Evaluating functional diversity in an organic intercropping system

View the project final report

• 2011 annual report
• 2012 annual report

Commodities

• Agronomic: peanuts
• Fruits: melons
• Vegetables: peppers

Practices

• Crop Production: biological inoculants, cover crops, crop rotation, double cropping, intercropping, irrigation, multiple cropping, nutrient cycling, tissue analysis
• Education and Training: demonstration, display, participatory research
• Farm Business Management: community-supported agriculture
• Natural Resources/Environment: biodiversity, carbon sequestration
• Pest Management: biological control, competition, soil solarization
• Production Systems: agroecosystems, holistic management, organic agriculture
• Soil Management: nutrient mineralization, organic matter, soil analysis, soil chemistry, soil microbiology, soil quality/health

An incremental increase in functional crop diversity in an organic intercropping system has the potential of improving crop yield on a per acre basis. Land equivalent ratio data from year 2 of the study suggests there is an overall increase in productivity when incorporating a more complex intercropping combination using 3 or 4 functionally diverse species. Productivity on a per plant basis was also increased in some crops but was dependent upon planting date and competitive interactions with neighboring species. Additionally, weed dry biomass was significantly reduced and fruit quality does not appear to be adversely affected by multicropping treatments.

Introduction

Intercropping is an agricultural practice that promotes biological interactions and diversifies crop production in order to introduce biodiversity into agroecosystems (Mohler and Stoner 2009). Biodiversity has evolved in order to fill the multiplicity of niches that exist in the worlds ecosystems (Koocheki et al. 2008) and, in turn, provides the foundations for nutrient cycling efficiency and natural pest and disease control (Altieri 1999) and counteracts the deterioration of genetic resources that have been found in many field crops by increasing the gene pool (Baudry 1989).
Some researchers have emphasized the importance of functional differences between species and the relationship between species in space and time rather than species richness per se on improving ecosystem functioning (Landis et al. 2000). Snapp et al. (2010) suggested that management strategies and intensity are responsible for enhancing soil health, not biodiversity. However, their study did not incorporate the concept of functional diversity, but only the number of species present. Thus, we proposed to choose crop species that add a specific function to the community, such as nitrogen fixation, pollinator attractant, herbivore repellant etc.

Small farmers in tropical forest areas have long utilized intercropping systems and have incorporated a variety of crops with different growth forms, which creates a complex multi-layered habitat that closely mimics nature (Denevan 1995). In agroforestry systems of the tropics, it has been observed that deep-rooted trees bring nutrients up from deeper soil layers, thereby increasing nutrient use efficiency and reducing leachate (van Noordwijk et al. 1996). The “three sisters” intercropping system of squash, bean and corn practiced by the Native Americans is another well documented example of a multi-layered agroecosystem (Mohler and Stoner 2009). In these types of systems, each crop occupies a functional group niche and contributes in a different way to the overall functioning of the ecosystem (Vitousek and Hooper 1993). In the case of the “three sisters”, squash suppresses weed growth (smother crop), bean as the nitrogen-fixer, and corn as structural support (Mohler and Stoner 2009).
Despite the rising popularity of intercropping in developed countries (Kahn 2010), multi-layer architecturally complex intercropping systems have not been studied extensively in the Southern United States. There are few studies that have quantitatively evaluated the role of functional diversity on ecosystem functioning, pest resistance and suppression, and yields in intercropping systems. We proposed to quantify and mechanistically explain the effects of a functionally diverse crop community on regulating pests, soil health, and on resource-use efficiency and plant productivity.

• SARE Final Report Appendix

1. To evaluate the effectiveness of intercropping systems on sustaining or enhancing crop yield and quality
2. To determine how incremental increases in functional diversity affect weed suppression and disease incidence and severity