Evaluation, Design and Control of Sustainable Horticultural Cropping Systems

As all other human activities, horticulture is accountable for its impact on the resources available, now and in the future, to our societies. The problem is of particular importance in production systems that are often intensive and require high amounts of inputs. To fit with the increasing number of regulations and contracts growers have to respect, tools must be created to evaluate existing cropping systems and design and control original ones with respect to sustainability. Whatever the adopted technique, a systemic approach is required. Evaluation is possible either beforehand or during the implementation of the sequence and spatial combination of crops and corresponding technical operations that constitute a cropping system. Sets of agro-ecological indicators have been designed to evaluate the fittingness to specifications of ecological sustainability of the various components of cropping systems. They can be used to assess the global environmental impact of cropping systems on environmental resources. Existing or novel management strategies can also be evaluated with simulation models. Conception of crop management strategies consistent with objectives of sustainability has been made possible by the use of specific techniques belonging to the fields of linear programming and artificial intelligence. They make possible the generation of original crop successions and sequences of technical operations. At last an on-line control of the cropping system is compulsory to keep it within the limits of the strategic plan. To this end, indicators can be organised in a control board, and combined to decision rules. Artificial intelligence provides a way of formalising decision rules based on either scientific or expert knowledge, and generate decisions at a tactical level. Such examples show that indicators, models and decision support systems are relevant tools to assess the fittingness of horticultural cropping systems to the new standards of resource management. INTRODUCTION During the recent years, an increasing number of public regulations and private contracts have converged to orientate horticultural production towards a better control of the environmental impact of the cropping systems and an improvement of the quality and health value of their products. For example, through the Common Organisation of the agricultural Markets, the European Union supplies financial incentives to producers’ organisations provided they achieve the objectives of the market organisation (improved productivity and marketing and greater attention to the environment). Specific regulations have been set up: e.g. the Nitrates Directive (1991) defines nitrate vulnerable zones in which action programmes aiming at limiting nitrate pollution must be carried out. Such regulations often converge with the contracts linking producers and their clients and defining not only the required properties of the products (for example specifications limiting the nitrate content of leafy vegetables) but also the characteristics of the Present address: UMR SYSTEM (Agro.M-CIRAD-INRA), CIRAD, Campus Lavalette, TA 40/01, avenue Agropolis, 34398 MONTPELLIER Cedex 5. Email: [email protected] Proc. XXVI IHC – Sustainability of Horticultural Systems Eds. L. Bertschinger and J.D. Anderson Acta Hort. 638, ISHS 2004 Publication supported by Can. Int. Dev. Agency (CIDA) 46 production process itself (for example specifications prescribing integrated protection and production). In this changing social and economic context, new scientific concepts and methods are required in horticulture, based on systemic approaches (Rabbinge and Rossing, 2000). The concept of sustainability is multidimensional; it includes ecological, social and economic objectives. I will focus here on the ecological dimension of sustainability and present some examples of novel scientific approaches designed to face three major challenges for research in this field: (i) the fittingness of cropping systems to the specifications of sustainability must be evaluated, (ii) in many cases, innovative cropping systems must be designed and, (iii) a closer control of these systems is required. EVALUATION OF THE ECOLOGICAL SUSTAINABILITY OF CROPPING SYSTEMS Cropping systems can be evaluated with sets of indicators. Indicators can be defined as variables that provide information about a complex system for users to take appropriate decisions (Gras et al., 1989; Mitchell et al., 1995). Various indicator-based methods have recently been analysed and compared (van der Werf and Petit, 2002). They usually require input information that is easily available on farm. Among them, methods designed for industrial processes such as life cycle assessment are being introduced in agriculture and horticulture (Antón et al., 2002; Mempel and Meyer, 2002). Simulation models provide an alternative tool to predict the various outputs of a management strategy and the degree of realisation of the manager’s objectives. Their formalisms and parameters are more dependent on scientific knowledge. Use of Agro-ecological Indicators: the Example of the Indigo Method In the Indigo method, a set of agro-ecological indicators has been defined to evaluate the impact of various cultivation practices on a range of environmental variables (Bockstaller et al., 1997; Girardin et al., 1999). In contrast to other evaluation methods, Indigo indicators are based on the effects of cultivation practices on the environment rather than on cultivation practices as such (van der Werf and Petit, 2002). The Indigo method has been used for cereals and vineyards; specific features are in development for fruit production. The major cultivation practices that have been analysed are related to the management of not only production factors (nitrogen and phosphorus fertilisation, use of pesticides, irrigation, use of energy, tillage, management of organic matter) but also other dimensions of the cropping system (crop diversity, soil cover, non productive components). The environmental variables that are considered are the surface and underground water quality, the air quality, the soil depth, structure and composition, the use of non-renewable resources, the biodiversity and the landscape quality. Each cultivation practice affects a particular set of environmental variables. For example, the use of pesticides is related to the quality of surface and underground water, to the quality of air, and to biodiversity whereas nitrogen fertilisation is mostly related to the quality of underground water and to the quality of air. Quantitative as well as qualitative information can be used in the construction of an indicator. Simple models were used for nitrogen fertilisation and irrigation whereas an expert system was designed for the pesticide use. In the latter case, the risks for underground water, surface water, air and biodiversity linked to pesticide use have been rated. Rating results from the combination of several variables. For example, the risk for air quality depends on the volatility of the pesticide molecules, their half-life, the acceptable daily intake for humans, and the spraying conditions. Different users may find interest in such an analysis. For example, growers willing to evaluate their strategy of plant protection would focus on the associated indicator whereas institutions or companies involved in the protection of water resources would integrate all the indicators linked with one component of the environmental impact, water quality. Growers willing to fit with specifications of e.g. integrated protection and