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on flue-cured tobacco yield and quality were conducted during. 2000, 2001, and 2003; but the effects of irrigation and water stress on the quality and chemical ...
Field Crops Research 119 (2010) 269–276

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The effect of irrigation scheduling and water stress on the maturity and chemical composition of Virginia tobacco leaf Recep C¸akir a,∗ , Ulviye C¸ebi b a b

C¸anakkale Onsekiz Mart University, Lapseki Vocational College, 17100 Lapseki/C¸anakkale, Turkey Ataturk Soil and Water Resources Research Institute, 39100 Kirklareli, Turkey

a r t i c l e

i n f o

Article history: Received 3 February 2010 Received in revised form 21 July 2010 Accepted 22 July 2010 Keywords: Tobacco Irrigation Water stress Maturity Chemical traits Relationships

a b s t r a c t The study was carried out in order to determine the effect of different irrigation scheduling programs and water stress, imposed at different growth stages, on the maturity and leaf chemistry of Virginia tobacco (Nicotiana tabacum L.). Field experiments and lab investigations were carried out during 2000–2003, on a silty loam Entisol soil, poor in organic matter and rich in potassium, on the fields of Atatürk Soil and Water Resources Research Institute in Kirklareli, Turkey. A randomized complete block experimental design with three replications was applied, and K-326 Virginia tobacco cultivar was used in the experiment. Three known stages of the plant – vegetative (V), yield formation (F), and ripening (R) – were considered, and a total of 14 irrigation treatments (including rain-fed) were applied. All the experimental treatments were irrigated on the same day of VFR and were irrigated at each growth stage with the amount of water required to fill the 0–90 cm soil depth to field capacity; and three levels of water reductions (0%, 40% and 60%) were done at each development stage. Results of the investigations show that irrigation scheduling and the water stress imposed during different stages of growth influenced the ripening dynamics of Virginia tobacco leaves and that severe water stress causes delay in the ripening of the leaves. Favorable moisture conditions considerably decrease the nicotine and nitrogen content of the Virginia tobacco leaves, both of which are hazardous for humans, to the ranges of 0.85–1.21% versus 2.1–2.2% under stress (for nicotine), and 1.4–1.6% versus 1.8–2.0%, and 2.0–2.4% versus 2.9–3.1% (for nitrogen) for 2001 and 2003, respectively. However the percentage of chloride and sodium in the leaf increases if the amount of seasonal water is increased. It was determined also that close linear relationships exist between seasonal irrigation water amounts or seasonal evapotranspiration and any of the chemical traits. Mutual relationships between nicotine and each of the traits – i.e. nitrogen, chloride, potassium, and sodium – were also established. © 2010 Elsevier B.V. All rights reserved.

1. Introduction In Turkey, tobacco is a crop of high importance since it brings in significant income. The main part of tobacco production is obtained from an Oriental type of tobacco grown mainly in the Black Sea and Aegean regions of Turkey. Virginia tobacco is also a high-value cash crop, grown lately in other parts of the country, such as the Thrace Region (NW Turkey), where irrigation is a factor of vital importance, especially during the critical growth stages of the plant. Despite the economic importance of Virginia tobacco in the country, few publications relate to the effects of water supply on growth and dry matter accumulation dynamics (C¸akir and C¸ebi, 2006), and on yield and yield response to water (C¸akir and C¸ebi, 2009), and no experimental data have been reported earlier that were related to

∗ Corresponding author. Tel.: +90 286 522 6104/07x1011; fax: +90 286 522 6101. E-mail addresses: [email protected], [email protected] (R. C¸akir). 0378-4290/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.fcr.2010.07.017

the effect of water supply on the quality and chemical composition of dry leaves. The dynamics of maturity and the quality of dried tobacco yield depend on almost all the factors that control plant growth and development: temperature, sunlight, precipitation, etc. Parker (2009) reported that the environmental factor that most frequently causes alterations of leaf quality is rainfall and, most often, its poor distribution rather than mere insufficiency. The association of high alkaloids/low sugars with drought and, conversely, of low alkaloids/high sugars with wet weather is well known (Weybrew and Woltz, 1975; Campbell et al., 1982). On the other hand, McCants and Woltz (1967) reported that the magnitude of the effects of soil moisture on quality depends on the duration and the growth stage at which it occurs. In general the effects of insufficient or excess moisture on quality are due to an excess of or deficiencies in nitrogen (Elliot, 1970; Elliot and Court, 1978). Moreover excess soil moisture can also affect soil microbial populations, leading to a decrease in nitrification (Coyne, 1999).

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According to Gaines et al. (1983), water may affect tobacco leaf maturity. Ample water contributes to an increase in sugar content, alkalinity, ash content, and potassium content, while at the same time decreasing nitrogen, nicotine, and chlorine within the tobacco leaf. The grade and yield of tobacco leaf improve during years of adequate soil water and decline during years of insufficient soil water. Excess soil water by rainfall or irrigation, however, may change the leaf chemistry away from a desired level. Irrigation may even be a tool for moderating leaf nitrogen levels (thus modifying starch and alkaloids) prior to harvest in order to obtain a more desirable leaf chemistry (Maw et al., 1997, 2009). McNee et al. (1978) have studied the effect of water stress in Queesnland, Australia, on the yield and quality of flue-cured tobacco and have determined that depending on the timing, water stress during rapid growth has detrimental effects on leaf yield and quality. Several studies related to the relationships among various aspects of tobacco irrigation and leaf chemical composition have been published recently. A few of them are related to the effect of irrigation with saline water and chloride concentration on the growth and yield components (Sifola and Postiglione, 2002; Sifola, 2005; Karaivazoglou et al., 2005; Gul et al., 2006) of broad leaf Virginia or Burley tobacco types, and on the quality characteristics of field-grown oriental tobacco (Karaivazoglou et al., 2006), while others (Ju et al., 2008; Bilalis et al., 2009) have discussed the effects of irrigation systems and fertilization on the growth, yield, and nicotine content of tobacco leaves. In field studies carried out recently, it has been demonstrated that the frequency of irrigation and the amount of water used are associated not only with the quantity, but also with the quality and chemical composition of tobacco leaves (Assimi et al., 2004; Biglouei et al., 2010), or with grade rated index (GRI) value of the produce (Caldwel et al., 2010). Mogaddam et al. (2009) claimed that the tobacco quality and the chemical compound of the cured leaf are as important as the yield; and in order to obtain tobacco production with good taste and flavor, special attention should be given to irrigation at the right time with an appropriate amount of irrigation water. Thus the aims of this publication are (i) to study the effect of irrigation applications and water stress, imposed during different growth stages, on the chemical composition of cured tobacco leaf and to find an irrigation scheduling program providing the most desirable nicotine content, and (ii) to discuss the relationships between seasonal irrigation water amounts and chemical compounds of the leaf.

2. Materials and methods 2.1. Experimental site and experimental procedure The field experiments for investigating the effect of water stress on flue-cured tobacco yield and quality were conducted during 2000, 2001, and 2003; but the effects of irrigation and water stress on the quality and chemical composition of cured tobacco leaf were studied in 2001 and 2003. Research plots were laid out in different locations across a larger field of the Soil and Water Resources Research Institute in Kirklareli (41◦ 42I N and 27◦ 12I E). Undisturbed and disturbed soil samples, collected in three replications from different layers (0–30, 30–60, 60–90 and 90–120 cm) of each location, were analyzed following procedures given by Richards (1954). Through soil analysis it was determined that the experimental soils were poor in organic matter and rich in potassium, and that the salinity levels of the layers mentioned varied in the ranges of 0.68–0.81, 1.29–2.34, and 1.41–2.04 dS/m, respectively, for 2000, 2001, and 2003. More details related to the physical and chemical properties of the experimental soils are given in Table 1. Seedlings of K-326 Virginia tobacco, the most popular in the region, were transplanted during the second half of May in each experimental year, on a 0.5 m × 1.0 m grid, over a total area of 42 plots, each 9.0 m × 6.0 m. Nitrogen fertilizer at 80 kg N ha−1 in the form of ammonium nitrate was applied before transplanting each year. A completely randomized block design with three replications was used in the study. All the experimental plots were surrounded with earth dikes, and a distance of 3 m between plots was left bare in order to prevent the lateral spread of water. Three known stages of the plant development – vegetative (V), yield formation, (F) and ripening (R) – were considered, and a total of 14 irrigation treatments (including rain-fed) were applied (Table 2). Plant growth stages were determined as described by Lucas (Doorenbos and Kassam, 1979), and the irrigation periods given in Table 3 were followed. All the experimental treatments were irrigated using surface irrigation methods, on the same day of the VFR stages, and irrigated at each growth stage with the amount of water required to fill the 0–90 cm soil depth to field capacity. In order to obtain various stress levels, three reductions in the water amount (0%, 40% and 60%) were applied at each development stage. Single irrigation was applied during the second part of the vegetative stage, while subsequent water applications were done at the 50% and 70% depletion level during the yield formation and ripening stages, respectively. The water amounts and number of irrigation practices applied to the control (VFR) treatments are summarized in Table 4. More details related to irrigation periods and experimental treatments, irrigation scheduling, moisture monitoring, irrigation

Table 1 Physical and chemical characteristics of the experimental soil. Years

Depth (cm)

Field capacity (%)

Wilting point (%)

Bulk density (g/cm3 )

Organic matter (%)

Electrical condactivity (dS/m)

pH

Soil texturea

2000

0–30 30–60 60–90 90–120

22.1 23.4 19.4 22.4

9.1 10.0 9.9 11.5

1.53 1.49 1.57 1.57

1.9 1.7 1.3 1.5

0.81 0.67 0.66 0.68

7.8 7.9 7.9 7.9

L L SCL SCL

2001

0–30 30–60 60–90 90–120

22.7 19.8 10.8 13.2

9.7 9.0 5.1 6.7

1.46 1.52 1.54 1.63

2.1 1.5 0.9 0.9

2.34 2.06 1.29 1.58

7.7 7.7 7.7 7.8

L SCL SL SL

2003

0–30 30–60 60–90 90–120

20.3 22.2 22.6 23.7

7.8 9.5 9.5 10.8

1.54 1.54 1.56 1.57

1.2 1.1 0.9 0.8

1.41 1.56 1.80 2.04

7.8 7.8 7.8 7.8

SL SCL SCL SCL

a

L, loam; SL, sandy loam; SCL, sandy clay loam.

R. C¸akir, U. C¸ebi / Field Crops Research 119 (2010) 269–276 Table 2 Irrigation treatments applied in the study. Experimental treatments

VFR VF VR FR V F R V1 FR V2 FR VF1 R VF2 R VFR1 VFR2 Rain-fed

that is the average long-term rainfall amount. The last experimental year (2003) received a total of 78 mm rainfall in this same period. Similar differences in the years of experiment were observed in average air temperatures and humidity values, as well as in evaporation amounts. In general, June, July, and August of 2000 and 2001 were characterized by higher average temperature and evaporation values, and lower relative humidity, compared to 2003 as well as to the long-term averages.

Growth stages Vegetative (V)

Yield formation (F)

Ripening (R)

I I I 0 I 0 0 I1 I2 I I I I 0

I I 0 I 0 I 0 I I I1 I2 I I 0

I 0 I I 0 0 I I I I I I1 I2 0

271

2.3. Harvesting, curing, and sample analysis procedures The harvesting started generally with the topping stage of the plant when the lower leaves also became mature. Harvesting proceeded up the stalk as more leaves matured and was generally completed by the end of six harvests. The mature leaves of the plants on a central part of the 20 m2 area of each experimental plot, with a total of 54 m2 , were harvested at each harvesting date; the leaves were fresh weighed, placed into metal boxes, and put into curing barns. The weighed leaves were cured in a typical oven for Virginia tobacco following the standard curing procedure. After the curing process was finished, the cured leaves obtained from each individual experimental plot were weighed, and the dry leaf yield was determined. In order to avoid variations in the chemical traits of the leaves according to their position on a plant stalk, samplings from the lower leaves (1st priming) and upper leaves (5th and 6th priming) were omitted. Composite samples from all commercial fractions of the 2nd, 3rd, and 4th primings in 2001 and the 3rd and 4th primings of 2003 were prepared and used for chemical analyses. The samples were analyzed for nicotine, nitrogen, chloride, potassium, and sodium. All the analyses were done in triplicate, and the percentage of the chemical constituents was determined on a moisture-free basis. Nicotine analysis was performed following a procedure published by Willits et al. (1973), while total nitrogen was analyzed employing the Kjeldahl procedure (Bremmer and Mulvaney, 1982). All of the other soil and water analyses were performed following procedures given by Richards (1954). Statistical procedures using the experimental data were conducted using SAS statistical software (SAS Instute Inc., 1987), and the Duncan mean separation test was applied also. Data obtained from all the primings and experimental years were subjected to an ANOVA test, and year × treatment interactions were evaluated. The mean values of each year were tested for homogeneity of variance; and since homogeneity was not statistically proved, data from the years of study were not pooled and evaluated together. Since the

I, full irrigated at a given stage; I1 and I2 irrigated at a given stage with reduced water amounts of 40% and 60% respectively; 0, irrigation omitted.

application, procedures for evapotranspiration determination, etc., were presented in a paper published earlier (C¸akir and C¸ebi, 2009). Water for the study was provided from the water reservoir of the irrigation project of the Soil and Water Resources Research Institute in Kirklareli. The chemical characteristics of the irrigation water applied are presented in Table 5. Analysis performed in laboratories of the Research Institute showed that irrigation water applied to experimental plants is S3 salinity class, containing relatively high levels of sodium (2.32–2.72 me/l) and a very high concentration of chloride (2.67–3.08 me/l). 2.2. Meteorological events during the years of study Daily weather climatic parameters were measured at a weather station located adjacent to the experimental site; and the precipitation and evaporation amounts, and average air temperature and humidity values during the experimental years, as well as the longterm averages for those values, are presented in Table 6. Total rainfall in the last experimental year (2003) was close to the long-term average, while 2000 and 2001 were much drier than normal. The experimental years differed also with regard to the distribution of precipitation during the different parts of the growing season. The total monthly rainfall amounts during the periods of rapid vegetative growth and yield formation stages (June–August) in the first and second experimental years were about 35 and 13 mm, respectively, much lower than the 100.6 mm Table 3 Periods of water applications during the experimental years. Name of the period

Starting

Ending

Rapid vegetative growth (V) Yield formation (F) Ripening (R)

30 days after transplanting 8–10. Leaf stage Beginning of flowering

8–10. Leaf stage Beginning of flowering 4. Harvest

Table 4 Irrigation water amounts applied to full irrigated flue-cured tobacco at different stages of the experimental years. Year and stage of development

Water application a

Vegetative (V)

Yield formation (F)

Ripening (R)

2000

Application date Irrigation water, mm

33 125b

49/55/62 90/90/91

72/81/91/103/116 106/116/111/116/102

2001

Application date Irrigation water, mm

29 129

53/60/67/74 92/77/77/81

83/93/104/128 90/94/90/85

2003

Application date Irrigation water, mm

33 72

52/57/69 71/75/75

76/95/117 69/125/100

a b

Days after transplanting. Water amounts applied at each stage to full irrigated (VFR) treatment. However 40% and 60% less water was applied to treatments I1 and I2 , respectively.

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Table 5 Chemical composition of irrigation water applied in the experiment. Exp. years

pH

EC (dS/m)

Cations (me/l) +

2000 2001 2003

7.0 6.8 7.1

1.12 1.04 0.97

Anions (me/l) 2+

Na

Ca Mg

2.72 2.60 2.32

9.14 8.90 8.72

2+

+

K

CO3

0.25 0.21 0.14

– – –

2−

HCO3 6.70 6.50 6.20





Cl

SO4

3.08 2.80 2.67

2.33 2.41 2.31

RSC

SAR

Class

– – –

1.26 1.23 1.11

S3A1 S3A1 S3A1

2−

Table 6 Some meteorological data for the years and months of study. Month and meteorological event

October

Seasonal

Yearly

Precipitation, mm—long year average 2000 2001 2003

51.7 34.4 19.2 31.9

45.4 13.4 5.2 21.1

30.8 0.6 3.2 46.8

24.4 20.8 5.0 0.0

29.8 18.4 60.8 10.0

51.7 21.2 2.8 96.8

233.8 108.8 96.2 206.6

594.7 315.4 375.2 546.0

Relative humidity, %—long year average 2000 2001 2003

69 66 67 67

63 60 59 61

61 47 57 64

62 57 59 60

68 67 66 72

75 79 73 86

92.9 129.4 137.5 132.8

116.5 145.1 141.8 153.5

158.6 192.8 164.0 128.5

159.1 147.2 154.1 154.4

108.4 90.7 105.7 88.9

64.5 34.0 57.0 53.0

700.0 739.2 760.1 711.1

17.0 16.7 16.9 18.4

21.2 20.7 20.9 22.5

23.2 25.2 25.5 23.8

22.5 23.4 24.6 24.5

18.8 18.7 20.1 17.7

13.7 13.1 15.0 13.6

19.4 19.6 20.5 20.1

Evaporation, mm—long year average 2000 2001 2003 Average air temperature, ◦ C—long year average 2000 2001 2003

May

June

differences among primings concerning concentration of the chemical traits were quite small, evaluations of the data related for any trait were done on the basis of averages for each experimental year. Regression was used to evaluate the amount of irrigation water, the nicotine content, and the seasonal evapotranspiration–nicotine content relationship. In addition, relationships between irrigation water and nitrogene, chloride, etc., were also evaluated using the techniques of statistical regression. 3. Results The results from experiments carried out between 2000 and 2003 showed that irrigation scheduling and water stress imposed during different stages of growth affect not only leaf yield, as discussed earlier by C¸akir and C¸ebi (2009), but also maturity dynamics of the tobacco leaves. A statistical analysis of the data for the cumulative harvested yield of the total yield pointed to the significant effect (p < 0.01) of irrigation programs on the maturity of the leaves (Table 7). The data related to the cumulative yield harvested in primings during the research years indicate that these interactions were more pronounced under conditions of severe water stress in the drier years of 2000 and 2001. As a general rule a greater percentage of the leaves (40–50%) from all the experimental plots in 2000 and 2001 were harvested in the last of the 6 primings. Nevertheless, some differences in the ripening dynamics of the leaves were observed under the treatments, including severe water stress, where an average of 30–40% of the yield was harvested in the first and second primings. Data obtained from the laboratory analysis showed that the irrigation scheduling and soil moisture regime had a significant effect (p < 0.01) on the nicotine, nitrogen, chloride, sodium and potassium content of the cured tobacco leaves from all primings during the experimental years. The percentage of nicotine is one of the most important traits of tobacco (Gaines et al., 1983). It has been established that total alkaloids should be 2.14–3.37%, preferably around 2.95%, though nowadays taking into account the harmful effects of nicotine on

July

August

September

66.3 62.7 63.5 68.3

73 72 74 76

13.0 13.4 13.6 12.4

the health of smokers, great attention is given to searching ways to decrease nicotine content to around 1%. The average values of nicotine content of the leaves from all primings of the some of the treatments are plotted in Fig. 1. As is evident from the figure, irrigation scheduling and water stress conditions in the soil profile had a statistically significant decreasing effect on the nicotine content of the tobacco leaf. Thus, while the average nicotine content in the leaves of the plants irrigated at each growing stage and grown under more favorable moisture conditions of VFR were 1.01% and 0.81%, respectively for 2001 and 2003, the average values in the leaves of the plants irrigated only during the single yield formation (F) or ripening (R) stages were 1.33% and 1.21%, and 1.25% and 1.22%, respectively. A much higher nicotine concentration (average 2.26% and 2.12%) was determined for plants under severe water stress during the entire growing season (rain-fed) or plants irri-

Fig. 1. The effect of irrigation scheduling and water stress on mean values of nicotine in the cured leaf within each experimental year, p < 0.01.

R. C¸akir, U. C¸ebi / Field Crops Research 119 (2010) 269–276

Fig. 2. Nitrogen content of tobacco leaves under various irrigation regimes within each year, p < 0.01.

gated only once during rapid vegetative growth stage (V) and left under stress conditions during the remainder of the season. Irrigation produced a statistically significant (p < 0.01) effect, decreasing the nitrogen content of tobacco leaves during 2001 and 2003 experimental years (Fig. 2). In general, it is undesirable to have a high level of nitrogen in the tobacco leaf at harvest because an accumulation of nitrogen late in the growing season may restrict the level of starch in the leaf, as well as prevent the conversion of starch to reducing sugars. Results for 2001, as plotted in Fig. 2, showed that the nitrogen content of the leaves of plants grown under the favorable moisture conditions of VFR and FR treatments varied in the range of 1.61–1.63%, while the average content of the most stressed treatment exceeded the desired level of 2%. Much higher nitrogen concentrations in the leaves were determined during 2003, the year in which much less irrigation water was used. In contrast to the favorable results related to decreasing the nicotine and nitrogen concentrations in the leaves with increasing amounts of water applied, the content of chloride, which is an undesirable trait since it reduces tobacco quality and depresses burning (Sifola, 2005), increased with irrigation during the experimental years. Thus, while average chloride concentrations in the leaves of plants grown under severe water stress during the entire season (rain-fed) or during the major part of the growing season (V) of 2001 were determined as 2.3% and 2.7%, the chloride content of the leaves of plants irrigated at each growth stage reached

273

Fig. 3. The effect of irrigation applications on chloride content of tobacco leaf during the experimental years, p < 0.01.

a range of 4.0–4.5% (Fig. 3). The inverse of the situation with the nicotine content of the leaf, chloride concentrations in the leaves of all treatments during 2003 were much lower than in 2001, the year when 25–35% more irrigation water was applied. Similar results for those relating to chloride were obtained for the sodium content of the leaves, concentrations increased with irrigation, especially during 2001 when sodium percentage of the plants irrigated at each growth stage exceeded 4% as opposed to 2.70% and 2.27% in the leaves of plants under severe water stress (data not presented). Lower sodium contents in the tobacco leaves of treatments with more frequent irrigation were determined during the rainier 2003, though the sodium percentages of rain-fed and those receiving (V) treatment irrigated only once, were at the same levels as 2001. The effect of various irrigation water amounts, applied with the various irrigation programs included in the study, on the chemical traits of tobacco leaf was supported by the regression statistical analysis between seasonal irrigation water amounts and the percentage of chemical traits in tobacco leaves (Figs. 4–6). The regression curves and equations presented in the figures show that seasonal irrigation water amounts had a significant effect on the nicotine, chloride, nitrogen, sodium, and potassium contents of cured leaves from almost all primings in experimental years. In addition, all the relationships related to seasonal irrigation water amount and nicotine and/or chloride percentage, and almost all

Table 7 The effect of irrigation programs on maturity dynamics of tobacco leaves (% of total yield). Treatments and priming

VFR VF VR FR V F R V1FR V2FR VF1R VF2R VFR1 VFR2 Non-irr. * ** ***

2000

2001

2003

1.

3.

5.

6.

1.

3.

5.

6.

1.

3.

5.

6.

8.5b *** 13.8ab 11.7b 9.2b 17.6ab 12.6ab 8.4b 9.7b 7.7b 9.0b 10.1b 9.5b 10.1b 22.6a

31.2hij 41.5cd 43.4c 28.9ijk 66.2b 39.2de 37.2efg 32.1hi 28.4jk 26.9k 37.7de 34.3fgh 34.2fgh 69.9a

57.5e 61.1cd 64.3cd 48.7g 85.1b 64.5cd 53.6f 55.6ef 49.3g 49.3g 60.9d 64.2cd 64.7c 93.1a

100 100 100 100 100* 100 100 100 100 100 100 100 100 100*

11.3cd 14.8b 8.6e 9.7de 18.6a 10.9cd 3.3f 10.1de 10.7cde 11.8cd 11.1cd 12.5c 11.8cd 15.4b

29.2de 36.6b 29.5de 29.9cde 45.0a 32.3f 16.2cde 29.9cde 30.4cde 28.0e 27.7e 30.6cde 33.2c 37.2b

57.8h 74.8c 62.4fg 65ef 84.2a 69.0d 41.5i 60.6gh 60.2gh 62.8fg 68de 67.3de 67.4de 80.5b

100c 100c 97.0bc ** 100c 84.2a ** 100c 91.3bc ** 100c 100c 100c 100c 100c 100c 80.5a **

8.2e 8.6de 9.4d 9.0de 17.1a 12.4b 11.9bc 9.3d 8.5de 8.6de 11.3c 8.6de 8.2e 12.2bc

30.3g 36.5c 36.1c 34def 47.1a 39.9b 33.4ef 32.1fg 31.3g 34.7cde 36.7c 35.7cd 35.3cde 48.1a

87.0b 80.6d 72.4f 71.7f 87.0b 80.3d 60.7g 83.5c 73.2f 78.2de 79.9de 77.2e 80.8d 90.1a

100 100 100 100 100 100 100 100 100 100 100 100 100 100

5. Priming is not done due to maturity delay, and 6. priming performed 6 days after the 6. priming of the other treatments. Some of the upper leaves are not harvested at 6. priming due to maturity delay. The rest of the leaves are harvested 8 days latter. Means within columns not followed by the same letter are significantly different at the p < 0.01 level by Duncan’s Multiple Range Test.

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Fig. 4. Relationship between irrigation water amount and average nicotine content of tobacco leaves, p < 0.01.

the regression lines of the average of the primings from the experimental years are similar. Since seasonal irrigation water is the major component of seasonal evapotranspiration, the results of the regression analysis in terms of the relationship between seasonal evapotranspiration and the nicotine percentage of the tobacco leaf were also statistically significant (p < 0.01) for the both experimental years (detailed data not presented). Results from the regression analysis between the seasonal irrigation water amount and the average nitrogen content of the leaf showed that linear relationships exist between these parameters for both the experimental years, though the statistical significance is not as high as in the case of nicotine (Fig. 5). Thus, while all the relationships related to seasonal water amounts and nicotine percentage were statistically significant at the (p < 0.01) level, the relationship between seasonal irrigation water quantities and the mean nitrogen content for 2003 were significant at the p < 0.05 level. Quite a different type of relationship was determined in the case of the chloride content of the leaf, which considerably increases with an increase in the amount of irrigation water (Fig. 6). Although the results of the regression analysis were statistically significant at p < 0.01 level for both the study years, the relationship between the seasonal water amount and the chloride concentration of the leaf was much more evident and consistent during the drier 2001 experimental year when more water with high chloride concentration was used for irrigation.

4. Discussion

Fig. 5. Relationships between irrigation water amounts and average nitrogen content of tobacco leaf, p < 0.01.

relationships for the nitrogen and sodium were statistically significant at the (p < 0.01) level. As is evident from Fig. 4, the nicotine content of the leaves decreases linearly with an increase in irrigation water amounts applied during the experimental years. In addition, the slopes of

Fig. 6. Relationships between irrigation water quantity and average chloride percentage of tobacco leaf, p < 0.01 (2001) and p < 0.05 (2003).

The effect of irrigation or water stress applied at any stage of growth on the maturity dynamics of flue-cured tobacco is not well studied, though Walker and Vickery (1959) reported that weekly irrigation leads to higher maturity indices that could be of advantage in some years. De Roton et al. (1997) believe that degree of maturity has a great effect on nicotine content of the tobacco plant, and as tobacco plant maturity increases it has a higher quality index, with higher nicotine and sugar content and less total nitrogen. In this study that the significant part of the yield of the most stressed (non-irrigation and V) treatments were harvested in the first and second priming, while the last priming was delayed, appears to be a contradiction. This phenomenon could be a result of the effect of irrigation water and the soil moisture deficit on the ripening dynamics of the leaves. The growth and ripening of the lower leaves of the stressed treatments continues while some moisture is still available in the soil, whereas the process of formation and elongation of the upper leaves occurs in the period when water deficit is at its peak, and ripening is delayed or even does not occur at all. This explanation is supported by the results for maturity dynamics obtained during the rainy experimental year (2003), when the cumulative rate of the yield harvested at a certain priming was similar; and the last priming of all treatments, including the most stressed, was performed on one and the same day. A significant delay in leaf maturity due different precipitation characteristics during the final growth stages of the Virginia tobacco plant is reported by Biglouei et al. (2010). Marchetti et al. (2006) determined the delay in leaf maturity and harvest time caused by high N rates which could be viewed as a risk for the tobacco farmers since autumn rainfall may interfere with the harvesting operations and air temperature decrease may impede leaf ripening. The nicotine content of Nicotiana tabacum varieties grown commercially generally ranges from 0.3% to 3%, though 5% and even 7% have been recorded in some tobaccos. According to Beljo et al. (1999) based on chemical properties the quality and usability of tobacco is dependent on cultural prac-

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tices, including irrigation which decreases the nicotine content of the leaves. The drastic decrease in the levels of nicotine under the conditions of irrigation at each growth stage observed in our study supports the view of Sifola and Postiglione (2002) that when tobacco is grown in fields with abundant water, the percentage of nicotine in the leaf decreases. Actually average nicotine contents in the ranges of 0.85–1.14% in the leaf of adequately irrigated tobacco are close to the level of 1% obtained by grafting tobacco onto tomato rootstock, as reported by Ruiz et al. (2009), to reduce the harmful effects of this alkaloid on the health of smokers. Almost the same nicotine contents have been observed in the leaves of the first priming of Virginia tobacco grown in outdoor conditions of Drama, North Greece (Karaivazoglou et al., 2005). Low nicotine concentrations of 0.6–0.9% in the leaves of drip or sprinkler irrigated organic tobacco were determined by Bilalis et al. (2009). Our results contradict data published for the same cultivar (K-326) by Jerell (2001), since even the nicotine content of the most stressed rain-fed treatment (2.26%) was much lower than the 3.3–3.4% found by the author in VA, USA. Relatively higher alkaloid contents in the ranges of 2.5–4.0% were reported for flue-cured Virginia tobacco grown under various irrigation regimes in GA, USA (Maw et al., 1997, 2009), and 2.88–2.92% alkaloids found by Parker (2009) under the conditions in North Carolina. High nicotine contents of the middle leaves of the flue-cured tobacco grown in two different localities of China and in the Billate region of Ethiopia were determined by Ju et al. (2008) and Tassew (2007) respectively. The linear decrease in the nicotine content in both the experimental years of our study supports the view of Biglouei et al. (2010) that nicotine percentage decreases with an increase of irrigation ˇ level. Cavlek et al. (2006) reported that constant maintenance of soil moisture at a higher level resulted in better quality and a reduced nicotine concentration in tobacco leaf. An acceptable range for total nitrogen in the cured leaf would be 1.8–2.2%, with the desirable amount around 2.0% (Gaines et al., 1983; Maw et al., 1997, 2009). As a general rule, the nitrogen contents of the leaves in our study are similar to those from studies published by other researchers from different countries (Karim et al., 1999; Maw et al., 2009) and are within acceptable ranges for total nitrogen in cured leaves given by Gaines et al. (1983), Maw et al. (1997), and Maw et al. (2009). The differences between the nitrogen values of the leaves during 2001 and 2003 could be explained by the different amounts of irrigation water applied. Sifola and Postiglione (2003) indicated that nitrogen accumulation in the plant depended on both N and water, and the amount of N in the plant increased in response to N fertilization of irrigated plants. The lower nitrogen levels in the leaves under all treatments during the first year of our study probably occurred because of the leaching of the nitrogen from the effective root depth due to the application of 25–35% more water, under equal soil and fertilizer conditions. Moreover, Karaivazoglou et al. (2007) reported that various soil and weather conditions might contribute to the differences in nitrogen absorption, nitrogen and nicotine content of flue-cured tobacco leaves, and that under high precipitation levels, there might be a higher nitrogen uptake by tobacco plants. Reynolds and Rosa (1995) reported that in highly irrigated soils, N is leached; and its absorption by the tobacco plant and the accumulation in the leaves is decreased. The close relationship between seasonal irrigation water, or seasonal evapotranspiration, and the nitrogen content of the leaf determined in our study demonstrates that the nitrogen content of the leaves decreases with increasing water amounts, though the rate of the decrease varies from year to year. This inconsistency may be due to the effect of N fertilization and the relationship between N in the soil and irrigation water. Sifola and Postiglione (2003) indicated that the accumulation of nitrates in the leaf did not follow the patterns of N uptake by the plant and that nitrate accumulation in

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the leaf increased with the amount of N applied to the soil in irrigated plots during the period 36–49 DAT, but not in the late part of the growing season. Chloride is one of the most important chemical traits affecting the quality of flue-cured tobacco and high chloride levels in the leaf is a major concern to the tobacco industry as a whole. Cadersa and Atawoo (2001) pointed out that an excess level of chlorine produces poor burning capacity, muddy appearance and an undesirable odor, as well as other unfavorable characteristics in tobacco leaves. The threshold value for chloride in a good acceptable tobacco leaf is usually set at below 1.5% (Chari, 1995). In our study the highest mean concentrations of chloride during 2003 were about 2.7–2.8% versus 4.42–4.45% in 2001. No doubt these differences between the experimental years occurred due to both the different amounts of irrigation water and the high chloride content in the irrigation water, ranging from 2.67 to 3.08 me/l (Table 3). Moreover, Gaines et al. (1983) reported that a negative relationship exists between soil moisture content and chloride in tobacco leaf, while Juan and Castillo (1986) claimed that growing plants under rain-fed (dry) conditions produces tobacco with low chloride content. On the other hand, chloride values obtained during the rainy 2003 are comparable with those of 2.69–2.81% as published by Karim et al. (1999) for Virginia tobacco topped at different stages, and the maximum values of 2.5% obtained by Karaivazoglou et al. (2005) for tobacco irrigated with saline water under the soil and climatic conditions of Drama, Greece. Nonetheless even the lower concentrations of chloride determined in 2003 are higher than those of 1.0% and 2.1% reported by Peedin (1999) in the lower and upper leaves of flue-cured tobacco. The content of this chemical trait in the leaves of plants during both years of study was lower than the averages of 5.2–5.4% given for Burley tobacco that was irrigated with saline water in Southern Italy (Sifola, 2005). Our results for the linear increase of chloride in tobacco leaves with increasing water amounts agrees with those published earlier. Both chloride uptake and accumulation are often reported to increase linearly over a wide range of chloride concentration in the soil or in water used for irrigation. Some authors (Collins and Hawks, 1993; Peedin, 1999) have released studies showing that in flue-cured tobacco, leaf chloride concentration increases linearly with an increasing level of chloride in the soil, while the others (Cadersa and Atawoo, 2001) found no relationship between leaf chloride concentration and soil chloride level and concluded that other factors must be influencing chloride uptake and its mobilization into the leaf. This view supports the conclusion of Murthy (1965) that plant chloride level seems to be more closely related to the chloride level of irrigation water than soil chloride content. Sifola (2005) has studied the effect of irrigation with saline water on the quality characteristics of Burley tobacco and has determined that leaf accumulates chloride linearly with the rate of application within the ranges of 40.3–5100 kg ha−1 and that no further accumulation appears beyond those levels, due to chloride saturation of the leaf. Karaivazoglou et al. (2005) reported that the chloride concentrations in the leaves of all primings had a significant linear response to irrigation water chloride. However, Tsai (1979) pointed out previously that the increase in chloride concentration in flue-cured tobacco leaves is curvilinearly related to the amount of chloride added by irrigation water.

5. Conclusions From the results of the field experiments and the lab analysis done in 2000–2003, we can conclude that irrigation scheduling and water stress imposed during different stages of growth influenced the ripening dynamics of Virginia tobacco leaves. Severe water stress during the major part of or through the entire growing period

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causes a delay in the ripening of the leaves, which could have fatal consequences for tobacco production in regions with early autumn freezes. The irrigation regime and water stress are factors of great importance in terms of the quality of cured tobacco leaf. Favorable moisture conditions during the entire growing period or during the sensitive growth stages drastically decrease the nicotine and nitrogen content of the Virginia tobacco leaves, both of which are hazardous for humans. However, the percentage of chloride in the leaf, an undesirable trait that decreases the burning quality of tobacco, increases with increasing seasonal water amounts. Close linear relationships were determined between the seasonal irrigation water amount and the chemical traits content on the one hand, and the seasonal evapotranspiration and chemical traits on the other. Mutual relationships of high significance between nicotine and each of the traits – i.e. nitrogen, chloride, potassium, and sodium – were also established. Based on the results of the study, irrigation in general and the seasonal amount of irrigation water and irrigation scheduling, in particular, could be used as tools for moderating leaf nicotine, nitrogen, and chloride levels, and may provide a more desirable tobacco leaf chemistry.

Acknowledgements This paper includes part of the results obtained from a research project funded by the former General Directorate of Rural Services, Ankara. The authors acknowledge Ali Gidirislioglu (Agr. Engineer), Hayrullah C¸etinel (Field Technician), and Nedim Guven and Erol Buyukdere (Lab. Technicians), for technical support during the years of the study.

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