Nitrogen budgets of three experimental and two commercial dairy farms in the Netherlands

(~ 1997 Elsevier Science B. V. All rights reserved Perspectives for Agronomy - Adopting Ecological Principles and Managing Resource Use M.K. van lttersum and S.C. van de Geijn (Editors)

171

Nitrogen budgets of three experimental and two commercial dairy farms in the Netherlands J.J. Neeteson *, J. Hassink Research Institute for Agrobiology and Soil Fertility (AB-DLO), P.O. Box 129, NL-9750 A C Haren, The Netherlands Abstract

Results of recent Dutch research on the quantification of nitrogen (N) budgets of grazed grassland fields and dairy farms are reviewed to obtain a better quantitative insight into the contribution of the various processes in the N cycle to N losses on dairy farms. The results are also used to investigate the feasibility of possible future regulations on maximum permissible values of the N surplus on dairy farms. The N surplus of grassland fields was assumed to equal the difference between N input through fertilizer, urine and dung, and atmospheric deposition, and the N output through harvested grass. Under experimental conditions the N surplus of grassland fields was found to be high, ranging from about 200 to almost 700 kg N ha -1 yr-1. With few exceptions it was not possible to explain the surplus entirely by measured N losses and N accumulation in soil organic matter. The N surplus on the complete-farm scale, i.e. the difference between the annual input of N to the farm and the annual output from the farm through agricultural products, did not exceed 200 kg N ha -1 yr -1 on a farm where a major effort is put into matching economic and environmental demands. At commercial farms managed according to "good agricultural practice" the value of the complete-farm N surplus is higher, about 250 kg N ha -1 yr-~. There is a strong positive linear relationship between the N fertilizer application rate and the complete-farm N surplus. It is concluded that the N surplus on dairy farms can be reduced considerably by a combination of measures such as reducing N fertilizer inputs and applying limited grazing. It is technically possible to meet the most severe standards proposed for the N surplus on dairy farms.

Keywords: Nitrogen budget; Nitrogen surplus; Nitrogen loss; Dairy farms; Nitrogen management; Regulations

1. Introduction

While producing agricultural goods farmers have to meet both economic and environmental requirements. Obviously, farming should be profitable to the farmer himself. Society, however, demands that agricultural production takes places in a sustainable manner, which implies that no severe ecological damage occurs. Nitrogen (N) may have a harmful effect on the environment through nitrate leaching or runoff, nitrous oxide emission and ammonia vol-

* Corresponding author. AB-DLO, P.O. Box 129, 9750 AC Haren, The Netherlands. Telephone: +31-505337204, fax: +31-505337291.

atilization. As far as N is concerned, farm management should be directed to minimizing N losses. In other words, the difference between the total N input into the farm by fertilizers, manures, fodder, concentrates, seeds, atmospheric deposition and symbiotic N fixation and the total N output by agricultural products should be as small as possible. Future Dutch regulations on N management will be based on this difference, the N surplus. The Dutch government proposes to set maximum permissible values for the N surplus on arable land and grassland. The values proposed for 1998 are 175 and 300 kg N ha -1 yr -1 for arable land and grassland, respectively. It is intended to decrease the values stepwise to 100 kg N ha -1 yr -1 for arable land and 180 kg N ha -1 yr -1 for grassland in the year 2008.

172

This paper reviews results of recent Dutch research on the quantification of N budgets of grazed grassland fields and dairy farms to obtain a better quantitative insight into the contribution of the various processes in the N cycle to nitrogen losses on dairy farms and to investigate the technical feasibility of the criteria proposed for the N surplus. The paper focuses on dairy farms because about twothirds of the total Dutch farmland is used as grassland by dairy farmers. Moreover, since the total amount of nitrogen cycling annually on dairy farms is among the highest in agricultural production systems, a relatively small improvement in the efficiency of the system may have a great impact on decreasing N losses on the national scale. The research presented has been conducted by the Research Institute for Agrobiology and Soil Fertility (AB-DLO) in Wageningen and Haren, the Experimental Station for Cattle, Sheep and Horse Husbandry (PR) in Lelystad, the Department of Agronomy of Wageningen Agricultural University (WAU), the Winand Staring Centre for Integrated Land, Soil and Water Research (SC-DLO) in Wageningen, the Nutrient Management Institute (NMI) in Wageningen, and the Centre for Agriculture and Environment (CLM) in Utrecht.

was executed in two blocks of four paddocks of each 1-1.5 ha. Four annual rates of N fertilizer were applied: 250, 400, 550 and 700 kg N ha -1. The paddocks were stocked with spring-calving Friesian dairy cows according to a put and take continuous grazing system. Stocking rates were adjusted regularly to keep a target sward height of 6 cm. Averaged over the three-year experimental period the number of cow grazing days was about 600. Further experimental details are described by Deenen (1994). 2.2. De Meenthoeve

The experiment was carried out on a sand soil in Achterberg (province of Gelderland). The soil had been under grass for a great number of years and in 1981 the old sward was reseeded. In 1986 and 1987 a rotational grazing experiment was conducted with young steers on paddocks of 0.2 ha. Averaged over the experimental period the number of cow grazing days was about 800. Four annual rates of N fertilizer were applied" 250, 400, 550 and 700 kg N ha -1. Further experimental details are described by Deenen (1994). 2.3. De Marke

The materials and methods used to obtain the resuits discussed in this paper are only briefly presented here. Full details can be found in the original publications to which reference is made. The data presented originate from medium-term field experiments at the experimental dairy farms De Minderhoudhoeve, De Meenthoeve, De Marke and from monitoring the commercial dairy farms Kloosterboer and Achterkamp.

Detailed measurements were performed at a wet and at a dry grazed grassland site at the experimental dairy farm De Marke on a sand soil in Hengelo (province of Gelderland). The experiment was conducted during the period 1992-1994. The average annual N fertilizer application rate was 115 and 151 kg N ha -1 at the wet and dry site, respectively. The average annual N input with slurry, exclusive of dung and urine from the grazing herd, amounted to 196 and 171 kg N ha -1 to the wet and dry site, respectively. Further experimental details are described by Hack-Ten Broeke et al. (1996).

2.1. De Minderhoudhoeve

2.4. Kloosterboer

The experiment was carried out on a well drained young sedimentary calcareous silty loam soil in Swifterbant (province of Flevoland). The soil had been under grass for more than 20 years. In August 1985 the sward was reseeded with perennial ryegrass. In 1986, 1987 and 1988 a continous grazing experiment

The commercial dairy farm of Mr. Kloosterboer is located on a sand soil in Laren (province of Gelderland). In 1993/1994 the farm consisted of 21.8 ha grassland and 11.2 ha arable land used for silage maize porduction. Annual nitrogen inputs to and outputs from the farm were monitored during six

2. Materials and methods

173

years. The N bookkeeping took place from 1 May 1988 to 30 April 1994. The stocking rate was 1.8 milking cows per ha exclusive of accompanying young cattle. Annual milk production reached about 7500 kg per cow. Further farm and farm management characteristics are given by Den Boer et al. (1996).

2.5. Achterkamp The commercial dairy farm of Mr. Achterkamp is located on a clay soil in Oosterhout (province of Noord Brabant). In 1994/1995 the farm consisted of 40.7 ha grassland and 16.2 ha arable land used for silage maize production. Annual N inputs to and outputs from the farm were monitored during five years. The nitrogen bookkeeping took place from 1 May 1990 to 30 April 1995. The stocking rate was 1.3 milking cows per ha exclusive of accompanying young cattle. In 1995 the annual milk production reached about 7500 kg per cow. Further information on farm characteristics and on farm management is given by Den Boer et al. (1996). 2.6. Methods used to quantify the contribution of the

various processes in the N cycle Nitrate leaching at De Meenthoeve and De Marke

was determined with porous ceramic cups, whereas at De Minderhoudhoeve drain water was analysed. Ammonia volatilization was measured at De Minderhoudhoeve with the micrometeorological mass balance method (Bussink, 1994). At De Meenthoeve and at De Marke it was estimated on the basis of assumptions made by Biewinga et al. (1992). Denitrification was determined at De Marke in undisturbed soil samples which were incubated with acetylene (Ryden et al., 1987). Acetylene blocks the transformation of N20 to N2 and the N20 production is then a measure of the rate of denitrication. At De Minderhoudhoeve and at De Meenthoeve denitrification was estimated from the difference between soil mineral N in autumn and spring minus the amount of nitrate leached during winter. Changes in the amount of N in soil organic matter at De Minderhoudhoeve and De Meenthoeve were quantified by determining total soil organic N and the bulk density in each spring and autumn in the top 10 cm of soil and the 10-25 cm soil layer (Hassink and Neeteson, 1991). Five replicates were taken per layer, each replicate being a combination of 10 cores. At De Marke, it was quantified by determining the amount of N in the active fractions of the soil organic matter pool and the bulk density in each spring and autumn in the top 10 cm of soil and the 10-25 cm soil layer (Hassink, 1996).

Table 1 N budget (input/output, kg N ha -1 yr -1) of grazed grassland fields at De Minderhoudhoeve (loam soil) and De Meenthoeve (sand soil). The values given are average values of three (De Minderhoudhoeve) or two years (De Meenthoeve). After Hack-Ten Broeke et al. (1996) and Hassink and Neeteson (1991). Entry

N fertilizer application rate (kg N ha -1 yr -1) De Minderhoudhoeve

Fertilizer Urine Dung Atmospheric deposition Total input Output through gross grazed and mown Surplus Ammonia volatilization Denitrification Nitrate leaching Accumulation in SOM a Total losses and accumulation Unaccounted for aSOM = Soil organic matter

De Meenthoeve

250

400

550

700

250

400

550

700

251 165 70 40 526 330 196 19 8 11 250 288 -92

398 234 80 40 752 424 328 25 22 31 250 328 0

552 281 86 40 959 491 468 30 35 44 250 359 109

694 297 87 40 1118 515 603 31 44 53 250 308 295

268 279 85 40 672 405 267 47 88 59 0 196 71

406 323 86 40 855 449 406 53 96 75 0 224 182

517 343 84 40 984 466 518 56 115 134 0 305 213

672 353 80 40 1145 472 673 56 2 !6 163 0 435 238

174 Table 2 N budget (input/output, kg N ha -1 yr -1) at sites of grazed grassland at De Marke (sand soil). After Hassink et al. (1996). Entry

Dry site Wet site

Fertilizer Slurry, dung and urine Atmospheric deposition Symbiotic N fixation Total input Output through grass grazed and mown Surplus Ammonia volatilization Denitrification Nitrate leaching Accumulation in soil organic matter Accumulation in stubble and roots Total loss and accumulation Unaccounted for

151 307 50 34 542 278 264 14 11 83 101 55 264 0

115 282 50 19 466 308 158 11 27 22 73 24 157 1

The quantification of the N content in fertilizer, urine, dung, harvested grass, milk and meat and the estimation of the amount of N deposited from atmosphere are described by Deenen (1994).

3. Results

3.1. N budgets of dairy farms." the field scale In Table 1 N budgets of grazed grassland fields with various levels of N fertilizer application are presented. The budgets pertain to experimental fields at De Minderhoudhoeve (loam soil) and De Meenthoeve (sand soil). The N surplus of the fields was assumed to equal the difference between N input through fertilizer, urine and dung, and atmospheric

Entry

Farm year

/

60O

II

~lb

Y

94/95

37 82 53 0 49 12 5 238 65 11 21 97 141

0 123 74 0 49 12 0 258 6 68 0 74 184

deposition, and the N output through grass harvested (grazed+mown). The N surplus appeared to be high, ranging from about 200 to almost 700 kg N ha -1 yr -1. The surplus increased with increasing levels of N fertilizer. Independent of the level of N fertilizer the surplus at De Meenthoeve was about 70 kg N ha -1 higher than it was at De Minderhoudhoeve. This was due to the higher stocking rate at De Meenthoeve causing a higher N input through urine which was only partially matched by a higher N output through grass harvested. Since ammonia volatilization, nitrate leaching, and N accumulation in soil organic matter were also quantified at the fields studied, it is possible to investigate to which extent the calculated N surplus

4OO

800

93/94 Roughage from elsewhere Concentrates Fertilizer Manures from elsewhere Atmospheric deposition Symbiotic fixation Miscelaneous Total input Meat Milk Miscelaneous Output through produce Surplus

N sur

N sur flus (kg N/ha.W)

400

Table 3 Complete-farm N budgets (input/output, kg N ha -1 yr -1) of the dairy farm De Marke (sand soil). Each recorded year runs from 1 May to 30 April. After De Vries (1995) and Van Keulen et al. (1995).

)lus (kg N/ha.w)

I

300

I

2OO 100

200

N fertilizer application rate (kg N/ha.w)

Fig. 1. Relationship between N fertilizer application rate to grazed grassland fields and N surplus at the field scale.

0

100

200

300

N fertilizer application rate (kg N/ha.w)

400

Fig. 2. Relationship between N fertilizer application rate and N surplus of dairy farms.

175 Table 4 Complete-farm N budgets (input/output, kg N ha -1 yr -1) of the dairy farm Achterkamp (clay soil). Each recorded year runs from 1 May to 30 April (Den Boer et al., 1996). Entry

Farm year

Roughage from elsewhere Concentrates Fertilizer Manures from elsewhere Atmospheric deposition Symbiotic fixation Total input Meat Milk

Miscelaneous Output through produce Surplus

90/91

91/92

92/93

93/94

94/95

0 45 237 33 46 4 365 9 45 45 99 266

6 44 178 0 46 4 278 10 55 -24 41 237

30 92 222 0 46 4 394 9 55 38 102 292

12 66 239 0 46 4 367 10 52 24 86 281

1 68 187 0 46 4

could be explained in terms of losses and accumulation. The data presented in Table 1 show that averaged over the four N fertilizer application rates 80% of the surplus at De Minderhoudhoeve could be ascribed to losses and accumulation. At De Meenthoeve, however, only 62% of the surplus could be explained. The values of N accumulation at De Minderhoudhoeve in Table 1 are similar for all fertilizer treatments, because differences among treatments were non-significant, notwithstanding a lower N accumulation at the lower N fertilizer application rates. When making N budgets it is seldomly possible to take full account of the contribution of all N flows.

306 11 54 14 79 227

Detailed measurements at two sites with contrasting soil water status at the experimental farm De Marke, however, showed that it is possible to set up closed N budgets of grazed grassland fields by taking explicitly account of N accumulation in soil organic matter (Table 2). The calculated N surplus could thus be entirely explained by measured N losses and accumulation. In Fig. 1 the N surpluses given in Tables 1 and 2 are plotted against the respective N fertilizer application rates. Fig. 1 shows that there is a strong positive linear relationship. The N surplus at the field scale thus is largely determined by the level of N fertilizer application.

Table 5 Complete-farm N budgets (input/output, kg N ha -1 yr -1) of the dairy farm Kloosterboer (sand soil). Each recorded year runs from 1 May to 30 April (Den Boer et al., 1996). Entry Roughage from elsewhere Concentrates Fertilizer Manures from elsewhere Atmospheric deposition Symbiotic fixation Total input Meat Milk

Miscdaneous Output through produce Surplus

Farm year 88/89

89/90

90/91

91/92

92/93

93/94

0 72 305 34 52 5 468 14 64 4

0 82 201 17 52 4 356 8 72 5

1 84 196 0 52 4 337 12 69 - 1 80 257

0 90 156 0 52 4 302 12 70 - 20 62 240

29 134 146 0 52 4 365 13 70 17 100 265

0 94 182 0 52 4 332 14 67 12 93 239

82

85

386

271

176

3.2. Nitrogen budgets of dairy farms: the complete-farm scale Table 3 presents the complete-farm N budgets of the experimental farm De Marke. At this farm the objective is to fulfil both economic and environmental objectives. Farm management aims at increasing the use of internal N flows within the farm in order to reduce demand for N inputs to the farm in the form of roughage and fertilizers. By doing so, the N surplus at the whole-farm scale, i.e. the difference between the annual input of N to the farm and the annual output from the farm through agricultural products, did not exceed 200 kg N ha -1 yr -1 (Table 3). On commercial farms managed according to "good agricultural practice" the value of the complete-farm N surplus is higher, about 250 kg N ha -1 yr -1 (Tables 4 and 5). Tables 4 and 5 also show that there was little between-year and between-farm variation in the N surplus. The relationship between N fertilizer application rate and the complete-farm N surplus was established from the data presented in Table 3, Tables 4 and 5. The strong positive linear relationship (Fig. 2) suggests that the N fertilizer application rate has a major impact on the N surplus.

4. Discussion

4.1. N budgets The N budgets of grazed grassland fields (field scale) and dairy farms (complete-farm scale) presented in this paper show that annual N inputs are high, several hundreds kg N ha -1. Annual N output in agricultural products, however, is low. At the field scale it was about 50% of the total annual N input (Tables 1 and 2) and at the farm scale only about 25% (Table 3, Tables 4 and 5). The low N efficiency of dairy farming systems is well-known (Van Der Meer and Van Uum-Van Lohuyzen, 1986). With few exceptions (Table 2) the difference between total N input and N output through products, the N surplus, calculated at the field scale could not be explained entirely by the measured N losses and accumulation into soil organic matter. This can be due to insufficient account that was taken of soil and

crop heterogeneity while measuring the contribution of the various processes and interpreting the data obtained. The values assessed may differ widely from the "real" values when errors are made in sampiing procedures and statistical analyses. It is also possible that relevant processes through which N losses occur have not been quantified at all, e.g. N2-emission after nitrification of ammonium (Pel et al., 1997). The data presented in Tables 1 and 2 show that nitrate leaching and in some instances denitrification are major loss mechanisms of N at grazed grassland fields. It should be noted that the values for denitrification at De Meenthoeve given in Table 1 seem to be unrealistically high. This is probably due to the indirect manner the values have been determined, i.e., from changes in soil mineral N which were corrected for nitrate leaching (see Materials and Methods). By doing so, the values for denitrification are likely to be overestimated, since all loss mechanisms during winter with the exception of nitrate leaching are then ascribed to denitrification.

4.2. N surplus The complete-farm N surpluses presented in this paper are less than 200 kg N ha -1 yr -1 when a major effort is made to reach environmental goals (Table 3) and about 250 kg N ha -1 yr -1 when good agricultural practice is followed (Tables 4 and 5). These values are considerable lower than the values of about 600 and 400 kg N ha -~ yr -~ reported by Van Keulen et al. (1995) for current intensively and extensively managed dairy farms, respectively. In 1990/1991 the average N surplus of 2099 Dutch commercial dairy farms calculated on the basis of general assumptions and some farm data available, appeared to be 419 kg N ha -1 (Bronwasser, 1992). The values calculated ranged from 159 to 618 kg N ha -1 yr -1, depending on total N application rate per ha, milk production per ha and stocking rate (Bronwasser, 1992). Other studies suggest that production intensity and/or N application rate can not be used as simple indicators for the N surplus, since there were large differences in the calculated N surplus among farms with similar production intensity and/ or N application levels (Anonymous, 1994; Daatselaar, 1989; Daatselaar et al., 1990). However, the results presented in this paper, which

177

were derived from actual measurements rather than assumptions, indicate that the N surplus largely depends on the N fertilizer application rate, both on the field scale (Fig. 1) and on the farm scale (Fig. 2).

4.3. Strategies to reduce the N surplus It is possible to reach a low N surplus at the farm level for various farming types (Anonymous, 1994). Farms with a high production intensity should make better use of the N in their internal flows of nutrients and feed. External inputs by fertilizers and feed produced elsewhere can then be lowered. Farms with a low production intensity by using no or little N fertilizer, generally reach a low N surplus. The results presented in Fig. 2 suggest that reducing N fertilizer application rates may have a large effect on lowering the N surplus. This is confirmed by model calculations of Van Der Putten and Vellinga (1996) who found a reduction of the N surplus of more than 60 kg N ha -1 yr -~ when 100 kg fertlizer N ha -1 yr -t less was applied than when the current recommendation was followed. The nitrogen surplus could be further reduced with 50 kg N ha -1 yr -1 when limited grazing instead of rotational grazing was applied together with reduced N fertilizer application rates. Adjustment of farm management can considerably reduce the N surplus. The best strategy is to take several measures simultaneously such as lower application rates of N fertilizer, limited grazing, lower stocking rates combined with increased per-cow production, and injection of slurries into the soil. Most of these measures have little effect on farmers' profitability, except limited grazing which requires extra costs for fodder ensilage and slurry collection and application (Mandersloot and Van Scheppingen, 1994).

4.4. Feasibility of governmental norms for the N surplus The Dutch governement intends to set up regulations to limit the N surplus on dairy farms. Maximum permissible values proposed range from 300 kg N ha -1 yr -1 in 1998 to 180 kg N ha -1 yr -1 in 2008. Although it may not be scientifically justified, it was a political decision to exclude symbiotic N fixation

and atmospheric deposition from the calculation of the N surplus used in the proposed legislation. The N surplus obtained at commercial farms with "good agricultural practice" (Tables 4 and 5) then reaches values of about 200 kg N ha -1 yr -1. The N surplus obtained at the experimental farm De Marke with a major effort to match both economic and environmental objectives (Table 3) then amounts to about 100 kg N ha -1 yr -1. This suggests that it is technically possible to reach the governmental norms for the N surplus. With "good agricultural practice" the most stringent criterion can almost be reached. From the results obtained at De Marke it can be expected that even the most severe criteria will not be exceeded when farm management moves somewhat from "good agricultural practice" towards management which takes more account of environmental objectives.

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