Strip-tilled Cover Cropping for Managing Nematodes, Soil Mesoarthropods, and Weeds in a Bitter Melon Agroecosystem

A field trial was conducted to examine whether strip-tilled cover cropping followed by living mulch practice could suppress root-knot nematode (Meloidogyne incognita) and enhance beneficial nematodes and other soil mesofauna, while suppressing weeds throughout two vegetable cropping seasons. Sunn hemp (SH), Crotalaria juncea, and French marigold (MG), Tagetes patula, were grown for three months, strip-tilled, and bitter melon (Momordica charantia) seedlings were transplanted into the tilled strips; the experiment was conducted twice (Season I and II). Strip-tilled cover cropping with SH prolonged M. incognita suppression in Season I but not in Season II where suppression was counteracted with enhanced crop growth. Sunn hemp also consistently enhanced bacterivorous and fungivorous nematode population densities prior to cash crop planting, prolonged enhancement of the Enrichment Index towards the end of both cash crop cycles, and increased numbers of soil mesoarthropods. Strip-tilled cover cropping of SH followed by clipping of the living mulch as surface mulch also reduced broadleaf weed populations up to 3 to 4 weeks after cash crop planting. However, SH failed to reduce soil disturbance as indicated by the Structure Index. Marigold suppressed M. incognita efficiently when planted immediately following a M. incognita-susceptible crop, but did not enhance beneficial soil mesofauna including free-living nematodes and soil mesoarthropods. Strip-tilled cover cropping of MG reduced broadleaf weed populations prior to cash crop planting in Season II, but this weed suppression did not last beyond the initial cash crop cycle.     

Pest suppression potential varies across 10 bioenergy cropping systems

Top-down suppression of herbivores is a fundamental ecological process and a critical service in agricultural landscapes. Adoption of bioenergy cropping systems is likely to become an increasingly important driver causing loss or gain of this service in coming decades. We measured natural pest suppression potential in ten model bioenergy crops in a long-term experimental array by deploying plasticine sentinel caterpillar mimics, which record imprints from predator attacks. Cropping systems included three intensive annual row crop systems and a range of simple perennial monocultures and more complex polycultures. We compared attack rates across the ten cropping systems and assessed differences over time within a growing season and between the ground level and canopy. We found strong differences in attack rates across cropping systems, usually with more attacks in perennial crops than annuals. However, outcomes varied in space and time, both within and among cropping systems. Birds and small mammals were responsible for most, and sometimes all, attacks in annual crops and were most important early in the season. Chewing arthropod attacks increased over the course of the growing season and were responsible for most attack events in perennial systems. In late summer there were almost no attacks in annual crop canopies, while attack rates in perennial canopies at the same time were quite high and were carried out almost entirely by chewing arthropods. Our results underscore the lack of trophic complexity in annual bioenergy cropping systems relative to perennials. They also illustrate the dramatic changes in predator activity and predation intensity that occur both seasonally and between the ground and plant canopy. Policies and practices that increase the footprint of annual crops for bioenergy are likely to cause a deficit in pest suppression services at local and landscape scales.     

覆盖作物的种植现状及其对下茬作物生长和土壤环境影响的研究进展

覆盖作物指的是在农业生产间隙种植,使土壤在时间或空间上减少或避免裸露的一种作物。其能使农田土壤免受风蚀、水蚀和人为扰动的影响,被认为是一种新型的保护性耕作方式。本文简要介绍了农田覆盖作物的种植管理情况,包括种植品种、耕作模式和绿肥作物的灭生还田方式等,可为推广覆盖作物在农田休闲期的高效大面积种植提供参考。基于国内外研究综述了绿肥种植对经济作物、土壤质量、杂草抑制、温室气体排放和土壤微生物等的影响及研究进展,阐明了覆盖作物对农田生态系统的诸多益处。尽管覆盖作物存在局限性,例如短期收益不明显、管理措施不当会造成作物减产等,但其在改善土壤质量、实现农业可持续发展方面仍然具有重要的应用价值。     

Effects of Crop Diversity on Agroecosystem Function: Crop Yield Response

Understanding the role of diversity in the functioning of ecosystems has important implications for agriculture. Previous agricultural research has shown that crop rotation and the use of cover crops can lead to increases in yield relative to monoculture; however, few studies have been performed within the broader context of diversity–ecosystem function theory and in the absence of chemical inputs. We performed a field experiment in SW Michigan, USA, in which we manipulated the number of crop species grown in rotation and as winter cover crops over a 3-year period to test if varying the number of species in a rotation affected grain yield, a critical metric of ecosystem function in row-crops. The experimental design was unique in that no fertilizer or pesticides were used, and the only management variable manipulated was number of species in the rotation, thus providing a strong comparison to grassland diversity–ecosystem function experiments. Treatments included continuous monocultures of three row-crops, corn Zea mays L., soybean Glycine max (L.) Merr., and winter wheat Triticum aestivum L., and 2- and 3-year annual rotations with and without cover crops (zero, one, or two legume/small grain species), encompassing a range of crop diversity from one to six species. Crop yields and weed biomass were measured annually for 3 years and plant available soil nitrogen was measured over the course of the growing season in the final year of the study. In all 3 years, corn grain yield increased linearly in response to the number of crops in the rotation. Corn yields in the highest diversity treatment (three crops, plus three cover crops) were over 100% higher than in continuous monoculture and were not significantly different from the county average for each of the 3 years despite the absence of chemical inputs. Corn yields in the diversity treatments were strongly correlated with the availability of inorganic soil nitrogen, which was likely influenced by the number of different legume species (crops and cover crops) present in the rotation. In soybean and winter wheat, yield differences among crop diversity treatments were also significant, but of lower magnitude (32 and 53%, respectively), and showed little direct relationship to the number of crop species grown in a rotation. Results demonstrate that agricultural research motivated by ecological theory can provide important insights into the functioning of agroecosystems and enhance our understating of the linkages between diversity and ecosystem function. Importantly, these results suggest that reduced chemical inputs do not necessarily result in yield penalties and provide support for incorporation of crop or species diversity when determining how ecosystem services can be included in food, fiber, and biofuel production.     

Strategies to decrease nitrate leaching in the Brimstone Farm Experiment,Oxfordshire, UK, 1988–1993: the effects of winter cover crops and unfertilised grass leys

Nitrate losses in drainflow were measured over five years on eight hydrologically isolated field plots, pairs of which had the following cropping regimes: (a) a 3-yr unfertilised, ungrazed grass ley followed by winter and spring cereals, (b) mixed cropping including winter cover crops, spring cereals, winter cereals, winter fallow and spring beans, (c) a similar sequence to (b) but with a winter fallow replacing the cover crop in the first year and a winter cover crop replacing the fallow in the third year, and (d) continuous winter cereals (control plots). Less nitrate was lost in winter drainflow from winter cover crops than from the winter fallows, but over all five years less nitrate was leached from the continuous cereal plots than from those with mixed cropping. Most of the extra nitrate lost from the mixed cropping regimes probably resulted from mineralisation of the cover crop residues, which occurred at times when subsequent crops could not take advantage of the mineral nitrogen released. Crops grown after the grass ley and cover crops did not benefit from their residues, in terms of either grain yield or of total nitrogen uptake. We conclude that on heavy clay soils in UK a cropping regime of continuous winter cereals offers the best compromise between profitable crop production and minimised nitrate loss to surface waters.     

The use of cover crops in cereal-based cropping systems to control nitrate leaching in SE England

Field experiments were done to evaluate the extent to which cover crops can be used to help farmers comply with current legislation on nitrate leaching from arable land in nitrate vulnerable zones. Nitrate leaching was measured in sandy loam and chalky loam soils under a range of early sown (mid-August) cover crops at two sites in SE England, and in the subsequent winter following their incorporation. Cover crop species tested were forage rape, rye, white mustard, a rye/white mustard mixture, Phacelia and ryegrass. Additional treatments were weeds plus cereal volunteers, a bare fallow and a conventional winter barley crop sown one month later than the cover crops and grown to maturity. Cover crop and bare fallow treatments were followed by spring barley. This was followed by winter barley, as was the conventional winter barley crop. In the winter immediately after establishment, early sown cover crops decreased nitrate leaching by 29–91% compared to bare fallow. They were most effective in a wet winter on the sandy loam where nitrate leaching under bare fallow was greatest. There was little difference between cover crop species with respect to their capacity to decrease nitrate leaching, but losses were consistently smaller under forage rape. The growth of weeds plus cereal volunteers significantly decreased nitrate leaching on the sandy loam compared with a bare fallow, but was less effective on the chalky loam. Nitrate leaching under the later sown winter barley was often greater than under cover crops, but under dry conditions leaching losses were similar. In the longer-term, in most cases, the inclusion of cover crops in predominantly cereal-based cropping systems did not significantly decrease cumulative nitrate leaching compared with two successive winter cereals. In summary, early sown cover crops are most likely to be effective when grown on freely drained sandy soils where the risk of nitrate leaching is greatest. They are less likely to be effective on poorer drained, medium-heavy textured soils in the driest parts of SE England. In these areas the regeneration of weeds and cereal volunteers together with some additional broadcast seed may be sufficient to avoid excessive nitrate losses. In the short-term, mineralization of N derived from the relatively small cover crops grown once every 3–4years in cereal-based cropping systems is unlikely to contribute greatly to nitrate leaching in later years and adjustments to fertilizer N recommendations will not usually be necessary.     

Weed species differ in their ability to emerge in no‐till systems that include cover crops

No‐till cropping systems that include cover crops could lead to important changes in weed communities by decreasing some annual weed populations. In this study, we predicted that seed burial depth and the presence of cover crop would affect the emergence and initial growth success of annual weed species. We tested two factors on 14 weed species in a greenhouse: the seed burial depth of weeds (buried versus soil surface) and the presence/absence of a cover crop (ryegrass). We counted the emerged seedlings and measured the height of weeds and cover crops (Hweed, Hcover), the dry matter content of weeds and cover crops (DMCweed, DMCcover) and the number of leaves of weeds (NLweed) on 1433 weed and 390 ryegrass individuals. Emergence of five weed species (AMBEL, ANGAR, BROST, CENCY and EPHHE) was affected by the seed location (?10.3% on average for unburied seeds), five other weed species (ALOMY, CAPBP, SONAS, VERPE and VLPMY) were affected by cover (on average ?9.5% for seeds emerged in the presence of cover crop), and four weed species (GERDI, LAMPU, POAAN and VIOAR) were not affected by either. Weed growth of all weed species also decreased with the presence of a cover crop (on average Hweed: ?49.9%, DMCweed: ?87.2% and NLweed: ?55.4%) and for unburied seeds (on average Hweed: ?33.7%, DMCweed: ?70.6% and NLweed: ?43.3%), with various responses according to species. This study indicates that annual weeds could be disadvantaged by no‐till systems using cover crops.     

Divergence of mycorrhizal fungal communities in crop production systems

Mycorrhizal fungi are present in all arable soils and colonize nearly all crops and weed pests of crops. They may be involved as mutualists or pathogens of crops in well known but poorly understood phenomena such as crop rotation and green manure effects on soil productivity. Crop change effects on mycorrhizal fungal community parameters were evaluated in three field experiments. In Experiment 1, soybean (Glycine max (L.) Merr. cv. Douglas) was grown continuously or rotated with corn (Zea mays L.), milo (Sorghum bicolor (L.) Moench), or fescue (Festuca arundinacea Schreb cv. Johnstone) for two years, then soybean was grown on all plots. Continuous soybean plots were dominated byGigaspora spp., while rotated crops were dominated byGlomus spp. Differences in communities and community indices of continuous soybean and rotated plots were reduced after growing soybeans on rotated plots. In Experiment 2, a fescue sod was plowed and pearl millet (Pennisetum americanum Leeke) or crabgrass (Digitaria sanguinalis (L.) Scop.) grown. Both hosts resulted in great changes in populations of individual species, decreases in community dominance, and increases in community diversity and equitability. Crabgrass also resulted in reduced species richness. In Experiment 3, tobacco (Nicotiana tabacum L.) or fescue was planted on adjacent tracts of land with a long-term history of either fescue (30 yr) or sorghum-sudangrass (Sorghum bicolor (L.) Moench. ×S. sudanense (Piper) Staph.) (3 yr). The long-term cropping history had major effects on the mycorrhizal fungal communities which were related to the expression of mycorrhizal stunt disease of tobacco. Changes occurred in these communities in response to either current-season crop. These experiments suggest that crop rotation causes large changes in mycorrhizal fungal communities, that these changes may be involved in the rotation effect on soil productivity, and that design of cropping systems should take mycorrhizal fungal communities into consideration.     

Recent cover crop adoption is associated with small maize and soybean yield losses in the United States

Cover crops are gaining traction in many agricultural regions, partly driven by increased public subsidies and by private markets for ecosystem services. These payments are motivated by environmental benefits, including improved soil health, reduced erosion, and increased soil organic carbon. However, previous work based on experimental plots or crop modeling indicates cover crops may reduce crop yields. It remains unclear, though, how recent cover crop adoption has affected productivity in commercial agricultural systems. Here we perform the first large-scale, field-level analysis of observed yield impacts from cover cropping as implemented across the US Corn Belt. We use validated satellite data products at sub-field scales to analyze maize and soybean yield outcomes for over 90,000 fields in 2019–2020. Because we lack data on cover crop species or timing, we seek to quantify the yield impacts of cover cropping as currently practiced in aggregate. Using causal forests analysis, we estimate an average maize yield loss of 5.5% on fields where cover crops were used for 3 or more years, compared with fields that did not adopt cover cropping. Maize yield losses were larger on fields with better soil ratings, cooler mid-season temperatures, and lower spring rainfall. For soybeans, average yield losses were 3.5%, with larger impacts on fields with warmer June temperatures, lower spring and late-season rainfall, and, to a lesser extent, better soils. Estimated impacts are consistent with multiple mechanisms indicated by experimental and simulation-based studies, including the effects of cover crops on nitrogen dynamics, water consumption, and soil oxygen depletion. Our results suggest a need to improve cover crop management to reduce yield penalties, and a potential need to target subsidies based on likely yield impacts. Ultimately, avoiding substantial yield penalties is important for realizing widespread adoption and associated benefits for water quality, erosion, soil carbon, and greenhouse gas emissions.     

江苏省棉区棉田杂草群落发生分布规律的数量分析

在对江苏省四大主产棉区８２个样点７２７块田地共５７．５ｈｍ＾２棉田杂草群落及草害进行７级目测法调查采集数据后,对其进行主成分分析（ＰＣＡ）,并赋以生态学意义的解释。研究表明,江苏省棉田杂草的发生和分布与轮作种植制度和地理区域性密切相关,其中轮作制度导致的田间水分的巨大差异是决定杂草群落结构特征的最深刻的原因,导致全省水旱轮作棉田的杂草群落有趋向性。而地理区域构成的土壤、气候等生态因子的显著影响表现     

江苏省棉区棉田杂草群落发生分布规律的数量分析

在对江苏省四大主产棉区８２个样点７２７块田地共５７．５ｈｍ＾２棉田杂草群落及草害进行了７级目测法调查采集数据后,对其进行主成分分析,并赋以生态学意义的解释,研究表明,江苏省棉田杂草的发生和分布与轮作种植制度和区域性化作制度导致的田间水分的巨大差异是决定杂草群落结构特征的最深刻的原因,导致全省水旱轮作棉 杂草群落有趋同性。     

Weed control and cover crop management affect mycorrhizal colonization of grapevine roots and arbuscular mycorrhizal fungal spore populations in a California vineyard

Arbuscular mycorrhizal (AM) fungi naturally colonize grapevines in California vineyards. Weed control and cover cropping may affect AM fungi directly, through destruction of extraradical hyphae by soil disruption, or indirectly, through effects on populations of mycorrhizal weeds and cover crops. We examined the effects of weed control (cultivation, post-emergence herbicides, pre-emergence herbicides) and cover crops (Secale cereale cv. Merced rye, × Triticosecale cv.Trios 102) on AM fungi in a Central Coast vineyard. Seasonal changes in grapevine mycorrhizal colonization differed among weed control treatments, but did not correspond with seasonal changes in total weed frequency. Differences in grapevine colonization among weed control treatments may be due to differences in mycorrhizal status and/or AM fungal species composition among dominant weed species. Cover crops had no effect on grapevine mycorrhizal colonization, despite higher spring spore populations in cover cropped middles compared to bare middles. Cover crops were mycorrhizal and shared four AM fungal species (Glomus aggregatum, G. etunicatum, G. mosseae, G. scintillans) in common with grapevines. Lack of contact between grapevine roots and cover crop roots may have prevented grapevines from accessing higher spore populations in the middles.     

Modeling biogeochemical impacts of bioenergy buffers with perennial grasses for a row‐crop field in Illinois

Current research on the environmental sustainability of bioenergy has largely focused on the potential of bioenergy crops to sequester carbon and mitigate greenhouse gas emissions and possible impacts on water quality and quantity. A key assumption in these studies is that bioenergy crops will be grown in a manner similar to current agricultural crops such as corn and hence would affect the environment similarly. In this study, we investigate an alternative cropping system where bioenergy crops are grown in buffer strips adjacent to current agricultural crops such that nutrients present in runoff and leachate from the traditional row‐crops are reused by the bioenergy crops (switchgrass, miscanthus and native prairie grasses) in the buffer strips, thus providing environmental services and meeting economic needs of farmers. The process‐based biogeochemical model Denitrification‐Decomposition (DNDC) was used to simulate crop yield, nitrous oxide production and nitrate concentrations in leachate for a typical agricultural field in Illinois. Model parameters have been developed for the first time for miscanthus and switchgrass in DNDC. Results from model simulations indicated that growing bioenergy crops in buffer strips mitigated nutrient runoff, reduced nitrate concentrations in leachate by 60–70% and resulted in a reduction of 50–90% in nitrous oxide emissions compared with traditional cropping systems. While all the bioenergy crop buffers had significant positive environmental benefits, switchgrass performed the best with respect to minimizing nutrient runoff and nitrous oxide emissions, while miscanthus had the highest yield. Overall, our model results indicated that the bioenergy crops grown in these buffer strips achieved yields that are comparable to those obtained for traditional agricultural systems while simultaneously providing environmental services and could be used to design sustainable agricultural landscapes.     

Crop identity and memory effects on aboveground arthropods in a long‐term crop rotation experiment

Agricultural landscapes are globally dominated by monocultures under intensive management. This is one of the main reasons for biodiversity loss and insect population decline in many regions all over the world. Agroecosystem biodiversity in these areas can be enhanced by cropping system diversification, such as crop rotations. Yet, long‐term studies on effects of crop rotations on aboveground agrobiodiversity are lacking. We set up a 10‐year long‐term crop rotation experiment in Central Germany and monitored the temporal dynamics of aboveground arthropods over a full cultivation period to investigate influence of current and preceding crop identity and cropping system diversification on activity density, species richness, and community structure. We found that species composition was strongly influenced by currently grown crop although effect on arthropods varied between species groups. Especially, winter oilseed rape strongly affects arthropod community structure. Interestingly, we were also able to show an influence of the preceding crops, indicating an ecological memory effect in the aboveground arthropod community. Our results show that crop identity of both currently and previously grown crops in crop rotations may lead to an increase in arthropod activity density and changes in species composition. Diversified crop rotations including appropriate crops can be an easily implemented tool to increase arthropod biodiversity and biomass at large spatial and temporal scales, particularly in areas dominated by a single crop (e.g., wheat, maize). Our results may help to design optimized crop rotations for large‐scale enhancement of insect biodiversity in agroecosystems.     

Influence of Seeding Ratio,Planting Date,and Termination Date on Rye-Hairy Vetch Cover Crop Mixture Performance under Organic Management

Cover crop benefits include nitrogen accumulation and retention, weed suppression, organic matter maintenance, and reduced erosion. Organic farmers need region-specific information on winter cover crop performance to effectively integrate cover crops into their crop rotations. Our research objective was to compare cover crop seeding mixtures, planting dates, and termination dates on performance of rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth) monocultures and mixtures in the maritime Pacific Northwest USA. The study included four seed mixtures (100% hairy vetch, 25% rye-75% hairy vetch, 50% rye-50% hairy vetch, and 100% rye by seed weight), two planting dates, and two termination dates, using a split-split plot design with four replications over six years. Measurements included winter ground cover; stand composition; cover crop biomass, N concentration, and N uptake; and June soil NO₃ ^--N. Rye planted in mid-September and terminated in late April averaged 5.1 Mg ha^-1 biomass, whereas mixtures averaged 4.1 Mg ha^-1 and hairy vetch 2.3 Mg ha^-1. Delaying planting by 2.5 weeks reduced average winter ground cover by 65%, biomass by 50%, and cover crop N accumulation by 40%. Similar reductions in biomass and N accumulation occurred for late March termination, compared with late April termination. Mixtures had less annual biomass variability than rye. Mixtures accumulated 103 kg ha^-1 N and had mean C:N ratio <17:1 when planted in mid-September and terminated in late April. June soil NO₃ ^--N (0 to 30 cm depth) averaged 62 kg ha^-1 for rye, 97 kg ha^-1 for the mixtures, and 119 kg ha^-1 for hairy vetch. Weeds comprised less of the mixtures biomass (20% weeds by weight at termination) compared with the monocultures (29%). Cover crop mixtures provided a balance between biomass accumulation and N concentration, more consistent biomass over the six-year study, and were more effective at reducing winter weeds compared with monocultures.     

Steeply Increasing Growth Differential Between Mixture and Monocultures of Tropical Trees

Studies of biodiversity and terrestrial ecosystem functioning have concentrated almost exclusively on temperate grasslands. To broaden the reach of biodiversity‐functioning research, five fast growing species, comprising three eudicot trees and two congeneric palms (none symbiotic with nitrogen‐fixing microorganisms), were grown for 13 yr in a replacement‐series mixture and monocultures on a fertile soil in a high‐rainfall area of lowland Costa Rica. The mixture accrued more biomass and had greater net productivity than the average, but not the most productive, monoculture. Relative Land Output (a measure of comparative yield) increased steeply. The combined evidence points to an increase in resource partitioning or facilitation among species over time. Spatial partitioning of aboveground space (for light capture) and soil (possibly for retrieval of deep nitrogen), and facilitation of phosphorus availability by one species, are mechanisms that may account for the inferred complementarity. Extending the generalized findings on biodiversity–productivity relationships from well‐studied grasslands to tropical forests is warranted. Mixtures of fast growing trees can out‐perform the average of their component monocultures, whether the metric is biomass accrual or productivity. The modular growth of long‐lived structure enables arborescent species to retain crown space previously captured and may lead to increased spatial partitioning and facilitation of resources over time.     

Host location and oviposition of lepidopteran herbivores in diversified broccoli cropping systems

1 Host location and oviposition are crucial steps in the life cycles of insect herbivores. A diversified cropping system may interfere with these processes, ultimately reducing pest colonization of crops and the need for chemical interventions. 2 In the present study, nonhost vegetation was added to a broccoli (Brassica oleracea var. italica) cropping system to determine the effect of plant diversification on host location and colonization of broccoli by Lepidopteran pests. The two diversification strategies applied consisted of a broccoli/potato (Solanum tuberosum) strip crop, made up of 1.65 m (tractor width) replications of two rows of potatoes and two rows of broccoli, and a cereal rye (Secale cereale) cover crop, which formed a sacrificial planting that was killed and rolled flat to minimize weed competition and improve the agronomic performance of the subsequent broccoli crop. 3 Diamondback moth Plutella xylostella eggs, and subsequent larvae and pupae, were less abundant on broccoli with the cover crop, probably due to interference with host location and oviposition processes. The strip crop had no effect. 4 Numbers of cabbage white butterflies Pieris rapae eggs and larvae did not differ among treatments, probably due to the superior ability of these Lepidoptera to visually locate hosts and their active egg‐dispersing behaviour. 5 These results of the present study indicate that the success of crop diversification strategies are contingent on the relative ability of the target herbivore to locate its host plant and the scale of diversity (e.g. the distance between the host and the nonhost plants), rather than diversity itself.     

Effects of cover crops, weeds and plant debris on development of Mycocentrospora acerina in caraway

This paper reports on the search for inoculum sources of Mycocentrospora acerina on caraway (Carum carvi L.). Obvious suspects are cover crops of biennial caraway and preceding crops of annual caraway. Other suspects are weeds in or alongside the field. Finally, survival structures of the fungus, chlamydospore chains, packed in plant debris or naked, are suspected. M. acerina is able to infect many plant species, including cover crops of caraway such as spinach for seed production and peas. However, the agronomical suitability of a crop to serve as a cover crop of biennial caraway proved to be a more important factor in determining caraway yield than the susceptibility of the cover crop to M. acerina. This finding was corroborated by the fact that spinach and peas as preceding crops had no significant effects on M. acerina development in spring caraway sown the next year. Dill, barley and four weed species were found as new hosts of M. acerina. The role of weed hosts, susceptible crops and plant debris in the survival of the fungus in years without caraway is discussed. Caraway sown on soil containing infested caraway straw, infested debris of other plant species or chlamydospores grown in pure culture, became infected by M. acerina. Only high inoculum densities of chlamydospores in the soil caused severe damping-off of caraway seedlings. The opportunity for disease management by agronomical means is quite limited.     

Intercropping drives plant phenotypic plasticity and changes in functional trait space

The relevance of intercropping, where two or more crop species are simultaneously grown on the same land space, is growing due to its potential for improving resource use and maintaining stable yields under variable weather conditions. However, the actual growth of intercropped species may differ resulting from the idiosyncratic effect of crop diversity, and with this, the realized benefits from intercrops are found to depend critically on the cultivar, species, management and environmental conditions. This study aimed to apply a trait-based approach, in which ecological niche spaces are defined through n-dimensional hypervolumes, to identify the contribution of species/cultivar, cultivation design (sole crop or intercrop) and management (low or high fertilization) to the trait diversity of four crop species, pea-barley and faba bean-wheat, when grown as sole crops and intercrops. Four traits were used as trait axes for the trait space analysis: canopy height, shoot biomass, tiller/node number, and grain yield. We found that trait spaces differed with crop species and cultivars, and whether they were grown as intercrops or sole crops. Trait spaces differed between high and low fertilization only for the cereals grown in the more productive site (i.e. Denmark). Species grown as intercrops had larger volumes than when grown as sole crops, as a result of trait plasticity. This response to intercropping was apparent in almost all the species grown in Sweden and Denmark, except for wheat in Denmark. The study demonstrated that individual species responded to intercropping compared to sole cropping through the plasticity of traits, which influenced the shape of the hypervolumes to divide up the trait space between the species. The findings are important in illustrating the plastic responses of arable crops, which are relevant for understanding the productivity of species grown in intercrops as compared to sole crops.     

Plant: soil interactions in temperate multi-cropping production systems

Background and scope

Multi-cropping approaches in production systems, where more than one crop cultivar or species are grown simultaneously, are gaining increased attention and application. Benefits can include increased production, effective pest, disease and weed control, and improved soil health. The effects of such practices on the range of interactions within the plant-soil system are manifest via plant interspecific competition, pest and disease attenuation, soil community composition and structure, nutrient cycling, and soil structural dynamics. Interplant diversity and competition effectively increases the nature and extent of root networks, tending to lead to more efficient resource use in time and space. Increased competitive ability at a system level, and allelopathic interactions, can reduce weed, pest and disease severity. Soil biotic communities are affected by plant diversity, which can increase abundance, diversity and activity of functional groups. Attendant rhizosphere-located processes can facilitate nutrient uptake between component crops. Whilst there are few studies into multi-cropping effects on soil structure, it is hypothesised that such processes are manifest particularly via the role which the belowground biota play in soil structural dynamics. A deeper understanding of eco-physiological processes affecting weed, pest and disease dynamics in the context of multiple cropping scenarios, and breeding cultivars to optimise mutualistic and allelopathic traits of crop mixtures could significantly increase productivity and adoption of more sustainable farming practices.

Conclusions

Wider consideration needs to be given to plant: soil interactions when crop plants are grown in the context of mixtures, i.e. as communities as opposed to monotonous populations. In particular, a better understanding is required of how root systems develop in the context of mixtures and the extent to which resultant interactions with the soil biota are context-dependent. A significant challenge is that crop cultivars or production systems optimised for monocultural circumstances should not be assumed to be most suited for multi-cropping scenarios, and hence alternative strategies for developing new production systems need to take this into account.