While decades of rising consumer demand for organic food has reduced the agricultural use of prohibited substances such as pesticides and synthetic fertilizers, U.S. food retailers have struggled to develop policies that proactively promote a broader range of sustainable farming activities, including ecosystem protection, renewable energy, water conservation and workers’ rights, Food Tank says.

Whole Foods’ Responsibly Grown program introduced a wide range of ambitious standards in 2014 designed to elevate the performance of conventional as well as organic farmers, and it was quickly attacked by organic producers. Their key criticism was that the program undermined farmers’ investments in the U.S. Department of Agriculture’s (USDA’s) organic certification.

Under the Whole Foods program, conventional growers could attain a “Best” designation while continuing to use a small number of pesticides that were prohibited by the USDA’s organic certification process. Organic farmers also resented paying anywhere from $5,000 to $20,000 to comply with the Responsibly Grown program.

The program has since been modified, and it’s anyone’s guess how Amazon might change it even further.

A team of Stanford University researchers found another retail program in South Africa where they studied Woolworths, one of the five largest supermarket chains in the country.

The program’s success was based on the farmers’ willingness to adopt the Farming for the Future program, instead of imposing prescriptive rules as Whole foods did. The program built a partnership that featured input from agricultural experts and feedback from farmers.

The farmers reported that they benefited from the valuable advice provided by farm auditors, who included trained agronomists, soil scientists and environmental scientists. This technical assistance ranged from insights on soil management, water use, biodiversity, waste disposal and pest management to carbon footprint assessment and environmental laws.

One powerful lesson from the study was the value of creating long-term partnerships between buyers and farmers to foster a spirit of friends, not foes.