In 2017, approximately 35,600 t of raspberry (Rubus idaeus L.) were produced in Washington and Oregon and valued at over $57 million (U.S. Department of Agriculture, 2019). Washington leads the United States in the production of red raspberry for processing, and it is an important crop to the Pacific Northwest (PNW; U.S. Department of Agriculture, 2019). Red raspberry is also a unique perennial fruit crop as it has an expansive perennial root system and biennial canes that fruit on 1-year-old floricanes. The production of red raspberry in the PNW is on a 5 to 8-year cycle. Because suitable land is limited, red raspberry is often replanted in the same location following field renovation and a possible short-term winter cover crop (Rudolph et al., 2017). Replanted fields are usually broadcast fumigated in the fall before replanting (Walters et al., 2011). The following spring, 0.5 m-wide raised beds are formed and then planted with raspberry either as tissue culture plugs, roots, or bare-rooted plants.
In the PNW, and in western Washington specifically, alleyways of established red raspberry plantings are commonly kept bare and maintained by repeated and frequent rototilling to suppress weeds and unwanted canes (Barney et al., 2007; Walters et al., 2011). Alleyway cover cropping, annual or perennial, is not common practice. Over 3800 ha of raspberry were harvested in Washington alone in 2018 (U.S. Department of Agriculture, 2019). Only 20% of those hectares are occupied by red raspberry plants, which means that ≈3075 ha of soil is being disturbed by repeated rototilling and passage of heavy machinery and equipment for harvesting and other field operations.
Over time, repeated rototilling can have negative impacts on soil quality. Soil quality has been defined as the “continued capacity of the soil to function” as a living ecosystem that sustains plants, animals, and humans (Karlen et al., 1997; U.S. Department of Agriculture, 2001). Soil quality involves physical, chemical, and biological properties. Tillage can directly or indirectly affect any of these properties. Repeated tillage can increase soil erosion, which leads to the loss of soil quality and productivity (Pierce and Lal, 1994). Tillage can also cause soil compaction, contribute to the loss of soil physical structure, reduce the nutrient and water holding capacity of the soil, and increase dust during the dry season—which may increase spider mite (Tetranychus spp., Eotetranychus spp., and Panonychus spp.) activity and reduce photosynthetic capacity of plants (Barney et al., 2007; Golchin et al., 1995; Jackson et al., 2003; Magdoff and van Es, 2009; Tanigoshi et al., 2003). The highest percentage of soil organic matter is present on or near the soil surface, which makes it especially susceptible to wind and water erosion. Losses of soil organic matter from erosion have been shown to affect soil productivity (Bauer and Black, 1994). Cover crops may counteract the effects of repeated tillage. Cover crops are annual, biennial, or perennial living groundcovers that are grown with, before, or after a cash crop to the benefit of the cash crop and the surrounding soil. Cover crops can produce more biomass than resident vegetation, leading to enhanced rainfall infiltration and decreasing the potential for soil erosion and runoff (Dabney, 1998). Additionally, cover crops can improve soil structure; suppress weeds, pests, and pathogens; promote beneficial insect and soil microorganisms; and improve nutrient cycling (Forge et al., 2000; Freyman, 1989; Magdoff and Van Es, 2009; Mazzola and Gu, 2002; Sarrantonio, 2007; Zebarth et al., 1993).
Although challenging to demonstrate, the physical and chemical benefits to soil from the long-term use of cover crops and groundcovers have largely been accepted (Dabney et al., 2001; Hartwig and Ammon, 2002; Magdoff and Van Es, 2009; Sarrantonio, 2007). However, the biological ramifications are even more complex to establish. Soil microorganisms play an important role in soil quality and nutrient cycling by decomposing soil organic matter and storing nutrients (Turco et al., 1994). Soil disturbance through tillage can alter the soil environment and the associated microbial community structure, which has been shown to change dramatically following tillage (Calderón et al., 2000; Jackson et al., 2003; Peixoto et al., 2006). However, total microbial biomass in tilled soils has been shown to be both reduced (Angers et al., 1993; Beare et al., 1997) and not (Jackson et al., 2003; Reicosky et al., 1997) when compared with reduced tillage or no-till practices. Biological activity, specifically fungal, can also be reduced in compacted soil (Whalley et al., 1995).
Alleyway groundcovers are common in other perennial systems such as grape (Vitis spp.) and blueberry (Vaccinium spp.) (Hartwig and Ammon, 2002; Julian et al., 2011). Raspberry growers in the PNW cite concern for potential competition for water and nutrients between the cover crop and the raspberry crop, a situation that could decrease fruit yield and fruit quality. Previous results from cover crop trials in raspberry were mixed and only evaluated a small number of cover crop species. The Fraser Valley of British Columbia is geographically like the northwestern Washington region where much of the floricane red raspberry is grown. Zebarth et al. (1993) conducted a field study in the Fraser Valley and observed reduced primocane diameter of ‘Willamette’ raspberry when grown adjacent to perennial grasses (Lolium spp.). However, raspberry yield was not significantly affected. Bowen and Freyman (1995) observed a significant reduction in raspberry yield when alleyways were planted with perennial ryegrass (Lolium perenne L.) compared with bare soil in the same region. In the same study, when alleyways were planted with white clover (Trifolium repens L.), there was no difference in yield compared with bare soil. Freyman (1989) also observed reduced fruit yield and primocane diameter when alleyways were planted to perennial ryegrass in the Fraser Valley, but this was not consistent across all 3 years of the study. On Prince Edward Island, ‘Festival’ raspberry grown adjacent to oat (Avena sativa L.) that was annually seeded in alleyways produced similar fruit yields to raspberry grown adjacent to bare soil alleyways during a 4-year study (Sanderson and Cutcliffe, 1988).
The objectives of this study were to evaluate effects on the physical, chemical, and biological aspects of soil quality of one perennial and eight annual cover crops grown in the alleyways between raised beds of raspberry relative to the industry standard of cultivated, bare soil alleyways. We hypothesized that cover crops would improve physical and chemical properties of alleyway soil compared with bare, repeatedly cultivated soil.
AlexopoulosC.J.MimsC.W.BlackwellM.1996Introductory mycology. 4th ed. John Wiley & Sons Inc. Hoboken NJ
AngersD.A.BissonnetteN.LégèreA.SamsonN.1993Microbial and biochemical changes induced by rotation and tillage in a soil under barley productionCan. J. Soil Sci.733950
AnishaC.RadhakrishnanE.K.2015Gliotoxin-producing endophytic Acremonium sp. from Zingiber officinale found antagonistic to soft rot pathogen Pythium myriotylumAppl. Biochem. Biotechnol.17534583467
ArshadM.A.LoweryB.GrossmanB.1996Physical tests for monitoring soil quality p. 123–141. In: J.W. Doran and A.J. Jones (eds.). Methods for assessing soil quality. Soil Sci. Soc. Amer. Madison WI
BarneyD.L.BristowP.CoggerC.FitzpatrickS.M.HartJ.KaufmanD.MilesC.MillerT.MooreP.P.MurrayT.RempelH.StrikB.TanigoshiL.2007Commercial red raspberry production in the Pacific Northwest. Pacific Northwest Ext.: PNW 598
BealeR.E.PittD.1992Studies on Minimedusa polyspora a biological control agent of soilborne plant pathogens p. 249–253. In: E.S. Tjamos G.C. Papavizas and R. Cook (eds.). Biological control of plant diseases. Plenum Press New York NY
BeareM.H.HuS.ColemanD.C.HendrixP.F.1997Influences of mycelial fungi on soil aggregation and organic matter storage in conventional and no-tillage soilsAppl. Soil Ecol.5211219
BlevinsR.L.ThomasG.W.SmithM.S.FryeW.W.CorneliusP.L.1983Changes in soil properties after 10 years continuous non-tilled and conventionally tilled cornSoil Tillage Res.3135146
CalderónF.J.JacksonL.E.ScowK.M.RolstonD.E.2000Microbial responses to simulated tillage in cultivated and uncultivated soilSoil Biol. Biochem.3215471559
CookR.LewisG.C.MizenK.A.1991Effects on plant-parasitic nematodes of infection of perennial ryegrass, Lolium perenne, by the endophytic fungus, Acremonium loliiCrop Prot.10403407
ForgeT.A.InghamR.E.KaufmanD.PinkertonJ.2000Population growth of Pratylenchus penetrans on winter cover crops grown in the Pacific NorthwestJ. Nematol.324251
FuntF.C.RossD.S.2013Soil and water management p. 103–119. In: R.C. Funt and H.K. Hall (eds.). Raspberries. CABI Oxfordshire UK
GardesM.BrunsT.D.1993ITS primers with enhanced specificity for basidiomycetes—Application to the identification of mycorrhizae and rustsMol. Ecol.2113118
GolchinA.ClarkeP.OadesJ.M.SkjemstadJ.O.1995The effects of cultivation on the composition of organic matter and structural stability of soilsAust. J. Soil Res.33975993
GoswamiJ.PadneyR.K.TewariJ.P.GoswamiB.K.2008Management of root knot nematode on tomato through application of fungal antagonists, Acremonium strictum and Trichoderma harzianumJ. Environ. Sci. Health43237240
JacksonL.E.CalderónF.J.SteenwerthK.L.ScowK.M.RolstonD.E.2003Responses of soil microbial processes and community structure to tillage events and implications for soil qualityGeoderma114305317
JangidK.WilliamsM.A.FranzluebbersA.J.SchmidtT.M.ColemanD.C.WhitmanW.B.2011Land-use history has a stronger impact on soil microbial community composition than aboveground vegetation and soil propertiesSoil Biol. Biochem.4321842193
JulianJ.W.StrikB.C.YangW.2011Blueberry economics: The cost of establishing and producing blueberries in the Willamette Valley. Oregon State Univ. Ext. Serv. AEB 0022
KarlenD.L.MausbachM.J.DoranJ.W.ClineR.G.HarrisR.F.SchumanG.E.1997Soil quality: A concept, definition, and framework for evaluation (a guest editorial)Soil Sci. Soc. Amer. J.61410
KerstersK.De VosP.GillisM.SwingsJ.VandammeP.StackebrandtE.2006Introduction to the proteobacteria p. 3–37. In: M. Dwarkin S. Falkow E. Rosenberg K.H. Schleifer and E. Stackebrandt (eds.). The prokaryotes. 3rd ed. vol. 5. Springer New York NY
KlindworthA.PruesseE.SchweerT.PepliesJ.QuastC.HornM.GlöcknerF.O.2013Evaluation of general 16S ribosomal RNA gene PCR primers for classical and next-generation sequencing-based diversity studiesNucleic Acids Res.41111
KruysA.HuhndorfS.M.MillerA.N.2015Coprophilous contributions to the phylogeny of Lasiosphaeriaceae and allied taxa within Sordariales (Ascomycota, Fungi)Fungal Divers.70101113
MagdoffF.van EsH.2009Building soils for better crops: Sustainable soil management. 3rd ed. Sustainable Agriculture Research and Education (SARE) Brentwood MD
MaloneyK.E.WilcoxW.F.SanfordJ.C.1993Raised beds and metalaxyl for controlling Phytophthora root rot of raspberryHortScience2811061108
MazzolaM.GuY.2002Wheat genotype-specific induction of soil microbial communities suppressive to disease incited by Rhizoctonia solani Anastomosis Group (AG)-5 and AG-8Phytopatholology9213001307
OksanenJ.BlanchetF.G.FriendlyM.KindtR.LegendreP.McGlinnD.MinchinP.R.O’HaraR.B.SimpsonG.L.SolymosP.StevensM.H.H.SzoecsE.WagnerH.2017Vegan: Community ecology package. R package version 2.4-3. <https://CRAN.R-project.org/package=vegan>
PierceF.J.LalR.1994Monitoring the impact of soil erosion on crop productivity p. 235–263. In: R. Lal (ed.). Soil erosion research methods. 2nd ed. St. Lucie Press Delray Beach FL
PeixotoR.S.CoutinhoH.L.C.MadariB.MachadoP.L.O.A.RumjanekN.G.Van ElsasJ.D.SeldinL.RosadoA.S.2006Soil aggregation and bacterial community structure as affected by tillage and cover cropping in the Brazilian CerradosSoil Tillage Res.90628
R Studio Team2017RStudio: Integrated development for R. RStudio Inc. Boston MA
RudolphR.E.ZasadaI.A.DeVetterL.W.2017Annual and perennial alleyway cover crops vary in their effects on Pratylenchus penetrans in Pacific Northwest red raspberry (Rubus idaeus)J. Nematol.49446456
SarrantonioM.2007Building soil fertility and tilth with cover crops p. 16–24. In: A. Clark (ed.). Managing cover crops profitably. 3rd ed. Sustainable Agriculture Research and Education College Park MD
TanigoshiL.K.MurrayT.A.GerdemanB.S.2003Spider mites on red raspberry. Wash. Sta. Univ. Ext. Bul. 1959E
TurcoR.F.KennedyA.C.JawsonM.D.1994Microbial indicators of soil quality p. 73–90. In: J.W. Doran D.C. Coleman D.F. Bezdicek and B.A. Stewart (eds.). Defining soil quality for a sustainable environment. Soil Sci. Soc. Amer. Madison WI
U.S. Department of Agriculture2001Soil quality test kit guide. 2 July 2017. <https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs142p2_050956.pdf>
U.S. Department of Agriculture2019Noncitrus fruits and nuts 2017 summary. 15 Aug. 2019. <https://www.nass.usda.gov/Publications/Todays_Reports/reports/ncit0619.pdf>
WaltersT.GigotJ.ZasadaI.2011Preplant soil fumigation and alternatives for berry production. Wash. Sta. Univ. Ext. Bul. FS064E
Washington State University (WSU) AgWeatherNet2017Washington State University Lynden historic data. Subset used: Yearly data total precipitation 2008 to 2015. 12 Oct. 2017. <https://weather.wsu.edu/?p=93250>
WhiteT.J.BrunsT.LeeS.TaylorJ.W.1990Amplification and direct sequencing of fungal ribosomal RNA genes for phylogenetics p. 315–322. In: M.A. Innis D.H. Gelfand J.J. Sninsky and T.J. White (eds.). PCR protocols: A guide to methods and applications. Academic Press New York NY
WicklowD.T.RothS.DeyrupS.T.GloerJ.B.2005A protective endophyte of maize: Acremonium zeae antibiotics inhibitory to Aspergillus flavus and Fusarium verticillioidesMycol. Res.109610618
YaoY.R.TianX.L.ShenB.M.MaoZ.C.ChenG.H.XieB.Y.2015Transformation of the endophytic fungus Acremonium implicatum with GFP and evaluation of its biocontrol effect against Meloidogyne incognitaWorld J. Microbiol. Biotechnol.31549556
ZarraonaindiaI.OwensaS.M.WeisenhorncP.WestK.Hampton-MarcellaJ.LaxeS.BokulichfN.A.MillsfD.A.MartingG.TaghavidS.van der LeliedD.GilbertJ.A.2015The soil microbiome influences grapevine-associated microbiotaAmer. Soc. Microbiol. J.6114
ZebarthB.J.FreymanS.KowalenkoC.G.1993Effect of ground covers and tillage between raspberry rows on selected soil physical and chemical parameters and crop responseCan. J. Soil Sci.73481488