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Nitrogen and phosphorus surpluses on Danish dairy and pig farms in relation to farm characteristics
Livestock Production Science 96 (2005) 97 – 107 www.elsevier.com/locate/livprodsci
Nitrogen and phosphorus surpluses on Danish dairy and pig farms in relation to farm characteristics A.H. Nielsen*, I.S. Kristensen Danish Institute of Agricultural Sciences, Department of Agroecology, P.O. Box 50, DK-8830 Tjele, Denmark
Abstract N and P surpluses per hectare at farm level were determined on 63 private pilot farms with data from 2 to 7 years between 1997 and 2003 (a total of 245 observations). Farms were classified in the following four farm types: Conventional mixed dairy, organic mixed dairy, conventional pig farms (indoor) and conventional pig farms with outdoor sows. Import of nutrients with concentrate and fertilizer was the major input to all conventional farm types. On the organic dairy farms major input was N fixation, but also import of nutrients with concentrate and manure were important inputs. Output from the dairy farms was dominated by nutrients in milk. On pig farms nutrients in meat dominated the output, but also export of nutrients with cash crops and manure were important outputs. Farm type, year and farm within farm type significantly affected both N and P surpluses per hectare. Farm type was the major source of variation in both N and P surpluses. In the period investigated N surplus decreased by 6.5 kg N ha 1 yr 1 and P surplus decreased by 0.7 kg P ha 1 yr 1. The N and P surpluses observed on the conventional dairy farms significantly exceeded surpluses observed on the organic dairy farms. At equal number of livestock units (LU) per hectare (1.28 LU ha 1) the difference was 43 kg N ha 1 and 6 kg P ha 1. At equal rates of N or P in manure to fields (147 kg N ha 1, 29 kg P ha 1, respectively) the difference was 45 kg N ha 1 and 4 kg P ha 1. Conventional dairy farms and pig farms with sows indoors had equal N and P surpluses at equal rates of N or P in manure to fields. Corrected to the average year (1999.5) the estimated average N and P surpluses showed highest levels on pig farms with outdoor sows (251 kg N ha 1, 42 kg P ha 1) and lowest levels on organic dairy farms (113 kg N ha 1, 7 kg P ha 1). Surpluses on the conventional dairy farms were 175 kg N ha 1 and 16 kg P ha 1 and on the indoor pig farms they were 123 kg N ha 1 and 13 kg P ha 1. The N and P surpluses observed on Danish conventional mixed dairy farms were comparable with intensive dairy farming systems in other European countries. D 2005 Published by Elsevier B.V. Keywords: Farm gate balances; Nutrient use efficiency; Pilot farms; Dairy farms; Pig farms
1. Introduction
* Corresponding author. Tel.: +45 89991202; fax: +45 89991200. E-mail address: [email protected] (A.H. Nielsen). 0301-6226/$ - see front matter D 2005 Published by Elsevier B.V. doi:10.1016/j.livprodsci.2005.05.012
Losses of nitrogen (N) and phosphorus (P) from agriculture are of public concern due to environmental consequences such as reduced quality of drinking
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water and eutrophication. Farm nutrient surplus is widely used in Europe as an indicator of nutrient use efficiency and potential losses of nutrients from farming systems (Halberg et al., 2005). In Denmark farmers can now receive a state funded grant to calculate farm level nutrient balances. This has led to a number of approx. 300–500 nutrient balances calculated each year. Software has been implemented so that local agricultural advisors can calculate nutrient balances by routine. These subsidised nutrient balances have to comply with certain quality standards. Advisors are liable to make a technical review where they evaluate the nutrient surplus obtained. The evaluation must include a plan showing how surplus could be reduced. This has raised questions as to what level of nutrient surplus would be attainable for a farm under a certain set of conditions and to what indicates good or bad nutrient household. Halberg et al. (1995) showed that in Denmark organic dairy farms had a lower N surplus and a higher N efficiency than conventional dairy farms. N surplus was positively correlated with the number of livestock units per hectare on the conventional farms and there was no effect of soil type. Since Halberg et al. (1995) recorded their data in 1989/ 1990 nutrient turnover of Danish agriculture has undergone great changes, and more data have become available for different types of farms. The aim of the present paper was to study sources of variation in N and P surpluses on Danish dairy and pig farms and to establish updated benchmarking values for N and P surpluses at farm level.
Funen. The farms are not representative for Danish agricultural as a whole, but the farmers have been selected to be progressive and interested in cooperation with experts. From the database farms representing four main farm types were selected. Only farms with data from at least two consecutive years were included. Dairy farms were grouped as conventional and organic dairy farms. Dairy farms which also produced pigs or had data from less than 4 years of production after initiating conversion to organic farming were excluded. Specialised pig farms and arable farms with pig livestock were grouped according to housing of the sows. Farms with sows outdoors were denoted bOut-pigQ and farms with all livestock indoors were denoted bIn-pigQ. Based on these criteria a total of 63 farms with data from 2 to 7 years (a total of 245 farms year) were available for further analysis (Table 1). Major key figures describing the four farm types are given in Table 2. Average milk yield was 8448 kg ECM1 cow 1 year 1 on the conventional dairy farms and 7726 kg ECM cow 1 year 1 on the organic dairy farms. This is about 13% above the national average level in 1999 (Kristensen et al., 2005). Due to a greater number of milking cows per hectare the conventional dairy farms had 7693 kg ECM ha 1 compared with 4772 kg ECM ha 1 on organic dairy farms. Some pig farmers only fed pigs for slaughter, some only had sows and sucklings and some had a fully integrated production. One integrated pig farm also produced young slaughter pigs (fed from 35 to about 60 kg). 2.2. Nutrient balance calculation
2. Materials and methods 2.1. Farm data Since 1997, detailed information about all the major aspects of the production on approximately 75 private farms has been collected in accordance with a protocol (Anon., 2004) by local farm advisors and assistants. All major external and internal mass flows on the farms have been measured or set by standards. After comprehensive quality control, data have been stored in a database (MS Access). Each farm has generated data in one to seven consecutive years. Most of the farms are located in Jutland and on
A subsystem balance approach was used to calculate farm level nutrient surplus (Fig. 1). The production of nutrients in manure was calculated from a livestock nutrient balance. Flow of nutrients with manure to the fields was calculated from a manure storage balance. Farm level N balance was then calculated from surface balances by adding standard estimated gaseous losses of N from housing of animals and storage of manure and straw treated with ammonia (Poulsen et al. (2001), an update from Poul-
1
ECM: energy corrected milk.
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Table 1 Pilot farms with data from two to seven consecutive years, number of farms per year and per farm type
Conventional dairy Organic dairy In-pig Out-pig Total
Year farm per year
Total
1997
1998
1999
2000
2001
2002
2003
year farm
no. farms
17 2 15 4 39
20 4 15 4 44
18 5 10 5 39
13 11 11 5 41
16 8 11 5 41
13 9 7 – 30
9 8 – – 17
106 47 69 23 245
25 13 19 6 63
sen and Kristensen (1998)). For P the farm level balance equals the surface balance directly since no P is lost to air. Calculations followed the principles described in Halberg et al. (1995) and further developed by Sveinsson et al. (1998), Kristensen and Hermansen (2002) and Kristensen (2002). All the amounts of animal feedstuff used, bedding materials, fertilizer, seeds, manure imported and exported, milk produced, crops harvested and the numbers and weights of animals entering or leaving the herd were recorded on the farms on a regular basis according to a protocol (Anon., 2004). Concentrations used for calculating nutrient content were obtained by chemical analysis (primary fodder crops) or set by standards.
Total
Nitrogen fixation in pure legume crops was estimated from crop yields as described by Høgh-Jensen et al. (2004) and Høgh-Jensen et al. (2003). Fixation in clover grass was estimated from dry matter yield and amount of plant available N from applied fertilizer and manure (Hvid, 2004). Deposition was set by a standard (15 kg N ha 1; Ellermann et al., 2003). Nutrient use efficiency at farm gate (N or P eff.ANIMAL PRODUCTS) was calculated as nutrients in sold milk and meat divided by nutrients in fertilizer, N2-fixation, deposition, irrigation, seeds and net imported feed and manure (Halberg et al., 1995). Some pig farms exported more nutrients with cash crops than with animal products and therefore nutrient
Table 2 Major characteristics for the analysed pilot farms Unit
Dairy farms Organic
Livestock Cows Heifers Calves for slaughter Sows Piglets Slaughter pigs Livestock rate
Animala Animal Animal Animal No. produced year 1 No. produced year 1 LUb ha 1
Field production Farm land Permanent grass Set aside Cereal for harvest Other crops for sale Maize, fodder beets and whole crop Grass/clover in rotation Net yield crop production
hectare/farm %c % % % % % SFUd ha 1
a b c d
Pig farms Conventional
104 101 9 – – –
107 109 17 – – –
1.14
142 7 3 16 1 16 40 4446
1.54
111 8 5 23 4 29 22 6218
Indoor
Sows out door
– – –
– – –
126 3043 3063 1.54
221 4454 1364 1.69
124 1 8 72 20 0 0 6507
67 1 7 65 7 2 19 4355
365 feeding days. Livestock units; 1 LU is equal to 0.85 Holstein dairy cow or 4.3 sows in 1 year or 175 piglets at 7 kg or 36 slaughter pigs fed 30–100 kg. Percentage of farmland. Scandinavian Feeding Units, 1 SFU = 7.88 MJ net energy.
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Concentrate Fodder grain
Animal
Herd
Milk
Animal Manure
Straw import
Bedding matr.
Manure import
Manure storage
Manure export
Fodder crop storage Roughage, foddergrain and straw
Grazing
Manure from grazing
Manure from storage
Field Seeds
Grain
N fertilizer Deposition N2 fixation
Cash crops
Fig. 1. Flows accounted for in the calculations of N and P balances at farm level.
use efficiency at farm level was not calculated for the pig farms. Nutrient use efficiency for the herd (N or P eff.HERD) was calculated as nutrients in animal products divided by nutrients in animal feed. Nutrient use efficiency for the field (N or P eff.FIELD) was calculated as nutrients in harvested crops divided by nutrients inputs for the field (fertilizer, manure, N2-fixation, deposition, irrigation, seeds). 2.3. Statistical methods Effects of year, farming system and production intensity on N and P surpluses were assessed by analysis of variance using the SAS System for General Linear Models. Model 1 was used to test the effect of year, farm type and farms within farm type. Yijk ¼ l þ Ei þ Tj þ Fk ð jÞ þ eijk
ð1Þ
where Yijk was the N or P surplus of the kth farm of jth farm type in the ith year, l was the overall mean, E i was the effect of year, T j was the effect of farm type
and F k( j) was the effect of farm within farm type. e ijk was the residual error, which was assumed independent and identically distributed as N(0, d 2). The effect of farm type was tested against the variation between farms within farm type. Model 2 used average data from 2 to 7 years per farm to test the effect of production intensity on N and P surpluses. Yearly surpluses over two consecutive years are related due to buffer capacity of the soil. Due to low number of observations, pig farms with sows outdoors (bOut-pigQ) were excluded prior to these analyses. On four pig farms average livestock rates exceeded 2.1 LU ha 1. Their average export of manure was 249 kg N ha 1. Ammonia lost during storage of the manure for export is included in the farm N surplus. Therefore, these four farms were excluded as well due to divergent N surpluses. Available for further analysis was 53 observations (25 conventional dairy farms, 13 organic dairy farms and 15 indoor pig farms). Yij ¼ l þ Tj þ bLi þ eij
ð2Þ
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ents in milk. On pig farms nutrients in meat dominated the output, but also export of nutrients with cash crops and manure were important outputs. There was a large variation within farm types, especially within the indoor pig farms. This category includes arable farms with low pig production and also specialized pig farms with low export of cash crops. However, high input also gives high output and the variation in N surplus within the indoor pig farms is considerably lower than the variation in concentrate input and export of meat and manure. Year, farm type and farm within farm type significantly affected both N and P surpluses (Table 5). Farm type was the major source of variation in both N and P surpluses. Estimated average N and P surpluses showed highest levels on pig farms with outdoor sows (251 kg N ha 1, 42 kg P ha 1) and lowest
where Yij was the response variable of the ith farm of jth farm type. The coefficient b was regression coefficient for the livestock rate or amount of nutrient in manure to the fields (L i ). e ij was the residual error, which was assumed independent and identically distributed as N(0, d 2).
3. Results For each of the four farm types mean values of inputs, outputs and surpluses are listed in Tables 3 and 4. Import of nutrients with concentrate and fertilizer was the major input to all farm types except for organic dairy farms where especially N fixation and also net import of manure were important inputs. Output from the dairy farms was dominated by nutri-
Table 3 N inputs, N outputs and N balance for four farm types, mean and standard deviation (std), 63 Danish pilot farms with data from 2 to 7 years between 1997 and 2003 Dairy, conv., n = 25 kg N ha 1
Dairy, organic, n = 13 kg N ha 1
Pig, indoors, n = 19 kg N ha 1
Pig, sows outdoors, n = 6 kg N ha 1
Mean F Std
Mean F Std
Mean F Std
Mean F Std
Inputs Concentrate Fodder grain Straw Manure imported Fertilizer N fixation Deposition and irrigation Seed Inputs, total
112 F 49 2F4 3F5 34 F 46 86 F 24 27 F 19 16 F 1 2F1 280 F 57
31 F15 3F2 5F4 24 F 13 0F0 78 F 21 16 F 2 2F0 159 F 25
245 F 212 12 F 30 0F0 24 F 24 70 F 18 3F5 15 F 0 2F0 372 F 214
324 F 78 0F1 5F8 1F2 68 F 8 3F3 15 F 1 2F0 419 F 82
Outputs Milk Meata Manure exported Cash crops Grain Straw Outputs, total
42 F 12 9F3 29 F 43 5F9 17 F 19 1F2 103 F 45
28 F 6 6F1 6 F 10 1F3 2F3 0F1 44 F 13
0F0 98 F 79 68 F 108 18 F 11 51 F 29 7F4 242 F 183
0F0 92 F 21 14 F 12 5F7 46 F 21 2F3 158 F 43
Storage change Manure Fodder crops N balance N eff.ANIMAL PRODUCTS, farmgate, % N eff.HERD, % N eff.FIELD, %
3 F 12 1 F15 175 F 39 23.6 F 3.9 22.1 F1.5 49.6 F 4.9
3F7 6 F 10 106 F 13 26.3 F 3.2 20.5 F 1.1 61.2 F 4.6
1 F12 0F1 128 F 46
4 F 17 2F6 254 F 78
35.4 F 2.5 55.6 F 11.7
28.3 F 4.6 30.4 F 10.3
a
Net production of nutrient in meat (sold minus import minus gain).
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Table 4 P inputs, P outputs and P balance for four farm types, mean and standard deviation (std), 63 Danish pilot farms with data from two to seven years between 1997 and 2003 Dairy, conv., n = 25 kg P ha 1
Dairy, organic, n = 13 kg P ha 1
Pig, indoors, n = 19 kg P ha 1
Pig, sows outdoors, n = 6 kg P ha 1
Mean F Std
Mean F Std
Mean F Std
Mean F Std
Inputs Concentrate Fodder grain Straw Manure imported Fertilizer Seed Inputs, total
22 F 9 0F1 0F1 8 F 10 5F4 0F0 36 F 13
9F4 1F0 1F0 6F3 0F0 0F0 16 F 3
52 F 47 3F6 0F0 7F7 2F4 0F0 64 F 48
73 F 21 0F0 1 F1 0F1 2F1 0F0 76 F 21
Outputs Milk Meata Manure exported Cash crops Grain Straw Outputs, total
7F2 3F1 5F8 1 F1 3F3 0F1 19 F 8
5F1 2F0 1F2 0F0 0F1 0F0 9F3
0F0 20 F 16 19 F 31 3F1 9F5 1 F1 52 F 46
0F0 19 F 4 4F4 1F2 8F4 0F0 32 F 9
1F3 0F2 16 F 8 46.3 F 20.2
0F2 1 F1 6F4 67.7 F 26.2
1 F 5 0F0 13 F 10
1F5 0F1 42 F 24
25.5 F 2.7 60.0 F 11.6
26.1 F 2.0 77.7 F 13.5
36.2 F 6.1 65.8 F 25.4
26.5 F 6.0 28.8 F 13.3
Storage change Manure Fodder crops P balance P eff.ANIMAL PRODUCTS, farmgate, % P eff.HERD, % P eff.FIELD, % a
Net production of nutrient in meat (sold minus import minus gain).
levels on organic dairy farms (113 kg N ha 1, 7 kg P ha 1) (Table 6). The model with year, farm type and farms within farm type explained 87% of the variation in N surplus and 79% of the variation in P surplus. A subset of data where all farm types were represented in all years (1997–2001) was analysed. This showed
similar effects of year, farm type and farms within farm type except for effect of year on P surplus, which was no longer significant (results not shown). As an overall average it was estimated that N surplus decreased by 6.5 F 2.41 kg N year 1 and P surplus by 0.7 F 0.65 kg P year 1 over the years
Table 5 Sources of variation in farm level surplus of N or P, mean squares and F values DF
Nitrogen surplus, farm level MS * 10
Year Farm type Farm within farm type Error Effect of farm type tested against variation between farms within farm type
1 3 59 181 3.59
189.1 1165.6 60.1 6.7
2
Phosphorus surplus, farm level
F
Level of significance
MS * 102
F
Level of significance
28.25 174.19 8.98
*** *** ***
2.8 57.0 3.0 0.5
5.82 118.43 6.25
* *** ***
19.39
***
18.95
***
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Table 6 Average levels of N and P surpluses for each farm type in the average year of the data set (1999.5), estimate F 95% confidence interval Farm type (no. farms)
Livestock rate LU ha 1
Manure kg N ha 1 kg P ha 1
Conventional dairy (25) Organic dairy (13) Pigs indoors (19) Pigs/sows outdoors (6)
1.54 1.14 1.54 1.69
175 148 108 182
Phosphorus surplus kg P ha 1
175 F 16.2a 113 F 24.6b 123 F 21.6b 251 F 34.6c
16 F 3.6a 7 F 5.5b 13 F 4.8a 42 F 7.7c
Results followed by the same letter were not significantly different at P b 0.05.
included (1997–2003). By use of the estimated coefficients the N and P surpluses in the latest year for the three main farm types were estimated: Conventional dairy: 155 kg N ha 1, 14 kg P ha 1; Organic dairy: 98 kg N ha 1, 5 kg P ha 1; Pig indoors: 98 kg N ha 1, 10 kg P ha 1 (2002). To search for possible explanations for the decrease observed in N surplus eight conventional dairy farms with data from 1997 to 2002 and five organic dairy farms with data from 2000 to 2003 were selected. N surplus on the eight conventional dairy farms decreased from app. 190 kg N ha 1 to about 155 kg N ha 1 (Fig. 2). These farms reduced the import of N in fertilizer from 104 to 57 kg N ha 1, but increased net import of feeds (fodder grain, by-products and concentrate) from 91 to 137 kg N ha 1. N surplus on the five organic dairy farms decreased from a level of 111 kg N ha 1 to 87 kg N ha 1 (Fig. 3). These farms reduced their import of nutrients in concentrate and by-products from 31 kg N ha 1 to 23 kg N ha 1 (Fig. 3). In neither of the two sub-groups of dairy
30
200
25 150
20
100
15 10
50
5
0
0 1997 1998 1999 2000 2001 2002
Fig. 2. Trend in average N surplus (n), fertilizer (.), import of concentrate, by-products and fodder grain (D) and N efficiencyANIMAL PRODUCTS () on eight Danish conventional dairy farms, 1997–2002.
35
250
30
200
25 150
20
100
15 10
50
5 0
0 2000
2001
2002
N eff.ANIMAL PRODUCTS, %
35
N eff.ANIMAL PRODUCTS, %
Nitrogen, kg N/ha
250
farms the livestock rate decreased significantly over the years included. Average nutrient use efficiency at farm level (N eff.ANIMAL PRODUCTS) increased from app. 24% to app. 29% in both groups. Six of the indoor pig farms had data from 1997 to 2002, but these farms were so heterogeneous (arable farms with low pig production to highly specialized pig farms) that no common trends could be identified. The relation between nutrient surplus and the production intensity measured as livestock rate or amount of nutrient in manure available per hectare was analysed. Only data from farms where produced manure was used mainly within the farm area were included in these analyses. Four indoor pig farms with an average export of 249 kg N ha 1 in manure were excluded. The remaining 15 indoor pig farms had an average livestock rate of 0.98 LU ha 1 and average nutrient surpluses of 114 kg N ha 1 and 12 kg P ha 1. Also the few outdoor pig farms were excluded. The analysis showed that N and P surpluses increased significantly with increasing livestock rate, but not in a way that differed significantly between farm types. At an average livestock rate (1.28 LU
Nitrogen, kg N/ha
a
33 26 29 53
Nitrogen surplusa kg N ha 1
2003
Fig. 3. Trend in average N surplus (n), import of concentrate, byproducts and fodder grain (D) and N efficiencyANIMAL PRODUCTS () on five Danish organic dairy farms, 2000–2003.
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Table 7 Modelled N and P surpluses at farm level at the average livestock rate (1.28 LU ha 1), estimate F 95% confidence interval Farm type (no. farms)
Nitrogen surplusa, kg N ha 1
Conventional dairy (25) 158 F 10.3a Organic dairy (13) 115 F 13.3b Pigs indoors (15) 134 F 13.1c
Phosphorus surplus, kg P ha 1 14 F 2.9a 8 F 3.7b 15 F 3.7a
a Results followed by the same letter were not significantly different at P b 0.05.
ha 1) N and P surpluses on conventional dairy farms exceeded surpluses of organic dairy farms significantly by 43 kg N ha 1 and 6 kg P ha 1 (Table 7). N surplus on conventional dairy farms exceeded N surplus on indoor pig farms significantly—by 24 kg N ha 1—whereas the two farm types had equal P surpluses. The average effect of increasing livestock rate by 1 LU ha 1 was estimated at 64 F 16.1 kg N ha 1 and 9 F 4.5 kg P ha 1. N and P surpluses also increased significantly with increasing amount of manure available for the field and also not in a way that differed significantly between farm types. At an average level of N or P in manure available for fields (147 kg N ha 1, 29 kg P ha 1, respectively) N and P surpluses on conventional dairy farms exceeded surpluses on organic dairy farms significantly—by 45 kg N ha 1 and 4 kg P ha 1 (Table 8). Neither N nor P surplus differed significantly between conventional dairy farms and indoor pig farms at an average level of N or P in manure available for fields. The average effect of N in manure on N surplus was estimated at 88 F 13.0 kg N ha 1 per 100 kg N ha 1 in manure. The average effect of P in manure on P surplus was estimated at 7.7 F 1.1 kg P ha 1 per 10 kg P ha 1 in manure. Inclusion of the four indoor pig farms with high export of manure neither changed the grand mean of N in manure available for the field nor the estimated N surplus at an average manure rate for the dairy farms (results not shown). However, the estimated N surplus for the indoor pig farms at an average manure rate (147 kg N ha 1) increased by 13 kg N ha 1 to 169 kg ha 1 compared to the level shown in Table 8. This was mainly due to the ammonia losses from the stable and manure related to exported manure, since these losses are not exported, but included in the N surplus of the farm.
4. Discussion The farm gate surplus represents the amount of nutrient lost to the environment or accumulated within the soil pools and surplus calculations offer an integrative measure for the overall potential environmental impact (Oenema et al., 2003; Halberg, 1999). After correction for different livestock rate or amount of nutrient in manure available for the field it was found that N and P surpluses of conventional dairy farms exceeded levels of organic dairy farms significantly—by app. 44 kg N ha 1 and 5 kg P ha 1 (Tables 7 and 8). Halberg et al. (1995) reported a difference of 85 kg N ha 1 (30 farms in 1989/1990) and Halberg (1999) found a difference of 53 kg N ha 1 (15 farms in 1995–1997). Although the method for estimating N2 fixation was not exactly the same in all of the studies referred to above, the gap between conventional and organic dairy farming with respect of N surplus is closing. A general decrease in N surplus (6.5 F 2.41 kg N year 1) and P surplus (0.7 F 0.65 kg P year 1) was observed. Within the dairy farms two sub-groups of farms with the longest time series of data were selected to search for possible explanations. The average N surplus on eight conventional dairy farms decreased by 18% between 1997 and 2002 (Fig. 2). Over the period these farms reduced their import of N with fertilizer by 40% but this was counterbalanced by increased net import of feed protein. The average N surplus on five organic dairy farms decreased by 22% between 2000 and 2003 (Fig. 3). Over the 4 years these farms reduced their net import of feed protein by 25%. Both groups of farms increased their nutrient use efficiency at farm gate from app. 24% to app.
Table 8 Modelled N and P surpluses at farm level at the average rate of manure available for the fields (147 kg N ha 1 or 29 kg P ha 1), estimate F 95% confidence interval Farm type (no. farms)
Nitrogen surplusa, kg N ha 1
Conventional dairy (25) 151 F 7.8a Organic dairy (13) 106 F 9.3b Pigs indoors (15) 156 F 10.4a
Phosphorus surplus, kg P ha 1 13 F 1.5a 9 F 2.0b 14 F 1.8a
a Results followed by the same letter were not significantly different at P b 0.05.
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29%. The results indicate that the decrease in farm N surplus originates from a farm type specific combination of changes in the relation between input and output and the efficiency of the internal flows. Other findings of decreasing N surplus on conventional farms relate this to reduced purchase of mineral fertilizer (Swensson, 2003; Van Beek et al., 2003). Over the last 20 years Danish agriculture as a whole has responded to the demand for improved resource use efficiency. The total N surplus in Danish agriculture has decreased by 38% to a level of approximately 310.000 tonnes (116 kg ha 1) and the overall N use efficiency has increased from 20% to 36% (Kyllingsbæk, 2003). Levels of 340–370 kg N ha 1 and 23–51 kg P 1 ha have been reported for specialized dairy farms in the Netherlands (Hoogeveen et al., 2002 c.f. Bos et al., 2005; Ondersteijna et al., 2003),2 186 kg N ha 1 in Northern Germany (Kristensen et al., 2004) and 236 kg N ha 1 in Flanders (Mulier et al., 2003). The Dutch levels are higher than found in our results, even if corrected for the higher stocking rate (app. 2.5–3 LU ha 1 and app. 12.000–14.000 kg milk ha 1). In Southern Sweden 110 dairy farms with output from both livestock and crop had average N and P surpluses of 157 kg N ha 1 and 5 kg P ha 1 (Swensson, 2003). In the same study 28 dairy farms without cash crops had average N and P surpluses of 180 kg N ha 1 and 7 kg P ha 1. After correction for app. 12% lower milk yield per ha the Swedish dairy farmers have an N surplus of about the same level as found in our study. This is contradictory to the opinion of Swensson (2003) after comparing with older Danish data (Halberg et al., 1995). Watson et al. (2002) collated a total of 88 nutrient budgets from different organic farming systems in nine European countries. The overall average N and P surpluses for 67 organic dairy farms were 82 kg N ha 1 and 3.1 kg P ha 1. This is below the findings in our study, but may probably be explained by a lower level of total input (118 kg N ha 1 compared with 159 kg N ha 1 (Table 3)). No narrow conclusion is possible, but the level of N surplus on Danish conventional dairy farms seems to be comparable with intensive dairy farming sys-
2 255–280 kg N ha 1 plus 90 kg N ha 1 added to correct for missing inputs (N2 fixation and deposition), (Bos et al., 2005).
105
tems in other European countries. Although comparisons to literature can be made it is of greatest importance to pay attention to differences in calculation methodology, farm classification, etc. There seems to be a lack of international comparative studies involving farm data. By taking an overview of the balance accounts in Tables 3 and 4 it can be seen that relatively low levels of inputs and outputs characterize organic dairy farming. Input to organic dairy farms is restricted (no mineral fertilizer, and since year 2001 no import of conventional feedstuff) and outputs are low due to a lower livestock rate, lower milk yield per cow and lower crop yields. High internal recycling is a common trait for dairy farming, but this cycle is running at a higher level on conventional dairy farms than on organic dairy farms. Conventional pig farms have high levels of both input and output. Pig farms with sows outdoors represent a special pig production system. The farms of this type had the highest level of nutrient import with concentrate (324 kg N ha 1; Table 3). Problems with low feeding use efficiency and feed waste in outdoor sow herds (Larsen and Kongsted, 1999) may increase the import of nutrients with animal feed. Even though livestock rate was higher on pig farms with sows outdoors these farms exported much less manure than did pig farms with sows indoors. The sows deposit their excreta directly within the sow paddocks, and fields used for grazing of sows are subject to high loads of nutrients with bhot spotQ problems (Eriksen et al., 2002). There was a large variation within farm types, especially within the indoor pig farms. This category included both arable farms with little pig production and specialized pig farms with little export of cash crops. Choice of relevant criteria for classification of farms into farm categories is a crucial question in relation to the use of nutrient surplus for benchmarking. The significant effect of farm within farm type to both N and P surpluses (Table 5) indicates that the surplus of the individual farms is not a random result, but systematically reflects the situation of the farm. This bfarm effectQ may be a factor related to farm management that can be altered by the farmer on a short term (e.g. feeding practice, manure spreading practice, fertilization level) or on a longer
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term (e.g. type of housing, choice of crop types). It may also be factors related to soil quality or climatic conditions. Calculated efficiency coefficients are shown in Tables 3 and 4, but they were not included in any statistical analysis. Nutrient use efficiency is often referred to as a useful indicator. However, it is difficult to compare the nutrient utilization between farms, especially if their production systems are different (Seuri, 2002; Oenema et al., 2003). If a farm exports both animal and crop products the nutrient use efficiency at farm level will primarily reflect the relationship between animal and crop production. This makes it an indicator difficult to interpret in relation to farm management. It can also be questioned whether nutrients in exported manure should be added to the numerator (as a farm product) or deducted from the divisor (resulting in reduced import). Both solutions create a somewhat artificial increase in farm gate nutrient use efficiency on manure exporting farms. Compared to farm data from 1989 to 1990 (Halberg et al., 1995) there has been an increase in the N efficiencyANIMAL PRODUCTS (conv.:+ 44%, org.:+ 27%) and the difference between organic and conventional dairy farming has decreased (25–11%). The variation in efficiency is more precisely described at herd and field level. Kristensen et al. (2005) found that average N-efficiencyHERD was 6% lower and average N-efficiencyFIELD was 20% higher on organic than on conventional dairy farms. This in good agreement with what was found here. At www.LCAFood.dk Danish standard N efficiencies can be seen together with estimated emissions per product unit (milk and pork). It can be argued that direct comparisons of average levels of N and P surpluses in Table 6 are not particularly meaningful due to differences in, e.g., livestock rate and import and export of manure. However, some of these differences are system characteristics caused by the respond of the farming systems to, e.g., environmental regulation (e.g. intensive pig farms export manure in excess of 1.4 LU ha 1 due to harmony rules). Nevertheless, environmental effects of the exported manure will appear at the places to where it is exported. Aspects like that can only be addressed properly in studies at a higher scale level (e.g. all farms in a region).
5. Conclusion It is concluded that different levels of N and P surpluses should be expected for different farm types, even at an equal stocking rate, expressed as animal units per hectare. Production intensity measured as livestock rate or manure rate affects N and P surpluses, but not in a way that differs between farm types. N and P surpluses of conventional dairy farms exceeded levels at organic dairy farms significantly— by 44 kg N ha 1 and 5 kg P ha 1 compared at equal livestock rates or amount of nutrient in manure available for the field. The dairy and pig farms included in this study have demonstrated a significant decrease in N and P surpluses over the period from 1997 to 2003. One of the main reasons is lower fertilizer input.
References Anon., 2004. Registreringsvejledning Studielandbrug. Available (in Danish) at: http://www.lr.dk/driftsoekonomilbf/informationsserier/ studielandbrug/lbfs-reg-vejl.htm. Bos, J., Aarts, F., Schro¨der, J., Biewinga, E., Schils, R., Velthof, G., Willems, J., 2005. The Netherlands. In: Bos, J., Pflimlin, A., Aarts, F., Verte´s, F. (Eds.), Nutrient management at farm scale: How to attain policy objectives in regions with intensive dairy farming? First workshop of the EGF Working Group dDairy Farming Systems and EnvironmentT, Quimper, France, 23–25 June 2003. Plant Research International B.V., Wageningen, Report 83. EGF Working Group dDairy Farming Systems and EnvironmentT, Report 1, 185–204. Ellermann, T., Hertel, O., Hovmand, M.F., Kemp, K., Ambelas Skjøth, C.A., 2003. Atmospheric deposition 2000. NOVA 2003. NERI Tech. Rep. 374 (88 pp.). Eriksen, J., Petersen, S.O., Sommer, S.G., 2002. The fate of nitrogen in outdoor pig production. Agronomie 22, 863 – 867. Halberg, N., 1999. Indicators of resource use and environmental impact for use in a decision aid for Danish livestock farmers. Agric. Ecosyst. Environ. 76, 17 – 30. Halberg, N., Kristensen, E.S., Kristensen, I.S., 1995. Nitrogen turnover on organic and conventional mixed farms. J. Agric. Environ. Ethics 8, 30 – 51. Halberg, N., Verschuur, G., Goodlass, G., 2005. Farm level environmental indicators; are they useful? An overview of green accounting systems for European farms. Agric. Ecosyst. Environ. 105 (1–2), 195 – 212. Høgh-Jensen, H., Loges, R., Jensen, E.S., Jørgensen, F.V., Vinther, F.P., 2003. Empirical Model for Quantification of Symbiotic Nitrogen Fixation in Leguminous Crops, pp. 1 – 31. http:// orgprints.org/316/. Høgh-Jensen, H., Loges, R., Jensen, E.S., Jørgensen, F.V., Vinther, F.P., 2004. Empirical model for quantification of symbiotic
A.H. Nielsen, I.S. Kristensen / Livestock Production Science 96 (2005) 97–107 nitrogen fixation in grass–clover mixtures. Agric. Syst. 82, 181 – 194 (http://orgprints.org/3085/). Hoogeveen, M.W., Daatselaar, C.H.G., Luesink, H.H., Oudendag, D.A., Wisman, J.H., 2002. The manure and ammonia policy: monitoring 2000 (in Dutch). Paper 02.04, LEI, Den Haag, 32 pp. Hvid, S.K., 2004. Beregning af kvælstoffiksering. Landskontoret for planteavl, Landscentret Planteavlsorientering nr. 07-497, 26 (http:// www.lr.dk/planteavl/informationsserier/planteavlsorientering/ pl07-497.htm). Kristensen, I.S., 2002. Principles and methods for collecting and evaluating nutrient balances. http://web.agrsci.dk/jbs/demolit/ Principles%20and%20methods.pdf. Lithuanian Dairy Farms Demonstration Project. Danish Institute of Agricultural Science, pp. 29 – 40. Kristensen, T., Hermansen, J.E., 2002. Concepts for farming system research. (http://web.agrsci.dk/jbs/bepro/concept%20pdf%20 format.pdf). Lithuanian Dairy Farms Demonstration Project. Danish Institute of Agricultural Science, pp. 1 – 15. Kristensen, I.S., Halberg, N., Nielsen, A.H., Dalgaard, R., Hutchings, N., 2005. Denmark Part II: N turnover on Danish mixed dairy farms. In: Bos, J., Pflimlin, A., Aarts, F., Verte´s, F. (Eds.), Nutrient management at farm scale: How to attain policy objectives in regions with intensive dairy farming? First workshop of the EGF Working Group dDairy Farming Systems and EnvironmentT, Quimper, France, 23–25 June 2003. Plant Research International B.V., Wageningen, Report 83. EGF Working Group dDairy Farming Systems and EnvironmentT, Report 1, 91–110. Kristensen, I.S., Kelm, M., Kristensen, T., 2004. Effects of grassland renovation on farm-gate nitrogen balances and losses. In: Lu¨scher, A., Jeangros, B., Kessler, W., Huguenin, O., Lobsiger, M., Millar, N., Suter, D. (Eds.), Land Use Systems in Grassland Dominated Regions. Proceedings of the 20th General Meeting of the European Grassland Federation Luzern, Switzerland, 21–24 June 2004, pp. 756 – 758. Kyllingsbæk, A., 2003. Baggrundsnotat til Vandmiljøplan II- slutevaluering. Totale kvælstofbalancer pa˚ landsplan. http:// www.agrsci.dk/var/agrsci/storage/original/application/phpE6.tmp. pdf Danmarks JordbrugsForskning. 11 pp. http://www.agrsci.dk/ var/agrsci/storage/original/application/phpE6.tmp.pdf. Larsen, V.A., Kongsted, A.G., 1999. Management of outdoor sow herds—basis for improvements. In: Gagnaux, D., Racord, R., Gibon, A., Poffet, J.R., Sibbald, A.R. (Eds.), Livestock Farming Systems, Integrating Animals Science Advances Into the Search for Sustainability, EAAP Publication, vol. 97, pp. 273 – 278.
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Mulier, A., Hofman, G., Baecke, E., Carlier, L., De Brabander, D., De Groote, G., De Wilde, R., Fiems, L., Janssens, G., Van Cleemput, O., Van Herck, A., Van Huylenbroeck, G., Verbruggen, I., 2003. A methodology for the calculation of farm level nitrogen and phosphorus balances in Flemish agriculture. Eur. J. Agron. 20, 45 – 51. Oenema, O., Kros, H., De Wris, W., 2003. Approaches and uncertainties in nutrient budgets: implications for nutrient management and environmental policies. Eur. J. Agron. 20, 3 – 16. Ondersteijna, C.J.M., Beldmanb, A.C.G., Daatselaarb, C.H.G., Giesena, G.W.J., Huirne, R.B.M., 2003. Farm structure or farm management: effective ways to reduce nutrient surpluses on dairy farms and their financial impacts. Livest. Prod. Sci. 84 (2), 171 – 181. Poulsen, H.D., Kristensen, V.F., 1998. Standard values for farm manure. A Revaluation of the Danish Standard Values Concerning the Nitrogen, Phosphorus and Potassium Content of Manure, Animal Husbandry, vol. 7. Danish Institute of Agricultural Science report, pp. 1 – 160. Poulsen, H.D., Børsting, C.F., Rom, H.B., Sommer, S.G., 2001. Kvælstof, fosfor og kalium i husdyrgødning - normtal 2000. DJF Rapp., Husdyrbrug 36, 1 – 152. Seuri, P., 2002. Nutrient utilization with and without recycling within farming systems. Urban Areas–Rural Areas and Recycling—The organic way forward? Proceedings from the NJFseminar No. 327 Copenhagen, Denmark 20–21 August 2001. DARCOF Report, vol. 3, pp. 175 – 181. Sveinsson, Th., Halberg, N., Kristensen, I.S., 1998. Problems associated with nutrient accounting and budgets in mixed farming systems. In: Van Keulen, H., Lantinga, E.A., Van Laar, H.H. (Eds.), Mixed Farming Systems in Europe. Workshop Proceedings Dronten, The Netherlands, 25–28 May 1998. APMinderhoudhoeve-reeks nr, vol. 2, pp. 135 – 140. Swensson, C., 2003. Analyses of mineral element balances between 1997 and 1999 from dairy farms in the south of Sweden. Eur. J. Agron. 20, 63 – 69. Van Beek, C.L., Brouwer, L., Oenema, O., 2003. The use of farmgate balances and soil surface balances as estimator for nitrogen leaching to surface water. Nutr. Cycl. Agroecosyst. 67, 233 – 244. Watson, C.A., Bengtsson, H., Ebbesvik, M., Løes, A.-K., Myrbeck, A., Salomon, E., Schroder, J., Stockdale, E.A., 2002. A review of farm-scale nutrient budgets for organic farms as a tool for management of soil fertility. Soil Use Manage. 18, 264 – 273.
Nitrogen and phosphorus surpluses on Danish dairy and pig farms in relation to farm characteristics A.H. Nielsen*, I.S. Kristensen Danish Institute of Agricultural Sciences, Department of Agroecology, P.O. Box 50, DK-8830 Tjele, Denmark
Abstract N and P surpluses per hectare at farm level were determined on 63 private pilot farms with data from 2 to 7 years between 1997 and 2003 (a total of 245 observations). Farms were classified in the following four farm types: Conventional mixed dairy, organic mixed dairy, conventional pig farms (indoor) and conventional pig farms with outdoor sows. Import of nutrients with concentrate and fertilizer was the major input to all conventional farm types. On the organic dairy farms major input was N fixation, but also import of nutrients with concentrate and manure were important inputs. Output from the dairy farms was dominated by nutrients in milk. On pig farms nutrients in meat dominated the output, but also export of nutrients with cash crops and manure were important outputs. Farm type, year and farm within farm type significantly affected both N and P surpluses per hectare. Farm type was the major source of variation in both N and P surpluses. In the period investigated N surplus decreased by 6.5 kg N ha 1 yr 1 and P surplus decreased by 0.7 kg P ha 1 yr 1. The N and P surpluses observed on the conventional dairy farms significantly exceeded surpluses observed on the organic dairy farms. At equal number of livestock units (LU) per hectare (1.28 LU ha 1) the difference was 43 kg N ha 1 and 6 kg P ha 1. At equal rates of N or P in manure to fields (147 kg N ha 1, 29 kg P ha 1, respectively) the difference was 45 kg N ha 1 and 4 kg P ha 1. Conventional dairy farms and pig farms with sows indoors had equal N and P surpluses at equal rates of N or P in manure to fields. Corrected to the average year (1999.5) the estimated average N and P surpluses showed highest levels on pig farms with outdoor sows (251 kg N ha 1, 42 kg P ha 1) and lowest levels on organic dairy farms (113 kg N ha 1, 7 kg P ha 1). Surpluses on the conventional dairy farms were 175 kg N ha 1 and 16 kg P ha 1 and on the indoor pig farms they were 123 kg N ha 1 and 13 kg P ha 1. The N and P surpluses observed on Danish conventional mixed dairy farms were comparable with intensive dairy farming systems in other European countries. D 2005 Published by Elsevier B.V. Keywords: Farm gate balances; Nutrient use efficiency; Pilot farms; Dairy farms; Pig farms
1. Introduction
* Corresponding author. Tel.: +45 89991202; fax: +45 89991200. E-mail address: [email protected] (A.H. Nielsen). 0301-6226/$ - see front matter D 2005 Published by Elsevier B.V. doi:10.1016/j.livprodsci.2005.05.012
Losses of nitrogen (N) and phosphorus (P) from agriculture are of public concern due to environmental consequences such as reduced quality of drinking
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water and eutrophication. Farm nutrient surplus is widely used in Europe as an indicator of nutrient use efficiency and potential losses of nutrients from farming systems (Halberg et al., 2005). In Denmark farmers can now receive a state funded grant to calculate farm level nutrient balances. This has led to a number of approx. 300–500 nutrient balances calculated each year. Software has been implemented so that local agricultural advisors can calculate nutrient balances by routine. These subsidised nutrient balances have to comply with certain quality standards. Advisors are liable to make a technical review where they evaluate the nutrient surplus obtained. The evaluation must include a plan showing how surplus could be reduced. This has raised questions as to what level of nutrient surplus would be attainable for a farm under a certain set of conditions and to what indicates good or bad nutrient household. Halberg et al. (1995) showed that in Denmark organic dairy farms had a lower N surplus and a higher N efficiency than conventional dairy farms. N surplus was positively correlated with the number of livestock units per hectare on the conventional farms and there was no effect of soil type. Since Halberg et al. (1995) recorded their data in 1989/ 1990 nutrient turnover of Danish agriculture has undergone great changes, and more data have become available for different types of farms. The aim of the present paper was to study sources of variation in N and P surpluses on Danish dairy and pig farms and to establish updated benchmarking values for N and P surpluses at farm level.
Funen. The farms are not representative for Danish agricultural as a whole, but the farmers have been selected to be progressive and interested in cooperation with experts. From the database farms representing four main farm types were selected. Only farms with data from at least two consecutive years were included. Dairy farms were grouped as conventional and organic dairy farms. Dairy farms which also produced pigs or had data from less than 4 years of production after initiating conversion to organic farming were excluded. Specialised pig farms and arable farms with pig livestock were grouped according to housing of the sows. Farms with sows outdoors were denoted bOut-pigQ and farms with all livestock indoors were denoted bIn-pigQ. Based on these criteria a total of 63 farms with data from 2 to 7 years (a total of 245 farms year) were available for further analysis (Table 1). Major key figures describing the four farm types are given in Table 2. Average milk yield was 8448 kg ECM1 cow 1 year 1 on the conventional dairy farms and 7726 kg ECM cow 1 year 1 on the organic dairy farms. This is about 13% above the national average level in 1999 (Kristensen et al., 2005). Due to a greater number of milking cows per hectare the conventional dairy farms had 7693 kg ECM ha 1 compared with 4772 kg ECM ha 1 on organic dairy farms. Some pig farmers only fed pigs for slaughter, some only had sows and sucklings and some had a fully integrated production. One integrated pig farm also produced young slaughter pigs (fed from 35 to about 60 kg). 2.2. Nutrient balance calculation
2. Materials and methods 2.1. Farm data Since 1997, detailed information about all the major aspects of the production on approximately 75 private farms has been collected in accordance with a protocol (Anon., 2004) by local farm advisors and assistants. All major external and internal mass flows on the farms have been measured or set by standards. After comprehensive quality control, data have been stored in a database (MS Access). Each farm has generated data in one to seven consecutive years. Most of the farms are located in Jutland and on
A subsystem balance approach was used to calculate farm level nutrient surplus (Fig. 1). The production of nutrients in manure was calculated from a livestock nutrient balance. Flow of nutrients with manure to the fields was calculated from a manure storage balance. Farm level N balance was then calculated from surface balances by adding standard estimated gaseous losses of N from housing of animals and storage of manure and straw treated with ammonia (Poulsen et al. (2001), an update from Poul-
1
ECM: energy corrected milk.
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Table 1 Pilot farms with data from two to seven consecutive years, number of farms per year and per farm type
Conventional dairy Organic dairy In-pig Out-pig Total
Year farm per year
Total
1997
1998
1999
2000
2001
2002
2003
year farm
no. farms
17 2 15 4 39
20 4 15 4 44
18 5 10 5 39
13 11 11 5 41
16 8 11 5 41
13 9 7 – 30
9 8 – – 17
106 47 69 23 245
25 13 19 6 63
sen and Kristensen (1998)). For P the farm level balance equals the surface balance directly since no P is lost to air. Calculations followed the principles described in Halberg et al. (1995) and further developed by Sveinsson et al. (1998), Kristensen and Hermansen (2002) and Kristensen (2002). All the amounts of animal feedstuff used, bedding materials, fertilizer, seeds, manure imported and exported, milk produced, crops harvested and the numbers and weights of animals entering or leaving the herd were recorded on the farms on a regular basis according to a protocol (Anon., 2004). Concentrations used for calculating nutrient content were obtained by chemical analysis (primary fodder crops) or set by standards.
Total
Nitrogen fixation in pure legume crops was estimated from crop yields as described by Høgh-Jensen et al. (2004) and Høgh-Jensen et al. (2003). Fixation in clover grass was estimated from dry matter yield and amount of plant available N from applied fertilizer and manure (Hvid, 2004). Deposition was set by a standard (15 kg N ha 1; Ellermann et al., 2003). Nutrient use efficiency at farm gate (N or P eff.ANIMAL PRODUCTS) was calculated as nutrients in sold milk and meat divided by nutrients in fertilizer, N2-fixation, deposition, irrigation, seeds and net imported feed and manure (Halberg et al., 1995). Some pig farms exported more nutrients with cash crops than with animal products and therefore nutrient
Table 2 Major characteristics for the analysed pilot farms Unit
Dairy farms Organic
Livestock Cows Heifers Calves for slaughter Sows Piglets Slaughter pigs Livestock rate
Animala Animal Animal Animal No. produced year 1 No. produced year 1 LUb ha 1
Field production Farm land Permanent grass Set aside Cereal for harvest Other crops for sale Maize, fodder beets and whole crop Grass/clover in rotation Net yield crop production
hectare/farm %c % % % % % SFUd ha 1
a b c d
Pig farms Conventional
104 101 9 – – –
107 109 17 – – –
1.14
142 7 3 16 1 16 40 4446
1.54
111 8 5 23 4 29 22 6218
Indoor
Sows out door
– – –
– – –
126 3043 3063 1.54
221 4454 1364 1.69
124 1 8 72 20 0 0 6507
67 1 7 65 7 2 19 4355
365 feeding days. Livestock units; 1 LU is equal to 0.85 Holstein dairy cow or 4.3 sows in 1 year or 175 piglets at 7 kg or 36 slaughter pigs fed 30–100 kg. Percentage of farmland. Scandinavian Feeding Units, 1 SFU = 7.88 MJ net energy.
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Concentrate Fodder grain
Animal
Herd
Milk
Animal Manure
Straw import
Bedding matr.
Manure import
Manure storage
Manure export
Fodder crop storage Roughage, foddergrain and straw
Grazing
Manure from grazing
Manure from storage
Field Seeds
Grain
N fertilizer Deposition N2 fixation
Cash crops
Fig. 1. Flows accounted for in the calculations of N and P balances at farm level.
use efficiency at farm level was not calculated for the pig farms. Nutrient use efficiency for the herd (N or P eff.HERD) was calculated as nutrients in animal products divided by nutrients in animal feed. Nutrient use efficiency for the field (N or P eff.FIELD) was calculated as nutrients in harvested crops divided by nutrients inputs for the field (fertilizer, manure, N2-fixation, deposition, irrigation, seeds). 2.3. Statistical methods Effects of year, farming system and production intensity on N and P surpluses were assessed by analysis of variance using the SAS System for General Linear Models. Model 1 was used to test the effect of year, farm type and farms within farm type. Yijk ¼ l þ Ei þ Tj þ Fk ð jÞ þ eijk
ð1Þ
where Yijk was the N or P surplus of the kth farm of jth farm type in the ith year, l was the overall mean, E i was the effect of year, T j was the effect of farm type
and F k( j) was the effect of farm within farm type. e ijk was the residual error, which was assumed independent and identically distributed as N(0, d 2). The effect of farm type was tested against the variation between farms within farm type. Model 2 used average data from 2 to 7 years per farm to test the effect of production intensity on N and P surpluses. Yearly surpluses over two consecutive years are related due to buffer capacity of the soil. Due to low number of observations, pig farms with sows outdoors (bOut-pigQ) were excluded prior to these analyses. On four pig farms average livestock rates exceeded 2.1 LU ha 1. Their average export of manure was 249 kg N ha 1. Ammonia lost during storage of the manure for export is included in the farm N surplus. Therefore, these four farms were excluded as well due to divergent N surpluses. Available for further analysis was 53 observations (25 conventional dairy farms, 13 organic dairy farms and 15 indoor pig farms). Yij ¼ l þ Tj þ bLi þ eij
ð2Þ
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101
ents in milk. On pig farms nutrients in meat dominated the output, but also export of nutrients with cash crops and manure were important outputs. There was a large variation within farm types, especially within the indoor pig farms. This category includes arable farms with low pig production and also specialized pig farms with low export of cash crops. However, high input also gives high output and the variation in N surplus within the indoor pig farms is considerably lower than the variation in concentrate input and export of meat and manure. Year, farm type and farm within farm type significantly affected both N and P surpluses (Table 5). Farm type was the major source of variation in both N and P surpluses. Estimated average N and P surpluses showed highest levels on pig farms with outdoor sows (251 kg N ha 1, 42 kg P ha 1) and lowest
where Yij was the response variable of the ith farm of jth farm type. The coefficient b was regression coefficient for the livestock rate or amount of nutrient in manure to the fields (L i ). e ij was the residual error, which was assumed independent and identically distributed as N(0, d 2).
3. Results For each of the four farm types mean values of inputs, outputs and surpluses are listed in Tables 3 and 4. Import of nutrients with concentrate and fertilizer was the major input to all farm types except for organic dairy farms where especially N fixation and also net import of manure were important inputs. Output from the dairy farms was dominated by nutri-
Table 3 N inputs, N outputs and N balance for four farm types, mean and standard deviation (std), 63 Danish pilot farms with data from 2 to 7 years between 1997 and 2003 Dairy, conv., n = 25 kg N ha 1
Dairy, organic, n = 13 kg N ha 1
Pig, indoors, n = 19 kg N ha 1
Pig, sows outdoors, n = 6 kg N ha 1
Mean F Std
Mean F Std
Mean F Std
Mean F Std
Inputs Concentrate Fodder grain Straw Manure imported Fertilizer N fixation Deposition and irrigation Seed Inputs, total
112 F 49 2F4 3F5 34 F 46 86 F 24 27 F 19 16 F 1 2F1 280 F 57
31 F15 3F2 5F4 24 F 13 0F0 78 F 21 16 F 2 2F0 159 F 25
245 F 212 12 F 30 0F0 24 F 24 70 F 18 3F5 15 F 0 2F0 372 F 214
324 F 78 0F1 5F8 1F2 68 F 8 3F3 15 F 1 2F0 419 F 82
Outputs Milk Meata Manure exported Cash crops Grain Straw Outputs, total
42 F 12 9F3 29 F 43 5F9 17 F 19 1F2 103 F 45
28 F 6 6F1 6 F 10 1F3 2F3 0F1 44 F 13
0F0 98 F 79 68 F 108 18 F 11 51 F 29 7F4 242 F 183
0F0 92 F 21 14 F 12 5F7 46 F 21 2F3 158 F 43
Storage change Manure Fodder crops N balance N eff.ANIMAL PRODUCTS, farmgate, % N eff.HERD, % N eff.FIELD, %
3 F 12 1 F15 175 F 39 23.6 F 3.9 22.1 F1.5 49.6 F 4.9
3F7 6 F 10 106 F 13 26.3 F 3.2 20.5 F 1.1 61.2 F 4.6
1 F12 0F1 128 F 46
4 F 17 2F6 254 F 78
35.4 F 2.5 55.6 F 11.7
28.3 F 4.6 30.4 F 10.3
a
Net production of nutrient in meat (sold minus import minus gain).
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Table 4 P inputs, P outputs and P balance for four farm types, mean and standard deviation (std), 63 Danish pilot farms with data from two to seven years between 1997 and 2003 Dairy, conv., n = 25 kg P ha 1
Dairy, organic, n = 13 kg P ha 1
Pig, indoors, n = 19 kg P ha 1
Pig, sows outdoors, n = 6 kg P ha 1
Mean F Std
Mean F Std
Mean F Std
Mean F Std
Inputs Concentrate Fodder grain Straw Manure imported Fertilizer Seed Inputs, total
22 F 9 0F1 0F1 8 F 10 5F4 0F0 36 F 13
9F4 1F0 1F0 6F3 0F0 0F0 16 F 3
52 F 47 3F6 0F0 7F7 2F4 0F0 64 F 48
73 F 21 0F0 1 F1 0F1 2F1 0F0 76 F 21
Outputs Milk Meata Manure exported Cash crops Grain Straw Outputs, total
7F2 3F1 5F8 1 F1 3F3 0F1 19 F 8
5F1 2F0 1F2 0F0 0F1 0F0 9F3
0F0 20 F 16 19 F 31 3F1 9F5 1 F1 52 F 46
0F0 19 F 4 4F4 1F2 8F4 0F0 32 F 9
1F3 0F2 16 F 8 46.3 F 20.2
0F2 1 F1 6F4 67.7 F 26.2
1 F 5 0F0 13 F 10
1F5 0F1 42 F 24
25.5 F 2.7 60.0 F 11.6
26.1 F 2.0 77.7 F 13.5
36.2 F 6.1 65.8 F 25.4
26.5 F 6.0 28.8 F 13.3
Storage change Manure Fodder crops P balance P eff.ANIMAL PRODUCTS, farmgate, % P eff.HERD, % P eff.FIELD, % a
Net production of nutrient in meat (sold minus import minus gain).
levels on organic dairy farms (113 kg N ha 1, 7 kg P ha 1) (Table 6). The model with year, farm type and farms within farm type explained 87% of the variation in N surplus and 79% of the variation in P surplus. A subset of data where all farm types were represented in all years (1997–2001) was analysed. This showed
similar effects of year, farm type and farms within farm type except for effect of year on P surplus, which was no longer significant (results not shown). As an overall average it was estimated that N surplus decreased by 6.5 F 2.41 kg N year 1 and P surplus by 0.7 F 0.65 kg P year 1 over the years
Table 5 Sources of variation in farm level surplus of N or P, mean squares and F values DF
Nitrogen surplus, farm level MS * 10
Year Farm type Farm within farm type Error Effect of farm type tested against variation between farms within farm type
1 3 59 181 3.59
189.1 1165.6 60.1 6.7
2
Phosphorus surplus, farm level
F
Level of significance
MS * 102
F
Level of significance
28.25 174.19 8.98
*** *** ***
2.8 57.0 3.0 0.5
5.82 118.43 6.25
* *** ***
19.39
***
18.95
***
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Table 6 Average levels of N and P surpluses for each farm type in the average year of the data set (1999.5), estimate F 95% confidence interval Farm type (no. farms)
Livestock rate LU ha 1
Manure kg N ha 1 kg P ha 1
Conventional dairy (25) Organic dairy (13) Pigs indoors (19) Pigs/sows outdoors (6)
1.54 1.14 1.54 1.69
175 148 108 182
Phosphorus surplus kg P ha 1
175 F 16.2a 113 F 24.6b 123 F 21.6b 251 F 34.6c
16 F 3.6a 7 F 5.5b 13 F 4.8a 42 F 7.7c
Results followed by the same letter were not significantly different at P b 0.05.
included (1997–2003). By use of the estimated coefficients the N and P surpluses in the latest year for the three main farm types were estimated: Conventional dairy: 155 kg N ha 1, 14 kg P ha 1; Organic dairy: 98 kg N ha 1, 5 kg P ha 1; Pig indoors: 98 kg N ha 1, 10 kg P ha 1 (2002). To search for possible explanations for the decrease observed in N surplus eight conventional dairy farms with data from 1997 to 2002 and five organic dairy farms with data from 2000 to 2003 were selected. N surplus on the eight conventional dairy farms decreased from app. 190 kg N ha 1 to about 155 kg N ha 1 (Fig. 2). These farms reduced the import of N in fertilizer from 104 to 57 kg N ha 1, but increased net import of feeds (fodder grain, by-products and concentrate) from 91 to 137 kg N ha 1. N surplus on the five organic dairy farms decreased from a level of 111 kg N ha 1 to 87 kg N ha 1 (Fig. 3). These farms reduced their import of nutrients in concentrate and by-products from 31 kg N ha 1 to 23 kg N ha 1 (Fig. 3). In neither of the two sub-groups of dairy
30
200
25 150
20
100
15 10
50
5
0
0 1997 1998 1999 2000 2001 2002
Fig. 2. Trend in average N surplus (n), fertilizer (.), import of concentrate, by-products and fodder grain (D) and N efficiencyANIMAL PRODUCTS () on eight Danish conventional dairy farms, 1997–2002.
35
250
30
200
25 150
20
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15 10
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5 0
0 2000
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2002
N eff.ANIMAL PRODUCTS, %
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N eff.ANIMAL PRODUCTS, %
Nitrogen, kg N/ha
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farms the livestock rate decreased significantly over the years included. Average nutrient use efficiency at farm level (N eff.ANIMAL PRODUCTS) increased from app. 24% to app. 29% in both groups. Six of the indoor pig farms had data from 1997 to 2002, but these farms were so heterogeneous (arable farms with low pig production to highly specialized pig farms) that no common trends could be identified. The relation between nutrient surplus and the production intensity measured as livestock rate or amount of nutrient in manure available per hectare was analysed. Only data from farms where produced manure was used mainly within the farm area were included in these analyses. Four indoor pig farms with an average export of 249 kg N ha 1 in manure were excluded. The remaining 15 indoor pig farms had an average livestock rate of 0.98 LU ha 1 and average nutrient surpluses of 114 kg N ha 1 and 12 kg P ha 1. Also the few outdoor pig farms were excluded. The analysis showed that N and P surpluses increased significantly with increasing livestock rate, but not in a way that differed significantly between farm types. At an average livestock rate (1.28 LU
Nitrogen, kg N/ha
a
33 26 29 53
Nitrogen surplusa kg N ha 1
2003
Fig. 3. Trend in average N surplus (n), import of concentrate, byproducts and fodder grain (D) and N efficiencyANIMAL PRODUCTS () on five Danish organic dairy farms, 2000–2003.
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Table 7 Modelled N and P surpluses at farm level at the average livestock rate (1.28 LU ha 1), estimate F 95% confidence interval Farm type (no. farms)
Nitrogen surplusa, kg N ha 1
Conventional dairy (25) 158 F 10.3a Organic dairy (13) 115 F 13.3b Pigs indoors (15) 134 F 13.1c
Phosphorus surplus, kg P ha 1 14 F 2.9a 8 F 3.7b 15 F 3.7a
a Results followed by the same letter were not significantly different at P b 0.05.
ha 1) N and P surpluses on conventional dairy farms exceeded surpluses of organic dairy farms significantly by 43 kg N ha 1 and 6 kg P ha 1 (Table 7). N surplus on conventional dairy farms exceeded N surplus on indoor pig farms significantly—by 24 kg N ha 1—whereas the two farm types had equal P surpluses. The average effect of increasing livestock rate by 1 LU ha 1 was estimated at 64 F 16.1 kg N ha 1 and 9 F 4.5 kg P ha 1. N and P surpluses also increased significantly with increasing amount of manure available for the field and also not in a way that differed significantly between farm types. At an average level of N or P in manure available for fields (147 kg N ha 1, 29 kg P ha 1, respectively) N and P surpluses on conventional dairy farms exceeded surpluses on organic dairy farms significantly—by 45 kg N ha 1 and 4 kg P ha 1 (Table 8). Neither N nor P surplus differed significantly between conventional dairy farms and indoor pig farms at an average level of N or P in manure available for fields. The average effect of N in manure on N surplus was estimated at 88 F 13.0 kg N ha 1 per 100 kg N ha 1 in manure. The average effect of P in manure on P surplus was estimated at 7.7 F 1.1 kg P ha 1 per 10 kg P ha 1 in manure. Inclusion of the four indoor pig farms with high export of manure neither changed the grand mean of N in manure available for the field nor the estimated N surplus at an average manure rate for the dairy farms (results not shown). However, the estimated N surplus for the indoor pig farms at an average manure rate (147 kg N ha 1) increased by 13 kg N ha 1 to 169 kg ha 1 compared to the level shown in Table 8. This was mainly due to the ammonia losses from the stable and manure related to exported manure, since these losses are not exported, but included in the N surplus of the farm.
4. Discussion The farm gate surplus represents the amount of nutrient lost to the environment or accumulated within the soil pools and surplus calculations offer an integrative measure for the overall potential environmental impact (Oenema et al., 2003; Halberg, 1999). After correction for different livestock rate or amount of nutrient in manure available for the field it was found that N and P surpluses of conventional dairy farms exceeded levels of organic dairy farms significantly—by app. 44 kg N ha 1 and 5 kg P ha 1 (Tables 7 and 8). Halberg et al. (1995) reported a difference of 85 kg N ha 1 (30 farms in 1989/1990) and Halberg (1999) found a difference of 53 kg N ha 1 (15 farms in 1995–1997). Although the method for estimating N2 fixation was not exactly the same in all of the studies referred to above, the gap between conventional and organic dairy farming with respect of N surplus is closing. A general decrease in N surplus (6.5 F 2.41 kg N year 1) and P surplus (0.7 F 0.65 kg P year 1) was observed. Within the dairy farms two sub-groups of farms with the longest time series of data were selected to search for possible explanations. The average N surplus on eight conventional dairy farms decreased by 18% between 1997 and 2002 (Fig. 2). Over the period these farms reduced their import of N with fertilizer by 40% but this was counterbalanced by increased net import of feed protein. The average N surplus on five organic dairy farms decreased by 22% between 2000 and 2003 (Fig. 3). Over the 4 years these farms reduced their net import of feed protein by 25%. Both groups of farms increased their nutrient use efficiency at farm gate from app. 24% to app.
Table 8 Modelled N and P surpluses at farm level at the average rate of manure available for the fields (147 kg N ha 1 or 29 kg P ha 1), estimate F 95% confidence interval Farm type (no. farms)
Nitrogen surplusa, kg N ha 1
Conventional dairy (25) 151 F 7.8a Organic dairy (13) 106 F 9.3b Pigs indoors (15) 156 F 10.4a
Phosphorus surplus, kg P ha 1 13 F 1.5a 9 F 2.0b 14 F 1.8a
a Results followed by the same letter were not significantly different at P b 0.05.
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29%. The results indicate that the decrease in farm N surplus originates from a farm type specific combination of changes in the relation between input and output and the efficiency of the internal flows. Other findings of decreasing N surplus on conventional farms relate this to reduced purchase of mineral fertilizer (Swensson, 2003; Van Beek et al., 2003). Over the last 20 years Danish agriculture as a whole has responded to the demand for improved resource use efficiency. The total N surplus in Danish agriculture has decreased by 38% to a level of approximately 310.000 tonnes (116 kg ha 1) and the overall N use efficiency has increased from 20% to 36% (Kyllingsbæk, 2003). Levels of 340–370 kg N ha 1 and 23–51 kg P 1 ha have been reported for specialized dairy farms in the Netherlands (Hoogeveen et al., 2002 c.f. Bos et al., 2005; Ondersteijna et al., 2003),2 186 kg N ha 1 in Northern Germany (Kristensen et al., 2004) and 236 kg N ha 1 in Flanders (Mulier et al., 2003). The Dutch levels are higher than found in our results, even if corrected for the higher stocking rate (app. 2.5–3 LU ha 1 and app. 12.000–14.000 kg milk ha 1). In Southern Sweden 110 dairy farms with output from both livestock and crop had average N and P surpluses of 157 kg N ha 1 and 5 kg P ha 1 (Swensson, 2003). In the same study 28 dairy farms without cash crops had average N and P surpluses of 180 kg N ha 1 and 7 kg P ha 1. After correction for app. 12% lower milk yield per ha the Swedish dairy farmers have an N surplus of about the same level as found in our study. This is contradictory to the opinion of Swensson (2003) after comparing with older Danish data (Halberg et al., 1995). Watson et al. (2002) collated a total of 88 nutrient budgets from different organic farming systems in nine European countries. The overall average N and P surpluses for 67 organic dairy farms were 82 kg N ha 1 and 3.1 kg P ha 1. This is below the findings in our study, but may probably be explained by a lower level of total input (118 kg N ha 1 compared with 159 kg N ha 1 (Table 3)). No narrow conclusion is possible, but the level of N surplus on Danish conventional dairy farms seems to be comparable with intensive dairy farming sys-
2 255–280 kg N ha 1 plus 90 kg N ha 1 added to correct for missing inputs (N2 fixation and deposition), (Bos et al., 2005).
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tems in other European countries. Although comparisons to literature can be made it is of greatest importance to pay attention to differences in calculation methodology, farm classification, etc. There seems to be a lack of international comparative studies involving farm data. By taking an overview of the balance accounts in Tables 3 and 4 it can be seen that relatively low levels of inputs and outputs characterize organic dairy farming. Input to organic dairy farms is restricted (no mineral fertilizer, and since year 2001 no import of conventional feedstuff) and outputs are low due to a lower livestock rate, lower milk yield per cow and lower crop yields. High internal recycling is a common trait for dairy farming, but this cycle is running at a higher level on conventional dairy farms than on organic dairy farms. Conventional pig farms have high levels of both input and output. Pig farms with sows outdoors represent a special pig production system. The farms of this type had the highest level of nutrient import with concentrate (324 kg N ha 1; Table 3). Problems with low feeding use efficiency and feed waste in outdoor sow herds (Larsen and Kongsted, 1999) may increase the import of nutrients with animal feed. Even though livestock rate was higher on pig farms with sows outdoors these farms exported much less manure than did pig farms with sows indoors. The sows deposit their excreta directly within the sow paddocks, and fields used for grazing of sows are subject to high loads of nutrients with bhot spotQ problems (Eriksen et al., 2002). There was a large variation within farm types, especially within the indoor pig farms. This category included both arable farms with little pig production and specialized pig farms with little export of cash crops. Choice of relevant criteria for classification of farms into farm categories is a crucial question in relation to the use of nutrient surplus for benchmarking. The significant effect of farm within farm type to both N and P surpluses (Table 5) indicates that the surplus of the individual farms is not a random result, but systematically reflects the situation of the farm. This bfarm effectQ may be a factor related to farm management that can be altered by the farmer on a short term (e.g. feeding practice, manure spreading practice, fertilization level) or on a longer
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term (e.g. type of housing, choice of crop types). It may also be factors related to soil quality or climatic conditions. Calculated efficiency coefficients are shown in Tables 3 and 4, but they were not included in any statistical analysis. Nutrient use efficiency is often referred to as a useful indicator. However, it is difficult to compare the nutrient utilization between farms, especially if their production systems are different (Seuri, 2002; Oenema et al., 2003). If a farm exports both animal and crop products the nutrient use efficiency at farm level will primarily reflect the relationship between animal and crop production. This makes it an indicator difficult to interpret in relation to farm management. It can also be questioned whether nutrients in exported manure should be added to the numerator (as a farm product) or deducted from the divisor (resulting in reduced import). Both solutions create a somewhat artificial increase in farm gate nutrient use efficiency on manure exporting farms. Compared to farm data from 1989 to 1990 (Halberg et al., 1995) there has been an increase in the N efficiencyANIMAL PRODUCTS (conv.:+ 44%, org.:+ 27%) and the difference between organic and conventional dairy farming has decreased (25–11%). The variation in efficiency is more precisely described at herd and field level. Kristensen et al. (2005) found that average N-efficiencyHERD was 6% lower and average N-efficiencyFIELD was 20% higher on organic than on conventional dairy farms. This in good agreement with what was found here. At www.LCAFood.dk Danish standard N efficiencies can be seen together with estimated emissions per product unit (milk and pork). It can be argued that direct comparisons of average levels of N and P surpluses in Table 6 are not particularly meaningful due to differences in, e.g., livestock rate and import and export of manure. However, some of these differences are system characteristics caused by the respond of the farming systems to, e.g., environmental regulation (e.g. intensive pig farms export manure in excess of 1.4 LU ha 1 due to harmony rules). Nevertheless, environmental effects of the exported manure will appear at the places to where it is exported. Aspects like that can only be addressed properly in studies at a higher scale level (e.g. all farms in a region).
5. Conclusion It is concluded that different levels of N and P surpluses should be expected for different farm types, even at an equal stocking rate, expressed as animal units per hectare. Production intensity measured as livestock rate or manure rate affects N and P surpluses, but not in a way that differs between farm types. N and P surpluses of conventional dairy farms exceeded levels at organic dairy farms significantly— by 44 kg N ha 1 and 5 kg P ha 1 compared at equal livestock rates or amount of nutrient in manure available for the field. The dairy and pig farms included in this study have demonstrated a significant decrease in N and P surpluses over the period from 1997 to 2003. One of the main reasons is lower fertilizer input.
References Anon., 2004. Registreringsvejledning Studielandbrug. Available (in Danish) at: http://www.lr.dk/driftsoekonomilbf/informationsserier/ studielandbrug/lbfs-reg-vejl.htm. Bos, J., Aarts, F., Schro¨der, J., Biewinga, E., Schils, R., Velthof, G., Willems, J., 2005. The Netherlands. In: Bos, J., Pflimlin, A., Aarts, F., Verte´s, F. (Eds.), Nutrient management at farm scale: How to attain policy objectives in regions with intensive dairy farming? First workshop of the EGF Working Group dDairy Farming Systems and EnvironmentT, Quimper, France, 23–25 June 2003. Plant Research International B.V., Wageningen, Report 83. EGF Working Group dDairy Farming Systems and EnvironmentT, Report 1, 185–204. Ellermann, T., Hertel, O., Hovmand, M.F., Kemp, K., Ambelas Skjøth, C.A., 2003. Atmospheric deposition 2000. NOVA 2003. NERI Tech. Rep. 374 (88 pp.). Eriksen, J., Petersen, S.O., Sommer, S.G., 2002. The fate of nitrogen in outdoor pig production. Agronomie 22, 863 – 867. Halberg, N., 1999. Indicators of resource use and environmental impact for use in a decision aid for Danish livestock farmers. Agric. Ecosyst. Environ. 76, 17 – 30. Halberg, N., Kristensen, E.S., Kristensen, I.S., 1995. Nitrogen turnover on organic and conventional mixed farms. J. Agric. Environ. Ethics 8, 30 – 51. Halberg, N., Verschuur, G., Goodlass, G., 2005. Farm level environmental indicators; are they useful? An overview of green accounting systems for European farms. Agric. Ecosyst. Environ. 105 (1–2), 195 – 212. Høgh-Jensen, H., Loges, R., Jensen, E.S., Jørgensen, F.V., Vinther, F.P., 2003. Empirical Model for Quantification of Symbiotic Nitrogen Fixation in Leguminous Crops, pp. 1 – 31. http:// orgprints.org/316/. Høgh-Jensen, H., Loges, R., Jensen, E.S., Jørgensen, F.V., Vinther, F.P., 2004. Empirical model for quantification of symbiotic
A.H. Nielsen, I.S. Kristensen / Livestock Production Science 96 (2005) 97–107 nitrogen fixation in grass–clover mixtures. Agric. Syst. 82, 181 – 194 (http://orgprints.org/3085/). Hoogeveen, M.W., Daatselaar, C.H.G., Luesink, H.H., Oudendag, D.A., Wisman, J.H., 2002. The manure and ammonia policy: monitoring 2000 (in Dutch). Paper 02.04, LEI, Den Haag, 32 pp. Hvid, S.K., 2004. Beregning af kvælstoffiksering. Landskontoret for planteavl, Landscentret Planteavlsorientering nr. 07-497, 26 (http:// www.lr.dk/planteavl/informationsserier/planteavlsorientering/ pl07-497.htm). Kristensen, I.S., 2002. Principles and methods for collecting and evaluating nutrient balances. http://web.agrsci.dk/jbs/demolit/ Principles%20and%20methods.pdf. Lithuanian Dairy Farms Demonstration Project. Danish Institute of Agricultural Science, pp. 29 – 40. Kristensen, T., Hermansen, J.E., 2002. Concepts for farming system research. (http://web.agrsci.dk/jbs/bepro/concept%20pdf%20 format.pdf). Lithuanian Dairy Farms Demonstration Project. Danish Institute of Agricultural Science, pp. 1 – 15. Kristensen, I.S., Halberg, N., Nielsen, A.H., Dalgaard, R., Hutchings, N., 2005. Denmark Part II: N turnover on Danish mixed dairy farms. In: Bos, J., Pflimlin, A., Aarts, F., Verte´s, F. (Eds.), Nutrient management at farm scale: How to attain policy objectives in regions with intensive dairy farming? First workshop of the EGF Working Group dDairy Farming Systems and EnvironmentT, Quimper, France, 23–25 June 2003. Plant Research International B.V., Wageningen, Report 83. EGF Working Group dDairy Farming Systems and EnvironmentT, Report 1, 91–110. Kristensen, I.S., Kelm, M., Kristensen, T., 2004. Effects of grassland renovation on farm-gate nitrogen balances and losses. In: Lu¨scher, A., Jeangros, B., Kessler, W., Huguenin, O., Lobsiger, M., Millar, N., Suter, D. (Eds.), Land Use Systems in Grassland Dominated Regions. Proceedings of the 20th General Meeting of the European Grassland Federation Luzern, Switzerland, 21–24 June 2004, pp. 756 – 758. Kyllingsbæk, A., 2003. Baggrundsnotat til Vandmiljøplan II- slutevaluering. Totale kvælstofbalancer pa˚ landsplan. http:// www.agrsci.dk/var/agrsci/storage/original/application/phpE6.tmp. pdf Danmarks JordbrugsForskning. 11 pp. http://www.agrsci.dk/ var/agrsci/storage/original/application/phpE6.tmp.pdf. Larsen, V.A., Kongsted, A.G., 1999. Management of outdoor sow herds—basis for improvements. In: Gagnaux, D., Racord, R., Gibon, A., Poffet, J.R., Sibbald, A.R. (Eds.), Livestock Farming Systems, Integrating Animals Science Advances Into the Search for Sustainability, EAAP Publication, vol. 97, pp. 273 – 278.
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Mulier, A., Hofman, G., Baecke, E., Carlier, L., De Brabander, D., De Groote, G., De Wilde, R., Fiems, L., Janssens, G., Van Cleemput, O., Van Herck, A., Van Huylenbroeck, G., Verbruggen, I., 2003. A methodology for the calculation of farm level nitrogen and phosphorus balances in Flemish agriculture. Eur. J. Agron. 20, 45 – 51. Oenema, O., Kros, H., De Wris, W., 2003. Approaches and uncertainties in nutrient budgets: implications for nutrient management and environmental policies. Eur. J. Agron. 20, 3 – 16. Ondersteijna, C.J.M., Beldmanb, A.C.G., Daatselaarb, C.H.G., Giesena, G.W.J., Huirne, R.B.M., 2003. Farm structure or farm management: effective ways to reduce nutrient surpluses on dairy farms and their financial impacts. Livest. Prod. Sci. 84 (2), 171 – 181. Poulsen, H.D., Kristensen, V.F., 1998. Standard values for farm manure. A Revaluation of the Danish Standard Values Concerning the Nitrogen, Phosphorus and Potassium Content of Manure, Animal Husbandry, vol. 7. Danish Institute of Agricultural Science report, pp. 1 – 160. Poulsen, H.D., Børsting, C.F., Rom, H.B., Sommer, S.G., 2001. Kvælstof, fosfor og kalium i husdyrgødning - normtal 2000. DJF Rapp., Husdyrbrug 36, 1 – 152. Seuri, P., 2002. Nutrient utilization with and without recycling within farming systems. Urban Areas–Rural Areas and Recycling—The organic way forward? Proceedings from the NJFseminar No. 327 Copenhagen, Denmark 20–21 August 2001. DARCOF Report, vol. 3, pp. 175 – 181. Sveinsson, Th., Halberg, N., Kristensen, I.S., 1998. Problems associated with nutrient accounting and budgets in mixed farming systems. In: Van Keulen, H., Lantinga, E.A., Van Laar, H.H. (Eds.), Mixed Farming Systems in Europe. Workshop Proceedings Dronten, The Netherlands, 25–28 May 1998. APMinderhoudhoeve-reeks nr, vol. 2, pp. 135 – 140. Swensson, C., 2003. Analyses of mineral element balances between 1997 and 1999 from dairy farms in the south of Sweden. Eur. J. Agron. 20, 63 – 69. Van Beek, C.L., Brouwer, L., Oenema, O., 2003. The use of farmgate balances and soil surface balances as estimator for nitrogen leaching to surface water. Nutr. Cycl. Agroecosyst. 67, 233 – 244. Watson, C.A., Bengtsson, H., Ebbesvik, M., Løes, A.-K., Myrbeck, A., Salomon, E., Schroder, J., Stockdale, E.A., 2002. A review of farm-scale nutrient budgets for organic farms as a tool for management of soil fertility. Soil Use Manage. 18, 264 – 273.