Impact of upstream soil nutirient losses on soil fertility in paddy fields

This presentation reports on the five years of an on going research project on nutrient balances in a composite swidden agroecosystem. The study is being carried out in Tat hamlet, a small settlement of Da Bac Tay ethnic minority people in Hoa Binh province in Vietnam's Northern Mountain Region. Nutrient flows from the upland to the paddy field were directly proportional to the amount of rainfall and prevailing soil surface/cropping conditions. Nutrients flows from the upland to paddy fields in this experiment increased from 97 to 227 kg total N between 2000 and 2001 and decreased sharply thereafter, to 78 kg N in 2002 and to 50 kg in 2004. P and K outflows from the watershed showed similar trends. A conference paper of this presentation is also held in the Mountain Forum on-line library.