Plant and Soil 252: 313–323, 2003.© 2003 Kluwer Academic Publishers. Printed in the Netherlands.

313

The effect of nitrogen fertilization on nitrogen use efficiency of irrigatedand non-irrigated tobacco (Nicotiana tabacum L.).

M.I. Sifola1 & L. PostiglioneDepartment of Agricultural Engineering and Agronomy, University of Naples Federico II, Via Universita 100,80055 Portici (NA), Italy. 1Corresponding author∗

Received 3 January 2002; accepted in revised form 5 December 2002

Key words: agronomic efficiency, leaf nitrate, N uptake rate, physiological efficiency, recovery fraction, soil N

Abstract

Burley tobacco (Nicotiana tabacum L.) plants were grown in the field with or without irrigation and fertilizedwith 0, 120, 240 or 360 kg N ha−1 over two growing seasons to assess nitrogen use under Mediterranean climateconditions. Kjeldahl-N and NO3-N in leaves and stems and NO3-N and NH4-N in the soil at two depths (0–0.3and 0.3–0.6 m) were determined. The effect of N fertilization on total N accumulated in the canopy biomass wasmarkedly different between irrigated and non-irrigated plants. Under non-irrigated conditions N accumulated inthe plant did not depend on the amount of N applied. In both years, the amount of N in irrigated plants increased inresponse to the amount of N applied, starting from 49 to 56 days after transplanting (DAT). The average amount oftotal N in the canopy of irrigated plants, measured across all sampling dates of both years, ranged from 30 kg ha−1

of the unfertilized control to 88 kg ha−1 of the 360 kg ha−1 of N applied. The average amount of plant NO3-Nwas 2.6 and 4.4 kg ha−1 for non-irrigated and irrigated plots across all N treatments (means of 1996 and 1997).Nitrogen uptake rate (NUR) of non-irrigated plants was high between seedling establishment and the period ofrapid stem elongation in 1996 (from 36 to 50 DAT) and until flowering in 1997 (from 42 to 71 DAT), but muchless or negligible at later stages of plant development. Irrigation increased NUR dramatically in the second partof the growing season. Maximum NUR was estimated for plants receiving 240 or 360 kg N ha−1 in both years.The year of study did not affect the recovery fraction (RF), physiological efficiency (PE) or agronomic efficiency(AE). Irrigation and N fertilization had significant effects on both RF and AE, but not on PE. Maximum values ofRF were 45 and 22% for irrigated and non-irrigated treatments, respectively. In irrigated plots there was a negativerelationship between RF and increasing N levels at all sampling dates.

Abbreviations: AE – agronomic efficiency; DAT – days after transplanting; N – nitrogen; NUE – nitrogen useefficiency; NUR – nitrogen uptake rate; PE – physiological efficiency; RF – recovery fraction

Introduction

One of the main problems of tobacco productionin Mediterranean areas is that growers apply largeamounts of nitrogen fertilizers. Excessive nitrogen fer-tilization increases production costs and may result inpollution of ground and surface waters, without be-neficial effects on yield. Accumulation of nitrates inthe leaf due to excessive N applied is also detrimentalfor leaf quality. Nitrates, nitrites and nicotine have

∗ FAX No: +39-081-7755129. E-mail: sifola@unina.it

been reported to be precursors of tobacco specific N-nitrosamines, which are potentially carcinogenic (Tso,1990). In addition, a high protein content results in lowburning capacity (McCants and Woltz, 1967).

Appropriate management of N fertilization is animportant objective for tobacco growers. In cerealsit has been shown that a high efficiency in nitrogenuse is one of the most important factors to maximizeyield, and reduce cultivation costs and environmentalpollution (Raun and Johnson, 1999). Several studiesevidenced the effects of factors like root development

314

or source-sink relationships on the use of N with re-spect to applied N in cereal crops (Moll et al., 1982;Novoa and Loomis, 1981). In general, nitrogen use ef-ficiency (NUE) depends on soil processes, fertilizationpractices (amount, chemical form, mode and timing offertilizer distribution), and physiology (uptake, trans-location, assimilation and partitioning). Little workhas been carried out on the NUE of tobacco. In astudy where several genotypes were tested, Sisson etal. (1991) reported that NUE increased from the old-est to the most recently developed cultivars, and thatchanges in NUE were the result of changes in both Nuptake and the efficiency of utilization for dry matteraccumulation. In Burley tobacco, MacKown and Sut-ton (1997) investigated the effects of different levelsof N applied, either broadcast or side-dressed, at theonset of rapid growth in two different areas in Ken-tucky. They reported that fertilizer N use efficiencywas 36.6% when N was broadcast and that total Nin above-ground organs at harvest increased with in-creasing N supply, but N fertilizer recovery tended todecrease. Interestingly, N distributed at side-dressingincreased recovery (43 and 54% of the applied N at thetwo locations).

Soil moisture availability is the main factor influ-encing nitrogen uptake by the root and transport tothe leaf (Atkinson et al., 1969; Novoa and Loomis,1981; van Bavel, 1953). In a field experiment whereBurley tobacco was grown at two levels of N with orwithout irrigation, Atkinson et al. (1969) reported thatboth plant size and yield were increased by either ir-rigation or N fertilization. The effect of N was greaterin irrigated plots than in non-irrigated ones. Despitethe fact that tobacco Burley type is usually irrigatedand heavily fertilized, little work has been done onthe combined effect of irrigation and N fertilization onNUE under Mediterranean climate conditions.

In Southern Italy irrigation is indispensable forcommercial cultivation of Burley tobacco. In the SeleRiver plain, irrigation improved quality and increasedyield of plants fertilized with 120, 240 or 360 kg Nha−1, but not for those which received no N (Sifolaand Postiglione, 2002b). Under irrigated conditionsthe best results in terms of cigarette quality were ob-tained at N doses ranging between 120 and 240 kgha−1; however, there were no significant differencesin yield between irrigated plots fertilized with thethree different amounts of N (Sifola and Postiglione,2002b). These results are good evidence of the poten-tial for reducing the amount of N applied during thegrowing season. Nevertheless, irrigated tobacco fields

are almost always overfertilized in Southern Italy, andespecially on sandy soils.

The main objective of the present work was toestimate the combined effects of irrigation and Nfertilization on N uptake and RF, PE and AE offield-grown tobacco plants (Burley type) under Medi-terranean climate conditions. Nitrogen use efficiencywas determined at different stages of development inplants fertilized with 0, 120, 240 or 360 kg N ha−1

under irrigated and non-irrigated conditions.

Materials and methods

Plant material and experimental conditions

Trials were conducted on tobacco plants (Nicotianatabacum L.) ‘Burley’ type cv. C104 at the experi-mental farm of the University of Naples in the SeleRiver Plain (40◦37′N; 14◦58′E) in 1996 and 1997.Soil characteristics, cultural practices and precedingcrops were previously described (Sifola and Postigli-one, 2002b). In brief, seedlings were transplanted at a1.0 × 0.5 m distance in plots of 100 m2 on 5 June and20 May in 1996 and 1997, respectively. Fifty-three kgha−1 of P and 83 kg ha−1 of K were added to the top0.2 m of soil at transplanting. All plants were toppedat flowering (63 DAT in 1996 and 76 DAT in 1997)at a height of 24–25 leaves. An average of 64 plantsper treatment were harvested for yield determinationfrom the central part of each plot (32 m2) when about50% of leaves were ripe, 25% were overripe and 25%were unripe (97 and 118 DAT in 1996 and 1997, re-spectively). After harvest, canopies were air-cured inventilated rooms (Sifola and Postiglione, 2002a).

Irrigated and non-irrigated plots were fertilizedwith 0, 120, 240 and 360 kg N ha−1. Nitrogen was dis-tributed as follows: 50% as ammonium sulfate (21%N) at transplanting, and 50% as ammonium nitrate(26% N) at side dressing. The latter was split into twoapplications: (a) at seedling establishment, 22 and 30DAT in 1996 and 1997, respectively; (b) at the be-ginning of rapid stem elongation, 34 and 38 DAT in1996 and 1997, respectively (Sifola and Postiglione,2002b).

The non-irrigated tobacco plants received only15 mm of water at transplanting for seedling establish-ment. Plants were furrow irrigated 15 and 11 times fora total volume of 425 and 333 mm in 1996 and 1997,respectively (Table 1). Irrigated treatments receivedan amount of water equal to crop evapotranspiration

315

Table 1. Monthly distribution of the number of irrigations, irrigation volumes and rainfall in the2 years of study. The irrigation at transplanting (15 mm) was not included

Month No. of irrigations Volume (mm) Rainfall (mm)

1996 1997 1996 1997 1996 1997

May – – – – 48.7 13.3

June 3 2 45.0 30.0 32.3 5.2

July 7 5 219.2 131.1 – 31.2

August 5 4 160.4 172.3 – 37.2

September § – – – – – 5.8

§Plants were harvested within the first decade.

calculated as in Sifola and Postiglione (2002a). Tem-peratures and rainfall were recorded using a weatherstation on site and the seasonal courses were pre-viously reported (Sifola and Postiglione, 2002a). In1996, 82 mm of precipitation were concentrated inMay and June; in the summer 1997 it rained 93 mm,prevalently in July and August.

Plant nitrogen analysis

For the determination of N in the above-ground bio-mass, two plants per plot were sampled three andfour times starting from 36 and 42 DAT in 1996 and1997, respectively (Sifola and Postiglione, 2002b).The sampling intervals were: (I1) 36–49 and (I2) 50–79 DAT in 1996; (I1) 42–57, (I2) 58–71, and (I3)72–118 DAT in 1997. In 1996 samples were takenduring the following phenological stages: rosette (36DAT), rapid stem elongation (49 DAT), ripeness ofbasal and middle-lower leaves (79 DAT); in 1997:rosette (42 DAT), rapid stem elongation (57 DAT),flowering (71 DAT), commercial harvest (118 DAT).Nitrogen concentration in the plants was not measuredat commercial harvest in 1996, so that parameters de-rived from N concentration cannot be reported for thisstage.

For the determination of N, the tissue was oven-dried at 60 ◦C to constant weight, ground, and sievedthrough a 2-mm screen. One gram of dry tissue wasdigested with 8 mL of concentrated H2SO4 and 5mL H2O2 for 40 min in the presence of a cata-lyst (Se+CuO) and K2SO4, using a DK20 digester(DK42/26, VELP Scientific, Milan, Italy). Sodiumhydroxide (32% w/w) was added to distill the sampleusing an automatic unit (UDK 140, VELP Scientific).Nitrogen was collected as ammonia (NH3) in a 4%boric solution and titrated with H2SO4 in the presenceof an indicator (bromocresol green and methyl red in

95% ethanol). The Kjeldahl-N was calculated usingthe following equation:

Kjeldahl − N (%) = (mL H2SO4 used for titration

×NH2SO4 × 1.4)/sample dry weight (1)

where NH2SO4 was the normality of H2SO4 used fortitration.

Plant nitrate content (NO3-N) was determined by acolorimetric assay. Half gram of dry tissue was finelychopped, added to 100 mL of de-ionized water, andthen vortexed for 1 min, the slurry decolorized with2 g of activated charcoal powder. Then, 10 mL of thefiltered aqueous extract were diluted to 25 mL withde-ionized water and one Nitraver 5� powder pillow(Hach Company, Loveland, CO, USA) added. Absorb-ance was read at 500 nm using a Hach 2000 spectro-photometer (Hach Company). Total N was calculatedby summing the Kjeldahl-N and NO3-N.

Soil nitrogen analysis

To determine the mineral (NO3-N + NH4-N) in thesoil, samples were collected at two depths (0–0.3 and0.3–0.6 m) twice (before transplanting and at harvest)in both years. One sample was taken from the centralarea of each plot. For the determination of mineral N,3.5 mL of oven-dried soil (at 60 ◦C) were extractedwith 25 mL de-ionized water, then 0.02 g of NitrateExtraction Powder� (Hach Company, Loveland, CO,USA) was added. After shaking for 30 s, 1 mL ofthe aqueous extract was diluted into 25 mL deion-ized water. Ammonia-N was measured by adding 1mL of Nessler reagent before absorbance was read at425 nm. Nitrate-N was determined by adding one Ni-traver 6� powder pillow (Hach Company) and thenreading absorbance at 500 nm.

316

Figure 1. The effect of different amounts of N applied on aboveground dry matter of tobacco plants grown under non-irrigated (o)and irrigated (•) conditions. Plants were harvested at 97 and 118DAT in 1996 and 1997, respectively. Symbols are means ± standarderrors of the mean of three replicate blocks. Regression equations:(o) 1996 y = 0.3036 x + 1791.4, R2=0.100; (•) 1996 y = −0.0331x2

+ 23.033x + 2676.5, R2 = 0.996; (o) 1997 y = 2.365x + 2484.8, R2

= 0.643; (•) 1997 y = −0.0616x2 + 27.062x + 4137.8, R2 = 0.988.

Nitrogen uptake and nitrogen use efficiency

The N contents of leaf and stem were calculated bymultiplying the N concentration in each organ by therespective dry matter. Plant uptake was obtained bysumming the N contents of above-ground parts.

The daily rates of N uptake were calculated on ahectare basis (kg N ha−1 day−1), using the followingequation:

NUR = Ndm(n) − Ndm(n−j)

t(n) − t(n−j)

, (2)

where Ndm(n) − Ndm(n−j) represented the change in Ncontent on a dry matter basis between two subsequentsampling dates, and t(n)−t(n−j) was the time interval.

The RF, PE and AE were calculated according toNovoa and Loomis (1981). The RF, expressed as apercentage of the amount of N applied, was estimatedassuming that N taken up by plants receiving no ni-trogen represented soil N reserves available for cropgrowth.

RF = rNf − rN0

N× 100, (3)

where N was the amount applied with fertilization (kgN ha−1), rNf and rN0 indicated that accumulated inthe above-ground parts of fertilized and non-fertilizedplants, respectively. The RF was calculated three timesduring each growing season.

The PE was calculated as:

PE = LYf − LY0

rNf − rN0, (4)

where LYf and LY0 were the yields of cured leavesobtained from fertilized and non fertilized plants, re-spectively, and (rNf − rN0) were the values measuredduring the growing season at the third sampling date.The AE was calculated by multiplying RF by PE:

AE = RF × PE = LYf − LY0

N(5)

Experimental design and statistical analysis

The experimental design was a split-plot with theirrigation/dry-land treatments as main plots and N ap-plications as sub-plots replicated over three blocks.The data were usually analyzed by regression pro-cedures using COSTAT (CoHort Software, Monterey,CA, USA). Treatment means of RF, PE and AE wereseparated by least significant differences (LSD) afteranalysis of variance (ANOVA).

Results

In both years the amount of N applied had no effecton above-ground dry matter of plants grown withoutirrigation, but N fertilization increased dry matter ofirrigated tobacco plants (Figure 1). In 1996, maximumdry matter was obtained for the treatment fertilizedwith 360 kg N ha−1, whereas in 1997 it was reachedat 240 kg N ha−1. The dry matter of cured leaves in-creased in response to N application under irrigatedconditions with maximum yield achieved at 240 kg Nha−1 (Figure 2). Leaf yield of non-irrigated plants did

317

Figure 2. The effect of different amounts of N applied on yield ofair-cured leaves in tobacco plants grown under non-irrigated (o) andirrigated (•) conditions in 1996 and 1997. Plants were harvested at97 and 118 DAT in 1996 and 1997, respectively. Symbols are means± standard errors of the mean of three replicate blocks. Regressionequations: (o) 1996 y = 0.0053x2 + 2.4722x + 536.67, R2 = 0.762;(•) 1996 y = −0.0166x2 + 9.1694x + 667, R2 = 0.992; (o) 1997 y =1.3898x + 954.46, R2= 0.995; (•) 1997 y = −0.0081x2 + 5.4747x +1231.1, R2 = 0.994.

not show any change in response to N application in1996, but a linear increase in 1997.

The effect of N fertilization on total N accumu-lated in the above-ground dry biomass was differentbetween irrigated and non-irrigated plants. Under non-irrigated conditions the amount of N in the plant didnot depend on the amount of N applied and did notvary from 36 through 79 DAT in 1996 (Figure 3). In1997, there was an initial increase in total N contentfrom the 42nd to the 57th DAT, but the effect of N ap-plied was minor again. In both years, the N content ofirrigated plants increased from the second to the thirdsampling date in response to the amount of N applied(Figure 3). In 1997 all levels of N applied had a strong

effect on the N in the above-ground biomass at the dateof commercial harvest.

Nitrogen uptake rate of non-irrigated plants washigh between seedling establishment and the periodof rapid stem elongation, but much less or negligibleat later intervals (Table 2). Under dry-land conditionsmaximum NUR was obtained for the 120 kg N ha−1

dose for the first interval (I1) in both years, and forthe 360 kg N ha−1 at sampling interval I2 in 1997.Irrigation increased NUR dramatically at interval I2and maximum NUR was estimated at 240 and 360 kgN ha−1 for all intervals in 1997 (Table 2). Negativevalues of NUR were calculated for non-irrigated plotsat I2 in 1996 and at I3 in 1997 (except for the 120 kgN ha−1).

There was a negative relationship between increas-ing N levels and RF for irrigated plants at all samplingdates (Figure 4). The slopes of the regression lineswere steeper in 1997 than in 1996. For non-irrigatedplants the slopes were relatively flat, except at the 57DAT sampling date in 1997. Maximum RF was 22%for the 120 kg N ha−1 treatment at 57 DAT in 1997,i.e., during the period of rapid stem elongation. Theaverage RF across all N fertilization treatments was8.5%. Under dry-land conditions there were no signi-ficant differences in RF when either sampling dates orN treatments were compared. With irrigation, apparentN recovery increased with crop age and decreased withN supply, but never exceeded 45%.

Table 3 reports the main effects of year, irrigationand N fertilization on RF, PE and AE. The year ofstudy did not affect any of these efficiency indexes.Irrigation and N fertilization had significant effects onboth RF and AE, but not on PE. The percentage in-crease in RF and AE due to irrigation was 253 and242% of the value of non-irrigated plots, respectively.In general, there were parallel changes in RF and AEin response to irrigation or N fertilization, but no sig-nificant interaction between the treatments on NUEcomponents.

Above-ground biomass NO3-N content increasedin response to increasing levels of N applied. The av-erage amount of NO3-N taken up by the plant was 2.4vs. 4.6 kg ha−1 for non-irrigated and irrigated plotsacross all N treatments in 1996, and 2.8 vs. 4.2 kg ha−1

in 1997 (data not shown).During the 1996 growing season, the leaf nitrate

concentration increased for irrigated plots which re-ceived at least 120 kg N ha−1. At 49 DAT there was alinear increase in leaf nitrate concentration in responseto the amount of N applied in irrigated plots, whereas

318

Figure 3. The effect of different amounts of N applied (0, 120. 240, 360 kg ha−1) on total N content in above-ground parts of non-irrigatedand irrigated plants in 1996 and 1997. Bars indicate standard errors of the mean of three replicates.

Table 2. The effect of irrigation and N fertilization on the nitrogen uptake rate (kg ha−1 day−1) at different intervals during the growingseason. Data are means ± standard errors of three replicates. Legend: (I1) 36–49 and (I2) 50–79 DAT in 1996; (I1) 42–57, (I2) 58–71, and(I3) 72–118 DAT in 1997. The sampling dates corresponded to the following phenological stages: in 1996, rosette (36 DAT), rapid stemelongation (49 DAT), ripeness of basal and middle-lower leaves (79 DAT); in 1997, rosette (42 DAT), rapid stem elongation (57 DAT),flowering (71 DAT), commercial harvest (118 DAT)

Nitrogen 1996 1997

(kg ha−1) Non-irrigated Irrigated Non-irrigated Irrigated

I1 I2 I1 I2 I1 I2 I3 I1 I2 I3

0 1.28 −0.39 1.13 0.45 1.20 0.67 −0.01 2.02 1.63 −0.21

±0.35 ±0.04 ±0.19 ±0.16 ±0.13 ±0.23 ±0.15 ±0.06 ±0.56 ±0.33

120 1.61 −0.32 1.35 1.94 2.15 0.34 0.13 3.60 1.99 −0.22

±0.02 ±0.07 ±0.29 ±0.29 ±0.39 ±0.12 ±0.0003 ±0.10 ±0.03 ±0.06

240 1.45 −0.63 2.40 1.90 1.85 1.61 −0.09 4.14 2.29 −0.13

±0.24 ±0.30 ±0.37 ±0.60 ±0.70 ±0.49 ±0.32 ±0.49 ±0.25 ±0.32

360 1.11 −0.27 3.41 2.49 1.31 2.57 −0.06 3.60 2.60 1.04

±0.19 ±0.09 ±0.66 ±0.18 ±0.56 ±0.88 ±0.34 ±0.35 ±0.58 ±0.36

319

Figure 4. The effect of different amounts of N applied on the recovery fraction of non-irrigated and irrigated plants in 1996 and 1997. Symbolsare means ± standard errors of the mean of three replicate blocks. DAT, days after transplanting.

Table 3. The effect of the year of study, irrigation and Nfertilization on recovery fraction, physiological efficiency andagronomic efficiency of Burley tobacco. Samples were harves-ted at 79 and 71 DAT in 1996 and 1997, respectively. The meanvalues of each year were tested for homogeneity of variancebefore data for both years were pooled together

Recovery Physiological Agronomic

fraction1 efficiency1 efficiency1

(%) (kg kg−1) (kg kg−1)

Year

1996 20.0a 14.0a 2.6a

1997 18.6a 18.1a 2.7a

Irrigation

NI 8.5B 18.0a 1.2b

I 30.0A 14.0a 4.1a

N fertilization

120 24.3a 16.4a 3.5a

240 18.6a 14.8a 2.5ab

360 14.9a 16.8a 2.0b

1For definition see Materials and methods.NI, non-irrigated; I, irrigated. Different letters indicate leastsignificant differences at P < 0.05; P < 0.01 (capital letters).

in non-irrigated plants leaf nitrate concentrations weresimilar across all N treatments (120, 240 and 360 kgha−1) (Figure 5). In 1997, leaf nitrate concentrationsin irrigated plots fertilized with 240 and 360 kg N ha−1

were significantly higher than those receiving no N,starting from 42 DAT. The amount of N applied de-termined a linear increase in leaf nitrate concentrationin both irrigated and non-irrigated plants, except for ir-rigated plots at 118 DAT, when leaf nitrate was similaracross all N treatments (Figure 5).

In 1996, the soil NO3-N pool before transplant-ing was 47.7 and 48.4 kg ha−1 for the 0–0.3 and the0.3–0.6 m layers, respectively, whereas in 1997 initialvalues were only 15.6 and 27.3 kg ha−1. Soil NO3-Npool at harvest was markedly higher in non-irrigatedthan irrigated plots. The mean values across all depthsand N treatments were 189.1 vs. 75.3 kg ha−1 in 1996,and 88.1 vs. 10.4 kg ha−1 in 1997, for non-irrigatedand irrigated plots, respectively. In both years therewere no differences due to soil depth for the irrigatedtreatments, whereas in 1997 under dry-land conditionsthere was a higher NO3-N content in the topsoil (0–0.3 m) than in the 0.3–0.6 m layer (Figure 6). Before

320

Figure 5. The effect of different amounts of N applied on leaf nitrate content of non-irrigated and irrigated plots in 1996 and 1997. Symbolsare means ± standard errors of the mean of three replicate blocks. DAT, days after transplanting.

transplanting soil NH4-N was 60.7 and 86.9 kg ha−1

(0–0.3 and 0.3–0.6 m depth, respectively) in 1996, and140.4 and 117 in 1997. There were no differences insoil NH4-N due to watering regime, N fertilization orsoil depth at 97 and 118 DAT (commercial harvest in1996 and 1997, respectively) in both years (data notshown).

Discussion

In both irrigated and non-irrigated plants N fertiliz-ation affected yield of cured leaves and dry matteraccumulation at harvest in a similar way. This impliesthat in Burley tobacco growth sustains yield over thewhole growing season regardless of the amount of Nsupplied through the soil, differently from grain cropswhere yield depends on reproductive processes oftenin competition with vegetative growth. The previouslyreported greater dry matter partitioning into leaves

of plants fertilized with 360 kg N ha−1 (Sifola andPostiglione, 2002b) did not correspond to greater yieldof cured leaves, because more leaves remained unripeand produced greater cull at the maximum level of Napplied.

Nitrogen accumulation in the plant depended onthe availability of both N and water. The amount of Nin the plant increased in response to N fertilization inirrigated plants only, and the rate of accumulation wasgreater during stages of active growth as also reportedby Below (1995). In flue-cured tobacco, Goenaga etal. (1989a) showed that N partitioning between plantparts reflected the growth rates of different tissues andthat little remobilization from older to younger tissuesoccurred when N uptake from the soil was appreciable.Atkinson et al. (1969) reported that plant NO3-N in-creased with N fertilization, but that the effect ofirrigation depended on the amount of N applied. Ir-rigation decreased the content of nitrogen compounds(including nitrates) in cured leaves of plants receiving

321

Figure 6. The effect of different amounts of N applied on soil NO3-N content of non-irrigated and irrigated plots in 1996 and 1997. Soilsamples were taken at 0–0.3 and 0.3–0.6 m depths. Symbols are means ± standard errors of the mean of three replicate blocks.

low amounts of N, but increased that of plants treatedwith high doses of N.

In our study the high NO3-N in the soil of non-irrigated plots throughout the growing season waspresumably the effect of less N uptake due to low soilmoisture availability. In Burley tobacco, Phillips et al.(1991) showed that different levels of soil moistureinfluenced N uptake, yield of cured leaves, plant dryweight and total N in the plant.

The accumulation of nitrates in the leaf did not fol-low the patterns of N uptake by the plant (Figures 3and 5). Nitrate accumulation in the leaf increased withthe amount of N applied to the soil in irrigated plotsduring the period 36–49 DAT, but not in the late partof the growing season 1996. In 1997 the relatively wetsummer made the effect of N fertilization on the leafnitrate content evident for a longer period and also innon-irrigated plants. Atkinson and Sims (1973) alsoshowed the positive correlation between N applied andleaf nitrate content, but did not report any data on theeffect of irrigation.

The decrease in leaf nitrate content of irrigatedBurley tobacco measured starting from early flower-

ing was beneficial for cigarette quality (Sifola andPostiglione, 2002b), since nitrates and quality arenegatively correlated in tobacco leaves (Tso, 1990).Although we did not investigate the reason why leafnitrates declined, it is likely that nitrates were con-verted into amino acids and other compounds morereadily utilized during leaf ripening.

The efficiency of N absorption by the plant, ex-pressed as RF, was quite low. Maximum values ofRF (45%) were measured for irrigated plants fertil-ized with 120 kg N ha−1 after flowering (71 DAT in1996 and 79 DAT in 1997). The N recovered increasednot only during periods of active growth of irrigatedplants in both years, but also in non-irrigated plantsin 1997 when the precipitation regime was more fa-vourable to N uptake. Under dry-land conditions, RFreached a maximum of 22% in plants fertilized with120 kg N ha−1 in 1997 (means across all samplingdates were 9.9 and 15.7% in 1996 and 1997, respect-ively) and decreased to 3.6 and 7% (means across allsampling dates) in plants that had received 360 kg Nha−1 in 1996 and 1997, respectively. MacKown andSutton (1997) reported comparable RF values (43–

322

54%) for Burley tobacco fertilized with 168 kg N ha−1

at side-dressing, using our same approach (differencemethod) to calculate the recovery fraction. It should benoted that, although their experiments were conduc-ted under dry-land conditions, both sites in Kentuckyreceived much more rain than ours in the Sele RiverPlain. Values of RF ranging between 30 and 55% havebeen also reported for various cereal crops (Muchow,1990; Novoa and Loomis, 1981; Raun and Johnson,1999; Sifola et al., 1997). The high amount of re-sidual mineral N at the end of the growing seasonand losses due to the topping of plants may explainthe low RF values. Alternatively, factors responsiblefor N losses that could explain the low RF valuesincluded denitrification, leaching, errors in method-ology for calculating RF, timing of application, andoverfertilization (Novoa and Loomis, 1981). Our res-ults do not allow to determine which of these factorsplayed the most important role, but the data reportedin Figure 4 and Table 3 indicate that RF was decreasedby high amounts of N applied. Similarly, Santhi andPonnuswamy (1993) compared two levels of N fertil-ization (75 and 150 kg N ha−1) on different cultivarsof chewing tobacco and showed that NUE decreasedwith increasing amounts of N applied and reached amaximum of 39% for the 75 kg N ha−1 level in thebest performance cultivar. Translocation of soluble Nand carbohydrates from the above-ground parts to theroot and root growth has been utilized to explain thelittle uptake of N in flue-cured tobacco during the lastpart of the growing season (Goenaga et al., 1989a,b).

The PE was not affected by either irrigation or Ntreatment. This is in contrast with previous works re-porting that PE was affected by N fertilization and bythe cultivar in flue-cured tobacco (Sisson et al., 1991)and maize (Moll et al., 1982). Moll et al. (1982) hypo-thesized that the negative correlation between PE andN fertilization could be explained by less N translo-cated to the grains at high regimes of N fertilization.When we calculated PE based only on leaf N con-tent, we found that N partitioned to the leaf of Nfertilized non-irrigated plants was less than that alloc-ated in irrigated plants which received no N. The PEof non-irrigated plants was also higher, although nonsignificantly, than that of irrigated ones (Table 3), in-dicating that water deficit could increase the efficiencyof N utilization within the plant. Since growth anddry matter partitioning to the stem are also reduced intobacco plants grown under dry-land conditions (Si-fola and Postiglione, 2002b), it is likely that less N istranslocated to the stem when soil moisture is low.

Although tobacco leaves are probably a weakersink than reproductive sinks of cereals which may in-fluence the effect on PE, we do not have conclusiveevidence about the reason for the absence of any effectof N treatment on PE.

Changes in AE mainly reflected those in RF andthe efficiency of N uptake. The AE was lower underdry-land than irrigated conditions and diminished withincreasing levels of N applied. Novoa and Loomis(1981) reported changes in AE due to increasing levelsof N fertilization that changed the harvest index ofcereals, i.e. the strength of reproductive sinks.

In conclusion, reducing the amount of N appliedin the field decreases fertilization costs and soil con-tamination by increasing the proportion of fertilizer Ntaken up by the plant. Nitrogen should be give in atleast two applications at side dressing. The efficiencyof nitrogen utilization is slightly increased under dry-land conditions, which may indicate that managingirrigation to impose predetermined periods of waterdeficit is useful to save both water and N under Medi-terranean conditions. Under irrigated conditions theamount of N should not exceed 240 kg ha−1. However,recommendations of N applications for tobacco grow-ers should be conservative to reduce the environmentalimpact of doses of N in soils where mineral supply be-fore transplanting are already high. It should be notedthat, at the present, tobacco growers in Campania tendto overfertilize and that current recommendations aremostly empirical.

More work is needed to determine the range of soilmoisture availability for the most efficient use of N byBurley tobacco.

Acknowledgements

The authors gratefully acknowledge Antonio Punzofor excellent technical assistance. This research workwas carried out with the financial support of the Com-mission of The European Community – CommunityFund for Tobacco Research and Information – Com-mission Regulament (EEC) n. 2427/93. It does notnecessary reflect the views of the Commission and inno way anticipates its future in this area.

References

Atkinson W O and Sims J L 1973 The influence of variety and fer-tilization on yield and composition of Burley tobacco. TobaccoInt. 175, 97–98.

323

Atkinson W O, Ragland J L, Sims J L and Bloomfield B J 1969 Ni-trogen composition of Burley tobacco. I. The influence of irrig-ation on the response of Burley tobacco to nitrogen fertilization.Tobacco Sci. 13, 123–126.

Below F E 1995 Nitrogen metabolism and crop productivity. InHandbook of Plant and Crop Physiology. Ed. M Pessarakli. pp.275–301. Marcel Dekker Inc., New York.

Goenaga R J, Long R C and Volk R J 1989a Uptake of nitrogenby flue-cured tobacco during maturation and senescence. I. Par-titioning and remobilization of reduced-N fractions. Plant Soil120, 141–147.

Goenaga R J, Volk R J and Long R C 1989b Uptake of nitrogen byflue-cured tobacco during maturation and senescence. II. Parti-tioning of nitrogen derived from soil and fertilizer sources. PlantSoil 120, 133–139.

McCants C B and Woltz W G 1967 Growth and mineral nutrition oftobacco. Adv. Agron. 19, 211–269.

MacKown C T and Sutton T G 1997 Recovery of fertilizer nitrogenapplied to Burley tobacco. Agron. J. 89, 183–189.

Moll R H, Kamprath E J and Jackson W A 1982 Analysis and in-terpretation of factors which contribute to efficiency of nitrogenutilization. Agron. J. 74, 562–564.

Muchow R C 1990 Effect of nitrogen partitioning and yield in grainsorghum under differing environmental conditions in the semi-arid tropics. Field Crops Res. 25, 265–278.

Novoa R and Loomis R S 1981 Nitrogen and plant production. PlantSoil 102, 177–204.

Phillips R E, Leggett J E, Chaplin J F and Zeleznik J M 1991 Ef-fects of water stress on growth, assimilation, and partitioning ofcarbon and nitrogen in burley tobacco. Tobacco Sci. 35, 22–27.

Raun W R and Johnson G V 1999 Improving nitrogen use efficiencyfor cereal production. Agron. J. 91, 357–363.

Santhi P and Ponnuswamy K 1993 Varietal performance and nitro-gen management of chewing tobacco (Nicotiana tabacum L.) inalfisol of lower Bhavani project area. New Bot. 20, 37–41.

Sifola M I and Postiglione L 2002a The effect of increasing NaClin irrigation water on growth, gas exchange and yield of tobaccoBurley type. Field Crops Res. 74, 81–91.

Sifola M I and Postiglione L 2002b The effect of nitrogen fertiliz-ation and irrigation on dry matter partitioning, yield and qualityof tobacco (Nicotiana tabacum L.) Burley type. Agric. Med. 132,33–43.

Sifola M I, Mori M and Ceccon P 1997 Biomass and nitrogen parti-tioning in sorghum (Sorghum vulgare L.) as affected by nitrogenfertilization. Ital. J. Agron. 1–2, 103–109.

Sisson V A, Rufty T W and Williamson R E 1991 Nitrogen-useefficiency among flue-cured tobacco genotypes. Crop Sci. 31,1615–1620.

Tso T C 1990 Production, physiology and biochemistry of tobaccoplant. Ideals Inc., Beltsville, MD, USA. 753 p.

van Bavel C H M 1953 Chemical composition of tobacco leaves asaffected by soil moisture conditions. Agron. J. 45, 611–614.

Section editor: Z. Rengel