The study was conducted in the agricultural areas with or without dike protection at levels of dike construction and cropping systems, including (1) completely by dike action and are cultivated with rice and flutinous rice in Kien An village, Cho Moi district; demi-dike protection with cropping ratation of 8 rice crops per 3 years in Tan Hoa village, Phu Ta district and in Phu My village, Phu Tan district and (3) control area without dike action in Tan Trung village, Phu Tan district. The aims of this study were to assess the soil relate to the different cultivation systems and dike types.
The results showed that quantity of fertilizer application had been increasing since dikes contructed in these areas. In Kien an village, especially, the amount of fertilizer (as N, P, was increased from 394 kg/ha/year to 914 kg/ha/year after dike built. Despite intensive and fertilizer were applied, rice yield had a trend of decreasing.
Result from analyzing soil physical and chemical properties showed that soil EC ranged 0.10 to 0.85 ?S/cm and these values did not cause problems in soil. Within the depth from soil surface, total nitrogen was in medium content, range from 0.10% to 0.31% the deeper soil layer, from 20 to 40 cm, total nitrogen was poor or medium, varied from to 0.12%, Total phosphorus content in soil was poor or medium, ranged from 0.01 to. The contents of NO3- and NH4+ were medium at the depth from 0 to 20 cm, and poor at both from 20 - 40 cm.
Because farmers did not use organic fertilizer, soil organic matter contents in Kien An and were medium whlie that in Tan Hoa and Tan Trung was poor, ranged from 0.06 to. Soil cation exchange capacity (CEC) was from 9.70 - 21.90 meq/kg which was ranked medium.
Keywords: dikes, chemical soil properties, flood control, physical soil properties.
