Effects of crop and livestock segregation on phosphorus resource use: A systematic, regional analysis

Europ. J. Agronomy 71 (2015) 88–95

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European Journal of Agronomy journal homepage: www.elsevier.com/locate/eja

Effects of crop and livestock segregation on phosphorus resource use: A systematic, regional analysis Thomas Nesme a,b,∗ , Kalimuthu Senthilkumar c , Alain Mollier d , Sylvain Pellerin d a

Bordeaux Sciences Agro, Univ. Bordeaux, UMR 1391 ISPA, F-33175 Gradignan, France McGill School of Environment, McGill University, Montréal, QC, Canada Africa Rice Center (AfricaRice), East and Southern Africa, P.O. Box 33581, Dar es Salaam, Tanzania d INRA, UMR 1391 ISPA, F-33883 Villenave d’Ornon, France b c

a r t i c l e

i n f o

Article history: Received 19 June 2014 Received in revised form 2 August 2015 Accepted 5 August 2015 Available online 2 September 2015 Keywords: Crop and animal segregation Fertilisers Integrated farming systems Manure Non-renewable resource Phosphorus

a b s t r a c t The integration of crops and animals is an option to reduce mineral fertiliser use through the recycling of nutrients in animal manure on croplands. But the increasing specialisation and spatial segregation of crop and livestock production systems both at the farm and the district scale may hamper the proper recycling of nutrients between these two activities. However, the effect of such segregation has only been investigated on some case-studies – mostly at the regional and the local scale – while we still lack of systematic assessment of this segregation in terms of mineral fertiliser use on a range of scales. In this paper, we estimated the effect of this segregation on nutrient resource use at the district scale. Phosphorus (P) fertiliser was considered since it is produced from a finite resource that needs to be more efficiently recycled in agriculture and France was chosen as a case study, representative of industrial countries with a wide range of variations in crop and livestock segregation. We quantified the effect of livestock density on mineral P fertiliser use and the effect of crop and livestock spatial segregation on P fertiliser use and its substitution with P in animal manure. Our results showed that P fertiliser use decreased with increasing livestock density at the district scale. However, the substitution of P fertiliser with P in animal manure was only partial (probably due to more N- than P-oriented decision making by farmers and low N:P ratio of organic manure), leading to large nutrient surpluses in districts with high livestock densities (>1.1 livestock unit per agricultural area). Finally, P fertiliser use increased with the spatial segregation of crops and livestock. Overall, our results demonstrated that lower segregation of crops and animals could help to save non-renewable resources, and that improvements in manure management are required. © 2015 Elsevier B.V. All rights reserved.

1. Introduction Contemporary agricultural production systems have become highly dependent on a number of critical, non-renewable resources such as phosphate rocks, groundwater and fossil energy (Tilman et al., 2002). Limiting the use of such resources in agriculture is of primary importance in order to preserve their stocks for future consumption and to mitigate harmful environmental effects (van Keulen, 2007; Hazell and Wood, 2008; Foley et al., 2011). Recycling natural resources within agricultural production systems should in particular be a major objective of farming system design and future agricultural policies (Dawnson and Hilton, 2011; Lehmann, 2013; Senthilkumar et al., 2014).

∗ Corresponding author at: UMR 1391 ISPA, Bordeaux Sciences Agro, 33175 Gradignan, France. E-mail address: [email protected] (T. Nesme). http://dx.doi.org/10.1016/j.eja.2015.08.001 1161-0301/© 2015 Elsevier B.V. All rights reserved.

Many reports have indicated that agricultural production systems that promote spatial and functional integration of crops and livestock are certainly key solutions to reduce natural resource consumption and in particular mineral fertiliser use (Naylor et al., 2005; Herrero et al., 2010; Lemaire et al., 2014; Peyraud et al., 2014): they stressed the key role played by livestock production in global nutrient cycles, either as a supplier of nutrient in manure or as a driver of mineral fertiliser demand through feed crop consumption (Matsumoto et al., 2010; Metson et al., 2012; Senthilkumar et al., 2012a; Cooper and Carliell-Marquet, 2013; Herrero and Thornton, 2013). Due to the expected increase in global livestock production, such a role in nutrient cycling should be once again reinforced in the next decades (Bouwman et al., 2013). In that context, recycling nutrients in manure on croplands is likely to drive global nutrient cycles and to play a significant role in meeting future fertiliser demand. However, there is growing evidence that crop and livestock production systems are increasingly segregated both at the global

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and regional scale (Gerber et al., 2005; Ramankutty et al., 2008; Neumann et al., 2009; Peyraud et al., 2014), in particular due to the agglomeration processes in livestock production (Gaigné et al., 2011). Previous studies have demonstrated that this segregation is likely to play a role on nutrient cycling and mineral fertiliser use but that this effect depends on the spatial scale: at the local scale (10–100 km2 ), segregation remains compatible with material exchanges (e.g., manure against grain) among neighbouring, specialised farms, thus enabling the local recycling of manure on croplands and reducing overall mineral fertiliser use (Nowak et al., 2013, 2015). On the contrary, at the regional scale (104 –105 km2 ), such exchanges are virtually absent due to manure transport costs: manure recycling on croplands is hampered and mineral fertiliser use is instead fostered to meet crop demand (Bateman et al., 2011; Senthilkumar et al., 2012b). However, these effects have been assessed on a limited set of case-study. In addition, while most of these studies focussed on manure recycling, they did not pay much attention to the effect on mineral fertiliser use. Finally, nutrient cycling at the intermediate spatial scale (103 –104 km2 ) has been poorly characterised so far. The question therefore remains about the systematic effect of crop and livestock segregation on fertiliser use on a range of scales and case-studies. We addressed this question in this paper while hypothesising that this segregation fostered mineral fertiliser use through limited manure recycling. Hereafter, we provide a systematic quantification of the effects of crop and livestock segregation on mineral fertiliser use under a wide range of segregation conditions. Segregation was defined as the clustering — or agglomeration — of livestock production. It encompassed both the spatial separation of livestock and crop production and the lack of functional interaction between specialised arable and livestock farms. It was assessed using the coefficient of variation of animal stocking rate at the department scale as a proxy. We used France as a case study, representative of countries with intensive agriculture, moderate livestock density and with a wide range of crop and livestock segregation conditions. This paper is primarily focused on the phosphorus (P) resource and mineral P fertiliser use. Since mineral P fertilisers are produced from phosphate rocks whose future availability is becoming increasingly bleak (Cordell et al., 2009; Van Vuuren et al., 2010), there is a clear need to design agricultural production systems that improve P resource recycling and limit mineral P fertiliser use. This study will contribute to understanding the drivers of mineral fertiliser use and will provide evidence for public policies aiming at conserving the non-renewable production resources on which agriculture depends.

2. Materials and methods 2.1. Geographic scale of study and data collection The effect of crop and livestock segregation on mineral P fertiliser use was assessed at the department scale for France. A department is a geographic and administrative unit of approximately 5000 km2 (70 × 70 km), further divided into some 30 cantons of approximately 150 km2 (12 × 12 km). Seventy-six departments were considered in this study out of a total of 96 departments (excluding overseas territories). The remaining 20 departments were either urban (e.g., the seven departments of the Paris area) or had more than 20% of their agricultural area under horticultural crops (viticulture, vegetables, fruits or perfume crops), making them subject to very specific P management decision-making (Nesme et al., 2011). For each department, the agricultural mineral P fertiliser use was calculated as the annual mineral P fertiliser delivery at the department scale, divided by the agricultural area of the depart-

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Table 1 Livestock unit equivalent and annual P excretion per animal category. Animal type

Livestock Unit equivalent

Annual P excreta (kg P animal−1 yr−1 )a

Bovines Dairy cow Beef cow Dairy heifer Beef heifer Calf

1.00 0.85 0.70 0.70 0.30

17.6 16.2 9.2 9.4 3.6

Ovines and caprines Goat Ewe Lamb

0.17 0.15 0.06

2.6 2.6 1.2

Equines Horse Donkey and mule

0.73 0.70

11.4 11.4

Pigs Sow Piglet Young pig (20-50 kg) Fattening pig (> 50 kg)

0.31 0.06 0.16 0.26

6.1 0.9 0.9 2.8

Poultry and rabbits Hen Chick Broiler Duck Turkey Goose Guinea fowl Rabbit

0.01 0.01 0.01 0.01 0.01 0.02 0.01 0.12

0.1 0.05 0.07 0.2 0.3 0.2 0.1 1.9

a For animals bred for less than one year (e.g., poultry), the annual P excretion was calculated as the P excretion per animal multiplied by the number of animal batches per year. The annual P excretion data were extracted from published synthesis reports for bovines (CORPEN, 1999a, 2002), ovines, caprines and equines (CORPEN, 1988), pigs (CORPEN, 2003), poultry (CORPEN, 2006) and rabbits (CORPEN, 1999b).

ment (calculated as the sum of croplands and grasslands). The data concerning mineral P fertiliser delivery were collected from the ‘Union des Industries de la Fertilisation’ (UNIFA, n.d.), which records mineral fertiliser deliveries to farmers. Data concerning agricultural areas were collected from the statistical division of the French Ministry of Agriculture (AGRESTE, n.d.). Data concerning the stocking rate were expressed in Livestock Units (LU, see Table 1) and were also collected from AGRESTE (n.d.). For each department (or canton), the stocking rate was calculated as the ratio between the number of livestock units in the department (or canton) divided by the agricultural area of the department (or canton), and was expressed in LU ha−1 of agricultural area. The stocking rate ranged from 0.1 to 3.9 LU ha−1 of agricultural area among the different departments (Fig. 1a), and from 0 to 7.8 LU ha−1 of agricultural area among the different cantons (Fig. 1b). Data concerning mineral P fertiliser use corresponded to the annual average of the years 2002–2006. Data concerning the stocking rate corresponded to the year 2000 which was the most recently available year at the time of the study. 2.2. Effect of animal stocking rate on mineral P fertiliser use The correlation between the animal stocking rate and mineral P fertiliser use was examined over the 76 selected departments. In addition, we estimated the substitution of mineral P fertiliser with organic P. The organic P fertiliser application corresponded to P supply to soils through animal excretion. It was calculated by estimating P in animal excretion based on a linear regression between livestock unit equivalents and individual annual P excretion in kg P LU−1 yr−1 for the different animal categories (see Table 1 and Fig. 2). Then, for each department, the organic P fertiliser application was

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a

b

Fig. 1. Animal stocking rate (in livestock unit per ha of agricultural area) per department (a) and per canton (b).

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Fig. 2. Livestock unit and annual P excretion (in kg P animal−1 yr−1 ) for the different animal categories reported in Table 1.

calculated by multiplying the number of livestock units by the slope of the regression, i.e., 16.5 kg P LU−1 (Fig. 2). We considered that P import and export in animal manure among departments were negligible and that manure was applied on croplands and grasslands at the same rate. Finally, the correlation between stocking rate and mineral P fertiliser substitution was examined across the 76 departments. We also compared the total P supply (organic + mineral) to crop P removal in harvested biomass (both grain crops and grasslands) at the department scale. P removal in harvested biomass was considered as a proxy for crop P requirements: since soil P status is generally high in France (Follain et al., 2009), we assumed that additional P fertiliser application in excess of crop P removal was not needed to enrich soil P. The crop P removal was calculated by multiplying crop production per department by their respective P content (Table S1). Crop production per department was collected from AGRESTE (n.d.) for the years 2002–2006. Supplementry material related to this article found, in the online version, at http://dx.doi.org/10.1016/j.eja.2015.08.001. Finally, due to lower N:P ratio in livestock manure than in ˜ crop products (Penuelas et al., 2013; Withers et al., 2015) and due to the critical importance of N management for crop productivity, one can hypothesise that farmers better align their N supply to crop removal than they do their P supply, leading to some P over-fertilisation. To test this hypothesis, we compared the total N supply (organic + mineral fertilisation + biological fixation) to crop N removal at the department scale. The crop N removal was calculated by multiplying crop production per department by their respective N content (data not shown). Organic fertilisation corresponded to N supply to soils through animal excretion. It was calculated by multiplying the number of livestock units by the slope of the regression between livestock unit equivalents and individual annual N excretion, i.e., 88.7 kg N LU−1 (Fig. S1). Mineral N fertiliser use data were collected from UNIFA (n.d.). Both organic and mineral fertilisations were corrected for losses through leaching and volatilisation according to IPCC guidelines (http://www.ipcc-nggip. iges.or.jp/public/2006gl/vol2.html, accessed on July 10th, 2015), namely 50 and 40% for organic and mineral fertilisation, respectively. The biological N fixation was calculated as the area under legume crops multiplied by their average N fixation rates. The area under legume crops were collected from AGRESTE (n.d.) whereas the average N fixation rates were extracted from the literature (Smil, 1999). Based on these methods, we found average N:P ratios of crop products and animal manure (accounting for gaseous N losses) of 6.5 and 2.7, respectively which was in good agreement with the literature (Sadras, 2006; Toth et al., 2006). Supplementry material related to this article found, in the online version, at http://dx.doi.org/10.1016/j.eja.2015.08.001.

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Fig. 3. Relationship between the animal stocking rate (in LU ha−1 ) and mineral P fertiliser use (in kg P ha−1 yr−1 ) at the department scale. Each point represents one French department. The break point of the segmented regression model is 1.2 LU ha−1 (standard error: 0.2 LU ha−1 ).

2.3. Effect of crop and livestock segregation on mineral P fertiliser use To estimate the effect of crop and livestock segregation on mineral P fertiliser use, we used the variation coefficient of the stocking rate over the cantons of a department as a proxy for crop and livestock segregation at the department scale. For a given department, the animal stocking rate was extracted for each canton from AGRESTE (n.d.). All the cantons for which the agricultural area was less than 30% of the total area were then eliminated, making it possible to retain only agricultural cantons. Subsequently, for each department, both the mean stocking rate and the standard deviation of the stocking rate over the cantons were calculated. Finally, the variation coefficient of the stocking rate was calculated as the ratio between the standard deviation and the mean stocking rate at the department scale. The higher the variation coefficient was, the more aggregated the animals within a given department were and, as a result, the more segregated the crops and livestock were. The variation coefficient of the stocking rate ranged from 10 to 137%, indicating a wide range of crop and livestock segregation (Fig. S2). Mineral P fertiliser use and the variation coefficient of the stocking rate were then compared using linear regression over the 76 departments. Additionally, mineral P fertiliser use was compared between departments using variation coefficients both greater and lower than 60% using an ANOVA followed by a Tukey test. Supplementry material related to this article found, in the online version, at http://dx.doi.org/10.1016/j.eja.2015.08.001. Data treatments were performed with R software (R Development Core Team, 2009). Maps were produced with the sp package. Regression models with segmented relationships between the response and the explanatory variables were fitted with the segmented R package. This procedure helped to determine breakpoints in piecewise linear relationships. 3. Results 3.1. Effect of animal stocking rate on mineral P fertiliser use As expected, the results showed that mineral P fertiliser use decreased with increasing animal stocking rates at the department scale (Fig. 3). However, a high variability in mineral P fertiliser use remained for departments with moderate stocking rates (<1 LU ha−1 ). In addition, mineral P fertiliser use remained approximately constant, between 5 and 10 kg P ha−1 yr−1 for departments with high stocking rates (>1.2 LU ha−1 ).

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Fig. 4. Relationship between the organic P fertiliser use divided by mineral plus organic P fertiliser use (unitless) and animal stocking rate (in LU ha−1 ) at the department scale. Each point represents one French department. The break point of the segmented regression model is 1.1 LU ha−1 (standard error: 0.1 LU ha−1 ).

Fig. 5. Relationship between mineral P fertiliser use (in kg P ha−1 yr−1 ) and crop P removal minus organic P fertilisation (in kg P ha−1 yr−1 ). Each point represents one French department: departments with stocking rate lower than 1.1 LU ha−1 were represented with green circles whereas those with stocking rate greater than 1.1 LU ha−1 were represented with red triangles. The dotted line represents the 1:1 line.

3.2. Effect of animal stocking rate on mineral P substitution The contribution of mineral P fertiliser to P fertilisation of agricultural lands decreased with increasing livestock population: the ratio of organic P fertiliser use divided by mineral plus organic P fertilisation increased with increasing stocking rates for the 76 selected departments (Fig. 4). However, similar to the pattern observed in Fig. 3, this ratio hardly increased for departments with animal stocking rates greater than 1.1 LU ha−1 . This suggests that mineral P fertiliser was not entirely substituted with P in animal manure even for departments with high stocking rates. The mineral P substitution was also assessed by comparing the mineral P fertiliser use with the difference between crop P removal and organic P fertilisation (Fig. 5). This difference between crop removal and organic P fertilisation represented an estimator of the mineral P fertiliser demand, whereas the 1:1 line corresponded to a theoretical full substitution situation. The results indicated that almost all the departments were above the 1:1 line. This illustrates that most departments exhibited over-fertilisation, in particular due to significant mineral fertiliser supply. Once again, this suggests a general, only partial substitution between mineral and organic P even for departments with moderate stocking rates (<1.1 LU ha−1 , see Fig. 5).

Fig. 6. Relationship between P application to agricultural soils (in kg P ha−1 yr−1 ) and crop P removal (in kg P ha−1 yr−1 ) at the department scale. P application to soils is expressed as mineral P fertiliser (‘Mineral’), organic P fertiliser through animal manure (‘Organic’) and the sum of both (‘Total’). Each point represents one French department. The dotted line represents the 1:1 line.

The application of mineral + organic P fertiliser to agricultural soils was in great excess when compared to annual crop P removal for many of the departments: up to 3.5 times crop P removal (Fig. 6). P fertilisation excess increased with the animal stocking rate: total P fertilisation was always greater than twice the crop P removal for departments with stocking rates higher than 2 LU ha−1 (data not shown). This excess resulted from moderate mineral P fertiliser applications, often combined with much larger organic P application through animal manure (Fig. 6). For many departments, the mineral P fertiliser applications were lower than crop removal, but organic P application alone was greater than crop removal in 42 out of the 76 departments. The comparison of crop N removal with N supply through organic + mineral fertilisation and biological N fixation showed that N supply was in better agreement with crop removal than was P supply. On average the N excess was +26 kg N ha−1 yr−1 , which is 26% of average N removal, whereas the P excess was +11 kg P ha−1 yr−1 , which is 71% of average P removal (Fig. S3 and Fig. 6). N supply to soils was close to crop requirements for highest crop requirement values, but in excess for lowest values. This suggests that N oriented fertilisation strategy and low N:P ratio of organic manure may be responsible for excess P, at least for the most intensive situations. Supplementry material related to this article found, in the online version, at http://dx.doi.org/10.1016/j.eja.2015.08.001. 3.3. Effect of crop and livestock segregation on mineral P fertiliser use Crop and livestock segregation at the department scale was associated with increased mineral P fertiliser use: a weak (r2 = 0.34) but highly significant (p < 0.001) correlation between the variation coefficient of the stocking rate and mineral P fertiliser use was observed for the 76 selected departments (Fig. 7). In addition, departments with a low coefficient of variation (<60%) exhibited an average annual mineral P fertiliser use of 8.9 kg P ha−1 yr−1 , whereas those with high variation coefficients (>60%) exhibited an average mineral P fertiliser use of 14.3 kg P ha−1 yr−1 (p < 0.01). To control for the possible effects of extreme values of the stocking rate, mineral P fertiliser use was calculated by selecting departments with a smaller range of stocking rate (between 0.5 and 1.5 LU ha−1 , n = 48 departments): the same result was observed since departments with a variation coefficient lower than 60% exhibited an average annual mineral P fertiliser use of 8.0 kg P ha−1 yr−1 , whereas those with a variation coefficient

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Fig. 7. Relationship between the variation coefficient of the stocking rate (in %) and P fertiliser use (in kg P ha−1 yr−1 ) at the department scale. The line indicates the linear regression between the two variables.

greater than 60% exhibited an average mineral P fertiliser use of 12.3 kg P ha−1 yr−1 (p < 0.1). Similar results were observed when plotting the estimated, theoretical mineral P fertiliser demand (calculated under a full substitution assumption) instead of the observed mineral P fertiliser use vs. the variation coefficient of the stocking rate (data not shown). 4. Discussion The increased scarcity of rock phosphate resources at the global scale calls for sparing use of mineral P fertiliser and for the design of agricultural production scenarios that improve P resource recycling locally (Dawnson and Hilton, 2011; Cordell et al., 2012), for example through direct spreading of animal waste on croplands (Elser and Bennett, 2011). However, the feasibility of these scenarios is highly dependent on functional and spatial integration of crop and livestock production (Lemaire et al., 2014; Peyraud et al., 2014). The results presented here provide elements and a platform to discuss and develop such scenarios. 4.1. Effect of livestock density on mineral P fertiliser use Our results showed that, as expected, mineral P fertiliser use decreased with increasing animal stocking rate at the department scale (Fig. 3). These results indicated that farmers have probably substituted a part of mineral fertilisers with animal manure. In other words, this suggests that crop and livestock integration helps to reduce mineral fertiliser use at moderate spatial scale (103 –104 km2 ). However, our results also showed that the substitution of mineral P with P in animal manure was not total, particularly for departments with stocking rates greater than 1.1 LU ha−1 (Fig. 4). Even for departments where P in animal manure could compensate for crop P exports, mineral P fertiliser use was still significant (Fig. 5). Therefore, our results call for a less optimistic view of the role of livestock in providing a source of nutrients to be substituted for mineral fertilisers. Such partial substitution should be considered in scenarios of mineral nutrient use under global changes in animal production (Bouwman et al., 2009; Bouwman et al., 2013), at least under the current economic and technological conditions and for situations of intensive agriculture similar to those found in France. This partial substitution resulted in large soil nutrient surpluses in many cases (Fig. 6) and, thus, in potential impacts on terrestrial and aquatic ecosystems (e.g., on fresh water eutrophication). P surpluses may also result from more ‘N-oriented’ than ‘P-oriented’ decision-making by farmers: due to the critical role played by N fertilisation in temperate crop production, farmers may prefer their

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fertilisation to match crop N requirements instead of crop P requirements. As the N:P ratio of livestock products is lower than that of crop products (Withers et al., 2015), this may result in P overfertilisation. This is in agreement with Fig. S3 which shows that N fertilisation was in better agreement with crop N requirements than was P fertilisation. Moreover, for seven departments with high stocking rates (in particular for the 5 departments of Britany where large livestock industries have been concentrated), P supply to agricultural soils through animal manure largely exceeded crop exports. Even if mineral P fertiliser use was set to 0 for these departments, the P budget would remain positive. Such a situation is common in many regions that are highly specialised in animal production, e.g., the Netherlands, Belgium, western England, SouthEast Asia and the east coast of China (Gerber et al., 2005; Bateman et al., 2011). In these regions, the observed stocking rates are highly questionable from an environmental standpoint. When combined, these two effects may partially explain the strong imbalance in nutrient supply to agricultural soils that is observed worldwide (Gerber et al., 2005; MacDonald et al., 2011). While many authors have reported similar P fertilising values of animal manure when compared to mineral fertilisers (He et al., 2004; El-Motaium and Morel, 2007; Sa and Lal, 2009; Otinga et al., 2013; Slaton et al., 2013), this partial substitution is questionable. It may result from a series of factors related to farmers’ practices given that farmers systematically underestimate the P fertilising value of manure (Bateman et al., 2011), probably due to uncertainties in P fertilising value estimation (Pellerin et al., 2014). Moreover, farmers may not assign the same roles to mineral fertilisers compared to animal manure. Previous studies have demonstrated that farmers use mineral P fertilisers to boost initial crop growth, even in soils with high soil P status (Nesme et al., 2011). Additionally, since manure is cumbersome, its management is more complex than mineral fertiliser in terms of storage, handling and spreading, making the substitution of mineral fertilisers difficult with typical over-application of manure close to farm buildings and animal stables (Bellon and Demarque, 1994; Aubry et al., 2006; Tittonell et al., 2007). Differences in animal type may also explain this partial substitution: while animal manure can be efficiently collected for housed animals (e.g., swine and poultry), such collection is more complicated for grazing animals, thus limiting opportunities for manure recycling on arable crops. In other words, our assumption of similar application rates of manure on croplands vs grasslands (see Section 3.2) may be too simplistic. However, the lack of detailed data on monogastric vs ruminant stocking rate and on manure application practices did not allow us to investigate these possible effects. Finally, the full substitution of mineral fertiliser at the department scale would assume that animal manure may be exchanged among specialised farms, which did not appear to be the case (see below). 4.2. Effect of crop and livestock segregation on mineral P fertiliser use Our results confirmed previous case studies that analysed the role of crop and livestock segregation on mineral fertiliser use at global or regional scales (Mishima et al., 2010; Bateman et al., 2011; Schipanski and Bennett, 2012; Senthilkumar et al., 2012b). In addition to providing innovative results at the intermediate spatial scale, our analysis expanded on previous findings through a systematic exploration of the effect of crop and livestock segregation over a wide range of variations in segregation intensity: mineral P fertiliser use on croplands increased with the coefficient of variation of the stocking rate at the department scale, even when focussing on departments with limited range of the stocking rate (Fig. 7). Compared to previous studies, our results suggest that the effect of crop and livestock segregation was significant at

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the moderate spatial scale of a French department (with a radius of approximately 70 km). Overall, these results demonstrated that the segregation of agricultural production systems could result in large over-fertilisation through excess of manure, leading to highly positive soil nutrient budgets despite some substitution. Segregation also acted as a driver of mineral fertiliser use and probably explained some of the partial substitution of mineral fertiliser with organic P: in addition to farm specialisation that compromises inner-farm nutrient recycling from livestock to croplands, the spatial segregation of crop and livestock production makes the development of material exchanges among specialised farms (e.g., manure vs. grain) more difficult. As a result, the potential to recycle nutrients from manure and to close the nutrient loop is dramatically altered in such specialised production basins (Nowak et al., 2015) and leads to strong imbalances in nutrient management, i.e., both increased mineral fertiliser use in arable areas and local excess of nutrient supply to soils in livestock areas (Gerber et al., 2005; Vitousek et al., 2009; Liu et al., 2010; MacDonald et al., 2011). In the context of livestock aggregation at different scales (Neumann et al., 2009), these results demonstrated that in addition to major environmental issues related to livestock aggregation such as pasture over-grazing, biodiversity conservation and disease propagation (Maton et al., 2005; Herrero and Thornton, 2013; Eisler et al., 2014), mixed agricultural regions tend to perform better in terms of conservation of non-renewable resources such as phosphorus. 5. Conclusion This study demonstrated that crop and livestock segregation, estimated by livestock agglomeration at the department scale, is associated with strong impact on the P cycle and with increased mineral P fertiliser use. It also demonstrated that although mineral fertiliser use decreased when the stocking rate increased at the department scale, the substitution of mineral P with organic P was not total. When combined with situations where – as a result of high stocking rates – organic nutrients are in great excess compared to crop P removal, this partial substitution led to soil nutrient excess in many French departments. These results contribute to the accrued interest in integrated, mixed crop-livestock farming systems for non-renewable resource conservation. In particular, they suggest that the integration of crops and livestock at the intermediate spatial scale (103 –104 km2 ) could help to better close the local P cycle and to save mineral P resources, provided that greater efforts are made to substitute mineral fertilisers with organic sources. Acknowledgements This work was funded by Bordeaux Sciences Agro (Univ. Bordeaux) and the “Environment and Agronomy” Division of INRA. We thank Philippe Eveillard (UNIFA) for providing the data concerning fertiliser use and Gail Wagman and John Regan for improving the English. References Aubry, C., Paillat, J.-M., Guerrin, F., 2006. A conceptual model of animal wastes management in the Reunion Island. Agric. Syst. 88, 294–315. Bateman, A., van der Horst, D., Boardman, D., Kansal, A., Carliell-Marquet, C., 2011. Closing the phosphorus loop in England: the spatio-temporal balance of phosphorus capture from manure versus crop demand for fertiliser. Resour. Conserv. Recycl. 55, 1146–1153. Bellon, S., Demarque, F., 1994. Gestion des fumiers dans des exploitations de polyculture-élevage ovin dans les Préalpes. Fourrages 140, 523–541. Bouwman, A.F., Beusen, A.H.W., Billen, G., 2009. Human alteration of the global nitrogen and phosphorus soil balances for the period 1970-2050. Glob. Biogeochem. Cycles 23, GB0A04. Bouwman, A.F., Goldewijk, K.K., van der Hoek, K.W., Beusen, A.H.W., Van Vuuren, D.P., Willems, J., Rufino, M.C., Stehfest, E., 2013. Exploring global changes in

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