This study focuses on the agro-ecological background of an intensive cultivation system called ngolo, which has been practiced for over 100 years among the Matengo people in southern Tanzania. The ngolo system is highly sustainable, as it both conserves soil and water and matures the soil; moreover, the high productivity of this system allows for a steady food supply to the Matengo. The other cropping systems in Matengo agriculture, which are closely related to ngolo, economically support

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... s. For example, coffee cultivation provides cash to support the local economy, and it also enables farmers to purchase chemical fertilizers. These fertilizers are applied to ngolo fields in the highlands, where fields cannot be left fallow because of high human population densities. Immigrants from the highlands to the woodlands practice a normal ridge system of cultivation called mitumbila, and a slash-and-burn cultivation called matema/malala. These systems are the initial stages in the process of creating suitable soil conditions for ngolo cultivation, and they are major sources of income in new villages where coffee trees are too young to be harvested. Emigrants have succeeded in maintaining ngolo cultivation, even in underpopulated villages, although the cultivation system was originally conceived and sustained under conditions of high population pressure. The system is able to conserve land in new villages that experience similar natural conditions, such as hilly landscapes and intense rainfall. However, social constraints and agricultural effects are not the only reasons why the Matengo have successively used ngolo; they have trusted in ngolo cultivation based on past experience, and it might therefore be a foundation of their culture.