9
This article was downloaded by: [Cornell University Library] On: 19 November 2014, At: 02:15 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Acta Agriculturae Scandinavica, Section B — Soil & Plant Science Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/sagb20 Crop uptake of 15 N labelled fertilizer in spring wheat affected by application time J. Petersen a Department of Agroecology, Research Centre Foulum , Danish Institute of Agricultural Sciences , P.O. Box 50, DK-8830, Tjele, Denmark Published online: 02 Sep 2006. To cite this article: J. Petersen (2004) Crop uptake of 15 N labelled fertilizer in spring wheat affected by application time, Acta Agriculturae Scandinavica, Section B — Soil & Plant Science, 54:2, 83-90, DOI: 10.1080/09064710410024453 To link to this article: http://dx.doi.org/10.1080/09064710410024453 PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions

Crop uptake of 15 N labelled fertilizer in spring wheat affected by application time

  • Upload
    j

  • View
    212

  • Download
    0

Embed Size (px)

Citation preview

Page 1: Crop uptake of               15               N labelled fertilizer in spring wheat affected by application time

This article was downloaded by: [Cornell University Library]On: 19 November 2014, At: 02:15Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: MortimerHouse, 37-41 Mortimer Street, London W1T 3JH, UK

Acta Agriculturae Scandinavica, Section B — Soil &Plant SciencePublication details, including instructions for authors and subscription information:http://www.tandfonline.com/loi/sagb20

Crop uptake of 15N labelled fertilizer in spring wheataffected by application timeJ. Petersena Department of Agroecology, Research Centre Foulum , Danish Institute of AgriculturalSciences , P.O. Box 50, DK-8830, Tjele, DenmarkPublished online: 02 Sep 2006.

To cite this article: J. Petersen (2004) Crop uptake of 15N labelled fertilizer in spring wheat affected by application time,Acta Agriculturae Scandinavica, Section B — Soil & Plant Science, 54:2, 83-90, DOI: 10.1080/09064710410024453

To link to this article: http://dx.doi.org/10.1080/09064710410024453

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) containedin the publications on our platform. However, Taylor & Francis, our agents, and our licensors make norepresentations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose ofthe Content. Any opinions and views expressed in this publication are the opinions and views of the authors,and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be reliedupon and should be independently verified with primary sources of information. Taylor and Francis shallnot be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and otherliabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to orarising out of the use of the Content.

This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in anyform to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions

Page 2: Crop uptake of               15               N labelled fertilizer in spring wheat affected by application time

Crop Uptake of 15N Labelled Fertilizer inSpring Wheat Affected by ApplicationTime

Introduction

Nitrogen (N) fertilizers enriched with the stable 15N

isotope have commonly been used for determination of

crop utilization of fertilizer N as affected by N-form

(Recous et al., 1988, 1992; Malhi et al., 1996; Petersen

et al., 2004), application method (Malhi et al., 1989,

1996; Malhi & Nyborg, 1991), placement geometry

(Petersen, 2001) and precipitation after surface appli-

cation (Hartman & Nyborg, 1989; Powlson et al.,

1992). Similarly, the 15N labelling method can be used

to investigate the crop recovery affected by application

time. In experiments with two or three application

times, the crop 15N recovery at maturity was increased

by postponing the time of N application from the

tillering phase to the beginning of stem elongation

(Leitch & Vaidyanathan, 1983; Riga et al., 1988;

Limaux et al., 1999). However, in these experiments

there was about six weeks between the first and second

application, and the course of change in crop 15N

recovery may not be estimated satisfactorily with such

a wide span in application times.

Detailed knowledge about the variation in crop

utilization of fertilizer N applied during the vegetative

phase is useful for farmers’ decisions regarding time of

application of fertilizer.

In addition, crop 15N recovery at maturity may be

affected by losses during the grain-filling period of

previously recovered 15N (Recous et al., 1988; Peter-

sen, 2001). Several pathways for N losses have been

suggested (Wetselaar & Farquhar, 1980), but the

magnitude of each pathway depends on the growth

conditions. Nevertheless, the sum of losses may be of

significance and may interact with the time of fertiliza-

tion (Yoneyama, 1983). Therefore recordings at har-

Petersen, J. (Department of Agroecology, Danish Institute of Agricultural

Sciences, P.O. Box 50, DK-8830 Tjele, Denmark). Crop uptake of 15N

labelled fertilizer in spring wheat affected by application time. Accepted

February 20, 2004. Acta Agric. Scand., Sect. B, Soil and Plant Sci. 54:

83�/90, 2004. # 2004 Taylor & Francis.

Time of nitrogen fertilizer application on crop recovery was studied in a

field experiment at Foulumgaard, Denmark, in 2001. A solution of 15N-

ammonium-15N-nitrate was applied in bands parallel to a single row of

spring wheat grown in frames of 30 cm�40 cm. The labelled fertilizer

was applied on 16 dates with intervals of 4�/5 days from tillering to the

start of grain-filling. Crop 15N recovery increased by 0.47%-point day�1

when the time of fertilizer application was postponed from tillering untilthe second node stage (GS32). On the other hand, a decrease in crop 15N

recovery of �/0.19%-point day�1 was recorded from GS47 to maturity

(GS85�/87). The effect of the 16 application times on 15N recovery was

described by two straight lines having intersection at the time of full

expanded flag leaf and ear emergence halfway (GS55). It was concluded

that leaf area expansion is important for crop N demand and 15N

recovery.

J. Petersen

Department of Agroecology, ResearchCentre Foulum, Danish Institute ofAgricultural Sciences, P.O. Box 50, DK-8830 Tjele, Denmark

Key words: 15N-ammonium-15N-nitrate, direct injection, fertilizer time,pulse-labelling, recovery.

DOI: 10.1080/09064710410024453 83

Dow

nloa

ded

by [

Cor

nell

Uni

vers

ity L

ibra

ry]

at 0

2:15

19

Nov

embe

r 20

14

Page 3: Crop uptake of               15               N labelled fertilizer in spring wheat affected by application time

vest may be affected by both the time of fertilization

and losses during the grain filling period.

The present study had two aims. The first aim was

methodological, concerning determination of the in-

fluence of sampling time on the crop uptake of applied

fertilizer N, especially exposure to any interaction

between sampling time and time of fertilizer Napplication. The second and principal aim was to

obtain detailed information about the changes in crop

recovery of fertilizer N applied many times at regular

intervals of a few days during the vegetative growth

phase of a small-grain cereal crop.

Materials and methods

A field experiment on 15N pulse labelling was carried

out in micro-plots at Research Centre Foulum, Den-

mark (56830? N, 9835? E). The soil was a TypicHapludalf according to Soil Survey Staff (2003), with

a topsoil of loamy sand characterized by 9% clay, 13%

silt (2�/20 m), 45% fine sand (20�/200 m), 31% coarse

sand (200�/2000 m), 1.6% C and a pH(CaCl2) of 6.2.

The entire experimental area had 60 kg N

ha�1 applied as ammonium nitrate using a commer-

cial granular NPK fertilizer (16:4:12) for basic fertili-

zation before seedbed preparation. This basicfertilization represents about half the normal N rate

for spring wheat, and may delay a serve shortage of

nutrients without overshadowing the effects of the 15N

treatments. Flexible plastic frames of 30 cm�/40 cm

bordering each of the 114 micro-plots were inserted

into the soil to a depth of 11�/13 cm to prevent 15N

uptake by plants outside the micro-plot. A single 33

cm row of spring wheat (Triticum aestivum L. cv.

Vinjett) was sown on 17 April 2001 in each frame, andemergence was recorded on 3 May. The inter-seed

distance was 0.8 cm to ensure an uninterrupted row.

Weeds were removed frequently, by hand using a claw-

like weeding tool.

Treatment and sampling

A total of 38 treatments (Table 1) in three replicateswere laid out in a randomized complete block design.

A solution of ammonium nitrate (2.624 M , 3.3824 (s.e.

0.0007) and 3.2922 (s.e. 0.0135) 15N atom% for

ammonium-N and nitrate-N, respectively) was applied

by injection as subsurface bands parallel to the crop

row. A 15N pulse was applied at one of 16 dates with

intervals of 4�/5 days from 10 May to 18 July (Fig. 1).

This period corresponds to growth stages (GS) 11�/ 67at the BBCH scale (Lancashire et al. , 1991) and covers

the entire vegetative growth phase of the spring wheat

crop. For all 16 15N pulses, and a treatment without15N pulse (unfertilized), plants were grown to maturity

Table 1. Times of 15N application and sampling: growth stages (GS) are according to the BBCH scale (Lancashireet al., 1991)

Samplings and growth stage

Time of 15N application(pulse number)

I: Opening of flagleaf sheath, GS47

II: End offlowering, GS67

III: Grain-filling,milky ripe,GS75�/77

IV: Yellow ripeness,dough stage,GS85�/87

1 �/ �/ �/ �/

2 �/ �/ �/ �/

3 �/ �/ �/ �/

4 �/ �/ �/ �/

5 �/ �/ �/ �/

6 �/ �/ �/ �/

7 �/ �/ �/ �/

8 �/

9 �/

10 �/

11 �/

12 �/

13 �/

14 �/

15 �/

16 �/

Unfertilized �/

J. Petersen

84

Dow

nloa

ded

by [

Cor

nell

Uni

vers

ity L

ibra

ry]

at 0

2:15

19

Nov

embe

r 20

14

Page 4: Crop uptake of               15               N labelled fertilizer in spring wheat affected by application time

and sampled on 15 August, 104 days after emergence

at sampling IV (Table 1). In parallel plots, plants that

had been 15N pulse fertilized at one of the first seven

dates, GS11-32, were sampled on 27 June, 16 July and

30 July, indicated by Samplings I, II and III, respec-

tively (Table 1, Fig. 1).

The fertilizer band was located 2 cm from the crop

row and 8 cm below the soil surface. The depth and

distance from the crop row were both within an

accuracy of less than 9/0.5 cm. The fertilizer band

was divided into 33 points, 1.0 cm apart. A 0.18 cm ¥needle, used for injection at each point, was connected

to a PiP1CKC pump (Fluid Metering Inc., USA). A

total volume of 5.13 ml was applied to each plot. The

pump ensured that 1/33 of the total volume per plot

was applied at each point. The application rate of

0.377 g N plot�1 corresponded to 31 kg N ha�1.

Number of plants, shoots and ears were counted in

plots grown to maturity on 15 May, 12 June and 4 July,

respectively, and the ear:shoot ratio was calculated.

Mean air temperature and precipitation during the

experimental period are shown in Fig. 1.

The plants were cut by shears 0.5�/1 cm above the

soil surface, avoiding contamination by soil particles.

Total plant dry matter (DM) was determined after 18

h of drying at 808C. The grain DM at maturity was

determined after threshing, and the straw was coarse-

ground using a Retsch SM2000 cutting mill. All

samples were finely-ground in a Retsch MM2000 ball

mill (Retsch GmbH & Co, Germany).

Percentage of total N and 15N atom abundance was

measured on a continuous-flow isotope ratio mass

spectrometer (ANA-MS method) (Jensen, 1991). The

natural 15N abundance in plants was determined in

unfertilized plants (0.3682 15N atom%, s.e. 0.00015).Calculation of crop 15N recovery was performed

according to IAEA (1976).

Statistics

The number of days from spring wheat emergence to

the time of 15N application, Fday, and the number ofdays from spring wheat emergence to the time of

sampling, Sday, were both included for the analysis of

crop 15N recovery, Y, at the first seven dates of

fertilization (Eqn 1). In addition, the interaction of

fertilization and sampling time was included using the

procedure GLM (SAS Institute, 1996).

Y �a�b Fday�c Sday�d Fday Sday (1)

Crop 15N recovery at maturity, Y, was analysed using a

segmented model consisting of two linear regressions

(Eqn 2a and 2b), having miximum at (Fday(max ), Ymax ),

where the straight lines intersect.

Y �a1�b1 Fday if Fday 5Fday(max) (2a)

Y �a1�b1 Fday if Fday]Fday(max) (2b)

The segmented model was also used for the ear:shoot

ratio, and the parameters were estimated by the

procedure NLIN (SAS Institute, 1996). For the grain

nitrogen concentration and nitrogen derived fromfertilizer (Ndff) in grain as well as straw, a simple

single linear regression model was applied, using the

procedure GLM (SAS Institute, 1996).

Results

Time of fertilization and sampling

The interaction between time of fertilization and

sampling in Eqn (1) was insignificant with respect to

crop 15N recovery, and therefore was excluded in

estimation of the parameters. This means that the

effects of fertilization and sampling time on crop 15N

recovery are additive. Postponement of the fertilizertime increased crop 15N recovery by 0.47%-point

Fig. 1. Mean air temperature (line) and precipitation (bars) during

the experimental period. The 16 dates for fertilization (triangles) and

the four sampling times (dots) are indicated. Filled triangles

correspond to the seven fertilizer pulses also sampled at times I-

III. All 16 application dates were represented at sampling IV.

Table 2. Recovery of applied 15N (%). Estimates 9/standard errors for the parameters in Eqn (1)

Intercept, a Estimate for b (Fday) Estimate for c (Sday) DF R2

67.39/3.26 0.4679/0.0704 �/0.1879/0.0342 72 0.52

Uptake of 15N affected by application time

85

Dow

nloa

ded

by [

Cor

nell

Uni

vers

ity L

ibra

ry]

at 0

2:15

19

Nov

embe

r 20

14

Page 5: Crop uptake of               15               N labelled fertilizer in spring wheat affected by application time

day�1 until the second node stage (GS32) (Table 2).

This positive effect was counteracted by a decrease of

0.19%-point day�1 during the grain-filling period.

Sampling at maturity

Application of the 15N fertilizer solution increased dry

matter yield and N uptake compared to the basic

fertilization only (Table 3). The average grain andstraw dry matter yield of 15N fertilized plots corre-

sponds to 3.9 and 6.2 t ha�1, respectively, using the

framed plot area as the basis. N uptake was not

affected by application time (data not shown), and

only a weak decrease in DM by time was observed

(Fig. 2a). The decrease in DM was estimated by linear

regression (R2�/0.10) to �/0.394 (P�/0.04) and

�/0.166 (P�/0.03) g DM plot�1 day�1 for totalDM and grain DM, respectively.

In contrast, crop 15N recovery (Fig. 2b) and the

ear:shoot ratio (Fig. 2c) depends on the application

time. The description of grain 15N recovery using the

segmented model (Eqn 2) was better than for total

crop 15N recovery (Table 4). The numbers of plants

and shoots were not affected by the time of fertilizer

application (data not shown), whereas the segmentedmodel was able to describe the effect on the ear:shoot

ratio, despite a low R2 value (Table 4).

The estimates in Table 4 were used for preparing the

straight lines in Fig. 2b and c. Fday(max ) was solved

setting the right sides of Eqn 2a and 2b equal to each

other and inserting the estimated parameters, and then

Ymax was calculated inserting Fday(max ) in Eqn 2 (Table

4).The NLIN procedure was not able to fit Eqn. 2 to

straw 15N recovery, and a simple linear regression

(R2�/0.24) shows a significant decrease of only

�/0.055%-point day�1. Therefore the recovery in

grain has a major influence on the recovery in the

total crop, and the difference between the estimates of

the slopes (b1 and b2 in Eqn. 2) for grain and total crop

is moderate (Table 4), resulting in a near parallelcourse of both parts of the segmented model in Fig. 2.

Both 15N recovery in grain and total crop are at

maximum at fertilization on day 58, whereas

the ear:shoot ratio is at maximum 3 weeks earlier

(Table 4).

In contrast to both the 15N recovery and the

ear:shoot ratio, the grain N-concentration was in-

creased linearly (Fig. 3), corresponding to an increase

by 0.04%-point protein for every day the N application

was postponed (calculated from Table 5). However, the

Table 3. Average dry matter yields and N uptake in plots with and without application of 15N fertilizer solution.9/ standard errors

Basic fertilized (n�/3) Basic fertilized�/15N fertilizer solution (n�/46)

Dry matter (g plot�1) N uptake (g plot�1) Dry matter (g plot�1) N uptake (g plot�1)

Grain 41.89/2.43 0.829/0.057 46.89/1.66 0.999/0.030Straw 75.69/5.66 0.279/0.013 73.99/2.44 0.309/0.011Total 117.39/7.61 1.099/0.069 129.69/4.03 1.299/0.040

Fig. 2. Dry matter (a), crop recovery of applied 15N (b) and ear:

shoot ratio (c). The recorded values for the 16 application dates are

mean 9/ standard error. The regression lines in (b) and (c) are based

on the estimates in Table 4 using Eqn. (1). The regressions for the

lines in (a) are mentioned in the text.

J. Petersen

86

Dow

nloa

ded

by [

Cor

nell

Uni

vers

ity L

ibra

ry]

at 0

2:15

19

Nov

embe

r 20

14

Page 6: Crop uptake of               15               N labelled fertilizer in spring wheat affected by application time

segmented model was also able to describe changes in

N concentration (R2�/0.61), but the higher degree ofexplanation depends very much on the low values

recorded on days 34 and 39 (Fig. 3), that may be

caused by the low temperatures during a rainy period

(Fig. 1). Grain Ndff also increased linearly with

postponement of fertilization time, accompanied by a

decrease in straw Ndff. In total, Ndff for the total crop

increased.

Discussion

Sampling time and loss of 15N

There was a minimum time interval of three weeks

between fertilizer application and sampling, to ensure

that maximum crop 15N recovery was obtained

(Petersen, 2001). However, the crop is not exclusively

a sink for fertilizer N (Recous et al. , 1988), as therealso are losses of 15N previously taken up. The mean

decline of crop 15N recovery was 0.19%-point day�1,

corresponding to 9.3%-point from sampling I to

sampling IV for the first seven dates of N application.

In this experiment, the decline in crop 15N recovery

during the grain-filling period was not significantly

affected by the fertilizer application time, but it is likely

that losses during grain filling may reduce earlier and

more pronounced differences. Thus, during the growth

of winter wheat to maturity, Yoneyama (1983) re-ported reductions of 15N recoveries for fertilizer

applied at the very beginning of the growth cycle.

The average decline in crop 15N recovery during the

grain-filling period was below the 12%-point observed

by Petersen (2001), but above the values reported by

Nielsen & Jensen (1986) and Recous et al. (1988). The

decline depends on application rate and year (Schjør-

ring et al., 1989) who suggested ammonia volatilizationfrom the aerial parts of the plants as the major source.

Thus, sampling time had an important influence on

the evaluation of treatments earlier applied. Losses

from the crop need to be explored further, and

attention must be drawn to the crop as more than

simply a sink for N. Despite a significant loss of

previously recovered 15N and the potential for inter-

action with time of sampling, the recordings atsampling IV for the 16 treatments were used for

estimation of the effect of fertilization time.

Time of fertilization

Averaged over of the four sampling dates, the crop 15N

recovery increased by postponement of the time of

fertilization from tillering to the second node stages

(GS32). However, the recovery at the sixth fertilization

pulse was low compared with the fifth and seventhfertilization pulse, irrespective of sampling time (see

Fig. 2b for sampling IV). Powlson et al. (1992)

reported that unrecorded 15N (expressing the loss

from the plant:soil system) was linearly related to the

accumulated precipitation during the three weeks

succeeding fertilizer N application. Thus, the 21 mm

precipitation received on the first two days succeeding

the sixth application pulse (Fig. 1) may have caused Nlosses, explaining the low recovery for this pulse.

Plant availability of the remaining 15N may be

further reduced by immobilization, which potential

depends on the distribution of the applied mineral N

in the soil volume. Petersen et al. (2004) used the same

soil type as reported here and found that 13% of the

applied N was immobilized by broadcasting, but

Table 4. Estimates9/approximately standard errors of the parameters in the segmented model (Eqn. 2) for crop15N recovery and the ear:shoot ratio

Increasing line (Eqn. 2a) Decreasing line (Eqn. 2b) Maximum

Parameter a1 b1 a2 b2 DF R2 Fday(max) Ymax

Recovery; grain (%) 33.49/1.65 0.4529/0.0465 101.89/20.74 �/0.7229/0.300 42 0.72 58.3 59.7Recovery; total (%) 47.79/1.95 0.3979/0.0547 119.69/24.40 �/0.8289/0.353 41 0.59 58.7 71.0Ear:shoot ratio (%) 64.69/3.47 0.5099/0.1575 93.89/6.38 �/0.3309/0.111 42 0.31 35.0 82.3

Fig. 3. Grain nitrogen concentration in grain for 16 application

dates (mean 9/ standard error). The regression line is based on the

estimates in Table 5.

Uptake of 15N affected by application time

87

Dow

nloa

ded

by [

Cor

nell

Uni

vers

ity L

ibra

ry]

at 0

2:15

19

Nov

embe

r 20

14

Page 7: Crop uptake of               15               N labelled fertilizer in spring wheat affected by application time

immobilization did not occur by banding ammonium

sulphate. A similar difference has been obtained for

urea, but the quantity depends on the soil immobiliza-

tion potential (Tomar & Soper, 1981). Thus, fertilizer

banding increases the amount of plant available

fertilizer N compared with incorporation into the

topsoil. These results are in accordance with the

findings of increased crop recovery of banded 15N-

urea (Tomar & Soper, 1981, 1987; Carter & Rennie,

1984; Malhi et al., 1989, 1996; Malhi & Nyborg, 1991).

In a pulse-labelling experiment applying eight pulses at

two-week intervals, Recous & Machet (1999) recorded

immobilization of 13�/16% of applied N, irrespective

of the date of application, and in addition, immobili-

zation was affected by neither the applied N-form

(Recous et al., 1992) nor soil type (Powlson et al.,

1992). These observations, together with the use of

fertilizer banding, make it implausible that immobili-

zation is the cause of the variation in the obtained data

for crop 15N recovery.

Hence, minimizing immobilization by banding, the

crop 15N recovery was described by a segmented linear

function using Fday, the day of fertilization counted

from emergence, as an independent variable. The

maximum recovery in the total crop was estimated to

58 days after emergence corresponding to fully ex-

panded flag leaf and ear emergence halfway (GS55).

The ability of cereals to translocate N from vegetative

to reproductive organs is presumably the reason why

the straw 15N recovery was only modestly affected by

the application time. Therefore, the total crop 15N

recovery was nearly parallel to the grain 15N recovery

(Fig. 2) with an estimated maximum also on day 58.

Applying the segmented linear model (Eqn 1) to the

results of Recous & Machet (1999), the maximum

recovery of total crop sampled one or two weeks after

pulse-labelling was obtained about two weeks before

ear emergence (heading). Applying the segmented

linear model to the recorded total crop 15N recovery

in a pot experiment using seven pulse-labellings with

7�/14 day intervals (Esala, 1991) maximum was

estimated to day 42, corresponding to the flag leaf

stage. Thus, there is a general indication that max-

imum crop 15N recovery takes place in the final part of

the elongation phase, around the flag leaf stage.

Leitch & Vaidyanathan (1983) suggested that the

crop N demand expressed by crop growth rate and

development stage may explain the increased 15N

recovery with applications late in the vegetative growth

phase. However, due to crop growth, the crop N

demand changes with time and therefore the effects

of time and crop N demand are linked. Limaux et al.

(1999) isolated the effect of crop N demand per area

unit by changing the plant density, and they found that

crop 15N recovery at maturity was linearly related to

the crop growth rate at fertilization. For pre-anthesis

growth of winter wheat, Olesen et al. (2002) found that

N uptake was a linear function of the green leaf area

(indexed and designated as GAI), and a declining

function of crop dry matter. Thus the green leaf area is

a very important parameter for crop N demand, and

combining three well-known functions, the daily leaf

expansion may be described as the minimum of either,

1) the exponential increase of GAI in thermal time, 2)

a minimum leaf area:soil area ratio, or 3) a minimum

GAI:N-uptake ratio (Olesen et al., 2002). In wheat, the

flag leaf represents a significant part of the green area,

and the flag leaf emerges and unfolds in the final part

of the elongation phase. It is therefore suggested that

maximum 15N recovery is related to the flag leaf

growth.

However, the farmer’s decision regarding applica-

tion time may not exclusively be based on maximum

crop 15N recovery. An essential criterion is also that

the applied fertilizer has to be available to the crop. An

immediate availability of surface applied fertilizer N is

obtained by precipitation or irrigation events immedi-

ately after application, whereas the fertilizer may

remain at the surface in dry conditions (Hartman &

Nyborg, 1989). However, excessive precipitation in-

creases the losses of applied N (Powlson et al., 1992).

Thus weather forecast information is important for

decisions regarding application time. The direct injec-

tion application method used in this experiment

prevents fertilizer stranding at the soil surface, and

the applied N is assumed to be immediately available

to the roots. Another criterion for the timing of

application may be a high concentration of protein

in the grain. Contrary to crop 15N recovery, a linear

model was able to describe the increase in grain N

Table 5. Estimates9/standard errors of linear regression parameters for grain N concentration and Ndff for grain,straw and total crop

Parameter Intercept, a Slope, b DF R2

Grain N concentration (%) 1.919/0.039 (6.129/0.86)�/10�3 42 0.56Grain Ndff (%) 13.99/1.34 0.1329/0.0251 42 0.44Straw Ndff (%) 18.29/1.01 �/0.0639/0.0190 41 0.29Total crop Ndff (%) 14.99/1.25 0.0879/0.0234 41 0.33

J. Petersen

88

Dow

nloa

ded

by [

Cor

nell

Uni

vers

ity L

ibra

ry]

at 0

2:15

19

Nov

embe

r 20

14

Page 8: Crop uptake of               15               N labelled fertilizer in spring wheat affected by application time

concentration from application time 1 to 16 (Fig. 3).

The increased grain N concentration may be related to

the increase in grain-N derived from fertilizer (grain-

Ndff) with postponement of the application time (Table

5). The increase in grain-Ndff was in favour of straw-

Ndff, and Riga et al. (1988) observed a similar change

in N partitioning between plant parts for threeapplication times during the elongation phase of

winter wheat. Along with N utilization expressed as

crop 15N recovery, and grain quality expressed as

protein concentration, the grain yield is also a

significant parameter for optimizing decisions for

fertilization. The basic N application plus the miner-

alization of organic N created a high concentration of

mineral N in the soil, corresponding to 90 kg N ha�1.Thus, the crop in this experiment had been well

supplied with N for growth, and this may be the

reason for the limited effect of the 16 fertilization

pulses on dry matter grain yield and N uptake in grain.

This illustrates that effects of N application time may

be difficult to reveal without the use of a 15N labelled

source. Also the ear:shoot ratio may be a part of the

basis for decision, but in contrast to 15N recovery themaximum ear:shoot ratio was obtained very early in

the growth period on day 35 (Table 4) corresponding

to GS32�/33 where the second and third nodes were

visible.

Even though N taken up in the vegetative phase was

lost during grain-filling, and the crop for that reason

may not be considered exclusively as a sink for applied

N, the crop recovery of applied fertilizer N depends onthe time of fertilizer application. It is likely that crop

recovery of fertilizer N is related to the crop N demand

determined by the expansion of green leaves, and this

may explain that maximum crop recovery of fertilizer

N was obtained from application at the time of

expansion and unfolding of the flag leaf. However,

this time did not coincide with the obtained maximum

in the ear:shoot ratio or the continuous increase ingrain N concentration.

The consequence of these findings is that, irrespec-

tive of the time of fertilizer N application, it may not

be possible to maximize all parameters simultaneously.

Thus, farmer’s decision on the optimal time for

application may depend on the actual crop condition

and how he wishes the crop to be managed.

Acknowledgements

Thanks are expressed to technician Kai Eskesen for

invaluable assistance during the experiment, and for

preparing the samples for analysis. Senior clerk Margit

Schacht has contributed with valuable linguistic com-

ments on the manuscript. The experimental work was

funded by the Ministry of Food, Agriculture and

Fisheries, Danish Directorate for Development (pro-

ject TEK97-DJF-2). The 15N analysis was carried out

at Research Centre Risø and funded by the Norsk

Hydro Foundation, Denmark.

References

Carter, M. R. & Rennie, D. A. 1984. Crop utilization of placed and

broadcast 15N-urea fertilizer under zero and conventional tillage.

Can. J. Soil Sci. 64, 563�/570.

Esala, M. 1991. Split application of nitrogen: effects on the protein

in spring wheat and fate of 15N-labelled nitrogen in the soil-plant

system. Annal. Agric. Fenn. 30, 219�/309.

Hartman, M. D. & Nyborg, M. 1989. Effect of early growing season

moisture stress on barley utilization of broadcast-incorporated

and deep-banded urea. Can. J. Soil Sci. 69, 381�/389.

IAEA 1976. Tracer manual on crops and soils. International Atomic

Energy Agency, Vienna, Austria.

Jensen, E. S. 1991. Evaluation of automated analysis of 15N and

total N in plant material and soil. Plant Soil. 133, 83�/92.

Lancashire, P. D., Bleiholder, H., Boom, T., van den, Langeluddeke,

P., Stauss, R., Weber, E. & Witzenberger, A. 1991. A uniform

decimal code for growth stages of crops and weeds. Ann. Appl.

Biol. 119, 561�/601.

Leitch, M.H. & Vaidyanathan, L.V. 1983. N use by winter wheat

established in cultivated and direct-drilled soils. J. Agric. Sci.,

Camb. 100, 461�/471.

Limaux, F., Recous, S., Meynard, J -M. & Guckert, A. 1999.

Relationship between rate of crop growth at date of fertiliser N

application and fate of fertilizer N applied to winter wheat. Plant

Soil. 214, 49�/59.

Malhi, S. S. & Nyborg, M. 1991. Recovery of 15N-labelled urea:

influence of zero tillage, and time and method of application. Fert.

Res. 28, 263�/269.

Malhi, S. S., Nyborg, M. & Solberg, E. D. 1989. Recovery of 15N-

labelled urea as influenced by straw addition and method of

placement. Can. J. Soil Sci. 69 (3), 543�/550.

Malhi, S. S., Nyborg, M. & Solberg, E. D. 1996. Influence of source,

method of placement and simulated rainfall on the recovery of15N-labelled fertilizer under zero tillage. Can. J. Soil Sci. 76, 93�/

100.

Nielsen, N. E. & Jensen, H. E. 1986. The course of nitrogen uptake

by spring barley from soil and fertilizer nitrogen. Plant Soil. 91,

391�/395.

Olesen, J. E., Berntsen, J., Hansen, E. M., Petersen, B. M. &

Petersen, J. 2002. Crop nitrogen demand and canopy area

expansion in winter wheat during vegetative growth. Eur. J.

Agron. 16, 279�/294.

Petersen, J. 2001. Recovery of 15N-ammonium-15N-nitrate in spring

wheat as affected by placement geometry of the fertilizer band.

Nutr. Cycling Agroecosyst. 61, 215�/221.

Petersen, J., Hansen, B. & Sørensen, P. (2004; available online 26

August 2003). Turnover and crop uptake of 15N-labelled ammo-

nium fertilizer injected in bands. Eur. J. Agron.

Powlson, D. S., Hart, P. B. S., Poulton, P. R., Johnston, A. E. &

Jenkinson, D. S. 1992. Influence of soil type, crop manage-

ment and weather on the recovery of 15N-labelled fertilizer

applied to winter wheat in spring. J. Agric. Sci., Camb. 118, 83�/

100.

Recous, S. & Machet, J-M. 1999. Short-term immobilization and

crop uptake of fertiliser nitrogen applied to winter wheat: effect of

date of application in spring. Plant Soil. 206, 137�/149.

Uptake of 15N affected by application time

89

Dow

nloa

ded

by [

Cor

nell

Uni

vers

ity L

ibra

ry]

at 0

2:15

19

Nov

embe

r 20

14

Page 9: Crop uptake of               15               N labelled fertilizer in spring wheat affected by application time

Recous, S., Machet, J. M. & Mary, B. 1988. The fate of labelled 15N

urea and ammonium nitrate applied to a winter wheat crop. II.

Plant uptake and N efficiency. Plant Soil. 112, 215�/224.

Recous, S., Machet, J. M. & Mary, B. 1992. The partitioning of

fertilizer-N between soil and crop: comparison of ammonium and

nitrate applications. Plant Soil. 144, 101�/111.

Riga, A., Francois, E., Destain, J. P., Guiot, J. & Oger, R. 1988.

Fertilizer nitrogen budget of Na15NO3 and (15NH4)2SO4 split-

applied to winter wheat in microplots in a loam soil. Plant Soil.

106, 201�/208.

SAS Institute. 1996. SAS/STAT Software: Changes and enhance-

ments through release 6.11 Cary, NC, USA.

Schjørring, J. K., Nielsen, N. E., Jensen, H. E. & Gottschau, A.

1989. Nitrogen losses from field-grown spring barley plants

as affected by rate of nitrogen application. Plant Soil. 116, 167�/

175.

Soil Survey Staff. 2003. Keys to soil taxonomy, 9th edition. United

States Department of Agriculture/Natural Resources Conserva-

tion Service, 322 pp. http://soils.usda.gov/technical/classification/

tax_keys/keysweb.pdf.

Tomar, J. S. & Soper, R. J. 1981. Fate of tagged urea N in the field

with different methods of N and organic matter placement. Agr. J.

73, 991�/995.

Tomar, J. S. & Soper, R. J. 1987. Fate of 15N-labeled urea in the

growth chamber as affected by added organic matter and N

placement. Can. J. Soil Sci. 67, 639�/646.

Wetselaar, R. & Farquhar, G. D. 1980. Nitrogen losses from tops of

plants. Adv. Agron. 33, 263�/302.

Yoneyama, T. 1983. Distribution of nitrogen absorbed during different

times of growth in the plant parts of wheat and contribution to the

grain amino acids. Soil Sci. Plant Nutr. 29, 193�/207.

J. Petersen

90

Dow

nloa

ded

by [

Cor

nell

Uni

vers

ity L

ibra

ry]

at 0

2:15

19

Nov

embe

r 20

14