Tree intercropping: An agroecological approach to more resilient and sustainable citrus production

Commodities

Practices

This project will test a diversified agroecosystem to enhance resilience and productivity of citrus and co-cultivated subtropical and temperate tree crops. Citrus is an emblematic fruit crop of the Gulf Coast region of the southeastern US, but it is challenged by climatic conditions and invasive pests and diseases. High summer temperatures and high-wind tropical storms, both likely to increase in intensity and frequency as a result of climate change, and high sunlight combine to reduce growth and yields. Citrus greening disease has dramatically reduced fruit yields and increased the cost of production, forcing small-scale producers (less than 100 acres) out of production. Approaches to management under endemic citrus greening have increased the use of insecticides and mineral fertilizers. However, we have found that production practices that alter the light environment can both reduce pest pressure and improve citrus tree health without increasing pesticide or fertilizer inputs. In Florida, shade on citrus trees grown in the understory of taller tree species improve tree health. Mild shade netting doubled yields of greening-infected sweet orange trees over three years. Shade and particle films reduce transmission of citrus greening by reducing the ability of the Asian citrus psyllid, the vector of the disease, to find the citrus trees. Shade also improves growth by keeping leaves from excessive heat and light, making them more water-use efficient and productive, while increasing uptake of water and nutrients from the soil, which may reduce leaching of mineral nutrients into sensitive aquifers and streams, a major environmental concern in Florida. Intercropping is expected to both reduce winds from tropical storms and reduce post-storm stress by ameliorating transpirational demand.  However, Florida growers have not adopted intercropping because the horticultural, economic, and ecological effects have not been assessed. Nor has intercropping been tested in peninsular Florida with a much warmer climate and greater climatic and disease challenges to its extensive (ca. 300,000 acres) citrus production systems, though some growers have begun to test intercropping on a limited basis. We hypothesize that intercropping will reduce the need for insecticides, reduce mineral nutrient leaching, and enhance plant health and horticultural profitability, especially through heatwaves and wind storms exacerbated by climate change. We have responded to grower interest in better understanding these systems, gathering a group of growers from Georgia to southern peninsular Florida, who have committed to testing intercropping in citrus. Our objectives are to 1) assess the effects of intercropping other tree species on the horticulture of citrus, including economics, microclimate, and growth; 2) determine the effect of intercropping citrus on nutrient leaching from the soil profile; 3) determine the impact of intercropping and particle films on pest ecology of citrus, and 4) enhance grower experience with citrus intercropping systems and particle films, creating demonstration plots in growers’ farms throughout the region. This project is likely to impact citrus production methods. It is designed as a collaborative grower-integrated interdisciplinary project. Because of the degree of integration with growers, growers are likely to adopt these practices if we mutually find they are beneficial.

1. Assess the effects of intercropping other tree species on the horticulture of citrus, including economics, microclimate, and growth.
2. Determine the effect of intercropping citrus on nutrient leaching from the soil profile.
3. Determine the impact of intercropping on pest ecology of citrus.
4. Enhance grower experience with citrus intercropping systems, creating demonstration plots in growers’ groves throughout the region.