J. Agronomy & Crop Science, 158, 187—189 (1987)© 1987 Paul Parey Scientific Publishers, Berlin and HamburgISSN 0931-2250

Department of Soil Science, University of Manitoba,Winnipeg, Man. R3T 2N2, Canada

An Evaluation of Fertilizer and Soil Nitrogen Uptake by Wheat

U. R. SANGAKKARA and C. M. CHO

Authors' addresses: Dr. U. R. SANGAKKARA, Faculty of Argriculture, University of Peradeniya, Peradeniya/Sri Lanka, and Prof. Dr. C. M. C H O , Department of Soil Science, University of Manitoba, Winnipeg, Man.R3T 2N2/Canada.

mth 3 tables

Received June 10, 1986; accepted September 1, 1986

Abstract

Nitrogen utilization and uptake patterns of wheat was studied using '^N labelled fertilizer at four rates ofapplication. Plants harvested at maximum tillering and at flowering indicated that plant N levels stabilizedwith time. Fertilizer N uptake and utilization of added fertilizer increased with time. However, uptake of soilN was not affected by rates of fertilizer at early stages. Increases were observed only at higher rates at the laterharvest.

Key words: Nitrogen — Utilization — uptake — wheat

Introduction

The ultimate objective of research on appliednitrogen (N) is better use of the resource incrop production. However, a major problemconfronting the scientists is the poor utiliza-tion made of the available N (BARTHOLOMEW

1971). Documented evidence (e.g. ROGERS

1961, HAUCK and BREMNER 1976) indicate thatplant recovery of available N ranges between50—60 %.

There is increasing emphasis for maximizingthe efficiency of fertilizer N use in crops.Emphasis is placed on cereals and grasses dueto their high requirements of fertilizer N whencompared with other tropical crops, especiallylegumes.

Some studies (e. g. BROADBENT 1965) haveindicated increased availability of total N withaddition of fertilizer nitrogen. However, stu-dies on the utilization patterns of applied andsoil N are less abundant. Thus, a growthchamber experiment was carried out using ^^N,to evaluate the utilization patterns of both

applied and soil N by wheat {Triticum aesti-vum) when increasing rates of N are added.The fertilizer additions were based on commonrates generally recommended for wheat.

Materials and Methods

The study was carried out in a phytotron, withenviroment conditions of 22 °C — 50% RH day/15»C — 80% RH night, with a 16 hour daylength.Plastic pots filled with a very fine sandy loam (pH7.8, 3.6 ppm NO3') was used. A basal fertilizerapplication equivalent to 30 kg P/ha'' and 200 kg K/ha"' was added to each pot prior to sowing.

The N fertilizer rates selected were 25, 50, 75 and100 kg N/ha"'. Thus pots received 62.5, 125.0, 187.5and 250.0 mg N to correspond to the selected rates.Application of fertilizer N was made prior to seed-ing, by adding the appropriate volumes of a solutioncontaining enriched NH4NO3.

Pots were sown with eight seeds (cv. Glenlea) andplaced in the phytotron. Treatments were replicatedthree times, completely randomized. Pots werewatered daily to 85 % of the field capacity of thesoil, with deionized water. Plants were thinned to sixper pot soon after germination.

U.S. Copyright Clearance Center Code Statement: 0931-2250/87/5803-0187$02.50/0

188 SANGAKKARA and CHO

Harvesting was carried out at 30 and 55 days aftergerminition, to correspond to maximum tillering andflowering, as these stages indicate high levels of N inwheat (WITHERS and PALENSKI 1984). Three plantswere harvested at a time and dried at 80°C for 48hours to determine dry matter production. Total Nwas determined by Kjeldahl as described by JACK-SON (1958). Abundance of tracer '*N of enrichedplant material was determined by mass spectrome-try, using a modification of the method described byBREMNER (1965).

Results and Discussion

The higher rates of N significantly increaseddry weights of wheat at 30 days (Table 1),along with the percentage N in plants. Thisindicates increased growth of plants and up-take of N with increasing fertilizer rates atearly stages. Hence, the increase in total Nuptake by plants (Table 2) at this stage couldbe considered a resultant feature of either vig-orous growth, increased levels of plant N orboth, depending on the rates of applied N.

The dry weights of plants differed at all ratesat the second harvest (Table 1), although

percentage N in plants were similar. Thisshows that after a period of time, the N con-tent of wheat plants stabilizes even with increa-sed rates of N fertilizer. The increase in total Nper plant (Table 2) at this stage could thereforebe attributed to greater vegetative growth andnot to increased levels of N in the plant.

Evaluation of rates of total N uptake at thetwo harvests show that this phenomenon issignificantly increased with fertilizer rates atthe second harvest (Y = 0.5366X -I- 0.4013; r= .998), when compared with the first harvest(Y = 0.1783X -I- 0.2892; r = .965). Thus, theincreased vegetative growth observed at thelater stage with increased applications of Ncould be considered an effect of this pheno-menon.

Utilization patterns of fertilization N at thetwo harvests are presented in Table 2. Ferti-lizer N uptake per plant differs significantlywith increasing rates of N at both harvests.The rate of uptake of fertilizer N at the secondharvest was also greater (Y = 0.398IX -0.1057; r = .960) than at first harvest (Y =0.1813X + 0.6800; r - .994). The difference

Table 1. Effect of increasing rates of N fertilizer on dry matter Production (g/plant"') and N percentage inwheat

Rates of fertilizer

Dry weight (g/plant"')Harvest 1Harvest 2

Percentage NHarvest 1Harvest 2

Table 2: Nitrogen uptake patterns

Rates of fertilizerkg N/ha-'

Harvest 1Total NFertilizer N•"'Difference

Harvest 2

Total NFertilizer N•'•Difference

25

2.5686.571

1.5771.162

(mg/por')

25

40.5611.8428.72

76.3416.2060.14

50

2.5676.828

2.0071.451

in wheat with

N50

49.5022.8726.63

99.1235.4463.68

75

2.7709.272

2.3191.605

100

3.13110.180

2.3441.615

increasing rates of fertilizer

uptake (mg N/pot"')

75

64.2536.1328.12

148.8365.9082.93

100

72.2945.2027.59

171.5188.9985.52

LSD (P = .05)

0.1620.141

LSD

6.452.354.10

5.043.785.91

An Evaluation of Fertilizer and Soil Nitrogen Uptake by Wheat 189

Table 3. Utilization of fertilizer N by-

Rates of fertilizerkg N/ha-'

Percent utilization of added fertilizer

Harvest 1Harvest 2

Percent N derived from fertilizer

Harvest 1Han'est 2

wheat with

25

18.9525.93

29.2321.21

increasing rates of

50

18.3028.35

46.1935.76

fertilizer

75

19.2135.14

56.1644.27

100

18.0836.39

62.1351.85

between total and fertilizer N uptake per plantis considered as N derived from soil. Evalua-tion of this parameter indicates no increaseduptake of soil N at the first harvest. This couldbe attributed to the abundance of readily avail-able fertilizer N at this stage. Soil N uptakewas increased significantly at the late harvest,especially at higher rates of fertilizer N. Thisdata suggests that soil N utilization increaseswith time, and high rates of N causes a syner-gistic effect on the uptake of soil N at thisstage. This could arise due to increased growthof the plant (Table 1) or due to increasedmineralization of soil N at these rates due to aneffect of priming action (BROADBENT 1965).

Utilization of added fertihzer increases sig-nificantly with time indicating better use offertilizer at later stages (Table 3). However,there is no difference in the pattern of fertilizeruse amongst treatments at the first harvest.This pattern changes at the second harvest anduse of added fertilizer increases with increasingrates. This illustrates the capacity of plants toutilize added fertilizer more efficiently athigher rates of N at later stages.

The efficiency of N derived from fertilizer(NDFF) increases significantly between treat-ments (Table 3) at at both harvest. In contrast,there is a reduction in derivation of N fromfertilizer with time. Thus plants seem to obtaina greater portion of their N requirements fromfertilizer at early stages, although the percent-age utilization of added fertilizer increaseswith time.

ZusammenfassungBewertung der Aufnahme von Stickstoff ausDlingern und Boden bei WeizenDer Verlauf der Stickstoffnutzung und -auf-nahme durch Weizen wurde unter Verwen-dung von '^N markiertem DiJnger und vierDiingermengen untersucht. Pflanzen, die zum

Zeitpunkt der maximalen Bestockung und zurBliite geerntet wurden, zeigten, dafi die N-Konzentrationen sich mit der Zeit stabilisier-ten. Die Aufnahme von Diingungs-N undNutzung ausgebrachten Dungers nahmen mitder Zeit zu. Allerdings war die Aufnahme vonbodenburtigem N nicht durch die Menge derDungung in friiheren Stadien beeinflufit. Zu-nahmen wurden nur bei hoheren Mengen zueinem spateren Erntetermin beobachtet.

Acknowledgements

The senior author is grateful to the InternationalAtomic Agency, Vienna, Austria for the award of aresearch fellowship. Gratitude is expressed to Dr. G.J. RACZ, Head, Department of Soil Science, Uni-versity of Manitoba, Canada, for providing facilitiesto carr)' out this study.

References

BARTHOLOMEW, W . V., 1975: '^N research on theavailability and crop use of N. In Nitrogen 15 insoil plant studies. Proc. Research coordinatingmeeting, IAEA, Vienna, pp. 1—20.

BREMNER, J. M., 1965: Isotope ratio analysis of N inNitrogen 15 investigations. In: BLACK, C. A. (ed.).Methods of soil analysis Part 2, pp. 1274—1282.Monograph of American Agronomy Society,Madison, Wisconsin.

BROADBENT, F . E., 1965: Effect of fertilizer N onrelease of soil nitrogen. Soil Science Society ofAmerica Proceedings 29, 692—694.

HAUCK, R. D. , and J. M. BREMNER, 1976: Use of

tracers for soil and fertilizer nitrogen research.Advances in Agronomy 28, 219—266.

JACKSON, M . L., 1958: Nitrogen determination forsoil and plant tissue. In: Soil chemical analysis, pp.183—189. Prentice Hall Inc. New York, U.S.A.

ROGERS, T . H . , 1961: Recovery of applied N bycrops. Proceedings of Southern Agricultural Work-ers 58''̂ Annual Conf., pp. 86—87.

WITHERS, N . J., and PALENSKI, F., 1984: An evalua-tion of the nitrate sap test for use on spring sownwheat. Proceedings of Agronomy Society, NewZealand 14, 17—21.