ABUJA, Dec 7 (Reuters) - African heads of state agreed a new plan of action against hunger on Thursday, the latest in a series of declarations that have so far failed to reduce the problem of food insecurity in the poorest continent. Africa has made little progress in improving the volume and quality of its crops and 27 percent of Africans are chronically undernourished despite a series of past summits and resolutions. "Our meeting today is critical because Africa is still largely food-insecure despite the fact that the interventions required to turn things around for the better have been identified," said Nigerian President Olusegun Obasanjo. After four days of talks by technocrats and ministers in the Nigerian capital Abuja, heads of state endorsed recommendations to increase intra-African trade, invest more in agriculture, improve infrastructure and expand a school-feeding programme. The resolutions also included lowering and harmonising tariffs on agricultural goods, encouraging development banks to offer loans to farmers, and finding new funding mechanisms. At the launch of the summit on Monday, technocrats had said the talks should focus on implementation as the fight against hunger had got bogged down by too many objectives and not enough action. The Abuja summit, convened by the 53-nation African Union, produced another 15 resolutions. The heads of state also launched a new plan against desertification called the "Green Wall Sahara Programme". This was billed as the first concerted effort by all countries bordering the Sahara to combat its encroachment into farmlands. "Protecting and restoring dry lands will help relieve the growing burdens on Africa's threatened areas, thereby contributing to greater peace, economic stability and security," Obasanjo said. The programme is expected to yield cross-border efforts to replant trees in affected areas and improve water management, among other measures. A booklet presenting the initiative said it would start with a two-year study phase in which experts would identify key measures and conduct a pilot programme. After that, implementation would start with action plans stretching 10 years into the future and more.