Arable weed decline in Northern France: Crop edges as refugia for weed conservation?

The maintenance of biodiversity in agro-ecosystems is often viewed as an insurance against an uncertain future, yet, there is increasing evidence of biodiversity loss in agricultural landscapes. Here, we examined long term trends in the arable weed flora of North-East France by revisiting 158 arable fields initially surveyed in the 1970s. We assessed changes in species richness, density and frequency of occurrence in weed communities as well as for subgroups that are recognised for their conservation value. We also evaluated the importance of crop edges as potential refugia for the threatened arable weeds. Among the 121 species recorded in both surveys, 40% had significantly declined in frequency while 10% had significantly increased. At the field level, we recorded a 42% decline in species richness and a 67% decline in species density. Trends were comparable for weed species of particular conservation value. In the 2000s survey, crop edges harboured levels of weed diversity that were intermediate between those found in field cores in the 1970s and in the 2000s survey. Our results indicated that many species of conservation value had disappeared or seriously decreased in the field core but still persisted in the crop edge. The consequences of this general decline and possible conservation options are discussed in the light of the results.     

Autumn-sowing of cereals reduces breeding bird numbers in a heterogeneous agricultural landscape

The switch from spring-sown to autumn-sown cereals and the loss of habitat heterogeneity are often suggested to be key drivers of breeding bird decline on arable farmland. Yet, both factors are interlinked and it remains uncertain whether autumn-sown cereals reduce breeding bird numbers also in the structurally complex arable farmland of northern Europe. We tested whether autumn-sowing of cereals at both local and landscape scales affected the breeding bird community in a heterogeneous agricultural landscape of south-central Sweden. Rotation between sowing types was used as a semi-experiment based on 34 spring- vs. 41 autumn-sown cereal plots centred on infield non-crop islands of similar structure, size and surroundings. Species richness and territory abundance of ground-foraging species were significantly lower in autumn- than in spring-sown cereal plots both in the crop fields and the infield non-crop islands during the breeding season. No such effect was observed among foliage gleaning birds. Species richness in spring-sown cereal plots was less the more autumn-sown crops in the surrounding landscape within a 500 m radius. Average skylark densities did not differ between autumn- and spring-sown cereal plots because habitat preferences changed; densities declined in autumn-sown cereals during the growing season whereas they increased on spring-sown fields which had shorter swards throughout the breeding season. Our results indicate that negative effects of autumn-sown crops on breeding bird numbers spill over into both neighbouring non-crop and crop habitats. We conclude that agri-environmental schemes should place more emphasis on facilitating the value of the cropped area of fields as a foraging and nesting habitat. The retention of various non-crop habitats alone may not provide sufficient food close to nest sites for farmland birds that rely on crop fields for foraging.     

Population trends of brown hares in Switzerland: The role of land-use and ecological compensation areas

Over the last decades, agricultural land-use practices have been intensified throughout Europe. As a consequence of the resulting loss of habitat heterogeneity, numerous species associated with traditional farmland have undergone severe population declines. To mitigate the negative effects of intensive agriculture on farmland biodiversity, agri-environment schemes (AES) have been adopted in various European countries since the early 1990s. The effects of AES have been evaluated for different taxa, but rarely for larger mammals like the brown hare (Lepus europaeus), a characteristic species of traditional open farmland.Using spotlight counts from 58 brown hare monitoring study sites over 17 years, we analysed the effects of land-use and several agri-environment scheme options on brown hare density in the Swiss lowland. We used open-population binomial mixture models to jointly model abundance and detection probability, thereby accounting for imperfect detection of hares.Mean observed counts of brown hares in Switzerland from 1992 to 2008 suggested a slight decline followed by a recovery in arable study sites, whereas a sustained decline was apparent in grassland sites. Mean detection probability ranged widely from year to year (arable: 0.33–0.70; grassland: 0.21–0.80). When accounting for imperfect detection, a population recovery was apparent in both land-use types, although hare densities remained at low levels compared to other European countries.The amount of extensively managed hay meadows seemed to have a positive effect on brown hare abundance both in arable and grassland sites. Hedgerows were also positively related to hare density, although only in arable study sites. The amount of set-asides/wildflower strips and brown hare density were related neither in arable nor in grassland sites. This result was probably caused by the fairly low percentages of this AES option in our study sites.Habitat improvements by means of AES indicate some positive effects on brown hare populations in Switzerland, but the quantity and quality of AES must still be increased. Combined with a binomial mixture model correcting for imperfect detection, spotlight counts are an effective tool for estimating population trends, especially for large-scale and long-term surveys like the Swiss brown hare monitoring.     

Marsh woundwort, <Emphasis Type="Italic">Stachys palustris</Emphasis> L. (Lamiaceae): an overlooked food plant

The aim of this article is to study the geographical distribution and historical patterns of use of a little known root crop native to Europe—marsh woundwort Stachys palustris L. The species grows in wet grasslands and arable fields. It produces edible tubers. Both ethnographic literature and archival sources were searched. Seventeen reliable references concerning the consumption of S. palustris in southern and south–eastern Poland were found. The tubers were usually dried and powdered, and then added to soups or to bread dough. They were also eaten as raw snacks. The plant was used mainly during food shortages in spring, until the turn of the nineteenth and twentieth century, and later only as an occasional raw snack until the 1970s. Marsh woundwort was also eaten in western Ukraine (one reference). There are many references to the edibility of marsh woundwort in the eighteenth and nineteenth century European economic botany literature, particularly in Sweden and Great Britain. These publications tried to popularize the use of S. palustris as food. However, there is no firm evidence from these countries that marsh woundwort was used as food there. Marsh woundwort was also used, throughout northern and central Europe, as pig fodder and as a medicinal plant, particularly for healing wounds. Further studies on the nutritive value of this forgotten crop should be undertaken, particularly that there is little knowledge of the chemical composition of both marsh woundwort and its Asian relative Stachys affinis widely cultivated in China as a vegetable.     

Effects of agri-environment management for stone curlews on other biodiversity

Two-hectare unsown, tilled fallow plots put in place under agri-environment schemes for stone curlews Burhinus oedicnemus in England were surveyed for other bird species, brown hares Lepus europaeus, carabid beetles, vascular plants, butterflies and bumblebees. The results were compared with those from surveys within the crop in the same field and in neighbouring fields. This was done to test whether agri-environment management targeted at a single species also provided benefits to wider biodiversity. All groups except carabid beetles were more abundant, more likely to be recorded, or more species rich on plots than within the crop. Carabid beetle activity–density and species richness did not differ between the plot and the crop; activity–density of one functional group (predators) was lower on plots than in the crop. Six rare arable plant species were recorded, predominantly from plots, and the plots are considered to perform comparably to other agri-environment options available in England designed specifically for arable plants. One red-listed bird species of conservation concern (skylark Alauda arvensis) was more abundant on plots than in the crop, and three other red-listed species (linnet Carduelis cannabina, yellowhammer Emberiza citrinella, corn bunting E. calandra) were more likely to be recorded on plots than in the crop. A fifth (lapwing Vanellus vanellus) was almost exclusively recorded from plots, and was more likely to be recorded on plots categorised as in good condition for stone curlews. These results demonstrate that fallow plots that have been put in place for the recovery of stone curlews have considerable value for a range of other farmland biodiversity, although management for stone curlews may be detrimental to some taxa, such as carabid beetles, that are sensitive to the relatively frequent spring tillage that these plots receive.     

Could soil degradation contribute to farmland bird declines? Links between soil penetrability and the abundance of yellow wagtails Motacilla flava in arable fields

Major changes to the extent and quality of farmland habitats, brought by the intensification of agricultural practice, are thought to be the main factors driving declines in a suite of farmland bird species in Europe. Recent changes in agricultural techniques have also contributed to widespread soil degradation, arising from increased soil exposure to erosion forces, declining soil organic content and increasing soil compaction. Although soils have a fundamental influence on ecosystem properties, the implications of soil degradation for farmland biodiversity have received little attention. In this study, we measure the influence of soil conditions on the distribution of a declining insectivorous farmland bird, the yellow wagtail Motacilla flava, relative to other habitat features in arable fields. Soil penetrability was found to have a significant influence on the abundance of territorial yellow wagtails at the field scale, together with crop type. Other measured habitat features had little effect on territory abundance, including soil organic content, crop height (within preferred crop types), field boundary habitats and availability of bare ground. Monitoring of invertebrate abundance across 20 cereal fields revealed a significant influence of both soil penetrability and soil organic content on aerial invertebrate capture rates. This relationship was strongest during the latter part of the breeding season, implying that settling yellow wagtails could use soil penetrability as a predictive indicator of prey abundance during the chick-rearing period. The strong relationship between yellow wagtails and soil penetrability suggests a potential causative link between soil degradation and population decline. The role of soils in determining abundance patterns and population declines of other farmland species may have been overlooked in previous studies.     

The Role of Nutrient Efficient Plants in Improving Crop Yields in the Twenty First Century

In the 21st century, nutrient efficient plants will play a major role in increasing crop yields compared to the 20th century, mainly due to limited land and water resources available for crop production, higher cost of inorganic fertilizer inputs, declining trends in crop yields globally, and increasing environmental concerns. Furthermore, at least 60% of the world's arable lands have mineral deficiencies or elemental toxicity problems, and on such soils fertilizers and lime amendments are essential for achieving improved crop yields. Fertilizer inputs are increasing cost of production of farmers, and there is a major concern for environmental pollution due to excess fertilizer inputs. Higher demands for food and fiber by increasing world populations further enhance the importance of nutrient efficient cultivars that are also higher producers. Nutrient efficient plants are defined as those plants, which produce higher yields per unit of nutrient, applied or absorbed than other plants (standards) under similar agroecological conditions. During the last three decades, much research has been conducted to identify and/or breed nutrient efficient plant species or genotypes/cultivars within species and to further understand the mechanisms of nutrient efficiency in crop plants. However, success in releasing nutrient efficient cultivars has been limited. The main reasons for limited success are that the genetics of plant responses to nutrients and plant interactions with environmental variables are not well understood. Complexity of genes involved in nutrient use efficiency for macro and micronutrients and limited collaborative efforts between breeders, soil scientists, physiologists, and agronomists to evaluate nutrient efficiency issues on a holistic basis have hampered progress in this area. Hence, during the 21st century agricultural scientists have tremendous challenges, as well as opportunities, to develop nutrient efficient crop plants and to develop best management practices that increase the plant efficiency for utilization of applied fertilizers. During the 20th century, breeding for nutritional traits has been proposed as a strategy to improve the efficiency of fertilizer use or to obtain higher yields in low input agricultural systems. This strategy should continue to receive top priority during the 21st century for developing nutrient efficient crop genotypes. This paper over views the importance of nutrient efficient plants in increasing crop yields in modern agriculture. Further, definitions and available methods of calculating nutrient use efficiency, mechanisms for nutrient uptake and use efficiency, role of crops in nutrient use efficiency under biotic and abiotic stresses and breeding strategies to improve nutrient use efficiency in crop plants have been discussed.     

Rhizosphere Phosphorus Solubility and Plant Uptake as Affected by Crop in a Clay Soil from the Central Plateau Region of Haiti

Phosphorus (P) is commonly a limiting nutrient affecting crop yields in tropical cultivated systems, and a high P-sorption capacity in many of these soils can decrease the effectiveness of fertilizer use. Smallholder farmers, such as those in rural Haiti who do not have sufficient access to P fertilizers, may benefit from crops that are efficient at scavenging for P. To evaluate commonly grown and potentially useful plants for this purpose, a pot study was conducted in a controlled-environment chamber set to approximate ambient May–June conditions in Haiti's Central Plateau with seven treatments (six legume and one grass species) using soil from an Ustalf taken in the region. Velvet bean (Mucuna pruriens [L.] DC) produced the largest amount of biomass, though no difference in P uptake among treatments was observed. Phosphorus uptake and rhizosphere P were positively correlated, indicating plants with a larger capacity to solubilize P took up more P.     

The influence of field shape, area and surrounding landscape on plant species richness in grazed ex-fields

Over the past 100 years species-rich semi-natural grasslands have decreased dramatically in Western Europe, where former arable fields (ex-fields) are used instead as pasture. The disappearance of semi-natural grasslands has caused a threat to the biodiversity in agricultural landscapes. Many typical grassland plants are dispersal limited, thus grazed ex-fields can be used to investigate if species spontaneously colonise these new grassland habitats. We examined the relationship between surrounding landscape, field area, shape, distance between edge and centre, and plant species diversity in ex-fields that had been grazed for 15-18 years. The results showed that there were 35% more plant species in fields surrounded by commercial forestry production compared to those surrounded by open agricultural landscape. Area and shape did not influence species richness, although there was increasing number of species in the centre with decreasing distance from the edge. Twenty-five percent of the species where typical grassland species, and ex-fields surrounded by forest had 91% more grassland species compared to those in the open landscape. It is possible to increase grassland plant occurrences by grazing ex-fields surrounded by forest or other grassland remnant habitats, particularly in landscapes where grazed semi-natural grasslands are scarce.     

The role of shoot residues vs. crop species for soil arthropod diversity and abundance of arable systems

Removal of crop residues has become common practice in arable systems, however, little is known about how soil arthropod communities change in response to reduced resource availability and habitat complexity associated with residue removal. We added maize residues to wheat and maize fields and investigated soil arthropod diversity and abundance over the period of one year. Residue addition did not affect the diversity and little affected the abundance of soil arthropods in wheat and maize fields with the latter being restricted to few taxonomic groups, suggesting that at least in the short-term soil arthropods benefit little from crop residue-mediated increase in food supply and habitat structure. Contrasting the minor effects of residue addition, densities of soil arthropods were much higher in wheat than in maize fields, presumably due to more dense and more continuous coverage by plants, and higher input of root residues. Furthermore, in wheat fields density of arthropods more strongly varied with season, presumably due to more pronounced pulses of root exudates and root residues entering the soil in wheat as compared to maize fields in summer and winter, respectively. Low density and little variation in densities of soil arthropods in maize fields reflect that environmental conditions and resource supply varied little with crop coverage and season. Overall, the results point to low importance of aboveground crop residues for soil arthropod communities and highlight that belowground plant resources, i.e. root exudates and root residues are the major driver of soil arthropod communities of arable systems. Thus, at least in short term removal of crop residues for e.g., biofuel production is likely to be of minor importance for soil arthropod communities. In contrast, changing crop species from wheat to maize markedly reduces the density of soil animals threatening the ecosystem functions they provide.     

Identifying difficulties in rapeseed root penetration in farmers’ fields in northern European conditions

Tap‐rooted rapeseed is generally considered sensitive to soil compaction. We examined 473 Finnish rapeseed fields sown in 2007 to 2009 to both spring turnip rape Brassica rapa L. (dominant crop) and oilseed rape Brassica napus L. Roots were rated late in the growing season according to penetration capacity. Roots in each field were rated from G1 (no problems with root penetration) to G5 (failure to penetrate deeper soil layers). There were significant effects of year, crop species, soil type, special soil properties and soil cultivation methods on frequency of G1 and G4+5 roots. Restricted root penetration was a common phenomenon. Typically, fields had <30% G3 and G4+5 roots, however, some fields had >70% G4+5 roots and were cases for serious concern. Yield loss was linearly related to the incidence of G4+5 plants in 2007, but there was no relationship with the other years. Oilseed rape had a greater proportion of G4+5 roots than turnip rape and twice the proportion of G4+5 roots occurred in direct‐drilled fields than in reduced or fully tilled fields. Rapeseed yield decline may at least partly be related to poor root penetration and it is a useful indicator crop to demonstrate the degree of soil compaction and should be cultivated in fields where sufficient root penetration is possible.     

The conservation of arable plants on cereal field margins: An assessment of new agri-environment scheme options in England, UK

Agri-environment (AE) schemes aim to arrest declines in arable biodiversity through cereal field margin management options. We evaluated the effectiveness of uncropped cultivated margins (UCM), spring fallow (SF) and cropped conservation headlands with (CH) or without fertiliser inputs (CH(NF)) in sustaining plant species diversity and rare species, in England, UK. Sampling was stratified at 1 m, 3 m and 5 m from the edge of the margin and in eight regions to assess environmental influences on species composition. Species diversity, including rare species, was highest on UCM, followed by SF and CH(NF) margins. Diversity was generally lower on cropped margins due to competition from the crop. Fertilised CH margins were the least diverse option and were similar to cereal crop controls. Species diversity was greatest at the edge of all except UCM margins and there was a strong latitudinal decline in overall diversity and rare species. AE management accounted for more variation in species composition than habitat context, physical/climatic variables, soil properties or region. At cropped sites, there was overlap between margin type and other variables but soil properties explained less variation. At uncropped sites, management and physical/climate variables explained most variation but soil properties were more important than at cropped sites. These findings confirm that AE schemes are effective in conserving arable plants, including rare species, across a variety of landscape types. More precise geographical targeting, improved control of competitive species and research on the habitat requirements of rare species will improve the overall efficacy of schemes in the future.     

Plaggic Anthrosol: Soil of the Year 2013 in Germany: An overview on its formation,distribution, classification,soil function and threats

The Plaggic Anthrosol (German: Plaggenesch) has been elected “Soil of the Year 2013” in Germany. This article reviews present knowledge on the formation, distribution, classification, soil functions, and threats of Plaggic Anthrosols. As the colors of Plaggic Anthrosols differ, we introduce a “Grey Plaggic Anthrosol” and a “Brown Plaggic Anthrosol”. The term Plaggic Anthrosols is used in WRB, whereas those soils are classified as Agrosems according to the Russian, as Plagganthrepts according to the US Soil Taxonomy, and Plaggenesch according to the German taxonomy. The formation of Plaggic Anthrosols is the result of a former arable land use technique, the plaggen agriculture, starting ≈ 1000 y ago and lasting since the introduction of mineral fertilization. During processing plaggen agriculture, plaggen or sods of humic topsoil horizons were cut in the landscape, carried to the stables, enriched with dung, and subsequently spread out onto the fields as an organic‐earthy manure. The manure decomposed and humified, whereas the mineral fraction remained and raised the land surface by 0.1 cm y^–1 in average. Hence, the diagnostic horizon, a thick (70–130 cm) humus‐rich man‐made epipedon, often containing artefacts, was formed over time. The main region of spatial distribution of Plaggic Anthrosols is NW Germany, The Netherlands and NE Belgium. Minor occurrences are reported from other parts of Europe. Compared to the associated soils, Plaggic Anthrosols hold considerable natural, archive and utilization functions, but are threatened by degradation when their use as arable soil is rendered.     

<Emphasis Type="Italic">Helianthus tuberosus</Emphasis> L. agg. in the Carpathian Basin: a blessing or a curse?

Helianthus tuberosus agg., an herbaceous perennial plant from the Asteraceae family, is native to North America and was introduced as a crop to Europe in the seventeenth century. The status of this plant has been rather controversial in the Carpathian Basin. This paper reviews its taxonomy, chorology, and ethnobotany in this region, using data obtained from herbarium specimens, ethnobotanical surveys performed in Transylvania, and data published earlier, documenting the invasive features of the plant since the beginning of the nineteenth century. Our results suggest that (1) Helianthus tuberosus agg. has been present in the Carpathian Basin from the nineteenth century, (2) its taxonomy is problematic since the first part of the nineteenth century; (3) ethnobotanical surveys confirmed that the plant’s tuber has been locally used mostly as a food in Transylvania, collected from cultivation. Overall, Helianthus tuberosus agg. is both a ‘blessing and a curse’ at the same time, it is a valuable crop with beneficial nutritional value, and also an environmentally dangerous invasive element for the diversity of the flora of the Carpathian Basin.     

What drives farmers to increase soil organic matter? Insights from the Netherlands

Soil organic matter (SOM) is an important resource base for arable farming. For policies on SOM to be effective, insight is needed on why and under which conditions farmers are willing to increase SOM content. This study used the theory of planned behaviour to analyse what prevents or encourages Dutch farmers to increase the SOM content of their fields. In an online survey, 435 arable farmers were asked questions to understand their attitude (perceived benefits), subjective norm (social pressure) and perceived behavioural control (anticipated impediments and obstacles) related to management of SOM. Farmers’ answers were related to their intention to increase SOM content, use of organic materials and perceived increase in SOM content. Our results showed that Dutch farmers are well aware of the possible benefits of SOM content for crop productivity. Farmers’ attitude, subjective norm and perceived decrease in SOM content were significantly related to their intention to increase SOM content. In our farm survey, this intention was very strong: 90% of the farmers stated a high or very high intention to increase the SOM content of their fields. A higher intention to increase SOM content was correlated with the use of organic materials as expressed as total and effective C (P  = 0.003 and P  = 0.002, respectively), but this did not lead to a perceived increase in SOM content. From a farmer's point of view, this indicates that increasing SOM content is to a large degree beyond their direct influence. The Dutch Manure and Fertiliser Act, costs of organic inputs and the need to cultivate profitable crops (such as potatoes or sugar beet) were indicated as important impeding factors for increasing SOM content.     

Multi-site validation of a soil organic matter model for arable fields based on generally available input data

The paper describes a simplified carbon balance model, derived from the CANDY model, which works in annual time steps requiring only clay content, soil type of the German classification system “Reichsbodenschätzung”, average air temperature and rainfall as site characteristics, a value for organic carbon content as the initial value as well as crop yield and organic matter amendments as management data.The Candy Carbon Balance (CCB) model has been validated using a dataset from 40 long-term experiments situated in Central Europe including 391 treatments with a total number of 4794 C_org observations. Statistical measures to prove model validity were mean error (ME = − 0.001) and root mean square error (RMSE = 0.119). In addition a number of tests were performed to make sure that the model has no systematic error for different types of site conditions and management activities. After this successful validation the CCB model is considered applicable for advisory service for arable fields on a wide range of site conditions. Due to the poor representation of clay soils in this study some more model tests on these soils would be recommendable.     

The demography and flora of the ouse Washes,England

The Ouse Washes remain as the last, large, extensively flooded washland in the fenland region of East Anglia. They mainly comprise high marsh and grassland with minority areas of low marsh and open water. Their principal functions remains as a storage site for excess winter flood water which restricts the agricultural use to seasonal grazing and mowing. Drainage developments have allowed about three-quarters of the remaining area of washland to be converted into arable land.The main plants of the ditches, rivers, pools and fields are described. Phalaris arundinacea and Glyceria maxima predominate in the fields and the latter is the dominant emergent in the aquatic habitats. The main biotic factors diversifying the habitats and flora are pool creation, ditch clearance and cattle grazing. This is of benefit to the breeding and wintering waterbirds.     

The role of hedgerows in the recolonisation of arable fields by epigeal Collembola

The role of hedgerows as reservoirs for beneficial arthropods in agroecosystems has been extensively studied, but their importance as habitats for springtails (Collembola) is largely unknown. Population recovery in arable fields by epigeal Collembola can occur either from population sources in non-crop habitats or in-situ reproduction of field-dwelling species. In this study we investigated the recovery of springtail populations in a spring-sown cereal crop following a physical disturbance due to tillage. To investigate the role of a hedgerow in population recovery, replicated lengths of hedgerow were isolated from the field using exclusion barriers.Some species of Collembola (e.g. Isotomurus spp., Bourletiella hortensis) were consistently more abundant next to the hedgerow than within the field. Areas of the field adjacent to barriered sections of hedgerow developed significantly different populations and community structures compared to unbarriered ‘controls’. Abundance of several species in the field (e.g. Isotoma viridis, Sminthurinus elegans, Sminthurus viridis) was reduced by hedgerow barriers, providing the first evidence that hedgerows could be important source habitats for the colonisation or recolonisation of arable fields by Collembola.     

Composition and stability of soil aggregates in Fluvisols under forest,meadows, and 100 years of conventional tillage

Conversion of meadow and forest ecosystems to agricultural land generally leads to changes in soil structure. This comparative study presents the composition and stability of structural aggregates in humus horizons (0–30 cm) of noncarbonate silty‐clay Fluvisols in the Kolubara River Valley, W Serbia. Aggregates collected from under a native forest were compared to aggregates from meadows and arable fields which underwent crop rotation for > 100 y. The results show that size distribution and stability of structural aggregates in the humus horizons of arable soil are significantly impaired due to long‐term anthropogenization. In the humus horizons, the content of the agronomically most valuable aggregates (0.25–10 mm) decreased by a factor of ≈ 2, from 68%–74% to 37%–39%, while the percentage of cloddy aggregates (>10 mm) increased by a factor of ≈ 2, from 23%–31% to 48%–62%, compared to forest aggregates. The long‐term‐arable soil had significantly (p < 0.05) lower aggregate stability, determined by wet sieving, than meadow and forest soils. The lowest aggregate stability was found in aggregates > 3 mm. Their content is ≈ 2.5–3 times lower in arable soil (13%–16%) than in forest soil (32%–42%) at a depth of 0–20 cm. The largest mean weight diameters of dry aggregates (dMWD) with a range between 12.6 and 14.7 mm were found in arable soil, vs. 9.5–9.9 mm in meadow and 6.5–8.3 mm in forest. The arable soil had significantly lower mean weight diameters of wet‐stable aggregates (wMWD) and a lower structure coefficient (Ks) than forest and meadow soils. The dispersion ratio (DR) of arable soil was significantly higher than that of forest and meadow soils. Forest and meadow showed a significantly higher soil organic‐matter content (SOM) by 74% and 39%, respectively, compared with arable soil, while meadow uses decreased the SOM content by 57% compared with forest at a depth of 0–10 cm. In conclusion, the results showed that long‐term conventional tillage of soils from natural forest and meadow in the lowland ecosystems of W Serbia degraded soil aggregate–size distribution and stability and reduced SOM content, probably resulting in lower productivity and reduced crop yields.     

The role of crop waste and soil in Pseudomonas syringae pathovar porri infection of leek (Allium porrum)

Pseudomonas syringae pv. porri, the causal agent of bacterial blight of leek, is a current threat for leek (Allium porrum) production in the Netherlands. The roles of post-harvest crop waste and plant invasion from soil in leek plant infection was investigated with the purpose to gain better understanding on the ecology and epidemiology of this pathogen. In a survey done over 167 leek fields, P. syringae pv. porri was present in 101 fields. About a tenfold higher P. syringae pv. porri average infection rate was recorded in leek plants from fields where post-harvest crop waste was returned than in those from fields where no waste was returned. P. syringae pv. porri could survive for at least 1 month in shredded plant material made from infected plants (mimicking crop waste in practice). Field experiments done over three successive years revealed that leek plants that were treated with crop waste at the nursery and production growth stages consistently showed higher infection rates than plants that remained untreated. Plants that were treated with crop waste only at one of both stages revealed intermediate infection rates. In a plant–soil microcosm study, it appeared that P. syringae pv. porri strain P55R colony numbers in the leek rhizosphere were approximately 4 orders in magnitude higher than in corresponding bulk soils. P. syringae pv. porri was shown to colonize leek roots and cells of the pathogen were also present in the leaves. It was concluded that post-harvest crop waste play an important role in the epidemiology of P. syringae pv. porri in leek production. The following route for primary infection of leek plants is proposed, from crop plant residues via soil to leek roots and plants.