The Swiss Soil Monitoring Network NABO assesses and documents the soil quality at 111 monitoring sites. The selected NABO sites represent a combination of land use, soil type, geology, altitude and other site properties that are typical of Switzerland. Approximately two thirds are agricultural sites (arable land, permanent grassland, special crops) and one third are located in forests. The monitoring areas are neither marked, closed off nor otherwise protected so that the assessed conditions of agricultural or silvicultural use are as close to the actual situation as possible. Through these means, undesired developments can be recognised and the development of environmental protection methods can be examined.
Most NABO sites have been inspected regularly since the mid 1980`s. Soil samples are collected at least every 5 years. Consequently, consistent time series over more than 30 years are available. In Europe or worldwide, there are only few comparable data sets. The initial focus of NABO was on chemical soil properties, for example pollutants, nutrients and soil carbon. Since 2012, annual collections of the soil biology from selected sites have also been examined. Recently, physical properties of soil have also been recorded, primarily soil compaction.
Various measures are required for quality assurance in order to produce reliable data over longer periods. The exact same areas of 10 m x 10 m are always sampled to ensure the repeated surveys of one location are comparable. The status of the soil when taking samples also influences the composition of the soil sample. Because the soil is a dynamic body that can swell or shrink depending on the water content. Therefore, so-called auxiliary physical parameters are determined at every sample collection, such as the water content and apparent density of fine soil. Finally it must also be ensured that the soil samples are always processed in the same manner and that the analysis in the laboratory remains stable over time.