To increase incentives for farmers, the selection of surrounding plants should integrate information about farmers’ choices to increase potential adoption by farmers. The proper implementation of EE in combination with farmers’ choice of crops is a promising solution towards sustainable rice production.
Since the Green Revolution in the 1960s, rice agroecosystems in Southeast Asia are mostly associated with intensified rice monoculture. The trend of intensified rice production and increasing harvested areas is associated with increasing agrochemical inputs like fertilizers and pesticides. The importance of pesticides has dramatically increased in recent decades since many farmers have increased their pesticide use as they believe it is the only way to prevent pest outbreaks.
However, pesticides can be harmful not only for the targeted rice pests but also to the environment and human well-being, since pesticides are often the first choice for pest management. To improve the stated situation, habitat management as a form of biological control has increasingly gained interest.
One promising approach to increase landscape diversity and to counteract pesticide inputs is ecological engineering (EE). EE is associated with habitat management and aims to design ecosystems in a sustainable way that benefits both humans and the environment.
EE can act as “bottom–up” control in form of habitat manipulation as well as “top–down” control in the form of promoting natural enemies. Habitat manipulation in rice agroecosystems can be implemented by cultivating additional plants on rice bunds, which are earthen mounds surrounding rice fields to keep the water level in the fields.
EE is a relatively new approach applied to rice agroecosystems in East and Southeast Asia. Field studies that were mainly done in China, the Philippines, Vietnam, and Thailand showed contradicting results on the effect of additional plants on rice bunds on arthropod communities, which seems to depend on the selected plants.
However, all studies concurred that the withholding of pesticides enhances biological control in the form of natural enemies in rice fields.
Despite the ecological advantages of bund plants, considerable agronomic constraints have been raised in cultivating additional plants—including labor, seeds, fuel, and other capital. This shows how the human dimension is an important factor in the adoption and impacts of EE. This, however, is often neglected in scientific studies on EE.
Two aspects are especially essential for the successful implementation of EE:
- First, the willingness to implement additional plants in the surroundings of rice fields as well as the preference of farmers regarding additional plants need to be tested;
- Second, the ecological impacts of such plants on the ecosystem should be considered, particularly their effects on important insect functional groups like predators, parasitoids, detritivores, and herbivores within the rice fields. Studies on both the economic benefit-cost ratio as well as the ecological effects of habitat manipulation are limited, which warrants further research.
Here, we implemented an approach that considers both human and natural systems. Through a farmer participatory method (gender-informed survey and experiments in the fields of farmers), we tested crops potentially suitable to use for EE in rice fields. We considered that following the preferences of farmers in a farmer participatory experiment covers aspects such as skill, tools, and labor for cultivation as well as seed sources.
At the same time, involving farmers in our field experiments helped to gain information on plants that are both preferred by farmers and can be used for EE. Crops cultivated on the bunds should be familiar and have perceived benefits for farmers to create incentives to use the approach of EE in the future.
These could help to address the agronomic constraints for EE. At the same time, we tested the effect of crops selected by farmers, on arthropod natural enemies and herbivores in rice fields as well as the effect on insect family richness. Furthermore, we estimated the socio-economic effects of EE by performing partial benefit-cost calculations, focusing on paid-out costs, which are a key consideration for smallholder farmers.
In our study, farmers gained additional yield by growing crops on bunds and reduced cost by withholding pesticides. Mung bean, sesame, and sponge gourd are suitable plants to grow on rice bunds and offer multiple opportunities for farmers to diversify and manage pests without relying on pesticides.
Parasitoid abundance was higher in fields without pesticide treatments during the wet season, which indicated that pesticides might be the main driver for a reduction in parasitoid abundance. We found higher family richness in EE fields than in conventionally farmed fields during the dry season.
Although we found no clear trend of increasing natural enemy abundance by bund crops, EE seems to be a good incentive for farmers to prevent pesticide use and gain additional income.
To increase incentives for farmers, the selection of surrounding plants should integrate information about farmers’ choices to increase potential adoption by farmers. The proper implementation of EE in combination with farmers’ choice of crops is a promising solution towards sustainable rice production.
As a next step, the approach of EE should be implemented at the landscape scale with the farmers’ choice of bund plants to increase (i) the resources for insect natural enemies which might show significant effects; and (ii) to increase the participation of farmers in the EE approach.
Read the study:
Sattler C, Schrader J, Flor RJ, Keo M, Chhun S, Choun S, Hadi BAR, Settele J. (2021) Reducing Pesticides and Increasing Crop Diversification Offer Ecological and Economic Benefits for Farmers—A Case Study in Cambodian Rice Fields. Insects. 12(3):267.
