Spatial and temporal variability of soil quality in typical black soil area in Northeast China in 20 years

Geographical information system(GIS)combined with Geostatistics were applied to reveal the spatial and temporal variability of soil fertility quality in the topsoil(0～20cm)in the northeastern area of China during last two decades.Soil fertility quality indices in this study include pH,organic matter,available P,available K and clay.The results show that soil pH,organic matter and available K significantly decrease during the past 20 years while the available P increases with the biggest variation coefficient.The areas with the first and second grade of soil fertility quality were over 80% in 1980,whereas nearly 98% belonged to the second and third grade in 2000.So the soil fertility quality has declined in this area due to the intensive cultivation in the past 20 years.