Ivanka ŽUTIĆ, Nina TOTH, Bruno NOVAK

Zavod za povrćarstvo, Agronomski fakultet, Sveučilište u Zagrebu, Hrvatska (E-mail: izutic@agr.hr)

Uvod

Kineska raštika, u nas malo poznata orijentalna vrsta lisnatog povrća, prisutna je na hrvatskom tržištu tijekom zimskog razdoblja uvezena iz mediteranskih zemalja. Mala potreba za toplinom (Vogel 1996) omogućuje njen uzgoj i u našem kontinentalnom području u ozimom roku u negrijanom zaštićenom prostoru, kao i u proljetnim rokovima na otvorenom, bez dodatne zaštite od hladnoće (Lešić et al. 1994; Žutić et al. 1994; Borošić et al. 1995). Tehnološka zrelost ove kulture definirana je masom rozete traženom na tržištu (Vogel 1996), pri čemu treba voditi računa o udjelu vlakana u peteljkama biljaka velike mase, koja mogu uzrokovati konzumnu neprihvatljivost namirnice (Granges 1989; Siomos 1999). Cilj je istraživanja utvrditi utjecaj gustoće sklopa biljaka i dinamike berbe na kvalitativna svojstva rozete u različitim rokovima uzgoja, kao i dopunskog izravnog prekrivanja usjeva netkanim polipropilenskim filmom u ozimom roku uzgoja.

Materijal i metode

Istraživanje je provedeno na pokušalištu Zavoda za povrćarstvo u Zagrebu u razdoblju 1998. do 2000. godine, uzgojem na otvorenom i u negrijanom zaštićenom prostoru. Tlo je gnojeno sa 650 kg/ha NPK 8-26-26. Usjevi su zasnivani iz presadnica s grudom supstrata (cv. Hypro F1), a očekivana masa rozete u berbi je 200 do 400 g.

Uzgoj na otvorenom - Proveden je u dva proljetna i ljetno-jesenskom roku uzgoja (sadnja 24.4., 6.5. i 27.8.1998. te 14.4., 3.5. i 23.8.1999). Pokusi su postavljeni po shemi split-plot u 5 ponavljanja, pri čemu je glavni faktor sklop biljaka (16.7 i 22.2 biljke/m2), a podfaktor rok berbe (30, 37 i 44 dana nakon sadnje).

Ozimi uzgoj u negrijanom zaštićenom prostoru - Monofaktorijelni je pokus postavljen po shemi slučajnog bloknog rasporeda u šest ponavljanja (izravno prekrivanje usjeva radi dopunske zaštite od hladnoće netkanim polipropilenskim materijalom "Lutrasil" težine 30 g/m2 i bez prekrivanja). Presadnice su sađene 23.10.1998. i 5.11.1999. (sklop 16.7 biljaka/m2), a berba je obavljena 17.3.1999. i 20.3.2000.

U svježim uzorcima listova analizirana je količina nitrata Xylenol metodom te vitamin C. Udio ukupnih pre-hrambenih vlakana u lisnim peteljkama određen je encimatsko-gravimetrijskom metodom po Aspu et. al. (1983). Ukupni dušik određen je metodom po Kjeldahlu, ukupni kalij plamenfotometrijski, fosfor spektro-fotometrijski, a ostali mineralni elementi (Ca, Mg, Fe, Mn, Zn, Cu) atomskom apsorpcijskom spektrometrijom.

Statistička analiza podataka provedena je metodom analize varijance F-testom, a značajnost razlika između srednjih vrijednosti testirana je Duncanovim multiplim testom rangova na razini značajnosti pŁ0.05 i pŁ0.01.

Rezultati i diskusija

Sukladno Grangesu (1989), udio suhe tvari u plojkama uglavnom je dvostruko veći nego u peteljkama, a u proljetnim rokovima (do 8.7 %) gotovo dvostruko veći nego u ljetno-jesenskom roku uzgoja (5.3 %).

Količina ukupnih prehrambenih vlakana u peteljkama (tablica 1) jednaka je glede sklopa biljaka, kao i dopunskog prekrivanja usjeva u ozimom roku uzgoja, Signifikantne, ali neujednačene razlike vidljive su obzirom na dinamiku berbe unutar rokova uzgoja na otvorenom, a isto tako i obzirom na rokove uzgoja. Količine ne prelaze literaturne vrijednosti i nisu ograničavajući čimbenik konzumne upotrebljivosti pri masi rozete do 500 g (Vogel 1996; Siomos 1999).

Tablica 1. Količina ukupnih prehrambenih vlakana u peteljkama kineske raštike (g/100 g svježe tvari)

Prosječne vrijednosti rangirane su po rokovima uzgoja i istraživanim faktorima Duncanovim multiplim testom rangova na razini signifikantnosti (a) pŁ0.05 i (A) pŁ0.01

Prosječna količina vitamina C u rozeti (mg/100 g svježe tvari) podjednaka je kod oba sklopa biljaka, kao i kod sva tri roka berbe (51.6 do 54.3 mg), što je u granicama literaturnih vrijednosti (Vogel 1996). Evidentno je manja u ljetno-jesenskom roku uzgoja (43.3 mg) te pri izravnom prekrivanju usjeva u ozimom roku (11.5 mg), zbog porasta temperature zraka (Mahmud et al. 1999).

Najveće prosječne količine nitrata u svježoj tvari rozete znatno su manje od literaturnih vrijednosti (Echim i Saul 1994), a zabilježene su u prvoj berbi u ljetno-jesenskom roku uzgoja (1408 mg/kg) te u ozimom roku uzgoju uz izravno prekrivanje "Lutrasilom" (1309 mg/kg). Razlog toga treba tražiti prvenstveno u nedovoljnoj količini svjetlosti u ovim rokovima uzgoja, kao i većem udjelu lisnih peteljki, koje sadrže dvostruko više nitrata nego plojke.

Količine biogenih makroelemenata (grafikon 1), a također i mikroelemenata u rozeti kineske raštike razlikuju se prema rokovima uzgoja. U ljetno-jesenskom su roku uzgoja na razini literaturnih vrijednosti (Granges 1989; Vogel 1996), dok su u proljetnim rokovima gotovo dvostruko veće, što se objašnjava većim udjelom suhe tvari u proljetnim rokovima uzgoja, prisutnim zbog većeg udjela plojki.

Grafikon 1. Količine biogenih makroelemenata u rozeti kineske raštike po rokovima uzgoja (prosjek dvije god.)

Zaključak

Promatrani sklopovi biljaka ne utječu značajno na kemijski sastav kineske raštike. Dinamika berbe djelomično utječe na udio suhe tvari u peteljkama i plojkama, na količinu ukupnih prehrambenih vlakana u peteljkama te na količinu nitrata u rozeti, dok rokovi uzgoja značajno utječu na sva promatrana kemijska svojstva. Najkvalitetnije se rozete dobivaju u proljetnim rokovima uzgoja (veći udio suhe tvari, vitamina C, vlakana i biogenih elemenata), uz najmanju količinu nitrata. U ozimom uzgoju ne preporuča se dopunsko izravno prekrivanje usjeva polipropilenskim materijalom.

Literatura

1. Asp N.G. i Johansson C.G, (1984). Dietary fibre analysis. Nutrition Abstracts and Reviews in Clinical Nutrition - Series A. Vol. 54(9): 735-752

2. Borošić J., Žutić I. i Heblin D., (1995). Spring crops of lettuce, carrot and pak-choi grown under direct covers. Poljoprivredna znanstvena smotra 60(3-4): 355-365

3. Echim T.H. i Saul A., (1994). Neue Gemüsearten für die Winterkultur. Gemüse 12:714-716

4. Granges A., (1989). Experimentation et development pratique de deux nouveaux legumes en Suisse: le pak-choi (Brassica chinensis L.) et l' hymenia (Brassica pekinensis Lour. Rurp.). Acta Hort 242: 277-289

5. Lešić R., Žutić I., Toth N. i Borošić J., (1994). Evaluation of new vegetable species in Croatia. Proceedings of the symposium: New technologies in vegetable and flower production, Ohrid, vol. 1: 47-52

6. Mahmud T.M.M., Atherton J.G., Wright C.J., Ramlan M.F. i Ahmad S.H., (1999). Pak choi (Brassica rapa ssp. chinensis L.) quality response to pre-harvest salinity and temperature. Journal of the Science of Food and Agriculture, 79(12):1698-1702

7. Siomos A.S., (1999). Planting date and within-row plant spacing effects on pak choi yield and quality characteristics. Journal of Vegetable Crop Production 4(2): 65-73

8. Vogel G., (1996). Pak Choi (Brassica rapa L. ssp. chinensis (L.) Hanelt). U: Handbuch des speziellen Gemüsebaues. Ulmer, Stuttgart: 346-354

9. Žutić I., Lešić R. i Toth N., (1994). Malo poznata vrsta povrća kineska raštika (Brassica chinensis L.). Poljoprivredne aktualnosti 30(1-2): 57-62

Ivanka ŽUTIĆ, Nina TOTH, Bruno NOVAK

University of Zagreb - Faculty of Agriculture, Vegetable Crops Department, Zagreb, (E-mail: izutic@agr.hr)

Introduction

Pak choy, in Croatia less known oriental leafy vegetable species, can be found on the Croatian market in the winter period as an import from other Medditerranean countries. Its low heat requirements (Vogel 1996) enable its cultivation also in our continental areas not only in unheated protected spaces during overwinter period, but also as an early spring crop grown in the open field (Lešić et al. 1994; Žutić et al. 1994; Borošić et al. 1995). The technological maturity is determined by the mass of its rosette as required by the market, however, it is necessary to pay attention to the fibre content in the leaf petioles, which can cause consumer unacceptability of rosettes with a large mass (Granges 1989; Siomos 1999). The objective of the research was to determine the effect of plant density and harvest dynamics on quality characteristics of the rosette in different cultivation terms, as well as the influence of additional direct cover of crop with nonwoven propylene film in overwinter cultivation.

Material and Methods

IThe research was conducted on the experimental field of the Vegetable Crops Department in Zagreb in the period from 1998 to 2000. The soil was fertilized with 650 kg/ha of NPK 8-26-26. The crops were grown from transplants with a substrate lump (cultivar Hypro F1); expected mass of the rosette at harvest was 200 to 400 g.

Open field cultivation - was conducted in two spring and one summer-autumn cultivation terms (planting dates: 24 April, 6 May, 27 August 1998 and 14 April, 3 May, 23 August 1999). The trials were set up in split-plot design with 5 replications; the main factor was plant density (16.7 and 22.2 plants/m2), with harvest date (30, 37 and 44 days after planting) as the subfactor.

Overwinter cultivation in unheated plastic house - The monofactorial trial was set up in randomized block design with 6 replications (direct cover of crops for additional protection from cold with nonwoven propylene material "Lutrasil", weight 30 g/m2, and without cover). Transplants were planted on 23 October 1998 and 5 November 1999 (plant density of 16.7 plants/m2), and harvested on 17 March 1999 and 20 March 2000.

Nitrate (Xylenol method) and vitamin C levels were analysed in fresh leaf samples. Total dietary fiber content in leaf petioles was determined by enzymatic gravimetric method according to Asp et. al. (1983). Total nitrogen was determined by Kjeldahl method, total potassium by flame photometric detection, phosphorus by spectro-photometric analysis, and other mineral elements (Ca, Mg, Fe, Mn, Zn, Cu) by atomic absorbtion spectrometry.

Statistical data analysis was conducted by applying the analysis of variance, while the significance of the differences between mean values was tested by the Duncan's Multiple Range Test.

Results and Discussion

According to Granges (1989), total dry matter contents in the leaf blades are double than in the petioles. In the spring period they are nearly double (up to 8.7 %) when compared to the summer-autumn period (5.3 %).

Total dietary fibre content in the petioles (Table 1) is equal in view of plant density, which also applies to additional cover of the crop in the overwinter cultivation period, whereas significant but uneven differences are evident in relation to harvest dynamics within cultivation periods in the open field. These quantities do not exceed the values found in literature, and are no limiting factor in relation to consumer usability at the rosette mass of up to 500 g (Vogel 1996; Siomos 1999).

Table 1 Total dietary fibre content in the leaf petioles of pak choy (g/100 g fresh weight)

Average values are ranked based on cultivation dates and researched factors according to Duncan's Multiple Range Test at significance levels of (a) pŁ0.05 and (A) pŁ0.01

The average quantity of vitamin C in the rosette (mg/100 g fresh weight) was approximately equal at both plant densities and for all three harvest dates (51.6 to 54.3 mg), which is within the value range found in the literature (Vogel 1996). It is evidently lower in the summer-autumn cultivation period (43.3 mg) and in case of direct cover of the crop in the overwinter period (11.5 mg), due to increased air temperature (Mahmud et al. 1999).

The highest average nitrate levels in the rosette's fresh weight were much lower than the values found in the literature (Echim and Saul 1994), and were recorded during the first harvest of the summer-autumn cultivation period (1408 mg/kg), and in the overwinter cultivation period with the application of direct cover of "Lutrasil" (1309 mg/kg), the primary reason being the insufficient quantity of light in this two growing periods, as well as a higher content of the petioles, which have double nitrate levels than the leaf blades.

The quantities of biogenic elements in the rosette differ based on the cultivation periods (Graph 1). In the summer-autumn period their values are comparable to the values found in the literature (Granges 1989; Vogel 1996), whereas in the spring periods they are generally double, which can be explained by a higher total dry matter content in this cultivation periods due to a higer content of the leaf blades.

Graph 1 Quantities of biogenic macroelements in the rosette of pak choy based on cultivation dates (2-year average)

Conclusions

Observed plant densities have no significant effect on the chemical composition of pak choy. Harvest dynamics has a partial influence on total dry matter content in the petioles and leaf blades, as well as on total dietary fibre content in the petioles and nitrate levels in the rosette, whereas growing dates have a significant influence on all observed chemical characteristics. The best quality of rosette was obtained in spring cultivation periods (higher dry matter, vitamin C, dietary fibre and biogenic elements contents), along with the lowest nitrate level. Additional direct cover of crop with nonwoven propylene film in overwinter cultivation is not recommended.

References

1. Asp N.G. i Johansson C.G, (1984). Dietary fibre analysis. Nutrition Abstracts and Reviews in Clinical Nutrition - Series A. Vol. 54(9): 735-752

2. Borošić J., Žutić I. i Heblin D., (1995). Spring crops of lettuce, carrot and pak-choi grown under direct covers. Poljoprivredna znanstvena smotra 60(3-4): 355-365

3. Echim T.H. i Saul A., (1994). Neue Gemüsearten für die Winterkultur. Gemüse 12:714-716

4. Granges A., (1989). Experimentation et development pratique de deux nouveaux legumes en Suisse: le pak-choi (Brassica chinensis L.) et l' hymenia (Brassica pekinensis Lour. Rurp.). Acta Hort 242: 277-289

5. Lešić R., Žutić I., Toth N. i Borošić J., (1994). Evaluation of new vegetable species in Croatia. Proceedings of the symposium: New technologies in vegetable and flower production, Ohrid, vol. 1: 47-52

6. Mahmud T.M.M., Atherton J.G., Wright C.J., Ramlan M.F. i Ahmad S.H., (1999). Pak choi (Brassica rapa ssp. chinensis L.) quality response to pre-harvest salinity and temperature. Journal of the Science of Food and Agriculture, 79(12):1698-1702

7. Siomos A.S., (1999). Planting date and within-row plant spacing effects on pak choi yield and quality characteristics. Journal of Vegetable Crop Production 4(2): 65-73

8. Vogel G., (1996). Pak Choi (Brassica rapa L. ssp. chinensis (L.) Hanelt). U: Handbuch des speziellen Gemüsebaues. Ulmer, Stuttgart: 346-354

9. Žutić I., Lešić R. i Toth N., (1994). Malo poznata vrsta povrća kineska raštika (Brassica chinensis L.). Poljoprivredne aktualnosti 30(1-2): 57-62