S

GMa

b

a

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Agricultural Water Management 120 (2013) 11– 22

Contents lists available at SciVerse ScienceDirect

Agricultural Water Management

j ourna l ho me page: www.elsev ier .com/ locate /agwat

oil water and nitrate distribution under drip irrigated corn receiving pig slurry

. Arbata,∗, A. Rosellób, F. Domingo Olivéb, J. Puig-Barguésa, E. González Llinàsb,. Duran-Rosa, J. Pujola, F. Ramírez de Cartagenaa

Department of Chemical and Agricultural Engineering and Technology, University of Girona, C/de Maria Aurèlia Capmany, 61. 17071 Girona, SpainIRTA Mas Badia., 17134 La Tallada d’Empordà, Spain

r t i c l e i n f o

rticle history:vailable online 22 August 2012

eywords:ig slurryitrogen managementertilization strategiesitrate leachingYDRUS-2Dicro-irrigation

orn yield

a b s t r a c t

Intensive swine production in Catalonia (NE Spain) has great economic importance. Applying the resultingpig slurry as fertilizer is technically sound, but there is a risk of nitrate leaching. It is therefore importantto determine the amount of pig slurry that will achieve an acceptable crop yield yet prevent environ-mental risks. In an experiment carried out in 2009 irrigation water and grain yield in a silt loam soil werecompared for furrow and drip irrigation with two emitter spacings (30 and 50 cm). The results showedthat using drip irrigation improved water use efficiency (WUE) and that WUE and corn yield were not sig-nificantly different for emitters spaced at 30 and 50 cm. Based on these results, in 2010 the irrigation wascarried out using emitters spaced 50 cm apart. Two different pre-planting fertilization treatments (0 and120 kg N/ha from pig slurry) were applied. In addition, each of those two treatments was subjected to tendifferent side-dress fertilization treatments, with the rate of nitrogen applied through fertigation rangingfrom 0 to 300 kg N/ha. Soil water distribution simulated with HYDRUS-2D showed good agreement withobserved values.

Most of the nitrate leaching was produced after physiological maturity associated with high precipita-−

tions that produced drainage and NO3 -N leaching, especially in the treatments that received excessive

amounts of nitrogen.With relatively low initial soil nitrate content, side-dress application rates of 40–75 kg N/ha combined

with pig slurry applied at pre-planting produced nearly maximum grain yield with minimum N leachingand did not contravene the existing EU directives on nitrate pollution. On the other hand, nitrogen appli-cations over 150 kg N/ha during the growing season did not increase yield but did significantly increasethe concentration of nitrate in the leached solution.

. Introduction

Furrow irrigation is currently the most common system usedy corn producers in Alt and Baix Empordà (northeast Spain),s well as in many other production areas around the world.owever, drought events have forced farmers to restrict agri-ultural irrigation in this region of Spain (DOGC, 2007), andome farmers are considering changing from furrow irrigation toicro-irrigation, which is generally considered to use water more

fficiently (Clemmens and Dedrick, 1994; Hanson et al., 1994;asberg and Or, 1999; Ayars et al., 2007). However, experiences

ith micro-irrigation for corn production in the characteristic allu-

ial soils of the region are limited and the most adequate lateralnd emitter spacings are unknown. Increasing lateral and emit-er spacing significantly reduces the installation costs of the drip

∗ Corresponding author. Tel.: +34 972 41 84 59; fax: +34 972 41 83 99.E-mail address: gerard.arbat@udg.edu (G. Arbat).

378-3774/$ – see front matter © 2012 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.agwat.2012.08.001

© 2012 Elsevier B.V. All rights reserved.

irrigation system (Lamm et al., 1997; Arbat et al., 2010). Lammet al. (1997), Lamm and Trooien (2003), and Mailhol et al. (2011)reported that a lateral spacing around 1.5 m would be technicallysound for subsurface drip irrigation (SDI). Using surface drip irri-gation (DI) for corn, Bozkurt et al. (2006), Mailhol et al. (2011), andLekakis et al. (2011) reported high yield and water use efficiencywith laterals located between corn rows and spaced at 1.4, 1.5, and1.6 m respectively. More variability has been found in the emitterspacing. In a three-year field study using SDI in deep silt loam soilsof the U.S. Great Plains, Arbat et al. (2010) did not encounter dif-ferences in corn yield or water productivity for emitter spacingsranging from 30 to 120 cm. Emitter spacings ranging from 20 cmto 50 cm have been reported with DI for corn (Bozkurt et al., 2006;Mailhol et al., 2011; Lekakis et al., 2011; Wan et al., 2012), but the

results did not show a direct correlation between emitter spacing,yield, and water use efficiency. Presumably, the change from furrowto drip irrigation would reduce the wetted soil volume and allowthe application of nitrogen fertilizer through fertigation after plant-ing, thereby reducing deep drainage to the aquifer (Dasberg and Or,

12 G. Arbat et al. / Agricultural Water Management 120 (2013) 11– 22

200 30

P Historical P ETo T Historical T

150

100

20

50

P

reci

pit

atio

n,

ETo

(mm

) .

10

Tem

per

ature

(ºC

)

0

DecNovOctSepAugJulJunMayAprMarFebJanDecNovOctSepAugJulJunMayAprMarFebJan

0

2009 2010

F ean aia

1bcu12

oitbBtwtys

coa(tft22tt2ofl

hsd

dsris

ig. 1. Monthly precipitation (P), reference ET (ET0, FAO-Penman Montheit) and mnd T in the experimental site.

999; Ayars et al., 2007). In addition, the potentially higher distri-ution uniformity for micro-irrigation and maintaining soil waterontent near field capacity during the crop cycle could reduce waterse and/or increase corn yield (Hanson et al., 1994; Dasberg and Or,999; Karimi and Gomrokchi, 2011; Lekakis et al., 2011; Wan et al.,012).

In areas where intensive pig production is important, like thene in this study, applying pig slurry (PS) as pre-planting fertilizern corn production is a common practice that could reduce fertiliza-ion costs (Buman, 1998), but the risk of nitrate leaching must note neglected (Nielsen and Jensen, 1990; Daudén and Quílez, 2004;erenguer et al., 2008; Yagüe and Quílez, 2010). It should also beaken into consideration that most of the region where this studyas carried out was designated as a nitrate vulnerable zone. In

hose zones the maximum total application rate is 350 kg N/ha perear, of which no more than 170 kg N/ha can be organic fertilizersuch as PS (DOGC, 2009).

Under irrigated conditions in the Ebro Valley (northeast Spain),orn yields range from 11 to 15 Mg/ha and plant N uptake isver 250–300 kg/ha (Berenguer et al., 2009). Similar corn yieldsnd plant N uptake rates are expected in the region of this studyDomingo et al., 2005, 2006). Different authors have highlightedhat soil mineral N content before planting was one of the mainactors determining the amount of N leached and it should beaken into account in fertilization practices (Arregui and Quemada,006; Berenguer et al., 2008; Yagüe and Quílez, 2010; Cela et al.,011). With high yield irrigated corn it is commonly acceptedhat in addition to pre-planting fertilization, side-dress applica-ions of mineral fertilizer would be convenient (Berenguer et al.,008; Yagüe and Quílez, 2010). Using DI allows the applicationf nutrients through the irrigation system, providing the capacityor precise nutrient management and reducing loss through nitrateeaching (Thompson et al., 2007; Gallardo et al., 2011).

To the best of the knowledge of the authors no previous studiesave analyzed the risks of nitrogen leaching in high yield corn whenlurry was applied pre-planting and fertigation was used for side-ress applications.

The use of models can help to understand water and nitrate

istribution in the soil: Cameira et al. (2007) used RZWQM toimulate the fate of nitrogen in corn fields in the Mediterraneanegion; Jégo et al. (2012) used STICS to simulate nitrate leach-ng; and, in the same experimental field as that of the presenttudy, Poch (2012) used STICS to simulate the risk of nitrate

r temperature (T) for the years 2009 and 2010 and historical period (1984–2010) P

leaching in furrow irrigated corn, receiving mineral nitrogen fer-tilizer. One of the conclusions of Poch (2012) was that the risk ofnitrate lixiviation is associated with situations where the waterdrains below 120 cm depth. Cote et al. (2003), Gärdenäs et al.(2005), and Hanson et al. (2006) used HYDRUS-2D to analyze theeffect of different fertilization strategies on water and nitrate distri-bution under micro-irrigation. However, very few other works havestudied nitrate distribution under micro-irrigation from experi-mental field data. Li et al. (2004), from a laboratory experiment,and Hanson et al. (2006), applying a simulation model, showedthat nitrate distribution is determined by the shape and dimen-sions of the wetted soil volume. Both studies demonstrated that,due to nitrate’s high solubility in water, its concentration tendsto be higher at the periphery of the wetted bulb. Hanson et al.(2006) observed an accumulation of nitrate mass in the soil pro-file to a depth of about 150 cm under the typical crop conditions ofCalifornia.

The main objectives of the current study were: (1) to assess cornyield and water use efficiency using surface drip irrigation emittersspaced at 30 and 50 cm; (2) to use the well-known HYDRUS-2Dmodel to predict soil water distribution and drainage under dripirrigation for corn production; and (3) to analyze the effect of differ-ent N fertilization strategies, when applying PS at pre-planting anddifferent N rates at side-dress from fertigation, on corn productionand their effect on soil nitrate distribution and leaching.

2. Materials and methods

2.1. Field studies and site description

The field studies were conducted at the Mas Badia ExperimentalStation (La Tallada d’Empordà, Spain). In 2009 an irrigation studywas carried out to compare the corn yield and water use efficiency(WUE) for furrow and drip irrigation, with emitters spaced at 30 cmand 50 cm. In 2010, a fertilization study was carried out with orwithout PS application at pre-planting and with different rates of

side-dress N applications through fertigation. Drip emitters werespaced at 50 cm (according to the results obtained in 2009).

The region has a Mediterranean climate with an average annualprecipitation of 674 mm (1984–2010). The spring and fall are typ-ically rainy and the summer is typically dry (Fig. 1). Due to the

G. Arbat et al. / Agricultural Water Management 120 (2013) 11– 22 13

Table 1Soil properties in the field studies.

Depth (cm) Sand (%) Silt (%) Clay (%) Bulk densitya (g/cm3) Organic matter (%) Ks (cm/d)

0–30 31.9 51.9 16.8 1.402 (5) 1.71 18.3330–60 28.1 56.8 15.1 1.500 (3) 1.09 13.4960–90 31.9 56.9 11.2 1.457 (4) 0.51 22.41

Tts corr

wt

Ovmocidtc

psT3mss

2

wowotg

90–120 35.9 54.5 9.6

he depth indicated in the table corresponds to the soil sampling range.a Bulk density determined in the same field by Poch (2012). The values in bracke

ater deficit during the corn growing period, irrigation is neededo obtain good yields.

The studies were conducted on silt loam soil, classified asxyaquic Xerofluvents (SSS, SSS, USDA, 2010). It is an alluvial soil,ery deep, moderately well drained, without salinity problems. Theain soil properties corresponding to four consecutive soil layers

f 30 cm are summarized in Table 1. The percentage of sand, silt andlay are very similar in the different layers, and silt loam was foundn all four. The bulk density was slightly higher at the 0–30 cm soilepth and greater at 30–60 cm. This can be attributed to the soilillage that increased the porosity of the superficial soil layer andompacted the soil layer below the tillage depth (Poch, 2012).

Although the soil is fairly heterogeneous, a silt-loam texture isredominant with 0.329 cm3/cm3 and 0.141 cm3/cm3 volumetricoil water contents at 33 and 1500 kPa, respectively (Poch, 2012).he organic matter content was 1.71%, 1.09%, and 0.51% in the 0–30,0–60, and 60–90 cm soil depths respectively (Table 1). The organicatter in the deeper layers is very high, which is frequent in alluvial

oils. The water holding capacity of this soil is also very high: the 1 moil profile could hold 188 mm of available water at field capacity.

.1.1. Description of the 2009 irrigation studyIn the 2009 field study there were three irrigation treatments

ith three replications of each. The irrigation treatments consisted

f a furrow irrigation treatment and two drip irrigation treatmentsith emitters spaced 30 cm and 50 cm apart, referred to from now

n as D30 and D50. Each plot was 100 m long and 4.5 m wide, andhe field slope was 0.005 m/m. Each replication of the furrow irri-ation treatment consisted of six furrows 75 cm apart. In the drip

600

500ETc 2009

P+I, Drip D30 2009

400

.

P+I, Drip D50 2009

P+I, Furrow 2009

ETc 2010

300

P+I, Drip 2010

200

ET

c, p

reci

pit

atio

n +

irr

igat

ion (

P+

I) (

mm

)

100

0

28/68/619/529/49/4

Date

(dd/mm

Fig. 2. Crop evapotranspiration (ETc) and precipitation plus irrig

1.457 (4) 0.38 25.40

espond to the variation coefficient in %.

irrigation treatments the lateral spacing was 150 cm and the cornrows were spaced 75 cm apart. The laterals were located betweencorn rows, each of which was 37.5 cm away from the closest lateral.The discharge rate of the drip irrigation emitter was 1.6 L/h. In eachof the three treatments the amount of irrigation applied was mea-sured using commercial-grade flow accumulators with an accuracyof ±2%.

The corn yield was obtained from the mechanical harvesting of15 m2 at the beginning, the middle, and the end of the rows. Dueto a water shortage during 2009, in the drip irrigation treatments adeficit irrigation allocation of about 170 mm was applied, dividedabout evenly throughout the corn growing season in a way simi-lar to one of the strategies followed by Payero et al. (2009). In thefurrow irrigation treatment, the water applied in each irrigationevent could not be reduced because water had to reach the endof the furrows, and the irrigation criterion used was based on thecrop condition and soil appearance (USDA, 1998), which is the cri-terion most commonly used by farmers in the region. Finally, thistreatment received the approximate water needs estimated follow-ing the procedure described in Section 2.2: a total of 4792 m3/hawas delivered, divided among seven irrigation events during thegrowing season (Fig. 2).

The corn variety PR32G49 was planted on 7/4/2009 at anapproximate rate of 83,000 plants/ha. According to the N bud-

get results, following the method described in Domingo et al.(2006, 2007), the corn field did not receive any pre-planting fer-tilization and conventional side-dress fertilization using calciumammonium nitrate was applied at a rate of 150 kg N/ha at the V6stage.

ETc 2010

P+I, Furrow 2009

P+I, Drip 2010

ETc 20092009

P+I, Drip D30 2009

P+I, Drip D50 2009

16/927/87/818/7

)

ation (I + P) during the 2009 and 2010 irrigation seasons.

14 G. Arbat et al. / Agricultural Water Management 120 (2013) 11– 22

Table 2Nitrogen fertilization treatments at side-dress, rate and application date offertigation.

Treatment kg N/ha applied Total amount(kg N/ha)

13/7/2010 21/7/2010 30/7/2010

T1 0 0 0 0T2 40 0 0 40T3 40 0 35 75T4 40 35 0 75T5 40 35 75 150T6 75 75 0 150T7 75 75 75 225

2

uoP2tpfwv(

1mg2taacn

sfrtnaauttta

7wv

tt(sosa

s

Fig. 3. Finite element mesh and volumetric soil water content distribution from the

T8 150 75 0 225T9 150 75 75 300T10 150 150 0 300

.1.2. Description of the 2010 fertilization studyIn the 2010 fertilization study the whole field was irrigated

sing emitters spaced 50 cm apart and a set-up identical to thatf the drip irrigation study carried out in 2009. The corn varietyR32T16 was planted on 24/4/2010 at the same rate as that of009. The same irrigation water was applied at each fertilizationreatment: the approximate irrigation needs calculated from therocedure described in Section 2.2 (Fig. 2). There were two dif-erent pre-planting fertilization treatments with PS, and each oneas combined with ten different side-dress fertilization treatments

ia fertigation, giving a total of 20 different fertilization treatmentsTable 2).

Pre-planting fertilization treatments consisted of applying 0 or20 kg of PS N/ha on 16/4/2010. Nitrogen content in the PS was esti-ated from electrical conductivity (EC), which previously showed

ood agreement with N content (Domingo et al., 2009; Parera et al.,010). As the EC was 11 dS/m, the N content in the PS was estimatedo be 1.75 kg N/m3, and therefore PS was applied at a target rate ofpproximately 70 m3/ha in order to achieve 120 kg N/ha. Such anpplication rate is a practice commonly followed by farmers andomplies with the limit of 170 kg N/ha per year of organic fertilizerot to be exceeded in nitrate vulnerable zones (DOGC, 2009).

The PS was applied with high uniformity on 16/4/2010 using alurry tanker dribble bar with outlets spaced at 30 cm. Side-dressertilization treatments consisted of applications via fertigationanging from 0 to 300 kg N/ha (Table 2). The liquid fertilizer con-ained 16% ureic nitrogen, 8% ammonium nitrogen, and 8% nitricitrogen. It was applied using a variable-flow metering pump (with

maximum flow rate of 60 L/h). The fertilizer was dosed with volumetric flow meter logged to an irrigation controller. Man-al valves were installed in the laterals of each experimental ploto control fertigation, so that only the treatments that receivedhe same side-dress fertilization rates were irrigated at the sameime. Fertigation dates were 13/7/2010 (at tasseling), 21/7/2010nd 30/7/2010 (Table 2).

Each elemental plot was composed of six corn rows spaced5 cm apart, with a length of 10 m (the surface area of each plotas 45 m2). The corn yield was obtained from the mechanical har-

esting of 15 m2 in the middle of each plot.Initial soil NO3

−-N content was determined before and afterhe PS application on 15/4/2010 and 20/5/2010. Soil samples wereaken at 0–30, 30–60, 60–90, and 90–120 cm soil depth intervalsknown as 15, 45, 75, and 105 cm), using a representative mixedample composed of the set of treatments that received PS and thenes that did not. Each sample was composed of six different sub-

amples taken at different positions at the 0–30 cm depth intervalnd three different sub-samples at the other soil sampling depths.

During the crop season, from 30/7/2010 to 16/9/2010, theoil was sampled weekly in the three replications of treatment

lateral position (0,0 at the crossing point of the axis) corresponding to 11/8/2010simulated with HYDRUS-2D (contour plot) and measured from soil samples (num-bers on the white labels).

T4 (75 kg N/ha), with and without PS at pre-planting. Sampleswere taken at 0, 37.5, and 75 cm from the lateral, at depths of15, 45, 75, and 105 cm (Fig. 3) to determine the soil water con-tent by gravimetric method. The nitrate concentration (NO3

−-N)was also determined using 1:1 water extraction and the colori-metric method with Merckoquant® test strips and a Nitracheck®

reader. Moreover, the soil solution was collected on the follow-ing dates: 28/7/2010, 3/8/2010, 11/8/2010, 17/8/2010, 24/8/2010,31/8/2010, 16/9/2010, 22/9/2010, 28/9/2010 and 8/10/2010 withsuction cups installed at a depth of 100 cm in treatments T1(0 kg N/ha), T4 (75 kg N/ha) and T9 (300 kg N/ha), each of whichreceived 120 kg N/ha of PS as pre-planting fertilization.

2.2. Irrigation water needs

Irrigation needs were calculated using:

Irrigation water needs (mm) = ET0Kc(mm)

−effective precipitation (mm) (1)

where ET0 is Penman-Monteith reference evapotranspiration (ET0)(Allen et al., 1998) with data from the Mas Badia weather station.This meteorological station is located 150 m from the experimen-tal field and belongs to XEMA (the Catalan network of automaticweather stations). Effective precipitation was considered to be 80%of the recorded precipitation (Dastane, 1974) and crop coefficients(Kc) were determined from proposed values for Spain (Allen et al.,1998).

2.3. Water use, water use efficiency and deficit

In order to compare the results from the different years, severalindexes were defined.

ter M

W

W

W

W

d

w

d

Itw

2

tow2dc

wafw

m1wt

2

eeopmalaR(Tv3gav

1(oitaw

G. Arbat et al. / Agricultural Wa

Water use (WU) was determined for several treatments using:

U (mm) = irrigation (mm) + effective precipitation (mm) (2)

ater use efficiency was calculated following:

UE (kg/m3) = mean yield (Mg/ha)WU (mm)

× 100 (3)

ater deficit was obtained from:

eficit (mm) = ETc (mm) − WU (mm) (4)

ith ETc being crop evapotranspiration.The deficit, expressed as a percentage, was computed as follows:

eficit (%) = ETc (mm) − WU (mm)ETc (mm)

× 100 (5)

t is noteworthy that the definition of the WU in this paper did notake into account the soil water storage as the soil water contentas not measured in 2009.

.4. Weather conditions and irrigation requirements

The annual precipitation values for 2009 and 2010 were respec-ively 455 mm and 887 mm, compared with the long term averagef 674 mm (1984–2010). The annual ET0 values for 2009 and 2010ere respectively 998 and 965 mm. The annual precipitation in

009 was clearly below the average; however, the precipitationuring the spring of that year was not under average values, espe-ially in April, with more than 100 mm of precipitation (Fig. 1).

As seeding and emergence dates for the two irrigation seasonsere slightly different, accumulated crop evapotranspiration (ETc)

nd effective precipitation plus irrigation (I + P) are shown (Fig. 2)rom the emergence date to 15 days after the dough (R4) stage,hen irrigation events had already ended.

In 2009, ETc was higher than WU in the two drip irrigation treat-ents (D30 and D50 emitter spacings), the deficit being 165.2 and

73.3 mm, respectively. The deficit in the drip irrigation treatmentsas due to the shortage of water that year. In 2010, WU was prac-

ically the same as ETc.

.5. Soil water modeling

Soil water distribution was simulated based on Richards’quation and taking into account a sink term to consider cropvapotranspiration. The numerical solution of the equation wasbtained using HYDRUS-2D (Simunek et al., 2006). Soil hydraulicroperties were considered using the van Genuchten–Mualemodel (VG–M). The soil water retention curve was obtained from

representative homogenized soil sample of the predominant silt-oam texture using pressure plates. The fitted VG–M parameters,ssuming that m = 1 − 1/n, were obtained by Poch (2012) using theECT code (van Genuchten et al., 1991), with residual water content�r), alfa and n equal to 0 cm3/cm3, 0.012 and 1.311, respectively.he saturated water content (�s) was fixed using the measuredalue of 0.420 cm3/cm3 and the hydraulic conductivity (Ks) at each0 cm soil layer was estimated using the Rosetta Lite program, inte-rated in HYDRUS-2D, from sand, silt and clay content. Bulk densitynd the soil water contents at 33 and 1500 kPa, the estimated Ks

alues are shown in Table 1.Soil water distribution was simulated from 30/7/2010 to

6/9/2010. The flow domain was 75 cm wide and 150 cm deepFig. 3), and was divided in triangular finite elements with 0.5 cm

f side length near the drip emitter. The dimension of the elementsncreased with depth and horizontal distance from the emitter untilhey reached 2 cm of side length. The shorter length of the elementst the soil surface was selected because at this position water fluxesere more active. A no-flow boundary condition was imposed on

anagement 120 (2013) 11– 22 15

both sides of the domain because of its symmetry. At the soil surfacetwo different regions were defined. Within 20 cm of the emitter, aconstant-flow boundary condition during the irrigation events wasdefined, in agreement with the close-to-saturation surface regionbesides the lateral. In the region from 20 to 75 cm, a variable-flowboundary condition was defined to take into account precipitationand evaporation. At the bottom of the flow domain a unit verti-cal hydraulic gradient to simulate drainage was imposed as theboundary condition.

Feddes’ water uptake reduction model (Feddes et al., 1978) wasused in the simulations. The value of the limiting pressure headbelow which roots can no longer extract water at the maximumrate was assumed to be −31.9 kPa, according to the values proposedby Wesseling (1991).

Plant water extraction was considered to occur from 0 to 110 cmdepth, with a rate that falls as the depth increases. The extrac-tion rate was considered to be proportional to the observed rootlength density at nearby experimental corn fields (Ramos, 2005),which observed that mean values (±standard deviations) of theroot length density (cm/cm3 soil) at the tassel stage decreased from5.14(±0.59) at the 0–30 cm depth interval to 0.93(±0.13) at the90–120 cm depth interval.

Once the simulations were carried out the soil water contentobtained at the points indicated in Fig. 3 were compared with themeasured ones from the soil samples at the corresponding posi-tions throughout the entire simulated period. The observed andsimulated soil water contents were compared to predict the good-ness of the predictions. The coefficient of determination (R2), theindex of agreement (d) (Willmott, 1981), and the root mean squareerror (RMSE) were used for the comparisons. The R2 indicates thedegree of linear correlation between the observed and predictedvalues, varying from 0 to 1, with the higher values indicating bet-ter agreement with the model. But this statistic has been criticizedbecause values near to 1 could be obtained when model-simulatedvalues differ considerably in magnitude (Willmott, 1981; Legatesand McCabe, 1999). The index of agreement (d) has an interpre-tation similar to R2, but corrects the mentioned inconvenience,and the RMSE has the advantage of expressing the error with thesame units of the variable, which can provide more informationabout model efficiency. R2 and RMSE have been previously used tocompare predicted and measured soil water contents in differentdrip irrigation experiments (Skaggs et al., 2004; Arbat et al., 2008;Kandelous and Simunek, 2010).

Lastly, the nitrate leaching for treatments receivingPS—T1(0 kg N/ha), T4 (75 kg N/ha), and T9 (300 kg N/ha)—wascalculated from the nitrate concentration collected in the suctioncups multiplied by the water flow below 100 cm depth simulatedwith HYDRUS-2D. For the dates in which the nitrate concentrationin the leachate was not analyzed, its value was assumed to varylinearly from the previous and following dates.

2.6. Statistical analyses

The GLM (general linear model) procedure of the SAS statisti-cal package (SAS Institute, Cary, NC, USA) was used to carry outan analysis of variance at 0.05 of significance level. It analyzedthe soil nitrate content including as fixed effects the pre-plantingfertilization application, the soil depth, the horizontal distanceto the lateral, and their interactions. The model used to analyze

the nitrate concentration in the leached solution includes as fixedeffects the post-planting fertilization treatment, the date, and theirinteractions. The model used to analyze the yield included the irri-gation treatment (furrow, D30 and D50) in 2009 and the pre- andpost-planting fertilization and their interactions in 2010. Tukey’s

16 G. Arbat et al. / Agricultural Water M

Table 3Yield and irrigation indexes for the irrigation treatments in 2009.

Furrow Drip D30 Drip D50

Corn yield (Mg/ha) 13.99A 13.70AB 12.92B

Irrigation water (mm) 479.2 249.6 241.5WU (mm) 532.3 302.7 294.6WUE (kg/m3) 2.63B 4.53A 4.39A

Deficit (mm) −64.4 165.2 173.3Deficit (%) −13.8 35.3 37.0

ACP

pw

3

3

d(

ceswi2

In 2010, the soil water content (SWC) throughout the irrigation

Faw

negative value of the deficit means that the WU was greater than ETc.orn yield and WUE means with different letters are significantly different at the

< 0.05 probability level.

airwise comparison was used to identify and compare means thatere different at probabilities of 0.05 or less.

. Results and discussion

.1. Results of the irrigation study in 2009

In the 2009 experiment much less water was delivered in therip irrigation treatments than in the furrow irrigation treatmentTable 3), although the corn yield was not affected.

The remarkably high WUE in the drip irrigation field tests of 2009ompared with that shown in other works (Howell, 2001; Arbatt al., 2010) is explained because in its definition (Section 2.3) the

oil water depletion from the root zone during the growing seasonas not considered. Thus, taking into account that the water hold-

ng capacity of the shallower 1 m soil profile was 188 mm, and that00 mm of accumulated precipitation was registered before sowing

0.30

0.35

3)

0.20

0.25

3/c

m

0.10

0.15So

il w

ate

r co

nte

nt

(cm

0.30

0.35

/cm

3)

0.20

0.25

3

0.10

0.15Soil

wate

r co

nte

nt

(cm

01/0

4/10

15/0

4/10

29/0

4/10

13/0

5/10

27/0

5/10

10/0

6/10

24/0

6/10

08/0

7/10

22/0

7/10

05/0

Date (dd/mm /yy

ig. 4. Evolution of mean soil water contents at different soil depths (a) and horizontal dverage water content for a certain depth or distance taking into account the three replicater content at 33 kPa and 1500 kPa respectively.

anagement 120 (2013) 11– 22

(during February, March and April 2009), the water deficit of 165and 173 mm in the D30 and D50 drip irrigation treatments (Table 3)could be alleviated. Similar results were obtained when Payeroet al. (2009) studied the effects of a deficit irrigation allocation of150 mm in subsurface drip irrigated corn. These authors concludedthat dividing the allocation fairly evenly during the corn growingseason was a good strategy in some years, depending on in-seasonrainfall, weather conditions, and stored soil water at planting. Inthe present work the stored soil water together with the reducedirrigation could satisfy the corn water needs.

The yield and WUE was not significantly affected by the differentemitter spacings of 30 and 50 cm (Table 3), which suggests that thisrange of emitter spacing is acceptable even under deficit irrigation.The good water holding capacity for this deep, silt loam soil maybuffer differences that would likely occur between emitter spacingsand in coarser, sandier soils. Similar results were obtained with SDIby Arbat et al. (2010) when emitter spacings from 30 to 120 cm wereused in deep soils with good holding capacity. An emitter spacingof 50 cm has been previously reported to obtain high yields in asandy loam soil with corn in the Mediterranean region (Lekakiset al., 2011).

3.2. Soil water distribution under drip irrigation

season was significantly (P < 0.05) influenced by the depth and thehorizontal distance from the lateral, but not by the application ofslurry. The soil water content diminished as the horizontal distanceto the lateral and the depth increased (Fig. 4).

15 cm

a)

45 cm

75 cm

105 cm

at 33 kPa

at 1500 kPa

0 cm

b)

37.5 cm

75 cm

at 33 kPa

at 1500 kPa

8/10

19/0

8/10

02/0

9/10

16/0

9/10

30/0

9/10

14/1

0/10

)

istance from the lateral (b) in treatment T4. Each point in the plot represents theations. The continuous black line and the dashed line represent the volumetric soil

G. Arbat et al. / Agricultural Water Management 120 (2013) 11– 22 17

140

160 a)

80

100

120

- -N/h

a

15 cm

45 cm

75 cm

40

60

80

kg

NO

3

105 cm

0

20

120

140

160

cm

b)

60

80

100

kg

NO

3- -N

/ha 15

45 cm

75 cm

105 cm

0

20

40

01/0

4/10

15/0

4/10

29/0

4/10

13/0

5/10

27/0

5/10

10/0

6/10

24/0

6/10

08/0

7/10

22/0

7/10

05/0

8/10

19/0

8/10

02/0

9/10

16/0

9/10

30/0

9/10

14/1

0/10

Date (dd/mm /yy)

F eatmev t the tf

pdtA(tdtsd0t0rssoiwibstaa

ig. 5. Evolution of soil nitrate content at soil extract at different soil depths in trertical bars indicate the standard deviation for a certain depth, taking into accounrom 3 distances × 3 replications = 9 different measurements.

The SWC at 105 cm depth was higher that at the other sam-led depths (15, 45 and 75 cm) during the two first samplingates (15/4/2010 and 20/5/2010), just before planting and untilhe first vegetative stages (V3) before the irrigation period started.t these initial stages the SWC was approximately 0.27 cm3/cm3

this value corresponds to a low soil suction of about 100 kPa inhe soil water retention curve), while on the following samplingates (30/7/2010 and 4/8/2010 and 11/8/2010) the soil water con-ent at 105 cm decreased with the soil depth, coinciding with thetages of maximum water demand for corn (from tasseling toough). The SWC at this depth was reduced to a minimum (i.e.,.18 cm3/cm3) on 11/8/2010. From this date the SWC increased upo 0.21 cm3/cm3 on 16/9/2010 (during physiological maturity) and.23 cm3/cm3 on 8/10/2010 after the corn was harvested and theainfall events of September filled in the soil water capacity of theoil profile (Fig. 4).The SWC was maintained relatively high in alloil depths throughout the irrigation season. The minimum valuef 0.18 cm3/cm3 would correspond to a pressure head of approx-mately 400 kPa according the soil water retention curve (SWRC),

hich would not suppose an important restriction for corn accord-ng the model of Feddes et al. (1978) and the coefficients proposed

y Wesseling (1991). Therefore, taking into account that the soilamples were extracted at the mid-distance between two consecu-ive emitters, the adopted emitter spacing of 50 cm did not suppose

restriction for the water distribution along the lateral. This waslso confirmed by the irrigation field study carried out in 2009,

nt T4, (a) with application of pig slurry, (b) without application of pig slurry. Thehree replications. Therefore, each standard deviation of each value was calculated

where no significant differences in the yield and WUE were foundbetween emitters spaced at 30 and 50 cm (as previously shown inSection 3.1), and consequently 50 cm would be technically sound,as reported in other field studies (Arbat et al., 2010; Lekakis et al.,2011).

For purely illustrative purposes, the soil water content distribu-tion on 11/8/2010, simulated with HYDRUS-2D and measured inspecific soil locations, is shown in Fig. 3. The same tendency shownin this figure, i.e., that water content is greater at the soil surfaceand alongside the lateral, was observed throughout the irrigationseason (Fig. 4a and b). The wetting front reached the area wherethe plants grew (37.5 cm from the lateral) and the driest regionwas at the mid-point between two adjacent emitters (75 cm fromthe lateral). Similarly to the wetting patterns shown in Hansonet al. (2006) for a loam soil, the wetted region exhibited a verticallyelongated shape and extended from 60 cm to 75 cm horizontallyand 100 cm vertically. In the present study some overlap betweenthe wetting patterns produced by the laterals spaced 150 cm apartoccurred (Fig. 3).

Throughout the simulated period (30/7/2010 to 16/9/2010) theleaching fraction, LF (ratio between drainage and irrigation plus

precipitation), taking into account that the water drained below100 cm depth simulated with HYDRUS-2D, was 0.15. This value islower than that obtained with surface irrigated corn by Daudénand Quílez (2004), which ranged from 0.36 to 0.47, and was withinthe range of those obtained by Hanson et al. (2008) in subsurface

18 G. Arbat et al. / Agricultural Water Management 120 (2013) 11– 22

120 a)

80

100

3- -N

/ha 0 cm

37.5 cm

cm

20

40

60

kg

NO 75

0

100

120 b)

60

80

kg

NO

3- -N

/ha 0 cm

37.5 cm

75 cm

20

40

0

01/0

4/10

15/0

4/10

29/0

4/10

13/0

5/10

27/0

5/10

10/0

6/10

24/0

6/10

08/0

7/10

22/0

7/10

05/0

8/10

19/0

8/10

02/0

9/10

16/0

9/10

30/0

9/10

14/1

0/10

Date (dd/mm/yy)

F e laters into ac

dae

3H

tciesSsc2em2rpa0et

ig. 6. Evolution of soil nitrate content depending on the horizontal distance to thlurry. The vertical bars indicate the standard deviation for a certain distance, takingalculated from 4 depths × 3 replications = 12 different measurements.

rip irrigated tomato fields that ranged from 0.07 to 0.31 whenmounts of applied water ranged from 60 to 115% of the potentialvapotranspiration the LF values.

.3. Comparison of the SWC measured and simulated withYDRUS-2D

The SWC at the sampled locations (Fig. 3) and sampling dateshroughout the simulated period (30/7/2010 to 16/9/2010) wereompared with the simulated SWC using HYDRUS-2D. The R2, thendex of agreement (d) (Willmott, 1981), and the root mean squarerror (RMSE) were 0.61, 0.82 and 0.040 cm3/cm3, respectively,howing good agreement between the measured and simulatedWC. Similar results were obtained by Skaggs et al. (2004) who, in ahort-term SDI field tests comparing soil-core measured soil waterontents with the corresponding values calculated with HYDRUS-D, found that the RMSE ranged from 0.013 to 0.041 cm3/cm3. Arbatt al. (2008), when comparing the measured and simulated soilatric suction throughout an irrigation campaign using HYDRUS-

D with field calibrated soil hydraulic functions, found that R2

anged from 0.52 to 0.82. Kandelous and Simunek (2010) com-

ared SWC measured and simulated with HYDRUS-2D in laboratorynd field SDI tests and found that RMSE ranged from 0.011 to.045 cm3/cm3 and R2 from 0.57 to 0.99. Skaggs et al. (2004), Arbatt al. (2008), and Kandelous and Simunek (2010) found values forhe R2 and/or RMSE that were similar to that obtained in the present

al in treatment T4, (a) with application of pig slurry (b) without application of pigccount the three replications. Therefore each standard deviation of each value was

study and concluded that the predictions of HYDRUS-2D were ingood agreement with the experimental data and that this modelcould be a useful tool for monitoring and managing drip irrigationsystems. The same conclusion can be drawn from the present study.

3.4. Soil nitrate distribution under drip irrigation

Before the PS application on 15/4/2010 soil NO3−-N contents at

15, 45, 75, and 105 cm soil depths were respectively 33.7, 44.8, 35.5,and 40.2 kg NO3

−-N/ha, and after the PS application, on 20/5/2010,they were 36.2, 68.0, 49.7, and 12.8 kg NO3

−-N/ha in the plots thatreceived PS and 29.9, 40.8, 27.8, and 21.8 kg NO3

−-N/ha in the plotsthat did not (Fig. 5). Thus, in the plots that received PS the nitrateincreased from 15 to 75 cm soil depths and decreased at 105 cmprobably due to the important precipitation events that took placein May 2010 (Fig. 1), which accumulated nearly 150 mm. The initialsoil NO3

−-N content in the present study was lower than the onesshown in similar studies that received PS applications in previousyears (Daudén and Quílez, 2004; Berenguer et al., 2008, 2009; Yagüeand Quílez, 2010; Cela et al., 2011), because the field did not receiverecent, previous applications of organic fertilizer and, as explained

in Section 2.1, only 150 kg N/ha were applied in the previous yearbased on N fertilization recommendations resulting from the useof a nitrogen budget method (Domingo et al., 2006, 2007). In thisregard, Berenguer et al. (2008, 2009), Yagüe and Quílez (2010), andCela et al. (2011) found that soil NO3

−-N content before fertilization

ter Management 120 (2013) 11– 22 19

wfN

wbptPsmfam(i

tdsmoaitwNis

tcwwcnctil

sarotttc1(gap

3

pdot(ccc

G. Arbat et al. / Agricultural Wa

as influenced by N fertilization in previous years, and that the Nertilization recommendations should take into account the NO3

−- content before sowing in order to prevent N losses.

In the present study, except for a specific date (16/9/2010), thereere no significant differences (P > 0.05) in the soil nitrate content

etween the treatments that did or did not receive slurry beforelanting. The higher NO3

−-N content on this date in the treatmenthat received PS can be explained by the mineralization from theS. In furrow irrigated corn in the same field as that of the presenttudy, Poch (2012) used the LIXIM code (Mary et al., 1999) to esti-ate the mineralized N from the soil. With about 70 kg NO3

−-N/harom 0 to 90 cm depth before planting, his results showed that anverage of 136 and 165 kg N/ha were mineralized during the sum-ers of the years 2003 and 2004, respectively. Berenguer et al.

2009) estimated that N mineralized varied from 31 to 95 kg/han three studied corn seasons.

During most of the dates of the present study, the nitrate con-ent varied significantly depending on the depth, the horizontalistance from the lateral, and their interaction (Figs. 5 and 6). Theoil nitrate content in the first 15 cm of soil depth (Fig. 5) in treat-ent T4 (75 kg N/ha) was significantly higher (P < 0.05) than that

f the other soil depths on all the dates except the two initial onesnd 31/8/2010, showing the effect of the NO3

−-N applied from therrigation system. Once the crop was established (from 20/5/2010),he nitrate content evolution in the four sampled depth intervalsas very close (Fig. 5). With or without PS application, the soilO3

−-N content did not increase between 15/4/2010, before sow-ng, and 8/10/2010, after the harvest. This suggests there was nooil N enrichment during the growing season in this treatment.

Soil nitrate content close to the lateral (0 cm in Fig. 6) was lowerhan in the other sampled positions for most of the dates. The arealosest to the plant (37.5 cm) showed the highest values for nitrate,hile after 24/8/2010 the area farthest from the lateral (75 cm) washere the highest nitrate concentration was found. This date coin-

ided with the dough stage, at which the corn reduced its watereeds (Allen et al., 1998; Payero et al., 2009) and there was aonsequent reduction in soil water extraction. As the irrigation con-inued at the same rate as in the previous days, the wetted volumencreased its extension and dragged the nitrate further from theateral.

For illustrative purposes Fig. 7, corresponding to 11/8/2010,hows that the soil nitrate content was higher at the soil surfacend at 37.5 and 75 cm from the lateral, which agrees with theesults obtained by Hanson et al. (2006). The simulation resultsf these authors indicate that nitrate moves from the position ofhe emitters to the periphery of the wetting front and accumulateshere, due to root water uptake and dispersion during downwardransport (Hanson et al., 2006). The same was observed in non-ropped laboratory experiments by Bar-Yosef and Sheikholslami,976, Clothier and Sauer (1988), and Li and Liu (2011). Cote et al.2003), using models to simulate different irrigation strategies, sug-ested that it is preferable to apply the nitrate through fertigationt the end of the events to prevent it from being leached to theeriphery of the wetted soil volume.

.5. Nitrate concentration in the leached solution

In the leached solution from treatment T9 (PS applied at pre-lanting and 300 kg N/ha at side-dress), the NO3

−-N concentrationepended on the date, increasing significantly (P < 0.05) at the endf the crop cycle when crop extractions were reduced (Fig. 8). In

reatments T1 (which only received PS at pre-planting) and T4which besides PS received 75 kg N/ha at side-dress), the nitrateoncentration did not significantly depend on the date. The meanoncentration over the entire sampling period was not statisti-ally different between treatments T1 (42.6 mg/l NO3

−-N) and T4

Fig. 7. Measured distribution of the soil nitrate content on 11/8/2010 at treatmentT4, with application of pig slurry at pre-planting.

(35.0 mg/l NO3−-N), both of which were significantly smaller than

treatment T9 (104.9 mg/l NO3−-N).

The greatest differences in the NO3−-N concentration were

observed on 29/9/2010 (Fig. 8), just after harvest, and were sig-nificantly higher in treatment T9 (203.9 mg/l NO3

−-N) than intreatments T1 (5.9 mg/l NO3

−-N) and T4 (23.1 mg/l NO3−-N). Villar-

Mir et al. (2002) and Berenguer et al. (2008) pointed out thathigh rates of N fertilization (as was the case for treatment T9 inthe present study) generated high levels of soil residual NO3

−-N content which could increase the risk of N leaching duringautumn–winter, and constitute a potential source of environmen-tal problems. In the present study it is also noticeable that thehigher nitrate concentrations in the leached solution were obtainedjust after the harvest, when the crop was not able to extractnitrate.Treatments T1 and T4 did not show significant differences,although at the end of the cycle the NO3

−-N concentration in theleached solution tended to be lower in treatment T1 (without nitro-gen inputs during the growing season) than in T4. From 29/9/2010the nitrate concentration tended to decrease in all the treatments,due to the leaching produced by the precipitation events thatoccurred during this period. (From 16/9/2010 to 29/9/2010 therewas about 100 mm of accumulated precipitation.)

The water drainage below 100 cm depth simulated withHYDRUS-2D together with the nitrate content measured in thesolution recovered in the suction cups from 30/8/2010 to 28/9/2010showed that most of the nitrate leaching was produced from thedough stage (Fig. 9). The amount of nitrate drained was 17.8, 11.3,and 53.3 kg NO3

−-N/ha for treatments T1, T4, and T9 respectively.As can be seen, minimal differences were encountered between T1and T4 but the N drained in treatment T9 was more than three timesthe amount leached in the other two treatments. This corresponds

to the higher nitrate concentration found in the solution recoveredin the suction cups (Fig. 8).

In a furrow irrigation experiment that received PS as fertil-izer, Daudén and Quílez (2004) concluded that in Mediterranean

20 G. Arbat et al. / Agricultural Water Management 120 (2013) 11– 22

250

300

- -N

/ l

) . Treatment 1 Treatment 4 Treatment 9

200

3

100

150

50

0

28/07

/10

04/0

8/10

11/0

8/10

18/0

8/10

25/08

/10

01/0

9/10

08/0

9/10

15/0

9/10

22/09

/10

29/0

9/10

06/1

0/10

Nit

rate

in

th

e le

ach

ed s

olu

tion

(m

g N

O

Date (dd/mm/yy)

F 2010 dd ignificd

chpimardns(itYe

lQ

Fs

ig. 8. Evolution of the nitrate concentration in the leached solution during the year

ifferences (P < 0.05) among different dates. For each date, lower-case letters mean seviation for the three replications of each treatment.

limates with low rainfall, as opposed to studies carried out in moreumid climates, nitrate leaching mainly occurred during the crop-ing season. Nevertheless, in the present study, which used drip

rrigation, nitrate leaching during the irrigation season was mini-al and mainly occurred in the fall when important rainfall events

re typical. Similar results were obtained by Poch (2012) using fur-ow irrigation for corn in the same region where nitrate lossesuring the cropping season ranged from 138 to 276 kg N/ha. Theseitrate losses are much higher than those obtained in the presenttudy, in which drip irrigation was used. In this respect Kurunc et al.2011) concluded that switching from surface or furrow to sprinklerrrigation reduces the risk of nitrate pollution. The same would berue of drip irrigation, which achieves high irrigation uniformities.

agüe and Quílez (2010) also indicated that increasing irrigationfficiency and uniformity are essential for nitrate pollution control.

Although most of the authors agree that the risk of nitrateeaching depends on the weather and soil conditions (Daudén anduílez, 2004; Hu et al., 2008; Kurunc et al., 2011; Poch, 2012), in

40

30

35

20

25

10

15

Pre

cip

ita

tio

n a

nd

Dra

ina

ge

(mm

)

0

5

30/0

7/10

06/0

8/10

13/0

8/10

20/0

8/10

27/0

8/10

0

Date (dd/m

Precipitation Drainage at 1

ig. 9. Precipitation, drainage at 1 m soil depth and accumulated nitrate leaching (kg NOide-dress).

epending on the treatment. For each treatment, upper-case letters mean significantant differences (P > 0.05) among treatments. The vertical bars indicate the standard

studies using PS as a fertilizer, N is lost and the nitrate leachingis not always clearly related to the N fertilization rate (Berengueret al., 2009). In this respect, Yagüe and Quílez (2010) showed thatthe effects of fertilization strategies on nitrate concentration andmass in drainage waters were detected only after three years ofrepeated PS applications.

3.6. Corn yield

With regard to the 2010 experiment (Fig. 10), significant differ-ences (P < 0.05) in corn yield were observed between the mean yieldof the treatments that received organic fertilizer at pre-planting

and those that did not, 13,717 and 11,833 kg/ha, respectively. Therewere no significant differences among the individual treatments(Fig. 10). The treatments that did not receive PS at pre-plantingand also received the lower nitrogen fertilizer rates at side-dress(T1–T4, with less than 75 kg N/ha) produced less yield.

60

50

30

40

3- -N

/ha

20

kg

NO

0

10

3/09

/10

10/0

9/10

17/0

9/10

24/0

9/10

m/yy)

m T1 T4 T9

3−-N/ha) for treatments T1, T4 and T9 receiving PS and 0, 40 and 300 kg N/ha at

G. Arbat et al. / Agricultural Water Management 120 (2013) 11– 22 21

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

T1 T2 T3 T4 T5 T6 T7 T8 T9 T10

ment

Yie

ld (

kg

/ha

)

Without slurry

application

With slurry

application

F n with( devia

d(w(ctBPoycab3Pmrswiw(

4

tisoyatto

m

st

salri

Treat

ig. 10. Corn yield, in the 2010 field tests, depending on the dressing fertilizatioP > 0.05) were observed among treatments. The vertical bars indicate the standard

In the treatment that received low rates of mineral N at side-ress (T1–T4) but received 120 kg N/ha from PS at pre-planting70 m3/ha), the mean yield was not substantially reduced comparedith those treatments that received higher rates of N at side-dress

T5–T10) (Fig. 10), since the nitrogen needed for crop developmentould come from the organic application and the nitrification ofhe ammonia contained in the slurry. With this understanding,erenguer et al. (2008) already concluded that the application ofS at a rate of 60 m3/ha without the addition of any other kindf mineral N side-dress fertilization produced the maximum grainields (from 12 to 16 Mg/ha), suggesting that optimal grain yieldsan be obtained by fertilizing only with PS. On the other hand, Yagüend Quílez (2010) did not find significant corn yield differencesetween different fertilization strategies receiving PS at rates from0 to 120 m3/ha and reported that the pre-planting application ofS at 30 m3/ha supplemented with mineral N at side-dress was theost efficient from an environmental standpoint, as it increased the

elationship between grain yield and N leached.The present studyuggests that the application of 70 m3/ha of PS (120 kg NO3

−-N/ha)ith a minimal application of mineral N at side-dress (40–75 kg/ha

n T2–T4) would lead to optimal grain yields (about 14 Mg/ha),ithout contravening the existing EU directives on nitrate pollution

European Union, 1991).

. Conclusions

A preliminary irrigation experiment carried out in 2009 showedhat drip irrigation allowed the application of a controlled deficitrrigation of 170 mm distributed over the entire corn growing sea-on without reduction of corn yield compared with corn that wasnly furrow irrigated. There were no significant differences in cornield and water productivity for emitters spaced 30 and 50 cmpart, even under deficit irrigation, which suggests that both emit-er spacings are acceptable. The good water holding capacity forhis deep, silt loam soil may buffer differences that would likelyccur in coarser, sandier soils.

The following conclusions follow from the fertilization experi-ents in which PS was applied:The soil water contents predicted with the HYDRUS-2D model

howed good agreement with the measured from soil sampleshroughout the cropping season.

In 2010 the majority of nitrate leaching occurred after the dough

tage and was especially important after physiological maturityssociated with high precipitations that produced drainage andeached the residual soil NO3

−-N, especially in the treatments thateceived excessive amounts of N. Thus, it can be deduced that driprrigated corn with irrigation rates calculated from FAO 56 barely

and without application of pig slurry at pre-planting. No significant differencestion for the three replications of each treatment.

produced deep drainage or nitrate leaching during the growingseason.

The soil nitrate distribution throughout the irrigation seasonindicates that it moves through the water drawn from the lateral,accumulating at the periphery wetting volume, confirming its highmobility in the soil.

The mean grain corn yield increased from 11.8 to 13.7 Mg/hawhen 120 kg N/ha from PS were applied at pre-planting. With rel-atively low initial nitrate content in the soil, about 40 kg/ha at theshallower 105 cm of soil depth, the application of PS at pre-plantingmaintained the corn yield with minimal or no nitrogen applica-tions during the growing season. Application rates of 40–75 kg N/hacombined with 120 kg N/ha from PS produced near maximum grainyields with minimum N leaching and did not contravene the exist-ing EU directives on nitrate pollution. Nitrogen rates up to 150 kg/haat side-dressing increased the nitrate concentration in the leachatewithout increasing the corn yield.

Acknowledgement

The authors would like to express their gratitude to the VISpanish National Plan of Scientific Research, Devevelopment andTechnological Innovation 2008–2011 for its financial support of thisstudy through grant AGL2009-12897-C02-00.

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