integrated strategies for maize irrigation and fertilization under water scarcity and environmental...

IRRIGATION AND DRAINAGE

Irrig. and Drain. 53: 105–113 (2004)

Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/ird.104

INTEGRATED STRATEGIES FOR MAIZE IRRIGATION ANDFERTILIZATION UNDER WATER SCARCITY AND ENVIRONMENTAL

PRESSURE IN BULGARIAy

ZORNITSA POPOVA* AND MILENA KERCHEVA

N. Poushkarov Institute of Soil Science, 7, Shosse Bankya Str., Sofia 1080, Bulgaria

ABSTRACT

Integrated management of irrigation and fertilization could meet global increasing demand from maize production

and environmental pressures under water scarcity. The objective of this paper was to evaluate the long-term impact

of irrigation scheduling and rates and timing of fertilization on water stress indicators, nitrogen uptake and

leaching under maize on Chromic Luvisol (Sofia region). Modeling of the soil–plant system by the CERES-maize

model was used. Adjusted and modified CERES-maize was run with different irrigation and fertilization scenarios

and 30-year weather data. Scenario analyses proved that grain yield and N-uptake were severely affected on

drylands under the conditions studied. Drought indicators showed that irrigation was required in 70% of the years.

The sensitivity of maize drylands to precipitation in the critical (15 July–15 September) period caused great

variability in maize yield (Cv¼ 42%) and N-uptake (Cv¼ 25%) under nonlimited fertilization conditions. In

addition, low vegetative precipitation proved to be a reason for fallow state leaching on drylands. All the irrigation

scheduling tested improved N-uptake efficiency, mitigated drought and significantly reduced yield and N-uptake

variability (Cv¼ 5–6%). An integrated management strategy of N-application timed to coincide with the period of

maximum crop uptake and irrigation scheduled at 85% of field capacity reduced N available for leaching in the

risky years. A drainage-controlling scenario, developed for 75–80% of the required irrigation depth and satisfying

predominantly the most sensitive phases of maize development, saved up to 95 mm yr�1 of water and reduced

drainage in medium wet to wet fallow states by 30–40%. Significant early-season N-losses (25% of applied N)

were associated with precipitation extremes and poor N-dressing and could potentially happen in 3% of the years

studied. Exceedance frequency of N-uptake under nonlimited fertilization conditions and different irrigation

strategies was used to adjust more accurately the fertilizer rates and timing for the soil and climate variability

studied. Copyright # 2004 John Wiley & Sons, Ltd.

key words: irrigation scheduling; fertilization strategies; CERES-maize model; environment; climate variation

RESUME

Les consequences du deficit d’eau dans le systeme maıs–sol sont extremement severes pour un sol de faible

retention comme les Chromic Luvisol de la region de Sofia a cause de la coıncidence de la periode de secheresse

atmospherique et du stade d’evapotranspiration le plus intensif (du 15 juillet au 15 aout). Une gestion d’irrigation

et de fertilisation doit etre mise en place vu la demande globale croissante de production du maıs en situation de

contrainte pour l’environnement et l’eau. L’objectif de cet article est d’evaluer les consequences du regime

d’irrigation et l’utilisation d’engrais sur des indices de stress hydrique, le prelevement et le lessivage d’azote sur du

maıs cultive sur Chromic Luvisol dans la region de Sofia. Le modele CERES-maıs a ete utilise pour simuler des

Received 5 May 2003

Revised 21 June 2003

Copyright # 2004 John Wiley & Sons, Ltd. Accepted 29 July 2003

* Correspondence to: Dr Z. Popova, N. Poushkarov Institute of Soil Science 7, Shosse Bankya St., Sofia 1080, Bulgaria.E-mail: [email protected] integrees d’irrigation et fertilisation de maıs dans les conditions de deficit d’eau et pression environmentale en Bulgarie.

relations dans le systeme sol–plante–climat. Le modele a ete ajuste et modifie sous les conditions specifiques

bulgares et sa capacite predictive pour la disponibilite en eau et en azote dans le sol et la reponse du systeme

racinaire a ete approuvee comme acceptable et precise. CERES-maıs a ete execute avec differents scenarios

d’irrigation et d’application d’azote et des donnees meteorologiques de trente annees. Quatre traitements de

supplement d’eau ont ete consideres dans ces analyses dont un sans irrigation et trois avec des conditions

d’irrigation variable. Une strategie de controle du drainage a ete developpee sur la base de 75–80%

d’eau necessaire en satisfaisant completement le stade initial et les phases les plus sensibles de developpement

du maıs. Chaque traitement d’irrigation a ete simule avec trois scenarios differents d’application d’azote dont un

avec une seule application de 200 kg ha�1 N au printemps, un avec deux applications egales a la semence et juste

avant la periode de prelevement maximale et un avec deux applications equilibrees. Copyright # 2004 John Wiley

& Sons, Ltd.

mots cles: regimes d’irrigation; scenarios d’application d’azote; modele CERES-maıs; environnement; changement climatique

INTRODUCTION

Irrigation water is limited to Bulgarian farmers in some situations. The consequences of water deficit are extremely

severe for maize on soils of low water retention capabilities such as Chromic Luvisol, since regional periods of

atmospheric drought and highest crop water demand (from 15 July to 15 August) coincide. Integrated management

of irrigation and fertilization could meet increasing global demand for maize production and environmental

pressures under water scarcity. Factors such as weather variability, the complex nature of crop response to

irrigation and fertilization practices contribute to different levels of risk associated with year-to-year yield losses

and/or environmental hazards. Ritchie (1985), Algozin et al. (1988) and others demonstrated the use of crop

growth simulation models, such as CERES-maize (Jones and Kiniry, 1986), to evaluate acceptable water

management policies and risks associated with rainfed agriculture in the USA. Recent adaptation and modification

of the CERES-maize model for use under European conditions made it a powerful tool to predict a better ensemble

of processes in the cycle of water and nitrogen in the soil–crop system. The semi-empirical Darcy’s law of water

movement in the soil profile was implemented in the Water Flow Sub-model (Gabrielle et al., 1995). The N-

transformation routine (MINIMO) was substituted with the NCSOIL model (Molina et al., 1983) which proved

more accurate in the simulation of the processes involved in the soil N-cycle (Gabrielle and Kengni, 1996). The

model was adjusted and modified under specific Bulgarian conditions. CERES-maize simulations about soil water/

N-disposal and the maize biological response to it proved to be acceptably precise on Chromic Luvisol (Popova

et al., 1999, 2001b). The objective of this paper was to evaluate the long-term (30 years) impact of different

irrigation scheduling and rates and timing of fertilization on water stress indicators such as evapotranspiration and

productivity, N-uptake and leaching under maize on Chromic Luvisol in Chelopechene field (Sofia region,

Bulgaria). This soil–crop combination proved to be a typically risky one under conditions of water scarcity in

Bulgaria (Popova et al., 1999, 2001a) and a potential source of groundwater pollution (Stoichev et al., 2001).

MATERIALS AND METHODS

Modeling of the soil–plant system was used in this analysis. The North American model Crop–Environment

Resource Synthesis CERES-maize model (Jones and Kiniry, 1986; Gabrielle et al., 1995; Gabrielle and Kengni,

1996) had been calibrated, modified and validated on the basis of specific experiments carried out on Chromic

Luvisol in Chelopechene field, Sofia region. Soil conditions are characterized in terms of water retention

capabilities, saturated soil conductivity and texture in Table I.

Experimentally based data of water contents, N–NH4 and N–NO3 in the soil, dry weights and N-contents of the

plant in irrigated and rainfed plots and lysimeters (Final report, 1999), evapotranspiration and water fluxes (Popova

and Shopova, 2002) provided acceptable agreement with model outputs after detailed calibration procedures

(Popova et al., 1999, 2001b). Adjusted CERES-maize was used to evaluate the effect of different water and

fertilizer application scenarios over a series of 30 independent growing seasons. Daily weather data for

106 Z. POPOVA AND M. KERCHEVA

Copyright # 2004 John Wiley & Sons, Ltd. Irrig. and Drain. 53: 105–113 (2004)

precipitation, maximum and minimum air temperature and solar radiation were provided from references

(Meteorological annual and monthly references, 1960–1984) and the weather station of the Nikola Poushkarov

Institute of Soil Science (for the period 1985–89). Four water supply treatments were considered in the analyses,

one under rainfed conditions and three with varied irrigation application. Irrigation depths and timing in the

different irrigation application strategies were determined by the CROPWAT program (Smith, 1992). The maize

parameters varying with the phenological phases (according to Doorenbos and Pruitt, 1984) are presented in

Table II. The data for Kc-factors were determined for Bulgarian weather conditions (Popova and Feyen, 1996).

This input for the CROPWAT program was constant for all runs of the program.

Water application in the initial, development and mid-season growth stages was triggered on any day that soil

water content fell to 75% of field capacity (FC) with one irrigation scenario and to 85% of FC with another. These

trigger points occurred respectively at 20 and 40% depletion of total available soil water in the root zone. Water

application was scheduled in late season whenever 80% of the available water was depleted. Application depth was

set equal to the depleted soil water in the root zone. The third drainage-controlling scenario was developed on the

basis of 75–80% of the required irrigation depth by satisfying predominantly the initial and the most sensitive

phases of maize development (Varlev et al., 1995). Table III presents precipitation (Pr) and irrigation rate (I) under

the different irrigation scenarios and the studied conditions in average (1978), wet (1971) and dry (1987) maize

vegetation seasons, which correspond to 50, 94 and 6% probability of exceedance of precipitation.

Each irrigation treatment was simulated with three different N-application scenarios, one with a single fertilizer

application (200 kg ha�1 N) in the spring, one with partial equal application at sowing and just before the period of

Table I. Water retention capabilities, soil water conductivity at saturation (Ksat) and soil texture, Chromic Luvisol,Chelopechene field

Depth (cm) Field capacity Ksat Soil texture Soil particles, %(%w/w) (cm day�1) classification

Clay Silt Sand(<0.002 mm) (0.002–0.05 mm) (0.05–2.00 mm)

0–28 20.05 93.30 Clay loam 32 32 3633–45 21.09 15.90 Clay 43 27 3061–71 20.75 20.20 Clay 42 25 3395–130 18.60 39.90 Sandy clay loam 24 15 61

Table II. Maize parameters used as input of CROPWAT program

Growth stage Initial Development Mid Late

Crop coefficient 0.30 1.10 0.60Rooting depth (m) 0.10 1.30 1.30Yield response coefficient 0.40 0.60 1.00 0.80

Table III. Precipitation (Pr), irrigation depth (I) and drainage resulted from CERES-maize simulations (Dr) in mm with differentirrigation scenarios in the average (1978), wet (1971) and dry (1987) maize vegetation seasons Chromic Luvisol, Sofia

Irrigation strategy Average Wet Dry

Pr I Dr Pr I Dr Pr I Dr

0 61.9 0 21.7 0 0.375% of FC 171 43.3 113 61.9 359 98.285% of FC 169 26.4 412 135 41.7 153 408 97.5Drainage controlling 115 21.7 58 61.9 302 55.8

MAIZE IRRIGATION AND FERTILIZATION UNDER WATER SCARCITY 107


maximum crop uptake and one with partial adjusted application: one-third of the total rate at sowing and two-thirds

in the middle of the development stage. Dates of sowing and duration of initial, development, mid-season and late

phenological phases (Doorenbos and Pruitt, 1984) of the maize hybrid (FAO group 200–300) were found under

local conditions on the grounds of the relationship between the sum of day–night effective temperatures and dates

of germination, tasseling, milky and waxy ripening (Slavov, 1984).

CERES-maize simulations were performed for all treatments for 16 representative pairs of vegetation and post-

vegetation seasons. They covered uniformly the whole range of precipitation totals over 30 years with probability

of exceedance P (%): P¼ 3–10% (wet climate), P¼ 20–30% (moderately wet), P¼ 43–53% (medium), P¼ 65–

80% (moderately dry), P¼ 86–98% (dry). The long-term impact of integrated management scenarios of irrigation

and fertilization on water stress and nitrogen fate under maize was analysed by indicators of drought and

environmental hazards. Crop water uptake that resulted from each simulated treatment and growing season was

related to reference surface evapotranspiration ETo, calculated by the Penman-Monteith equation according to the

recent FAO methodology (Allen et al., 1998). Water and N-uptake, dry weights and N-leaching calculated for each

particular situation were sorted by probability of precipitation for vegetation and post-vegetation periods. Risks of

drought and N-leaching were related to precipitation extremes and/or sum during critical periods of crop

development. They were characterized by coefficient of variation of yield and N-uptake, frequency of economic-

ally significant yield losses and environmental hazards. N-rates and side-dress time were optimized under different

water supply for the soil and climate variability studied.

RESULTS AND DISCUSSIONS

Scenario analyses proved that water/N-uptake and subsequent grain yield were often affected by soil drought on

dryland on Chromic Luvisol. Year-to-year differences between maize evapotranspiration resulted from CERES-

maize simulation and reference surface evapotranspiration ETo (Figure 1) and losses of ear dry weight on dry lands

(Figure 2) showed that irrigation was required in 70% of the years in the soil–crop–climate combination studied.

The sensitivity of rainfed maize to precipitation in the critical (15 July–15 September) period caused great

variability of maize yield (Cv¼ 42 % under nonlimited fertilization) mostly in medium and dry years (Figure 2).

Irrigation depths for simulated scenarios varied from 0 to 359 mm over the 30-year period. The number of water

applications was 0–2 in wet irrigation seasons, 3–4 during medium ones and 4–7 in dry ones for the irrigation

scheduling at 75% of FC, and respectively 0–3, 3–5 and 5–12 for irrigation at 85% of FC. All the tested irrigation

scheduling mitigated drought (Figure 1) by significantly reduced variability of yield (Figure 2) and N-uptake

(Cv¼ 5–6%) and improved crop N-uptake efficiency (Figure 3). Precipitation in the critical ‘‘15 July to 15

September’’ period influenced not only maize productivity and N-uptake on drylands (in 97% of years in Figures 2

and 3) but also resulted in N-uptake reduction by 7–14% in half of the years under drainage controlling conditions

(Figure 3). The drainage-controlling irrigation strategy provoked some plant stress in only two of the studied years

when the yield was practically reduced up to 12%.

Drainage in vegetation (Dr) that resulted from different simulated treatments and growing seasons varied from 0

to 98 mm in 97% of the years studied (Table III). Exceptional early season precipitation events took place in the

remaining 3% of the growing seasons studied and provoked 237 mm deep percolation (in 1976). Increased water

application (I) in moderately dry and dry vegetation seasons resulted in larger quantity and increased variability of

drainage over irrigation treatment. Fallow state water drainage varied from 0 to 300 mm in the situations studied

(Figure 4). Higher fallow state water drainage occurred in case of water application scheduled at 75 and 85% of FC

(Figure 4). These irrigation treatments resulted in a rise of available soil water at the end of vegetation and poor

storage of possible post-vegetation precipitation. The drainage-controlling scenario saved irrigation up to

95 mm yr�1 of water by reducing drainage in medium wet to wet fallow states by 30–40% (Figure 4). Obtained

results should be conformed with nonuniformity of water application of existing irrigation systems in Bulgaria.

Small and frequent water application depths are possible only under stationary sprinkler irrigation systems.

Highest early seasonal N-losses (45.7 kg ha�1 N vegetation or up to 25% of the fertilization dose) were

associated with single N-application treatment and precipitation extremes in 1976. The chances of such losses



Figure 1. Totals (May–Sept) of reference surface evapotranspiration (ETo) and crop evapotranspiration (ET) under nonlimited fertilizationconditions and different irrigation scenarios ordered by probability of exceedance of vegetation precipitation (P, %) Chromic Luvisol, Sofia

region

Figure 2. Dry weights of ears under nonlimited fertilization conditions and different irrigation scenarios dependent upon probability ofexceedance of vegetation precipitation (P, %) Chromic Luvisols, Sofia region



Figure 3. N-uptake with nonlimited fertilization and different irrigation scenarios ordered according to the probability of exceedance (P, %) ofprecipitation for maize vegetation period (May–Sept) Chromic Luvisol, Sofia region

Figure 4. Drainage in fallow state ordered according to the probability of exceedance of precipitation in ‘‘October–April’’ period (Pf, %),Chromic Luvisol, Sofia region



could be reduced to 23 kg ha�1 N vegetation by applying a large N-amount (two-thirds of the total N) when the

crop was well established in the middle of the development stage. Low vegetative precipitation in 1962 (P¼ 97%

in Figures 1 and 2) proved to be a reason for poor N-use by plants in drylands and leaching (40 kg ha�1 N or 20% of

the total fertilization rate) during the fallow state.

Integrated management strategy of N-application timed to coincide to the period of maximum crop uptake and

irrigation scheduling of frequent and small water application depths (at 85% of FC) achieved maximal N-uptake

efficiency and minimal N-residual at the end of vegetation (Figure 5b) and fallow state N-leaching below

5 Kg ha� 1 (Figure 6) in 85% of the years.

Figure 5. N-uptake and residual N simulated for the day of the year (DOY) after 1.1.1962 under adjusted split N-application (1/3 at sowing and 2/3in the middle of the development stage) and two irrigation treatments: (a) drainage controlling irrigation; (b) irrigation scheduling at 85% of FC

Figure 6. N-leaching in fallow state resulted from simulations under irrigation at 85% FC and different fertilization treatments orderedaccording to the probability of exceedance of ‘‘October–April’’ precipitation Pf, (%), Chromic Luvisol, Sofia region



Exceedance frequency of N-uptake under nonlimited fertilization conditions and different irrigation strategies

(Figure 3) was used to adjust more accurately the fertilizer rates and dressing time to the studied situations, soil and

climate variability. N-rate was evaluated to be 200 kg ha�1 N under drainage-controlling irrigation treatment,

210 kg ha�1 N under other irrigation scenarios and 170 kg ha�1 N on drylands. These rates satisfied crop water

requirements in 75% of the years. Stable productivity and best groundwater protection from diffused N-leaching

under maize fields could be achieved with N-dressing of the recommended rates, one-third at sowing and two-

thirds in the middle of the development stage.

CONCLUSIONS

The long-term impact of irrigation scheduling and rates and timing of fertilization on water stress indicators,

such as evapotranspiration and productivity, N-uptake and N-leaching was studied under maize on Chromic

Luvisol (Sofia region). Modeling of the soil–plant system by CERES-maize model was used. The adjusted

and modified model was run with different crop growth strategies and 30-year weather data. Scenario analyses

proved that:

1. Grain yields and crop water/N-uptake were severely affected on drylands under studied conditions. Drought

indicators showed that irrigation was required in 70% of the years. The sensitivity of maize drylands to

precipitation in the critical (15 July–15 September) period caused great variability of maize yield (Cv¼ 42%)

and N-uptake (Cv¼ 25%) under nonlimited fertilization conditions. In addition low precipitation through the

vegetation period proved to be a reason for fallow state leaching (up to 40 kg ha�1 N in the driest vegetation).

Drainage below maize drylands varied from 0 to 62 mm in 97% of the vegetation seasons. Significant early-

season N-losses (45.7 kg ha�1 N) were associated with precipitation extremes that could potentially happen in

the remaining 3% of the studied years and single N-application of 200 kg ha�1 N at sowing. Splitting the N-rate

could halve such extreme losses and adjusting N-dressing to one-third of the total rate at sowing and the

remaining two-thirds in the middle of the development stage. The environmentally oriented rate of

170 kg ha�1 N satisfied crop requirements in 75% of the years under rainfed conditions.

2. Irrigation scheduling at 75 and 85% of field capacity (FC) under nonlimited fertilization conditions mitigated

biological drought and significantly reduced year-to-year variability of yield (Cv¼ 5.6–6%) and N-uptake

(Cv¼ 5%). Highest fallow state water drainage (up to 300 mm) occurred with water supply at 85% of FC.

Exceedance frequency of N-uptake allowed more accurate adjustment of the fertilizer rates and timing with

studied situations. An environmentally oriented N-rate of 210 kg ha�1 N satisfied crop requirements in 75% of

the years. Lowest fallow state N-leaching (below 2 kg ha�1 N) and maximum N-uptake efficiency were

achieved under any of these irrigation strategies and dressing of N-rate to one-third at sowing and two-thirds

in the middle of the development stage in 80% of the years when precipitation in the critical (15 July–15

September) period was less than 120 mm.

3. Drainage-controlling irrigation treatment under nonlimited fertilization conditions reduced potential grain yield

by 7–10% only in 12% of the years and N-uptake by 8–26 kg ha�1 N in 50% of them. This scenario saved

irrigation water (up to 95 mm/yr�1) and reduced the drainage in medium wet to wet fallow states by 30–40%.

An environmentally oriented N-rate of 200 kg ha�1 N under drainage-controlling irrigation treatment was

recommended. This rate would satisfy crop requirements and diminish fallow state N-leaching below

5 kg ha�1 N, if it is dressed one-third at sowing and two-thirds just before the most intensive crop uptake, in

75% of the years.

ACKNOWLEDGEMENTS

We would like to thank Dr Ghislain Gosse for securing financial support of 55 000 EU through the INCO-

COPERNICUS project ERBIC 15 CT 960101 on the evaluation of risks and monitoring of nitrogen and pesticide



fluxes at crop level on the Romanian and Bulgarian plain of the fourth Framework Program of EC. We wish to

thank Dr Plamen Petkov, director of Research Institute of Irrigation and Drainage, Sofia, for the opportunity to

work on four concrete lysimeters in the experimental field of Chelopechene for the purposes of this study.

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