In a dusty field in Kitui, eastern Kenya, farmers are being taught how to construct small, semi-circular barriers of earth that control the flow of water, slowing its run-off.

Strikingly, of the 90 farmers, few are men. The rest are women. It is a common sight in rural areas of Kenya and South Sudan, as most smallholder farmers are women. The men have gone to look for work in the towns and cities, leaving the women to tend to the crops. At bore holes – deep wells – it's the same story. Women or young girls have walked for miles to come and fetch water, a time-consuming process. Not only do they have to walk long distances, they may have to wait – an hour is not uncommon – for their turn.

The role of women and adolescent girls is spelt out in a report released on Friday by the Chicago Council on Global Affairs, Girls Grow: A Vital Force in Rural Economies (pdf). Its key point is that adolescent girls and women are the key to unlocking the full potential of agricultural development in poor countries and ensuring food security.

"If the world is to meet the challenge of feeding 9 billion people by 2050, we must invest in the human capital of those with the potential to transform agricultural economies – adolescent girls," said Catherine Bertini, the report's lead author. "Already, they carry much of families' burdens; with opportunity, they can be major change agents for rural communities and nations. As nations are rediscovering the importance of agricultural development, we want to ensure that the new definition of rural economies' strengths includes the critical role of adolescent girls."

Bertini, who was in London for the launch of the report, acknowledged that the issue of gender has been the subject of endless reports going back decades. "You could fill this hotel with reports about women," she said. "But now we are seeing people actually doing something about this."

Bertini, a former executive director of the UN World Food Programme, cited as examples USAid's Feed the Future programme, with its emphasis on the importance of investing in women in agriculture, and the work of the Alliance for a Green Revolution in Africa, chaired by Kofi Annan, the former UN secretary general. Bertini also thought the appointment of Michelle Bachelet as the head of UN Women, the new UN agency dealing with gender issues, would help promote the issue of women and agriculture.

"That is going to be a huge advantage," said Bertini. "I think Bachelet is going to be of great help."

The report makes a strong economic case for strengthening the role of women in agriculture. If women farmers were given the same access to resources such as finance, the results could be significant: women's agricultural yields could increase by 20% to 30%; national agricultural could rise by 2.5% to 4%; the number of malnourished could be reduced by 12% to 17%.

Yet despite their potential, rural adolescent girls are often the most disadvantaged, says the report: "The challenges of location, age and gender often combine to create a triple disadvantage. Girls are frequently undervalued within their societies – their existence, their contributions and their potential often given little credence. They often fulfil their duties while suffering from malnutrition. They may have little or no tie or opportunity for even the most basic education. The doors to productive economic livelihoods are often closed to them."

The report carries several recommendations, from including girls in country agriculture investment plans to providing them with comprehensive health information and services, and improving safety and security. Its most important recommendation, however, covers education: "Education is the single most vital component of improving the lives of rural adolescent girls and helping them to live up to their potential … education for girls has high returns in terms of income and livelihood opportunities, including increasing agricultural productivity."

Specifically, the report calls on governments to nationally mandate universal primary and secondary education, make schools girl-friendly, appoint more women teachers, put schools in rural locations to cut down on travelling time, and provide incentives to parents to keep girls in schools through scholarships, cash transfers and elimination of school fees.

Bertini acknowledged that some girls may want to leave farming after having been educated, but said not all would. "The current model is not sustainable for the long term. We do know women do most of the farming, and educated farmers will be more productive," she said. "We have to do what we can to provide leadership so that they can be more productive in the long term.

Another key recommendation is for governments to prepare adolescent girls to have a stake in agriculture and natural resource management. First, efforts have to be made to improve the attractiveness of agriculture as a way of life by sending researchers and scientists into rural communities to speak to adolescent girls about opportunities in agriculture.

The report goes into some of the important cultural barriers girls and women face – marital and inheritance laws that often exclude them from inheriting or securing access to land and other assets critical to increasing productivity. Examples of inheritance laws that put women at a disadvantage include those in Lesotho and Swaziland, where women are considered legal minors and cannot own property, enter into contracts or receive bank loans without a male relative.

Even where progressive legislation has been passed – such as in Ghana, Mozambique and Zimbabwe – the report says implementation often remains problematic because of women's inadequate access to information, their poor representation on local decision-making bodies, and their lack of access to capital to make productive use of land ownership. It's a delicate area, and Bertini treads carefully. She calls for funding for local groups that advocate changes in laws that discriminate against women.

In general, though, Bertini believes the renewed importance of agriculture following the rise in food prices and the drought in east Africa presents a tremendous opportunity for women in agriculture. "Now that the world has rediscovered agriculture," said Bertini, "it is an opportune time to rediscover girls."