1HDRA-IOR, Ryton Organic Gardens, Warwickshire, CV8 3LG, UK .... scale up data to consider impacts for a borehole catchment (Vinten and Dunn, 2001), a.
Optimizing N Use and Farm Income in Organic Vegetable Production
Can N Use and Farm Income be Optimized for Organic Field Vegetable Rotations in Europe? U. SCHMUTZ1, C. FIRTH1, F. RAYNS1 and C. RAHN2 HDRA-IOR, Ryton Organic Gardens, Warwickshire, CV8 3LG, UK 2 HRI Wellesbourne, Warwickshire, CV35 9EF, UK
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ABSTRACT Most fresh organic vegetables are produced in intensive rotations, which rely heavily on large inputs of nitrogen to maintain the yield and quality of produce demanded by customers. Field vegetable crops often use nitrogen inefficiently and may leave large residues of nitrogen in the soil after harvest, which can lead to damage to soil, water and air quality. The four-year project EU-ROTATE_N "Development of a model-based decision support system to optimize nitrogen use in horticultural crops rotations across Europe" aims to reduce some of these problems. The project, led by HRI Wellesbourne, started in January 2003 and involves seven research organizations from countries in northern, central and southern Europe. Work includes the evaluation of the effects of varying levels of N supply on both product quality and farm income for organic and conventional rotations, as well as case studies for the evaluation of agricultural strategies with respect to N losses and economics for vegetable crops in Europe. This paper describes the work carried out at HDRA which focuses on farm economics and organic field vegetable rotations. INTRODUCTION Most fresh vegetables, organic and conventional, are produced in intensive rotations with high financial inputs and outputs; there are consequently high production risks involved. Economic penalties for crops failing to meet market criteria are so high relative to the cost of nitrogen (N) input, that growers can be tempted to adjust their N applications as insurance, even significantly above the predicted optimum. While this is particularly true of conventional systems, organic farms which are seeking to meet supermarket specifications may face similar temptations in their use of permitted inputs. The need to include fertility-building phases within organic crop rotations may also add to the economic pressure on growers, causing high opportunity costs and forcing the other crops in the rotations to obtain high returns from the land to pay for fixed costs. IMPLICATIONS OF ORGANIC PRODUCTION STANDARDS FOR NITRATE LEACHING POTENTIAL Environmental problems associated with N leaching in conventional agriculture are widely recognised (e.g. Strebel et al., 1989). External costs of nitrates in drinking water originating from UK agriculture are estimated to be £16m/year (Pretty et al., 2000). In contrast, up to 50% lower nitrate leaching rates per hectare have been measured in organic systems (Stolze et al., 2000). If, however, nitrate leaching is expressed per unit output of grain or milk, the performance of organic systems is similar to conventional systems (Stolze et al., 2000). The rotational approach and restrictions of N inputs within organic farming systems tends to lead to a lower overall risk of nitrate leaching. However, there are some problems, like the management of residual N from fertility building leys or the use of increased amounts of organic fertilizer, e.g. chicken manure. 200
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The EU regulation (ECC 2092/91, 1991-2003) limits nitrogen input from manure to 170 kg N/ha/year across the whole farm; however, there are no specific recommendations for vegetable production. Member states may establish lower limits, taking into account the characteristics of the area concerned, the application of other nitrogen fertilizers to the land and the nitrogen supply to the crops from the soil. The UK Standards (UKROFS, 2001) mention this possibility but do not make use of it. Private standards in the UK (e.g. Soil Association Certification Ltd, 2002) do not mention supplementary N fertilization or environmental problems with N leaching in the horticultural production section of their standards. The general section of the standards state that the maximum permitted application is 250 kg N/ha for field crops as organic manure application. Higher rates may be permitted in protected cropping. Because organic N fertilizers are often used well before harvest, applications of manures may occur at a time of low crop demand and high leaching potential. Organic Farmers & Growers standards in the UK (Organic Farmers & Growers, 2001) suggest acceptable rotations with a nitrogen balance. One example is the following rotation where the two-year white clover/ryegrass ley followed by winter wheat has a significant potential for leaching much of the rotational N surplus: 5-year suggested rotation White clover/Ryegrass White clover/Ryegrass Winter wheat Potatoes Spring Barley & Clover undersown Balance
kg N/ha/year 0 400 -64 -126 30 240 kg N/ha
In Germany the Bioland Association restricts N applications in organic vegetable production to 110 kg N/ha in the field and 330 kg N/ha in the greenhouse (Bioland, 2002). Biokreis, another German sector body, specifies that only 110 kg N/ha can be applied as an average over the whole vegetable rotation; if more than 50% of the N is from manure then 140 kg N/ha can be used. In Switzerland to qualify for direct ecological payments, each main vegetable (including members of the same family) has to be followed by at least a 2-year break (Swiss Confederation, 2003). From the above limited consideration of organic production standards in Europe we conclude that potential environmental problems are possible even where farmers follow EU organic standards. Possible problems with N leaching are not addressed in detail by the production standards and there is no explicit control of the potential for N leaching. There is also scope to further optimize N use in field scale vegetable production both to reduce environmental impact and to make efficient use of this valuable N resource in organic horticulture. THE APPROACH TAKEN BY THE RESEARCH PROJECT EU-ROTATE_N The four-year project EU-ROTATE_N "Development of a model-based decision support system to optimize nitrogen use in horticultural crops rotations across Europe" is funded by the European Commission within the Fifth Framework Programme. It is led by HRI Wellesbourne and started in January 2003. The modelling approach builds on the previous N fertilizer prediction models N_ABLE and WELL_N (Rahn et al., 1996). The model includes generalized relationships for growth and its dependence on plant size, N 201
Optimizing N Use and Farm Income in Organic Vegetable Production
content and temperature, the development of roots, N uptake, N release from soil organic matter and incorporated crop residues, evapotranspiration, soil water content, and leaching. The model currently operates on a daily time-step and provides simulations for growth and N requirements for more than twenty different vegetable crops. The model is, however, based on the simulation of the N dynamics in single cropping seasons and does not include crop rotations or cover crops; it also makes no assessment of economic implications of crop management. The model is adapted to UK or central European conditions and does not include Scandinavian or Mediterranean climates or crops. On-going research therefore involves countries from northern, central and southern Europe and includes work packages on the evaluation of the effects of varying levels of N supply on product quality and farm income, the development and testing of a new decision support system for crop rotations in Europe, and case studies for the evaluation of agricultural strategies with respect to N losses and economics. Other work includes root growth modelling and the simulation of the influence of irrigation and freeze-thaw cycles on nitrogen dynamics. The result will be a model of N dynamics suitable for use in both conventional and organic field vegetable rotations and during conversion. ONGOING RESEARCH AT HDRA HDRA is responsible for compiling a database, containing selected economic data for all major field vegetables across the different European climate zones. The database is almost complete and includes prices, variable costs, and gross margin data for conventional and organic field vegetables.
Other crops, often found in organic or conventional field vegetable rotations, such as cereals or fertility-building legumes are also included. There are large differences in the amount of economic information available for each country. Once complete, the database will be linked with yields generated from the agronomic model, it will then be possible to examine the effect of varying the supply of N on the economics of vegetable rotations. The effect of sub-optimal nitrogen supply on marketable yields and management 202
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practices such as the inclusion of fertility-building crops in organic rotations will also be simulated. It is necessary to convert the dry matter yield produced in the agronomic part of the model into marketable yield used in the economic model. Different factors and algorithms for this conversion are currently being researched to allow the data to be used in both economic and agronomic models. In a different work package, the HDRA soil science team is sourcing information to enable simulations of N accumulation and release from green manure cover crops in the model. Field studies have also begun to validate the current model predictions of N release from the addition of organic manures to soils in organic systems. EXPECTED OUTPUTS - CALL FOR PARTICIPATION Upon completion and following validation of the model, we aim to examine the effects of using various strategies to optimize the use of N and to minimise nitrate leaching within the rotation on farm economics, for example through the use of winter cover crops in both conventional and organic rotations. Farmers, advisers or researchers are welcome to contact us and to contribute any ideas about which rotations and strategies are likely to be adopted by farmers and hence should be tested. In future, the model could also be used to scale up data to consider impacts for a borehole catchment (Vinten and Dunn, 2001), a Nitrate Vulnerable Zone, a vegetable producing region, or even for a EU member state. This would allow the implications of adopting various N management strategies to be evaluated on a wider scale, at farm and the broader macro-economic level. REFERENCES BIOLAND (2002) Bioland Organic Standards.. Mainz, Germany: Bioland. CONVEDERATIO HELVETICA (2003)Direktzahlungsverordnung SR 910.13, The federal authorities of the Swiss Confederation. ECC 2092/91 (1991-2003) Council Regulation (EEC) 2092/91 on organic production of agricultural products and indications referring thereto on agricultural products and foodstuffs. With annex and 2003 amendments. Brussels: EC European Commission, EU European Union. s. ORGANIC FARMERS & GROWERS (2001) Control Manual. Shrewsbury, UK. PRETTY, J. N., BRETT, C., GEE, D., HINE, R. E., MASON, C. F., MORISON, J. I. L., RAVEN, H., RAYMENT, M. D. and Van Der BIJL, G. (2000) An Assessment of the Total External Costs of UK Agriculture. Agricultural Systems, 65: 113-136. RAHN C, GREENWOOD D.J & DRAYCOTT A. (1996) Prediction of nitrogen fertilizer requirement with the HRI WELL_N computer model. Progress in Nitrogen Cycling (eds. O Van Cleemput et.al.). 255-258. SOIL ASSOCIATION CERTIFICATION LTD (2002) Organic standards and certification. Bristol. STOLZE M., PIORR A., HÄRING A. and DABBERT S. (2000) The Environmental Impacts of Organic Farming. University of Hohenheim. Stuttgart, Germany. 6. 127. STREBEL O., DUYNISVELD W. H. M. and BOTTCHER J. (1989) Nitrate pollution of groundwater in western Europe. Agriculture, Ecosystems & Environment, 26: 189-214. UKROFS (2001) UKROFS Standards for organic food production. DEFRA UK, UKROFS United Kingdom Register of Organic Food Standards. London. VINTEN A. J. A. and DUNN, S. M. (2001) Assessing the effects of land use on temporal change in well water quality in a designated nitrate vulnerable zone. The Science of the Total Environment, 265: 253-268. WEB SOURCES: www.hri.ac.uk/eurotate, www.hdra.org.uk/research
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