Soil Moisture Suction in Agricultural Soils: Analyzing Long-Term Tensiometer Measurements in the Swiss Central Plateau

Soil moisture is an important parameter for various fields of research and has many applications in agronomy. It is, for example, crucial for soil trafficability: wet soils are exposed to a high(er) risk of irreversible subsoil compaction. However, knowledge about the frequencies of wet soil conditions in Swiss agricultural soils and about potential influences of soil management on soil moisture is lacking. This study aims at closing these research gaps by analyzing the long-term (1996 – 2019) dataset of the Canton Bern across 13 different locations on six sites in the Swiss Central Plateau. Soil moisture suction (SMS) data measured with five tensiometers per location at a soil depth of 35 cm and precipitation sums per site for three measurement days (md) per week are used. On every site, at least one permanent grassland (PG) and one crop rotation (CR) location are present. Furthermore, the two tillage systems, no-till (NT) and mouldboard plough (MP), and 11 different crops occur in the dataset. In total, 22’947 md are analyzed, in addition to a spade test per location and a climate and weather characterization of the years 1996 – 2019. Periods with wet soil conditions (SMS < 6 cbar at a soil depth of 35 cm) during the vegetation period from April to October range from 41 % to 48 % of the md for different locations (average over all sites), while site-specific differences range from 31 % to 76 % on PG locations. The duration of wet soil conditions can exceed three months in extreme cases. A seasonal curve in SMS and influences of the longer-term (≥ 3 months) weather conditions, as well as of single precipitation events on SMS dynamics are found. Differences in SMS dynamics are big between different sites and years. While the seasonal curve and the annual fluctuations originate from climate and weather influences, the differences between the sites cannot be attributed to a specific factor. Differences between PG and CR locations can mostly be attributed to different crops’ evapotranspiration rates. Differences between NT and MP, based on the analysis on one site, are present but non-systematic. The spade tests reveal that tillage systems impact physical soil properties. This study shows that the trafficability of soils is often limited by wet soil conditions. As various factors influence SMS in agricultural soils, it provides recommendations for future study designs.