Jing FENG,Ruiping LIU,Hongyi LUO

College of Resources and Environment,Shandong Agricultural University,Taian 271018,China

Effect of Different Calcium Levels on Growth, Yield and Fruit Quality of Tomatoes in Substrate Culture

Jing FENG,Ruiping LIU,Hongyi LUO*

College of Resources and Environment,Shandong Agricultural University,Taian 271018,China

Tomato seedlings were grown in substrate culture with pots.The formulation of Holland Greenhouse Horticulture Research Institute was used (as CK)and the effects of different Ca concentrations（LCa,CK and HCa）on growth,yield,and fruit quality (protein,Vitamin C,nitrates,organic acid and soluble sugar)of tomato were studied keeping concentrations of other nutrients unchanged in the nutrient solution.The results showed that parameters related to the growth of tomato（plant height and Stem diameter）,changes of tomato yield per plant and quality of tomato fruits were the highest when the plants were grown at 20%Ca treatments.In the second study,increased EC concentrations of nutrient solution resulted in stronger plants with improved yields and quality.Four different concentration gradients of nutrient solution treatment were designed based on the results of the first research stage (EC=1.5,2.5,3.5,4.5 mS/cm,respectively).The single tomato plant had the highest production which is 2 268.994 g/plant,when the nutrient solution strength was at EC=1.5 mS cm,whereas they have the best fruit quality when the solution strength at EC 4.5 mS/cm.This suggests the need for wide popularization of the nutrient solution formula in large areas to improve the tomato production.

Calcium;Substrate culture;Nutrient solution;Tomato

T omato is an important vegetable grown under horticulture facilities in many places in China.With the development of plant technique in recent years,tomato is considered to provide high economic results under wide range of climatic areas[1-2].Because,it contains more Vitamin-c,soluble sugar and other substances with higher nutritive value compared to other vegetables,more tomato production is needed for fresh market and export.Because of its high market value,it encourages farmers to increase the cropped area under tomato.Tomato is normally grown under greenhouse conditions during the spring-summer and the fall-winter seasons to meet high demand of fresh tomato in both national and international markets.But,the production of tomato in soil faces a big challenge due to serious problem of soil quality in horticulture facilities.

Soilless cultivation has been de veloping rapidly in the protected vegetable cultivation at home and abroad in recent years[3-4].Compared to conventional soil cultivation,soilless culture has certain advantages,viz.,protection against adverse environment, overcoming obstacles of continuous cropping and increasing the area for planting vegetables[5].As the key point of soilless cultivation technology,the configuration and managementof nutrient solution is affected by the restriction of various factors,viz.,the species of crop,technical level of planter,cultivating environment,etc. Therefore,itis difficultto realize large-scale protection with soilless culture[6-7].The fitness of nutrient so lution formula directly related to the growth,yield and quality of crop, therefore it is critical for developing proper,therefore it nutrient solution formulation for success of soilless cultivation.

"Navel rot"is a common physiological disease of tomato cultivation, generally considered to be caused by Ca deficiency[8-10].As a necessary nutrient element for plants,Ca helps in the regulation of growth and response to environmental stress.The main aim of the present study is to get high crop yield by regulating Ca concentration in nutrient solution in the formulation of Holland Greenhouse Horticulture Research Institute.

Materials and Methods

The present study was divided into two stages.In the first stage,Ca concentration in the tomato nutrient solution formula of Holland Greenhouse Horticulture Research Institute was changed and its effect of the growth,yield and fruit quality of tomato was studied,so as to obtain the optimal Ca concentration in the nutrient solution.In the second stage,based on the optimal Ca concentration obtained from the first research stage, different concentration gradient of nutrient solution (represented by the electrical conductivity,EC)was designed to obtain the best EC value and its effect on the yield and quality of tomato fruit under greenhouse tomato production.

Plant materials and nutrient formulation

The experiments were conducted under plastic greenhouse situated at the experimental farm of Shandong Agricultural University in Taian,China in two consecutive growing seasons: fall season from September to December(experiment 1)and spring-summer season from March to July(experiment 2).The plants were grown under the natural light condition.Pots(diam-eter-30 cm and height-19 cm)experiment was conducted by filling each pot with 2.5 kg matrix peat.Seeds of "red tomato Kaige"was germinated in vermiculite on 19 September 2013(experiment 1)and Seeds of"Jingpeng 10"was germinated in vermiculite on 26 February 2014(experiment 2).

The formulation of Holland Greenhouse Horticulture Research Institute was used as CK,and Ca concentration in nutrient solution was taken as a single factor experimental design of nutrient solution(Table 1)in the first stage of experiment.In the second research stage,four different concentration gradient of nutrient solution treatment was designed based on the results of first experiment(expressed as EC,mS/cm).They were indicated in electrical conductivities(EC)of 0.6, 1.0,1.4 and 1.8 times of the nutrient solution obtained at the first research stage.In both the experiments(1 and 2),randomized complete-block design with five replicates was used to compare indices of tomato in different treatments.

Nutrient solution management

In both experiments,plants were fertilized with the following major nutrient solution (mmol/L):NH4-N(0.50), NO3-N (10.50),S (2.50),P (1.50),K (7.00),Mg(1.00),except the change in Ca element.The micro-element content in nutrient solution (mg/L):Mn-SO4·4H2O (2.13),H3BO3(2.86),Zn-SO4·7H2O(0.22),CuSO4·5H2O(0.05), (NH4)6Mo7O12·4H2O(0.02),Na2Fe-EDTA(50.00).

Each of the nutrient solutions was divided into A and B mother solutions and were stored in 10 L black plastic barrels and diluted 100 times as working solutions when needed.The tomato plants were watered every 2 days with 1 L working solution for each treatment and watered everyday as the tomato plants grew stronger.

Plant growth index analysis Determination of plant height,stem diameter and chlorophyll content Plant heightFive plants of different treatments were measured.In order to quantify their growth,the height of the plants from the plant base or the matrix was measured during initial stage of growth(10 days after transplanting), vigorous growth period (20 days after transplanting)and blossom period(30 days after transplanting).

Stem diameterThe coarse diameter from the middle fifth stem section was measured during initial stage of growth (10 days after transplanting),during vigorous growth period (20 days after transplanting)and during blossom period(30 days after transplanting).

Chlorophylldeterminationwas measured with a portable chlorophyll meter(TYS-A SPAD-502).

Determination of fruit quality

Three mature tomatoes were chosen and harvested from the third spike of each plant under different experiment were weighed and counted to determine the fruit yield and the number of fruits per plant.

Soluble sugar contentFor soluble sugar sugar analyses (glucose,fructose,and sucrose),0.2 g plant materials were extracted in the boiling water bath for 30 minutes,then filter into a 25 ml volumetric flask.When the standard curve was made,0.5 ml anthrone ethyl acetate reagent and 5 ml concentrated sulfuric acid were added and placed in boiling water bath for 1 min.

For the determination of extracted materials,0.5 ml anthrone ethyl acetate reagent and 5 ml concentrated sulfuric acid was added.At the same time measurement of the optical density at 630 nm wavelength was conducted,and the content of sugar was calculated by the standard linear equations.

Ascorbic acid (Vc)100 g plant samples was put into stamping machine and filter and 100 ml of 2%oxalic acid solution was added.Then 10 ml extract material was taken into 50 ml volumetric flask.The last step was titrated by using 2,6-chlorine antiphonals which was calibrated.

NO3-content2 g plant materials were extracted in the boiling water bath for 30 minutes,then filter in a 25 ml volumetric flask.To determine content of NO3-in tomato fruits,0.4 ml of 5% salicylic acid-sulfuric acid was added to slurry sample,9.5 ml of 8% NaOH then was added after 20 min. The optical density at 410 nm wavelength was measured at the last step, and then the content of NO3-in tomato fruits was calculated by the standard linear equations.

Soluble protein contentThe method of"Coomassie Brilliant Blue"was chosen for the determination of the soluble protein content[11]in tomato fruits.

Statistical analysis

The data were evaluated on SAS and DPS software to determine statistically significant differences.Different letters in the tables and the figures represent significant variations according to the LSD(P＜0.05)[12].

Experimental Results

Effect of different concentrations of Ca in nutrient solution on growth, yield and quality of tomato plants

Effect on growthIn the present study due to higher availability of nutrients the height of tomato plant significantly increased with increase in the concentration of Ca in nutrient solution (Fig.1).The HCa treatment had the obvious height advantage over other treatments.

Thestem diameteroftomato plantwith days aftertransplanting (Fig.2)was also influenced by the Ca concentratibn in nutrient solution.During the growth period,stem diameter of CK was the same as the HCa treatment.The stem diameter of CK was significantly higher than that of the others at blossom stage(P＜0.05).For all the growth period,results in Fig.1 also indicate that the plants have stronger stem diameter at lower concentration of Ca.

Effect on fruit yield and quality

The results (Table 2)indicated that yield of tomato per plants grown at CK was 15.09%higher than that of LCa (P＜0.05)and there was no significant difference between HCa and CK treatments.The yield of tomato per plants grown at HCa was 20.1%higher than that of LCa(P＜0.05).

The content of organic acid in tomato fruits decreased with the in-crease of Ca concentration.The organic acid content of L-Ca treatment significantly increased by 27.08%than that of CK (P＜0.05).The organic acid content of HCa treatment significantly decreased by 14.58%than that of CK (P＜0.05).

Table 1 The concentration of Ca in nutrient solution

Nitrate content(NC)is one of the most important indices for fruit quality. Results(Table 2)showed that fruit NC of LCa and HCa treatments were significantly higher than that of CK (P＜0.05).The fruit NC of LCa treatment was 2.39 times higher than that of CK; at the same time,the fruit NC of HCa treatment was 40.78%higher than CK. The fruit NC content of LCa treatment was 1.41 times higher than that of HCa (P＜0.05).The fruit NC of all the treatments were all lower than 432 mg/kg, which is the range of food safety index.

Vitamin-C(Vc)content is another important vegetable quality just as NC. The Vc content of tomato fruit was significantly affected by change in Ca concentration of nutrient solution. Compared to CK,the Vc content of tomato fruits grown atLCa was 56.22%lower(P＜0.05)while no significant difference in Vc content between HCa and CK treatments were observed.The fruit Vc content of HCa treatment was 58.6%higher than that LCa (P＜0.05).The results suggested increase in Vc content of tomato fruits increased with the increase of Ca concentration in nutrient solution.

The values of soluble sugar in tomato fruits(Table 2)in both HCa and LCa treatments were significantly higher than that of CK(P＜0.05).The soluble sugar content in tomato fruits of LCa and HCa treatments were 27.51 %and 31.4%higher than that of CK, respectively.No significant differences in soluble sugar content of tomato fruits between LCa and HCa treatments were recorded.

Results also suggest that the soluble protein content in tomato fruits of HCa and LCa treatments were significantly higher than that of CK(P＜0.05). The soluble protein content of tomato fruits of LCa and HCa treatments were was 30.03%and 28.91%higher than that of CK,respectively.No significant differences in soluble protein content of tomato fruits between LCa and HCa treatments were observed.

It can be concluded from the results that HCa treatment(CK)with electrical conductivity of 2.5 was the optimal concentration for the growth of tomato.

Effect of different EC values of nutrient solution on growth,yield and quality of tomato

Effect on growthThe plant growthparameters were significantly affected by the strength of nutrient solution.Despite the higher availability of nutrients, plant height was significantly reduced by increasing strength of nutrient solution in different growth periods(Fig.3). No difference in stem diameter of the plant was observed in growth period (10 days)at the EC2.5,EC3.5 and EC4.5 treatments(Fig.4).Stem diameter was significantly increased by strength of nutrient solution in blossom period and the full fruit period which was contrary with the plant height growth regularity.

Table 2 Fruit yield and quality of tomato with different Ca concentration in nutrient solution

Table 3 Fruit quality indicators of tomato grown in different EC values of nutrient solution

The content of chlorophyll reduced during the initial growth time (Fig.5).In the first growth period,the EC2.5 treatmenthad the highest chlorophyll content.The chlorophyll content was positively and significantly correlated with EC value during the plant growth in blossom period and full fruit period.

Effect on tomato fruit yieldFruit production was significantly affected by the strength of nutrient solution (Table 3).Despite the higher availability of nutrients,the fruit production was significantly reduced by the increase in the strength of nutrient solution.The fruit yield at EC 1.5 mS/cm was 29%higher than that of CK (P＜0.05).At the same time,the fruit yields at EC3.5 and EC4.5 treatments were 17.99%(P＜0.05)and 5.48%higher than that of CK.No significant differences in fruit yield were observed amongEC2.5,EC3.5andEC4.5 treatments.

Effect on tomato fruit qualitySoluble sugar,soluble protein and Vc content of vegetative tomato plants grown in EC4.5 were significantly affected compared to plants under other treatments (Table 3).It can be concluded that some fruit quality indices increased,while NC and organic acid in the fruits did not varied significantly with increasing strength of nutrient solution.Soluble sugar at EC4.5 increased by 36.99%compared to CK (P＜0.05).No significant difference in the content of organic acid was observed between EC1.5 and EC2.5 treatments.The average content of soluble protein at EC3.5 and EC4.5 was increased by 34.37%compared to CK (P＜0.05).The Nc in fruits was within the standard of healthy eating food even under increasing strength of nutrient solution.

Discussion

Effect of different Ca concentration in nutrient solution on the growth, yield and quality of tomato

Ca is essential for cell division and expansion and it promote the growth of root and the elongation of cell[8,13]. Ca is a major nutrient necessary for membrane stability and maintenance of cell integrity.The plant will have growth retardation,shorter stem section and weak growth potential under Ca deficiency.So,under invariable conditions the growth rate of plant depends on Ca level directly[10,14].In a study on spinach,Metin etal.[15]demonstrated that growth of spinach plants was significantly affected by the rate of lime (CaO)application.Dry matter content and N,P,K,Ca contents of spinach plants increased significantly with increased application of CaO (lime).Over application of lime gradually decreased the nutrient contents in plants.In tomato(Lycoperscicum esculentum L.)seedlings,Amor and Marcelis[16]found that total plant dry matter,total leaf area and dry matter growth were all significantly reduced by Ca withdrawal from nutrient solution.They attributed this to the role of Ca in cell division and expansion[9]. In the present study,the increased height of tomato plant with increasing Ca concentration supported the above conclusions.But,for stem diameter, the trend was different from plant height with changing Ca concentration in nutrient solution.This possibly due to the fact that only Ca concentration in nutrient solution changed while other nutritional elements were kept constant.This suggested the needs of other nutrients for plant growth in addition to Ca.The growth of the plants needs not only Ca,but also other nutrient elements,such as N,K,and P and so on.In the present study,tomato plant with high Ca treatment grew very fast,while the uneven proportion and ratio of other large elements did not provided enough nutrition for vascular and cell wall growth and resulted in weaker plants[17]in comparison to other treatments.

The fruit yield and quality were very strongly affected by the concentration of Ca in nutrient solution[18].High Ca in plant cells was known to activate pentose phosphate pathway and biosynthesis of amino acid resulting in increased protein and starch synthesis.Similar results were obtained in the present study.Higher tomato fruit yields were obtained at high Ca(HCa) in nutrient solution(Table 2)compared to other two Ca concentrations.Sufficient Ca helps the plants to grow better and attain reproductive growth period earlier than other treatments[19-20]. As a result,the average yield per plant increased with the concentration of Ca in nutrient solution.

Sugar-acid ratio is one of the important indices for the identification of fruit taste and quality.Results in Table 2 indicated that tomato plants grown at high Ca concentration had higher soluble sugar,but lower acid content especially when expressed as sugaracid ratio,in accordance with the results of previous studies.Increased concentration of Ca in nutrient solution helps in improving the quality of tomatoes[21-22].

Growth,yield and quality of tomato at different EC values of nutrient solution

With increase in EC value of nutrient solution,the tomato stem diameter and chlorophyll content increased while the plant height decreased.This is attributed to stronger plant growthwith good vascular structure,full developmentofcellwalland more chlorophyll content in these plants under high strength of nutrient solution[23-24].On the contrary,under low concentration of nutrient solution, tomato grow faster than others at vegetative growth stage having loose cell wall were loose,slender cells and small stem diameter.

Indices related to fruit increased with increase in the strength of nutrient solution.This was resulted from two essential factors;nutrient solution and nutrient imbalance from the fertilizer. The concentration of ion in nutrient solution was high enough to provide sufficient nutrients for plant growth and nutrient distribution in different parts of tomato which may influence the fruit quality[25-28].

Conclusions

Optimum concentration of Ca in the formulation of Holland Greenhouse Horticulture Research Institute keeping other nutrients unchanged was investigated.Increased EC concentrations of nutrient solution resulted in stronger plants with improved yields and quality under green house conditions suggesting regulatory effect of nutrient solution on vegetative growth and reproductive growth of tomato. Highest production of 2 268.994 g/plant was recorded with EC at 1.5 mS/cm while high EC4.5 value provided higher fruit quality.This suggests the need for wide popularization of the nutrient solution formula in large areas to improve the tomato production.

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Responsible editor:Xiaoxue WANG

Responsible proofreader:Xiaoyan WU

*Corresponding author.E-mail:hot68168@163.com

Received:June 5,2015 Accepted:July 17,2015