The dataset comprises detailed mappings of two communities of interacting populations of white clover (
White clover (
Various mechanisms have been proposed to cause population oscillations and formation of clover patches in pastures and swards. Amongst them are facilitation and exploitation [
Thus, both the temporal and spatial variation in clover abundance may be relevant to deduce mechanisms that cause the dynamics. The above theories suggest it is especially relevant to study the spatiotemporal dynamics of clover-grass systems under contrasting environmental conditions that differ with respect to nitrogen availability and disturbance regimes. Simulation models have been developed to explore the spatiotemporal dynamics of white clover populations [
We have constructed an experiment with swards dominated by white clover and smooth meadow-grass (
Both the spatial distribution and abundance of white clover and grass were recorded during four or five years by digital photography and image analyses. The results were further processed to gridded data appropriate as inputs to spatial statistical analyses as suggested by Pedersen et al. [
Site description and experimental layout are as follows. The experiment was initiated in 2001 and undertaken at two sites in pastures/leys dominated by white clover and smooth meadow-grass. The first one was located at Mære Agricultural School (63°56′N, 11°25′E, 40 m a.s.l.) in central Norway in a pasture previously grazed by dairy cattle. The species sown in 1993 besides smooth meadow-grass and white clover were timothy (
The second experimental site was located at Kvithamar Research Centre (63°29′N 10°52′E, 40 m a.s.l.) in a ley sown in spring 2000 with white clover (variety Norstar, Graminor AS, Stange, Norway) and smooth meadow-grass (variety Entopper, Innoseeds b.b., Vlijmen, The Netherlands). Altogether 18 main plots (4 m × 8 m each) were split into small plots (0.5 m × 0.5 m) and sown either with white clover at a rate of 0.8 g m−2 or smooth meadow-grass at a rate of 1.7 g m−2 or a mixture of both species (0.5 g m−2 + 1.5 g m−2). The three types of small plots were randomly distributed within main plots and the respective numbers of them in each main plot were 20 with clover, 20 with grass, and 88 with a mixture of the two species. The leys were cut once in late summer 2000 and were not fertilized until spring 2001. The soil at the site is a silt loam (20–25% clay and 55–65% silt) and the content of organic matter in the topsoil is 8%.
From spring 2001 until autumn 2004 (Mære)/spring 2005 (Kvithamar), a factorial experiment with two harvesting regimes combined with three nitrogen-fertilizer levels was conducted at both sites. At Mære the treatments were replicated four times on 4 m × 4 m plots within a total area of 480 m2 and at Kvithamar there were three replicates laid out on 4 m × 8 m plots within an area of 684 m2. Plots were bordered with 20 cm wide strips kept free from vegetation by regular spraying with glyphosate. The plots were cut at a stubble height of 5 cm either two (late June and late August) or four times (late May, late June, late July, and late August) each growing season. The first/second and second/fourth cuts were always synchronised.
Nitrogen was supplied from a compound mineral fertiliser (N-P-K, 18 : 3 : 15) at rates of 0, 10, or 30 g m−2 yr−1. In the first treatment, 1.5 g P and 5.1 g K m−2 were supplied from a P-K fertilizer.
In the two-cut regime, 60% of the fertiliser was distributed in early spring and 40% after the first cut, whereas in the four-cut regime 40% was supplied in spring and 20% after each of the cuts in late May, late June, and late July.
Dry yields were recorded at each of the cuts at Kvithamar. For the years 2002–2005, the content of clover in plotwise subsamples of the yield was determined by Near Infrared Reflectance Spectroscopy [
Orientation of the maps at Kvithamar: (a) 18 plots (4 m × 8 m plots each) and (b) 128 subplots (small plots: 0.5 m × 0.5 m plots each).
Orientation of the maps at Mære: (a) 24 plots (4 m × 4 m plots each) and (b) 64 subplots (small plots: 0.5 m × 0.5 m plots each).
Plots harvested two times per season and supplied with high levels of N were, by time, invaded by tussock forming and more erect and high yielding grass species than smooth meadow-grass. They were
Determination of plant coverage image acquisition and processing was as follows. To determine the coverage of clover, grass, and dicotyledonous weeds in the experimental fields, they were mapped by means of digital photography about ten days after the cuts in late June and August every year from 2001 and onwards (Figure
Positioned image acquisition to map the grass-clover sward.
The area to be photographed was shielded from sunlight by an opaque parasol and the internal blitz of the camera was used to eliminate shadows and ensure even illumination. The camera was mounted to a rack on the metal frame such that the distance from the camera to the ground was kept constant at 80 cm. A digital Olympus Camedia C-3040Zoom camera was used, and the images were stored in a compressed format that gave a spatial resolution of approximately 1600 × 1600 pixels m−2.
The information from the digital colour photographs was processed by software (“Trifolium.exe”) specially designed for the purpose. The software classifies each pixel in the image as clover, grass, weeds, and bare ground. A thorough description of the image analysis techniques is given by Bonesmo et al. [
Outputs at sequential steps in the analysis of (a) a digital colour image by the software Trifolium.exe, (b) grey level image, (c) edge image, and (d) classified image, where red indicates clover, blue indicates grass, and black indicates soil (published with permission from Taylor & Francis Group, and previously printed in [
Image
Grey level image
Edge image
Classification
An example of a 4 m × 4 m plot with patterns occurring from identification of pixels either as clover (red), grass (blue), bare ground (black), or dicotyledonous weeds (white).
The dataset associated with this Dataset Paper consists of 21 items which are described as follows.
The dataset presented here will contribute a unique basis for validation and further development of previously published models for the dynamics and population oscillations in grass-white clover swards. The set documents the spatial dynamics of the two species that followed from a wide range of spatial configurations that arose during the experiment. It should therefore be well suited for estimating parameters in spatially explicit versions of these models, like neighborhood based models that incorporate both the dispersal and the local nature of plant-plant interactions (e.g., [
The dataset associated with this Dataset Paper is dedicated to the public domain using the
There is no conflict of interests in the access or publication of this dataset.
Anne Stine Ekker and Anne Langerud have contributed substantially to this work. The Norwegian Research Council and Bioforsk are acknowledged for financial support.