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Agricultural Water Management 150 (2015) 46–56

Contents lists available at ScienceDirect

Agricultural Water Management

jou rn al hom epage: www.elsev ier .com/ locat e/agwat

ow much do sod-based rotations reduce nitrate leaching in a cerealropping system?

aise Robinson Kunratha,b, Christophe de Berrangerc, Xavier Charrierc, Franc ois Gastal c,aulo César de Faccio Carvalhob, Gilles Lemairea, Jean-Claude Emilec,ean-Louis Duranda,∗

Unité de Recherche Pluridisciplinaire Prairies et Plantes Fourragères, INRA, Lusignan 86600, FranceUniversidade Federal do Rio Grande do Sul, Av. Bento Gonc alves 7712, 91501-970 Porto Alegre, RS, BrazilUnité Expérimentale Ferlus, INRA, 86600 Lusignan, France

r t i c l e i n f o

rticle history:eceived 13 August 2014ccepted 26 November 2014vailable online 18 December 2014

eywords:itrateater

eachingrasslandrop rotationrainage

a b s t r a c t

Nitrogen is essential to improving agricultural production systems, explaining why the contaminationof groundwater by this nutrient is widespread. The aim of this paper was to describe data collectedover 9 years on estimated leaching levels using a simple computation procedure and measurementsof soil water content and water balance, nitrate concentrations in drainage water and meteorologicaldata, and to assess the impacts of the duration of the grassland phase and the level of nitrogen fertil-ization on grassland on the drainage water quality. The study was carried out at a site of the Long-termEnvironmental Research Observation and Experimentation facility (SOERE) for Environmental Research-Agro-ecosystems, Biogeochemical Cycles and Biodiversity, run by the INRA experimental unit of Lusignan.The experimental treatments were sequences of maize, wheat and barley with different grassland rota-tional periods (a pure arable crop rotation; three or six years of grassland receiving high-level nitrogenapplications; six years of grassland with a low N application rate and long-term grassland with nitrogenapplication). The study covered the period from April 2005 to June 2013, during which most drainageoccurred in the autumn and early winter. Treatments with the longest duration of grassland exhibitedless drainage than those containing a higher proportion of arable crops. The average nitrate concentrationwas 52.7 ± 38.63 mg NO3 L−1 under a pure crop rotation, compared to 14.9 ± 14.76 mg NO3 L−1 under apermanent grassland treatment. There were significant differences (P < 0.0001) in cumulative nitrogen

−1 −1

leaching between the different cropping systems, ranging from 9 to 37 kg N ha year . The introduc-tion of mowed grassland sequences into this arable crop rotation caused a marked reduction in thenitrate levels in groundwater, and the greater the proportion of grassland within the rotation the moremarkedly was the NO3

− concentration reduced, whatever the level of N fertilization during the grasslandsequence.

© 2014 Elsevier B.V. All rights reserved.

. Introduction

Nitrogen is crucial to agriculture production systems. On an his-oric timescale, improving nitrogen availability has been the mainriver of improvements in crop yield (Sinclair and Rufty, 2012), and

∗ Corresponding author. Tel.: +33 549556094.E-mail addresses: taiserk@gmail.com (T.R. Kunrath),

hristophe.deberranger@lusignan.inra.fr (C. de Berranger),avier.charrier@lusignan.inra.fr (X. Charrier), Francois.Gastal@lusignan.inra.frF. Gastal), paulocfc@ufrgs.br (P.C. de Faccio Carvalho),illes.Lemaire@lusignan.inra.fr (G. Lemaire), Jean-claude.emile@lusignan.inra.fr

J.-C. Emile), jean-louis.durand@lusignan.inra.fr (J.-L. Durand).

ttp://dx.doi.org/10.1016/j.agwat.2014.11.015378-3774/© 2014 Elsevier B.V. All rights reserved.

data aggregated at a worldwide level and over several decades haveshown a strong link between agriculture production and fertilizeruse (Tilman et al., 2002). Nevertheless, the use of large quanti-ties of N in intensive agricultural systems has, through nitrogencascades (Galloway and Cowling, 2002), led to severe environ-mental contamination (Robertson and Vitousek, 2009; Datta et al.,1997; Guillemin and Roux, 1992; Addiscott et al., 1991). The nitratecontamination of surface water and groundwater is common inwatersheds dominated by agricultural activities (Jégo et al., 2012;

Townsend et al., 2003). Nitrate leaching is a serious issue in largeareas of cultivated land. The European Union has implemented aprocedure that intends to restore good quality water resources by2015 (Directive 2000/60/EC), and the Nitrate Directive (91/676/EC)

ater

intIgsanwmiTbsN2tsdtriapgt2

atayacal

2

2

tacwuos

bmwaata4rgGi(id

T.R. Kunrath et al. / Agricultural W

ncluded a law designed to control nitrogen pollution by limitingitrate concentrations to <50 mg L−1 in water. Land use is a key fac-or in nitrate pollution (Kopácek et al., 2013a; Kvítek et al., 2009).ndeed, several studies have shown that leaching is reduced inrasslands (Kopácek et al., 2013a; Kvítek et al., 2009) because oftrong coupling between the C and N cycles, associated with plantutotrophy and intense microbial biomass turnover under perma-ent vegetation (Soussana and Lemaire, 2014). Furthermore, evenith high N fertilization rates, nitrate leaching under grasslandsanaged by cutting remains very limited, whatever the origin of N

nputs: N mineral fertilization or N2 fixation (Ledgard et al., 2009).he introduction of grasslands into arable cropping systems as sod-ased rotations, or ley farming within integrated crop–livestockystems, could therefore be considered as an option to reduce local

emissions into hydrosystems (Lemaire et al., 2014; Attard et al.,011; Franzluebbers, 2007). However, several questions still needo be answered concerning the environmental benefit of theseystems, concerning: (i) quantification of the grassland effect onrainage water quality at the level of a whole crop rotation as a func-ion of the duration of the “grassland” phase and then regarding theelative importance of grassland areas versus arable cropping areasn a land use system; (ii) the impact of the level of intensification –nd more specifically of N fertilization use – during the grasslandhase, and (iii) an analysis of a risk of peak nitrate leaching afterrassland re-cultivation as a consequence of higher N mineraliza-ion associated with increased soil organic matter (Bot and Benites,005), particularly in cases where cereals are cropped with tillage.

Long-term experiments are therefore necessary to assess themount of nitrogen that is leached under different systems withhe same soil and climate conditions (Kopácek et al., 2013b). Theim of this paper was therefore to supply data collected over 9ears to estimate leaching using a simple computation procedurend measurements of soil water content and water balance, nitrateoncentrations in drainage water and meteorological data, and tossess the impact of the duration of the grassland phase and theevel of grassland nitrogen fertilization on drainage water quality.

. Materials and methods

.1. Study site and experimental design

The INRA Lusignan site (46◦25′12.91′′N; 0◦07′29.35′′E) is part ofhe SOERE ACBB (Long-term Environmental Research Observationnd Experimentation facility for Agro-ecosystems, Biogeochemi-al Cycles and Biodiversity; http://www.soere-acbb.com/) and itas set up in 2004. This site was designed by INRA to increase ournderstanding of the effects of temporary grassland managementn the environmental outputs of mixed arable cropping/grasslandsystems.

The experimental treatments are sequences of maize, wheat andarley with different grassland rotational periods (Fig. 1). Treat-ent 1 (C) is a pure arable crop rotation of maize/wheat/barleyith N fertilization rates adjusted to the potential yield achiev-

ble for each of these crops in this region. Treatments 2 (C3G3)nd 3 (G6C3) are rotations of maize/wheat/barley alternating withhree or six years of grassland receiving high nitrogen applicationsdjusted to achieve near maximum forage production. Treatment

(G6C3N−) is similar to treatment 3 but with a low N applicationate during the grassland phase. Treatment 5 (G) is a long-termrassland with nitrogen applications as for treatments C3G3 and6C3. The grassland is composed of a mixture of Festuca arund-

nacea (Cv Soni), Lolium perenne (Cv Milca) and Dactylis glomerataCv Ludac). Management of the crop sequence was ensured accord-ng to agricultural practices to achieve a yield close to the potentialetermined in the region by soil and climate. The N fertilization

Management 150 (2015) 46–56 47

application rates and the timing of all crop sequences were adjustedevery year using the PC-AZOTE software program (Angevin, 1999).For grassland sequences, regular estimations of the Nitrogen Nutri-tion Index (NNI) were made according to the method describedby Farruggia et al. (2004) and Duru (2004). The timing (at sow-ing for maize, February and heading for barley and wheat) andrates (Table A.1) of fertilizer applications were regulated to main-tain an NNI of between 0.9 and 1.0, i.e. close to a non-limiting Nnutrition allowing for potential herbage production (Lemaire et al.,2008).

The experimental period of this study lasted from April 2005to June 2012. The varieties sown, together with the dates of plant-ing, harvesting and applications of nitrogen are shown in Table A.1(Appendix A). The five treatments were designed on a two blockexperimental system with individual plots of 4000 m2 each. Foreach plot, the grass was cut to 5–7 cm stubble height and harvested(Haldrup) four times each year and herbage was removed from thefield.

2.2. Soil and meteorological data

The soil is a Cambisol with a silty-loamy texture in the sur-face horizon and clay in the subsoil horizon (Chabbi et al., 2009;Hubert, 2008). The percentage of clay at the study site ranges from17% in the topsoil to 48% in the deep soil horizon (Moni et al.,2010).

Data on 20 clay, silt and sand profiles were used to determine thefield capacity (Hfc) of each soil horizon according to the equationdeveloped by Campbell (1985) using SoilPar 2.00 software (Acutisand Donatelli, 2003) after comparison with other approachesand measurements of water content in the field (data notshown).

Volumetric soil water content was measured by TDR sensorsunder each treatment. These measurements were collected every30 min. Eight sensors were placed in each replicate plot, with onesensor at −10, −20, −30 and −80 cm and two sensors at −60 and−100 cm. The minimum water content (Hmin) registered during theperiod of each crop was used to calculate the maximum soil wateravailable, referred to below as the water reserve.

Daily rainfall data (Fig. 2), maximum and minimum air tem-peratures and relative humidity at a height of 2 m, irradiance andwind speed (2 m) were measured on the site of the experiment andavailable on the data base Climatik maintained by INRA AgroClim.

2.3. Collection of water samples and determination of nitratelevels

In order to measure nitrate levels in drained waters, grav-itational soil solutions were collected using zero-tension platelysimeters (ZTL) according to the methodology described in thepaper by Ranger et al. (2001). Two ZTL devices were inserted in thesoil at a depth of −105 cm in each plot of blocks 1 and 2 before theexperiment started, in 2004. Water drained from each plate dur-ing each period was cumulated in glass collection bottles locatedin pits built near the plots beneath the plate level. Samples werecollected during each drainage event lasting less than 15 days, orevery 15 days during drainage periods longer than 15 days. 500 mLaliquots of the pooled material were then analysed for their nitrateN concentrations (NO3

−N) using ion chromatography at the certi-fied IANESCO laboratory in Poitiers. Although the open ZTL systemdid not enable a quantitative evaluation of the water drainage flow,

it offered a reliable sampling method for a qualitative approach(Ranger et al., 2001). To quantify the nitrate flow to groundwater,it is necessary to carry out a separate estimation of the soil waterbalance and drainage.

48 T.R. Kunrath et al. / Agricultural Water Management 150 (2015) 46–56

C

C3G3

G6C3

G6C3N-

G

Maize Wheat Barley Grassland

F the ec

2d

rcrwdfdwt

olierdt

ig. 1. Sequence of land occupation for the different treatments. The period betweenorresponds to bare soil.

.4. Calculation of evapotranspiration, the soil water reserve andrainage

Evapotranspiration (ET) was calculated as a function ofeference evapotranspiration values (ET◦) multiplied by cropoefficients (Kc). The ET◦ was calculated as a function of globaladiation, temperature, humidity and wind speed. These valuesere routinely computed and downloaded from the Climatikata base. Crop coefficients could be found in the FAO documentor wheat, maize, barley and grassland for each stage of cropevelopment (Allen et al., 2006). Actual evapotranspiration ratesere further reduced in line with the relative soil water con-

ent.In order to take account of the impact of soil water content

n ET, the soil was divided into three layers (Fig. 3): a surfaceayer of 0–20 cm; a layer explored by roots (for each crop) whichncreased in depth from 0 at sowing to a maximum depth at flow-

ring; and a deep layer which was the maximum depth reached byoots throughout the period studied (2005–2013). The maximumepth was estimated using the water content profiles determinedhroughout the experiment.

Fig. 2. Rainfall and mean air temperature at 2 m height on the site of the experiment

nd of each crop sequence (harvest) and the beginning of the following crop (sowing)

Kc was updated daily in line with crop development, assumingit was 0.3 at sowing (i.e. bare soil Kc) and maximum at flowering.Flowering dates were derived from the growing degree days val-ues supplied for maize, wheat or barley (Table A.1—Appendix A).In each case, the maximum value for Kc was taken from the FAOguidelines (Allen et al., 2006). Root depth was proportional to Kc,increasing from zero at sowing to maximum root depth on the dayof flowering. The maximum root depth was computed for each cropand plot using the minimum soil water content profile observedover 100 cm, extrapolating the depth at which soil water contentwould be equal to field capacity (e.g. Fig. 4). Further details of thecomputation of ET and drainage are given in Appendix B.

2.5. Statistical methods

The data were subjected to analysis of variance and contrasts,

the level of significance being fixed at 5%. The drainage data werealso analysed for each period (crop). The GLM and Mixed programsunder the SAS software (SAS, 2002) package were used for theseanalyses.

at the INRA Agroclim network weather station located on the site of the study.

T.R. Kunrath et al. / Agricultural Water Management 150 (2015) 46–56 49

Fig. 3. Change with time of the three soil layers defining the water reserves modeledfor the estimation of soil water fluxes and nitrogen leaching. The ground surface(R20) is divided into a reservoir at least 20 cm deep, a reservoir (Rroot) between 20 cmand rooting depth (where roots reach deeper than 20 cm) and a reservoir betweenrooting depth and maximum depth observed during the 9 years of the study (Rmax).At sowing, rooting depth was set to 0 and later on proportional to the crop coefficient(Kc), hence also increasing as a function of the sum of temperature. Drainage wascmc

3

3

ton

tlh

Fm(tu

Table 1Soil water reserve in the top 20 cm soil layer (mm), maximum water available forcrop water use (mm) and maximum rooting depth (cm) for each replicate of eachtreatment.

Soil water reserve (mm) Rmax depth (cm)

20 cm Maximum

C 1 34 155 155C 2 38 163 143C3G3 1 41 148 168C3G3 2 48 179 139G6C3 1 46 181 138G6C3 2 51 194 143G6C3N− 1 43 153 125G6C3N− 2 39 148 130G 1 42 168 137

alculated as the difference between the water balance of each reservoir and itsaximum available water holding capacity value when higher. Lateral flows and

apillary rise were considered negligible.

. Results

.1. Computation of drainage

The maximum soil water reserve (Table 1) was similar underhe different treatments (P = 0.0957), thus enabling an evaluationf the effects of the treatments on water draining from the soil anditrogen leaching.

Water content of the soil profiles varied between years andreatments. The driest year (intensity and duration) was 2006, fol-owed by 2009. The relative soil water content remained quiteigh during the other years, with 2007 and 2013 experiencing the

-160

-140

-120

-100

-80

-60

-40

-20

00,00 0,05 0,10 0,15 0,20 0,25 0,30 0,35

Soil

deph

(cm

)

Hmin Hfc Hj Es�ma�on

Humidity

ig. 4. One example of soil volumetric water content profiles illustrating theethodology for calculating the maximum rooting depth and the soil water reserve

treatment G on 20 Oct 2010). The maximum root depth (approximately 137 cm inhis example) was estimated extrapolating the water content increase with depthntil it reached the water content at field capacity.

G 2 41 171 136

wettest conditions (Fig. 5). As expected, under grassland, the soildried out more rapidly and the conditions were drier than withcrops. However, the deepest root activity measured (approximately155 cm) was observed under continuous cropping with cereals.

Fig. 6 shows a good correspondence between the determina-tion of the drainage events observed directly by the ZTL devicesand the period of drainage calculated using the model, thus demon-strating the reliability of this measurement methodology regardingthe sampling of gravitational soil water contributing to drainage.Throughout the nine-year period, a large proportion of the drainageoccurred in autumn and early winter (Fig. 6). However, drainagewas also observed during the spring of 2013 because of theheavy rainfall (Fig. 2). The cumulative drainage during the 9 years(Fig. 7) differed between cropping systems (P < 0.0001). Treatmentswith the longest duration of grassland (G and G6C3) exhibitedless drainage than treatments with a higher proportion of arablecrops: 1991 and 1943 mm, respectively, for G and G6C3 versus2658 and 2357 mm, respectively, with C and C3G3, while G6C3N−

remained intermediate (2147 mm). The two periods during whichthe largest difference between treatments occurred were the win-ters of 2007–2008, and 2010–2011, i.e. under a long period of baresoil between the barley harvest in early summer and maize sowingthe next spring.

3.2. Nitrate levels in drainage water

Considerable variations over time could be observed regardingthe nitrate levels in gravitational soil water collected fromthe ZTL (Fig. 6) for all drainage periods under grassland (G)or a pure arable crop system (C), in each situation. Under apure crop rotation, nitrate concentrations ranged from 5 to145 mg NO3 L−1, while under grassland this amplitude was lessmarked, from 0 to 64 mg NO3 L−1. The average nitrate concentrationwas 52.7 ± 38.63 mg NO3 L−1 under the C treatment as comparedto 14.9 ± 14.76 NO3 L−1 under the G treatment. As expected, landoccupied by grassland and managed by cutting led to a markedreduction in the nitrate levels of drained water when comparedwith a pure arable crop rotation. On average, treatments with ahigh proportion of grassland (G, G6C3, G6C3N−) provided waterwith approximately 15 mg NO3 L−1 by comparison with a pure croprotation (C: 53 mg NO3 L−1), while the C3G3 treatment produced anintermediate result of 31 mg NO3 L−1 (P = 0.0003).

Although this comparison was based on the average values ofgravitational water samples, it only generated an approximationof the overall nitrate concentration of drained water. A more rel-

evant estimate of drained water quality required the weighing ofeach sample to determine its contribution to the volume of drainedwater. This was achieved using drainage on the one hand and the

50 T.R. Kunrath et al. / Agricultural Water Management 150 (2015) 46–56

-180

-160

-140

-120

-100

-80

-60

-40

-20

0

G

So

il w

ater

dep

leti

on

(cm

)

e wat

to

3

scosbcosalNN1

t2lt2gpanfaiNaa

blot

C C3G3

Fig. 5. Changes with time of soil the depletion of th

otal quantity of nitrate lixiviated over a particular period, on thether.

.3. Nitrate leaching

For each drainage period, the nitrate concentration in a waterample was multiplied by the quantity of water drained in order toalculate the quantity of nitrate leached. The quantities cumulatedver the 9 years of the experiment are shown in Fig. 8. There wereignificant differences (P < 0.0001) in cumulative nitrogen leachingetween the different cropping systems (Fig. 8). In the pure arablerop system, 340 kg N ha−1 were leached over the 9 years, i.e. a lossf 37 kg N ha−1 year−1, while under the long term grassland (G) andystems including 6 years of grassland, (G6C3 and G6C3N−), anverage of only 70 kg N ha−1 over the 9 years was recorded, i.e. aoss of 8 kg N ha−1. Over the entire 9-year period studied, reducing

fertilization did not result in any further significant decrease in leaching. The C3G3 system produced an intermediate value of65 kg N ha−1, corresponding to a loss of 18 kg N ha−1 year−1.

A more detailed analysis was made for the period followinghe 6-year or 3-year grassland treatments, i.e., April 2011–July013, when a common arable crop sequence was initiated fol-

owing 6 years of different types of land use (Table 2). With allreatments, N leaching followed a two-step pattern: Winter–Spring012 and Winter–Spring 2013. No additional N leaching due torassland ploughing and cultivation was detected during these twoeriods for C3G3 or G6C3. Although limited, the effect of N fertilizerpplication on grassland N leaching after its re-cultivation was sig-ificant (34 versus 17 kg N ha−1 for G6C3 and G6C3N−, respectively,

ollowing the wheat crop) but did not persist thereafter. Under continuous grassland treatment (G), N leaching was relativelymportant during the second period as compared to the very low

leaching seen during the previous years. This might have beenssociated with the intense drought experienced in the summernd autumn of 2012 (Fig. 5).

The overall nitrate concentration in drainage water could then

e calculated for each treatment as the ratio between the cumu-

ated loss of nitrogen per hectare (Fig. 8) and the cumulated volumef drainage water (Fig. 7), giving the best estimate of the con-ribution of each treatment to the quality of groundwater. The

6C3 G6C3N- G

er reserve for the five treatments over the 9 years.

ratio between the cumulated NO3 leached and the quantity ofwater drained throughout the period showed that water from thecrop rotation had a concentration of approximately 56 mg NO3 L−1,while treatments with continuous or 9, 6 or 3 year grassland treat-ments produced 14, 19 and 31 mg NO3 L−1, respectively (Fig. 8).Water from the 6-year grassland rotation with low N application(G6C3N−) had the same average concentration as the continuousgrassland with a high N application (G): 12 mg NO3 L−1.

4. Discussion

4.1. Effect of land use and management system on drainage

During this study, drainage periods were usually observedbetween October and April since the evaporative demand in sum-mer was generally sufficient to restrict drainage to infrequentevents of very intense rainfall at this time of year (Cuttle andScholefield, 1995). Drainage under land use systems favouringperiods of bare soil was higher because of lower evapotranspira-tion than under permanent vegetation. The difference in drainagebetween land use systems differing in terms of the proportion ofgrassland was seen more specifically during these periods of baresoil (Fig. 6 and Table 2). As a result, the introduction of grasslandinto a cereal rotation led to a reduction in the quantity of leachingwater. Quantification of the current rate of aquifer recharge is thusa prerequisite for efficient and sustainable groundwater resourcemanagement in dry areas, where this resource is often the key toeconomic development (Vries and Simmers, 2002). The balancebetween land areas covered by grasslands and cropping areas at acatchment scale needs to be obtained in order to ensure sustainablewater resource management.

4.2. Effects of land use on nitrate leaching and gravitationalwater quality

The leaching of nitrates into groundwater, and their presence in

surface runoff, depends on mineral nitrogen excess, the hydrolog-ical regime, land use, soil type and climatic conditions (Shepherdet al., 2001; Oenema et al., 2005). Several studies have highlightedthe relationship between land use and nitrogen leaching (Kvítek

T.R. Kunrath et al. / Agricultural Water Management 150 (2015) 46–56 51

0

10

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Oct

-06

Dec

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Feb

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Dra

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and N

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once

ntr

atio

n (

mg/L

)

Maize Wheat Barley D crop %N crop

0

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20

30

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Dra

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once

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Maize Wheat Barley D grassland %N grassland

a

b

F il solu

efel

TC

O D F A Ju Au

O D F A Ju Au

O D F A Ju Au

ig. 6. Estimated daily drainage and mean nitrate concentration (mg NO3 L−1) of so

t al., 2009). Nitrate concentrations in drainage from grassland ororest are usually low (Addiscott, 2005). The same author consid-red that in the context of systems with rotating annual cropseaving the soil bare for part of the year meant that soil nitrogen

able 2umulative nitrogen leaching and rainfall over the three years following ploughing of the

Nitrogen leaching (kg N ha−1)

C C3G3 G6C

Apr–Sep/11 (maize) 5 0 0Sep–Nov/11 (bare soil) 0 0 0Nov/11–Jul/12 (wheat) 39a* 21bc 34Jul–Nov/12 (bare soil) 0 0 0Nov/12–Jul/13 (barley) 22a 33a 36aTotal 66a 54ab 70a

* Different letters mean differences between treatments in each period (P = 0.0004) or

F A Ju Au

O D F A Ju Au

O D F A Ju Au

O D F A Ju

tion collected by Zero Tension Plates lysimeters for treatments C (a) and G (b).

is vulnerable to leaching because no live plants are present to cap-ture it. Also important is the fact that grasses spread their rootsat soil depths which allows the plants to capture nitrate beforeit can leach and contaminate water, or be leached (Franzluebbers

grassland.

Rainfall (mm)

3 G6C3 N- G

0 0 280 0 0 68.5ab 17c 15c 618

0 0 163.5 34a 26a 893.5 51ab 41b 2023.5

for the total (P = 0.0096).

52 T.R. Kunrath et al. / Agricultural Water Management 150 (2015) 46–56

0

300

600

900

1200

1500

1800

2100

2400

2700

Cum

ula

tive

dra

inag

e (m

m)

Maize Wheat Barley C C3G3 G6C3 G6C3N- G

* *

A

B

C

D

D

F e 5 tred treat

epivr

wAtatadwo

Fe

ig. 7. Change with time of the cumulative drainage (mm) over the 9 year study in thifferent letters on the right hand side mean highly significant differences between

t al., 2014). Moreover, the permanency of carbon flow througherennial vegetation to the soil under grassland enables a rapid N

mmobilization-mineralization turnover by soil microbes that pre-ents an accumulation of N as nitrate in soil and thus reduces theisk of leaching (Premrov et al., 2012; Tlustos et al., 1998).

The initial events during each period of drainage were thoseith the highest levels of nitrogen in gravitational water (Fig. 6).t the end of summer, high soil temperatures and the restora-

ion of soil water content favours N mineralization leading to anccumulation of mineral N in soil and increasing the nitrate concen-ration in gravitational water (Engström et al., 2011; Torstensson

nd Aronsson, 2000; Stenberg et al., 1999). According to the modeleveloped by Burns (1974), the nitrate concentration in drainageater is high at the start of the drainage period towards the end

f autumn, and due to the leaching effect tends to fall as the

0

50

100

150

200

250

300

350

Cu

mu

lati

ve

nit

rogen

lea

chin

g (k

g N

/ha)

Maize Wheat Barley C * * *

ig. 8. Change with time of the cumulative nitrogen leaching between the 5 treatments

pisodes; different letters on right hand side of the figure mean highly significant differen

atments. * Significant difference between treatments during the drainage episodes;ments; P > 0.0001.

volume of water drained increases. So, according to this model,as the volume of drainage water increases bringing about a dilu-tion process, the average NO3

− concentration in drainage watershould decrease. As a consequence, any reduction in the volumeof water drainage should automatically increase the average NO3

−

concentration of this water. However, an analysis of the relation-ship between the volume of drainage water and correspondingaverage NO3

− concentrations revealed a positive correlation acrosstreatments and across years (r = 0.93 P < 0.0001), which seemed incontradiction with what could have been expected from Burns’model. In fact, for each drainage period, a tendency towards a “dilu-

tion” of nitrate concentrations as the volume of water drainageincreased was observed as expected. But because soil N mineraliza-tion remained active throughout the winter and increased in earlyspring, this “dilution” process was largely attenuated or eliminated

C3G3 G6C3 G6C3 N- G

A

B

C

C

C

***

over the 9 years. * Significant differences between treatments during the drainageces between treatments for cumulated nitrogen leaching; P > 0.0001.

T.R. Kunrath et al. / Agricultural Water

[NO3] = 52 .87 e-0,19x

R² = 0.9564 P>0.000 1

0

10

20

30

40

50

60

0 2 4 6 8 10

Nit

rate

conce

ntr

atio

n (

mg N

O3

ha- 1

)

Duration of grass land (years)

C C3G3 G6C3 G6C3N- G

Fo

wtfbnlwtetcb

ulaesqa(sunitmpilw

4

trdgCrdaaltsl

ig. 9. Average nitrate concentration of drained solution (mg NO3 L−1) as a functionf the duration of grassland in a mixed cropping system over 9 years.

hen analysed at the whole year level. Therefore any reduction inhe drainage water volume, due either to reduction in annual rain-all or an increase in evapotranspiration through better soil covery vegetation, would have contributed to increasing the averageitrate concentration of drainage water. The high capacity of grass-

ands to intrinsically decrease the accumulation of nitrate in soilas therefore not impaired here by its greater capacity to reduce

he volume of water through a lower “dilution” effect. The findingsstablished here may not hold for different soils exhibiting less win-er microbial activity or shallower horizons. Also, in regions withooler winters and springs a different pattern of NO3 leaching mighte found.

Even with higher N fertilization application rates than thosesed on maize, wheat and barley (Table A.1—Appendix A), grass-

and cover always produced both a lower level of nitrate leachingnd a lower nitrate concentration in drainage water. This could bexplained by the absence of soil disturbance and of periods of bareoil during the “grassland phase”. In arable cropping systems, largeuantities of the nitrogen that remains in soil or is mineralizedfter harvest may be leached before the next crop is establishedSapkota et al., 2012). It is interesting to note here that the con-iderable increase in the fertilizer N application rate on grasslandnder the G6C3 treatment compared to the G6C3N− treatment didot lead to any substantial increase in the risk of nitrate leach-

ng. This underlines the considerable capacity of mown grasslandso restore groundwater quality, even under a relatively intensive

anagement system enabling potentially near-optimum herbageroduction (Table A.1—Appendix A). Therefore, as shown in Fig. 9,

ncreasing the proportion of grassland in cereal rotations wouldead to a marked exhaustion of the nitrate concentration in drainage

ater, according to an exponential function.

.3. Effects of grassland removal and re-cultivation

Some authors have stressed that the benefit of introducingemporary grasslands into arable cropping rotations in terms ofeducing nitrate concentrations in groundwater could be losturing the 2-year period following the conversion of land fromrassland to annual crops (Kaspar et al., 2012; Vertès et al., 2007;uttle and Scholefield, 1995), because of the high mineralizationate of soil organic matter incorporated in soil after grasslandestruction and re-cultivation. In our situation we did not observeny lasting effect of the preceding land use system (continuousrable cropping, alternation of 3 years of crops and 3 years of grass-

and, or 6 years of grassland with high or low N fertilization) duringhe 3 subsequent years of a maize, wheat, and barley rotation. Ashown in Table 2, the maize crop sown in April 2011 just after grass-and removal which received a relatively low level of N fertilization

Management 150 (2015) 46–56 53

according to indications of the PC-AZOTE software (Angevin, 1999)prevented nitrate leaching until November 2011. Only two periodsof N leaching were observed under wheat (2012) and barley (2013),and the amounts of nitrate losses by leaching after grassland neverexceeded the amount lost under a continuous cropping system.This absence of excessive N leaching after grassland conversion intoan arable crop was achieved by a moderate N fertilization rate onmaize, allowing this crop to take up most of the supplemental Nmineralized after grassland ploughing. An agronomic analysis ofthe N balance across the different treatments was not the objectiveof this paper, but it is interesting to note that variations in maizegrain yield (Table A.1: 7.6; 7.7; 8.4; and 7.0 t ha−1, respectively, withC, C3G3, G6C3 and G6C3N−) probably only reflected minor differ-ences in plant N nutrition. Therefore, if grassland destruction isfollowed immediately by a crop with a high N uptake capacity (suchas maize) with a moderate N fertilization application rate, then therisk of increasing N leaching should be small. It was interesting tonote that during this experiment the grasslands were only usedunder mowing, while most of the studies that have indicated anincreased risk of nitrate leaching after grassland destruction werecarried out under grazing management.

4.4. Comparison of the systems

The experimental design used here was an attempt to analysethe effect of certain forcing variables such as the land use system(crop versus grassland) and the level of N fertilization applied tograssland, on the quantity and quality of drainage water. This sys-tem was therefore able to answer “What if.?”, but could not answer“What is necessary for. . .?”. In other words, it enabled an analysisof the consequences of certain agricultural management decisions,but could not provide direct assistance in terms of providing thebest decisions in response to a given set of production and/or envi-ronmental goals in a particular situation. The pure cropping systemcould have been managed with the introduction of catch cropsduring the periods of bare soil. It has indeed been demonstratedthat including catch crops should reduce some of the risk of nitrateleaching under arable cropping systems (Kaspar et al., 2012; Justeset al., 2012; Vertès et al., 2007; Cuttle and Scholefield, 1995). How-ever, because maize is harvested in late October (or even later), andgiven the short period of time available for sowing and crop setting,it is very difficult to expect any significant nitrate uptake during thewinter using catch crops. In such a cereal system, the use of catchcrops would only be possible between the barley harvest in Julyand the sowing of maize in April the following year, which repre-sents the period with the highest risk of nitrate leaching. Justes et al.(2012) and Ter Steege et al. (2001) showed that, based on experi-mental data and modelling simulations, the introduction of catchcrops into annual cropping systems could reduce nitrate leachingby up to 50%, corresponding to the abatement achieved with ourC3G3 treatment.

These early analyses of the experimental data obtained by theSOERE-ACBB at INRA-Lusignan over its first 9 years of existenceallow us to draws some initial conclusions:

(i) In the soil and climatic conditions of central western France, theuse of a pure cereal cropping system managed with sufficientN fertilization to achieve the target potential grain yield forthe region caused an average nitrate concentration in drainagewater that was higher than the 50 mg NO3

− L−1 limit accept-able for drinking water.

(ii) The introduction of mowed grassland sequences into thisarable crop rotation caused a marked reduction in the nitrateconcentration of groundwater; the higher the proportion ofgrassland in the rotation, the more the NO3

− concentration

5 ater

(

(

oquo

TV

4 T.R. Kunrath et al. / Agricultural W

was reduced, whatever the level of N fertilization during thegrassland sequence.

iii) The destruction of grasslands by ploughing and re-cultivationdid not lead to excessive N leaching, so the benefits gainedduring the grassland phase with respect to water quality wereconserved throughout the sod-based rotation.

iv) Nevertheless, in regions where water availability is closelydependent on recharging aquifers in winter, there could be atrade-off between the benefits of introducing grassland into anarable cropping system in terms of groundwater quality, andthe possible disadvantages linked to reducing the volume ofdrainage water. Such a trade-off should be taken into particularaccount in terms of catchment management.

Several questions remain open for future analysis, based either

n other measurements used as co-variables relative to wateruality (pesticides, phosphate, sulphate and cations), or model sim-lations to test different crop system scenarios such as the usef catch crops, tillage versus non-tillage and the cutting-grazing

able A.1arieties, sowing and harvesting dates of crops, crop coefficient maximum, total amount of

Year Crop Varieties Sowing

C 2005 Maize Texxud 21/04

2006 Wheat Caphorn 24/10/20052007 Barley Vanessa 26/10/2006

2008 Maize Anjou 387 07/05

2009 Wheat Caphorn 29/10/2008

2010 Barley Vanessa 22/10/2009

2011 Maize PR38V12 PIONER 18/04

2012 Wheat Caphorn 16/11/2011

2013 Barley Limpid 16/10/2012

C3G3 2005 Maize Texxud 21/04/2005

2006 Wheat Caphorn 24/10/2005

2007 Barley Vanessa 26/10/2006

2008 Grassland Cocksfoot cvLudac + Fescue cvSoni + Ryegrass cv Milca

17/09/20072009

2010

2011 Maize PR38V12 PIONER 18/04/2011

2012 Wheat Caphorn 16/11/2011

2013 Barley Limpid 16/10/2012

G6C3 2005 Grassland Cocksfoot cvLudac + Fescue cvSoni + Ryegrass cv Milca

20/04/20052006

2007

2008

2009

2010

2011 Maize PR38V12 PIONER 18/04/2011

2012 Wheat Caphorn 16/11/2011

2013 Barley Limpid 16/10/2012

G6C3N− 2005 Grassland Cocksfoot cvLudac + Fescue cvSoni + Ryegrass cv Milca

20/04/20052006

2007

2008

2009

2010

2011 Maize PR38V12 PIONER 18/04/2011

2012 Wheat Caphorn 16/11/2011

2013 Barley Limpid 16/10/2012

G 2005 Grassland Cocksfoot cvLudac + Fescue cvSoni + Ryegrass cv Milca

20/04/20052006

2007

2008

2009

2010

2011

2012

2013

Management 150 (2015) 46–56

equilibrium. The conclusions drawn regarding a particular soil typeand climatic conditions should also be compared with the findingsof long-term studies performed at other sites.

Acknowledgements

The authors would like to thank Allenvi, CNRS-INSU, ANR (AbadChabbi, coordinator) and the Regional Council for Poitou-Charentesfor their financial support for the SOERE-ACBB and the opera-tional budget for of Taise Robinson Kunrath, who would alsolike to thank the Brazilian Ministry of Education ‘Coordenac ão deAperfeic oamento de Pessoal de Nível Superior’ (CAPES) for provid-ing financial assistance via CAPES/COFECUB Project 684/10; andDr. Abad Chabbi (the SOERE ACBB scientific coordinator) for hisvaluable comments.

Appendix A.

Table A.1.

nitrogen applied (kg N ha−1) and crop yield (kg DM ha−1) in the different treatments.

Harvesting Kc max Nitrogen applied Yield (kg ha−1)

22/09/2005 1.20 117 252419/07/2006 1.15 85 686428/06/2007 1.15 120 455917/10/2008 1.20 80 11,63816/07/2009 1.15 150 589806/07/2010 1.15 83 423527/09/2011 1.20 72 764424/07/2012 1.15 160 562716/07/2013 1.15 90 4638

22/09/2005 1.20 117 257719/07/2006 1.15 175 682528/06/2007 1.15 120 4443– 1.00 330 14,204

230 10,563210 5690

27/09/2011 1.20 36 770424/07/2012 1.15 160 544316/07/2013 1.15 90 4960

– 1.00 0 0170 10,673380 15,873330 12,087230 9592210 5495

27/09/2011 1.20 36 845524/07/2012 1.15 160 571416/07/2013 1.15 90 5170

– 1.00 0 030 583430 592930 486430 254330 1687

27/09/2011 1.20 36 704224/07/2012 1.15 160 590416/07/2013 1.15 90 5677

– 1.00 0 0170 11,035380 15,531330 12,609230 9173210 5303120 4436210 5767220 10,690

ater

A

B

etcu

E

bRu

R

a

R

wttu

u

E

jb

raa

R

wt

D

R

D

× 10

HMin20[(

H

Min80

)(M

USA. Agron. J. 99, 361–372.Galloway, J.N., Cowling, E.B., 2002. Reactive nitrogen and the world: 200 years of

T.R. Kunrath et al. / Agricultural W

ppendix B.

.1. Drainage computation

The soil was divided into three layers: the top 20 cm, the layerxplored by the roots of the current crop and the deepest root layer,hroughout the 8-year period studied. When the soil was bare, theontribution of the top 20 cm layer to ET on day j () was computedsing the following equation:

Tj20 = K20 × ETo × Min

(1;

Rj20

0.4RU20

)(B.1)

where K20 is set as a constant equal to 0.3 (Allen et al., 2006),eing the daily soil water reserve of the 20 cm layer on day j, andU20 is the maximum available water in the 20 cm layer. RU20 val-es were determined using the following equations:

j20 = Min

(RU20; Rj−1

20 + Pj − ETj20

)(B.2)

nd

U20 ={[(

Hfc10 − HMin

10

)× 10

]+[(

Hfc10 − HMin

20

)×10 +

(HMin

20 − HMin10

)× 5 +

(Hfc

20 − Hfc10

)× 5]}

(B.3)

here Rj−120 is the available water in the top layer on day j − 1, Pj is

he rainfall on day j, HMin is the minimum water content and Hfc ishe field capacity water content at each depth. Hfc was calculatedsing Soilpar 2.00 software (Acutis and Donatelli, 2003).

When the root depth was more than 20 cm, ET was computedsing the following equation:

Tj =[

Kc × ETo × Min

(1;

Rj−1R

0.4RUR

)− ETj

20

](B.4)

where Rj−1R and RUR are the soil available water content on day

− 1 and the maximum available water content in the root zoneelow 20 cm, respectively. Rj

R was determined using Eq. (B.5).Drainage between the top layer and root zone and beneath the

oot zone was computed by determining the balance in each layernd taking no account of capillary rise because the water table waspproximately 30 m under the ground (Eqs. (B.5), (B.7) and (B.9)).

jR = Min

(RUR; Rj−1

R −(

ETj − ETj20

)+ Dj−1

20

)(B.5)

here Dj−1R is the drainage under the root zone, determined using

he following equation:

j−120 =

(RU20 −

(Rj−1

20 + Pj − ETj20

))(B.6)

j = Min(

RU; Rj−1 −(

ETj − ETj20

)+ Dj−1

R

)(B.7)

RUR ={[(

Hfc10 − HMin

10

)× 10

]+[(

Hfc10 − HMin

20

)+[(

Hfc20 − HMin

30

)× 10 +

(HMin

30 −[(

Hfc30 − HMin

60

)× 30 +

(HMin

60 − HMin30

)× 15 +

(Hfc

60 − Hfc30

)× 15

]+

+[(

Hfc80 − HMin

100

)× 20 +

(HMin

100 − H

+[(

HfcMax depth − HMin

100

)×

j−1R =

(RUR −

(Rj−1

R + Pj − ETj))

(B.8)

Management 150 (2015) 46–56 55

+(

HMin20 − HMin

10

)× 5 +

(Hfc

20 − Hfc10

)× 5]

)× 5 +

(Hfc

30 − Hfc20

)× 5]

+

fc60 − HMin

80

)× 20 +

(HMin

80 − HMin60

)× 10 +

(Hfc

80 − Hfc60

)× 10

]× 10 +

(Hfc

100 − Hfc80

)× 10

]ax depth − 100)

2

]}(B.9)

where max depth is the maximum root depth for each crop in eachplot. For each plot, the RU20, maximum root depth and maximumRU values are given in Table 1.

The drainage under the maximum root depth on day j (Dj) wasdetermined according to the following equation:

Dj =(

RU −(

Rj−1R + Pj − ETj

))(B.10)

where RU is the maximum available water over the 9-year period.To calculate the amount of nitrate leached, the nitrate con-

centration (%Nitratej) in drained water on day j was linearlyinterpolated between two sample values. Nitrogen leaching wascalculated according to the following equation:

Nleaching = Dj × %Nitratej × 0.226 (B.11)

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