DOI: 10.5281/zenodo.13345223
title: Nash's Field grassland experiment Silwood Park, UK

description: Nash's Field is one of the field experiments of Imperial College London, Silwood Park campus and is part of The Ecological Continuity Trust (ECT). The experiment is a long-term study that aims to understand the degree to which nutrients, soil acidity and herbivory affect grassland ecology. It is a five-factor factorial experiment replicated in two blocks of plots using a split-plot design in a neutral grassland (MG5 Cynosurus cristatus/Centaurea debeauxii, under the UK National Vegetation Classification system). Overall, the experiment contains 8 invertebrate exclusion plots (± insects and ± molluscs, 22 x 44 m), 16 vertebrate exclusion plots (± rabbits, 22 x 22 m), 32 soil acidity plots (high vs low pH, 8 x 18 m), 96 plant competition plots (± grasses, ± herbs, 6 x 8 m) and 1,152 fertilization plots (12 combinations of N, P, K and Mg, 2 x 2 m). Except for herbicides, which were used only at the start of the experiment, all treatments have been applied continuously since 1992. Data of aboveground biomass or coverage per plant species of all herbaceous plants present has been collected annually for several years from 1992.
description: 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 (k, l, m, n, p, q, r, s) 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






Treatment



Code



Plot name





Insecticide spray



spr.mol



m





Insecticide spray



spr.mol



q





Molluscicide pellets



ins.pel



n





Molluscicide pellets



ins.pel



p





Insecticide spray and molluscicide pellets



spr.pel



s





Insecticide spray and molluscicide pellets



spr.pel



r





Nothing applied



ins.mol



l





Nothing applied



ins.mol



k





 

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. 

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






Treatment



Code



Minerals applied



Iron rod colour code





No nutrients



no.nutr



none



white





Plus K



plus.k



K



green





Plus Mg



plus.mg



Mg



yellow





Plus N



plus.n



N



red





Plus P



plus.p



P



blue





Plus P, K



plus.pk



P, K



blue-green





Minus P, K



min.pk



N, Mg



blue-green-white





Minus K



min.k



N, Mg, P



green-white





Minus Mg



min.mg



N, P, K



yellow-white





Minus P



min.p



N, K, Mg



blue-white





Minus N



min.n



K, Mg, P



red-white





All nutrients



all.nutr



N, Mg, P, K



blue-unpainted





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 specie were tested for germination rate and susceptibility to potential toxic effects of insecticide and molluscicide in greenhouse trials.

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.