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Yield response of corn to irrigation and nitrogen fertilization

in a Mediterranean environment

Elvio Di Paolo a,*, Michele Rinaldi b

a Centro per la Sperimentazione e Divulgazione delle Tecniche Irrigue, S.S. 16 Nord, 240-66054 Vasto, Italyb CRA, Unita di Ricerca per i sistemi colturali degli ambienti caldo-aridi, Via Celso Ulpiani 5, 70125 Bari, Italy

Received 18 June 2007; received in revised form 8 October 2007; accepted 9 October 2007

Abstract

Productivity and resource-use efficiency in corn (Zea mays L.) are crucial issues in sustainable agriculture, especially in high-demand resource

crops such as corn. The aims of this research were to compare irrigation scheduling and nitrogen fertilization rates in corn, evaluating yield, water

(WUE), irrigation water (IRRWUE) and nitrogen use (NUE) efficiencies. A 2-year field experiment was carried out in a Mediterranean coastal area

of Central Italy (175 mm of rainfall in the corn-growing period) and corn was subjected to three irrigation levels (rainfed and supply at 50 and 100%

of crop evapotranspiration, ETc) in interaction with three nitrogen fertilization levels (not fertilized, 15 and 30 g (N) m�2). The results indicated a

large yearly variability, mainly due to a rainfall event at the silking stage in the first year; a significant irrigation effect was observed for all the

variables under study, except for plant population. Nitrogen rates affected grain yield plant�1 and ear�1, grain and biomass yield, HI, WUE,

IRRWUE and NUE, with significant differences between non-fertilized and the two fertilized treatments (15 and 30 g (N) m�2). Furthermore,

deficit irrigation (50% of ETc) was to a large degree equal to 100% of the ETc irrigation regime. A significant interaction ‘‘N � I’’ was observed for

grain yield and WUE. The effect of nitrogen availability was amplified at the maximum irrigation water regime. The relationships between grain

yield and evapotranspiration showed basal ET, the amount necessary to start producing grain, of about 63 mm in the first and 206 mm in the second

year. Rainfed crop depleted most of the water in the 0–0.6 m soil depth range, while irrigated scenarios absorbed soil water within the profile to a

depth of 1.0 m. Corn in a Mediterranean area can be cultivated with acceptable yields while saving irrigation water and reducing nitrogen supply

and also exploiting the positive interaction between these two factors, so maximizing resource-use efficiency.

# 2007 Elsevier B.V. All rights reserved.

Keywords: Corn; Irrigation; Nitrogen; Water use efficiency; Grain yield; Nitrogen use efficiency

Corn (Zea mays L.) is extensively cultivated in Europe

(France, Italy, Romania); the Northern part of Italy has about

one million hectares and a mean grain yield of approximately

940 g m�2, while in Central and Southern Italy, characterized

by a Mediterranean climate, cultivation accounts for

130,000 ha and due to the water-limited conditions, the

average grain yield is about 740 g m�2 (ISTAT sources, 2006).

In such water-limited conditions, corn productivity is highly

dependent on irrigation supplies, but in many intensive

agricultural areas, irrigation water availability and quality

are constantly in decline as a result of climate change and

increasing consumption. Irrigation water is becoming an

increasingly limited resource in many areas of Southern

Europe and consequently, an appropriate choice of irrigation

scheduling in order to maximize water use efficiency and profit

is needed. Moreover, in many situations corn is grown mainly in

river basins, which are environments sensitive to underground

water nitrate pollution risk. An appropriate application of

irrigation water (I) and nitrogen (N) fertilizer has the vital

purpose of increasing water and nitrogen productivity and

reducing environmental pollution risk (English and Raja,

1996).

Evaluating the response of crops to irrigation in combination

with N fertilization could help identify the best allocation of

available resources among crops in the farm in order to

maximize profit and reduce groundwater pollution. Literature

on the effects of water and nitrogen on yield and related

parameters such as nitrogen use efficiency (NUE), water use

efficiency (WUE) and irrigation water use efficiency (IRR-

WUE) are reported in Dagdelen et al. (2006), Oktem et al.

(2003), Evett et al. (2000, 2001), Howell et al. (1998) and

www.elsevier.com/locate/fcr

Available online at www.sciencedirect.com

Field Crops Research 105 (2008) 202–210

* Corresponding author.

E-mail addresses: dipaolo@cotir.it (E. Di Paolo),

michele.rinaldi@entecra.it (M. Rinaldi).

0378-4290/$ – see front matter # 2007 Elsevier B.V. All rights reserved.

doi:10.1016/j.fcr.2007.10.004

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Howell (2001). Irrigation affects corn grain yield and the

highest yield is achieved with a complete restitution of crop

evapotranspiration although WUE, as well as IRRWUE,

decreases with an increase in irrigation water.

In a sub-Saharan environment, Pandey et al. (2000)

reported a linear yield response for corn with deficit irrigation

at all N levels. Generally, the greater the N supply, the more

yield was reduced by deficit irrigation. They concluded that

although deficit irrigation reduces the maximum potential

yield, if the practice is applied at irrigation district level,

overall corn production is achieved. Cakir (2004) evaluated

the effect of water stress at different development stages of

corn in the Thrace region of North-West Turkey. He found

that in cases of scarcity of irrigation water, the most beneficial

use of water could be achieved with irrigation supplies at the

tasseling and/or cob formation stages. Payero et al. (2006)

studied the response of corn to deficit irrigation in the semi-

arid environment of the US Great Plains. They found no

beneficial increase in WUE in that environment with deficit

irrigation, as the WUE increased linearly with the ratio of

actual crop evapotranspiration on potential crop evapotran-

spiration. Zand-Parsa and Sepaskhah (2001) worked out

equations to describe corn yield as a function of irrigation

water and N fertilizer. The objective was to achieve the best

possible compromise between production costs and proceeds

in order to maximize profit.

Environmental protection is one of the priorities of the new

aims of European agricultural policy (European Union,

2000); a compromise between the need to maximize yield and

profit and an adequate use of irrigation water and N fertilizer

is therefore required in order to reduce the impact of

cultivation on the environment. The aims of this study were:

(i) to evaluate the effect of irrigation scheduling in interaction

with N supply for corn cropped in a temperate Mediterranean

climate and (ii) to analyze water and nitrogen use efficiency

for corn.

1. Materials and methods

The field experiments were carried out in Vasto (Chieti,

Italy) (428100 lat. N; 148380 long. E, 30 m a.s.l) in 2000 and

2001 at the experimental farm of the CO.T.IR.—Centre for

Irrigation Techniques.

The soil is a vertisol of alluvial origin (Aquic Haploxerert),

silty-clay-loam with the following average characteristics in 0–

40 cm depth: clay 40.7%, silt 52.9%, sand 6.4%, pH (water)

8.2, total nitrogen 0.14%, organic matter 1.6%, NaHCO3�

extractable P 32 ppm, NH4O Ac-extractable K2O, 451 ppm,

bulk density 1.25 kg dm�3, field capacity (Richard’s plate,

�0.03 MPa) water content 0.40 m3 m�3; permanent wilting

point (�1.5 MPa) water content 0.22 m3 m�3, available soil

water 180 mm m�1. The climate is ‘‘attenuate thermo-

Mediterranean’’ (Unesco-FAO classification), with minimum

temperatures below 0 8C in the winter and about 34–36 8C as

maximum temperatures in the summer. Annual rainfall (mean

650 mm, considering 40-year-long term period) is mostly

concentrated during the autumn and spring months and class

‘‘A pan’’ evaporation fluctuates, during July and August,

between 6 and 8 mm d�1 on clear days.

Comparisons were made between three irrigation regimes;

I100, I50, I0, respectively, with the restitution of 100%, 50% of

the crop evapotranspiration (ETc) and rainfed, and three

nitrogen fertilizer levels; N0, N150 and N300, respectively, not

fertilized and fertilized with 15 and 30 g (N) m�2.

Nitrogen fertilizer recommendations for corn, with a grain

yield forecast of about 1200 g m�2, can vary between 20 and

28 g (N) m�2 for soils with sufficient N availability (such as

that used in the experiment), taking into account N soil

mineralization and N fertilization loss. In order to test the effect

of N fertilizer on corn production, doses both lower and higher

than that recommended were chosen. The nitrogen fertilizer,

such as ammonium nitrate, was applied splitting the rate into 1/

3 before sowing and 2/3 at the growth stage of six unfolded

leaves.

Irrigation was scheduled on the basis of a water balance,

calculated as the sum of estimated daily ETc, subtracting the

fraction of rainfall not exceeding the field capacity (equal to soil

moisture deficit, SMD). ETc was calculated as proposed by the

FAO, where reference evapotranspiration (ETo) was calculated

using the Penman–Monteith model, before being modified by a

crop coefficient (Allen et al., 1998). Every time the cumulated

SMD reached 40 mm, irrigation was applied with 40 and

20 mm for treatments I100 and I50, respectively. To ensure

uniform water distribution, a drip irrigation system was used,

with one emitter line per corn row and drippers with 2.5 L h�1

flow rate, 0.3 m apart. A water flow meter, one for each

irrigation treatment, was placed at the head of the experimental

field to measure the amount of irrigation water applied

accurately. Irrigation was stopped at the dough growth stage.

A split-plot design, replicated four times, was used,

arranging ‘‘I’’ in the main-plot and ‘‘N’’ in the sub-plot. The

experimental plots were located within an area planted with

corn and each experimental plot was 5.6 m � 10.0 m in size,

which accommodated eight corn rows. Individual plots were

separated from each other by 2 m wide border strips planted

with corn. The corn hybrid Tevere of the Asgrow company,

FAO class 600, was sown on 5 May 2000 and 26 April 2001,

with a four-row planter with 0.7 m row spacing at a seeding rate

of 8.7 seed m�2. The main details of the experiments are

reported in Table 1.

Phenology was recorded according to decimal code of

Zadoks and Konzak (1974). At physiological maturity, a

sample area of 8.4 m2 (the centre two rows of each plot, 6 m

long), were hand harvested and the mass of plants and grain

were determined. Samples of plants and grain were oven dried

at 65 8C until constant weight. Harvest index (HI) was

calculated as grain to above ground dry biomass ratio.

Soil water content was measured in all experimental plots at

sowing and harvest using the gravimetric method, based on the

conventional oven-dry weight and multiplied by the bulk

density (Qiu et al., 2001). Soil samples were taken in three

points of the central zone of each plot at five depths (0–20, 21–

40, 41–60, 61–80 and 81–100 cm). At the beginning of the crop

season, soil bulk density was also measured.

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Seasonal crop water use (WU) was estimated according to

the following water balance equation (Heerman, 1985):

WU ¼ �DSWCþ Rþ I� D

where ‘‘DSWC’’ is the variation, between sowing and harvest

dates, of the volumetric soil water content in the 0–1.0 m depth

layer, R the rainfall, I the irrigations and D is the water lost due

to deep percolation, all expressed in mm. The D term was

calculated according to a water balance approach, using daily

values of ETc, rainfall and irrigation and starting from mea-

sured soil water content at sowing with a gravimetric method.

Whenever field capacity was exceeded, the deep percolation

water was calculated subtracting soil water content from field

capacity: the soil water content was reset at field capacity. This

water balance model considers the losses for surface runoff and

capillary return to be negligible. The soil depth of 1 m is

justified by the presence of a compact clay layer, which does

not permit root penetration and water uptake.

Water use efficiency (WUE, kg m�3) was calculated as the

ratio of the dry grain yield (in g m�2) to the seasonal water use

(in mm). Irrigation water use efficiency (IRRWUE, kg m�3)

was also calculated as the ratio of increased yield with respect

to rainfed treatment with seasonal irrigation volume. Regres-

sion analysis was used to evaluate water use–yield relationships

using measured seasonal crop evapotranspiration and yield data

obtained from the experiment.

Soil total N, NO3-N and NH4-N were measured to a depth of

1 m at 0.2 m increments before N fertilization. The soil bulk

density was used to convert soil NO3-N and NH4-N to a mass

basis. Nitrate N was determined by ionic chromatography on a

10:1 extract/soil ratio using distilled water, while ammonium N

was determined by spectrophotometer on a 10:1 extract/soil

ratio using potassium chloride solution 2 M. Available N for the

crop was defined as the mineral N in the soil (NO3-N and NH4-

N) at sowing plus N fertilization. Nitrogen use efficiency

(NUE) was calculated as the ratio of corn grain yield to

available N (Pikul et al., 2005).

Analysis of variance was carried out for the 2-year period,

considering the year as a random effect; least statistical

difference (LSD) was used as a mean separation test. Linear and

quadratic components of N and I treatments were also evaluated

using an orthogonal contrast technique. Statistical procedures

were conducted using SAS statistical software (SAS Institute

Inc., 1987).

2. Results and discussion

2.1. Climate and phenology

Average temperatures in 2000 were similar to those of the

long-term series until the anthesis growth stage, then dropping

to lower than long-term temperatures (Fig. 1). In the second

year, average temperatures (except for July and August), were

always lower than average long-term temperature. Over the 2

years, these conditions were generally suitable for the thermal

requirements of corn, with daily temperatures in the range of

12–28 8C and slightly lower summer temperatures in the first

year. Furthermore, reference evapotranspiration (ET0) also

varied between the 2 years, with 608 and 683 mm in 2000 and

2001, respectively during the sowing-harvest period.

Total rainfall during the corn cycle was 169 mm in 2000 and

120 mm in 2001, respectively. In both years, a large part of this

Fig. 1. Daily average air temperature (Tmed) compared with daily long-term

temperature 1953–1999 (LT_Tmed). Cumulative rain in both years compared

with long-term data. Cumulative rain plus irrigation at I50 and I100 irrigation

regimes. In both years, corn anthesis occurred at 183 days of the year.

Table 1

Corn management carried out during the 2 years of experiment

Agronomic practices 2000 2001

Sowing date (DOY) 126 116

Plant population (per m2) 8 8

Pre-sowing fertilization (kg ha�1) (treatments N1 and N2) P2O5: 60, NH4NO3: 50 and 100 P2O5: 60, NH4NO3: 50 and 100

Top-dressed fertilization (kg ha�1) (treatments N1 and N2) NH4NO3: 100 and 200 NH4NO3: 100 and 200

Irrigation supplies 8 9

Seasonal irrigation amount (mm) treatments (I50 and I100) 185–346 190–373

Harvest date (DOY) 257 252

Length of growing season (days) 131 136

E. Di Paolo, M. Rinaldi / Field Crops Research 105 (2008) 202–210204

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precipitation fell at the beginning and end of corn growth cycle.

However, in 2000 the first 10 days of July saw a rainfall of

25 mm during the silking corn stage, which was significant both

in terms of grain yield formation and the response to irrigation

treatments. On the contrary, a very large precipitation

(>100 mm) recorded at corn physiological maturity during

the first year was not significant for grain yield.

No difference was observed in the phenology of corn

submitted to different I and N treatments. Despite the fact

that the 2001 crop was sown 10 days earlier than in 2000,

following the ‘‘6-leaf’’ stage all growing phases were

achieved almost simultaneously (Table 2) over the 2 years.

The lower maximum and minimum temperatures of April,

May and June in the second year (Fig. 1) affected the

accumulation of growth degree days on; as a result, the corn

emergence and 6-leaf stage occurred, respectively 2 and 10

days later than in the first year. The cold mid-June to mid-

July period in the first year delayed the corn dough stage,

physiological maturity and harvest, which in total were 10

days later than in the second year.

2.2. Grain yield and biomass production

Table 3 reports the analysis of variance results: for each

variable, only the higher order significant sources of variation

will be discussed.

Plant population at harvest differed between the years (7.5

vs. 8.1 plants m�2, in 2000 and 2001, respectively), but not

among ‘‘N’’ and ‘‘I’’ treatments (Table 4). Ear density was the

same over the 2 years, consequently a greater fertility expressed

as number of ears per plant in the first year was observed.

Irrigation treatments influenced the ear density with a value in

rainfed (4.5) that was significantly lower than in the two

irrigation treatments (7.3 and 7.7 ear m�2), which showed no

differences. The water stress greatly influenced the ear and

grain formation with a very low fertility in rainfed in both years

and at all nitrogen rates. Some authors found that the timing of

drought influenced corn yield components: ear numbers are

mainly reduced by water stress during the vegetative stage

(Cakir, 2004); kernel number and weight proved to be more

influenced by drought during the reproductive stage (Pandey

et al., 2000; Yudelman, 1994; Fapohunda and Hussain, 1990;

Garrity et al., 1983; Greenwood, 1976).

In this experiment, ‘‘N’’ fertilization rates did not affect ear

density and the number of ears per plant, because residual soil

N in both years was high enough for corn to control production.

The irrigation levels influenced both plant and ear

productivity (Table 4), with higher values in the two irrigation

treatments and lower in the rainfed. Furthermore, nitrogen

fertilization influenced plant and ear productivity with the non-

fertilized control that had less production with fertilized

treatment. No difference was observed between N150 and N300

fertilization rates.

The grain yield was significantly different between the 2

years: in 2000, the average grain yield was 900, while in 2001 it

was 710 g m�2 (Table 5). The greater yield of 2000 is mainly

explained by yield per plant (partly compensated by a lower

plant density in the first year) and by yield per ear, greater in the

first year than in the second (134 vs. 99 g of grain ear�1)

(Table 4). This can be explained by climatic conditions, which

were more favourable in 2000 for ear fertility (lower

temperatures and wet days in the post-anthesis period).

The corn grain yield differed between irrigation and nitrogen

treatment, but the interaction of ‘‘N � I’’ was significant. In

Table 2

Corn phenology in day of the year (DOY)

Phenological stages 2000 2001

Sowing 126 116

Emergence 133 125

6-Leaf stage 161 161

Anthesis 183 183

Silking 186 191

Dough stage 227 226

Physiological maturity 246 243

Harvest 257 252

Table 3

Significance levels of ANOVA of 2 years of corn data; ***, ** and * indicate, respectively, significance at 0.001, 0.01 and 0.05 P level

DF Plants m�2 Ears m�2 Ear

plant�1

Grain

yield plant�1

Grain

yield ear�1

Grain

yield

Biomass

yield

Harvest

index

WUE IRRWUE NUE

Year (Y) 1 *** ** ** * ** *** *

Rep 3 ***

E1 3

Irrigation (I) 2 *** *** *** *** *** *** *** *** *** ***

Irr lin 1 *** *** *** *** *** *** ** ** ***

Irr quad 1 ** ** ** * ** *** ** *

Y � I 2

E2 12

Nitrogen (N) 2 *** *** ** *** * *** * **

N lin 1 *** *** *** *** ** *** * ***

N quad 1 **

Y � N 2 **

N � I 4 * *

Y � N � I 4

E3 36

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fact, nitrogen availability amplified the irrigation effect and

vice versa. In rainfed conditions, nitrogen availability did not

show any influence on grain yield (Fig. 2); the differences

among nitrogen rates for each irrigation regime were small at

I50 (810, 960 and 1030 g m�2 for N0, N150 and N300,

respectively) while they were larger at I100 (800, 1240 and

1430 g m�2, respectively). This confirms the positive effect of

adequate soil water on nitrogen availability and the capacity

that the plant has for a simultaneous uptake of water and

nitrogen leading to their more effective use when both are at a

satisfactory level. O’Neill et al. (2004) reported a greater yield

response for corn with N application under adequate soil water

conditions and a lower one under deficit water conditions. They

also reported an average yield increase of 23% for adequate

versus deficit water supply and around 100% for adequate

versus deficit N levels in the US Great Plains region. In our

study, grain yield increments for irrigation water were 257% for

I100 versus I0 and 24% for I100 versus I50. The response to N

fertilizer level was less effective; grain yield increments were

53% for N300 versus N0 and 8% for N300 versus N150.

The yield of rainfed corn was very low: 390 and 260 g m�2

in 2000 and 2001, respectively (Table 5). This agrees with the

results of Dagdelen et al. (2006) in rainfed corn in Western

Turkey, an environment with similar climatic characteristics

with long-term precipitation of 657 mm falling mainly from

October to March. This indicates the difficulty of obtaining

satisfactory corn grain yield in these environments without

Table 4

Plants and ears density and fertility as affected by year, irrigation and nitrogen treatments

Plants m�2 (no.) Ears m�2 (no.) Ear plant�1 (no.) Grain yield plant�1 (kg) Grain yield ear�1 (kg)

Year

2000 7.48 6.47 0.86 0.120 0.134

2001 8.12 6.55 0.81 0.088 0.099

LSD(0.05) 0.19 n.s. n.s. 0.015 0.018

Irrigation

I0 7.73 4.49 0.58 0.042 0.071

I50 7.80 7.31 0.93 0.121 0.130

I100 7.86 7.72 0.99 0.148 0.148

LSD(0.05) n.s. 0.88 0.09 0.021 0.018

Nitrogen

N0 7.62 6.22 0.82 0.082 0.093

N150 7.85 6.63 0.84 0.111 0.125

N300 7.92 6.67 0.84 0.119 0.131

LSD(0.05) n.s. n.s. n.s. 0.018 0.020

Table 5

Dry grain yield and aboveground biomass of corn as affected by year, irrigation

and nitrogen treatments

Grain yield Biomass yield Harvest index

(t ha�1) (t ha�1) (t t�1)

Year

2000 8.97 18.67 0.46

2001 7.11 14.36 0.45

LSD(0.05) 1.12 2.07 n.s.

Irrigation

I0 3.24 8.59 0.36

I50 9.32 17.42 0.53

I100 11.57 23.54 0.48

LSD(0.05) 1.45 2.34 0.06

Nitrogen

N0 6.12 13.71 0.41

N150 8.64 17.05 0.49

N300 9.36 18.79 0.47

LSD(0.05) 1.37 2.16 0.04Fig. 2. Significant interaction ‘‘Nitrogen � Irrigation’’ for corn grain yield

(top) and water use efficiency (bottom).

E. Di Paolo, M. Rinaldi / Field Crops Research 105 (2008) 202–210206

Author's personal copy

irrigation applications, confirming that water is essential and

will become increasingly more so in the future.

Above ground, the corn biomass was greater in 2000

(1870 g m�2) than in 2001 (1440 g m�2). The response of

biomass yield at water availability was more linear than the

grain yield; the three ETc restitution levels differed (860, 1740

and 2360 g m�2) increasing linearly from I0 to I100 (the

quadratic component of I proved not to be significant, Table 3).

Nitrogen application increased corn biomass yield, but 15 g

(N) m�2 proved sufficient to reach maximum values because it

did not differ from the highest N application rate.

Water and nitrogen availability had different effects on

biomass and grain yield. This is evident when analyzing the

harvest index, a variable often used in breeding programs to

discriminate between cereal drought resistant genotypes. A

stable parameter was shown between the years, lower in N0 than

in the two fertilized treatments. The different effect of irrigation

on grain and biomass yield is combined and proved in the

harvest index, higher in I50, intermediate in I100 and lower in I0

treatments. This is evident in the corn grain yield, which in this

environment has been favoured by the partial ETc restitution

(I50) more than above-ground biomass yield (Table 5). With this

combination, the plant achieved a correct balance in the grain-

biomass (sink-source) dry matter production. Similar results

were obtained for N treatments.

2.3. Water use–yield relationship

In 2000, WUE was higher than in 2001 (+52%) due to better

climatic conditions that were favourable to photosynthesis and

carbon assimilation (Table 6).

The relationships between seasonal crop ET and grain yield

for the 2 years of experiment are reported in Fig. 3. The results

of the statistical regression analysis showed a close relation-

ships between seasonal crop ET and grain yield. Combining the

data of 2 years, the slope of the regression line decreased, as

well as the R2 value. The slopes of the regression lines, which

represent the increment of grain yield for unit increment of

seasonal crop ET, were similar over the 2 years, while the

intercepts varied widely. From the equations reported in Fig. 3,

the basal seasonal ETc necessary to start grain yield production

can be derived: in this study it was 63 and 206 m in 2000 and

2001, respectively (135 mm on average), and the difference can

be explained with average temperatures in the period

anthesis—dough stage (DOY 180-220): 22.3 and 24.0 8C,

respectively in 2000 and 2001. Tolk and Howell (2003)

reported that the slope of the relationships and the cross-over

point are affected by climate, soil properties and irrigation

practices. In a 2-year experiment on corn grain yield in the

environmental conditions of the US Great plains, Payero et al.

(2006) found values of basal ET of 152 and 160 mm. Cakir

(2004) reported values of 129, 224 and 131 mm for experiments

carried out in North-West Turkey from 1995 to 1997. Oktem

et al. (2003) evaluated the effect of deficit irrigation on sweet

corn and found a base seasonal ET of 170 and 235 mm for fresh

ear production in 1998 and 1999. These authors also reported a

high variability for slope and intercept values of the regression

lines between the years. The linear relation of corn grain yield

to water use found in the present study is in agreement with

those reported by Payero et al. (2006).

The ‘‘N � I’’ significant interaction of WUE, the ratio

between grain yield and water use (ETc), is displayed in Fig. 2;

higher values were obtained at the N300 rate, but at I50 and I100,

there were no differences between the irrigation levels. On the

contrary, at N0 the I50 had better yields than I100 irrigation

treatment. In this case, the yield limiting factor was nitrogen

availability and irrigation supply at 50% of ETc which proved

to be sufficient to achieve maximum WUE value.

The graph of corn yield versus ETc (Fig. 4) shows the

linearity of the regression for the N150 and N300 treatments, with

a slightly higher slope (WUE) in N300; on the contrary, N0

showed a deviation from linearity with a second order

relationship, highlighting the fact that after a water use

threshold, the soil nitrogen content became the grain yield

limiting factor. Goh and Haynes (1986) reported that the

Table 6

Water (WUE), irrigation water (IRRWUE) and nitrogen use efficiency (NUE) of

corn in grain production as affected by year, irrigation and nitrogen treatments

WUE (kg m�3) IRRWUE (kg m�3) NUE (kg kg�1)

Year

2000 2.36 3.08 20.38

2001 1.49 2.49 31.13

LSD(0.05) 0.44 n.s. 9.52

Irrigation

I0 1.44 – 9.92

I50 2.25 3.25 30.68

I100 2.09 2.33 36.68

LSD(0.05) 0.40 0.34 6.51

Nitrogen

N0 1.46 2.36 33.66

N150 2.08 2.67 25.00

N300 2.23 3.33 18.62

LSD(0.05) 0.33 0.73 6.27

Fig. 3. Relationship between seasonal crop evapotranspiration and grain yield.

Linear regression equations; ***, ** and * indicate, respectively, significance at

0.001, 0.01 and 0.05 P level.

2000 GY = 30.437ETc � 1924.8 R2 = 0.88**

2001 GY = 32.412ETc � 6680.1 R2 = 0.84**

2 years GY = 25.77ETc � 2115.1 R2 = 0.60*

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application of N to corn slightly increased grain yield under

water-deficit and greatly under full irrigation. They noticed that

at lower N rates, N was the most limiting yield factor and water

stress had a slight effect, but with adequate or excessive N,

water became the most limiting factor. Atkan (1976) found that

the WUE of winter wheat and barley was reduced markedly by

either a deficiency or an excess of N supply.

The soil water content was then evaluated at sowing and at

harvest as a function of soil depth. At harvest, soil water content

(Fig. 5) of the rainfed treatment was below wilting point in the

0–0.4 m depth due to the formation of cracks caused by the

montmorillonitic clay particle types. The soil moisture of rain

fed was lower in comparison to that of irrigated treatments: the

differences were higher in the 0–0.4 m soil layer, while they

remained constant in the 0.6–1.0 m depth.

Rainfed corn extracted more water than irrigated corn in all

the soil profiles, but most water was absorbed in the 0–0.6 m

soil layer (Fig. 5). These findings are in agreement with those

of Farre and Faci (2006) and Panda et al. (2004) who reported

that corn, grown on sandy loam soil, extracts most of the

water from 0.0 to 0.5 m soil layer. Gordon et al. (1995)

reported a little water depletion below 0.9 m soil depth for

rainfed corn.

Few differences were observed between irrigation treat-

ments I50 and I100 for soil water content at harvest and water

depletion.

2.4. Nitrogen use

NUE values, expressed as g of grain yield per g of

available nitrogen, are reported in Table 6. Average mineral

nitrogen (NO3� plus NH4

+), measured before N fertilizer

application in the soil depth 0–1.0 m, was 30.5 and 11.7 g

(N) m�2 in 2000 and 2001, respectively. This is the main

reason for a greater NUE in 2001, when the soil N content

lower than that of 2000 produced a greater effect of N supply.

Consequently, a significant ‘‘Y � N’’ interaction also

occurred at the analysis of variance. The effect of N rates

was increased in 2001 when the soil nitrogen content was not

enough to compensate for the plant requirement and,

consequently, the NUE at N0 level was about 120% of the

NUE at N300 and 52% of the NUE at N150 levels. On the

contrary, in 2000, the NUE of the three N fertilization levels

were very similar, with the only difference that between N0

and N300 (36%) (Fig. 6).

No significant difference was found between irrigation

regimes I50 and I100, but rainfed treatment significantly reduced

NUE at all nitrogen levels. This confirms how deficit irrigation

reduces the capability of the crop in its uptake and efficient use

of soil nitrogen.

Fig. 4. Relationship between seasonal crop evapotranspiration and corn grain

yield as a function of nitrogen treatments.

Fig. 5. Soil water content expressed in mm of crop available water (soil water

content minus wilting point water content) at corn sowing (initial swc) and

harvest, for each depth (top); soil water depletion has been calculated as the

difference between the above two variables for the three irrigation scenarios and

averaged over the 2 years (bottom). Fig. 6. Significant interaction ‘‘Year � Nitrogen’’ for nitrogen use efficiency.

E. Di Paolo, M. Rinaldi / Field Crops Research 105 (2008) 202–210208

Author's personal copy

In line with Halvarson et al. (2005), Pikul et al. (2005),

Ma et al. (1999) and O’Neill et al. (2004), our study showed

that NUE increased linearly with soil water availability and

decreased with applied N. Adequate soil water availability led

to both a better uptake and use of the N in the cell metabolic

processes, increasing crop biomass and yield, and for this

reason WUE and IRRWUE were also positively affected by the

amount of N fertilizer. N fertilizer levels increased grain yield at

I50 and I100 levels, while in rainfed treatment, the yield only

increased up to 15 g (N) m�2. The increase in grain yield of 160

and 180 g m�2 in 2000 and 2001, respectively did not produce

any effect on NUE. Our study confirmed that adequate N supply

can help corn grown in rainfed conditions to improve drought

resistance (Tesha and Eck, 1983) and use N more effectively in

biomass and yield production. Indeed, for rainfed corn, the N

fertilizing level N150 led to a mean yield increase of 76% in

comparison to N0 treatment.

The overall NUE mean value of 26 g of grain yield per g of

available N found in this study is similar to that found by Ma

et al. (1999) for corn fertilized with 20 g (N) m�2.

3. Conclusions

On the bases of these experimental results, irrigation

scheduling providing a partial restitution of crop ETat a basis of

50% allows us to save water (48% if I50 is compared to I100) and

ensures a good corn grain yield level (932 g m�2) in a

Mediterranean environment. Full irrigation in the silking

growth stage of corn could increase the performance of this

irrigation management criteria, thus helping to overcome

progressive water stress accumulation, as demonstrated in 2000

with a rain event during the critical corn growth stage.

Satisfactory grain yield was obtained with N fertilizer level

N150 despite the fact that higher N use efficiency was achieved

with N0 treatments for both years.

Irrigation was more effective than nitrogen in increasing

grain yield for both years and the irrigation water productivity

was higher with irrigation regime I50 as shown by the IRRWUE

values. Irrigation improved the crop N use as shown by the

increasing NUE at I50 level.

In conclusion, in order to reach high yield levels of corn

grain, obtain high water and nitrogen use efficiencies and

reduce the risk of nitrate pollution of groundwater in

Mediterranean regions, a valid compromise can be reached

by the use of irrigation to partially reduce crop ET restitution

and the application of N fertilization which is lower than that

suggested by soil analysis and yield goals.

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