Rothamsted Research at West Common, Harpenden, is the longest-running agricultural research institute in the world, with a history dating back to the middle of the 19th century.
Delta-T Devices has a long-standing connection to Rothamsted Research having supplied sensors and data loggers for many of its important scientific projects.
Long-term experiments at Rothamsted
Between 1843 and 1856 nine field experiments were established at Rothamsted, mainly focussed on crop nutrition with contrasting inorganic fertiliser and organic manure treatments. Seven of the experiments continue to this day.
Park Grass Experiment
The Park Grass Experiment was established in 1856 to study the effects of different types and amounts of mineral fertilisers and organic manures on the yield, botanical composition and quality of a mixed sward cut for hay.
Since 1965, liming treatments have been established which maintain subplots at target soil pH values of 7, 6 and 5, with an unlimed control. Plots are cut annually in mid-June to make hay, allowing seeds to be shed, with a second cut in late autumn.
The continuing effects of the treatments on herbage yields, botanical diversity and soil chemical properties, in the context of changes in atmospheric inputs and climate, has meant that Park Grass has become increasingly important to ecologists, environmental scientists and soil scientists.
Rothamsted selected the unlimed subplot of eight main treatment plots covering a range of inorganic fertiliser and organic manure inputs, and an additional four subplots which receive sufficient lime to achieve a target soil pH of 6.
In total, these selected 12 subplots covered a wide range of botanical composition (from 1 species to over 30 species) and herbage yield (from 2 to 7 tonnes of dry matter per hectare per annum) (Figure 2). In each of the 12 subplots three Delta-T Devices SM150T soil moisture sensors were installed horizontally at a depth of 20cm, with the cables relayed back to three GP2 data loggers through conduit piping (Figure 3).
The sensor installation was completed in February 2020 with the loggers interrogating the sensors every minute and recording the average, maximum and minimum soil water content every hour for upload to Delta-T Devices’s online data viewing and sharing platform – DeltaLINK-Cloud. This meant that real-time data could be viewed by the Rothamsted team remotely on mobile smart devices.
After some initial variation, as the soil recovered from installation of the sensors, the Rothamsted team are now recording data with generally good agreement between each SM150T sensor within any subplot.
A preliminary examination of the data indicated to the Rothamsted team that soils receiving lime have a greater soil water content than those which do not. It could be that the greater herbage yields and botanical diversity resulting from liming have led to a change in soil structure such that more water is stored at 20cm, enough to satisfy the greater above-ground biomass. The lowest water contents were found for the unlimed inorganic fertiliser treatment which has a very acidic soil (pH 3.4). The accumulation of partially decomposed plant material on the surface of this soil may impede movement of water into the mineral soil below and may in part explain the low water content measured.