INFLUENCE OF IRRIGATION AND PLACEMENT OF
NITROGEN FERTILIZERS ON THE UPTAKE OF

NITROGEN BY SPRING WHEAT

Armi Kaila and Paavo Elonen

University ofHelsinki, Department ofAgricultural Chemistry

Received December 18, 1969

Field experiments on arable crops seldom account for more than one half of the
nitrogen applied in fertilizers (Russell 1961, Cooke 1964, Kaila 1965 etc.). This may
be attributed to leaching or denitrification, to volatilization or immobilization. In any
case, a large part of the expensive fertilizer nitrogen is likely to be wasted.

Lack of movement into the root zone of even nitrates applied as surface dressing to
spring cereals was demonstrated in Finnish field experiments, and placement or working
in of nitrogen fertilizers was recommended (Kaila and Hänninen 1961). Because of the
usual dry period in the beginning of the summer in Finland, attention has also been paid
to the possibilities of improving the efficiency of nitrogen fertilizers by irrigation (Elonen
et. ai, 1967).

In the present paper results are reported from a field experiment which was conducted
to study the influence of sprinkler irrigation, and the placement and chemical composition
of the nitrogen fertilizer on the uptake of nitrogen by spring wheat.

Experimental

In 1969 a large field trial was carried out in southern Finland, in the neighbourhood
ofHelsinki, in cooperation with the Finnish Research Institute ofAgricultural Engineering.
Sprinkler irrigation was studied at four rates, and three kinds of nitrogen fertilizers were
either placed or applied as a surface dressing. The uptake of nitrogen by spring wheat
was followed by collecting samples of the aerial parts during the growing period.

The soil was silty clay with an average clay content of 50 per cent. The pH of the
ploughing layer was about 6 (in 0.01 M CaCl2), and the content of organic C was 4—5.5
per cent.

The nitrogen fertilizers studied were a Finnish ammonium nitrate-limestone, »Oulun-

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124

salpietari», urea and an American preparate of Ureaform contributed by Typpi Oy.
They were applied just before sowing with a »Juko»-fertilizer drill in amounts cor-
responding to 120 J; 1 kg N/ha, either on the surface with the plastic fertilizer tubes
outdrawn from the coulters, or at the depth of 8 cm with a spacing of 15 cm between
the rows.

The plots studied in the present work were irrigated with slow sprinklers in the night
June 9 and June 17, at both times with 30 mm of drainage ditch water, and compared
with plots without irrigation.

As a basal dressing 800 kg/ha of an ammoniated Finnish PK fertilizer was placed
at the depth of 7 cm with the »Juko»-fertilizer drill at right angles to the seed rows.
Thus, 16 kg N, 60 kg P and 100 kg K were applied per hectare.

All treatments were in four replicates. The total area of a plot was 2 X24 m 2, that
of the plot harvested was 1.68 X 16 m 2.

On May 8, »Ruso»-spring wheat was sown with row spacings of 12 cm at the depth
of 4.5 cm. The sprouting date was May 20, that of coming to ear July 2. The yield was
harvested on August 20.

The growing season was very dry. The precipitation was 37 mm in May, 22 mm
in June, 55 mm in July, and in August from the Ist to the 20th there was no rain. The
mean temperatures did not markedly differ from those of a normal season.

Plant samples were collected from each four replicate plots of the treatments studied
by cutting the aerial parts from carefully measured strips at the end of the plots. The
sampling area was 1.68 m 2 on June 2, 0.84 m 2 on June 16, 0.50 m 2 on June 30, and
0.42 m 2 on both July 21 and August 18. The ears were cut from the samples ofJuly and
August and analysed separately from the leaves and straw. The samples were air-dried
at room temperature and ground in a Wiley mill. Total nitrogen was determined with
the common Kjeldahl procedure.

The results reported of the grain yields represent winnowed material.
The statistical treatment of the data was performed by the new multiple range test

of Duncan (1955).

Results

The nitrogen content of the aerial parts of wheat plants collected in June are reported
in Table 1. Since the common Kjeldahl procedure was used, it is likely that nitrate, if
present, was not totally included. The treatment »Without N» did not get the additional
application of 120 kg/ha of nitrogen, only the 16 kg/ha in the basal dressing.

On June 2, or about two weeks after sprouting, the beneficial effect of the placement
of the nitrogen fertilizers is distinct. As a surface dressing, only ammonium nitrate-limestone
has produced plant material with a higher nitrogen content than that without theadditional
nitrogen fertilization. Later, even surface-applied urea did increase the nitrogen content,
but in each case, the placement significantly improved this effect. On the other hand,
placement ofammonium nitrate-limestone did not increase the effect on the irrigated plots.

On June 16, or about one week after the first irrigation, and on June 30, or about
two weeks since the second irrigation, the nitrogen content of the irrigated plants was
in most cases significantly higher than that of the unirrigated ones. This was the case
even when no additional nitrogen was applied.



125

Table 1. N in shoots, per cent of dry matter

June 2 June 16 June 30
Irrigation mm 0 0 30 0 30+3O
Without N 4.49a 2.71a 3.01 bc 1.53a 1.68bcd

Ammonium nitrate-limestone
surface 4.92 b 3.27 cd 4.12'% 1.85cd 2.42%
placement 5.26' 3.86' f 4.32» 2.08' 2.41%

Urea
surface 4.57 ab 3.16bcd 3.82' 1.87d 2.25'f
placement 5.22c 3.86'f 4.17% 2.09' 2.58»

Ureaform
surface 4.46a 2.84ab 3.27 cd 1.66bc 1.86cd

placement 4.86b 2.90b 3.45 d 1.68bcd 1.89d

Means for samples of the same date followed by a common letter do not differ at P = 0.05.

There was in no case any significant difference in the nitrogen content of plants treated
in the same way either with urea or with ammonium nitrate-limestone. Ureaform could
not compete with them.

The nitrogen content of the plants at later stages of development is reported in
Table 2. »Straw» stands for the vegetative aerial parts. In the samples of July 21, no
positive effect of irrigation on the nitrogen content can be found: the corresponding
values either do not differ from each other, or the plant material from the irrigated
plots is poorer in nitrogen than that from the respective unirrigated plots, as is the case
with the ears from the plots surface-dressed with ammonium nitrate-limestone. In the
samples collected just before harvest, or on August 18, this tendency of irrigation to lower
the nitrogen content of the ears is distinct, particularly, when additional nitrogen was

irrigation

Table 2. N in straw and ears, per cent of dry matter

Ammonium nitrate- Urea
Without N limestone

mm

Ureaform

July 21
Straw

surface placement surface placement surface placement

0 0.85a 1.34cd 1.52ef 1.31° 1.60f 1.04b 0.95ab

Ears

30 + 30 0.95ab 1.39cde 1.49def 1.38cde 1.45cdef 0.95ab 0.95ab

0 2.20 m 2.68 P 2.57 n°P 2.32 mn 2.59°p 2.37 mno 2.30m

August 18
Straw

30 + 30 2.21 m 2.40 mno 2.47 mn°P 2.36mno 2.45mn°P 2.20 m 2.23 m

0 0.38 a 0.54cd 0.67 ef 0.50bcd 0.7 lr 0.43 abc 0.43abc

Ears

30 + 30 0.35a 0.59 de 0.59de 0.52 cd 0.58 de 0.36a 0.36a

0 1.78m 2.55 V 2.75r 2.45p<i 2.70 r 2.06 n ° 1.95m“

30 + 30 1.80m 2.29 P 2.43P‘i 2.25°p 2.32P't 1.75m 1.83m

Means for samples of the same date followed by a common letter do not differ at P = 0.05



126

applied. Statistically significant difference also exists in the nitrogen content of the straw
between the irrigated and unirrigated plots with placed urea.

At these later stages ofdevelopment, the positive effect of the placement of ammonium
nitrate-limestone and urea is proved by the respective contents of nitrogen in the straw

samples from the unirrigated plots. On these plots placement of urea has also significantly
increased the nitrogen content of the ears.

According to the nitrogen content of the samples of July and August, ammonium
nitrate-limestone and urea have been equally effective. The only exception is found in
the nitrogen content of the ears from the surface-dressed, unirrigated plots in July. Urea-
form again, has been less effective than the two other fertilizers.

On the basis of the weight of the samples and their nitrogen content, the nitrogen
»yields» were calculated. These data are recorded in Table 3 expressed as N kg/ha.
On June 2, there is not yet any difference between the treatments. At the later sampling
dates, a distinct tendency to a marked increase in the uptake of nitrogen because of
fertilizer placement is apparent. Since there was a relatively large variation in the dry
matter yields of the replicates, these differences are not always statistically significant.
The same holds true also with the effect of irrigation. Even in July and August it has
tended to increase the amounts of nitrogen taken up by the plants, particularly on the
plots treated with ammonium nitrate-limestone and urea. It may be of interest to note
that in the samples of June 16, irrigation did not increase the uptake of nitrogen, if the
fertilizers were placed. After the second irrigation, however, an increase also in the uptake
of the placed fertilizer nitrogen is demonstrable.

Both irrigation and placement tended to improve also the uptake of nitrogen from
ureaform treated soil. Yet, only in the samples of June 30, more nitrogen has been accu-
mulated on the irrigated plots from ureaform than from the soil without the additional
nitrogen fertilizers. Later there is a similar tendency, but this is not statistically significant -

Table 3. N in plant samples, kg/ha

Irrigation Ammonium nitrate- Urea Ureaform
Date Without N limestone

mm surface placement surface placement surface placement

June 2 0 7a 8a 9a 8a 8a 7a 8a

June 16 0 22a 30ab 43d 28ab 40 cd 23a 25a

30 26a 39 cd 45d SS1» 43d 27ab 29ab

June 30 0 39a 52abc 69 cde 56abc 66 cd 39a 48ab
30 + 30 44a 89ef I03f 81 de 104f 63bc 70cde

July 21 0 55a 89bcd 101 de 89bcd 93cd 68ab 68ab

30 + 30 67a 119ef 128f« 119ef 140* 73abc 74abc

Augustia 0 59a 110bcd 135de 95abcd 126cdc 77ab 79ab
30 + 30 84abc 161 ef 180f 140def 168ef 76ab 98abcd

Means for samples of the same date followed by a common letter do not differ at P = 0.05



127

Ureaform is a poorer source of nitrogen for spring wheat than the two other fertilizers
which, on the basis of the present data, are equally effective in providing nitrogen under
the conditions of this field experiment.

Since the trial was harvested with a combine machine, only results of grain yield are
available. Data in Table 4 show that irrigation significantly increased the dry matter
yield of winnowed grains, but at the same time decreased their nitrogen content. Yet,
the total amount of nitrogen harvested in grains from the plots treated with ammonium
nitrate limestone or urea is distinctly increased by irrigation. Placement of these two
fertilizers improved the uptake of nitrogen only from unirrigated plots. No difference
may be found between the effect of ammonium nitrate limestone and urea in the dry
matter yield of grain, in their nitrogen content, or in the amount of nitrogen harvested
in grains. Ureaform did not give any significant response, except a slight increase in the
»nitrogen yield», when the fertilizer was placed and the soil was irrigated.

Table 4. Grain yield

Dry matter N % N in grains
kg/ha in dry matter kg/ha

Irrigation mm 0 30 + 30 0 30 + 30 0 30 + 30

Without N 1920a 2510bc 2.30bc 2.13ab 44a 53a

Ammonium nitrate-limestone surface 2640bcd 4210e 3.11 * 2.55 de 82° 107e

placement 3070d 4550' 3.07 f 2.57 d' 94d 117'

Urea surface 2740cd 4150' 2.94f 2.64' 81' 110'
placement 3050 d 441 O' 3.12f 2.65' 95b 117'

Ureaform surface 1990a 2560bc 2.42 cb 2.06a 48ab 53ab

placement 2170ab 2840 cd 2.40cd 2.10a 52ab 60b

Means in the two corresponding columns »0» and »30 + 30» followed by a common letter do not differ
atP= 0.05

Discussion

The results of the present study indicate that, under these conditions, both irrigation
and, apparently to a smaller extent, placement of nitrogen fertilizers distinctly improved
the uptake of nitrogen by spring wheat. It may be calculated, on the basis of data in
Table 4, that placement of ammonium nitrate limestone or urea did increase the amount
of nitrogen in the grain yields, on the average, by 13 kg/ha without irrigation, but not
significantly when irrigated. The irrigation, on the other hand, increased the nitrogen
content of grain yields, averagely, by 27 kg/ha when the fertilizers were applied on the
surface, and by 23 kg/ha when the fertilizers were placed. Thus, the higher dry matter
yield produced by irrigation more than compensated the typical decrease in the percentage
of nitrogen in the grains.



128

The additional nitrogen applied as ammonium nitrate limestone or as urea cor-
responded to 120 kg N/ha. Its apparent recovery in the grain yields, calculated as the
mean difference between the nitrogen yields of the respective treatments and that without
additional nitrogen, is the following:

without irrigation, surface dressing 31 %

placement 42 %

irrigated, surface dressing 54 %

placement 61 %

Thus, fertilizer placement with irrigation almost doubled the apparent recovery of
fertilizer nitrogen in the grain yield of spring wheat.

Unfortunately, straw yields were not available, but the plant samples collected on
August 18, only two days before harvest, may give an approximate basis for an estimation
of the apparent recovery offertilizer nitrogen in the total yield. The rather large variation
due to the small sampling area, decreases, of course, the accuracy and the reliability of
these estimations. The apparent recovery is, on average, the following:

without irrigation, surface dressing 36 %

placement 60 %

irrigated surface dressing 76 %

placement 96 %

These percentages are fairly well in accordance with the results obtained on the basis
of the grain yields, provided that there is in grains about twice as much nitrogen as in
the straw yield.

It is likely that the higher uptake of nitrogen from the irrigated soil is to some extent
due to a more rapid mineralization of soil nitrogen. On the other hand, the larger root
system of the irrigated plants (Kähäri and Elonen 1969) probably contains a larger
amount of fertilizer nitrogen than does the smaller root mass in the unirrigated plots.
Thus the apparent recovery of fertilizer nitrogen estimated on the basis of the aerial parts
of wheat may be slightly lower than the real uptake of fertilizer nitrogen by the whole
plants. This may be applicable also to the effects of the fertilizer placement.

In any case, it is beyond dispute that in this field trial placement of urea or ammonium
nitrate limestone, and irrigation in June twice with 30 mm water, resulted in an almost
quantitative apparent recovery of the 120 kg of nitrogen applied per hectare.

It is noteworthy that though irrigation decreased the nitrogen content of the dry
matter in the later stages of development, it did markedly increase the nitrogen content
of the wheat plants in June, in the period which in Finland is likely to be particularly
important in the development of spring cereals. Analyses for other nutrients also proved
the beneficial effect of irrigation on the contents of phosphorus, potassium, magnesium,
and calcium in the wheat plants in the middle and at the end of June. The higher uptake
of nitrogen due to the fertilizer placement, also to some extent, increased the content
of potassium, calcium, and magnesium in the plants which were not irrigated. A good
supply of these essential elements in the plants during the critical period apparently
offered favourable conditions for a higher production.



129

Summary

The effect of irrigation and fertilizer placement on the accumulation of nitrogen in
the aerial parts of spring wheat was studied in the relatively dry summer 1969, on the
basis of plant samples collected at various stages of development from a field trial on silty
clay soil. In addition to 16 kg/ha of nitrogen in the basal dressing, 120 kg/ha of nitrogen
was applied as ammonium nitrate limestone, as urea, or as Ureaform, either on the surface,
or in rows at the depth of 8 cm. 60 mm of water was applied by sprinkler irrigation,
one half about three, and the other half about four weeks after sprouting.

Under the conditions of this trial, spring wheat only slightly responded to Ureaform.
No significant difference in the effect of urea and ammonium nitrate limestone could
be detected. Placement of these two fertilizers tended to increase both the amount of dry
matter and its content of nitrogen; these effects were more significant without irrigation.
Though irrigation, usually, markedly increased the total amount of nitrogen in the aerial
parts of the plants, this was in the later stages of development due only to higher yields
of dry matter, since in July the positive effect of irrigation on the percentage of nitrogen
in plant dry matter changed to a negative effect.

In the grain yields the apparent recovery of nitrogen in urea or ammonium nitrate
limestone was estimated to be only about 30 per cent of the 120 kg N/ha applied as surface
dressing. Irrigation increased this recovery to 54 per cent, placement of the fertilizer to
42 per cent, and both placement and irrigation resulted in an apparent recovery of
61 per cent.

On the basis of plant samples collected two days before harvest, the apparent recovery
of nitrogen in urea or ammonium nitrate limestone by the aerial parts of wheat was
estimated to be, on the average, 36 per cent from the surface-dressing, and 60 per cent
when the fertilizers were placed. Irrigation increased the apparent recovery in the first
case to 76 per cent and in the latter case to 96 per cent.

Thus, in the field experiment the uptake of fertilizer nitrogen by spring wheat was
markedly increased by irrigation and to a lesser extent by fertilizer placement. Both
treatments together are recommended.

REFERENCES

Cooke, G. W. 1964. Nitrogen fertilisers. Proc. Fertil. Soc. No 80.
Duncan, D. B. 1955. Multiple range and multiple F tests. Biometrics 11: 1—42.
Elonen, P. & Nieminen, L. & Kara, O. 1967. Sprinkler irrigation on clay soils in southern Finland 11.

J. Sci. Agr. Soc. Finland 39: 78—89.
Kaila, A. 1965. Apparent recovery of fertilizer nitrogen. Ibid. 37: 163—174.
—»— & Hänninen, P. 1961. Fertilizer nitrogen in soil. Ibid. 33: 169—184.
Kähäri, J. & Elonen, P. 1969. Effect of placement offertilizer and sprinkler irrigation on the development

of spring cereals on the basis of root investigations. Ibid. 41: 89—104.
Russell, E. W. 1961. Soil conditions and plant growth. London, 688 p.



130

SELOSTUS

SADETUKSEN JA TYPPILANNOITTEIDEN SIJOITUKSEN VAIKUTUS
LANNOITETYPEN HYVÄKSIKÄYTTÖÖN

Armi Kaila ja Paavo Elonen

Yliopiston maanviljelyskemian laitos, Viikki

Sadetuksen ja typpilannoitteen sijoituksen vaikutusta kevätvehnän typen ottoon tutkittiin keräämällä
poikkeuksellisen kuivana kesänä 1969 näytteitä eri kehitysvaiheissa kasvin maanpäällisistä osista Pakan-
kylässä Maatalouskoneiden tutkimuslaitoksen kanssa suoritetusta kenttäkokeesta. Peruslannoituksena
annetussa ammonoidussa PK-lannoksessa tuli maahan 16 kg N/ha. Sen lisäksi annettiin 120 kg N/ha
Oulunsalpietarina, ureana tai Ureaform-valmisteena joko pintaan tai sijoitettuna riveihin 8 sm syvyy-
teen. 30 mm;n sadetus suoritettiin sekä 9.6. että 17.6.

Ureaformilla ei ollut juuri lainkaan vaikutusta tässä kenttäkokeessa. Urea ja Oulunsalpietari osoittau-
tuivat yhtä tehokkaiksi. Niiden sijoittaminen näytti lisäävän sekä kasvin kuiva-aineen määrää että sen
typenpitoisuutta, etenkin sadettamattomilla ruuduilla. Sadetus lisäsi tavallisesti merkitsevästi »typpisatoa»,
mutta heinä- ja elokuussa tämä johtui vain kuiva-aineen määrän lisääntymisestä; heinäkuusta alkaen
sadetuksen vaikutus rupesi ilmenemään tyypillisenä kasvin typenpitoisuuden alenemisena vastaavaan
sadettamattomaan verrattuna.

Jyväsatojen perusteella arvioitiin typpilannoitteiden näennäinen hyväksikäyttö, lannoitettujen ja
0-ruutujen »typpisatojen» erotuksen perusteella laskettuna, vain noin 30 %:ksi pintalannoituksena
annetusta (120 kg N/ha). Sijoitus lisäsi hyväksikäytön 42 %:ksi, sadetus 52 %:ksi ja molemmat toimen-
piteet 61 %:ksi.

Kahta päivää ennen sadonkorjuuta kerättyjen kasvinäytteiden analyysien perusteella arvioitiin koko
sadon ottaneen Oulunsalpietarista ja ureasta keskimäärin 36 % pintalannoituksena annetusta ja 60 pro-
senttia sijoitetusta. Sadetus paransi hyväksikäyttöä edellisessä tapauksessa 76 %:iin, jälkimmäisessä
96 %:iin.

Todettiin, että sadetus oli kuivana kasvukautena tehostanut merkittävästi helposti liukenevien typpi-
lannoitteiden hyväksikäyttöä, sijoitus vähemmän. Molemmat yhdessä antavat parhaan tuloksen.