Based on soil type, agro-ecological setting and history of cassava cultivation obtained from a preliminary survey and secondary data, the cassava production areas in Kampong Cham were divided into four agroecological zones (Figure 1). Zones I and II are located in Tbong Khmum
district, Zone III is located in Dambe district and Zone IV is located in Memout and Ponhea Krek districts. Zone I has both gravel and non-gravel red soils, while Zone II has non-gravel black soil. The landscape in both Zones I and II is gently undulating. Cassava has been grown in these two zones continuously without fertilizer application for about 25 years. Zone III soils comprise both gravel and non-gravel black soils, and cassava is grown on the gravel soils. The landscape in this zone is also gently undulating.