Management of permanent set-aside on arable land in Sweden

1. Set-aside fields have been an important element of the European agricultural landscape since the introduction of the set-aside scheme by the European Community. However, countries in the European Community differ in their rules for managing set-aside owing to different priorities.
2. In Sweden, a major goal is to reduce the total use of agricultural pesticides, consequently their use is prohibited in set-aside. The options for weed control are therefore cutting and/or the use of a cover crop.
3. In this study, we describe the course of succession following the abandonment of farmland managed in different ways. The floristic composition was followed over a 10-year period. Temporal trends in community development are described.
4. The experiment began in 1975 on farmland at six localities, distributed from southern to northern Sweden. The management treatments involving the application of fertilizers and cutting were applied to plots sown with a cover crop and to plots in which the succession started from bare ground.
5. We found that competitive interactions between species largely determined the successional course in our study. The competitive success of species was related to the management practices applied but there were also interactions between management and site conditions.
6. We propose that natural succession can be recommended on poor sites in combination with cutting, mainly to prevent the invasion of woody species. On fertile sites a cover crop should be used to suppress perennial weeds, and cutting is recommended mainly to increase species diversity.     

Vegetation development and floristical diversity of newly created sown and unsown field margin strips on ex arable land during the first 3 successional years

Early succesion of newly created sown/unsown margin strips on ex arableland, managed by two cuttings per year with/without removal of cuttings was characterised by the replacement of annuals in favour of perennials, a steadily increase in the importance of monocots and a decrease in non N-fixing dicots. Mowing with removal of cuttings delayed this succession pattern. Sorenson's qualitative similarity index (based solely on species occurrence) revealed that species composition of the sown communities (in terms of species occurrence) became increasingly similar to the unsown plots. Furthermore convergence in vegetation composition between sown and unsown plots occurred also in terms of species importance as assessed by Sorenson's quantitative index (based on the combination of species occurrence and importance). Similarity in species importance (but not of species occurrence) was significantly enhanced by cutting with removal of cuttings. During the first 3 successional years, species diversity of sown and unsown communities converged in time, irrespective of mowing regime or location. The decrease in species diversity, number of sown wildflower species and wildflower density of sown communities was more pronounced under a mowing regime without removal of cuttings. The annual addition of mown roadside herbage significantly enhanced species richness but not the importance of dicots.     

Vegetation development in sown field margins and on adjacent ditch banks

The creation of temporal and newly sown field margins for 6 years is a common agri-environment scheme (AES) in the Netherlands. Conservation profits resulting from AES vary over different areas and need further studying. We examined plant species richness in such field margins and adjacent ditch banks in the province of Zeeland, where these linear elements do not experience plant biomass removal after mowing as management strategy. First, during 2 years, we inventoried field margins sown with a wildflower mixture and related the species composition and richness to the age of the margins. In a second assessment, we studied plant species richness on ditch banks protected from arable fields by these margins. Major clusters in a principal component analysis (PCA) on species composition in the field margins showed a succession from sown and ruderal annual species (year 1), to sown perennial species (year 2) and ending with a dominance by tussock forming grass species and Urtica dioica (year 5–6). Total plant species richness decreased with increasing age of the margins, and this was caused by the combination of a decline in sown species and a stable number of not-sown species. The presence of field margins during several years did not result in an increase in plant species richness on adjacent ditch banks. In both the field margins and on the ditch banks, mowing management is not followed by the removal of the cuttings. For plant conservation, the results of these field margins are disappointing, probably due to the lack of a proper management. Therefore, we recommend implementing a hay-making and opening management, to increase plant richness and to reduce noxious weeds in the margins and on the ditch banks.     

Vegetation effects on phosphorus fractions in set-aside soils

As increasing amounts of arable land are being set aside, it is of importance to study the effect of vegetation on soil fertility. The fractionation of soil P under grassland, beech and spruce vegetation was investigated in sites previously fertilized with P by extracting sequentially with Resin, NaHCO₃, NaOH, HCl and finally NaOH after ultrasonic pretreatment. Under beech a large part of extractable P was found in inorganic fractions which are considered to be available for plants (Resin P₁ and Bicarbonate P₁). Under grass, a large part of the extractable P was found in potentially labile organic forms (Bicarbonate P_o and Fulvic acid P_o). After 25 years of permanent grass vegetation, the extractability of soil P was comparable to that from an adjacent arable plot. On spruce covered soils most of the added fertilizer P was rendered unextractable 20–30 years after application. However the available data does not allow a clear interpretation of this phenomena, as effects of soil parent material as well as vegetation may be taken into consideration. No decrease in P-extractability was found between beech and grass covered soils which had been fertilized for more than 200 years, when compared to less rich soils from the same area. On the basis of the current data it may be concluded that the vegetation affects the distribution of soil phosphorus fractions, and thus soil fertility. In the soils under investigation, grassland and beech vegetation conserved the phosphate availability to a high extent.     

Abundance of breeding farmland birds on arable and set-aside fields at forest edges

The aim with this study was to investigate whether abundance of farmland birds on fields at forest edges were associated with (I) type of field (young set-aside vs arable fields), (n) the length and structure of the field-forest edge zone, and/or (m) with residual habitats such as habitat islands, ditches, roads etc Twenty-eight farmland bird species (all nesting and/or foraging on open fields) were censused during the breeding season on 48 plots (open fields with adjoining forest edges) in the central parts of Sweden, covering a total area of 595 ha Skylark Alauda arvensis , linnet Carduelis cannabina , whitethroat Sylvia communis and whinchat Saxicola rubetra were found in significantly higher numbers in set-aside-plots than cereal ones However, the most important factor explaining variation in the abundance of most species was the structure of the field-forest ecotone, with the length of shrubby southern deciduous forest edges being the most important factor in 7 of the species Mixed forest edges seemed to be of some importance for the abundance of 3 species, while associations between abundance and length of the other deciduous and coniferous field-forest ecotones only were significant for one species each Skylarks, white wagtails Motaalla alba and whinchats were positively associated to ditches and yellowhammers Emberiza citrinella and linnets were significantly associated to habitat islands The observed preferences for set-asides and shrubby field forest edges are suggested to be results of reduced predation risk and increased food abundance     

The population dynamics of small mammals living in set-aside and surrounding semi-natural and crop land

Small mammals were found on set-aside and surrounding farmland. Wood mice showed a different pattern of demography at two sites, with higher densities, greater survival, heavier weights and longer breeding seasons at Aldroughty than at Newburgh. These differences were thought to be due to a difference in habitat productivity at the two sites. Field voles showed less of a difference in population dynamics between the two sites, and both species of vole maintained populations at low densities.     

Summer bird abundance and distribution on set-aside fields on intensive arable farms in England

The abundance and distribution of breeding birds were compared on paired fields comprising one set-aside field and one crop field, on 11 intensive arable farms in eastern and western England. A single observer made four visits to all set-aside and crop fields between April and July and recorded all birds seen during standardised counts and transects.
Rotational and non-rotational set-aside supported higher densities and more species of birds than fields of wheat, brassicas, root crops and seed rye. These differences in density, between set-aside and crops, were evident across a suit of species including waders, gamebirds, pigeons and passerines and were particularly marked on rotational set-aside. The majority of species recorded in fields away from boundaries would have been feeding rather than nesting there and higher bird densities on set-aside compared with adjacent arable crops probably reflects greater food abundance in the former.
The study is the first to demonstrate a clear habitat preference for set-aside by a wide range of bird species throughout the breeding season and it allows a number of recommendations to be made concerning the development of cost-effective agri-environment measures. The fact that the majority of birds utilised the outer 5 m, or in some cases 20 m, margin of the field suggests that many of the benefits of whole field set-aside may be derived from marginal strips. A slight, but not significant preference for rotational over non-rotational set-aside suggest such margins should be managed to maintain a patchy, relatively diverse sward of arable plants. A key feature of set-aside is the scale at which it has been incorporated into the arable landscape. Agri-enviromental schemes will only provide similar national benefits if they are implemented on a wide scale in such as way as to promote high uptake by farmers.     

Accumulation of carbon and nitrogen by old arable land reverting to woodland

The accumulation of carbon (C) and nitrogen (N) was measured on two sites on Rothamsted Farm that had been fenced off some 120 years ago and allowed to revert naturally to woodland. The sites had previously been arable for centuries. One had been chalked and was still calcareous; the other had never been chalked and the pH fell from 7.1 in 1883 to 4.4 in 1999. The acidic site (Geescroft wilderness) is now a deciduous wood, dominated by oak (Quercus robor); the calcareous site (Broadbalk wilderness) is now dominated by ash (Fraxinus excelsior), with sycamore (Acer pseudoplatanus) and hawthorn (Craetagus monogyna) as major contributors. The acidic site gained 2.00 t C ha^?1 yr^?1 over the 118‐year period (0.38 t in litter and soil to a depth of 69 cm, plus an estimated 1.62 t in trees and their roots); the corresponding gains of N were 22.2 kg N ha^?1 year^?1 (15.2 kg in the soil, plus 6.9 kg in trees and their roots). The calcareous site gained 3.39 t C ha^?1 year^?1 over the 120‐year period (0.54 t in the soil, plus an estimated 2.85 t in trees and roots); for N the gains were 49.6 kg ha^?1 yr^?1 (36.8 kg in the soil, plus 12.8 kg in trees and roots). Trees have not been allowed to grow on an adjacent part of the calcareous site. There is now a little more C and N in the soil from this part than in the corresponding soil under woodland. We argue from our results that N was the primary factor limiting plant growth and hence accumulation of C during the early stages of regeneration in these woodlands. As soil organic N accumulates and the sites move towards N saturation, other factors become limiting. Per unit area of woodland, narrow strips; that is, wide hedges with trees, are the most efficient way of sequestering C – provided that they are not short of N.     

A mathematical approach towards nitrogen cycling in arable land inCajanus cajan field

Summary A balance sheet of nitrogen has been presented for an arable land in aCajanus cajan field. Quantitative inventory and transfer rates are suggested for several compartments. On the basis of data, it has been concluded that due to microbial activities appreciable nitrogen was returned to the available nitrogen pool by means of root and litter disappearance. Twenty-five percent of the total soil nitrogen has been taken up by fine roots, out of which 63.39 percent nitrogen locked up in the form of organic nitrogen and the rest of nitrogen (36.61%) was being added to the soil which governed the soil fertility. Transfer matrix of process model for the nitrogen transformation explaining component transferred from one compartment to another compartment and groups responsible for this transformation are dealt with. By means of several proposed equations the amount of nitrogen in soil at different intervals of time can be predicted. The quantifications of microbial transformations and their role in nitrogen turnover has been exploited. A high nitrogen content in the original material was found to promote decomposition.     

The diet of the wood mouse Apodemus sylvaticus on set-aside land

The diet of wood mice on set-aside consisted of 87% plant material, 65% of which was green leaf materials. This diet contains very much less seed or animal material than does that of wood mice studied in other habitats. The poor diet reflected what was available in the area.     

Effect of one year rotational set-aside on immediate and ensuing nitrogen leaching loss

This paper reports results from a 3-year field experiment which examined Nitrogen (N) leaching loss from land under various set-aside managements. Four treatments were examined: three ploughed plots which were sown with wheat, ryegrass or maintained fallow; the fourth treatment was unploughed and natural weed growth (volunteers) permitted. The l-year set-aside was followed by two winter wheat test crops. Ceramic suction cups were installed at a depth of 90 cm and used to collect drainage water. N leaching loss was calculated by multiplying drainage volume, calculated from meteorological data, by its inorganic N concentration.Set-aside management significantly affected N leaching loss over the three years. During the set-aside year, the peak nitrate concentration from the unploughed treatment growing volunteer weeds was significantly lower than that from ploughed plots. Of the latter, by the spring, crop (i.e. wheat and ryegrass) assimilation of N significantly reduced N concentration compared to the fallow. The four set-aside treatments had a carry-over effect to the following year (first wheat test crop) resulting in significant differences in N losses. Leaching following the ryegrass treatment was very small and we believe that the grass residues minimised rates of net-N mineralization.The influence of set-aside management continued to the second wheat test crop where N loss was greater under the all wheat rotation because take-all had reduced yield and therefore crop N uptake.     

Population dynamics of wireworms (Coleoptera,Elateridae) in arable land after abandonment

The community of elaterid larvae of three sites (field and two fallows), representing different stages of secondary succession, were studied using soil sampling from 1986 to 1993. All three sites were abandoned arable land: a field cultivated until 1991, a fallow I abandoned in 1986, and a fallow II abandoned about 1976. The fallow II was used as a meadow after abandonment and was regularly mown until 1985, when cultivation stopped. Six species of Elateridae larvae were found at all three study sites. In the field, Agriotes obscurus, Athous niger, Athous subsuscus, Dalopius marginatus and Athous vittatus were found, A. niger and A. obscurus being the most abundant species. During cultivation, larval densities were very low, however, larval abundance increased up to 8.8 ± 8.3 ind. m^-2 when cultivation stopped. Only small A. obscurus larvae were found during cultivation, whereas larval size increased after abandonment. In fallow I A. obscurus, A. niger, A. subsuscus, D. marginatus, and Agrypnus murinus were found and the average annual abundance fluctuated between 0.8 ± 1.4 to 40.8 ± 10.9 ind. m^-2 with A. obscurus being the most abundant species. Fallow II supported the highest densities of wireworms from all plots studied (71.2±35.2 to 280.0±24.8 ind. m^-2). A. obscurus, A. niger, A. subsuscus and D. marginatus were found in fallow II. The abundance of all larval Elateridae as well as the dominant species A. obscurus decreased during the study period, while simultaneously the occurrence of small sized A. obscurus larvae decreased. The frequency of cultivation and time elapsed since last cultivation appeared to be the most important factors affecting elaterid occurrence in the field and fallow I. In fallow II, the decrease in abundance correlates with the accumulation of a dense litter layer, which may correspond with soil surface structure, plant community changes or predator pressure.     

Algal nitrogen fixation on temperate arable fields

Summary N₂-fixation by algae on the Broadbalk continuous wheat experiment was measured over a two year period using the acetylene reduction technique. The plots studied receive spring fertilizer treatments including farmyard manure and combinations of nitrochalk and Na, P, K and Mg which have remained much the same since the experiment started in 1843.Nitrogen applied at 196 kg ha^–1 in spring suppressed algal N₂-fixation until late in the season but at lower levels (48 kg N ha^–1) the denser plant canopy increased both surface moisture and fixation. Herbicide treatment decreased fixation on plots of moderate nutritional status early in the season but had little effect on unfertilised plots where weed cover was sparse. On plots where weed and crop cover was very dense herbicide treatment increased fixation in August.Algal N₂-ase activity, assayed by C₂H₂ reduction, continued throughout the night at a rate which averaged 33% of the midday value. Laboratory experiments indicate that dark fixation is very temperature sensitive and this value may represent a maximum. Algal crust in the field dried to 4.5–6.8% H₂O content became active 3 1/2 h after rewetting and reached a steady state after 7 h which represented only 6–22% of that at the previous maximum suggesting that many cells had been killed.In a year with average rainfall algae on plots receiving 48 kg N ha^–1 were estimated to fix 25–28 kg N ha^–1 and plots without fertiliser 13–19 kg N ha^–1. Algal fixation appeared to make a substantial contribution to the continuing fertility of unfertilised plots.     

Watershed modelling of nonpoint nitrogen losses from arable land to the Swedish coast in 1985 and 1994

Eutrophication problems in the Baltic Sea have drawn attention to the contribution of nutrients from surrounding countries. By using the HBV-N model in southern Sweden (145 000 km²) daily nitrogen leaching, reduction in rivers and lakes, net transport to the sea and source apportionment have been calculated in 3725 subbasins for the period 1985–1994, with calibration at 722 sites against measured time series. On average, 48% of the nonpoint losses from agriculture were reduced during the transport towards the sea, which left about 33 500 tonnes in annual mean net transport. This represents 45% of the total land-based load. Land cover and emissions for the years of 1985 and 1994 were used in two separate simulations of the 10-year period. The normalized gross leakage from arable land in 1985 was estimated to 29 kg N ha⁻¹ year⁻¹, which corresponds to 15 kg N ha⁻¹ year⁻¹ in net leakage to the sea. In 1994 these transports were reduced by 20 and 15%, and thereby the total load on the sea was decreased by 7%. This is still far from the Swedish goal of 50% reduction. The article presents the spatial variation of nitrogen leakage and retention within the southern half of Sweden, and emphasizes the importance of allocating measures where down-stream retention is low in order to achieve efficiency with respect to the sea. It is shown that the model approach may be used in the decision making process for best management practices in watersheds.     

Effects of small-scale animal disturbances on plant assemblages of set-aside land in Central Germany

Abstract. The distribution, density and cover of small-scale natural disturbances was surveyed in semi-natural and set-aside vegetation in a hilly landscape in Central Germany in the spring of 1995. More of the landscape was disturbed on set-aside agricultural land in valley s (1.02 %) and on warm south-facing slopes(1.33 %) than on rocky hilltops (0.3 %) and cool north-facing slopes (0.56 %). The major agents of disturbance on set-aside fields were moles, rodents (and their predators) and wild boars. In surrounding semi-natural grasslands, rabbit warrens were common on south-facing slopes and mound-building ants on north-facing slopes. Disturbances were significantly clustered and frequently superimposed. In order to investigate the effects of disturbance quality on plant assemblages in set-aside fields, two common types of disturbances were compared. These were grazing lawns (0.4–1.0 m²) maintained throughout the summer by common voles (Microtus arvalis), and excavations, 0.7–1.6 m² in area, where wild boars (Sus scrofd) grubbing for food had removed vegetation and top soil in early spring. Both types of disturbances increased plant species richness on the local scale. Wind-dispersed annual and pauciennial forbs of ruderal habitats (e.g. Carduus acanthoides, Cirsium vulgare, Matricaria maritima, Senecio vernalis) were most abundant on the superficial disturbances made by voles, whereas small, ephemeral field weeds (e.g. Polygonum aviculare, Anagallis arvensis, Chenopodium album, Fallopia convolvulus) predominated on patches grubbed by boars. This study confirms that small-scale disturbances by animals provide a variety of regeneration niches for field weeds and ruderals. The rate of decline in plant species richness on set-aside land is likely to be reduced where land is utilized by a variety of herbivorous and soil-moving mammals.     

Vegetation dynamics on the posttechnogenic territories of Usinsk raion, Komi Republic, after various species of permanent grasses were sown

In order to reveal the optimal plant species for the protection of disturbed territories from erosion, two comparative experiments on the row sowing of permanent grass seeds collected in the northern regions of Russia (experiment 1) or originating from North America (experiment 2) have been arranged on the territory of the former slurry pond of the Vozeyskoe oil field (Usinsk raion, Komi Republic) dumped with a 1-m layer of sand. The sowing of grasses adapted to Northern Europe, together with the application of fertilizers on the technogenic substrate, yields the rapid formation of a closed grass cover, substrate-fixing turfing, and a mulch layer accumulating various nutrients and providing the further development of phytocenosis.     

Comparative nesting and feeding ecology of skylarks Alauda arvensis on arable farmland in southern England with special reference to set-aside

1. A study of skylark Alauda arvensis L. breeding ecology in relation to crop type was carried out from April to August 1992 on arable land in southern England. Set-aside land was included in this comparative study.
2. Territory density averaged 0·15 ha⁻¹. It was 2–3 times higher in fields of set-aside and grass, especially permanent pasture, than in winter and spring-sown cereals.
3. Territory size was nearly twice as large in fields of winter cereals (4·5 ha) than in other crop types (2·5 ha). Where set-aside was present on one farm, territory size in set-aside (1·7 ha) was a third lower than in cereals and grass.
4. Nesting began in set-aside and permanent pasture in April and peaked in late May. Nesting was not detected in spring barley until late May and in silage grass until early June. The density of successful nests in set-aside fields was more than double that in any of the arable crop types.
5. Average clutch size at hatching was 3·91 eggs in fields of set-aside, over 15% higher than in silage grass (3·40) and in spring barley (3·27).
6. Fledging success did not differ according to crop type, but productivity, expressed as the number of fledglings produced per hectare, was 0·50 in set-aside, 0·13 in silage grass, and 0·21 in spring barley. Nests with chicks were not found in fields of winter cereals. The causes of chick death were thought to be predation in set-aside fields, farming practices in silage grass fields, and suspected starvation in spring cereals.
7. The potentially high nesting success of skylarks in set-aside implies that sympathetic set-aside management could play an important part in reversing its decline across the European Union.     

Maximal indirect development, set-aside cells, and levels of selection

The evolution of metazoan development as described by Davidson et al. (1995. Science 270:1319-1325) is readily interpretable in terms of levels-of-selection conflicts, for instance, as recently modeled by Michod (1999. Darwinian Dynamics, Princeton, NJ: Princeton University Press). Davidson et al. propose certain features of early bilaterians including small size, a small and fixed number of cell divisions during and subsequent to cleavage, and specification of cell fates prior to cell movement. These features suggest constraints on certain parameters of Michod's model, specifically t (the time available for cell division) and b (the benefit to cells of not cooperating in terms of their rate of replication). Such constraints clearly enhance between-cell cooperation and allow multicellularity to more easily evolve and be maintained. Nevertheless, these constraints are completely abrogated by the phenomenon of "set-aside cells," that is, undifferentiated cells that retain indefinite division potential. Levels-of-selection theory predicts that the evolution of these set-aside cells must be accompanied by features which alleviate cell-cell competition, and indeed the results of Ransick et al. (1996. Proc Natl Acad Sci USA 93:6759-6763) support this prediction: the evolution of "set-aside cells" in metazoans was accompanied by the evolution of the sequestration of the germ line.