Calculating environmental indicators for individual farms and fields: the case of potato cultivation in the Netherlands

Paper prepared for the 17th IFSA conference to be held in Florida (USA), November 2002

J.W.A. Langeveld1#, P.W.J. Uithol1#, B. Kroonen-Backbier2# and H. van de Akker3 1Plant Research International, 2Applied Plant Research, 3DLV Advisory Group #Wageningen University and Research Centre, the Netherlands

Abstract The Dutch project Telen met toekomst (‘Farming with a future’) designs and tests environmentally friendly arable farming systems, paying particular attention to nutrient emissions.To facilitate communication with farmers, environmental indicators are calculated for individual fields and farms. They are calculated using data from different sources that have been collected at different scales (field, crop, farm). The set-up of the special database created to manage the data is discussed and environmental indicators are calculated for potato farms in the south-east of the Netherlands. The indicators used for individual fields include (1) the mineral nitrogen present in the soil at harvest and (2) at the beginning of winter (the major period of nitrate leaching). The farm level indicators are the nitrogen surplus calculated with (3) a nutrient mass balance and (4) MINAS (MINeral Accounting System: the calculation method mandatory for Dutch farmers). The field-level indicators suggest that potato cultivation partly complies with the project’s objectives, but that the emissions from the farm as a whole are too high. This is partly explained by the fact that vegetable and pulse crops do not use available nitrogen efficiently. The data collection, management and analysis are discussed and improvements are suggested.

Introduction In order to reduce applications of chemical and organic fertilizers and agro-chemicals in the Netherlands, since the 1970s Dutch farmers have been subjected to increasingly stringent regulation. In relation to nutrient applications, there are permitted levels of manure application (methods, periods of the year), nitrogen applications from manure and nutrient surpluses. This policy has been successful: since 1990, agriculture-related acidifying emissions have fallen by 30 %, nitrogen loads to soils have fallen by 17 % and phosphorus loads have fallen by 17 %. However, much remains to be done. Recent initiatives include the project ‘Farming with a future’, to design and apply environmentally sound production systems. It focuses on the quality of groundwater and surface water on or adjacent to arable farms. The definition of “arable” includes farms growing field vegetables, tree crops, and bulbs. Each of these arable sectors is represented by an experimental farm and also a number of commercial farms (on which innovations developed on the experimental farms are tested). The project’s major objectives are to bring down nutrient emissions by setting maxima for phosphorus and nitrogen/nitrate concentrations in surface water and groundwater, and for annual ammonia emissions (Table 1). The maxima set for the experimental farms are much stricter, which forces them to apply strict fertilization practices. Table 1 Project maxima for nutrient emissions

Unit Commercial Experimental far ms Phosphorus concentration in groundwater: mg P/l n.a. 0.4 sand n.a. 3.0 Other soils Phosphorus concentration in surface water mg P/l 0.15 0.05 Nitrate concentration in groundwater mg N/l 11.3 5.6 Nitrogen concentration in surface water mg N/l 2.2 1 Ammonia volatilization kg N/ha per yr 15 5 Source: Booij et al. (2001)

It is considered extremely important to communicate effectively with pilot farms on their performance. Therefore, before the project started the fertilization practices in the previous three years were analyzed and the findings were discussed with the farmers. This led to a fertilization strategy being defined for each farm. Every year, helped by extension officers, the farmers draw up a fertilization strategy. Then the plan’s implications for project objectives are assessed and, if necessary, alternatives are suggested to the farmers. At the end of the year the fertilization practices, crop growth, crop yields and environmental impact are ascertained. The latter entails measuring the quality of the groundwater and surface water. However, as this is difficult and labor intensive, the results do not become available until nine months after harvest, by which time the next season is well under way. Our practical solution is to calculate indicators so that a farm’s environmental performance can be assessed rapidly before the next season starts. The indicators include nitrogen surplus (calculated with nutrient mass balance or with a specific mineral accounting system) and amount of mineral nitrogen that is found in the soil profile. For a discussion on the use and value of such indicators see Schröder et al. (2000). A maximum value has been set for each indicator. The values for nitrogen are presented in Table 2.

Table 2 Indicators of environmental performance

Indicator Value (kg nitrogen/ha) Clay soils Wet sandy soils Dry sandy soils Nutrient surplus (calculated with a mass 90 90 90 balance) Nutrient surplus (calculated with a MINeral 100 100 60 Accounting System (MINAS) balance)1 Mineral nitrogen in autumn 70 70 45 1: The MINeral Accounting System was introduced by the Dutch government in order to curb nitrogen and phosphorus applications. See Henkens and van Keulen (2001) for details. Source: Anonymous (2001)

The data used in the calculations are given in Table 3. They originate from measurements, literature or legislation. The nutrient mass balance calculations include nutrients involved at all stages of the farming process: fertilization, harvesting (and hence removal), but also nutrient input through deposition and nitrogen fixation. There are seven data sources, four of which originate from farmer’s registration sheets. Additionally, reference data are used from literature. Most data apply directly to the field level. The second indicator includes a mass balance calculation derived from the MINeral Accounting System (generally referred to as the MINAS balance). It excludes nutrient input generated from deposition and includes only limited types of additional non-fertilizer nutrient sources (for details on the MINAS system see Henkens and van Keulen, 2001). Nutrient removal is not measured but is calculated using the reference value given in the MINAS legislation. All data refer to the farm level. In theory, the farm level mass balance should equal the MINAS balance. In practice, however, this occurs very rarely, due to differences in the data sources.

Table 3 Type of data used to calculate indicators

Data type Character Source Level Nutrient mass balance Fertilizer application Measured Farm administration Crop Deposition Reference value Literature Region Nitrogen fixation Reference value Literature Crop Application of additional nutrient sources1 Measured Farm administration Crop Concentration of additional nutrient sources Reference value Literature Crop Crop yield and removal Measured Farm administration Crop Nutrient concentration in crop products/by-products Reference value Literature Crop MINeral Accounting System balance Fertilizer application Measured Farm administration Farm Nitrogen fixation Reference value Legislation Farm Application of additional nutrient sources2 Measured Farm administration Farm Concentration of additional nutrient sources Reference value Legislation Farm Nutrient removal by crops Reference value Farm administration Farm Mineral nitrogen in fall (0-90 cm) Measured Lab reports Field /extrapolated3 1: nutrients may be applied with soil ameliorators (e.g. peat, straw), or in the degradable pots used in vegetable cultivation; 2: in the MINAS system not all additional sources are included; this varies over time and per sector; 3: amount of mineral nitrogen is measured in two layers (0-30 and 30-60 cm) but including the 60-90 cm layer on four plots of each farm. Values for 0-90 cm on the other fields are then obtained using extrapolation Source: this study

The third indicator used in the project has to do with the amount of nitrogen that is expected to be leached during the wet winter period. As summers in the Netherlands are relatively dry and most rain falls during the winter, the amount of mineral nitrogen in the top 90 cm of the soil (soils in the Netherlands generally are deep) at the beginning of the winter is considered an important environmental indicator of the amount of nitrogen that will probably be leached. The amount of mineral nitrogen in fall in the top 60 cm can be measured in each field involved in the project. Measurements of the 60-90 cm layer, however, are too laborious and are made on only four fields per farm. These results are then extrapolated for each field, so that a value can be obtained for the 0-90 cm layer. As Table 3 demonstrates, calculating the indicators entails considerable data measurement, entry and management. The objective of this paper is to discuss how data from different sources at different scales are applied in the calculation of environmental indicators. This paper is organized as follows. First, the methodology followed is discussed. Next, results are presented for potato cultivation in the South-east of the Netherlands. The data used are from the pilot farms in the project. Using the results for 2001, environmental indicators are calculated. This followed by a discussion of how the outcome can be used when evaluating the environmental performance of the pilot farms and of Dutch potato cultivation in general.

Methodology As the project is primarily concerned with nutrient emissions (and to a lesser extent with reducing applications of agro-chemicals) most of the data collected are related to nutrient flows and agro-chemical applications. Data are collected on fertilization and farming activities such as mechanization, labor, agro-chemical application, harvest, etc. Registration includes inputs (labor, energy, nutrients, chemicals) and outputs (area treated, yield). Additionally, the results of soil and manure sample analyses are included. The data are input in two databases. One is a major registration and database system called FARM which has been operational for almost ten years. Features of this system are described elsewhere and will not be discussed here. FARM output is given in Excel format and includes nutrient flows at crop, field and farm levels. It is linked to additional soil sample data in a comprehensive multi-level database which is used to calculate environmental indicators: (1) the farm level nitrogen surplus calculated with a simple nutrient mass balance (2) the nitrogen surplus calculated following the MINAS specifications (MINAS has also been internalized in Dutch environmental legislation), (3) the amount of mineral nitrogen in the top 60 cm of a given field at harvest, and (4) as in (3), but in the top 90 cm at the beginning of the leaching season.

Results The information has been put into a database at crop, field and farm level. The data are linked through crop, field, farm and sample IDs. Figure 1 gives an overview of the database structure. Figure 1 Overview of database structure

Field and farm data for the four farms in the south-east pilot farm group are presented in Tables 4 and 5. These farms range in size between 27 and 56 ha. Crop rotation is based on a 1:4 rotation of potato cultivation. The other major crops include sugarbeet, silage maize, cereals and industrial crops (peas, French beans, scorzonera). Three farms are mixed and are therefore self- sufficient in manure, which is preferably applied on the farm as it is costly to remove. The soils are mostly sandy and wet. Table 4 gives the data on potato fields. Three of the farms have two fields of potatoes, ranging in size from 3 to 7 ha . One farm has four smaller potato fields. Early varieties of potato are preferred. As they are harvested younger, they require less nitrogen. On the other hand, most nitrogen uptake stops before mineralization of manure and organic material can provide additional nutrients, so it may be necessary to increase fertilization rates. The soils are generally moderate to highly sufficient in phosphorus. Potassium availability is variable. Organic matter content is generally around 2%, but higher figures occur.

Table 4 presents data on crop fertilization. In spring, some 30 to 90 kg of mineral nitrogen is already available in the soil profile. Additionally, all plots are manured, providing 130 to 200 kg of nitrogen per hectare. Depending on the type of manure applied and the period between manuring and crop cultivation, half to three quarters of the nitrogen applied will not become available to the crop during the growing season. Further, nitrogen will become available from mineralization of the previous year’s crop residues. These are generally catch crops, except for plot Ak07_4, which had previously been under grass. Together, this adds up to 110 to 270 kg of available nitrogen per hectare. Together with the nitrogen from chemical fertilizers, this means a total of 180 to 295 kg becomes available. About one third of this originates from chemical fertilizers. The data from Table 4 show no clear relation between early potato varieties and fertilization levels, early crops receiving both the smallest and the largest amounts of nitrogen. However, the differences between farmers are considerable, with Ak06 and Ak07 supplying the smallest amounts of nitrogen. Table 4 Total and available nitrogen applied on potato fields

Mineral Manure Crop Available Chemical Total Proportion available nitrogen Field, cv type

(kg/ha in Total Available (kg/ha) (kg/ha) (kg/ha) (%) (kg/ha) (%) 0-60 cm) (kg/ha) (kg/ha) (% of total applied) Ak06 Ak06_5 (early) 33 132 78 (59) - 111 72 183 39 81 192 44 Ak06_7 (regular) 331 132 78 (59) - 111 Ak07 Ak07_ 6 (early) 53 175 88 (50) - 141 68 209 33 238 29 Ak07_4 (regular) 37 180 133 (74) 100 270 68 Ak08 Ak08_1 (early) 66 70 53 (76) 20 139 62 201 31 283 20 Ak08_3 (early) 84 188 142 (76) 23 248 57 295 23 Ak08_4 (early) 91 180 136 (76) 18 245 68 227 17 Ak08_14 (early) 53 180 136 (76) - 189 38 Ak09 Ak09_5 (regular) 29 196 127 (65) - 156 113 269 42 206 35 Ak09_8 (regular) 41 153 91 (59) 2 134 72 1. assumed (no value was available; value taken from field 5 of same farm). Source: this study

A comparison with the fertilizer recommendations provided to the farmers (Table 5) shows that some farmers supply too much nitrogen (an excess of up to 90 kg) while others give too little (a deficit of up to 50 kg N/ha) of nitrogen. The latter is surprising, given the abundance of manure on the farms and in the region. The differences in nitrogen application rates are reflected in the mass balance nitrogen surpluses calculated for each plot, but not in the differences in the amount of mineral nitrogen measured at harvest or in the fall. Few farmers have bothered to find out the amount of mineral nitrogen at harvest, even though it takes only one phone call to get this measured for free. Table 5 Extent to which field level indicators are surpassed (kg/ha above project maxima)

Catch crop Advice1 Nitrogen surplus Mineral nitrogen

Farm and plot (kg/ha) (kg/ha) At harvest Fall (0-60 cm) (0-90 cm) Ak06 Ak06_5 No 215 23 n.a. 67 Ak06_7 No 220 1 n.a. 119 Ak07 Ak07_ 6 No 195 121 100 97 Ak07_4 No 230 67 95 115 Ak08 Ak08_1 Yes 206 -2 n.a. 109 Ak08_3 Yes 206 108 n.a. 75 Ak08_4 Yes 206 98 n.a. 95 Ak08_14 Yes 200 74 n.a. 82 Ak09 Ak09_5 No 225 157 n.a. 73 Ak09_8 No 222 -25 n.a. 105 Project target Yes 250-Nmin2 903 654 45 n.a. = not available; 1: local recommendtation for this region only; 2: no project maximum; value of 65 is used. See text for further explanation; 3: derived from the farm level maximum; 4: plus corrections for specific cultivars (early varieties receive 20 kg/ha less) and corrections for mineralization of last year’s crops residues.

Table 6 shows the farm level indicators. The surpluses of mineral nitrogen and nitrogen in the fall exceed the project maxima. This is partly explained by the cultivation of other crops, some of which require heavy applications of nitrogen and others of which do not use the applied nitrogen effectively. By and large, the differences in mass balance surplus figures reflect the findings shown in Table 5. Remarkably, the differences between farms in fall mineral nitrogen and mass balance nitrogen surpluses are rather small but the differences calculated using MINAS (the system mandatory for Dutch farmers, to force them to reduce their fertilization rates) are large. The likely reason is that the MINAS balance is calculated with a fixed nitrogen removal (165 kg ha1), whereas the mass balance uses real removal data. This suggests that the former is less realistic. Thus, although MINAS balances are easier to calculate (requiring less data), the fact that fixed rather than actual nutrient removal data are used will blur differences in farm performance (environmentally as well as economically) when there are large differences in crop yield (if comparable crops are cultivated) or in nutrient removal (if cultivated crops differ in nutrient removal). This will discourage farmers from optimizing real balance surpluses and will discourage measures that are potentially beneficial to farmers and the environment (e.g. cultivation and subsequent sale/removal of crop residues or nitrogenous (catch) crops that could become profitable if they help prevent MINAS fines). Table 6 Extent to which farm level indicators are surpassed (kg/ha)

Farm Mineral Nitrogen Nitrogen surplus (kg/h a) Fall Mass balance MINAS (0-90 cm) (kg N/ha) (kg N/ha) Ak06 84 86 94 Ak07 86 136 263 Ak08 77 140 92 Ak09 75 168 301 Objective 45 80 225

Information like that given in Tables 5 and 6 can be used to formulate general recommendations for potato cultivation. We analyzed a large number of fertilization experiments and concluded that after potato cultivation a field can be expected to contain a minimum of 60 to 70 kg of mineral nitrogen in the fall. Figure 2 shows that two thirds of the potato fields cultivated in the project have already realized amounts below this. Figure 2 also demonstrates that there is no clear relation between nitrogen application rate and mineral nitrogen content in the fall. This is attributable to differences in soil type, initial mineral nitrogen level in spring and mineralization.

Nmin at harvest Potato 0-60 cm soil layer (kg/ha) 12 0

10 0

8 0

6 0

4 0

2 0

0 10 0 12 5 15 0 17 5 2 0 0 2 2 5 2 5 0 2 7 5 3 0 0 available and applied N

Source: Smit et al. (in prep.)

Figure 2 Mineral nitrogen at harvest and nitrogenous fertilization for farms in the project

Discussion and conclusion The results for all indicators are used not only to check whether the project objectives are realized by a given farmer in a given year but also to communicate with farmers within and outside the project and with two Dutch ministries: Agriculture, Nature Management and Fisheries; and Housing, Spatial Planning and Environment. Farmers use the calculated indicators in their evaluation of a given year, to check whether a particular fertilization strategy has met their expectations. The indicators on mineral-nitrogen appear to be particularly useful for this. The nutrient balance figures are invaluable for comparing project results with farms not included in the project.

The data registration and management involved in the project are time-consuming and, therefore, expensive. But other problems have been encountered during the project, too. They are related to data collection and management: - not all data could be measured; sometimes values from the literature have had to be used, - the inputting of data requires a major effort from farmers as well as from researchers, and there is always a risk of errors creeping in - the data are collected at different scales (ranging from field to farm and requiring many internal links) - certain data are incompatible (the amount of mineral nitrogen in the fall, for example, is measured per field, even if that field contains several several different crops: this makes it cumbersome to apply this indicator in the evaluation of environmental performance) - there is a lack of continuity (as registration is based on annual inventories, information on previous activities in the same field is sometimes unobtainable. This occurs when plot size varies over the years). Possible improvements include the use of a geo-referenced data system (which can overcome problems related to changing plot size and will facilitate interpolation and long-term analysis), and measures to strengthen the link between data collection (farmers and extension workers, but also analysts of the soil/manure samples) and data inputting (farmers and researchers).

There are four practical ways in which the scheme could be improved. Firstly, the farmers could be given GPS units so that they can directly enter data on inputs to a given field or crop. Secondly, data could be collected and verified at several moments during the year, not just at the end of the farming year. Thirdly, the computers into which the data are input should provide simple feedback checks that can show typing or calculation errors (e.g. calculation of an average instead of a total). Fourthly – and finally – the data entry systems used should immediately calculate trends and produce elements such as figures and tables, so as to make data entry automatically part of the analysis (in contrast to the conventional system, where analysis only starts when data entry has been completed). Preferably, this innovative system should be on the project website, where data from different farmers can be compared as well as data from the same farm in earlier years. (Our experience is that few one of the best ways to motivate farmers is via competition, be it with themselves or with others either inside or outside the project.)

In spite of its limitations and the costs involved, the data system has worked satisfactorily. In the project, the use of a set of indicators facilitates discussion with farmers and policy makers on the performance of given fertilization practices. It enables fast analysis and feedback from researchers and extension workers, and thus stimulates commitment from the farmers whose enthusiastic cooperation is essential for the project.

Acknowledgements Telen met toekomst is supported by the Ministry of Agriculture, Nature Mangement and Fisheries and the Ministry of Housing, Spatial Planning and the Environment. This support is gratefully acknowledged. References Anonymous, 2001, Telen met toekomst voor telers met toekomst. Jaaroverzicht 2000. Wageningen: Plant Research International. Booij, R., W. van Dijk, B. Smit, F. Wijnands, H. Langeveld, J. de Haan, A. Pronk, J. Schröder, J. Proost, H. Brinks, P. Dekker and P. Ehlert, 2001, Detaillering projectplan 'Telen met toekomst'. Telen met toekomst Publicatie no. 3. Lelystad: Applied Plant Research. De Buck, A.J., F.J. de Ruijter, F. Wijnands, P.L.A. van Enckevort, W. van Dijk, A.A. Pronk, J. de Haan and R. Booij, 2000, Voorwaarts met de milieuprestaties van de Nederlandse open-teelt sectoren: een verkenning naar 2020. Wageningen: Plant Research International. Kroonen-Backbier, B., H. Langeveld and E. Hofstad, 2001, Groepsrapport ZON akkerbouw 2000. Telen met toekomst publicatie ZONak00. Lelystad: Applied Plant Research. Henkens, P.L.C.M., and H. van Keulen, 2001, Mineral policy in the Netherlands and nitrate policy within the European Community. Neth. J. of Agr. Sc. 49, Pp. 117-134. Neeteson, J. R. Booij, W. van Dijk, J. de Haan, A. Pronk, H. Brinks, P. Dekker and H. Langeveld, 2001, Projectplan 'Telen met toekomst'. Telen met toekomst Publicatie no. 2. Lelystad: Applied Plant Research. RIVM, 2001, Nationale Milieubalans. Bilthoven: National Institute of Public Health and Environmental Protection. Smit, A.L., F.J. de Ruijter, J.G. Groenwold and H. Smid (in prep.), Resultaten van metingen minerale stikstof in Telen met toekomst. Wageningen: Plant Research International. Schröder, JJ., J.J. Neeteson, O. Oenema and P.C. Struik, 2000. Does the crop indicate how to save nitrogen in maize production? Reviewing the state of the art. Field Crops Research 66, Pp. 151-164.

Hans Langeveld, Plant Research International, P.O. Box 16, 6700 AA Wageningen, the Netherlands. Phone +317 475950, fax +317 423110, [email protected]. Paper submitted for an oral presentation in theme 3, Farming systems knowledge and information systems.