Directory UMM :Data Elmu:jurnal:E:European Journal of Agronomy:Vol12.Issue2.March2000:

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Influence of sulfur on apparent N-use e

_ffi

ciency, yield

and quality of oilseed rape (

Brassica napus

L.)

grown on a calcareous soil

J. Fismes

_a

, P.C. Vong

_a,

*, A. Guckert

_a

, E. Frossard

_b

aLaboratoire Agronomie et Environnement ENSAIA-INRA, 54505 Vandoeuvre le`s Nancy cedex, France

bEcole Polytechnique Fe´de´rale de Zurich, Eschikon 33, CH-8315 Lindau, Switzerland

Accepted 4 October 1999

Abstract

In the Lorraine region, major soils used for winter oilseed rape are calcareous. Across two pot and two field experiments, we studied the influence of sulfur applied at different levels on apparent N-use efficiency (ANU ), yield, glucosinolate (GLS ) and oil content of seeds. The soil received a constant dose of 200 kg N ha−1 as ammonium nitrate, urea or cow slurry and three levels of S: 0, 30 and 75 kg ha−1as ammonium thiosulfate (ATS), MgSO

4or

ATS plus MgSO

4. Apparently, oilseed rape is a N-inefficient crop as revealed by low ANU values which varied within

36 and 53%from field experiment versus 25 and 61%under controlled conditions. In both cases, S additions improved N-use efficiency only at the highest dose of 75 kg S ha−1, which is not attained by ATS with 35 kg S ha−1(10%v/v). S fertilization increased the GLS contents that were found to be negatively correlated with plant N/S uptake ratios observed at maturity. The most important increase in GLS content by 52% was noted with cow slurry in the pot experiment. But, as a whole, the GLS levels remain below the European norm of 18mmol g seed−1. Moreover, the oil content (%DM ) of seeds decreased (but the total production increased ) when the soil was fertilized with N and with or without S. The results showed that N and S nutrition during the growth were tightly linked. Their interactions, as reflected by plant uptake, are synergistic at optimum rates and antagonistic at excessive levels of one of the both. Collectively, the results indicate that S fertilization is required to improve N-use efficiency and thereby maintaining a sufficient oil level and fatty acid quality. © 2000 Elsevier Science B.V. All rights reserved.

Keywords:Ammonium thiosulfate; Apparent N-use efficiency; Glucosinolate and oil content; N and S interactions; N and S nutrition; Oilseed rape

1. Introduction (Ceccoti, 1996). Consequently, the poor efficiency of N caused by insufficient S needed to convert N into biomass production may increase N losses Nitrogen and sulfur are both involved in plant

from cultivated soils (Schnug et al., 1993). protein synthesis. The shortage in S supply for

Oilseed rape (Brassica napusL.) is an important crops decreases the N-use efficiency of fertilizers

oilseed crop in the Northern agricultural region of France. In the region of Lorraine, major soils used

* Corresponding author. Tel.:+33-383-59-58-98;

for this crop are calcareous, rich in organic-N and

fax:+33-383-59-57-99.

organic-S, but a deficiency in available S at the E-mail address:[email protected]

(P.C. Vong) beginning of the growing season is often detected.

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This could be due to either important losses of in calcareous soils when S supply was above 30 kg ha−1, and an application of 60 kg S ha−1 sulfates by leaching during the winter, which can

reach 80 kg ha−1 (Suhardi, 1992), or slow min- increased the GLS content by 20%. However, with the general widespread use of double O cultivars, eralization hampered by both low spring

temper-ature and alkaline ntemper-ature of these soils (Merrien, reasonable levels of GLS can be achieved owing to the ability of these cultivars to store ( Zhao 1988).

Nutritionally, oilseed rape and Brassica species et al., 1993a) and to regulate ( Fismes et al., 1999) the excess of S in pod walls. Based on these in general require S during their growth ( Zhao

et al., 1993a), for the synthesis of both protein observations, sufficient S supply to maintain the optimum yield is required. For this purpose, ATS and naturally occurring glucosinolates. Oilseed

rape is thus particularly sensitive to S deficiency, is gaining in use, because besides the inhibitory actions on N, it contains high S concentration and in the last 10 years, significant yield responses

to S application jointly with N have been achieved (Goos, 1985). In field studies, apart from maize (Graziano and Parente, 1996), bromegrass (Janzen and Bettany, 1984; Merrien, 1988; Zhao

et al., 1993b; Withers and O’Donnel, 1994; (Lemond et al., 1995) and recently tall fescue (Sweeney and Moyer, 1997), its extension to other MacGrath and Zhao, 1996).

In general, higher plants assimilate N and S in crops such as rapeseed is scantily reported in the literature. On the other hand, there is a substantial amounts proportional to that incorporated into

amino acids and proteins, which suggests that N body of information on plant N nutrition and the data related to both N and S are still very poor, and S requirements are closely interrelated (Rendig

et al., 1976; Friedrich and Schrader, 1978). at least for rapeseed. Accounting for the above observations, this work aimed to examine how Increasing N fertilizer rates aggravate S deficiency

of oilseed rape and reduce seed yield when avail- increasing levels of S fertilization in such a calcare-ous soil could affect the efficiency of N utilization able S is limiting (Janzen and Bettany, 1984). A

N/S ratio value>16 in plant tissues indicates that and thereby the yield and the quality of seed, in particular the GLS and oil content. It also gives S is insufficient for protein formation in maize

(Cassel et al., 1996) and tall fescue (Sweeney and further information about the links which exist between N and S nutrition at the main stages of Moyer, 1997) and the excess of unassimilated

NO−

3–N, amides or free amino acids accumulates plant growth. (Sexton et al., 1997). Conversely, N addition

increases seed yield in S-sufficient conditions, and

an optimum oil quality and maximum yield 2. Materials and methods responses to both N and S applications are

obtained when the amounts of available N and S 2.1. Materials are balanced (Joshi et al., 1998).

Several works have also shown that S supply The soil used in this study is the typic Rendolls (Rendzina), the most representative of Lorraine may increase glucosinolate (GLS) content of

oil-seed rape (Janzen and Bettany, 1984; Merrien, soils for rapeseed crops. This soil contains 2.2% organic C, 0.28% organic N and 0.043% organic 1988; Schnug, 1991; Zhao et al., 1993b; Withers

and O’Donnel, 1994). Thus, if an insufficient S S. Its pH is alkaline (pH water: 8). According to Merrien (1987), this soil is high in organic-N and nutrition leads to a decline in seed yield, an

excessive S supply can affect meal quality by organic-S content. increasing seed GLS content. Indeed, the

glucosi-nolates are hydrolysed by the myrosinase enzyme 2.2. Experimental protocol upon seed processing to form undesirable tasting,

toxic and goitrogenic compounds (Rosa and 2.2.1. Pot experiments

To ensure ‘baseline samples’ that were influ-Rodrigues, 1998). Merrien (1988) observed a

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due to seasonal peaks in C, N and S inputs, the 2.2.2. Field experiments

In 1995–96 and 1996–97, the winter rapeseed soil for pot experiments was sampled in late

(cultivar Goeland ) was sown by CETIOM (Centre January before it had been fertilized.

Technique Interprofessionnel des Ole´agineux In 1995, the air-dried and sieved soil was

fertil-Me´tropolitains) on August with a density of ized with 200 kg N ha−1 as ammonium nitrate

65 g m−2and 40 cm between rows. Prior to sowing, (AN ), urea ( UR) or cow slurry (SL) and with or

a weeding with Trifuralin and a preventive treat-without 75 kg S ha−1 as ammonium thiosulfate

ment with Mercaptodimethur against slugs were (ATS ). The weight of soil taken for the

calcula-made. The level of sulfur as ATS was maintained tions of the corresponding nutrient rates per pot

at the normal dose of 30 kg ha−1 but comple-was 2400 t ha−1 (20 cm depth and 1.2 density).

mented or not with MgSO

4to keep the traditional After bringing the soil moisture to 80% of WHC

dose of S practised in the region for oilseed rape, with the above fertilizer solutions or distilled water

the level of N being constant to 200 kg ha−1. The for the control, the soil was transferred into PVC

experiment consisted of nine treatments distributed pots which contained an equivalent of 1 kg dry _{according to a complete randomized block design} soil (105°C ). Due to technical reasons, the experi- _{with four replicates each. Each plot had 16.7 m}₂_, ment with slurry was performed with the same soil _{but in order to minimize edge e}

ffects, the plants but three months later. The experiment consisted _{were sampled in an area of 10 m}₂_{. The annual} of seven treatments with five replicates each. In _{background fertilization of P and K were 35 and} each pot, five seeds of cultivar Hybridol (double _{83 kg ha}₋₁_{, respectively. N and S applications were} O spring rapeseed ) were sown and after germina- _{split into two fractions: 25%} _{in March and the} tion, only one plant was kept until maturity. remainder about one month later. P, K and During the plant growth, the pots were regularly MgSO

4were applied with this second fraction. For watered to maintain the soil moisture near to 80% reasons of e_fficiency, ATS was sprayed first onto of WHC. At two-leaf stage, a preventive treatment the soil prior to N application.

by Flusilazol and Carbendazim against Sclerotinia

2.3. Plant sampling and chemical analysis sclerotiorum and Erysiphe graminis was made.

In 1996, two levels of S were used: 30 kg ha−1

Sequential plant samplings ( Table 1) were made as ATS, in order to comply with the economically

at three growth stages (CETIOM, INRA, PV advised dose for ATS and 75 kg as ATS or

classification): at rosette stage, five open leaves MgSO

4, to respond to the traditional S fertilization _{(B5); at flowering stage (F2) and at seed maturity} of oilseed rape. In addition, the cow slurry was

(G5) under controlled conditions; and at green abandoned in the second year because it is not

bud ( E), at late flowering (F2) and late pod (G4) suitable for field-grown oilseed rape. The

experi-in field experiments. In these latter trials, seeds mental procedure was the same as previously

were harvested at maturity (G5) for seed analysis described. For this experiment, the Tanto cultivar

and seed yield determination. In the pot experi-was chosen. From three-leaf stage to flowering, a

ments, plants were separated from the soil for treatment with a solution of micro-nutrients was

analysis. Roots were not recuperated at the first performed due to the visual symptoms of deficiency

sampling date due to the low biomass production observed on the leaves. All pot experiments were _{at this stage. In field experiments, plants were cut} conducted in a growth chamber. The growth condi- _{at the soil surface in a square area of two rows} tions were: 14 h day at 16°C and 10 h night at _{and 1 m length (0.8 m}₂_{). Roots were not sampled} 12°C from sowing to flowering, 16 h day at 21°C _{in field experiments.}

and 8 h night at 16°C from flowering to maturity _{Plants were then separated into roots (pot} and 70% air humidity. The light intensities at the _{trials), leaves, stems, pod walls and seeds,} accord-plant canopy height varied from 250 to ing to growth stages. Samples were dried at 80°C 350mE m−2s−1 at the rosette and full flowering for 24 h and dry matter measured. The different plant parts of each replicate sample (five and four stage, respectively.

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Table 1

Details of the cultivation of oilseed rape (Brassica napusL.) in the two field and the two pot experiments

Field experiments Pot experiments

1995–96 1996–97 1995 1996

Previous cropping Winter wheat Spring wheat

Cultivar Goeland Hybridol Tanto

Sowing date 24/08/95 19/08/96 15/03/95 19/02/96

Sowing rate 65 g m−2 1 seed pot−1

Fertilizer applications (except NO and SO treatment)

First N dressing 50 kg ha−1, in March Equivalent of 200 kg ha−1, at sowing Second N dressing 150 kg ha−1, in April

First S dressing 10 kg ha−1, in March Equivalent of 30 or 75 kg ha−1, at sowing Second S dressing Remainder (20 or 65 kg ha−1), in April

Plant sampling dates and corresponding growth stages of oilseed rape

First sampling 25/4/96, E 16/4/97, E 18/4/95, B5 02/4/96, B5 Second sampling 21/5/96, F2 13/5/97, F2 19/6/95, F2 22/4/96, F2 Third sampling 03/6/96, G4 09/7/97, G4 24/7/95, G5 27/5/96, G5 Harvest date 19/7/96, G5 24/7/97, G5 24/7/95, G5 27/5/96, G5

replicates per treatment for pot and field trials, In 1995’s pot experiment, it is important to note respectively) were ground and total N and S that the only-N application as UR and AN caused contents were determined by the autoanalyzer NA total pod abortions, therefore the effect of S as 1500 (Carlo Erba) fitted for simultaneous analysis ATS cannot be determined. In contrast, slurry of total N and S. The GLS contents were analyzed fertilized with ATS at 75 kg S ha−1gave a signifi-by HPLC equipped with a pump ( ThermoQest _{cant seed yield increase compared with slurry} 8800), a sampler ( T.S.P. 8875), a Lichrospher _{treatment alone (}+20%). In 1996, with the cultivar chromatography column 5mm, 125×4 mm₂ _{Tanto, no pod abortions have been observed with} (Merck) and a UV detector ( Knauer 87000) and _{AN and UR application. But the lower dose of} the oil content by NMR. Both compounds were _{30 kg ha}₋₁ _{as ATS did not increase significantly} analyzed by the approved laboratory of CETIOM _{seed yields even compared with the control, except} using a pooled sample representative of the repli- _{the treatment AN}₊_ATS.

cates. This laboratory specializes in the GLS and _{In total, the seed yields from the growing season} oil content analyses according to the norm NF

1995–96 (field experiment) averaged about EN ISO 916 7-1.

3.26 t ha−1 versus 4.16 t ha−1 from 1996–97. The In consequence, except the data of oil and GLS

results showed that the fertilization either with N contents which indicated only the trends, the

alone or with N plus S increased significantly seed remaining data were subject to variance analysis

productions, but the complementary addition of S and statistically compared according to Tukey’s

had no significant influence (Table 3). The yields test at the 0.05 probability level.

from the second year were higher but, in terms of responses to fertilization, slightly lower (+71%) than the former (+82%) as compared with the 3. Results

controls. 3.1. Seed yields

3.2. S influence on N uptake The seed yields obtained from the pot

experi-ment ( Table 2) carried out in 1995 varied between

Similarly to seed yields and as expected, signifi-1.2 and 2.4 g pot−1 versus 0.74 and 2.17 g pot−1

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Table 2

Seed yield, nitrogen and sulfur uptake, glucosinolate (GLS ) and oil contents of spring oilseed rape grown in pot experiments. Means within a column followed by the same letter are not significantly different at the 95%confidence level (Tukey’s test)

Treatment 1995 1996

Seed yield N S GLS Oil Seed yield N S Oil

(g pot₋1) (mg pot₋1) (mg pot₋1) (mmol g₋1) (%DM ) (g pot₋1) (mg pot₋1) (mg pot₋1) (%DM ) Trial with AN and UR

S=0

Control

AN/UR 1.22 b 26.47 a 2.14 b 7.9 43.0 0.74 c 15.67 b 1.51 c nd

AN Pod abortion 1.41 ab 29.32 ab 2.66 bc 59.9

UR Pod abortion 1.32 ab 24.05 ab 2.14 bc 59.3

S=30 (ATS-S)

AN+ATS 0.98 bc 22.26 ab 2.48 bc nd

UR+ATS 1.38 ab 33.63 ab 3.76 ab nd

S=75 (ATS-S)

AN+ATS 1.56 a 28.03 a 3.12 a 8.2 45.9 2.17 a 44.11 a 5.32 a 54.4 UR+ATS 1.74 a 34.33 a 3.76 a 8.5 47.4 1.91 ab 36.37 ab 4.44 ab 53.0

S=75 (MgSO

4-S)

AN+MgSO

4 1.75 ab 35.84 ab 4.15 ab 54.1

UR+MgSO

4 1.76 ab 40.19 a 4.85 ab 56.1

Trial with SL S=0

Control

SL 1.63 c∞ 31.91 b∞ 2.78 b∞ 8.9 42.9

SL 2.03 b∞ 41.59 a∞ 3.62 b∞ 8.9 42.3

S=75 (ATS-S)

SL+ATS 2.43 a∞ 49.25 a∞ 5.34 a∞ 13.5 40.7

Table 3

Seed yield, nitrogen and sulfur uptake, total glucosinolate (tot GLS ), alkenyl glucosinolate (alk GLS ) and oil contents of field-grown winter oilseed rape. Means within a column followed by the same letter are not significantly different at the 95%confidence level ( Tukey’s test)

Treatment 1995–96 1996–97

Seed N S Tot Alk Oil Seed N S Tot Alk Oil

yield (kg ha₋1) (kg ha₋1) GLS GLS (% yield (kg ha₋1) (kg ha₋1) GLS GLS (% (t ha₋1) (mmol g₋1) (mmol g₋1) DM ) (t ha₋1) (mmol g₋1) (mmol g₋1) DM )

S=0

Control 1.79 b 45.7 b 2.73 a 13.3 10.8 54.0 2.43 b 66.27 b 2.81 a 16.8 13.6 52.5 AN 3.36 a 104.4 a 4.09 a 8.0 5.6 49.2 4.12 a 124.42 ab 4.82 a 10.0 7.5 50.3 UR 3.05 a 95.22 a 2.76 a 8.9 6.2 49.2 4.05 a 113.09 ab 4.21 a 11.5 8.3 50.6

S=30 (ATS-S)

An+S

30 3.28 a 103.38 a 3.06 a 12.1 9.2 49.2 4.24 a 122.10 ab 4.39 a 14.2 11.0 50.6

UR+S

30 3.26 a 104.55 a 3.43 a 13.0 10.0 49.0 4.14 a 126.56 ab 5.07 a 14.4 10.9 50.5

S=75 (ATS-S=30+MgSO

4-S=45)

AN+S

75a 3.12 a 100.74 a 6.51 a 13.2 10.3 48.6 4.21 a 131.72 a 4.99 a 16.7 13.2 50.2

UR+S

75a 3.26 a 99.58 a 3.17 a 14.2 11.1 48.5 3.82 a 110.46 ab 5.06 a 17.9 14.2 50.3

S=75 (MgSO

4-S)

AN+S

75b 3.39 a 112.22 a 5.53 a 14.4 11.3 48.8 4.47 a 127.81 a 5.16 a 16.8 13.5 50.4

UR+S

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only been observed when applied with slurry at of S. Thus, increasing values varying between 3.4 and 8.5%in 1995–96 and between 6.6 and 10.95% the rosette stage and maturity (Table 4).

Compared with slurry addition alone, S from ATS have been observed for the S levels 30 and 75 kg ha−1, respectively.

increased about 69% at rosette stage and 73% at maturity.

In field experiments, the total N uptake at 3.3. Glucosinolate and oil contents maturity amounted to a mean of 175 kg ha−1in

1996–97 versus 146.6 kg ha−1 in 1995–96 In pot experiments, the contents of GLS ranged from 7.9 to a maximum of 13.5mmol g−1with cow ( Table 5). We observed no significant effect of S

on N uptake during the growth of oilseed rape. slurry ( Table 2). With this latter fertilizer, a marked increase of GLS content of about 52% Nevertheless, averaged values over different

treat-ments with and without S showed a general trend was observed when ATS-S was added. On the contrary, this increase was not paralelled by the to an increase in N uptake with increasing doses

Table 4

N and S uptake by the whole plant at rosette, flowering and maturity, and by the vegetative parts (excluding pod walls and seeds) at maturity of spring oilseed rape from pot experiments in 1995 (A) and 1996 (B). Means within a column followed by the same letter are not significantly different at the 95%confidence level ( Tukey’s test)

Treatment Rosette Flowering Maturity

N S N S N S N/S N S

Whole plant Whole plant Whole plant Vegetative parts (mg pot−1) (mg pot−1) (mg pot−1) (mg pot−1) (A) Trial with AN and UR

S=0

Control

AN/UR 11.60 c 0.52 c 18.91 b 0.57 a 35.23 b 2.72 b 13.0 6.69 b 0.38 b

AN 34.40 ab 0.92 c 30.91 a 1.71 ab 19.92 c 0.99 c 19.9 19.92 a 0.99 ab UR 32.60 ab 0.84 c 29.22 a 0.91 b 20.28 c 0.59 c 33.8 20.28 a 0.59 b

S=75 (ATS-S)

AN+ATS 20.18 bc 1.90 b 25.99 ab 2.87 a 40.03 ab 4.17 a 9.5 9.49 b 0.85 ab UR+ATS 46.02 a 3.30 a 30.99 a 1.79 a 48.37 a 5.44 a 9.0 1.89 b 1.53 a Trial with SL

S=0

Control

SL 13.79 c∞ 0.79 b∞ 18.84 a∞ 0.54 b∞ 71.02 b∞ 3.06 c∞ 16.1 15.49 b∞ 0.21 b∞

SL 25.42 b∞ 1.38 b∞ 15.92 a∞ 0.21 b∞ 50.05 c∞ 4.68 b∞ 15.1 25.63 ab∞ 0.60 b∞

S=75 (ATS-S)

SL+ATS 42.98 a∞ 2.97 a∞ 18.10 a∞ 1.50 a∞ 86.68 a∞ 8.28 a∞ 10.4 31.98 a∞ 2.34 a∞

(B) S=0

Control 12.93 b 1.25 a 16.52 b 0.44 a 23.51 c 2.08 c 11.2 6.01 a 0.41 a AN 27.61 a 1.73 a 47.37 a 0.91 a 45.35 ab 3.18 bc 14.1 9.59 a 0.24 a UR 30.28 a 2.24 a 53.55 a 0.76 a 43.25 ab 2.39 c 18.0 12.28 a 0.13 a

S=30 (ATS-S)

AN+ATS 28.83 a 2.03 a 38.38 a 0.64 a 38.25 bc 3.26 bc 11.6 11.99 a 0.55 a UR+ATS 23.50 ab 1.26 a 42.96 a 0.83 a 51.16 ab 4.35 ab 11.9 12.08 a 0.50 a

S=75 (ATS-S)

AN+ATS 35.85 a 2.97 a 42.90 a 0.43 a 51.67 ab 6.44 a 9.7 9.37 a 0.26 a UR+ATS 31.66 a 2.38 a 48.43 a 0.80 a 53.57 ab 5.32 ab 10.1 9.72 a 0.40 a

S=75 (MgSO

4-S)

AN+MgSO

4 32.92 a 2.53 a 43.99 a 1.03 a 51.67 ab 4.83 ab 10.8 8.96 a 0.10 a

UR+MgSO

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Table 5

N and S uptake by the whole plant (excluding roots) at green bud, flowering and maturity, and by the vegetative parts at maturity of field-grown winter oilseed rape in 1995–96 (A) and 1996–97 (B). Means within a column followed by the same letter are not significantly different at the 95%confidence level ( Tukey’s test)

Treatment Rosette Flowering Maturity

N S N S N S N/S N S

Whole plant (kg ha−1) Whole plant (kg ha−1) Whole plant (kg ha−1) Vegetative parts (kg ha−1) (A) S=0

Control 26.86 b 2.16 c 38.48 c 1.04 a 66.89 b 7.09 ab 9.4 6.19 b 0.60 c AN 42.00 ab 4.85 a 110.95 a 4.06 a 160.45 a 6.82 ab 23.5 19.79 a 1.04 ab UR 37.80 ab 3.92 ab 73.92 b 2.93 a 140.15 a 5.25 b 26.6 17.53 a 0.95 bc

S=30 (ATS-S)

AN+S

30 53.11 a 4.85 a 97.14 ab 3.53 a 163.09 a 7.44 ab 21.9 19.88 a 1.25 ab

UR+S

30 51.21 a 4.26 ab 85.99 ab 3.62 a 147.92 a 7.12 ab 20.8 15.48 a 0.95 bc

S=75 (ATS-S=30+MgSO

4-S=45)

AN+S

75a 39.97 ab 3.18 bc 88.35 ab 2.19 a 162.22 a 11.33 ab 14.3 21.37 a 1.05 ab

UR+S

75a 41.70 ab 3.15 bc 94.88 ab 3.09 a 151.03 a 9.16 ab 16.5 16.38 a 1.31 ab

S=75 (MgSO

4-S)

AN+S

75b 42.53 ab 2.64 c 85.30 ab 3.80 a 166.67 a 12.98 a 12.8 21.09 a 1.61 a

UR+S

75b 41.14 ab 2.69 c 86.91 ab 2.46 a 159.42 a 10.59 ab 15.0 20.51 a 1.08 ab

(B) S=0

Control 37.17 b 5.42 a 31.45 b 1.53 b 90.53 c 7.55 a 12.0 9.08 b 3.22 a AN 80.69 a 9.81 a 78.21 a 5.68 ab 178.42 ab 9.15 a 9.5 20.16 ab 2.28 a UR 59.90 ab 6.39 a 73.13 a 4.43 ab 168.62 ab 8.40 a 20.1 16.28 ab 1.63 a

S=30 (ATS-S)

AN+S

30 59.91 ab 7.49 a 81.31 a 8.54 a 178.33 ab 9.44 a 18.9 22.29 a 3.42 a

UR+S

30 69.19 ab 9.38 a 84.73 a 6.64 a 191.90 ab 9.78 a 19.6 18.82 ab 1.97 a

S=75 (ATS-S=30+MgSO

4-S=45)

AN+S

75a 65.70 ab 8.15 a 76.84 a 5.91 ab 209.69 a 11.82 a 17.7 22.61 a 3.84 a

UR+S

75a 47.43 ab 7.27 a 73.51 a 3.54 ab 172.61 ab 13.75 a 12.5 16.78 ab 6.17 a

S=75 (MgSO

4-S)

AN+S

75b 71.14 ab 9.31 a 85.62 a 7.08 a 187.91 ab 13.40 a 14.0 21.56 a 5.84 a

UR+S

75b 64.60 ab 8.11 a 77.96 a 4.79 ab 197.15 ab 12.95 a 15.2 20.25 ab 5.35 a

oil, of which the content was slightly decreased by 1996–97 when compared with the control and the treatments with S application. Fertilization of S 4%. Unfortunately, in the second pot experiment,

the GLS contents were not determined due to increased the GLS contents but had no influence on oil contents ( Table 3). The results suggest a insufficient seed samples. For this experiment, S

applications at 75 kg ha−1led to a decrease of oil higher responsiveness of GLS than oil to the S fertilization.

content of about 10% when the soil was jointly fertilized with ATS-S and MgSO

4-S and about 7.5% with MgSO

4-S exclusively.

In field experiments, the average content of 4. Discussion GLS ( Table 3) was found to be relatively higher

for the second year (15.07mmol g−1 versus 4.1. Imbalanced N and S 9.44mmol g−1) and a slight increase in average oil

content has been observed (50.7% versus 49.5%). In pot experiments using the cultivar Hybridol, total pod abortions occurred when the soil was N applications alone decreased markedly the GLS

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This fact would be explained by the imbalanced (Anderson, 1990; Sexton et al., 1998). The path-N/S uptake ratios (Sweeney and Moyer, 1997), of way of S nutrition is the reduction of SO₂−

4 to which the values observed at rosette stage ( Table 4) cysteine in assimilatory sulfate reduction pathway are abnormally larger with 37 (AN ) and 39 ( UR) (Lappartient and Touraine, 1996). This pathway than those of the control (22.3) and slurry (18). is tightly linked to assimilatory nitrate reduction According to Janzen and Bettany (1984), the ( Kast et al., 1995), where O-acetyl-serine is severity of S deficiency is aggravated by higher formed. This latter compound reacts with sulfur rates of N application. Plants receiving no N _{reduced to form cysteine. In agreement with these} fertilizer showed no apparent S stress, whereas _{observations, the results indicate that N and S} plants receiving N fertilizer, particularly at higher _{taken up by rapeseed at maturity stage are} associ-rate without S, showed symptoms suggesting severe _{ated according to a polynomial equation of second} physiological disorder in N nutrition. _{order (Fig. 1). This implies that N and S nutrition} Sulfur mainly enhances the reproductive _{are linked and the process would be} down-regu-growth, and the proportion of the reproductive _{lated when one of them quantitatively overexceeds.} tissues (inflorescences and pods) in total dry matter _{Under controlled conditions with optimum} tem-was found to be significantly increased by S during _{perature and humidity, the correlation coe}_ffi_cients pod development (MacGrath and Zhao, 1996). _{between N and S uptake obtained over the two} Under S deficient conditions, the amount of amino _{years (1995 and 1996) of experiments ( Table 6)} acids and nitrates in leaves increases dramatically _{were found to be significant at rosette stage:} (Hue et al., 1991) and protein degradation within _r

2=0.59 (P<0.05), maturity: r₂=0.82 (P<0.01), chloroplasts occurred (Dannehl et al., 1995). _{and for the seeds:}_r

2=0.95 (P<0.01). By contrast, Besides, sulfur affects photosynthetic

characteris-the coefficient value was not significant at flower-tics (Sexton et al., 1997; Blake-Kalffet al., 1998).

ing. This could be attributed to the early irregular According to them, S deficiency limits protein

losses of leaves which occurred in the growth synthesis by limiting the amount of methionine

chamber. Major phenomena could be related to and cysteine available for the assembly of new

plant ontogeny caused by the regularly imposed proteins.

temperature, humidity and light intensity of con-Furthermore, Sunarpi and Anderson (1997)

trolled conditions which are different from the have shown that high levels of N inhibit the

usual requirements in the field (Sarwar and proteolysis process in soybean and so the export

Kirkegaard, 1998). of N and S from mature leaves to developing

Similar results were obtained in field experi-leaves or developing grains. In agreement with

ments ( Table 6) with highly significant correlation them, our results emphasize therefore the interest

coe_fficients at green bud stage:r2=0.83 (P<0.01) of applying S fertilizer in combination with N;

and for seeds: r2=0.72 (P<0.01). The lack of otherwise, oilseed rape that grows on S-limiting

statistically significant correlation between N and soils will suppress the development of reproductive

S noted at maturity may be due in part to the organs and even lead to pod abortion (MacGrath

flexible system of stems for regulating the nitrogen and Zhao, 1996; Zhao et al., 1997). Under imposed

supply to regions of demand. Indeed, as shown by conditions within the growth chamber, this work

Sunarpi and Anderson (1997), stems are able to also points out the higher sensitivity of cultivar

act as a source at low levels of N supply and as a Hybridol than Tanto to the imbalanced N/S ratios.

major sink of N when N supply is very high. Further study is needed to gain a better causal

Similar roles played by stems in regulating and understanding of this different sensitivity between

accumulating sulfur, especially as sulfate, have cultivars.

been reported as well (Sexton et al., 1998). The most marked point of our results ( Table 6) 4.2. N and S uptake relationships

is the strongly significant correlation values obtained in field trials at flowering: r2=0.73 The excess or the deficiency of one of both the

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controlled conditions than in the field. The absence of correlation between N and S taken up by seeds in the first field experiment (1995–96) would be due to the low remobilization of N and S from the vegetative parts (excluding pod walls and seeds), as clearly proved by the strong correlation coefficient of 0.79 (P<0.05). Indeed, there may have been either a sink limitation for N and S utilization within the seeds or simply a limited ability to reduce both N and S for amino acid synthesis, as attested by the non-significant correla-tion value noted for seeds ( Table 6). Presumably, climatic conditions would be one of the most important factors for such an event. As a result, the average N uptake in this first year ( Table 5) was relatively lower (146.6 kg ha−1) than that in the second year (175 kg ha−1), where strong corre-lations were recorded at each stage (Fig. 1). Therefore, monitoring N and S uptake curves during the growth could be an indicator for predic-ting good yield production.

The almost linear curve for N and S uptake at green bud stage (Fig. 1) indicates increasingly pro-portional N and S taken up by oilseed rape. Accordingly, this suggests the synthesis of reserve proteins in leaves which were intensively developed and almost fully expanded at this time. In parallel, during this stage, nitrate and sulfate transported in the xylem with the transpiration stream would be very important as well. According to Hell and Rennenberg (1998), part of the sulfate can undergo xylem-to-phloem exchange during the xylem trans-port. Thus, its distribution within the plant in this way may represent part of a plant internal sulfate cycle. For nitrate, this exchange during the xylem transport is not clear. However, for oilseed rape grown with high N fertilization, Colnenne et al. (1998) observed an important accumulation of non-assimilated N in the nitrate form at this early

Fig. 1. Curves of N and S taken up by field-grown winter oilseed stage when compared with wheat. In consequence,

rape in 1996–97 observed at green bud, flowering and maturity, _{at this critical stage ( later autumn and early spring)} and for seeds. For illustration, we present only the curves of _{any deficiency of N will a}

ffect the growth of aerial

this year. The other curves show similar trends. Each datum

parts including foliar areas and stems (Colnenne

point corresponds to a mean value of four replications.

et al., 1998), and S deficiency will lower the formation of reproductive organs that begin well at spring (Janzen and Bettany, 1984).

1996–97 when compared with pot trials in 1995

and 1996 (NS ). The explanation would be, as Under normal N and S nutrition conditions, the trends of curves associating N and S uptake mentioned before, the larger losses of leaves under

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Table 6

Correlation between N and S uptake. Correlation coefficient (r2) calculated on the average value of eight treatments for the 1995 pot experiment and nine treatments for the remaining experiments, and significance level (*P<0.05; **P<0.01)

Stage of plant Parts of plant Pot experiments Field experiments

1995 1996 1995 and 1996 1995–96 1996–97 1995–96 and 1996–97

Rosette Whole plant NS 0.80** 0.59* NS 0.81** 0.83**

Flowering Whole plant NS NS NS 0.73* 0.94** NS

Maturity Whole plant 0.83** 0.84** 0.82** NS 0.92** NS

Vegetative parts NS NS NS 0.79** NS NS

Seeds 0.96** 0.95** 0.95** NS 0.89** 0.72**

hold across the observed growth stages as well as Therefore, if N and S transports operate simulta-neously, the mechanisms which regulate the pas-during seed formation. This obviously implies the

same interaction mechanisms between N and S sage either between stems and pod walls or between pod walls and seeds remain to be elucidated, even during seed protein and secondary metabolite

synthesis. In particular, this underlines again the because they evidently influence yield and seed quality.

double resilient roles of stems (Sunarpi and Anderson, 1997; Sexton et al., 1998) and pod walls

(Zhao et al., 1993a; Fismes et al., 1999) as sink 4.3. Apparent N-use efficiency and source for N and S in regulating transport

between both the vegetative and reproductive Without 15N as tracer, the apparent N-use efficiency: ANU=[(N uptake from fertilized parts, and therefore an optimal protein synthesis

can be efficiently fulfilled within the seeds ( Fig. 1). plots−N uptake from controls)/N fertilizer applied ] can be expressed to examine the effect of The fully expanded leaves represent the most

important sink for S and N within plants (Sunarpi S supply on N uptake. The inhibitory action of ATS on N nitrification and urease activity was and Anderson, 1996; Blake-Kalff et al., 1998). In

this connection, the close relationships of N and well proved in laboratory experiments (Goos, 1985; Fairlie and Goos, 1986).

S uptake across the main growth stages obtained

in this study support the hypothesis of simulta- In pot trials, ATS had a significant impact only at the highest rate of 75 kg S ha−1. The ANU neously coordinated phloem transport of N and S

as various amino acids and/or small peptides from value obtained with the treatment slurry+ATS was 62% versus 43% with slurry alone. Similar mature leaves to other plant parts (Sunarpi and

Anderson, 1997). In agreement with them, the results were recorded with chemical fertilizers for which the averaged values shifted from 25% with transport of both elements is a common

mecha-nism because the putative transport from mature N-only application to about 40% when S was added (Fig. 2). Thus, S applied at the highest dose leaves of nitrogen as nitrate and/or ammonium

and sulfur as sulfate, after proteolysis, would of 75 kg S ha−1increased significantly N taken up by rapeseed in pot but not in field trials. involve at least two mechanisms. In addition, in

agreement with Sunarpi and Anderson (1997), our Agronomically, the dose advised for ATS is 10% (v/v), which corresponds to an equivalent of 30 kg results suggest that this proteolysis is promoted

when either N or S becomes limiting. However, S ha−1 (Goos, 1985). In field experiments, the values of ANU varied from 41.6% with N alone comparisons of N versus S as to the relative

intensity, the duration and the efficiency of remobi- to 49.5%with N plus S. Based on these low values of ANU, our results confirm those of Schjoerring lization remain to be clarified. As previously

shown, N and S can be abnormally sequestered et al. (1995), indicating that oilseed rape is appa-rently a N-inefficient plant compared with cereal and stored in the vegetative parts upon maturity.

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Fig. 2. Apparent N-use efficiency values from pot trial in 1996 and the two-year field trial (1995–96 and 1996–97). The results from the pot trial in 1995 are not presented due to pod abortions. Each datum represents the mean of eight values for the pot trial (one year) and 16 values for the field trials (two years). The bar corresponds to the standard error (±S.E.). For the legends, see Table 4 (B) and Table 5 (A) and (B).

crops, of which the values are generally higher and under conditions of S deficiency, sulfate-S is still present in a considerable proportion to total S in can reach the range of 75 to 90% (Delogu et al.,

1998). This is proved by the fact that oilseed rape oilseed rape. In contrast, the amount of S in GLS is small in vegetative tissues under the conditions is unable to withdraw all N from leaves before

they are lost (Schjoerring et al., 1995). of abundant supply of S. In addition, the ineffective xylem-to-phloem transfer of SO2₄−, because of its Furthermore, Shepherd and Sylvester-Bradley

(1996), by referring to N response in grain yield, higher accumulation in the vacuoles in the mature leaves compared with the middle or younger ones have demonstrated that for each 100 kg N ha−1

applied, the rapeseed provides N equivalent to (Blake-Kalff et al., 1998), may contribute to this inefficiency as well. The results evidently suggest 30 kg N ha−1for the following cereal. This

argu-ment again confirms oilseed rape as a N-inefficient that the oilseed rape crop is inherently inefficient in N and S utilization within the plant.

plant, and so its beneficial effects on succeeding cereal crops through increasing soil fertility and disease progression are amply pleaded by Sieling

4.4. Seed glucosinolate and oil contents and Christensen (1997).

The same tendency was obtained for the

appar-Sulfur applications increased the level of GLS ent sulfur-use efficiency (see data in Table 5) with

compared with the soil receiving only N fertiliza-low values not exceeding 8%(results not shown).

tion. Under controlled conditions, the GLS In fact, the calcareous soil used is rich in organic

content amounted to 13.5mmol g seed−1, a value S (about 1300 kg S ha−1), which level is largely

1.5-fold higher than the treatment receiving only superior to the limit of 400 kg S ha−1, above which

slurry without S. However, the values are very soils are considered to be well sufficient in S

close to those of the controls. Globally, the content (Merrien, 1987). Therefore, our results compare

of GLS from field experiments varied between 8 favorably with values varying between 10 and 15%

and 18mmol g seed−1and in any case, the observed obtained from the S-sufficient soils (Zhao et al.,

values do not exceed the threshold limit of 1993b). Likewise, oilseed rape is considered also a

18mmol g−1 fixed by the European norm. Over S-inefficient plant (MacGrath and Zhao, 1996).

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pro-Table 7

Correlation between N/S uptake ratio values on the whole plant basis (excluding roots) and the variables of glucosinolates from field-grown winter oilseed rape. Significant level (*P<0.05; **P<0.01)

Glucosinolate Alkenyl glucosinolate

1995–96 1996–97 1995–96 and 1996–97 1995–96 1996–97 1995–96 and 1996–97

N/S uptake NS NS −0.51* −0.69* −0.68* −0.56*

duced in response to 30 and 75 kg S ha−1as ATS-S GLS contents relies on the balanced fertilization of both N and S.

or MgSO

4-S varied between 12 and 18mmol g

seed−1. These results are in agreement with those As for the seed oil content, results from field trials indicate nearly constant values with the obtained by Zhao et al. (1997), indicating for an

application of 50 kg S ha−1, a higher elevation of fertilized treatments. But, the marked point is that in 1995–96, the percentage of oil was on average GLS from 10 to 20mmol g−1 on S-deficient sites

versus 15 to 17mmol g−1on S-sufficient sites. This about 1.2% lower than that of 1996–97. In fact, the mean value of seed N content (see Table 3) in shows again the richness of S in the soil used and

therefore the narrower variations of GLS pro- 1995–96 was slightly higher (3.11%) than in 1996– 97 (2.99%), which consequently leads, in accor-duction in response to S fertilization. Our results

show significant correlations existing between N/S dance with Andersen et al. (1996), to a decrease in oil content observed in 1995–96. The main uptake ratio values and the content of GLS

( Table 7 and Fig. 3), especially the alkenyl GLS, causes contributing to such a diminution of oil content would be likely attributed to the drought which are the predominant group present in seeds.

Their higher correlation coefficients observed conditions which directly influence the partitioning of C assimilated during the pod-filling phase prove their higher responsiveness to S addition,

because they are synthesized from chain-elongated (Bouchereau et al., 1996). Moreover, the non-distribution of N and S from the vegetative parts homologues of methionine ( Zhao et al., 1997), the

outcome product of N and S assimilatory pathway. previously noted at maturity stage ( Table 6) explains well this diminution.

These results clearly imply that a better control of

Fig. 3. Correlation curves between N/S uptake ratio values at maturity on the whole plant basis (excluding roots), and the variable of glucosinolates from the two-year field experiment. Each datum point represents a mean value of four replications.

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According to Andersen et al. (1996), seeds may optimal level conditions the process is synergistic and becomes antagonistic under the extreme condi-be regarded as consisting of nitrogen-free

struc-tural material, stored proteins and stored oil. The tions of excessive level of N or S. Monitoring the uptake of both elements across principal phenolog-proportion of structural material is expected to

decrease with increasing seed weight, while protein ical stages would be useful for predicting yield from fertilizer testings. N application alone to this and oil may compete for the remaining space in

seeds. Accordingly, these authors showed that the calcareous soil rich in organic-N and -S gave the same seed yield of field-grown oilseed rape as content of oil (Oc) is positively correlated with

seed weight (Sw) and negatively correlated with treatments with S application, and also the oil contents in seeds were not influenced by S, in nitrogen content (Nc) as follows: Oc=

63.3−7.37Nc+1.31Sw (r2=0.89, n=92). We contrast to glucosinolates, the contents of which were clearly increased by S fertilizers. In pot experi-found similar significant results as expressed by

the equation: Oc=68.0−5.74Nc−0.17Sw (r2= ments, higher S application significantly increased the ANU, which was not the case in field trials. 0.71, P<0.05, n=9). In our case, the slightly

negative relation with seed weight (Sw) would be There was only a non-significant tendency of S improving the ANU.

linked to the restricted observation numbers. But also, this means that seed nitrogen-free structure is more subject to intrinsic or year-to-year

variations. _{Acknowledgement}

In general, N fertilization without S reduced

total oil production due to the decrease in yield _{This work was carried out as part of a research} (Joshi et al., 1998). Besides, water shortage occur- _{program funded by the Commission of the} ring during the flowering or pod-filling stages may _European _Community _(Contract _AIR favor increased protein content and thereby _{3-CT94-1953).}

decreasing oil content (Bouchereau et al., 1996). Consequently, climatic conditions could also be considered as a determining factor for oil

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