Kofi Annan told the opening session of the U.N. Economic and Social Council that some 900 million people in rural areas live on less than $1 a day.
He called for investment in agricultural research, increasing employment and sustainable farming practices, and stressed that the international community must become more involved.
"All this can happen only with a real commitment to bring rural development back to the center of the development agenda," Annan said. "Nowhere will our commitment be put to the test more than in Africa, where food insecurity and AIDS are working in vicious tandem to thwart the continent's rural development."
UNAIDS and the Food and Agriculture Organization also chose the first day of the four-week meeting to launch a study that said AIDS has killed around 7 million agricultural workers since 1985 and likely will kill another 16 million by 2020.
The agencies said practical measures are needed to help farming families who have lost their main provider, such as the development of lighter farming tools that can be used by older children, women and the elderly. With a massive increase in the number of families headed by women, it is important that women have equal rights to land, credit and education, they added.
The study also called for ministries of agriculture to take HIV/AIDS into account in their budgets and pointed out that some ministries are themselves having trouble operating because of the AIDS death toll among their own employees.
Also Monday, Rubens Ricupero, secretary-general of the U.N. Conference on Trade and Development, made a plea for a big reduction in farm subsidies.
He told the meeting that huge subsidies programs in rich nations harm their own small farmers as well as developing countries.
Focusing on France and the United States, Ricupero said: "Over the past 15 years, as subsidies have expanded relentlessly, small farmers in these countries have become poorer and poorer in relation to the rest of the population, so much so that they are now a vanishing species."
On Tuesday a group of government ministers will debate a series of questions on rural development, including how to ensure that land is divided fairly between people.
The session, called by the International Land Coalition, will consider the problem of how to redistribute land to poor farmers.
"About 350 million of the 900 million people who are considered to be the 'rural poor' are landless or near-landless," said Bruce Moore, coordinator of the coalition which brings together the United Nations, the World Bank, the European Union and pressure groups.
"When people don't have ownership of land, they take away whatever they can get. They don't benefit from investing in its long-term productivity. And property rights are not only central to food security — conflicts are most frequently also over land," Moore told The Associated Press.
He added that studies have shown that productivity is higher on small farms, and they create more employment than large agricultural businesses. The coalition wants governments to start programs to buy land from its owners and give it to the poorest people.
Moore said land reformers should not be put off by the situation in Zimbabwe, where forced evictions of white farmers by the government has led to widespread famine.
"The issue in Zimbabwe is embedded in a much bigger political issue of (President Robert) Mugabe's party, and land reform is only one of the things that is being used to try to perpetrate their grip on power," he said.