Heavy fertilizer may increase crop yield and reduce land use, thereby enhancing agricultural sustainability, but this typically comes at the cost of heavy pollution. Earthworms are an important, natural, positive contributor to crop yield in wet and cool, but not dry and hot, climates; agriculture is nevertheless commonly practiced in the latter.
Theodore Evans (Commonwealth Scientific and Industrial Research Organization Ecosystem Sciences, Australia) and coworkers have conclusively found that ants and termites increase wheat yield in dry climates on a large-scale. This is an important development towards long-term agricultural sustainability, especially given that the size of human civilization continues to expand and some regions of the world may have less water in the future.
Increasing wheat yield.
The scientists' field site in Australia is near the northeast edge of wheat production in that country. Average annual temperature ranges from 56-81°F, average annual rainfall (largely in the winter) is 11 inches, and the soil is sandy and nutrient-poor.
Ants and termites are common at the study site due to recent changes in land use. They are not present at nearby conventionally-farmed sites.
Experiments were performed on five 81 square foot plots. No weed or plant-consuming insect pest outbreaks were observed over the study period.
Crops were sown in late May and harvested the following November. The scientists applied fertilizer at sowing, but neither herbicides nor insecticides at any time, except to exclude insects in half of the plots (typically greatly reducing insect prevalence).
Wheat yield was 36% higher in plots with ants and termites, relative to the insect-excluded plots. This increase in yield was due to a combination of factors, discussed next.
There were twice as many insect tunnels (enhanced soil aeration), and soil moisture tripled at a depth of 20 inches (after a rain event), where rain is more likely to be used by plants rather than evaporate. Furthermore, soil nitrogen also increased by approximately 70%, likely due to termite saliva and feces deposition along the tunnel walls.
Future directions.
Ants and termites may help to reduce fertilizer use in hot, dry farms by 1/4 or 1/3, reduce the need for irrigation, and increase crop yield. Future research should determine which (if any) of these insect species is more important than the others.
These experiments need to be repeated in and optimized for other regions of the world. Many global locations will likely get drier in the near-term (e.g. Spain and southern Chile), and consequently will need to adapt their farming practices to make optimal use of limited resources.
NOTE: The scientists' research was funded by the Commonwealth Scientific and Industrial Research Organization.
Evans, T. A., Dawes, T. Z., Ward, P. R., & Lo, N. (2011). Ants and termites increase crop yield in a dry climate Nature Communications, 2 DOI: 10.1038/ncomms1257