Nash's Field grassland experiment Silwood Park, UK

Description

Methods (English)

The study site is Silwood Park Campus from Imperial College London, Buckhurst Road, Ascot, Berkshire SL5 7PY, United Kingdom.  Silwood Park campus, with 78 ha, contains acid grasslands, scrubland, ancient woodlands and few decades old oak-dominated woodlands. Silwood Park experiences an average annual rainfall of 698mm with little seasonal pattern (1987-2022).  Mean hourly temperature is 10oC with July max of 23 oC and January min of 1.4 oC (1987-2022).

The experiment is a multi-factor factorial experiment replicated in two blocks of 22 x 44 m plots using a split-plot design. 

Factor 1: Invertebrate herbivore exclusion: There are eight 22 x 44 m plots. Four plots (s, l, m, n, p, q, r, k) separated at least 10 m from each other. Each plots is assigned a with and without insecticide, and with and without molluscicide treatment:

Table: PLOTTYPE

Pesticides are applied two or three times during the spring - summer period in April/May, May/June and June/July. Last application of insecticide is given to kill cinnabar moth caterpillars.  Insecticide spray is applied using a hand-pumped, backpack sprayer, during calm, dry spells. Molluscicide pellets are applied using a two-wheeled, hand-driver spreader.

Insects are excluded with a combination of knockdown (contact) insecticides with broad spectrum and systemic insecticides. Known products applied over the duration of the experiment. 

¹HSE issued permit for trial purposes until our molluscicide pellets supply finished. Permit # COP2022/00268

² Max recommended in packaging.

Factor 2. Large herbivore exclusion: Half of each 22 x 44 m plots is enclosed with a fence 1 m high and 3 cm square wire-mesh. The fence is supported by wooden posts and reinforced on the top with a rigid wire. Mesh was buried 5 cm deep with bottom 15 cm turned outwards to prevent rabbits digging through. Each fenced/unfenced square measures 22 m². Fence excludes rabbits but does not stop voles, wood mice or deer of entering the plot. Fences were replaced in November 2023 in all fenced plots.

Fenced squares are cut for hay with a hand-held sickle bar mower in late August each year, and cut herbage is raked and removed from the plots.  Tree samplings are removed from all plots.

Factor 3. Soil pH treatments: Fenced and unfenced squares are divided into two 8 x 18 m subplots, separated by 2 m, to create limed and unlimed treatments. Lime in Nash's Field has decreased soil acidity from 4.1 to 7. In Autumn 1991,1993,1994, 1999 and 2003, 20 tonnes ha^-1 or 2kg/m² of CaO were applied to all limed subplots. Most recently lime is applied every five years, last applications were done on February 2015 and 2020.

Plots where limed are applied are indicated in the field with a row of 9 iron rods painted white located in the southwest corner of each 2 x 2 m nutrient plot.  Unlimed plots' rods are unpainted.

Factor 4. Plant competition: Each 18 x 8 m subplot for both limed and unlimed treatments was subdivided into three 6 x 8 m plots to create three treatments: minus grass, minus herbs and control. 

Minus herbs treatment: herbs were removed with the selective herbicide, Pasturol (Dicamba  + MCPA  + Mecoprop at 2.7 kg active ingredient ha^-1) from Farmers Crop Chemicals, Inkberrow, Worcs, UK;

Minus grass treatment: grasses were removed with the selective herbicides Clout (alloxydim-sodium at 1.0 kg active ingredient ha^-1) from Hortichem, Ongar, Essex, UK, or Checkmate (sethoxydim at 870 g active ingredient ha^-1) from Rhone Poulenc Agriculture Ltd, Ongar, Essex, UK.

Herbicides were applied in late April each year from 1992 to 1994 following products instructions. Nothing was applied to control plots. No application of herbicides has been done since 1994.

Factor 5. Mineral fertilization: Each of the 6 x 8 m plant competition plots is split into 12 4m² subplots for the application of different combination of nutrients:  N, P, K and Mg.

Table: NUTTREAT

Minerals have been applied annually during the first weeks of April since 1992

N: Ammonium nitrate (NH₄NO₃) or prilled urea (CO(NH₂)₂) at 144 kg ha^-1year^-1

K: Muriate of potash (KCl:NaCl ) at 224 kg ha^-1 year^-1

P: Triple superphosphate (Ca(H2PO4)2·H2O) at 35 kg ha^-1 year^-1

Mg: Epsom salts (MgSO4.7H₂O ) at 11 kg ha^-1 year^-1

Content of soil minerals in Nash's field made in 1991 registered 5.6±0.47 mg kg^-1 NaHCO₃-soluble P (1 SE, n=8), 88.4±7.0 mg kg^-1 exchangeable K (1 SE, n=8), and 37.5±21 (1 SE, n=8) mg kg^-1 Mg. Modelled total atmospheric N deposition estimated are to be 22 kg N ha^-1yr^-1

A coloured iron rod on the northwest corner of each 2 x 2 m plot indicates the nutrient treatment received. Colour codes for each treatment appear in table NUTTREAT

Seed sowing: In spring 1996 seeds of 62 grassland species were sown into the southern half of all Plus Mg and Minus MG plots (1 x 2m subplots). 57 of these species were not found in Nash’s Field at the time. Seeds from John Chambers’ Wildflower seeds, Kettering, UK were applied at a rate of 5 g m^-2. Prior to sowing in the field, all species were tested for germination rate and susceptibility to potential toxic effects of insecticide and molluscicide in greenhouse trials.

Methods (English)

Data collected in Nash's Field experiment includes aboveground biomass and percentage cover of each species of herbaceous plant present in a sampled plot, total biomass, presence of species and soil pH.

 Aboveground biomass: measured in one 50 x 25 cm quadrat selected at random from the central 1 x 1 m section of each 2 x 2 m fertilized plot.  Plants are cut to ground level using scissors and then species are separated in the laboratory before being dried (24 h at 80 °C) and weighted.  Cut plant material that cannot be assigned to a plant species is also dried and weighed. This biomass is then divided and added to the biomass of each species present in the 2x2 m plot according to its relative proportion [B_a + ((B_a / B_t) * B_r)) where B_a is the biomass of plant a, B_t is total biomass for the 2 x 2 m plot and B_r is the biomass of the remaining plant material for the same plot].  Thus, although scale precision is two decimal places (0.01 g), precision in the biomass data table ranges from 0.1 to up 1 x 10^-9, due to the distribution of weight from each plot's residual biomass.

Percentage cover: measured for the whole area of each fertilized plot (2 x 2 m). The percentage of the plot covered by each plant species, bare soil, dead organic matter or bryophytes in each experimental plot is estimated by two people. Values entered are percentages agreed by both researchers. Estimations are done by eye standing by the border.  Because plant foliage can overlap with each other, for any given fertilized 2 x 2 m plot the added cover for all species present can be higher than 100%. For any given plant species, bare soil, dead organic matter or bryophytes with a percentage of cover lower than 1% a qualitative score of "+", "++", or "+++" is recorded. In the data table "+" was converted to 0.01% and "++" to 0.1% in years 2000, 2001 and 2004, and  "+" was converted to 0.1%, "++" to 0.2% and "+++" to 0.3% for cover data in years 2005, 2006, 2008 and 2012.

Percentage of dead matter and bryophytes cover is estimated from their present over bare soils and excluding any present under live vegetation.

 Biomass data 2018/2019. The presence of plant species in the whole 2x2 m plot was registered as well as the dry aboveground biomass for all plants combined for the central 0.5 x 0.5 m section of the plot (Tables: NashKS_presence.csv, NashKS_biomass_total.csv).  For two plots in the unfenced area of plot L, only the aboveground biomass of the entire 2x2 m plot was measured (Table: NashKS_biomass_UGRASS.csv).  Weight was measured at least 72 hours of drying at 75^oC. (Table: NashKS_biomass_total.csv).

Data soil pH 2019: Soil pH was measured on 2007 and February 2019 to assess the need of lime application on limed plots. For 2019 soil pH was measured in random nutrient plots (see Table: NUTTREAT) across all other treatments (invertebrate herbivores -plots K to S, vertebrate herbivores -fences, pH control and herbicides). A total of 96 plots were sampled. pH was measured with a Hanna Instruments GroLine soil pH tester -HI981030 calibrated with 7.0 and 4.0 pH buffer solutions. Two holes ca 8cm deep were done in the centre of each plot. One pH measure was read in each hole after soil was soaked with tap water. The probe was clean with tap water and dried between each measure (Table: NashKS_pH.csv). Three measures outside plots were done as controls. Three measures of soil temperature were done the last day of sampling (Feb 13) between 10 and 11 am with a glass and mercury thermometer. Soil temperature at about 8cm deep was in average 6,3 ^oC (5, 7, 7 ^oC).

Biomass data 2019: The dry aboveground biomass for all plants combined for the central 0.5 x 0.5 m section of some the plots were measured in the last week of July. Wet weight was measured one day after cutting and dry wet at least 72 hours of drying at 75^oC after that. (Table: NashKS_biomass_total.csv).

Plant traits data 2023: Measured as part of palatability study. Leaves for about five individual plants taken to estimate traits. Leaves were clipped and put in a sealed bag with spray water until set for rehydration in the lab. Rehydration was done by setting the plant in a flask with water or pressed between two sheets of water-soaked tissue and stored at 2 to 5^oC overnight. Leaves were then scanned on a A4-sized paper with scale line and area was estimated using ImageJ software. A portion of the fresh leave was then drilled to take disks for palatability experiment. The rest were then weighted fresh and after 72h of drying at about 70^oC.