Spatial and temporal measurement of soil moisture and nitrogen in a pasture field

This dataset contains soil nitrate and ammonium concentrations, and soil moisture, from ten locations and three depths (0-10 cm, 10-20 cm, 20-30 cm) from a single field, on a monthly basis between May 2018 and April 2019. From the same field, saturated hydraulic conductivity (Ksat) measurements were made at 27 locations on a single occasion, at the same three depths. The location of sampling points (British National Grid) is given for all field measurements. The field was pasture and occasionally grazed by livestock, and part of the North Wyke Farm Platform, a highly instrumented and documented farm system. Additional data are available to complement this dataset using the URL in the related output.

The data collection took place on the North Wyke Farm Platform (NWFP), a UK National Bioscience Research Infrastructure in SW England. The NWFP is split into a number of self-contained farms (‘farmlets’) that are managed according to different operation philosophies or practices. The NWFP is highly instrumented and monitored, and core NWFP datasets are open and include in-situ water flow and chemistry taken at 15-minute intervals; 15-minute Met measurements; 15-minute soil moisture measurements; 30-minute GHG emissions; soils, crop and botanical field survey data; livestock and crop performance data; farm operational activities; and contextual information. See the related output for links to information and the data portal.

Data were collected from a single field on the NWFP, known as Great Field, in 2018-19. This 6.34 ha field was permanent pasture until July 2013, when it was reseeded with perennial ryegrass (Lolium perenne, cv. AberMagic). The pasture may be grazed by livestock (beef cattle and/or sheep), and/or cut for silage. The soil is a clay loam topsoil over an impermeable
clay layer, meaning that water moves as surface or interflow runoff to a flume, where discharge rate and chemistry are measured. Detailed information about the soil is available in a report and meteorological information in an associated dataset, see the related information for links.

Soils for nitrate and ammonium concentrations, and soil moisture determination, were sampled from ten locations in 25 x 25 m grid cells near the centre of the field, chosen to be on lines of estimated water movement (see Fig 1 of doi.org/10.1016/j.catena.2023.107058; the data contain a Map_ref column with a letter-number notation that matches those in the figure). Each grid cell was revisited on a monthly basis between May 2018 and April 2019. Each time, approximately 100 g of soil was taken from each of three depths: top (0-10 cm), middle (10-20 cm) and bottom (20-30 cm). Each soil sample was sieved to < 2 mm to remove roots and stones. A quarter of the soil was used to measure ammonium and nitrate concentration in KCl extracts. The remainder of the soil was used to calculate soil moisture by drying at 105 deg C for at least 8 hours.

Soil hydro-physical properties are essential in understanding key processes of the hydrological cycle and in turn can ensure an efficient management of water resources. Saturated soil hydraulic conductivity (KSAT) is one such variable that typically exhibits high within-field spatial variability. However, for calibrating a process-based model, such soil hydro-physical properties are commonly taken at the field level only. To address this shortfall, within-field KSAT measurements were collected between March and July 2019 from 27 locations. These were from a larger area of the field than the soils for the determination of soil moisture, ammonium and nitrate. They were taken in a 50 x 50 grid cells, and are shown on Fig 1 of doi.org/10.1016/j.catena.2023.107058. Soils were again taken from three depths: top (0-10 cm), middle (10-20 cm) and bottom (20-30 cm). Undisturbed soil samples were taken using a 250 ml volume steel cylinder with 8 cm inner diameter and 5 cm height (cores were taken in the middle of each soil layer).

The Ksat measurement was performed using a KSAT® device (METER Group AG, Munich, Germany). Each soil core was covered by a saturation plate with a filter paper at the cut side, then placed into a water pan, keeping the cut side at the bottom. The water pan was filled with approximately 2 cm degassed tap water and tilted so that any trapped air bubbles could escape. The water level was then raised almost to the core height thus simulating an elevated water table. To ensure saturation, the core was kept in this state for 2 weeks. The pan was then filled with at least 12 cm water so that the core was flooded. The saturated porous plate on top of the sampling ring was sealed by turning the apparatus upside down under water and removing the saturation plate as well as the filter paper. After equilibration, the core was fitted 12 with a collar and an appropriate upper and lower screen (all included with the device) to prevent particles from escaping. This ensured all water passed through the substrate instead of passing outside of the core. The core was then fitted into the device and re-saturated from the base to replace any water lost during preparation. Using the device, KSAT was measured three consecutive times in the constant head measurement mode. Both KSAT (cm d-1) and time (minutes) to saturation (duration) measurements are given at three soil depths. For a further description of the method, including images, refer to the user manual at https://library.metergroup.com/Manuals/UMS/KSAT_Manual.pdf.