Nash's Field Experiment (plots K-S)
For over 24 years a section of grassland at Silwood Park has been manipulated to understand the degree to which the availability of nutrients and herbivory influence plant species composition and productivity and how their effects impact other organisms and ecosystem functions. The Nash' Field experiment (plots K-S) was established in 1991 with similar treatments to the Park Grass Experiment hosted by Rothamsted Research at Harpenden Hertforshire, United Kingdom, since 1856. The study site is located in a meadow with sandy, acidic soil of the Bagshot Series where introduced European rabbits (Oryctolagus cuniculus) have been particularly abundant since the 1950s. Before 1991 Nash's field was managed as a hay meadow dominated by Agrotis capillaris, Fetusca rubra, Holcus lanatus, Galium saxalite and Rumex acetosella and is currently surrounded by an oak (Quercus robur) and birch (Betula pendula) woodland and a bracken (Pteridium aquilinum) stand.
The overall objective of the Nash' Field experiment is to assess the effect of fertilizer nutrients and herbivore removal on grassland diversity and biomass. It is a six-factor factorial experiment replicated in two blocks of 22 x 44 m plots using a split-plot design. The experimental plot units (1.152 2 x 2 m plots) receive a combination of treatments that include application of four nutrients in different combinations (N, K, P, Mg), the exclusion of vertebrate (rabbits) and invertebrate (insects and molluscs) herbivores, the manipulation of soil pH through periodic applications of lime, and the application of selective herbicides. A related experiment running at Nash's field grassland (plots A-F) investigates the effect of grazing and disturbance in plant communities.
Data of aboveground biomass or coverage per plant species of all herbaceous plants present has been collected annually for several years from 1992 until 2013. More recently, the experiment has been used to study the effect that fertilization and herbivory has on soil microbial diversity and ecosystem functions.
This experiment was created by Professor Mick Crawley. Since 1991 it has been supported by the Department of Life Sciences at Imperial College London and more recently by NERC grants to Dr. Thomas Bell
- Changes in plant community due to exclusion of invertebrate herbivores became apparent only after 8 years of the experiment (Allan & Crawley 2011).
- Exclusion of insects cause an increase in the dominance of grass species (e.g. Holcus mollis), which in turn results in higher productivity but a loss of plant diversity. In contrast, the exclusion of molluscs, which feed selectively on seedlings of herbs, increase plant species richness but have no effect on biomass. Changes in plant composition due to the exclusion of molluscs occur when insects are present in the system (Crawley 2005, Allan & Crawley 2011).
- Fertilization with a combination of Nitrogen and Phosphorous, both limiting nutrients in the soil of Nash' Field, results in an increase of plant biomass and a substantial reduction in plant species richness (Crawley 2005).
- Given the magnitude of rabbit herbivory in the system, interspecific plant competition is the primary factor determining plant community structure in Nash's Field grassland. Invertebrate herbivores have lesser impact but their effect are substantial enough to change the biomass of individual species and thus modify the structure of the community (Del-Val & Crawley 2005).
- The addition of N significantly increases soil carbon sequestration when applied alone but not if combined with K, Mg and P. This effect is independent of soil pH or the composition of the plant community (Fornara et al. 2013).
- Exclusion of herbivores, particularly invertebrates, significantly decreases soil microbial biomass, community structure and abundance of microbial genes associated with biogeochemical cycles. These impacts appear to be driven by both the direct alteration of nutrient input into the soil and the indirect effect through changes in the plant community (Macdonald et al. 2015).
- Earthworm abundance decreases in herb-rich meadows with a more acidic soil. A decrease in earthworm abundance is correlated with the density of molehills in the area (Edwards et al. 1999).
Nash's k-s google map
Detail information Nash's plots K-S
Nash' Field experiment is a six-factor factorial experiment replicated in two blocks of 22 x 44 m plots using a split-plot design. It contains 8 invertebrate exclusion plots (22 x 44 m), 16 vertebrate exclusion plots (22 x 22 m), 32 soil pH plots (8 x 18 m), 96 plant competition plots (6 x 8 m) and 1.152 fertilization plots (2 x 2 m).
Factor 1 - Drainage: There are two blocks of four plots, each measuring 22 x 44 m. Four plots (S, L, M, N) separated at least 10 m from each other are set in presumably moister soil (upslope) and four plots (P, Q, R, K) in a dryer area (downslope).
Factor 2 - Invertebrate herbivore exclusion: Each of the four 22 x 44 m plots in each drainage block plots is assigned a with and without insecticide, and with and without molluscicide treatment. These pesticides are applied three times a year during the growing season.
|Insecticide and molluscicide||S||upslope|
|Insecticide and molluscicide||R||downslope|
Factor 3 - Rabbit exclusion: Half of each 22 x 44 m plot is enclosed with a fence that excludes rabbits but not other vertebrate herbivores like voles, wood mice or deer. Fenced squares are cut for hay in late August each year, and cut herbage is raked and removed from the plots. Tree saplings are also removed from unfenced plots.
Factor 4 - Soil pH: Each fenced and unfenced plot (22 x 22 m) is 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. Plots where lime are applied are indicated in the field with a row of 9 iron rods painted white and located in the southwest corner of each 2 x 2 m nutrient plot. Unlimed plots' rods are unpainted.
Factor 5 - Plant competition: Between 1992 to 1994, each 8 x 18 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. The exclusion of herbs and grass was done with selective herbicides.
Factor 6 - Mineral fertilization: Each of the 6 x 8 m plant competition plots is split into 12 2 x 2 m subplots for the application of different combination of minerals: N, P, K and Mg. The fertilizers applied are
- N: Ammonium nitrate - 144 kg ha-1
- K: Muriate of potash - 224 kg ha-1
- P: Triple superphosphate - 35 kg ha-1
- Mg: Epsom salts - 11 kg ha-1
A coloured iron rod on the northwest corner of each 2 x 2 m plot indicates the nutrient treatment received. Minerals have been applied annually during the first week of April since 1992. 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. Modeled total atmospheric N deposition estimated are to be 22 kg N ha-1yr-1
|Treatment||Minerals applied||Rod colour code|
|Plus P, K||P, K||blue & green|
|Minus P, K||N, Mg||blue, green & white|
|Minus K||N, Mg, P||green & white|
|Minus Mg||N, P, K||yellow & white|
|Minus P||N, K, Mg||blue & white|
|Minus N||K, Mg, P||red & white|
|All nutrients||N, Mg, P, K||blue & grey|
Data has been collected annually in July in all or a subset of experimental plot units (2 x 2 m). Two types of data have been collected in Nash's Field: aboveground biomass (years 1992-2000, 2004, 2006, 2013) and percentage cover (years 2000, 2001, 2004-2006, 2008, 2012) of each species of herbaceous plant present in a sampled plot. Some years have also included the measure of bare soil cover, dead organic matter biomass or cover and bryophyte biomass or cover. A change in the type of data collected from biomass to percentage of cover was necessary to adapt to the resources available for running the experiment. Both types of data were collected in 2000, 2004 and 2006 to aid in the comparison of results. A complete set of data (1.152 2 x 2 m plot units) is available for 1997 (biomass), 2000 (biomass and cover), 2005 and 2006 (cover). Data from a subset of plots were surveyed in all other years.
Crawley MJ (2005) Silwood Park and its history. In: Crawley MJ, ed. The Flora of Berkshire. Harpenden, Hertfordshire, UK: Brambleby Books, 215–253.
Del-Val E, Crawley MJ (2005) What limits herb biomass in grasslands: competition or herbivory? Oecologia 142: 202–211.
Edwards GR, Crawley MJ (1999) Herbivores, seed banks and seedling recruitment in mesic grassland. Journal of Ecology 87: 423–435.
Edwards GR, Crawley MJ, Heard MS (1999) Factors influencing molehill distribution in grassland: Implications for controlling the damage caused by molehills. Journal of Applied Ecology 36: 434–442.
Edwards GR, Bourdôt GW, Crawley MJ (2000) Influence of herbivory, competition and soil fertility on the abundance of Cirsium arvense in acid grassland. Journal of Applied Ecology 37: 321–334.
Rees M, Condit R, Crawley M, Pacala S, Tilman D (2001) Long-term studies of vegetation dynamics. Science 293: 650–655.
Allan E, Crawley MJ (2011) Contrasting effects of insect and molluscan herbivores on plant diversity in a long-term field experiment. Ecology Letters, 14: 1246–1253.
Fornara DA, Banin L, Crawley MJ (2013) Multi-nutrient vs. nitrogen-only effects on carbon sequestration in grassland soils. Global Change Biology 19: 3848–3857.
Macdonald CA, Crawley MJ, Wright DJ, Kuczynski J, Robinson L, Knight R, Al-Soud WA, Sørensen SJ, Deng Y, Zhou J, Singh B (2015) Identifying qualitative effects of different grazing types on below-ground communities and function in a long-term field experiment. Environmental Microbiology 17: 841–854.
Colour-coded rod indicating the corner of a 2 x 2 m plot, in this case with added Mg (yellow)
Sampling the insect community of Nash's plants using vortex suction, May 2016 (courtesy Sam North)
Setting of pitfall traps at Nash's Field plots to sample the insects, May 2016 (courtesy Sam North)
Fenced part of plot K March 2016. Plot K is a control for the exclusion of invertebrate herbivores
Unfenced part of plot K March 2016. Plot K is a control for exclusion of invertebrate herbivores
Plots N & M, March 2016