Intercropping System Optimization for Yield , Quality , and Weed Suppression Combining Mechanistic and Descriptive Models

concluded that the intercropping system needed to be optimized with respect to crop quality and weed supIntercropping leek (Allium porrum L.) with celery (Apium graveopression for successful implementation and suggested lens L.) is an option to reduce growth and reproductive potential of weeds while maintaining productivity. In this study, a combined applying ecophysiological simulation models to optimodeling approach is used to optimize a leek—celery intercropping mize the system. Earlier, Kropff and Van Laar (1993) system with respect to crop yield, product quality, and weed suppresadvocated the use of modeling to develop and optimize sion. An ecophysiological model for interplant competition was used weed management systems with respect to cost effecto simulate yield and product quality of the crops as well as biomass tiveness and minimization of environmental effects. and seed production of the weed Senecio vulgaris L. for a wide range Ecophysiological crop growth models can be very efof crop mixtures and weed infestations. The results of the simulations fective to evaluate and develop complex systems, such as were summarized using a descriptive hyperbolic yield–density model, multispecies plant communities (Kropff and Van Laar, which then allowed evaluation of the intercropping system in terms 1993). Based on physiological, morphological, and pheof productivity, product quality, and ability to suppress weeds. In a nological processes, such models provide insight into the weed-free mixture, the competitive ability of celery was six times higher than that of leek. With respect to late-emerging S. vulgaris, competitive relationships of the system. These models the relative competitive ability of leek was 5.4 times lower than that facilitate the exploration of complex systems without of celery. Replacing two leek plants of a leek monoculture by one extensive field experimentation to investigate all opcelery plant resulted in almost 20% biomass reduction of late-emergtions in a wide range of conditions. Empirical models ing S. vulgaris. Crop mixtures with a leek density of about 20 plants and regression techniques can help analyze the final m 2 and a leek/celery ratio of 2 proved to be the optimum intercropoutcome of competition trials and describe plant interping system, given the current price ratios. Compared with leek monoference in cropping systems. Approaches to describe culture, profitability was maintained, and late-season weed suppresinterplant relationships have been developed for a long sion was greatly increased, resulting in reduced weed seed production. time and have helped improve understanding of competitive effects between crops and between crops and weeds (De Wit, 1960; Kira et al., 1953; Shinozaki and R studies have addressed intercropping as an Kira, 1956). option for an integrated weed management, particThe current study attempts to combine a mechanistic ularly in farming systems with low external inputs (Capand descriptive modeling approach to optimize the sysorali et al., 1998; Itulya and Aguyoh, 1998; Liebman tem. A well-evaluated ecophysiological model, such as and Davis, 2000; Rana and Pal, 1999; Schoofs and Entz, INTERCOM (Kropff and Van Laar, 1993), provides 2000). Effects of crop diversification on weeds have the necessary insight into the processes and plant charbeen reviewed by Liebman and Dyck (1993), Liebman acteristics determining mutual competitive effects and and Ohno (1998), and Teasdale (1998). As an example allows generating a large number of data sets for a of functional biodiversity, intercropping leek (Allium wide range of densities and environments. Subsequent porrum L.) with celery (Apium graveolens L.) showed application of a descriptive model to the generated data various beneficial effects, such as the reduction of weeds sets can help summarize the results, calculate the RCA and pests and an improved resource capture, while cropof the system components, and describe yield and prodping practices were not hampered (Baumann et al., 2000, uct quality of the component crops in relation to plant 2001a). Celery improved weed suppression by the candensity and mixing ratios. The objective of this study opy by increasing its light interception. As a result, inwas to evaluate the use of combined modeling apcoming radiation was captured more efficiently by the proaches for analysis and design of a leek and celery intercrop canopy, and less radiation was available for intercropping system to optimize this system with regermination and growth of weeds. However, the strong spect to yield and quality while improving weed suprelative competitive ability (RCA) of celery in the interpression. cropping system resulted in a loss of leek quality because stem diameter was reduced to 20 mm (market criteMATERIALS AND METHODS rion) (Baumann et al., 2001a). The authors, therefore,