2006-Grain yield, and dry matter and nitrogen accumulation and remobilization indurum wh
Europ.J.Agronomy25(2006)
309–318
Grain yield,and dry matter and nitrogen accumulation and remobilization in durum wheat as affected by variety and seeding rate
I.Arduini a,?,A.Masoni a,L.Ercoli b,M.Mariotti a
a Dipartimento di Agronomia e Gestione dell’Agroecosistema,via S.Michele degli Scalzi2,56124Pisa,Italy
b Scuola Superiore Sant’Anna di Studi Universitari e di Perfezionamento,Piazza Martiri della Libert`a33,56127Pisa,Italy
Received8February2006;received in revised form13June2006;accepted19June2006
Abstract
The in?uence of crop density on the remobilization of dry matter and nitrogen from vegetative plant parts to the developing grain,was investigated in the durum wheat(Triticum durum Desf.)varieties Creso,Simeto and Svevo cultivated in the?eld at three seeding rates,200,250and400seeds m?2. Variety×seeding rate interaction was unsigni?cant for all recorded characters.Grain yield declined in the order Svevo>Simeto>Creso.Yield differences mainly depended on the different number of kernels per unit land and,secondly,on mean kernel weight.Spike components differed among varieties:Svevo and Simeto showed more kernels per spikelet and Creso more spikelets per spike.Grain yield was highest with400seeds m?2 primarily due to the higher number of spikes per unit area,and secondly,to the higher mean kernel weight.Post-heading dry matter accumulation was highest in Svevo and lowest in Creso,but varieties showed a reverse order for dry matter remobilization and contribution of dry matter remobilization to grain yield.The increase of seeding rate increased both the post-heading dry matter accumulation and the dry matter remobilization from vegetative plant parts to grain.Nitrogen uptake of the whole crop and N content of grain was higher in Simeto and Svevo than in Creso.The N concentration of grain did not vary among varieties,but Svevo showed a markedly lower N concentration and N content of culms at maturity,which may be consequence of the high N remobilization ef?ciency performed by this variety.The N uptake by the crop was highest with400seeds m?2,but the N concentration of culms,leaves and even grain was slightly lower than with the lower seed rates.The post-heading N accumulation was by far higher in Simeto and Svevo than in Creso,whereas remobilization was highest in Svevo and lowest in Simeto.The percentage contribution of N remobilization to grain N was by far higher in Creso than in the other two varieties.Post-heading N accumulation and N remobilization were highest with the highest plant density,but the contribution of N remobilization to N grain content did not differ between seeding rates.
?2006Elsevier B.V.All rights reserved.
Keywords:Triticum durum;Genotype;Row spacing;Yield;N-uptake;N-translocation
1.Introduction
In durum wheat as in most other grain crops,maximum grain yield results from an optimum balance of three yield compo-nents:(i)the number of spikes per unit land,(ii)the number of kernels per spike and(iii)the weight of single kernels(Gra?us, 1972;Prystupa et al.,2004).According to Freeze and Bacon (1990),these yield components have interdependent action and are able to compensate for one another in order to stabilize yield as cultural or climatic conditions change.
Seeding rate and row spacing strongly in?uence the use of environmental resources by wheat in that they change the rela-tive importance of intraplant and interplant competition for light,
?Corresponding author.Tel.:+39050599208;fax:+39050560633.
E-mail address:iard@agr.unipi.it(I.Arduini).water and nutrients during crop development(Darwinkel,1978; Tompkins et al.,1991a,b).Low seed rates decrease interplant competition especially during vegetative growth,but increase intraplant competition during grain?lling because plants tend to produce more spike-bearing tillers(Darwinkel,1978;Marshall and Ohm,1987).Thus,generally,low seed rates increase the number of spikes produced by each plant and the weight of single spikes,but decrease the number of spikes per unit land,whereas the opposite occurs with high seed rates(Wilson and Swanson, 1962;Tompkins et al.,1991a,b).Whaley et al.(2000)found that the number of kernels per spike increased by50%in wheat plants when crop density decreased from338to19plants m?2, but less than10%increases were reported by Ozturk et al.(2006) when seed rate was decreased from625to325seeds m?https://www.sodocs.net/doc/2b811657.html,-pared to the other yield components,kernel weight seems to be less affected by seed rate and was found to be either decreased, or increased or unaffected in response to increasing seed rate
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310I.Arduini et al./Europ.J.Agronomy25(2006)309–318
(Donaldson et al.,2001;Wood et al.,2003;Hiltbrunner et al., 2005).However,Tompkins et al.(1991a,b)reported that the increase of seed rate from65to400seeds m?2increased grain yield because the higher number of kernels per spike,obtained with the lower seed rates,was not able to compensate the low number of spikes per unit land.Conversely,Carr et al.(2003)and Wood et al.(2003)found that grain yield of wheat was higher with250than with450seeds m?2.
Climatic conditions and,especially,rainfall distribution dur-ing the growing season were found to modify the response of plants to different spacings.For instance,high seed rates were found to increase yield in well watered conditions,whereas the reverse was true with low soil moisture(Wilson and Swanson, 1962;Blue et al.,1990;Tompkins et al.,1991a,b).
Finally,no marked differences among varieties are reported in the response of grain yield to changing plant density(Spink et al.,2000;Holen et al.,2001;Geleta et al.,2002;Carr et al., 2003).However,Black and Aase(1982)reported that URSS winter wheat cultivars have a greater ability to maintain high kernels per spike at high plant density compared to USA cultivars and,according to Marshall and Ohm(1987)and Anderson and Barclay(1991),the optimal plant population changes according to variety and local conditions.Actually,in central Europe and in Italy narrow row spacings,comprised between12and18cm,and seed densities of about400seeds m?2are traditionally applied to wheat(Ercoli and Masoni,1995;Blankenau and Olfs,2001; Ghaffari et al.,2001),whereas densities around250seeds m?2 and even lower are considered optimal for Canada and the United States(Read and Warder,1982;Donaldson et al.,2001;Carr et al.,2003).
The protein content of grain is of high value for de?ning the end-use quality of both Triticum aestivum and T.durum grain(Gooding et al.,2003).In T.aestivum,Geleta et al.(2002) reported that grain protein concentration declined as seeding rate increased,probably because of a higher competition among plants for nitrogen.On the other hand,Tompkins et al.(1991a,b) found that grain protein concentration was slightly higher with 470than with115seeds m?2,which they considered a conse-quence of the higher water use ef?ciency they recorded in the narrow spaced plants.Finally,Carr et al.(2003)and Ozturk et al. (2006)found that seeding rate did not affect grain protein con-centration.The N-use ef?ciency differed markedly in16Italian cultivars of T.aestivum,and the modern high yielding varieties showed both an improved nitrogen uptake and use(Guarda et al.,2004).
In all grain crops the supply of assimilates to the develop-ing grain originates both from current assimilation transferred directly to kernels and from the remobilization of assimilates stored temporarily in vegetative plant parts(Gebbing et al., 1999).The reserves deposited in vegetative plant parts before anthesis may buffer grain yield when conditions become adverse to photosynthesis and mineral uptake during grain?lling(Austin et al.,1977;Tahir and Nakata,2005).The relative importance of current assimilation and remobilization changes among geno-types and is strongly related to environmental conditions.In 25durum wheat varieties grown in Central Italy,Mariotti et al.(2003)found that the contribution of pre-anthesis assimi-lates to kernel weight ranged from43to54%,and Przulj and Momcilovic(2001a)found that this contribution varied from4to 24%in20two-rowed spring barley cultivars.The latter authors also found differences among cultivars in the pre-anthesis accu-mulation of both dry matter and nitrogen that were related to differences in N translocation(Przulj and Momcilovic,2001b). Van Herwaarden et al.(1998)found that the apparent contribu-tion of stored assimilates to grain yield was37–39%under high rainfall conditions during grain?lling,but arised to75–100% under dry?eld conditions.Tahir and Nakata(2005),however, reported that post-anthesis heat stress increased the remobiliza-tion ef?ciency of non-structural carbohydrates but decreased that of nitrogen.
The effect of plant spacing on the remobilization of assim-ilates from vegetative plant parts to wheat grain has not been investigated previously.In durum wheat,the in?uence of plant density on remobilization patterns is of high concern because this crop is mainly grown in areas where climatic conditions are mostly favorable to pre-anthesis growth but drought con-ditions may severely limit C assimilation and mineral uptake during grain?lling.In bread wheat,Tompkins et al.(1991a,b) reported that pre-anthesis biomass was higher with high seed rates and Przulj and Momcilovic(2001a)found a high posi-tive correlation between biomass at anthesis and both yield and translocation.
The objectives of this study were to examine,under?eld con-ditions,the effect of different seeding rates on the grain yield and its components and on the nitrogen uptake of durum wheat (Triticum durum Desf.).The phenological development of the crop and the accumulation of dry matter and nitrogen at heading and at maturity were recorded too,in order to assess the contri-bution of pre-and post-anthesis assimilates to grain yield.Three varieties were used,in order to compare the response of old and recent Italian genotypes.
2.Materials and methods
The research was carried out in the years2001–2003at the experimental station of the Department of Agronomy and Agroecosystem Management of the University of Pisa,Italy, that is located at a distance of approximately10km from the sea(43?40 N,10?19 E)and1m above sea level.The climate is cold,humid Mediterranean with mean annual maximum and minimum daily air temperatures of20.2and9.5?C,respectively, and precipitation of971mm,with688mm received during the period of durum wheat cultivation,that is from November through July(Moonen et al.,2001).
Soil chemical and physical properties were34%sand (2mm>?>0.05mm),21%silt(0.05mm>?>0.002mm), 45%clay(?<0.002mm),7.2pH,2.2%organic matter(Walk-ley and Black method),1.2g kg?1total N(Kjeldahl method), 33mg kg?1available P(Olsen method),22mg kg?1available K(Dirks-Sheffer method).Field capacity and permanent wilt-ing point determined with the pressure chamber method were 34.1and21.2%at33and1500kPa soil water tension.
In each year,treatments were the durum wheat(T.durum Desf.)varieties Creso,Simeto and Svevo,and the seeding rates:
I.Arduini et al./Europ.J.Agronomy25(2006)309–318311
200,250and400seeds m?2.The seeding rates were obtained spacing rows at28,20and12cm,respectively,and leaving the same distance between plants within each row.
Creso(*IT40)is an old durum wheat variety(1974)that was widely cultivated in Central Italy in the past20years and is still in use.It is characterized by a moderate but constant yield and a high adaptability to different environmental conditions. Simeto(*IT60)and Svevo(*IT2)are more recent varieties characterized by taller size and higher productivity.
In both years the preceding crop was berseem(Trifolium alexandrinum L.).Soil was ploughed at40cm depth in Novem-ber and sowing was performed on17November2001and on14 November2002by means of a plot drill.
Nitrogen,as urea,phosphorus,as triple superphosphate,and potassium,as K2SO4fertilizers were applied before seeding at rates of30kg ha?1of N and150kg ha?1of P2O5and K2O.At the end of tillering,additional120kg ha?1of N,as urea,were applied.Fertilization was that conventionally applied to wheat in Tuscany(Italy).Weed control was performed at the stage of4th–5th leaf unfolded by distributing a commercial gramini-cide.In the second year,three irrigations were performed during grain?lling,in order to avoid severe water stress.Each time,a water volume equal to available water was applied by means of sprinkler irrigation.
To determine translocation during grain?lling,plants were harvested at heading(stage59,Zadoks scale,Zadoks et al., 1974)and physiological maturity(stage92,Zadoks scale).The experiment was arranged in a split-split-plot design with three replications.Year was the whole plot,durum wheat variety the sub-plot and seeding rate the sub-sub-plot.
The phenological stage of the wheat crop was periodically recorded following Zadoks et al.(1974).Heading was reached by the varieties Svevo and Simeto on22–26April and by the variety Creso on2–5May.Physiological maturity was achieved by all varieties on20–25June.At heading and at physiological maturity,plants from four adjacent rows of1m were manually cut at ground level.Plants were separated into culms,spikes and green and dead leaves at heading,and into culms,leaves, chaff and grain at maturity.For dry weight determination,sam-ples from all plant parts were oven dried at70?C to constant weight.At both harvests,the total number of culms and spikes was recorded,and the percentage of head bearing culms was calculated.At heading,the number of spikelets of50spikes for each replicate was counted and the area of green leaves was determined by means of a Leica Quantimet500image analyzer. At maturity,plant height and mean kernel dry weight were also determined,and the number of kernels per unit area,per spike and per spikelet and Harvest index(HI)were estimated.Plant samples were analyzed for nitrogen(microKjeldahl)concentra-tion and N content was calculated by multiplying the element concentration by dry weight.
The post-heading dry matter(DM)and N accumulation were calculated as the difference between DM or N content of the aerial plant part at physiological maturity and at heading.
The dry matter and N remobilization during grain?lling (DMR and NR)were calculated following Cox et al.(1986) and Papakosta and Gagianas(1991),as DMR=DM of the aerial plant part at heading
?(DM of leaves+culms+chaff at maturity);
NR=N content of the aerial plant part at heading
?(N content of leaves+culms+chaff at maturity).
For these estimates,it was assumed that all of the dry matter and N lost from vegetative plant parts were translocated to the developing grain,since losses of dry matter due to plant respi-ration and losses of N due to volatilization during grain?lling were not determined.
The dry matter and N remobilization ef?ciency(DMRE and NRE)were calculated as
DMRE=(DMR/DM of the aerial plant part at heading)×100;
NRE=(NR/N content of the aerial plant part at heading)×100.
The contribution of pre-heading DM and N assimilates to grain were calculated as
CDMRG=(DMR/DM of grain at maturity)×100;
CNRG=(NR/N content of grain at maturity)×100.
Data were statistically treated by ANOV A,in order to test the main effects of year,seed rate and variety and their interactions. Separate statistical analyses were conducted for dry matter and N accumulation and remobilization for each harvest.Because the main effect of year and its interactions were not signi?cant, a successive analysis of variance was carried out using years as replications.Duncan’s multiple range test was used to separate the means when the ANOV A F-test indicated a signi?cant effect of the treatment(Steel et al.,1997).
3.Results
In the years we carried out the research,temperature during the entire crop cycle and rainfall until anthesis were in line with the120-year averages(Moonen et al.,2001).In contrast,rainfall during grain?lling(May–June)diverged from the average and differed markedly between the2years(Fig.1).In particular, taking into account the last60years,only10times May and June were wetter than in2002,and these2months were never drier than in2003.Thus,in order to avoid water stress,in the second year,we irrigated starting from the beginning of May.As a consequence,the crop received an optimal water supply during grain?lling in both years,which probably caused the effect of year to be unsigni?cant in the present research.
The variety×seeding rate interaction was nonsigni?cant for all traits measured.Considering that Creso,Simeto and Svevo well represent the durum wheat varieties cultivated in Central Italy,these results provide evidence that the response of durum wheat to seeding rate is not affected by genotype.Therefore,
312I.Arduini et al./Europ.J.Agronomy25(2006)
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Fig.1.Minimum and maximum temperatures and rainfall recorded during the period of wheat growth(November–June)in2001–2002and2002–2003. only variety and seeding rate mean effects were discussed in the present paper.
The duration of the entire cycle did not vary signi?cantly among varieties and seeding rates,averaging215days.However, in the variety Creso the stage of?rst node detectable(31,Zadoks scale)was achieved6–9days later than in the varieties Simeto and Svevo,while the grain?lling period was6–8days shorter.
The highest grain yield was7.2t ha?1,and it was obtained with the variety Svevo sown at400seeds m?2.Averaged over seeding rates,grain yield of Svevo exceeded by67%that of Creso and by37%that of Simeto(Fig.2left).The higher grain yield of Svevo(Table1)depended mainly on the number of kernels per unit surface,that was by55and31%higher than in Creso and in Simeto,whereas the mean kernel weight con-tributed to a smaller extent,+7and+1%,https://www.sodocs.net/doc/2b811657.html,pared to Simeto,the increased number of kernels per unit surface of Svevo was mainly consequence of the higher number of spikes per unit surface(+21%),and only secondly of the number of kernels per spike(+9%),while,compared to Creso,the latter contributed more than the former(+36and+14%,respectively). The higher number of kernels per spike achieved in Svevo was due to the higher number of kernels per spikelet,that was by 63and15%higher than in Creso and Simeto,respectively.The number of spikelets per spike had an inverse trend compared to the other grain yield components(Table1).Finally,the var. Svevo also showed the highest harvest index,39compared to 32%of Simeto and28%of Creso,together with the highest size of plants at maturity,112compared to107cm(data not shown).
The green leaf area recorded at heading ranged from 514dm2m?2of the var.Svevo to564dm2m?2of Simeto and for all varieties it increased linearly with the increase of seeding rate(Table1).
Averaged over varieties,the grain yield obtained with 400seeds m?2was by42and21%higher than that obtained with200and250seeds m?2(Fig.2right).The increase in grain yield was essentially due to the increased number of kernels per unit area,and we found a positive relationship between these two parameters(Fig.3).The number of kernels per unit area depended primarily on the increased number of spikes per unit area(+45and24%),and secondly on the higher mean kernel weight(+12and5%)(Table1).In contrast,the number of ker-nels per spike decreased with the increase of seeding rate from 30to26,and the number of kernels per spikelet and that of spikelets per spike were not affected by seeding rate.Harvest index slightly increased with the increase of seeding rate from 200to400seeds m?2,and was32,34and35%.In addition, plants grown with the lowest seed rate were by8cm taller than other plants(114compared to106cm).
The dry weight of culms and leaves did not differ statisti-cally among varieties at both harvests,and that of spikes only at maturity and essentially in consequence of the differences in grain dry weight(data not shown).
Between heading and maturity,the number of spikes per unit area increased by5%in Creso,by13%in Simeto and by22%in Svevo(Table1).The dry weight of culms and leaves decreased, while that of spikes increased with patterns that differed among varieties mainly according to differences in grain yield(data not
Table1
Spike number,mean kernel weight,kernel and spikelet number and green leaf area of Triticum durum as affected by variety and seeding rate
Treatments Spike number(n m?2)Kernel weight
(mg)Kernel per square
meter(no.)
Kernel per spike
(no.)
Kernel per
spikelet(no.)
Spikelet per spike
(no.)
Green leaf area
(dm2m?2)
Heading Maturity
Variety
Creso434a455a38.2a10,209a22.4a 1.0a22.8a541.2ab Simeto380b430a40.6a12,069b28.1b 1.4b20.2b563.9a Svevo426a519b41.0a15,854c30.6c 1.6c19.1b513.6b Seeding rate(seeds m?2)
200341a388a39.3a11,450a29.5a 1.4a21.5a444.0a 250416b453b42.1ab12,603a27.9ab 1.4a20.4a575.2b 400483c563c44.0b14,545b25.8b 1.3a20.2a599.5b For each treatment,values in a column followed by the same letter are not signi?cantly different at P≤0.05as determined by the Duncan’s test.
I.Arduini et al./Europ.J.Agronomy 25(2006)309–318
313
Fig.2.Grain yield and grain N content of durum wheat as affected by variety (left)and seeding rate (right).Bars represent ±S.E.
shown).As a result,the overall post-heading dry matter accu-mulation of Svevo was by 60%higher than that of Simeto and by 174%than that of Creso (Fig.4left).The reverse occurred for dry matter remobilization that was by 21and 53%higher in Creso than in Simeto and in Svevo,respectively.Thus,in Creso post-heading DM accumulation and remobilization contributed equally to grain yield,while in Simeto accumulation was dou-ble than remobilization and in Svevo it was four-fold higher.So,grain yield depended for one half on remobilization in Creso,for a third party in Simeto and only for a ?fth party in Svevo.Finally,in all varieties,the cumulative dry matter remobilization from culms was approximately double than that from leaves.At both harvest stages,the dry weight of all plant parts increased with the increase of seed rate,with differences that were always statistically signi?cant between 200and 400seeds m ?2(Table 2).As a result,the dry weight of the aerial part increased by 30%between the lowest and the
high-Fig.3.Relationship between grain yield and grain number per unit area for different varieties and seeding rates.est seed rate at both stages.Between heading and maturity,the dry weight of spikes increased approximately six-fold,without appreciable variations among seeding rates.In the same period,the dry weight of culms and leaves decreased.The reduction of culm dry weight depended on seed rate,and increased from 1.4to 2.5t ha ?1with the increase of seed rate,whereas leaf dry weight was seed rate independent and was approximately 1t ha ?1.
Both post-heading dry matter accumulation and translocation increased with seeding rate (Fig.4right).The former,however,did not differ between the two lower seed rates,and increased by 30%with the highest one,whereas the latter increased most between 200and 250seeds m ?2(+64%)and then only by 11%.Post-heading dry matter accumulation was about three-fold higher than remobilization at the lowest seeding rate and two-fold higher with the other two rates.Finally,the contribution of remobilization to grain yield ranged from 25to 34%,with the
Table 2
Dry weight of culms,leaves,spikes and aerial part of Triticum durum at heading and physiological maturity as affected by seeding rate Seeding rate (seeds m ?2)
Dry weight (t ha ?1)Culms
Leaves Spikes Aerial part Heading 200 6.8a 2.6a 1.2a 10.6a 2507.8b 2.9b 1.3ab 12.0ab 4009.3c 3.0b 1.5ab 13.8b Maturity 200 5.4a 1.6a 7.0a 14.0a 250 5.8a 1.9ab 7.8a 15.5a 400
6.8b
2.2b
9.2b
18.2b
For each harvest,values in a column followed by the same letter are not signif-icantly different at P ≤0.05as determined by the Duncan’s test.
314I.Arduini et al./Europ.J.Agronomy 25(2006)
309–318
Fig.4.Post-heading dry matter accumulation,dry matter remobilization (DMR),and contribution of dry matter remobilization to grain yield (CDMRG)of durum wheat as affected by variety (left)and seeding rate (right).Bars represent ±S.E.
lowest value recorded with 200seeds m ?2and the highest with 250seeds m ?2.Culms translocated more dry matter than leaves and the ratio between the dry matter remobilized by culms and by leaves increased from 1.4to 2.0and to 3.1with the increase of seeding rate.
The N concentration of separate plant parts did not differ signi?cantly among varieties at heading.At maturity,the var.Svevo showed a lower N concentration of culms (2.5compared to 4.6g N kg ?1of Creso and Simeto)and the var.Simeto a higher N concentration of leaves (13.6compared to 10.2g N kg ?1of Creso and Svevo),whereas the N concentrations of spikes,grain and of the entire aerial part were not affected by variety (data not shown).The increase of plant density decreased the N concentra-tion of culms,leaves and grain,but differences were signi?cant only when plant density increased from 250to 400seeds m ?2(Table 3).
At heading,the N content of culms,leaves and spikes did not differ appreciably among varieties.At maturity,the N content of both culms and leaves was lower in the var.Svevo compared to the other two varieties,by approximately 45and 25%(Table 4).Conversely,grain N content was highest in the cv.Svevo,with values that were 30%higher than in Simeto and 73%higher than
in Creso (Fig.2left).Finally,the N content of the entire aerial part was approximately 190kg N ha ?1in Simeto and Svevo and 150kg N ha ?1in Creso (Table 4).
Between heading and maturity,N concentration and N con-tent of culms and leaves decreased in all varieties,whereas those of spikes and of the entire aerial part increased.
Table 3
Nitrogen concentration of culms,leaves,spikes,grain and aerial part of Triticum durum at heading and physiological maturity as affected by seeding rate Seeding rate (seeds m ?2)
Nitrogen concentration (g kg ?1)Culms
Leaves Spikes Grain Aerial part Heading 200 6.3a 18.7a 11.3a –9.9a 250 6.1a 18.2a 11.6a –9.6a 400 5.4b 16.5b 10.8a –8.4a Maturity 200 4.4a 12.2a 17.2a 22.8a 11.7a 250 4.3a 12.2a 17.4a 22.7a 11.6a 400
3.2b
9.7b
16.4a
21.0b
10.7a
For each harvest,values in a column followed by the same letter are not signif-icantly different at P ≤0.05as determined by the Duncan’s test.
I.Arduini et al./Europ.J.Agronomy 25(2006)309–318
315
Table 4
Nitrogen content of culms,leaves,spikes and entire aerial part of Triticum durum at heading and physiological maturity as affected by variety Variety
Nitrogen content (kg ha ?1)Culms
Leaves Spikes Aerial part Heading Creso 46.8a 54.1a 14.2a 115.1a Simeto 49.4a 52.1a 15.9a 117.3a Svevo 44.5a 44.5a 14.8a 103.8b Maturity Creso 26.7a 22.2a 100.0a 148.9a Simeto 28.1a 24.5a 133.9b 186.4b Svevo
15.0b
17.5b
157.6c
190.1b
For each harvest,values in a column followed by the same letter are not signif-icantly different at P ≤0.05as determined by the Duncan’s test.
The post-heading N accumulation of the var.Svevo was by 25%higher than that of Simeto and by 155%higher than that of Creso,whereas the N remobilization to grain was higher in Svevo than in Creso (+17%)and in Simeto (39%)(Fig.5left).A trend similar to N remobilization was observed for N remobi-
lization ef?ciency (NRE),that was 55%in Svevo,43%in Creso and 35%in Simeto (data not shown),whereas the contribution of remobilization to grain N content was 60%in Creso and approxi-mately 38%in the other two varieties (Fig.5left).Thus,nitrogen remobilization was by 45%higher than accumulation in Creso and by 40%lower in Simeto and Svevo.Remobilization from leaves was higher than from culms in Creso and Simeto,and lower in Svevo.
At heading,N content of culms and spikes increased by approximately 18%with the increase of plant density,whereas that of leaves was not affected (Table 5).At maturity,the N con-tent of grain linearly increased with the increase of seeding rate (Fig.2right),whereas that of culms and leaves was unchanged among treatments (Table 5).As a result,the N content of the aerial part was by about 25%higher with 400seeds m ?2com-pared to the two lower seed rates.With all treatments the N uptake of the aerial part exceeded the amount of N applied with fertilizers.The surplus ranged from 14kg N ha ?1with 200seeds m ?2to 44kg N ha ?1with 400seeds m ?2(Table 5).This nitrogen was probably left in soil by the preceding legumi-nous crop that was T.alexandrinum
.
Fig.5.Post-heading N accumulation,N remobilization (NR),and contribution of N remobilization to N grain content (CNRG)of durum wheat as affected by variety (left)and seeding rate (right).Bars represent ±S.E.
316I.Arduini et al./Europ.J.Agronomy25(2006)309–318
Table5
Nitrogen content of culms,leaves,spikes and entire aerial part of Triticum durum at heading and physiological maturity as affected by seeding rate
Seeding rate(seeds m?2)Nitrogen content(kg ha?1)
Culms Leaves Spikes Aerial part Heading
20042.8a48.6a13.6a105.0a 25047.6ab52.8a15.1b115.4b 40050.2b49.5a16.2b115.9b Maturity
20023.8a19.5a120.6a163.9a 25024.9a23.2a139.6b187.7b 40021.8a21.3a151.2c194.3c For each harvest,values in a column followed by the same letter are not signif-icantly different at P≤0.05as determined by the Duncan’s test.
Post-heading N accumulation and N remobilization increased almost linearly with the increase of seeding rate(Fig.5right), but N accumulation was between34and50%higher than remo-bilization.Nitrogen remobilization ef?ciency was42%with200 and250seeds m?2and fell to35%with400seeds m?2(data not shown),whereas the contribution of remobilization to grain N yield was unchanged by seeding rate and was approximately 40%(Fig.5right).Nitrogen remobilization from leaves was unchanged by seeding rate,while that from culms increased linearly with the increase of seeding rate.As a consequence, with the two lowest seed rates,remobilization from leaves was higher than from culms,while values equalled with the highest seed rate.It is noteworthy that during grain?lling the aerial part accumulated more than35%of the total N taken up during the entire cycle.
4.Discussion
The durum wheat varieties Creso,Simeto and Svevo did not differ in the patterns of response to plant density.Similar results were reported by several authors for a wide range of T.aestivum genotypes chosen among old and modern,short and tall ones (Spink et al.,2000;Donaldson et al.,2001;Geleta et al.,2002; Carr et al.,2003).Averaged over seed rates,however,the three varieties showed marked differences for most of the recorded characters.
The duration of the entire cycle was similar for the three varieties,but the older var.Creso had a longer vegetative phase and a shorter grain?lling period compared to the two modern ones.Earlier heading was also reported by Guarda et al.(2004) as a characteristic of modern Italian varieties of T.aestivum.
Varieties differed in both grain yield and yield components. Grain yield declined in the order Svevo>Simeto>Creso.The higher yield of the newer varieties Svevo and Simeto was essen-tially due to an increase in the number of fertile?orets within each spikelet and in the weight of single kernels.This differ-ences are consistent with those reported between ancient and modern wheat varieties by Siddique et al.(1989),Frederick and Bauer(1999)and Guarda et al.(2004),and are considered the result of an improved partitioning of assimilates to the head.
In the present research,the highest grain yield of durum wheat was obtained with the highest seeding rate.Accordingly, Ghaffari et al.(2001)found that seed rates comprised between 300and450seeds m?2are optimal for temperate conditions. The analysis of yield components showed that the higher grain yield was primarily due to the higher number of kernels per unit area,directly related to the number of spikes per unit area,and secondly,to the higher mean kernel weight.It is noteworthy that the number of kernels per spike progressively increased with the decrease of seeding rate but,differently from the?ndings of Darwinkel(1978)and Spink et al.(2000),this yield gain was not enough to fully compensate for the lower number of spikes per unit area.A positive correlation between seed rate and both grain yield and mean kernel weight was reported for T.aestivum by Wilson and Swanson(1962),Blue et al.(1990)and Geleta et al.(2002).Carr et al.(2003)found that the increase of seed density increased yield,but did not affect kernel weight.Oppo-site results were reported by Wood et al.(2003),who found that grain yield was higher with250than with350seeds m?2,due to the higher number of grains per ear and the higher mean kernel weight.
The var.Svevo showed a by far higher post-heading dry mat-ter accumulation compared to the var.Simeto and Creso,to which,however,corresponded a consistently lower remobiliza-tion.The var.Simeto showed intermediate values for these traits. As a result,the contribution of dry matter remobilization to grain yield differed markedly among the three varieties,being more than50%in Creso and less than20%in Svevo,which is con-sistent with the differences between older and newer varieties reported by Pheloung and Siddique(1991).Marked differences among varieties in the relative contribution of pre-and post-anthesis assimilates to grain yield were also reported by Przulj and Momcilovic(2001a)for two-rowed barley.These authors also observed that cultivars with a larger contribution of dry mat-ter translocation to grain yield tended to have lower yields.The contribution of pre-anthesis assimilates to grain may be crucial for maintaining yield when adverse climatic conditions reduce photosynthesis and water and mineral uptake(Van Herwaarden et al.,1998;Tahir and Nakata,2005).Thus,the high contri-bution of translocates to grain yield observed in Creso may be responsible of its known yield stability over years.Conversely, the low contribution of translocates could impair the var.Svevo to maintain high yield when high temperatures or water stress occur around anthesis,as it was suggested by Frederick and Bauer(1999)for modern high yielding wheat varieties.
The post-heading dry matter accumulation and the dry mat-ter remobilization from vegetative plant parts to grain increased with the increase of seeding rate.A possible explanation of increased accumulation is that the higher number of plants increased both the photosynthetizing area at heading(+35% between the lowest and the highest seed rate)and the volume of roots per unit soil surface,allowing the crop to improve the exploitation of environmental resources.Wall and Kanemasu (1990)reported that the early canopy closure obtained with high crop densities increased light interception ef?ciency and net pro-ductivity.In addition,the higher remobilization we found was probably linked to the higher dry matter of the crop at heading,
I.Arduini et al./Europ.J.Agronomy25(2006)309–318317
that represents the potential source for remobilization(Tompkins et al.,1991a,b;Przulj and Momcilovic,2001a).
Due to the higher dry matter yield,N uptake of the whole crop and N content of grain was higher in Simeto and Svevo than in Creso.The N concentration of grain did not vary among varieties,whereas the var.Svevo showed a markedly lower N content of culms and leaves at maturity,which may be conse-quence of the high N remobilization ef?ciency performed by this variety.The difference in N uptake and use we observed between Creso and Svevo is in agreement with results reported by Guarda et al.(2004)for Italian bread-wheat cultivars.
The N uptake by the crop was highest with400seeds m?2, but only in consequence of increased dry matter,because the N concentration of culms,leaves and even grain was slightly lower than with other treatments.Contrasting results are reported for the N-uptake of wheat crops in response to plant density.Accord-ing to Geleta et al.(2002),grain protein concentration declined as seeding rate and yield increased,suggesting that more fer-tilizer could be required to maintain a better end-use quality of wheat at higher seed rates.In contrast,Tompkins et al.(1991a,b) found that high seed rates increased grain protein concentration and,?nally,Carr et al.(2003)and Ozturk et al.(2006)found that grain protein concentration did not change also with wider ranges of seeding rate.Justes et al.(1994)proposed a valuable relationship between crop mass and crop N content to verify if the crop is or not in situation of non-limiting concentration.The application of this relationship to our data indicated that nitrogen was never limiting for crop growth.
Consistently to what observed for dry matter,also the post-heading N accumulation was by far higher in Simeto and Svevo than in Creso,whereas remobilization showed different patterns and was highest in Svevo and lowest in Simeto.Nevertheless, the percentage contribution of N remobilization to grain N was by far higher in Creso than in the other two varieties.In contrast, Przulj and Momcilovic(2001b)found that higher post-anthesis N accumulation was related to lower N remobilization in spring barley varieties.Our results suggest that the var.Svevo is very ef?cient in N use,similarly to bread-wheat varieties recently selected in Italy(Guarda et al.,2004).
The post-heading N accumulation of the durum wheat crop and the N remobilization were highest with the highest plant density,but the contribution of remobilization to N grain content did not differ between the lowest and the highest seeding rate.
In conclusion,the highest grain yield was obtained with 400seeds m?2,which caused a slight decrease in the N concen-tration of grain but did not affect the general N nutrition status of the crop estimated according to Justes et al.(1994).The grain yield increase was essentially due to the higher number of spikes per unit surface and to the higher biomass of the crop at heading that allowed a higher remobilization of resources to the develop-ing grain.The three varieties differed essentially in harvest index and in the post-heading accumulation and translocation of both dry matter and nitrogen.The highest grain yield was obtained with the variety Svevo,that showed the highest post-heading accumulation of both dry matter and nitrogen,the best N remo-bilization ef?ciency but the lowest dry matter translocation.We must mention that present results were obtained with optimal growth conditions,especially with respect to water supply dur-ing the grain?lling period.These conditions could have delayed senescence allowing plants to photosynthetize and assimilate for a longer period.
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