There are some ideas that seem too simple to be useful. The 'vetiver system' for soil and moisture conservation is one of these ideas. This natural system has been used in over 120 countries throughout the tropics in rain-fed farming areas and has been proven to improve crop yields and to provide a sustainable future for farmers in third world countries. It has been used for the last 50 years and continues to be a great success story.
One thing I can probably guarantee is that you've never heard of it. You can find out all you'd ever want to know about this system from the 'Vetiver Network...this not for profit organisation runs a website which includes links to global gateways and case studies illustrating the Vetiver System at work.