D-tray cultivation sys-tem (Fig. 1). For the last several years, a great deal ofeffort has gone into development of the D-tray cultiva-tion system in combination with low-node-order pinch-ing and high-density planting (LN&HD) in tomatoproduction (Egishi et al., 2012; Endo et al., 2007;Kiriiwa, 2008). The planting density is 3.6 to 5.4plants·m−2, which is about 2 to 2.5 times as dense as 2.1to 2.5 plants·m−2 in conventional tomato productionsystems by high wire layering. The distances betweenplants are usually 24 cm and 17 cm at 3.6 and 5.4plants·m−2 density, respectively. The structure of the D-tray (60 cm length, 20 cm width, 10 cm height) is char-acterized by 10 connected D-shaped pots (250 mL/pot)

The Horticulture Journal 84 (1): 37–45. 2015.doi: 10.2503/hortj.MI-003

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arranged in 2 rows, with each row including 5 pots.Owing to less water and nutrients being available in therestricted root zone, a high-frequency and small-volumefertigation system based on the integrated solar radia-tion amount should be required. Because the transporta-tion of seedlings from the greenhouse in which theywere raised, transplanting to the D-tray culture systemand cleaning after harvesting are very easy to perform,labor-saving operations can be realized. The D-tray cul-tivation system therefore enhances economic efficiencyfor tomatoes, especially in the case of LN&HD, inwhich 3.5 croppings per year are achieved in the case of3- to 4-node-order pinching (Tamai, 2014).

Compared with a tomato production system by highwire layering characterized by a normal-volume rock-wool slab substrate and nutrient solution of EC 1.6–2.0 dS·m−1 (Suzuki, 2006; Takakura, 2008), the consid-erable advantages of an ELVS cultivation system arethe low costs of nutrients and substrate material as wellas the labor-saving operations (Tamai, 2014). Whenusing a high-frequency and a small-volume, the use of alow concentration of nutrient solution below EC1.2 dS·m−1 was suggested to be feasible for tomatoesgrown in ELVS and LN&HD in our preliminary experi-ment (Egishi et al., 2012). Although the best fruit pro-duction was recorded at EC 1.2 dS·m−1, we assumedthat, if the fruit production could be improved up to thelevel of that at EC 1.2 dS·m−1 by increasing P and Kconcentrations on the basis of EC 0.9 dS·m−1 withoutincreasing vegetative growth, the plants could be keptin a compact state to accommodate an extremely smallplanting distance (17 to 24 cm).

Moreover, potassium deficiency (yellow-shoulderfruit and leaf margin chlorosis) and phosphorus defi-

Fig. 1. Structure of tomato growing system with extremely low-volume substrate.

ciency (purple color of the veins and stem, thin stemand poor cluster development) symptoms often ap-peared in the plants after they had experienced continu-ous rainy or cloudy weather caused by both lowintegrated solar radiation and a low nutrient solutionfertigation amount. The tomato fruit yellow-shoulderdisorder is characterized by sectors of yellow or greentissue under the peel, near the shoulder of the fruit.These areas will never ripen properly, and the tissue isoften hard even when the rest of the tomato is ripe(Francis et al., 2000). Unfortunately, the cause of thisdisorder is complex and not completely understood.Several lines of evidence have showed that nutritionalstatus, weather, plant genetics and their interactions areimportant factors influencing this condition (Hartzet al., 1999; Sacks and Francis, 2001). K content withinthe plant usually decreases one or two weeks prior tothe appearance of yellow-shoulder, and fruit exhibitingyellow-shoulder disorder often contains a lower K con-centration than normal, suggesting a role for K (Picha,1987; Winsor and Massey, 1958). Ikeda (2005) showedthat the fertilizer utilization efficiency was enhanced byhigh-frequency and small-volume application in thecase of soilless culture and also even in soil culture. InELVS culture, the utilization efficiency of mineral ele-mental nutrients is considered to be much greater thanin high-volume substrate culture. If this is true, toma-toes should be grown and produce a comparable yieldby applying a somewhat lower concentration of nutrientsolution. However, there was no evidence on this issue.Terabayashi et al. (2004b) confirmed that the averagerate of nutrient element uptake serves as a good criteri-on for estimating the amount of nutrient necessary forachieving the maximum yield of tomatoes grown hy-droponically (DFT&NFT). It is essential to examinehow the nutrients are absorbed and utilized for tomatoesgrown in ELVS, so as to establish an adequate fertiga-tion method by using low-concentration solution withfew physiological disorders. Furthermore, there is littleinformation about the nutrient uptake characteristics,especially the uptake patterns for tomato plants that arecharacterized by low-node-order pinching.

In the present study, the effects of nutrient solutionconcentration and supplemented K and P on plantgrowth, nutrient uptake and yellow-shoulder disorder offruit were investigated in ELVS. In order to modify thenutrient solution in the ELVS with LN&HD system,two experiments were conducted by using Enshi formu-la nutrient solution. Plants grown at three different con-centrations and under four treatments combined with Kor P supplementation were compared in Experiments 1and 2, respectively.

Materials and Methods

TreatmentsThe treatments consisted of 3 concentration levels of

diluted Enshi formula nutrient solution in Experiment 1

38 Y. Zhang, Y. Kiriiwa and A. Nukaya

(0.6, 0.9, and 1.2 dS·m−1 EC), and K and/or P were sup-plemented up to 5.8 and 4.6 me·L−1 on the basis of EC0.9 in Experiment 2, as shown in Table 1. Ca concentra-tion in EC 0.6 in Experiment 1 was increased to3.0 me·L−1, which was the same as in EC 0.9 for avoid-ing blossom-end rotted (BER) fruit. An experimentaldesign with three replicates for each treatment wasadopted, and each replicate contained 10 plants. Thus,90 and 120 plants were used in Experiments 1 and 2,respectively.

Plant materials and culture conditionsTomato seedlings ‘CF Momotaro York’ with 5 fully

expanded true leaves were planted into a D-tray(250 mL) filled with granular rock wool on Sep. 13,2012, in Experiments 1 and 2. All of the plants weresupplied with 1/2 strength Enshi formula nutrient solu-tion from germination until the beginning of the treat-ments. Treatments were initiated on Sep. 28 at theflowering stage of the first inflorescence. The experi-ments were conducted in a heated plastic greenhouse inwhich the minimum (heating) and ventilation air tem-peratures were 15°C and 23°C, respectively, and theaverage measured temperature was 20°C throughout theentire growing period. Flowers were vibrated manuallyto ensure pollination during anthesis. Periodic opera-tions of binding, fruit thinning, and lateral bud andbasal leaf pruning were carried out in a timely manner.Plants were trained vertically with a single stem andtopped at the 2nd upper leaf above the 3rd truss on Oct.29. Each truss was adjusted to have four fruit. Harvest-ing started on Nov. 27 and finished on Dec. 24. Nutrientsolution distributed through the drip fertigation systemto each plant was recirculated with a pump at a flowrate of approximately 25 mL·min−1. The fertigation fre-quency was controlled using a solar radiation controllerfor 90 s each time 1.0 MJ·m−2 solar radiation had accu-mulated. As a result, fertigation occurred approximately20–25 times per day on completely sunny days. Groupsof 10 plants were fertigated with the nutrient solutionfrom each 35 L reservoir. The solution in each reservoirwas refilled with an original solution to compensate forcrop water consumption every day and replaced by anew one every week.

Measurements and statistical analysesDaily measurements of the refilled volume of each

reservoir, EC and pH of the residual solution in the res-ervoir, and the nutrient solution fertigation volume wereconducted. Plant water uptake rate was determined asshown in equation (1).

Water uptake rate per plant (L/plant/week)= weekly solution amount refilled         in reservoir (L/week)/10 plants (1)

The concentration of nutrient in each reservoir was de-termined weekly. Spectrophotometry was used for theanalysis of NO3-N and PO4-P. The levels of K, Ca, andMg were determined by an atomic absorption method(iCE 3000 Series; Thermo Fisher Scientific Ltd.,Cambridge, UK). Owing to ELVS and high-frequencyand small-volume nutrient solution application, thefactors of evaporation and nutrient accumulation inmedium were negligible, so nutrient absorption wasmeasured just by the change of residual solution con-centration.

The weekly plant nutrient uptake rate was expressedby the difference between the sum of the nutrientamount included originally and the weekly refilled nu-trient solution, and the residual amount left after oneweek, as shown in equation (2).

Nutrient uptake rate per plant per week (me/plant/week)= [original concentration (me·L−1) × (35 (L/container) + weekly nutrient solution         refilled amount (L/container)) − concentration after one week (me·L−1) × 35 (L/container)]/10 (plants/container)   (2)

Fertilization (NO3-N) efficiency (kg·e−1) was calcula-ted in marketable yield (kg/plant) divided by uptakeamount of NO3-N (e/plant) (10 plants, 3 replications; n= 30).

Total fruit yield, marketable fruit yield, fruit numberand fruit weight were assessed over the course of theripening stage for each truss. The cracked and BERfruit were not included in marketable yield. The solublesolid content (SSC) of fruit juice in each truss squeezedby hand with a cheesecloth was determined with a handrefractometer (Model FR-100; Atago Co. Ltd., Tokyo,

Table 1. Nutrient solution composition and concentration in Experiments 1 and 2.

TreatmentEC

(dS·m-1)Mineral nutrients (me·L-1)

NO3-N PO4-P K Mg Ca NH4-N

Expt. 1 EC 0.6 0.85 4.0 1.0 2.0 1.0 3.0 0.3EC 0.9 1.05 6.0 1.5 3.0 1.5 3.0 0.5EC 1.2 1.35 8.0 2.0 4.0 2.0 4.0 0.7

Expt. 2 EC 0.9 1.05 6.0 1.5 3.0 1.5 3.0 0.5EC 0.9+P+K 1.54 6.0 4.6 5.8 1.5 3.0 0.5EC 0.9+P 1.36 6.0 4.6 3.0 1.5 3.0 0.5EC 0.9+K 1.33 6.0 1.5 5.8 1.5 3.0 0.5

Table 1. Nutrient solution composition and concentration in Experiments 1 and 2.

Hort. J. 84 (1): 37–45. 2015. 39

Japan).Fruit yellow-shoulder disorder was recorded at every

harvest time. The severity was classified into 4 levels asfollows: Severe = 3, Medium = 2, Light = 1, and None= 0, in which the yellow-colored area as a proportion ofthe total fruit shoulder area was more than 50%, 50–20%, less than 20%, and 0%, respectively (Fig. 2).‘Severe’ status was regarded as representing unmarket-able fruit, and “Medium”, “Light”, and “None” wereregarded as marketable fruit. Fruit yellow-shoulder in-cidence and the index (YSI) were calculated as shownin equations (3) and (4), respectively.

Fruit yellow-shoulder incidence (%)= (no. of yellow-shoulder fruit/total no. of fruit) × 100                 (3)

Fruit yellow-shoulder index (YSI)= [(0 × no. of degree 0 fruit) + (1 × no. of degree 1 fruit) + (2 × no. of degree 2 fruit) + (3 × no. of degree 3 fruit)]/total no. of fruit  (4)

All data were subjected to ANOVA and Scheffe’smultiple range test, as appropriate.

Results

Experiment 1Weekly variations of nutrient uptake rate are shown

in Fig. 3. Nutrient uptake rates were closely related tothe fertigation concentration, although the extent varieddepending on the kind of nutrient element. Weekly Kuptake rate tended to increase during flowering and theexpansion of upper leaves until the pinching stages, andwas maintained at a high level during fruit enlargementand ripening stages. The rate was reduced with decreas-ing fruit number during the harvesting stage, and wasfinally reduced to the same level in the last week underall treatments (Fig. 3). The uptake rate of K was great-est at EC 1.2, followed by EC 0.9 and then EC 0.6. Thepatterns of weekly N and Ca uptake rates during thegrowing period showed almost the same trend as K, ex-cept for the rates being maintained during the harvest-ing stage. In addition, Ca uptake rate in EC 0.6

Fig. 2. Levels of severity of fruit yellow-shoulder disorder classified as None, Light, Medium, and Severe from left to right.

Fig. 3. Changes in nutrient uptake rate of tomatoes grown in extremely low-volume substrate (Expt. 1). Nutrient uptake rate per plant per week(me/plant/week) = [original concentration (me·L−1) × (35 (L/container) + weekly nutrient solution refilled amount (L/container)) − concen-tration after one week (me·L−1) × 35 (L/container)]/10 (plants/container). Values are the means ± SE (n = 3).

40 Y. Zhang, Y. Kiriiwa and A. Nukaya

fluctuated at nearly the same level as EC 0.9, becausethe concentration was up-regulated to the same level asin EC 0.9 for the avoidance of BER fruit. The weeklyuptake rates of PO4-P and Mg were relatively stableduring the growing stage.

Daily variation of solution EC decreased regularlyfrom the beginning to the end of each week along withrefilling, and pH was maintained at a mean of around 7in all treatments throughout the entire cultivation period(data not shown).

Plant growth, and fruit production and quality asinfluenced by nutrient solution concentration areshown in Table 2. The shoot weight, stem diameterand total yield were greatly improved with a higher-concentration solution, while the fruit yellow-shoulder

incidence and index decreased (Table 2; Fig. 5a). Forthe shoot weight, that for EC 1.2 was significantlyhigher than those for EC 0.9 and EC 0.6, which wasattributable to the greatest expansion of upper leaveswith the former (data not shown). Owing to the highyield at the 2nd truss, the total yield in EC 1.2 wassignificantly higher than the others. The stem diameterbelow the 3rd truss and the 3rd truss yield in EC 0.9were significantly higher than in EC 0.6 (Table 2). TheYSI was 0.67 ± 0.04 in EC 0.6, which was double thosein EC 0.9 and EC 1.2 (Table 2). The incidence showedthe same tendency as the YSI. “Severe” fruit classifiedas being unmarketable accounted for 12% in EC 0.6,but only 3% in both EC 0.9 and EC 1.2 (Fig. 5a). Therewere no K- and P-deficiency symptoms of leaves in

Table 2. Tomato plant growth and fruit production as influenced by nutrient concentration in Experiment 1.

Treatment Shoot weightz (g/FW/plant)

Stem diametery (mm) Yield (kg/truss/plant) Marketable yield

(kg/plant)SSCx (%) YSIw

1st truss 3rd truss 1st truss 2nd truss 3rd truss Total

EC 0.6 229 cv 10.1 b 6.9 c 0.51 0.40 b 0.38 b 1.29 b 1.21 5.5 0.67 ± 0.04u

EC 0.9 308 b 10.4 b 7.9 b 0.51 0.49 b 0.49 a 1.49 b 1.37 5.5 0.31 ± 0.11EC 1.2 445 a 11.4 a 9.4 a 0.58 0.62 a 0.54 a 1.74 a 1.47 6.3 0.29 ± 0.14

z Leaf and stem fresh weights were measured at the end of the experiment.y Measured just below the 3rd truss at the end of the experiment.x Soluble solid content.w Fruit yellow-shoulder index (YSI) = [(0 × no. of degree 0 fruit) + (1 × no. of degree 1 fruit) + (2 × no. of degree 2 fruit) + (3 × no. of degree 3 fruit)]/

total no. of fruit.v DifferentletterswithinacolumnindicatesignificantdifferencesbyANOVAfollowedbyScheffe’stest(P < 0.05, n = 30).u Indicates mean ± SE (n = 3).

Table2.TomatoplantgrowthandfruitproductionasinfluencedbynutrientconcentrationinExperiment1.

Fig. 4. Changes in nutrient uptake rate of tomatoes grown in extremely low-volume substrate (Expt. 2). Values are the means ± SE (n = 3).

Hort. J. 84 (1): 37–45. 2015. 41

both experiments (data not shown). The fertilization(NO3-N) efficiency levels were 7.3, 6.1, and 4.9 kg·e−1

at EC 0.6, EC 0.9, and EC 1.2, respectively, and therewas a significant difference among them (P < 0.05, n =30) (data not shown).

Experiment 2As shown in Figure 4, the uptake rates of all nutrients

examined in this study were improved in the P supple-mentation treatment. Except for K, the uptake patternsof other nutrients in EC 0.9+P+K were similar to thosein EC 0.9+P, while those in EC 0.9+K were similar tothose in EC 0.9. EC 0.9+P and EC 0.9+P+K showedlarger fluctuations than EC 0.9 and EC 0.9+K. In con-trast, the uptake rate of nutrients was not influenced byenhanced K concentration, except for K itself. The Kuptake rate was enhanced by P supplementation. Theaverage weekly K uptake rates throughout the entire pe-riod in EC 0.9, EC 0.9+P+K, EC 0.9+P, and EC 0.9+Ktreatments were 9.2, 14.5, 12.2, and 11.2 me/plant/week, respectively. For the P-supplemented treatments,the average increment of weekly K uptake rate was3.1 me/plant/week in EC 0.9+P and EC 0.9+P+K com-

pared with those of EC 0.9 and EC 0.9+K, while the K-supplemented treatments of EC 0.9+K and EC 0.9+P+Kshowed an average increment of 2.2 me/plant/weekcompared with those of EC 0.9 and EC 0.9+P (Fig. 4).

Tomato plant growth and fruit production as affectedby P and K are shown in Table 3. In comparison withEC 0.9 and EC 0.9+K, the plant growth and fruit pro-duction were all improved in P supplementation treat-ments (EC 0.9+P and EC 0.9+P+K). Especially for EC0.9+P, the shoot weight, stem diameter, 2nd truss yield,and total yield were all significantly higher than in EC0.9. In contrast, the effect of EC 0.9+K on tomato plantgrowth and yield was not obvious. The YSI was re-duced to 0.20 ± 0.09 at EC 0.9+K and 0.15 ± 0.06 at EC0.9+P+K in contrast to 0.31 ± 0.11 in EC 0.9 and 0.25 ±0.06 in EC 0.9+P (Table 3). Furthermore, the incidencesof unmarketable fruit (Severe status) from high to lowwere 3% in EC 0.9, 2.2% in EC 0.9+K, 1.1% in EC0.9+P, and 0.3% in EC 0.9+P+K (Fig. 5b). Consequent-ly, the reduction of fruit yellow-shoulder disorder ten-ded to be greater in P- or K-supplemented treatment, orupon their combined usage.

Fig. 5. Fruit yellow-shoulder incidence as influenced by nutrient concentration or composition (a and b in Experiments 1 and 2, respectively).Values are the means ± SE (n = 3). Fruit yellow-shoulder incidence (%) = (no. of yellow-shoulder fruit/total no. of fruit) × 100.

Table 3. Tomato plant growth and fruit production as influenced by nutrient composition in Experiment 2.

Treatment Shoot weightz (g/FW/plant)

Stem diametery (mm) Yield (kg/truss/plant) Marketable yield

(kg/plant)

SSCx (%) YSIw

1st truss 3rd truss 1st truss 2nd truss 3rd truss Total

EC 0.9 308 cv 10.4 b 7.9 c 0.51 ab 0.49 b 0.49 1.49 b 1.37 ab 5.5 ab 0.31 ± 0.11u

EC 0.9+P+K 426 a 11.1 a 9.6 ab 0.56 ab 0.53 ab 0.58 1.67 ab 1.40 ab 5.5 ab 0.15 ± 0.06EC 0.9+P 377 ab 11.5 a 10.0 a 0.61 a 0.61 a 0.51 1.74 a 1.56 a 5.1 b 0.25 ± 0.06EC 0.9+K 360 bc 10.3 b 8.0 bc 0.50 b 0.47 b 0.51 1.48 b 1.31 b 6.3 ab 0.20 ± 0.09

z Leaf and stem fresh weights were measured at the end of the experiment.y Measured just below the 3rd truss at the end of the experiment.x Soluble solid content.w Fruit yellow-shoulder index (YSI) = [(0 × no. of degree 0 fruit) + (1 × no. of degree 1 fruit) + (2 × no. of degree 2 fruit) + (3 × no. of degree 3 fruit)]/

total no. of fruit.v DifferentletterswithinacolumnindicatesignificantdifferencesbyANOVAfollowedbyScheffe’stest(P < 0.05, n = 30).u Indicates mean ± SE (n = 3).

Table3.TomatoplantgrowthandfruitproductionasinfluencedbynutrientcompositioninExperiment2.

42 Y. Zhang, Y. Kiriiwa and A. Nukaya

Discussion

An appropriate balance between vegetative and re-productive growth is an indispensable consideration foraccommodating LN&HD cultivation of tomatoes grownin ELVS. A previous experiment showed that total Nconcentration of 6.5 me·L−1 in 0.9 dS·m−1 EC of nu-trient solution was sufficient for plant vegetativegrowth because of the optimal expansion of upperleaves (Egishi et al., 2012), and the yield once reachedup to 2 kg/plant (3 trusses) by using EC 0.9 dS·m−1 nu-trient solution in our preliminary experiment. As statedin the introduction, the planting distance is only 17 to24 cm in the D-tray cultivation system in the case ofLN&HD culture. It is necessary to keep plants in acompact state to accommodate a small planting dis-tance. In this study, fruit yield was expected to reach upto the same level as in EC 1.2 dS·m−1 by adding P or K,or upon their combined usage, based on EC 0.9 dS·m−1.As a result, leaf and stem fresh weight, and stem diame-ter in EC 1.2 were significantly higher than in EC 0.9and EC 0.6, and total yield was greatest at EC 1.2,which was the same as in previous research (Egishiet al., 2012). However, marketable yield and YSI weresimilar between EC 0.9 and EC 1.2 treatments, and fer-tilization (NO3-N) efficiency per marketable fruit at EC0.9 (6.1 kg·e−1) was significantly higher than at EC 1.2(4.9 kg·e−1). Therefore, EC 0.9 dS·m−1 was consideredas a comparable basis for fertilization reduction andavoiding expanded and overlapped foliage.

During the tomato reproductive phase of growth,fruit and stem are the major sink organs for K and car-bon assimilates from the source (Bar-Tal and Pressman,1996; Kanai et al., 2007). Moreover, K is the mostabundant cation present in the phloem sap (almost 80%of the total cations) as a consequence of sugar chargingand transport mechanisms/processes through thephloem into sink organs (Cakmak, 2005). In the presentstudy, the pattern of K uptake rate rose up to the highestlevel during the fruit enlargement and ripening stages,was then reduced with decreasing fruit number duringthe harvesting stage, and was finally reduced to thesame level at the end of harvest in Experiments 1 and 2(Figs. 3 and 4). These findings are the same as reportedby Ishihara et al. (2007). In addition, weekly averagesof 3.1 me/plant and 2.2 me/plant in terms of K uptakerate were increased in response to P and K supplemen-tation, respectively. K uptake seems more likely to beinfluenced by nutrient solution concentration or P playsan indirect role in the process of K uptake. Not only Kuptake but also the uptake of other nutrients including Pitself was greatly strengthened by enhancing P concen-tration, but this enhancement was not observed in Ksupplementation treatment.

There is evidence suggesting that high-P-concentration solution improved the uptake rate ofother nutrients (N, K, Ca, and Mg) in tomato DFT cul-

ture system (Terabayashi et al., 2004a). The effects of Pon early root growth, expansion and contraction ofstem, and fruit diameter are mainly attributable to theregulation of CO2 assimilation in leaf photosynthesis(Jacob and Lawlor, 1992). However, P affected plantgrowth directly through regulating the hydraulic con-ductivity of water in the roots (Clarkson et al., 2000;Fujita et al., 2003; Papadopoulos, 1991; Radin andMatthews, 1990). This change in hydraulic conductivityof the roots affected leaf expansion, which depends oncell multiplication and elongation of the newly formedcells in plants, and turgor pressure is a crucial factor forcell expansion (Hsiao, 1973; Munns et al., 2000). Thepartitioning of solutes to the fruit from the source leaf isdependent on adequate phloem turgor (Fujita et al.,2003). In the present study, supplemented P largely pro-moted sink organ growth and expansion of upperleaves, which were not observed in the EC 0.9+K treat-ment. The total yields in EC 0.9+P and EC 0.9+P+Kreached up to the same level as in EC 1.2 treatment inExperiment 1 (Table 2).

Fujita et al. (2003) reported that low P impaired sinkactivity, directly reducing the size of the fruit, and re-sulted in the suppression of leaf photosynthesis and re-duced stomatal conductance. Thus, both source andsink organs are parts of a single inseparable system andan effect on one part is bound to have a consequentialand concurrent influence on the other. In this study,stronger sink organs in P supplementation probablyneeded sufficient phloem turgor to maintain a goodsource-sink balance cycle in the plant, resulting inhigher uptake of nutrient elements (Fig. 4) and nutrientcontent in leaves (data not shown).

Fruit yellow-shoulder disorder was reduced in P andK supplementation treatment, as described previouslyin the results (Tables 2 and 3; Fig. 5). There was a di-rect relationship between higher K nutrition and a lowerincidence of yellow-shoulder disorders in the green-house environment (Picha, 1987; Picha and Hall, 1981).Soil-exchangeable K was reported to have a significantinfluence on yellow-shoulder disorders (Hartz et al.,1999). Alba et al. (2007) showed that higher exchange-able K and P nutrient status had a positive correlationwith tomato fruit color. In addition, fruit tissue affectedby coloring disorder contains less than half the P and Klevels when compared with red tissue (Picha, 1987),suggesting that both P and K are involved in tomatofruit coloring. It can be concluded that yellow-shoulderdisorder was reduced to different levels by supplemen-tation of P or K or both of them. As described earlier inthis paper, the improvement of K uptake was greater inEC 0.9+P (3.1 me/plant/week) than in EC 0.9+K(2.2 me/plant/week) throughout the entire period ofstudy (Fig. 4). The fact that K nutrition has a greaterrole in tomato fruit coloring disorder than P has previ-ously been reported. Evidence indicated that the appli-cation of K fertilizers can enhance the levels of

Hort. J. 84 (1): 37–45. 2015. 43

carotenoids in tomato, especially lycopene (Helyeset al., 2009; Ramírez S. et al., 2009; Trudel and Ozbun,1971). Furthermore, K may be involved in the activitiesof one or more enzymes, such as phytoene synthase andphytoene desaturase, that synthesize phytoene fromgeranylgeranyl diphosphate, which is the first com-mitted step in the carotenoid biosynthetic pathway(Taber et al., 2008). Consequently, it is necessary toclarify the relationship between yellow-shoulder disor-der and K and P uptake, and fruit carotenoid metabo-lism in further research.

In the case of ELVS culture, plant roots are restrictedto 250 mL volume, so the substrate conserves less wateror nutrient elements unless nutrient solution is appliedat high-frequency and a small-volume. The availablemineral elemental nutrients for plants are markedly lessthan for the conventional NFT or DFT system.Terabayashi et al. (2004a) showed that tomatoes can becultured in a DFT system with a limited supply ofnitrate and phosphorus at 50 and 20 me/plant/week,and the initial concentrations of NO3-N, PO4-P, and Kwere 8.0, 3.2, and 6.0 me·L−1, respectively. Moreover,Otsuka-A formula nutrient solution was used for tomatocultivation by high wire layering in a closed hydroponicsystem with substrate, in which NO3-N, P, and K con-centrations were 7.0, 2.0, and 3.7 me·L−1, respectively(Ishihara et al., 2007). In our preliminary experiment,P- or K-deficiency symptoms easily occurred whenwe used the Enshi formula nutrient solution at EC0.9 dS·m−1 for tomatoes grown in ELVS. In the presentstudy, P and K concentrations were regulated up to 4.6and 5.8 me·L−1, respectively, based on EC 0.9 dS·m−1,but NO3-N was kept at 6.0 me·L−1. Compared with con-ventional NFT or DFT, the nutrient solution concen-trations for tomatoes grown in ELVS culture arecharacterized by lower N and higher P and K concen-trations.

As a result of the present study, it was shown to beeffective to increase the P and K concentrations of nu-trient solution on the basis of Enshi nutrient solutionformula at EC 0.9 dS·m−1 in order to maintain optimaltomato vegetative growth, achieve higher yield compa-rable to that for EC 1.2 dS·m−1, and produce fewer P-and K-deficiency symptoms in the case of ELVScombined with LN&HD culture by a high-frequencyand small-volume application method.

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