Energy savings by efficient application of fertilizer

ELSEVIER Resources, Conservation and Recycling 13 (1995) 233-250

r e s o u r c e s ,

conservation and recycUng

Energy savings by efficient application of fertilizer

E. Worrell *, B. Meuleman, K. Blok Department of Science, Technology and Society, Utrecht University, Padualaan 14, 3584 CH Utrecht,

TheNetherlands

Accepted 15 September 1994

Abstract

A more efficient application of materials (e.g., nitrogen fertilizers) can have a major impact on the demand of industrial energy. In this study we describe a method of analysing the potential for reducing the application of nitrogen fertilizer. The potential savings are analyzed as well as the economics, using a costs-savings function. Eight measures for improving the efficiency of fertilizer utilization in the Nethedafids were investigated. These measures are applicable to six types of crops (responsible for 97% of fertilizer used ). The average amount of fertilizer applied (fertilization rate ) can be reduced from 228 kg N/ha in the year 1988 to 128 kg N/ha in the near future. This would reduce the fertilizer demand for fertilizer by 44% (minimum 28% and maximum 51%), thus from 458 ktonnes N to 258 ktonnes. As a result, the energy consumption would be reduced by 8 PJ. An economic assessment of the measures suggests that, from a national economic point-of-view, material savings of 41% are economically feasible.

Keywords: Fertilizer; Nitrogen; Economic assessment; Energy saving

1. Introduction

The production of materials consumes a great deal of energy. In the European Union and the Netherlands industry consumes nearly 36% and 40%, respectively, of the total primary energy supply [ 1 ]. In the Netherlands the largest energy-consuming industries are the petrochemical industry ( 15% of the national primary energy consumption in 1988), basic metal (6%) and fertilizer industries (5 %) [ 2 ]. In the future, environmental problems, such as global wanning, may lead to restrictions on the future consumption of (fossil) energy carriers for the purpose of reducing emissions of CO2 and other greenhouse gases. Energy saving, needed to reach CO2 emission reduction goals, can be achieved by 'energy efficiency improvement' in the production processes of the materials, and by improved application of

* Corresponding author.

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234 E. Worrell et al. / Resources, Conservation and Recycling 13 (1995) 233-250

these materials, which will reduce the energy required to produce materials. The latter is called 'material efficiency improvement' and is defined as reducing the demand for primary materials without substantially affecting the level of human activities. Energy and material efficiency improvement can complement each other, thus helping to create a cost-effective emission reduction strategy.

In this paper we will focus on nitrogen-based fertilizers (N-fertilizer) because the production is more energy intensive [ 3 ] than that of other fertilizers. The Netherlands is a large producer and user of N-fertilizers. Ammonia, the intermediate feedstock, for nearly all N- fertilizers is produced by the steam reforming of natural gas to produce hydrogen that reacts with nitrogen in the Haber-Bosch process. Therefore, reduction in the use of fertilizer will save natural gas resources and reduce the emissions of CO2 and of another greenhouse gas: nitrous oxide (N20). N20 is emitted by several sources, the most important of which are: manure, fertilizer, fossil fuel use, biomass burning and the production of adipic acid for nylon manufacture [4]. N20 is emitted directly by the production, and indirectly, after the application of fertilizers. The direct emissions are 0-2 kg N NzO per tonne N produced [5]. Because N20 has a direct global warming potential (GWP) of 270 [4], this is equivalent to 0-540 kg CO2/tonne N (compared to 2280 kg COJtonne N with respect to direct CO2 emissions, on the basis of 33.5 GJ natural gas/tonne ammonia [ 3 ] ). The indirect emissions are difficult to quantify as they are dependent on many factors, including soil, climate and weather conditions [6]. The total indirect N20 losses are estimated at 0.34% (0.14-1.5%) of the global fertilizer application [ 7 ]. The N20 losses depend on the fertilizer type; 1.63% for anhydrous ammonia, 0.4% for ammonium nitrate, 0.11% for urea and 0.03% for nitrate [7]. It should be noted that uncertainties about N20 fluxes are large [8]. To date no international policy goals have been formulated with regard to N20 emissions [9]. Since so little information is available regarding possible ways of reducing N20 emissions [ 10], we will not study these options in this article.

With a production of 3278 ktonnes of ammonia in 1988 [ 1 ] the Netherlands is the largest producer of ammonia in the European Union (EU) and the fourth largest producer in the World [ 11 ]. The Netherlands is also the most intensive user of N-fertilizer, expressed as fertilizer application per unit of agricultural land. The high specific average application rate of 228 kg N/ha ( 1 h a - 0.01 km 2) in the reference year 1987/1988 suggests that there is a potential for more efficient use of fertilizers. A reduction in the amount of fertilizers used is also included in other environmental policy objectives. The high nitrate concentration in surface and ground water, due to the use of manure and fertilizer and industrial emissions, has to be reduced to a concentration of 50 mg nitrate/1 groundwater in the period up to the year 2000 [ 12] if environmental standards have to be met and the public water supply is not to be endangered.

The energy savings that can be achieved in the production processes have been discussed elsewhere [13]. The aim of this paper is to explore the options that are available for increasing the efficiency of fertilizer application in the agricultural sector in the Netherlands in the short-term (by the year 2000). First we introduce the methodology that will be used to analyse the reduction potential. Then we give an overview of fertilizer applications in the Dutch agricultural sector, and next we identify specific measures that can be implemented. Information will be presented on the potential savings on fertilizer use and about

E. WorreU et al. / Resources, Conservation and Recycling 13 (1995) 233-250 235

the associated costs. The measures are evaluated according to the amount of fertilizer saved and the amount of energy saved. Finally the results are evaluated and conclusions are drawn.

2. Methodology

The use of N-fertilizers in Dutch agriculture will be analysed for the reference year 1988. The major crops are selected according to land and fertilizer use. On the basis of these data an analysis of reduction options can be made. 'Material efficiency' is in this case measured as the specific nitrogen consumption. The specific nitrogen consumption is defined as the amount of nitrogen fertilizer applied per unit of land. In this study we consider only the effects of individual measures for improving material efficiency; we will not study the gross reduction potential (based on material balances [ 14 ], or consumption pattern developments [ 15] ). For each measure, data are collected on the reduction potential and the associated costs. The total reduction potential is determined by crop types, potential application area and specific reduction potential of the measure. The results are presented as specific reduction, i.e., kg N/ha, yr, and the net total reduction in ktonne N per year for the Netherlands. The costs are assessed for each measure by the calculation of Csr~, which is the specific reduction cost of a specific measure, using Eq. 1.

Csp~.n --- or-I+ OM - SFPC + RIC (Dfl/tonne N) ( 1 )

where: a: annuity factor, depending on the interest rate r and the depreciation period n: a = r~

( 1 - (1 +r)-"); I: initial investments, expressed in Dfl per amount of fertilizer annually saved (in tonne N/yr ) ; OM: operation and maintenance costs expressed in Dfl (1988) per saved tonne N/ yr; SFPC: saved fertilizer purchase costs, expressed in Dfl (1988) per tonne N/yr; RIC: reduced income costs per tonne N that are saved annually, due to reduced crop production rate following the implementation of the measure.

The related energy savings are calculated by multiplying the amount of fertilizer saved by the gross energy requirement (GER) of the fertilizer (expressed as GJ/tonne N). The GER is defined as the amount of energy (in terms of enthalpy) required for the production of a specific product - including energy to produce the raw material - starting from primary energy carriers. In this article we will use the first-order GER. In order to calculate the specific costs for the related energy savings, Eq. 1 is adapted and expressed by Eq. 2:

a - I + OM - SFPC + RIC Csp~: GER (Dfl /GJ) (2)

where: a: annuity factor depending on the interest rate r and the depreciation period n: a = r~

(1-- (1 + r ) - " ) ; /: initial investments, expressed in Dfl per of fertilizer annually saved amount (in tonne N/yr) ;


Table 1 Nitrogen fertilizer types and consumption in 1987/1988

Fertilizer type Application ( ktonne N/yr )

CAN 309 (67%) Calcium nitrate 5 (1%) Magnesium AN ~ 56 (12%) NPK compound 77 (17%) Others 11 (2%) Total 458 (100%)

Source: [ 16]. ~Magnesium ammonium nitrate contains 22% N and 7% MgO.

OM: annual operation and maintenance costs expressed in Dfl (1988) per saved unit fertilizer; SFPC: saved fertilizer purchase costs, expressed in Dfl (1988) per tonne N/yr; RIC: reduced income costs per tonne N that are saved annually due to reduced crop production rate following the implementation of the measure. GER: gross energy requirement for the production of fertilizer (GJ/tonne N).

Costs are expressed in Dutch guilders (Dfl), equivalent in 1988 to approx. 0.5 US$ and 0.4 ECU. The annuity factor is calculated using a real interest rate of 10% and the lifetime of the technique as the depreciation time. Calcium ammonium nitrate (CAN) is the N- fertilizer that is applied most frequently in the Netherlands (see Table 1).

Fertilizer purchase costs in the period 1987/1988 are calculated at 1242 Dfl/tonne N, assuming CAN-fertilizers (with an N-content of 26% and costs of 323 Dfl/tonne CAN) [ 17]. The 1988 first-order gross energy requirement (GER) for the production of 1 tonne CAN is 10.4 GJ/tonne (LHV). This is equivalent to 40.0 GJ/tonne N [ 13].

The fertilizer reduction measures are listed in order of their cost effectiveness and are presented in the form of a supply curve, which shows the cumulative savings on fertilizer (or energy) consumption as a function of the specific costs. Potential savings are corrected for inter-measure influences, assuming measures are implemented in order of their cost- effectiveness.

3. Fertilizer consumption in the Netherlands

The historical development of fertilizer consumption in agriculture is depicted in Fig. 1. Both the annual total (ktonne N/yr) and specific consumption (kg N/ha,yr) are depicted as a function of the agricultural year. An agricultural year runs from the 1st July of the quoted year until 30th June of the following year. Fertilizer consumption has been decreasing since 1986 (see Fig. 1). In the reference year of our analysis the total consumption was 458 ktonnes N, which is equal to 228 kg N/ha on average. Fertilizer application varies with crop and soil types. The type of crop is more important than the type of soil.

We will limit our analysis to fertilizer application with respect to the major crops. The average annual fertilizer consumption for the major crops is presented in Table 2.

E. Worrell et al. / Resources, Conservation and Recycling 13 (1995) 233-250 237

t - O

~4oo t - O 0

. u : ~ _

200

100 . . . . . . . . . 9"s0 . . . . . . . . 1990 1970 1975 1 1985

Year

Total (ktonne N/yr) ~ Specific (kg N/ha.yr)

Fig. 1. Historical development of annual nitrogen fertilizer consumption in the Netherlands, depicted as specific nitrogen consumption (kg N/ha,yr) and as total consumption (ktonne/yr). The years are depicted as agricultural years, running from Ist July of the quoted year to 30th June of the following year.

Table 2 Annual N-fertilizer application, area and production rate in the Netherlands for the major crops (season 1987/ 1988)

Crop Area (1000 ha) Production (tonne Specific N-consumption Total N-consumption product/ha,yr) (kg N/ha,yr) a (ktonne N,yr)

Grass 1114 11.5 b 314 349.8 Silage maize 195 11.0 b 97" 18.9 Potato 144 41.9 c 196 31.5 Sugar beet 123 54.5 ¢ 148 18.3 Wheat 104 7.4 d 191 19.9 Barley 56 4.70 95 5.4 Others 276 - 53 14.6

Total 2012 - 220 458.2

Source: [ 18]. "Weighted average of the various soil types. bproduction expressed as dry matter. cProduction expressed as fresh product. dProduction expressed as cereal production containing 16% moisture. 9"lae actual annual N-fertilizer consumption for maize might in fact be lower (Pothoven, P., personal communication).


The average fertilization rate in the EU for the same period was 71 kg N/ha,yr [ 17], with a total consumption of 9300 ktonnes N/yr. The average N-fertilization rate in the EU increased slightly until 1987, but has been decreasing since then [ 19]. With regard to the specific fertilization rate, the largest users of N-fertilizers in the European Union are the Netherlands, Denmark, Germany and Belgium [ 17]. The world average fertilization rate is 17 kg N/ha,yr [ 17].

4. Reduct ion measures

We will now briefly describe the major technical measures available for improving fertilizer utilization, giving attention to the potential and costs of each measure. We describe technical aspects of the measure, applicability to crops and the associated costs, as well as the reduction in N-fertilizer consumption that can be achieved, relative to the reference year. The measures and the findings are summarized in Table 4.

4.1. Application o f the recommended fertilization level and increased use o f manure ( 'good housekeeping')

On the basis of their past experience of the relation between fertilization and crop production National Reference Centres (IKC-ATV) [20] have recommended fertilization levels. Recommendation levels are dependent on crop, soil type and mineral N-content of the soil in the spring. The recommendation levels are directed towards the best production from an economic point of view, considering the trade-off between crop production rate and fertilizer purchase costs. However, farmers often apply more fertilizer then necessary to be sure of the highest possible crop production. Therefore, the recommended level is still not used on a large scale. We will calculate the effect on the fertilizer use of the application at the recommended level for the various crops, by applying Eq. 3.

Avf= Vf.o-- (VA,f--x.Nmin) + ('qm" Vm,20oo) (kg N/ha,yr) (3)

where: A vr: reduction of specific application rate of fertilizer (kg N/ha,yr); Vf, o: specific fertilization rate in the reference year (kg N/ha,yr); VA.f: total recommendation level for nitrogen fertilization rate (kg N/ha,yr); x: a correction for the amount of mineralized nitrogen (given along with the recommendation level, see Table 3); Nmin: amount of nitrogen available in the soil in the spring (kg N/ha) on 0--60 or 0-100 cm depth (depending on the crop and the recommendation). rim: efficiency index for nitrogen application in manure (%); Vm.2Ooo: maximum rate of manure application in the year 2000, based on maximum phosphate application and the relation between P- and N-content of the manure (kg N/ha,yr);

The recommended level (as given in Table 3) is dependent on the amount of mineral nitrogen available in the soil in the spring. The amount of mineral N available varies between 50 and 100 kg N/ha, depending on soil type, weather conditions and fertilization in the past

E. WorreU et al. /Resources, Conservation and Recycling 13 (1995) 233-250 239

Table 3 Recommended fertilization levels [ 20,27,28], fertilizer application [ 18], manure application [ 29] and calculated saving on fertilizer application in the Netherlands

Crop Area Present specific Present specific Recommended Maximum Potential ( 1000 fertilizer manure fertilization level manure fertilizer ha) consumption consumption (kg N/ha,yr) application savings (kg

(kg N/ha,yr) (kg N/ha,yr) a 2000 (kg N/ N/ha,yr) c ha,yr) b

Grass 1114 314 300 400 269 48 (15%) Maize 195 97 484 175 183 14 (14%) Potato 144 196 70 2 8 3 - 1.4.Nmin d 171 70 (36%) Sugar beet 123 148 70 220 -1 .7 .Nmin 171 99 (67%) Wheat 104 191 70 200-Nmin 171 127 (66%) Barley 56 95 70 120-Nmin 171 25 (26%) Others 276 52 . . . .

Total 2012 220 - - - 46 (21%)

We assume an Nmin of 50 kg N/ha and an efficiency index of 50% for manure and the maximum application of manure, on the basis of the P-fertilization standards for the year 2000. aNt 1987/1988 data on manure consumption were available for this study; therefore, the 1984 manure consumption is given. Source [29]. The total manure production in 1987/1988 was 0.4% higher than in 1984 (expressed in ktormes N) [30]. bAssuming the maximum P-standards of 110 kg, 75 and 70 kg P2Os/ha for grass, maize and other crops, respectively, in the year 2000. The use of manure with a P-content of 1.8 kg P2Os/m 3 (efficiency index 100%) and 4.4 kg N / m 3 (with an efficiency index of 50%). The efficiency index indicates the effectiveness of the nitrogen in the animal manure compared with that of inorganic fertilizers. tit is assumed that manure is used at the level of maximum P-standards for the year 2000. The difference between recommended level and the manure N-rate (corrected for the efficiency index of manure) is made up by fertilizers. The savings represent the difference between this level and the 1987/1988 level. dThe average recommended value is mentioned. We have applied specific recommended levels for consumption potatoes on clay (285 -1 .1 .Nmin), consumption potatoes on sand (300 -1 .8 .Nmin) and factory potatoes (275 - 1.8 .Nmin) on areas of 87 000, 17 000 and 57 0130 ha, respectively.

[21 ]. We assume the (mineral) N-content of the soil in the spring to be 50 kg N/ha. Table 3 summarizes the average recommended levels for the Netherlands for the different crops. The recommended level is corrected for the soil type [20], by VA.y. In our analysis we will only take the soil type into account for potatoes, because data is available. The application of fertilizer is also dependent on the effectiveness of the nitrogen in the animal manure as compared with that of inorganic fertilizers and can be expressed as an efficiency index. The efficiency index is dependent on several factors (manure composition, crop, soil, spreading method, weather), and varies between 20 and 70% [22,23]. In our analysis we use an effectiveness of 50%. The application of manure can be increased, as there is a manure surplus in some agricultural areas. The utilization rate of manure is limited by the maximum phosphate-application rate. The maximum permissable levels depend on the crop [ 24]. The current ( 1991 ) maximum phosphate application rates are 200, 250 and 125 kg P2Os/ha for grass, maize and other crops, respectively. These figures will be reduced to 110, 75 and 70 kg P2Os/ha for grass, maize and other crops, respectively, in the year 2000 [24]. In our analysis we use the maximum P-levels for the year 2000 (the target year of the analysis).

240 E. Worrell et al. /Resources, Conservation and Recycling 13 (1995) 233-250

Furthermore, the savings depend on the relation between the P- and N-content of the manure. We will assume cattle manure with a P-content of 1.8 kg P2Os/m 3 and an N-content of 4.4 kg N/m 3 manure [20]. Phosphate has an efficiency index of 100% [22]. Weather, climate and soil conditions affect the recommendation level, but are not accounted for specifically, as the recommendation level is the result of many years of experience. The costs for the Nmin analysis are 60 Dfl [25 ], which is equivalent to 30 Dfl/ha on the basis of one analysis per 2 ha [ 26]. We will assume no negative effects on crop production, and hence no reduced income costs are involved in the introduction of the recommended level. However, annual weather conditions can lead to lower nitrogen availability and therefore a lower production rate. The results of the application of the recommended level are presented in Table 3.

Uncertainties in the results are introduced by the above-mentioned assumptions. We did not correct the recommended level for the soil type, which introduces an error of _ 15% for maize and 4-_20% for barley. The variation of Nmin introduces an error of 5- 1% into the total savings. The efficiency index for manure application varies between 20 and 70%, which (assuming a Nmin content of 50 kg N/ha) can lead to a variation of between 28 and 51% in the total reduction potential. The efficiency index is likely to improve, due to modem manure application technologies, e.g., manure injection (derived from [22,27] ). Current maximum levels allow greater use of animal manure, which increases the total fertilizer savings to 68% (on the same assumptions as mentioned above) and to 44% on the basis of the maximum levels for the year 2000.

4.2. Fertilizer spreader maintenance

The fertilizer spreader should be well maintained to ensure uniform spreading of the fertilizer over the land. This reduces excess fertilization of some parts of the land (and decreases damage to the crop) and prevents under-fertilization of other parts. In 1988, 80% of the spreaders in dairy farms (grass and maize) and 50% of the spreaders on arable farms (all other crops) were assumed to be not well maintained [ 31 ]. Good maintenance will save approx. 50 kg N/ha,yr at the current N-application levels (Heestermans, personal communication) of an average of 228 kg N/ha; equal to 22% savings. The total savings will be lower, because after the application of the recommended fertilization levels less fertilizer is applied (see Table 4). Increased annual maintenance costs vary between 141 and 153 Dfl/spreader [32]. In our analysis we assume the annual costs to be 150 Dfl/ spreader [ 31 ] or 146 Dfl/tonne of saved N on average. By better maintenance the spreading geometry improves. Therefore, less fertilized parts of the land will receive an equal amount of fertilizer, which will increase crop production. By uniform spreading the net production can increase by 60 Dfl/ha,yr for grass, and for the other crops by 200-700 Dfl/ha,yr [ 31]. In our analysis we will focus on the maximum possible reduction in fertilizer application, assuming constant productivity. The savings are dependent on the exact state of maintenance, which is not exactly known (Heestermans, personal comminucation). This will introduce an unknown uncertainty. Below we mention measures that involve analysis of the N-availability before sowing and during growth.

4.3. Reduction of fertilizer losses (fertilizer-free zone)

Goossensen (1992) has suggested that a 50 cm strip along each side of a field should be left unfertilized in order to reduce the fertilizer losses into ditches. It is estimated that this

E. Worrell et al. /Resources, Conservation and Recycling 13 (1995) 233-250 241

Table 4 Potential annual savings and costs of fertilizer-saving measures in the Netherlands for the reference year 1988

No. Measure Crop Corrected savings Costs Cs~c (Dfl/ tonne N/yr)

specific total production investments O&M RIC ( k g N / (ktonne energy (Dfl/tonne) (Dfl/t (Dfl/t ha/yr) N/yr) (PJ) N/yr) N/yr)

la Recommended grass 48 54 2.2 0 0 0 - 1242 level

lb maize 14 3 0.1 0 0 0 - 1242 lc potato 70 10 0.4 0 306 0 - 1007 ld sugar 99 12 0.5 0 226 0 - 1054

beet le wheat 127 13 0.5 0 205 0 - 1094 1 f barley 25 1 0.1 0 667 0 1254 2a Spreader grass 47 52 2.1 0 146 0 - 1069

maintenance 2b maize 15 3 0.1 0 146 0 - 1072 2c potato 14 2 0.1 0 146 0 - 1016 2d sugar 5 I 0.0 0 146 0 - 805

beet 2e wheat 7 1 0.0 0 146 0 - 809 2f barley 8 0 0.0 0 146 0 - 1044 3a Fertilizer-free grass 2 2 0.1 0 0 96 - 1104

zone 3b maize 1 0 0.0 0 0 258 - 878 3c potato 1 0 0.0 0 0 128 - 1019 3d sugar 0 0 0.0 0 0 169 - 674

beet 3e wheat 1 0 0.0 0 0 131 - 806 3f barley 1 0 0.0 0 0 263 - 841 4a Distribution grass 10 11 0.4 1370 0 0 - 9 1 9

geometry 4b maize 3 1 0.0 1370 0 0 - 924 4c potato 5 1 0.0 1370 0 0 - 849 4d sugar 2 0 0.0 1370 0 0 - 484

beet 4e wheat 2 0 0.0 1370 0 0 - 492 4f barley 3 0 0.0 1370 0 0 - 899 5a Need analysis grass 21 23 0.9 0 531 0 - 438 5b maize 10 2 0.1 0 1718 0 1320 5d sugar 6 1 0.0 0 1126 0 2757

beet 5e wheat 0 0 0.0 0 872 0 0 5f barley 0 0 0.0 0 •754 0 0 6 Row sugar 6 1 0.1 0 1689 0 5815

application beet 7 Fertilizer type various 1 1 0.0 0 0 0 1170 8 Leafstalk potato 27 4 0.2 0 1577 0 2175

analysis

Totals: 100 201 8.0

The measures have been corrected for inter-measure influences, assuming implementation in order of cost- effectiveness.


will save 4% on fertilizer use. This measure will probably lead to a reduction in the production yield. The reduction is different for grass and other crops and depends on the shape and size of the plot. The annual income is reduced by 25-35 Dfl/ha for grass, and by 20-30 Dfl/ha for other crops [20]. The costs for the various crops can be estimated using the specific reductions in fertilization (see Table 4).

4.4. Fertilizer distribution geometry

In the Netherlands in 1988 approx. 98 000 conventional fertilizer spreaders were used [ 17 ]. By adjustment of the distribution geometries, it is possible to prevent fertilizer losses into ditches alongside the field. In 1988 hardly any spreaders were adjusted (Heestermans, personal communication). Assuming 400 000 km ditch-side and a loss of 50 kg N/km,yr [ 31 ], the saving amount to 20 ktonne N/yr. The side-distribution adjustment of the spreader costs in total 280 Dfl/piece (average costs for ten types of spreaders [33] ). The spreader has a technical life-time of 10 years (Heestermans, personal communication).

4.5. Row application

Instead of traditional application, row application can reduce the amount of fertilizer that is required for optimum production [34]. In the traditional way fertilizer is spread over the land before sowing, while row application means that the fertilizer is spread simultaneously with the sowing in one or two rows near the seeds. The potential reduction in the fertilization rate depends on the type of crop; for potatoes figures range from no difference to a 16% reduction [34]. For sugar beet, reductions of 10-30% has been mentioned, with possible negative effects on the productivity [35], We will assume fertilizer savings of 16% for sugar beet [34].

In this study we will apply the measure only in the case of sugar beet, because no reduction potential has been proven for other crops and the results for potatoes are not clear [34]. In our calculations we will correct the figures for implementation of the previous measures. Extra annual labour costs for row fertilization are estimated at 50--100 Dfl/ha [34], or 1130-2250 Dfl/tonne N-saved.

4.6. Fertilizer need analysis

The need for N-fertilization of a crop depends on the amount of (mineral) nitrogen available in the soil during growing. The need is also dependent on the growing phase of the crop and on mineralization during the growing (which depends on the weather conditions). The availability of nitrogen in the soil is analysed, and used to calculate the optimum amount of fertilizer that needs to be applied by top-dressing. The soil analysis is repeated several times while the crop is growing [20]. This results in reductions of 10-20% in the fertilization rate [36]. We assume 15% savings with costs of 25 Dfl/ha,yr [37] for maize and sugar beet. The potential savings on grassland are estimated to be smaller, because on grassland fertilizer is applied in several stages, although without soil or crop analysis. For cereals, two stages are used. Therefore, for cereals the savings are estimated at I0%. We estimate the savings for grassland at 10%. The measure will not be applied with respect to


potatoes, because an alternative method is available (leafstalk analysis, see below). In the case of potatoes, the fertilizer need during the growing process can be identified

by the analysis of the nitrate content in leafstalks. The farmer takes four to five samples per season per lot [37]; these give information on the fertilization strategy that has to be followed. The potential savings are estimated at 50-70 kg N/ha,yr [37], based on current fertilization rates of 196 kg N/ha,yr. The annual costs are estimated at 93 Dfl/ha (de Witte, K., personal communication), or 1320-1850 Dfl/tonne N saved. The final savings will be limited due to previous implementation of other measures.

For cereals an optimum fertilizer application strategy is under development [38]. The savings and costs of this strategy are not yet clear. Therefore, we will not take this measure for cereals into account.

4. 7. Catch crops (green manure)

These can save up to 20 to 75 kg N/ha,yr [38] by binding nitrogen in the soil and releasing it the next season. The potential saving is dependent on the type of crop, time of harvesting of the crop, soil [ 39] and sowing time of the catch crop [ 20]. An average saving of 30 kg N/ha,yr is mentioned in the literature [20]. Costs incurred by seed purchase for the catch crop and land treatment are estimated at 175 Dfl/ha,yr [26]. However, if other measures have been implemented the sowing of the catch crop will be less effective and very expensive. Therefore, we do not take this measure into account in the analysis.

4.8. Fertilizer type

Applying alternative types of fertilizers can reduce the loss of nitrogen to the environment. The replacement of urea by calcium nitrate can reduce the N-losses due to evaporation by 12-35% [40], although figures up to 50% have been mentioned [41]. We assume a reduction of 0.5 ktonne N/yr (with an uncertainty of _+ 50%) of fertilizer demand, on the basis of an urea consumption of 2100 tonnes N/yr [ 16]. Application of CAN on clay-soils could lead to 50% of the ammonia being evaporated [40]. However, it should be noted that application of calcium nitrate could decrease the evaporation rate but increase the leaching of N (nitrate). The application of nitrate fertilizers will also reduce the N20 emissions [ 7 ]. Due to the large uncertainties the application of calcium nitrate as an alternative to CAN is not considered in this study.

4.9. Fertilizer quality

The quality of the fertilizer granule affects the fertilization spreading pattern and economics. Important parameters are uniform granule size [42], granule hardness [41] and the round shape of the granule [41]. The influence of these parameters on the fertilizer application are not yet clear, and are therefore not taken into account in this study.

4.10. Coating

The coating of fertilizer to regulate fertilizer release has been proposed [43 ] and investigated [44], but high costs (de Vlieger, personal communication) and possibly also

244 E. Worrell et al. /Resources, Conservation and Recycling 13 (1995) 233-250

problems associated with the release of the fertilizer have prevented further investigation. Application problems can be caused by weather conditions and changes in crop growing rate (and therefore fertilizer needs; Pothoven, P., personal communication). The technique needs to be further developed before it can be applied. Another possible development are 'coated seeds' with coating containing nitrogen fertilizer, but the fertilizer can also damage crops (due to the high salt concentration of the fertilizer during sprouting; Pothoven, P., personal communication). This has prevented further development.

5. Economic assessment of reduction potential

In this section we will evaluate the fertilizer-saving measures described above. First, we will present an economic analysis of the reduction potential for the amount of nitrogen fertilizer saved. Next, we assess the energy savings that result from the implementation of the fertilizer-saving measures by applying the GER-value of CAN and using the data presented in Table 4. The specific costs ( C ~ ) of each measure are presented in Table 4. The results are also shown in Fig. 2. The potential savings resulting from each measure have been corrected for inter-measure influences, by assuming that measures will be implemented in order of cost-effectiveness. Prior implementation of another measure will reduce the potential savings of the next (expressed in kg N/ha). The effect of prior implementation is approximated by using relative savings, namely a percentage of the fertilization rate, in cases where the fertilization rate has been determined by the measures implemented pre- viously.

2OOO

1600

1200

8OO

400

0

-400

-800

-1200

-1600

Z

r. r. 0

0

Id-f,3,4

3a lc,2a 2a ~ [ la,b \ \ I

I , ,

[

-40

-3O

-20 m

? -10 ~

-0 ~

-10 ~ 0

50

0% 10% 20% 30% 40% 50% Cumulative savings (%)

Fig. 2. A supply curve for the reduction in the fertilizer consumption in the Netherlands. The horizontal axis depicts the reduction potential in %. On the vertical axes the specific costs are depicted as function of the amount of fertilizer saved (in Dfl/tonne N) and as a function of the amount of production energy saved (in Dfl/GJ). The numbers refer to Table 4.

- - 3 0

- - 4 0

E. Worrell et al. /Resources, Conservation and Recycling 13 (1995) 233-250

Table 5 .Annual fertilization rates and reduction potentials for the selected crops in the Netherlands

245

Crop 1988 level (kg Economic level Economic savings Technical level Technical savings N/ha,yr) (kg N/ha,yr) (ktonne N,yr) (kg N/ha,yr) (ktonne N,yr)

Grass 314 187 142 187 142 Maize 97 65 6 55 8 Potato 196 106 16 63 22 Sugar beet 148 42 13 30 15 Wheat 191 54 14 54 14 Barley 95 59 2 59 23 Total 220 135 189 128 200

From Fig. 2, the national economically and technically feasible reduction potential of fertilizer consumption can be derived. The technically feasible potential is 44% of the fertilization rate in 1988, or 200 ktonnes of N. This equals an energy saving of 8.0 PJ, or 7% of the energy consumption of the Dutch fertilizer industry in 1988, due to the large production compared to the consumption in the Netherlands (see section 1 ). The economic potential of efficiency improvement (from a national point-of-view) is determined by the savings that have net negative or zero specific costs, The economic savings are calculated at 41% (189 ktonnes N/yr or 7.6 PJ/yr) . The potentials can also be assessed for each of the crops investigated. In Table 5, the fertilization rates and amounts of fertilizer saved are given for the 1988 application level. Also shown are the levels after implementation of the economically or technically feasible measures.

6. Discussion

The results show that there is a large economic and technical potential for a reduction in the use of fertilizer in the Netherlands. The savings are equal to 24% of the 855 ktorme surplus nitrogen [36], as revealed by the annual nitrogen balance of the Netherlands, The agricultural nitrogen surplus is lost by denitrification ( ~ 29%), ammonia volatilization ( ~ 21%), leaching ( ~ 18% ), accumulation ( ~ 11% ), while 20% is unaccounted for [ 45 ]. Dehitrification leads to emissions of N2 and N20, leaching results in nitrate losses to the surface water, while volatilization of ammonia is one of the local causes for acidic precip- itation.

In the assessment we considered only technical and readily implementable measures that have been tested and described in the literature. This approach yields results that differ from the calculations of a crop's minimum nitrogen need. The minimum nitrogen fertilization rate can be calculated from the N-content of the products and from the nitrogen available from other sources (deposition, mineralization). It is estimated that only a small part of the nitrogen applied is consumed by the crop, e.g., for maize 40-50% [46]. For cattle fanning the nitrogen utilization, expressed as the percentage of nitrogen recovered in milk and meat relative to the total applied nitrogen, is less than 30% [ 47 ]. Assessment of a crop' s minimum nitrogen need does not give information about the actions that need to be taken in order to reach the minimum. The current approach is also chosen so that the potential savings can


be evaluated economically. Long-term options (e.g., biotechnological adaptation of crops) and optimum allocation of land use are not considered, but could have a significant effect in the long term, as assumed in the study 'Ground for Choices' [ 14]. In that study, the minimum N-need is used to calculate the nitrogen consumption. In our study, the land use was determined by the situation in the reference year. We have excluded options that have a very negative effect on crop production rate.

The measures seem to have only a limited effect on the production rate. The potential savings are corrected for mutual influences in a proportional way, assuming that the measures are implemented in order of cost-effectiveness. Errors in the results are due to variations in fertilizer recommendation levels, variations in the mineralized N-content of the soil ( + 1% of the total result ), different soil types ( + 1%) and manure efficiency index (resulting in a variation of the potential savings between 28 and 51%). We have applied the year 2000 standard for P-application to determine the maximum manure application rate. Appli- cation of the 1991 standards, as given by [24], could increase fertilizer savings to 68%. Annual changes in climate, weather and soil type, which are not evaluated in this study, influence the figures.

In our analysis we have added together the effects of the various measures, correcting for their mutual influence in a mathematical way. However, other factors not evaluated in this study might affect the mutual influence. We did not find any such factors in our study, but for instance, a strong reduction in the fertilization rate might have more negative effects on the production rate than we found.

We have only investigated the energy saving resulting from the application of less fertilizer. An integrated assessment that includes energy consumption by the farmer might yield other figures for the energy saving achieved. However, we believe that the results will hardly differ, since no extra labour and machinery are needed to implement most of the measures. Only row application (for sugar beet) could lead to a minor increase in the farmers' energy consumption. In our analysis we do not consider the impact on the energy consumption of the farmer or the impact of implementing fertilizer-saving measures on the fuel costs for transport and traction. The energy consumption for transport is estimated at less than 3% of the first-order GER of CAN. 1

In the calculation of the specific costs we have not taken transaction costs into account, but have considered only the costs directly related to a measure. The transaction costs will depend on the implementation policy and instruments. For the economic assessment we have used a national economic approach, and not the farmers' point of view. Investments are not an important factor in the measures studied. The uncertainties in production yield will increase, and this will affect the financial position of the farmer. The extent to which the farmer implement measures will probably not be affected by economics alone. These factors, however, have not been studied. The cost data are average values for most options and could be different for individual agricultural firms. Care should be taken with the translation of the results to individual firms, also because the savings depend on the fertilizer rate applied and on the soil type. However, from Fig. 2 it can be derived that changes in costs will not influence the economic potential much, since in our study the measures that have the greatest influence are very cost-effective.

Assuming transport over an average distance of 200 km with a lorry using 1.5 MJ/tonne-kin [ 3], the energy consumption for transport will be 0.3 GJ/tonne CAN. The first-order GER of CAN is 10.4 GJ/tonne CAN [ 13].

E. Worrell et al. /Resources, Conservation and Recycling 13 (1995) 233-250 247

Translation of the results to other countries is difficult, due to the high fertilization rate • currently applied in the Netherlands. The fertilizer recommendation levels are not applicable to other countries. However, some measures are applicable to other countries, particulary spreader maintenance, a fertilizer-free zone and adjustment and the spreading geometry. The savings that can be achieved are dependent of the fertilizer and manure application rate in each country, and on the type of crop, crop productivity, soil types and climatic differences. Translation to other countries is also hindered by the limited availability of statistics. Measures applicable to the European Union are spreader maintenance, fertilizer-free zone, spreading geometry, replacement of urea by other fertilizers and the use of catch crops with respect to potatoes and maize. An approximate analysis, using the relative efficiency improvements (in percentages of the fertilizer application rate) in the Netherlands, shows economic and technical potential savings of upto 12% or 1.2 Mtonne/yr. This is equivalent to a saving of 48 PJ/yr. In 1992 a study of the long-term future of European agriculture was published [ 14]. The study concluded that it should be possible to achieve a 70--80% reduction in the total nitrogen losses (defined as the difference between the applied N and the removed N, due to crop harvesting) by the year 2015 (reducing losses to 2.1 to 2.8 Mtonne N/yr) . The figure is not equal to the reduction potential for fertilizer consumption, which is not reported on in that study. In that study, 'best technical means' are applied throughout the EU to maximize the nitrogen uptake and production yield and, therefore, minimize the use of nutrients and pesticides.

In a previous study we analysed the potential for energy efficiency improvements in the production of fertilizers [ 13 ]. It was shown that using today' s technologies an improvement of 16% can be achieved in the Netherlands. The technical savings of 44% on the fertilizer application rate represent a saving of 7% on the energy demand of the Netherlands fertilizer industry. With respect to energy savings per unit of fertilizer the saving on application is higher than on the energy demand for production. In many other countries larger energy saving on fertilizer production seems feasible [ 1 ] but saving on fertilizer application is likely to be lower, due to lower application rates. The effects of efficient fertilizer utilization on the energy consumption for production are not taken into account. Both negative effects (higher specific energy consumption due to reduced capacity utilization) and positive effects (closure of older plants, with comparatively high specific energy consumption) can be observed.

7. Conclusions

Improving the efficiency of the application of materials can contribute considerably to the reduction the energy consumption by reducing the production volume. We have studied the potential saving on fertilizer application in the Netherlands that can be achieved in the short term by assessing the technical options. Different crops have been considered. The methodology used gives an approximation of the currently achievable savings in fertilizer application. The potential technical savings are 44% (with a variation between 28% and 51%) relative to the reference year 1988. The annual nitrogen fertilizer consumption in the Netherlands can be reduced with 200 ktonnes N/yr. The average fertilization rate will be reduced from 228 kg N/ha, yr to 135 kg N/ha,yr for the economic level or 128 kg N/ha,yr


for the technical level. The technical potential is equivalent to a saving of 8 PJ / yr production energy. This is 7% of the annual energy consumption of the Dutch fertilizer industry. The economic potential (without considering transaction costs) , from the national viewpoint, is l imited to 41% of the demand. The total primary energy savings that can be achieved by energy efficiency improvement and by material efficiency improvement are comparable. The potential savings on fertilizer consumption are more cost-effective.

The Netherlands has the highest application rate of nitrogen fertilizer, especially on grass, in the world. Therefore, the results cannot be translated directly to other countries, until more information becomes available about fertilizer application for the different crops and also soil types and climatic differences in those countries.

Acknowledgements

The authors thank the Netherlands Energy Research Foundation (ECN) for providing financial support for the presented research, and are grateful to all the people who have provided information for this study. The authors wish to thank Prof. dr. W.C. Turkenburg (Utrecht Universi ty) for his suggestions and careful review of the paper. They also acknowl- edge the stylistic and linguistic assistance provided by S.M. McNab.

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