European Journal of Agronomy 16 (2002) 207–217

Potential N-losses in three scenarios for conversion toorganic farming in a local area of Denmark

Tommy Dalgaard *, Tove Heidmann, Lisbeth MogensenDepartment of Agricultural Systems, Danish Institute of Agricultural Sciences, P.O. Box 50, DK-8830 Tjele, Denmark

Received 6 April 2001; received in revised form 23 August 2001; accepted 23 August 2001

Abstract

Techniques are needed to investigate whether different strategies for conversion to organic farming might help toreduce N-losses. In this study, an N-balance technique was applied in a local area of Denmark; 25% of this area wasdesignated as environmentally sensitive with special interests to protect groundwater quality. Three scenarios, where25% of the local area was converted to organic farming, were compared to the present situation with conventionalfarming. The first two scenarios were conversion to organic dairy and pig production, respectively. The third scenariowas conversion of the whole area with special interests in clean groundwater to organic farming, self-sufficient infodder and fertiliser. Scenario 1 resulted in a lower N-surplus on the dairy farms, but the reduction was too small inorder to significantly reduce the N-surplus in either the whole local area or within the area with special interests inclean groundwater. Scenario 2 resulted in an analogous result. In Scenario 3, the N-surplus was reduced significantlywithin the area with special interests in clean groundwater, but not within the whole local area. The N-surplusreduction from conversion to organic farming was divided into an extensification and a management effect. Theextensification effect meant that the lower livestock density in the organic scenarios resulted in lower N-surpluses, dueto an exponential relationship between livestock density and N-surplus. The management effect was primarily causedby lower net imports of fodder and fertilisers to the organic farms and the following higher self-sufficiency in fodder.In addition, the distribution of animal manure between the organic farms was more uniform than between theconventional farms and because of the exponential relationship between livestock density and N-surplus, this causeda lower average N-loss potential. We conclude that organic farming can help to reduce potential N-losses inenvironmentally sensitive areas, but only if the conversion is designed with respect to that aim and takes account ofthe spatial distribution of farm types present. © 2002 Elsevier Science B.V. All rights reserved.

Keywords: Scenario; Environmentally sensitive area; Organic farming; Nitrogen; Agroecology

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1. Introduction

Organic farming aims to recycle nutrients andorganic matter and minimise the environmentalimpact of agriculture. Among other things, Dan-ish regulations forbid the use of synthetic fertilis-

Abbre�iations: GWA, area with special interests in cleangroundwater; LSU, livestock units; SFU, Scandinavian fodderunits.

* Corresponding author. Tel.: +45-8999-1732; fax: +45-8999-1819.

E-mail address: tommy.dalgaard@agrsci.dk (T. Dalgaard).

1161-0301/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved.

PII: S1161 -0301 (01 )00129 -0

T. Dalgaard et al. / Europ. J. Agronomy 16 (2002) 207–217208

ers and pesticides and restrict the animal densitycompared to conventional farming (Danish Min-istry of Food, Agriculture and Fisheries, 2000).Several studies have shown that conversion fromconventional to organic farming is one way toreduce nitrogen (N) losses (Cobb et al., 1999;Hansen et al., 2000; Korsaeth and Eltun 2000).However, it is not a simple case of conversionalone. Farm types, such as dairy farms, generallyhave a lower N-loss after conversion as a result oflower N-fertilisation (van der Werff et al., 1995).In contrast, N-loss might increase on the typicalDanish pig farm, because the outdoor, organic pigproduction is less N-efficient than traditionalhousing and slurry systems and because use ofchemical growth promoters and certain medicaltreatments are prohibited in organic systems (Dal-gaard et al., 1998).

The question whether conversion to organicfarming might help to reduce the N-loss is evenmore complicated if an area consisting of severalfarms is considered. The geographical distributionof farm types is unlikely to be uniform in spaceand would differ from one local area to another.Therefore, changes in the N-loss from conversionto organic farming will depend on the local farm-ing structure and on which farms convert. Somefarms in an area might also interact via the ex-change of manure and feed-stuffs and therebyincrease their N-efficiency compared to a situationwhere the opportunity for such exchange is ab-sent. Consequently, the type of farms which con-vert, the extent to which the conversion happenswithin the different farm type classes and thechange in interaction between farms before andafter conversion is important information for thecalculation of potential N-losses in future scenar-ios for conversion to organic farming.

The EU nitrate directive (Alders, 1991), ini-tiated a zoning of agricultural areas vulnerable forN-pollution and, in the future, more focus on thisagri–environmental question can be expected(Buller et al., 2000; Hansen et al., 2001). There-fore, we need methods to decide if organic farm-ing can or cannot help to reduce the N-loss inspecific areas with special interests in cleangroundwater.

In this paper, we describe the use of individualfarm-gate N-balances and aggregated farm-gatebalances to indicate the potential N-losses forthree scenarios for conversion to organic farming.A case study is carried out in a rural area ofDenmark. Of this rural area, 25% is designated asan area with special interests in clean groundwa-ter. In each scenario, 25% of the total rural areawas converted. Scenarios 1 and 2 involves farmswithin and outside the area with special interestsin clean groundwater and represents conversion tomilk and pig production, respectively. Scenario 3is the conversion of the whole area with specialinterests in clean groundwater to organic farmingself-sufficient in fodder and fertiliser. Our hypoth-esis is that Scenario 1 will lead to lower N-losses,while Scenario 2 will result in higher N-lossescompared to the existing situation. Finally, thequestion is whether Scenario 3 will result in N-loss reductions specifically within the area withspecial interests in clean groundwater and whatfuture agronomic changes might help to reduceN-losses further.

2. Materials and methods

2.1. Data collection in the study area

Data were collected within a rural area in theMidwest of Denmark (Fig. 1); 41 farms covering1970 ha of agricultural fields were studied. Ofthese farms, 13 or 25% of this area, were desig-nated environmentally sensitive with special inter-ests to protect groundwater quality. Therefore,there is a special interest in the reduction ofN-loss. Farm information was collected from pri-vate farmers, farm advisors and from nationalagricultural databases (Table 1).

Farm-gate inputs and outputs included prod-ucts with an N-content that were bought or sold.These data were obtained from the farm accounts.Where possible, 5-year data were collected, butfor some farms, mainly those producing arable orhorticultural crops for sale, not all input andoutput data were available. In these cases, it wasassumed that all harvested crops were sold andonly fertilisers and seeds were bought. Data on

T. Dalgaard et al. / Europ. J. Agronomy 16 (2002) 207–217 209

Fig. 1. Geographical location of the 1970-ha agricultural areain the Midwest of Denmark; 25% of the field area is desig-nated an environmentally sensitive area with special interestsin clean groundwater (GWA).

Table 2Farm type classification based on livestock density

Farm type Livestock density (LSU ha−1)

Dairy �0.4, more than two to three dairy cowsPig �0.4, more than two to three pigsMixed �0.4, not farm type dairy or pig

0.1–0.4Small�0.1Cash-crop

1 LSU corresponds to livestock producing 100 kg N in theform of manure from storage.

The field crops were categorised into cereals(grain and whole crop), grassland (permanent andin rotation), broad-leaved crops (rape, peas, pota-toes, etc.) and ‘set-aside’. The livestock numbersfor each farm were collected from the nationallivestock register (Danish Ministry of Food, Agri-culture and Fisheries, 1999). The N-fertilisation ofeach field and information about the import andexport of fertilisers to or from each farm wascollected from the farmer’s fertiliser plan. Forsome of the small farms, field crop level normfigures were used (Plantedirektoratet, 1999).

The data described above were linked to adigital field map, which is produced from thefarmer’s own maps and a digital ortho-photo. Thearea with special interests in clean groundwaterwas designated by Viborg County (1998) andincludes a 270-ha area, where the farmers canobtain special subsidies if they join a scheme forgroundwater protection plus an overlapping 529ha designated to protect drinking water boreholes.For the present case study, the boundary wasdrawn so that the total field area of 13 wholefarms was designated an environmentally sensitivearea, with special interests in clean groundwater.In reality, some of the chosen farms only havesome fields within the area with special interests inclean groundwater designated by the county.Conversely, other farms had fields within the area,but not in this study.

2.2. Farm type classification and organic croprotations

The farms were classified as dairy, pig, mixed,small and cash-crop farms (Table 2). Based on

purchases of fertiliser were obtained from thefarm’s annual fertiliser accounts. The year to yearchanges of N in farm products held in store,fertiliser in store and livestock were not accountedfor. However, most of these changes from year toyear are neutralised by the use of 5-year averagesfor the farm-gate inputs and outputs.

Table 1Type, source and extent of the data collected from the 41farms

ExtentType Source

Farm-gate Farm advisory Januaryinput/output service 1994–1998

OctoberFarmer’s fertiliserField crops andyields plans 1997–1998

Livestock National February 1998livestock register

OctoberFarmer’s fertiliserFertilisationplans 1997–1998

Field map Summer 1998Farmer’s maps,ortho-photoThe CountyGroundwater 1998

protection area(GWA)

T. Dalgaard et al. / Europ. J. Agronomy 16 (2002) 207–217210

empirical information from Danish organic farms,a typical crop rotation was defined for each farmtype (Bichel Committee, 1999 and Mogensen etal., 1999). The following crops were used in therotations: (1) grass/clover, (2) spring barley, (3)spring barley undersown with grass/clover, (4)spring barley and peas undersown with grass/clover, (5) winter wheat undersown with ryegrassand (6) broad beans. The organic rotation fordairy farms was defined as 1–1–3, for pig farms1–2–5–6–4 and for mixed, small or cash cropproducing farms 1–5–3–4, with the numbers re-ferring to the crop types.

2.3. Farm-gate and regional farm nitrogenbalances

In this study, we used farm-gate and regionalfarm N-balances as indicators of potential N-losses. The N-surplus (N-surp) was defined as thedifference between net N-output (o) from thefarm in the form of milk (o1) and meat and thenet input to the farm in form of net fodderimport, net fertiliser import and N from the atmo-sphere. The net meat export was calculated as Nin the meat exported (o2) minus N in importedlivestock (i5). The net fodder import (i) was calcu-lated as the sum of N in imported fodder (i1) andseeds (i2), minus N in cash-crops sold (o4). Im-ported straw was classified as fodder and exportedstraw as a cash-crop. The net fertiliser import wascalculated as the sum of N in imported syntheticfertiliser (i3) and manure (i4), minus N in ex-ported manure (o3). Finally, N from the atmo-sphere covered the sum i6+ i7, which areatmospheric N deposition and N fixed by legumes(Leguminosae sp.), respectively (Eq. (1)Fig. 2).

N-surp= i1+ i2+ i3+ i4+ i5+ i6+ i7−o1−o2

−o3−o4 (1)

Standard values for N-concentrations derived byStrudsholm et al. (1997) were used for calcula-tions of i1, i2, o1 and o4. Standard values fromPoulsen and Kristensen (1998) were used in thecalculation of i4 and o3. An N-content for liveanimals of 27 g N kg−1 was used for the calcula-tion of i5 and o2. Nitrogen deposited from theatmosphere (i6) was calculated from precipitation

data, with an average 1998 deposition of 14 kg Nha−1 per year within the case area (Grundahl andHansen, 1990). For clover (Trifolium sp.), i7 wasestimated with the model of Kristensen et al.(1995), where fixed N was made a function of theN fertiliser applied to each field. For otherlegumes, fixed N was estimated from the recordedharvest on each field (Kristensen and Kristensen,1992). By aggregation of farm-gate balances, N-surp can be calculated for a region, such as thearea with special interests in clean groundwater.The sum of farm inputs and outputs then ac-counts for the total N-input and N-output fromfarming within the area with special interests inclean groundwater and N-surp indicates the po-tential N-loss to the environment within this area.

2.4. Scenarios for con�ersion to organic farming

Three scenarios with different structures of con-version to organic farming were simulated. Ineach scenario, 25% of the total case area is con-verted and the remaining area is farmed with the1998 conventional management practice:1. Milk-scenario. A continuation of the present

development in Denmark, where it is primarilydairy farms that convert to organic farming

Fig. 2. Farm N-inputs (i1– i7), N-outputs (o1–o4) and N-sur-plus, i.e. in kg N ha−1 per year (after Dalgaard et al., 1998).The same balance can be calculated for a number of farmswithin a region.

T. Dalgaard et al. / Europ. J. Agronomy 16 (2002) 207–217 211

(Statistics Denmark, 2000). In the case study,this resulted in conversion of 38% of the areawith special interests in clean groundwater.

2. Pig-scenario. Conversion only of pig produc-tion, which result in 33% of the area withspecial interests in clean groundwaterconverted.

3. Groundwater-scenario. 100% of the area withspecial interests in clean groundwater, cover-ing 25% of the total case area, was convertedto organic farming and was self-sufficient infodder and fertiliser.

In the milk-scenario (1), all existing dairy farmsin the total area studied were assumed to convert,so that the total milk quota in the area (2993tmilk) was sustained. However, the total area ofthese dairy farms was �25% of the total areastudied and some of the conventional dairy farmshad a higher livestock density than allowed, ac-cording to Danish regulations, for organic farm-ing. The dairy farms with high livestock densitywere therefore assumed to co-operate with neigh-bouring farms, which were thereby also convertedto organic farming, so the total area convertedwas 25% of the total case area studied.

The pig-scenario (2) was calculated as thehighest possible organic pig production which canbe sustained by the crop production on 25% ofthe total study area, converted to organic farm-ing. According to Danish 1998 legislation, 75% ofthe fodder for ‘organic pig production’ must beproduced organically. In scenario 2, all this or-ganically produced fodder is produced within theconverted 25% of the total area. The total pigproduction was therefore reduced in comparisonwith the conventional 1998 situation and corre-sponds to the conversion of four selected conven-tional pig farms in the total case area. Togetherwith these farms, three crop production farms areconverted, so the area converted covers 25% ofthe total case area.

In the groundwater-scenario (3), full self-suffi-ciency in fodder and fertiliser was assumed withinthe area with special interests in clean groundwa-ter. According to the Bichel Committee (1999),this corresponds to an average organic productionof 1227 kg milk per hectare, 196 kg pig meat perhectare and 272 kg cereal grain per hectare. This

means that the livestock density in the area withspecial interests in clean groundwater was reducedfrom 1.4 to 0.7 LSU ha−1. One LSU correspondsto the livestock producing 100 kg N in the formof manure ex storage (i.e. after deduction of thelosses during storage). In the groundwater-sce-nario (3), dairy farms interacted with cash-crop,mixed and small farms as in the milk-scenario (1)and the pig farms decrease their production live-stock intensity as in the pig-scenario (2). How-ever, to ensure overall fodder and fertiliserself-sufficiency, the degree to which fodder andanimal manure were exchanged and the degree towhich the livestock intensity was decreased washigher than in the former scenarios.

In each scenario, a standard procedure to con-vert the farms from conventional to organic farm-ing was applied. In short, this procedure ensureda balance between livestock production and theresulting fodder use, manure production, fertilisa-tion practice, crop yields and needed fodder im-ports. In each scenario, the livestock number wascalculated as described in the scenario definitionsabove. The corresponding animal feed plans, milkand meat yields were decided specifically for eachfarm according to the principles in Bichel Com-mittee (1999). The manure production was calcu-lated from the fodder intake according to Poulsenand Kristensen (1998). If the livestock densityexceeded the limits according to Danish organicfarmer’s regulation (1.4 LSU ha−1 for dairyfarms and 1.7 LSU ha−1 for other farms), themanure surplus was exported to the nearest or-ganic farm within the area. Otherwise, the maxi-mum permitted amount of conventional manureaccording to Danish legislation (Plantedirek-toratet, 1999) is imported. The manure was dis-tributed to the crops according to 10 years ofrecorded practice on Danish organic farms(Mogensen et al., 1999) and the resulting cropyields after conversion were estimated with theHalberg and Kristensen (1997) model. Finally, therequired import/export of cereals and concen-trates were calculated. From this, the nitrogenbalances for each farm converted in each scenariowas calculated.

For the statistical comparison of N-surplusesfrom the different farm types and from farms

T. Dalgaard et al. / Europ. J. Agronomy 16 (2002) 207–217212

Table 3Average N-surpluses, with corresponding 95% confidence intervals and number of farms in the total case area and within andoutside the GWA in 1998

Within GWA Outside GWA TotalUnit

164�36N-surplus 169�42kg N ha−1 per year 168�31Dairy farms Number 4 5 9

NumberPig farms 4 7 111 4Number 5Mixed farms

NumberSmall farms 2 4 6Cash-crop farms 2Number 8 10

GWA, area with special interests in clean groundwater.

within and outside the area with special interestsin clean groundwater, it is assumed that the farm-level N-surpluses per area are normally dis-tributed within each farm group. Thereby, 95%confidence intervals are produced (Rudemo,1979). To investigate the relationships betweenlivestock densities and N-surpluses, a generalisedlinear modelling procedure is used (Dobson,1990).

3. Results

3.1. The 1998 situation

No significant difference was found between theaverage N-surp within and outside the area withspecial interests in clean groundwater (Table 3).However, there were differences between N-surpsfor the five defined farm types (Table 4). Dairyfarms had a significantly higher N-surp than pigfarms, cash crop farms and small farms. Therewas no significant difference between mixed farmsand pig farms, but the mixed farms had signifi-cantly higher N-surpluses than the livestock ex-tensive cash-crop and small farms.

A closer investigation of the individual entriesin the N-balances revealed the import of fodder asthe most important N-source on the dairy farmsand this import was significantly higher than oncash-crop and small farms. The difference be-tween the N-surp on dairy and pig farms cannotbe explained from differences in fodder imports,export of milk and meat or N from the atmo-sphere, but from a significantly different net im-

port in the form of synthetic fertilisers and animalmanure.

Using a generalised linear modelling procedure(Dobson, 1990), a significant (P�0.001) non-lin-ear relationship between livestock density and po-tential N-loss, indicated as N-surp, was found(Fig. 3). In addition, the effect of fertilisation inthe form of animal manure, synthetic fertilisersand green manure from N-fixing crops was inves-tigated. While the effect of the two former fertilis-ers was significant (P�0.01), no effect from greenmanure was observed. In line with the effect oflivestock density, N-surp could be explained as anexponential function of the fertilisation practicewithin the interval 128–405 kg N ha−1 peryear from animal manure (Nam) and syn-thetic fertiliser (Nsf) applied (N-surp=38.5·e[0.0047·Nam]·e[0.0059·Nsf]).

3.2. The scenarios for con�ersion to organicfarming

The N-balances of the converted farms in sce-narios 1–3, respectively, were calculated (Fig. 4)and compared to figures for the corresponding1998 farm types (Table 4). In Scenario 1, theaverage N-surp of the 14 converted dairy farmswas significantly lower than that of the dairyfarms in the 1998-situation. This was caused bysignificantly reduced fodder and fertiliser imports,whereas N fixed from the atmosphere was signifi-cantly increased. In Scenario 2, the conversion toorganic pig farming did not result in a reductionof the N-surp, primarily because the predictedincrease in atmospherically fixed N was higher

T. Dalgaard et al. / Europ. J. Agronomy 16 (2002) 207–217 213

Table 4Nitrogen surpluses (kg N ha−1 per year) and 95% confidence intervals for the five defined farm types and the distribution on netimport of fodder and dressing, input from the atmosphere and net export of milk and meat (1998 situation)

Net imported fodder Net imported dressing Atmosphere Net exported milk and meat N-surplus

143�17 40�7Dairy farms 64�21169�68 289�66Pig farms 95�65 84�36 26�10 64�27 141�36

116�25 36�1791�106 46�32Mixed farms 197�66101�13 29�18Small farms 12�5−25�18 93�12136�14 36�13−85�11 0�0Cash-crop farms 87�24116�13 41�6 39�12All farms 168�3149�39

than the predicted reduction in fodder and fer-tiliser imports. Finally, the 100% conversion ofthe area with special interests in clean groundwa-ter in Scenario 3 resulted in an average N-surp,which was significantly lower than the N-surp onall recorded conventional farm types except theconventional cash-crop farming.

The predicted N-surps within the area withspecial interests in clean groundwater in the threescenarios were compared to the 1998-situationwith conventional farming (Tables 3 and 5). Onlyin Scenario 3, where the area with special interestsin clean groundwater was converted 100% to or-ganic farming self-sufficient in fodder and fer-tiliser, the N-surp was significantly reduced. In thetwo other scenarios, with respectively 38 and 33%of the area with special interests in clean ground-water converted, no significant reduction of N-surp within the area with special interests in cleangroundwater occurred. For the total case areawithin and without the area with special interestsin clean groundwater, none of the 25% conversionscenarios resulted in a significant reduction of theN-surp.

3.3. Management and extensification effects ofcon�ersion to organic farming

A regression analysis (Dobson, 1990) was car-ried out to investigate whether the lower N-surpsin the organic scenarios could be fully explainedfrom the reduction in livestock density (the exten-sification effect) or whether a management com-ponent also has to be included. In line with thefinding for conventional farming, the analysis re-vealed a non-linear relationship between livestock

density and N-surp for the organic farms mod-elled in the three scenarios, but N-surp was sig-nificantly lower than that of the recordedconventional farms in the interval 0.1–2.1 LSUha−1 (Fig. 5).

4. Discussion

4.1. The farm le�el

The farm level analysis identified a potential forreduction of the N-surp by conversion to organicdairy farming. The average, modelled N-surpfrom the organic dairy farms in scenario 1 (138 kg

Fig. 3. Farm level N-surpluses for the five different farm typescompared to the 1998 livestock density (1 livestock unit (LSU)equals 100 kg total-N in the form of livestock manure fromstorages). The corresponding non-linear regression is illus-trated with the curve (y=77·e[0.56·x]).

T. Dalgaard et al. / Europ. J. Agronomy 16 (2002) 207–217214

Fig. 4. Average N-surplus for the 25% of the area which was100% converted to organic farming in each of the threescenarios: (1) organic milk production; (2) organic pig produc-tion; and (3) organic production self-sufficient in fodder andfertiliser within an area with special interests in clean ground-water (GWA).

Table 5Average N-surpluses (kg N ha−1 per year) and 95%-confi-dence intervals, for the three scenarios where 25% of the totalarea are converted to organic farming

Outside GWA TotalWithin GWA

144�341. Milk-scenario 130�20 133�17

172�422. Pig-scenario 168�31162�353. Groundwater 55�12a 169�42 133�33

-scenario

a Significantly reduced N-losses compared with the 1998-figures in Table 3.Figures from the total area and for the area within and outsidethe GWA are shown. GWA, area with special interests inclean groundwater.

(1998) and Halberg (1999), who reported N-surpsof 124 and 114 kg ha−1 per year, respectively, fororganic and 240 and 176 kg ha−1 per year, re-spectively, for conventional Danish, dairy farms.The N-surp levels in these two studies are differ-ent because they are calculated from independentfarm samples with different livestock densities,soil types, geographical locations, etc. and there-fore they are also different from the N-surp level

Fig. 5. Nitrogen surpluses for the farms converted to organicfarming in each of the three scenarios compared to the live-stock density (1 livestock unit (LSU) equals 100 kg total-N inthe form of livestock manure from storages). The two curvesare the regressions of N-surpluses from the 41 conventionalfarms in 1998 and the modelled organic farms.

ha−1 per year) was significantly lower than thatof the average recorded dairy farm before conver-sion (289 kg ha−1 per year). These results are inline with empirical studies by Dalgaard et al.

T. Dalgaard et al. / Europ. J. Agronomy 16 (2002) 207–217 215

in the present study. However, more importantly,both empirical studies show significant (P�0.05)differences between N-surps in organic and con-ventional dairy farming, a finding in accordancewith the present results.

Dalgaard et al. (1998) found a higher N-lossfrom organic than from conventional pig farming.This result was not confirmed by the presentcalculations, where no significant difference inN-surp was identified between the organic pigproduction farms in Scenario 2 and the recordedconventional pig farms. However, if N-surp wascorrected for the effect of livestock density (Fig.5), the modelled pig farms in Scenario 2 tended tohave a higher N-surp than that of the farms in theother two scenarios. This is supported by the factthat the only two converted farms with N-surpabove the regression line for the conventionalfarms are organic pig farms.

In the present scenarios, cash-crop, mixed andsmall farms converted to another farm type,where they cooperated with neighbouring dairy orpig farms and therefore, it is not possible tocompare N-surp from these farm types before andafter conversion. The effects of these neighbourfarm interactions are discussed below.

4.2. The regional le�el—effects of extensificationand management

The N-surp effect from conversion to organicfarming was divided into an extensification and amanagement effect. Similar extensification effectscaused by reduced livestock density were found byDoluschitz et al. (1992) and Halberg et al. (1995),who also documented an effect of management.However, in both studies, the relationship be-tween livestock density and N-surp was describedas linear in contrast to the non-linear relationshipfound here. The non-linearity adds an extra, re-gional-scale dimension to the extensification ef-fect, as the distribution of the livestock and thelivestock manure between farms within a regionalso becomes important. This can be illustrated bya small calculation example of a ‘region’ with twofarms, where a 100-ha dairy farm with 3 LSUha−1 is assumed to cooperate with a 100 hacash-crop farm with no LSU per hectare. If N-

surp is estimated from the equation in Fig. 3, thiswill result in an average N-surp of 245 kg N ha−1

per year. On the contrary, if the two farms coop-erate and the livestock units are distributedequally (1.5 LSU ha−1) on the 200 ha, the esti-mated N-surp would be reduced to 178 kg Nha−1 per year.

A clear extensification effect was identified inthe three scenarios for conversion to organicfarming. The groundwater-scenario with the low-est average livestock density also resulted in thelowest average N-surp, whereas the two otherscenarios both had a higher livestock density anda higher N-surp. Moreover, because of the inclu-sion of the exchange of manure and fodder be-tween farms, the livestock units were more evenlydistributed in the organic scenarios than in theconventional 1998-situation. The highest degree ofcooperation, expressed as the lowest variation inlivestock density, was found in the groundwater-and milk-scenarios (3 and 1). The pig-scenario (2)had a higher variation, but was still significantlylower than in the conventional situation (Figs. 3and 5).

A number of management practices, which af-fect the N-loss, are different in organic comparedto conventional farming. First, organic farms didnot use synthetic fertilisers, from which a signifi-cant effect on the N-surp was found on the con-ventional farms. In contrast, organic farms weremore dependent on green manure in the form offixed N from legumes and because of lower fieldcrop yields, a smaller livestock production couldbe sustained per area in organic compared toconventional farming. The statistical analysis ofthe conventional farm records revealed no signifi-cant N-surp effect from green manure, but thisfinding cannot be directly transferred to organicfarming, where the level of N-fixation is muchhigher, resulting in increased N-loss (Kristensen etal., 1995). The lower organic crop yields meantthat at a fixed livestock density, the net import offodder (i1+ i2−o4, Fig. 2) had to be higher fororganic compared to conventional farming yield-ing the same animal production. Consequently,conventional farming might leave space for someadditional cash-crop farming, which could exportcrop products and thereby reduce the N-surp.

T. Dalgaard et al. / Europ. J. Agronomy 16 (2002) 207–217216

However, the conventional cash-crop farms,recorded in the present study, have an averageN-surp of 87�24 kg N ha−1 per year which issignificantly higher than the average 55�24 kg Nha−1 per year N-surp from organic farming in thegroundwater-scenario (3). The organic manage-ment practice with self-sufficiency in fodder andfertiliser therefore reduced the N-surp in additionto the recorded N-surp reduction from livestockdensity extensification on the 41 conventionalfarms.

4.2.1. The regional le�el—nitrogen losses togroundwater protection areas

In future, more emphasis on N-loss in the formof nitrate (European Commission, 2000) and am-monia (Council of the European Union, 2000) isexpected. The technique presented here can beused to indicate whether organic farming mighthelp to reduce the overall N-loss. However, apartitioning into the different types of N-losswould require a combination with simulationmodels for nitrate leaching (Hansen et al., 2000;Børgesen et al., 2001) or ammonia volatilisation(Hutchings et al., 1996).

The analysis of N-loss from the area within andoutside the area with special interests in cleangroundwater reveals some interesting regionalscale interactions between farms where low N-surp coincides with high inter-farm exchange offodder and manure. However, if the scenarioswere carried out in another geographical area oron another geographical scale, these interactionsmight differ. In other geographical areas, the live-stock density variation between the conventionalfarms might be less than the variation between thepresently described 41 farms and therefore, theN-loss reduction from conversion to organicfarming with a more uniform livestock distribu-tion might not be significant. A generalisation ofthe pig-scenario (2) to the national scale would beunrealistic, because conversion of 25% of the na-tional, agricultural area to the defined type oforganic pig production would require more fod-der and manure imports than are available na-tionally. In contrast, the groundwater-scenario(3), where the converted organic farms are self-sufficient in fodder and fertiliser, could be gener-

alised to a national scenario, where 25% of thearea is converted to organic farming (Bichel Com-mittee, 1999). The groundwater-scenario (3) couldeven be used to illustrate the consequences of a100% conversion to organic farming, which is thecase within the area with special interests in cleangroundwater. However, the present results cannotbe directly transferred to the national level be-cause the national farming structure differs fromthe farming structure within the chosen area withspecial interests in clean groundwater, and there-fore, the strategy for conversion would also differ.

5. Conclusions

The N-surplus technique presented can be usedto investigate changes in the potential N-loss fromdifferent strategies for conversion to organicfarming, both at the farm level and for a localarea where the spatial distribution of farm typespresent must be considered. Conversion to or-ganic farming reduced the N-surplus by extensifi-cation of the livestock production and by changedmanagement practices. In particular, distributionof livestock manure between farms and lowerimport of feed stuffs and fertilisers reduced theN-surplus. The same driving forces might alsoreduce N-losses from conventional farming sys-tems, but this issue was not treated in the presentpaper. Organic farming can help to reduce poten-tial N-losses in the local area regarded and withinthe environmentally sensitive area with specialinterests to protect groundwater quality, but onlyif the conversion is designed with respect to thataim.

Acknowledgements

Thanks to The Danish Ministry of Food, Agri-culture and Fisheries and The Danish ResearchCentre for Organic Farming for funding the re-search projects ‘Land use and landscape develop-ment, illustrated with scenarios’ (ARLAS),‘Optimal redistribution of plant nutrient resourcesfrom animal manure’ and ‘Strategic and basicresearch into organic farming systems with special

T. Dalgaard et al. / Europ. J. Agronomy 16 (2002) 207–217 217

emphasis on biological and environmental aspects’,which made this article possible. We also thank thefarmers and the advisory service for cooperationwith the data collection and Peder Odderskær(NERI), Vibeke Langer (RVAU), RodrigoLabouriau (DIAS), Anders Højlund Nielsen(DIAS) and Inge Kristensen (DIAS) for usefulcontributions to the paper. Finally, Tommy Dal-gaard would like to thank his PhD supervisors NickHutchings and John R. Porter for commenting onthe paper and for additional PhD funding from theDanish Environmental Research Programme andThe Danish Institute of Agricultural Sciences.

References

Alders, J.G.M., 1991. The Nitrate Directive. EU Official Journal375 (91/676/EEC) 1–8.

Bichel Committee, 1999. Report from the Interdiciplinary Groupon Organic Farming. The Danish Environmental ProtectionAgency, Copenhagen 98 pp; ISBN 87-7909-292-6.

Børgesen, C.D., Djurhuus, J., Kyllingsbæk, A., 2001. Estimatingthe effect of legislation on nitrogen leaching by upscaling fieldsimulations. Ecol. Model. 136, 31–48.

Buller, H., Wilson, G.A., Holl, A., 2000. Agri–EnvironmentalPolicy in the European Union. Ashgate, Alderslot, UK pp.291; ISBN 1-84014-504-8.

Cobb, D., Feber, R., Hopkins, A., et al., 1999. Integrating theenvironmental and economic consequences of converting toorganic agriculture: evidence from a case study. Land UsePol. 16, 207–221.

Council of the European Union, 2000. Proposal for a directiveof the European Parliament and the Council on nationalemissions ceilings for certain atmospheric pollutants. Inter-Institutional File No. 99/0067, 27 June 2000, Brussels.

Dalgaard, T., Halberg, N., Kristensen, I.S., 1998. Can organicfarming help to reduce N-losses? Experiences from Denmark.Nutr. Cycl. Agroecosys. 52, 277–287.

Danish Ministry of Food, Agriculture and Fisheries, 1999.Directive for the Digital Danish Agricultural Registers(Forskrift for GLR/CHR Generelt Landbrugs Register/Cen-tralt Husdyrbrugs Register). Danish Ministry of Food,Agriculture and Fisheries, Copenhagen 200 pp.

Danish Ministry of Food, Agriculture and Fisheries, 2000.Administrative Order on Organic Farming. Directive No697:4210. 16th July, 2000.

Dobson, A.J., 1990. An Introduction to Generalised LinearModels. Chapman and Hall, London 174 pp; ISBN 0-412-31110-0.

Doluschitz, R., Welck, H., Zeddies, J., 1992. Stickstoffbilanzenlandwirtschaftlicher betriebe—einstieg in eine okologischebuchfuhrung? Ber. Landwirt 70, 551–565.

European Commission, 2000. Framework for Community action

in the field of water policy. Directive 2000/60/EC of theEuropean Parliament and of the Council, 23rd October, 2000.

Grundahl, L., Hansen, J.G., 1990. Atmosfærisk nedfald afnæringssalte i Danmmark. Miljøstyrelsen. Ministry of Envi-ronment, Copenhagen. NPo-forskning A6, 1–60.

Halberg, N., 1999. Indicators of resource use and environmentalimpact for use in a decision aid for Danish livestock farmers.Agric. Ecosys. Environ. 76, 17–30.

Halberg, N., Kristensen, I.S., 1997. Expected crop yield loss whenconverting to organic dairy farming in Denmark. Biol. Agric.Hort. 14, 25–41.

Halberg, N., Kristensen, E.S., Kristensen, I.S., 1995. Nitrogenturnover on organic and conventional mixed farms. J. Agric.Environ. Etic. 8 (1), 30–51.

Hansen, B., Kristensen, E.S., Grant, R., Høgh-Jensen, H.,Simmelsgaard, S.E., Olesen, J.E., 2000. Nitrogen leachingfrom conventional versus organic farming systems—a sys-tems modelling approach. Eur. J. Agron. 13, 65–82.

Hansen, B., Alrøe, H.F., Kristensen, E.S., 2001. Approaches toassess the environmental impact of organic farming withparticular regard to Denmark. Agric. Ecosys. Environ. 83,11–26.

Hutchings, N.J., Sommer, S.G., Jarvis, S.C., 1996. A model ofammonia volatilisation from a grazing livestock farm. Atmos.Environ. 30 (4), 589–599.

Korsaeth, A., Eltun, R., 2000. Nitrogen balances in conventional,integrated and ecological cropping systems and the relation-ship between balance calculations and nitrogen runoff in an8-year field experiment in Norway. Agric. Ecosys. Environ.79, 199–214.

Kristensen, E.S., Kristensen, I.S., 1992. Analysis of nitrogensurplus and efficiency on organic and conventional dairyfarms, Danish Institute of Animal Sciences. Research CentreFoulum 710, 1–54.

Kristensen, E.S., Høgh-Jensen, H., Halberg, N., 1995. A simplemodel for estimation of atmospherically-derived nitrogen ingrass/clover systems. Biol. Agric. Hortic. 12, 263–276.

Mogensen, L., Kristensen, T., Kristensen, I.S., 1999. ØkologiskKvægproduktion. DJF—Report No 10. 138 pp; ISBN1397-9892.

Plantedirektoratet, 1999. Guide for Fertiliser Accounting.Plantedirektoratet, Lyngby 68 pp; ISBN 87-601-8385-3.

Poulsen, H.D., Kristensen, V.F., 1998. Standard Values for FarmManure. DIAS—Report No. 7, 160 pp; ISSN 1397–9876.

Rudemo, M., 1979. Biostatistics. Part 2 (Statistik og Sandsyn-lighedslære med Biologiske Anvendelser, Del 2). DSR Forlag,Copenhagen ISBN 87-7432-170-6.

Statistics Denmark, 2000. Agriculture 1999. Statistics Denmark,Copenhagen.

Strudsholm, F., Nielsen, E.S., Flye, J.C., et al., 1997. Fodermid-deltabel 1997. Sammensætning og foderværdi af fodermidlertil kvæg. Danish Extension Service, Skejby, 69, 1–53.

van der Werff, P.A., Baars, A., Oomen, G.J.M., 1995. Nutrientbalances and measurement of nitrogen losses on mixedecological farms on sandy soils in The Netherlands. Biol.Agric. Hort. 11, 41–50.

Viborg County, 1998. Regional Plan 1997–2009 for ViborgCounty. Viborg County Council, Viborg. 135 pp.http:��gis.vibamt.dk�arealinfo