LENA RATHJEN1, V.D. TUAN1, LARS BOLL1, THOMAS HILGER1, CARSTEN MAROHN1, GERHARD CLEMENS2, T. L. NGUYEN3, TRAN DUC VIEN3, GEORG CADISCH1
1University of Hohenheim, Dept. of Plant Production and Agroecology in the Tropics and Subtopics, Germany
2University of Hohenheim, Department of Soil Science and Land Evaluation, Germany
3Hanoi Agricultural University, The Center for Agricultural Research and Ecological Studies (CARES), Viet Nam
In Viet Nam most of the land area is located in mountainous regions and uplands covering almost 75% of the national territory. With rising population and high world market prices for crops such as maize, the pressure on upland fields for agricultural production has strongly increased over the past decades. Forests have been converted into tree plantations or crop land and relatively sustainable swidden agriculture systems were substituted by continuous upland cropping of maize and cassava. Deep slopes, decreasing soil productivity and high erosion rates, however, did not hinder farmers of using such fields in mountainous regions. Erosion causes translocation of soil material and in consequence spatial variability of soil parameters which may have positive or negative impact on crop productivity. The goal of this study was to better understand the impact of spatial variability in SOM on yields of maize and cassava. Therefore maize- and cassava-based cropping systems were monitored during 2008 and 2009 in the Chieng Khoi Catchment of the Son La Province, NW Viet Nam. In total 12 fields were included in this study. Soil and plant samples were taken in top, middle and footslope positions of each field. SOM was determined by using Mid Infrared Spectroscopy (MIRS) and statistically related to maize and cassava yields. Preliminary evaluation indicates a strong impact of land use history on SOM content and its distribution across slopes which correspond well with the yield performance of both crops. Detailed evaluation, however, is ongoing. This study will contribute to recommendations on an improved crop management. Additionally, it will provide valuable insights on the impact of land use intensification on soil fertility in ecologically fragile and economically disadvantaged mountainous region of Southeast Asia.
Keywords: Cassava, field accessibility, land use history, maize, soil degradation, SOM, spatial variability