Weed vegetation and land use of upland maize fields in north-west Vietnam

Agriculture in upland Vietnam changes more and more from short cultivation-long fallow periods to short cultivation-short fallow periods or even permanent cropping. Soil degradation and high weed infestation are often the consequences. Thus, the objective of this study was to survey the weed vegetation and to investigate if certain species can be related to soil degradation parameters or land use intensity. Weed vegetation on 12 upland maize fields in Son La Province, a mountainous region of north-western Vietnam was investigated in 1998. The maize fields analysed had a maximum inclination of 35° and belonged to Black Thai farmers of three villages. Vegetation surveys covered only eight maize fields, whereas plant species collection included all 12 maize fields. In addition, analysis of different soil parameters took place. Two weed communities could be distinguished within the area for the surveys conducted. This differentiation was supported by differences in soil parameters (pH, CEC, content of organic matter and nitrogen) and land use intensity. In general, weed infestation did not seem to be yet at a crucial stage as reported for other fields in the study region. Land use intensity on the higher altitude fields was low as fields were cleared only a few years ago. Besides the negative aspects of weeds, their importance for soil conservation on steep slopes has to be taken into consideration. Therefore, the development of an integrated weed management - soil conservation strategy is needed. This revised version was published online in July 2006 with corrections to the Cover Date.