Seedling Production of Pak Choy (Brassica rapa L.) using Organic and Inorganic Nutrients

Pak Choy or Bok Choy (Brassica rapa L. var. chinensis) is one of favorite Chinese leafy vegetable for various dishes in Indonesia. In this study, it was used as a plant model to identify the appropriate organic hydroponic nutrient solution for leafy vegetable seedling production. The seed was sown on rock wool slabs submerged with 200 ml of a nutrient solution containing biofertilizer of Beyonic StarTmik@Lob (0, 25, 50, 75, and 100%). commercial hydroponic solution (0, 25, 50, 75, and 100%) and its combination (25, 50, and 75%). The experiments were arranged in a CRD. Meanwhile, the obtained data was analyzed using ANOVA followed by DMRT. The relationship among growth parameters was observed using Pearson correlation analysis. The result of the study showed that the combination of organic and inorganic nutrient (25% Beyonic StarTmik@Lob and 75% commercial hydroponic solution) resulted in the highest seedling growth parameters and leaf indices as well as the perfectly positive correlations among growth parameters. This result indicated that the use of organic nutrient alone was not appropriate for hydroponic seedling production of Pak Choy. Therefore, further study needs to be done to identify the hydroponic solution without inorganic nutrients towards the organic vegetable production.


INTRODUCTION
Pak Choy or Bok Choy (Brassica rapa) was introduced to South-East Asia in the 15 th century.Nowadays it is widely cultivated in this region including Indonesia.Pak Choy is one of favorite Chinese leafy vegetable in Indonesia.All above ground part of this vegetable is edible mainly its succulent petiole.It is not commonly eaten raw but used in main ingredients for soup and stir-fried dishes.Each of 100 g edible part of Pak Choy contains protein 1.7 g, fat 0.2 g, Carbohydrate 3.1 g, vitamins and minerals such as β-carotene (2.3 mg), vitamin C (53 mg) and Calcium (102 mg) (Tay & Toxopeus, 1994).The national production of Brassica in 2015 is 600,200 tons (Central Agency on Statistics of Indonesia, 2015).This vegetable is commonly produced by conventional farming using inorganic fertilizer to enhance crop productivity.Nowadays, the demand of organic vegetable is increased due to the public concern about healthy food, free from chemical residues.Organic farming of cauliflower (B.oleacera var.botrytis) in lowland area showed a better vegetative growth but not for generative growth (Widiatningrum & Pukan, 2010).Organic farming of another Brassica species (cauliflower) was successfully done.Therefore, the organic vegetable seedling production plays an important role, because it is the initial step in the practice of biological farming.Moreover, Kubota et al. (2013) stated that the use of high-quality planting materials is critical for success in greenhouse plant production.
The viability of small seed including Pak Coy is usually tested using a paper substrate (Purbojati & Suwarno, 2006).However, seedling production is commonly using a locally organic substrate such as peat and vermicompost (Tuzel et al., 2014), spent mushroom compost (Priadi et al., 2016) on tomato seedling, and coconut coir dust on lettuce (Lactuca sativa L.) (Hossain et al., 2016).Moreover, production of organic transplants involves more than organic fertilizer and substrates and avoiding the use of non-approved pesticides.These organic substrates are also as an organic nutrient source with or without the addition of inorganic and organic fertilizer.A study on the feasibility of organic nutrient solution for the hydroponic culture of leafy green vegetable was conducted by Ferguson et al. (2014).Also, the seedling production of peppermint and spearmint using inorganic and organic fertilization was previously performed by Akoumianaki-Ioannidou et al. (2010).In this study, we use both inorganic and organic nutrients using a hydropo-(Specific Leaf Area) and LAR (Leaf Area Ratio) were recorded to evaluate the seedling resistance at transplant (Herrera et al., 2008).The SLA is the ratio of leaf area to leaf dry weight.Meanwhile, LAR is the ratio of leaf area to dry seedling weight.
The experiments were arranged in a Completely Randomized Design (CRD) with 3 replications.Obtained data was analyzed using Analysis of Variance (ANOVA) followed by Duncan's Multiple Range Test (DMRT).The relationship among growth parameters was observed using Pearson correlation analysis.Data was processed using statistical software SPSS 16.0.

RESULTS AND DISCUSSION
Data in Table 2 showed that pH and EC value of the nutrient solution at the end of germination period were higher than that the initial.The higher pH is caused by anion uptake by the plant during plant growth period.Meanwhile, the higher EC is due to the high level of nutrient due to the additional nutrient solution for adjustment (Hossain et al., 2016).

Seedling Emergence
Seedling emergence is one of the important parameter as well as emergence rate.The highest all seedling growth parameter was obtained by the Pak Choy seed sown on the rock wool slabs containing 100% of groundwater (K0-1).It was not significantly different with K0-1 when the seed was sown on the rock wool slabs containing the mixture of organic and inorganic solution (25% Beyonic StarTmik@Lob and 75% commercial hydroponic solution).Contrary, the mixture of 75% Beyonic StarTmik@Lob and 25% commercial hydroponic solution (K3) resulted in the lowest seedling growth.A biofilm was formed on the root surface of the seedling in the hydroponic solution containing 100% Beyonic StarTmik@Lob (K0-3).Seedling growth of Pak Choy on K-03 was lower due to the biofilm formation.A study conducted by Chinta et al. (2015) found that a biofilm was formed on the root surface of organic hydroponic lettuce; in contrast, chemical hydroponics resulted in a lack of biofilm.Biofilm is formed as an interaction between beneficial microorganism and lettuce roots.Another study conducted by Fujiwara et al. (2012) on tomato seedlings found that a rhizosphere biofilm in the organic hydroponic may be responsible for the suppression of the bacterial wilt.In this study, we found that the use of Beyonic StarTmik@Lob alone as a nutrient solution for Pak Choy hydroponic seedling production seemed to be not appropriate to obtain optimal growth (Table 3).

Leaf Indices
The highest leaf number (5.067) was obtained from the hydroponic solution containing 100% commercial hydroponic solution (K0-2).It was not significantly different with those containing both K4 and K5.The mixture of inorganic and organic nutrient solution of K4 and K5 resulted in the best leaf area.The best SLA index was obtained from K4 nutrient solution.According to Herrera et al. (2008), the lower SLA value indicated, the higher transplant stress resistance.The LAR represents the relationship between photosynthetic material and respiratory material in the plant.It is also used for evaluation of seedling resistance at transplant.Higher LAR indicates more biomass production for seedling growth.Table 4 showed that there was not significantly different in both of SLA and LAR among the nutrient solution used except the K0-3.

Seedling dry weight
The highest Pak Choy seedling dry weight was obtained in the hydroponic solution containing biofertilizer of Beyonic StarTmik@Lob (K-03) (Table 5 and Figure 1).This biofertilizer was supported by PGPR (Plant growth promoting rhizobacteria) (Dewi et al., 2015).It was suggested that the higher seedling dry weight was affected by the hydroponic solution containing PGPR as explained by Bashan & de-Bashan (2010), since PGPR at the very early stage leading to better absorption of water and minerals.The result of this study agrees with a study conducted by Das et al. (2014) on organically cultivated mungbean using the organic manure containing PGPR.
The lower seedling dry weight was obtained on a mixture of organic and inorganic nutrient solution (25% Beyonic StarTmik@Lob and 75% inorganic nutrient solution).The dry seedling weight of Pak Choy seems to be affected by the availability of Beyonic StarTmik in the nut-rient solution.A study conducted by Ferguson et al. (2014) showed that hydroponic culture of Bok Choy using organic nutrient solution resulted in the lower yield compared with those low or highlevel inorganic nutrients.Nevertheless, the price of the organic product is much higher than the conventional product.

Correlation among growth parameters
Correlation among Pak Choy seedling growth parameters in the nutrient solution used is varied.There was perfectly positive correlation between total leaves (TL) and both stem dry weight (SW) and whole seedling dry weight (TW) as well as the correlation between leaf area (LA) and TW and between SW and TW on K4 nutrient solution (Table 6).It was reasonable that the increased in the whole seedling dry weight was affected by the increased of total leaves, leaf area and stem dry weight.Table 6 showed that the correlation among those seedling growth pa- Means in the same column followed by the different letter are significantly different (p<0.05) according to DMRT rameters seemed to be affected by the biofertilizer and inorganic nutrient proportion in the hydroponic solution of K-4 (25% K0-3+75% K02).In contrast, there was not any significant difference correlation among growth parameters in K-6 (75% K0-3+25% K02).A different result showed by tomato seedling grown on various compost types; there was a very significant correlation between leaf area and both dry leaf weight and whole seedling dry weight, as well as seedling height and diameter (Priadi et al., 2016).The correlation among seedling growth parameters seemed to    2011) on a hydroponic of lettuce and Pak Choy showed that the vegetable types varied on optimal solution concentration, and different vegetable cultivars exhibited specific growth characteristics.
The result of the study as explained above, found that the inorganic nutrient in the hydroponic solution could be decreased by using biofertilizer.However, further study needs to be done to obtain organic substances from inexpensive, and easily available materials for hydroponic seedling production towards the organic product since the hydroponic culture of vegetable crops is commonly applied by the urban community which has no space for conventional farming.By using the organic nutrient in the hydroponic solution is expected to be produced more healthy vegetable.

CONCLUSIONS
From this study, we concluded that the nutrient solution containing 25% Beyonic StarTmik@Lob and 75% commercial hydroponic solution (K4) was the appropriate nutrient solution for hydroponic seedling production of Pak Choy.The organic seedling production plays an important role because it is the initial step in the practice of biological farming.Therefore, further study needs to be done to obtain organic substances for hydroponic seedling production towards the organic product.

ACKNOWLEDGEMENT
This work was funded by DIPA Biovillage 2016 of Research Center for Biotechnology-LIPI entitled Use of Germplasm Garden Compost for Organic Vegetable Production.Authors would like to thanks, Dr. Enung Sri Mulyaningsih, Head of Plant Germplasm Garden of RC for Biotechnology for the use of the research facility.Thanks also to the technicians of the project, Heru Wibowo, A.Md., Yudi Slamet Hidayat, SP. and Roni Ramdani, SP. for their help in the experiments.

Table 2 .
Characteristic of nutrient solution of Pak Choy hydroponic culture

Table 3 .
Growth parameter of Pak Choy seedlings after 14-days sowing on rock wool slabs containing inorganic and organic nutrient solution in the screen house

Table 4 .
Leaf indices of Pak Choy seedlings after 14-days sowing on rock wool slabs containing inorganic and organic nutrient solution in the screen house

Table 5 .
Dry weight of Pak Choy seedlings after 14-days sowing on rock wool slabs containing inorganic and organic nutrient solution in the screen house