What do cover crops have to offer?

Amélie Gaudin

Assistant Professor of Agroecology,

Department of Plant Science UC Davis

J.Mitchell, A.Westphal, M.Yaghmour, C.Zuber, B.Hanson, K Jarvis-Shean, N.Williams, A.Hodson, H.Wilson, S.Solis

Graduate students: C.Creze, S. Haring, A. DeVincentis

Opportunities and Challenges for Almond systems

Orchard alleys are underutilized- Living soils = “Floors” - 5% of SA have a winter cover, majority is

resident vegetation

Unique constraintsOpportunity to intensify their use to

- Help adapt to the new Normal - Tackle Production and Sustainability

challenges

Winter postharvest is an ideal time:- Trees are dormant- Precipitations water available to produce

biomass

UCCE evaluations of cover crops 1922-1934

Field Peas in Tree Pruning Plot C,P,C Tuttle Left to right: grown on sandMellilotus, Tangier Peas, common vetch, field peas - Atwater

1995

How can it be successfully implemented in our modern intensive systems? What re the benefits/tradeoffs to consider?

Potential to tackle multiple production/sustainability challenges

Many Almond growers recognize the potential benefits of winter cover crops

Perceived benefits of cover crops (n=101)50%-50% users and non users

0 20 40 60 80 100 120 140 160 180

Belowground pest control

Aboveground pest control (NOW)

Weed control

Tree nutrition

Water infi ltration & retention

Pollinator habitat

Soil health

Perceived Benefits, Importance Score

C.Creze, A Gaudin

Large impact of perceived operational constraints

0 20 40 60 80 100 120 140

Complicated transition towards cover cropping

Seeding equipment availability

Difficult establishment

Difficult management of stand

Difficult termination

Difficult almond harvest (debris)

Perceived operational constraints, Importance score

C.Creze, A Gaudin

Agronomic barriers #1 Frost complications

#2 Difficult vertebrae pest management#3 Uncertainties about water needs/benefits

• 2 popular mixes for different objectives

• Perennial resident vegetation, mowed• Bare soil

Wegis&YoungKernCounty

BosqueVerdeLLCGlennCountry

ValleyPrideFarmingFresnoCounty

CastleFarmMercedCounty

Kearneyexperimentalstation,FresnoCounty

NEMATODE SUPRESSION

Infected orchard

Evaluating cover crops across a rainfall gradient

• 2 post bloom termination dates (March-April) with herbicide

Coefficient gradient

Final stage:

Overall performance

Ecosystem services

• Per cover crop combinations

• Based on coefficient

gradients of ecosystem

services

Site-SpecificStudies

DevelopingCoverCropSystemsforAlmondOrchardsCynthia M.Crézé1,JeffreyMitchell1,AndreasWestphal2,DanielleLightle3,DavidDoll3,MohammadYaghmour3,

Mae Culumber3,NealWilliams4 ,AmandaHodson4,BradHanson1,andAmélie C.M.Gaudin11Department ofPlant Sciences,University ofCalifornia– Davis

2DepartmentofNematology,University ofCalifornia– Riverside3 University ofCaliforniaAgriculture andNaturalResources – CooperativeExtension

4 Department ofEntomology andNematology,University ofCalifornia– Davis

Developfeasibleandpracticalwintercovercropsystem sforalm ondgrowers,whichm axim izeagronom ic

benefitsandreduceoperationalconcerns.Objective

Introduction ExperimentalSites

Wegis &YoungMohammadYaghmour,UCCE,KernCounty

BosqueVerdeDanielleLightle,UCCE,G lennCounty

ValleyPrideFarmingMaeCulumber,UCCEFresnoCounty

KearneyExperimentalStationFresnoCounty

CastleFarmDavidDoll,UCCE,MercedCounty

Temp/FROSTMONITORINGSoil,surfaceandtree

TERMINATIONDATESBeforeb loomorsummer

NEMATODESUPRESSIONInfectedorchard

COMPACTIONComparetoripping

Compaction Term inationdateFrost

ExperimentalDesign

2)PollinatorM ix(5species/1family)at8lbs./acre

ü 15%Bracco W hiteM ustard

(Brassicah irtum )ü 20%DaikonRadish

(Raphanus sativus)

ü 15%Nem fix Yellow M ustard

(Brassicajuncea )

ü 15%Com m onYellow M ustard(Brassicah irtum )

ü 35%Canola

(Brassicanapus)

Comparedto3)PerennialResidentVegetation4)Baresoil– conventionalherbicidecontrol

Acknowledgem entsFinancial support for this research is provided by The Almond Board of California (Modesto, CA).

The authors would like to thank Steve Gruenwald, Herb Kalar, Jeff Bergeron and Greg Wegis for

providing the sites to conduct this research. The authors would also like to acknowledge CindyMontes, Cameron Zuber and members of the Gaudin Lab for their help in orchard operations.

Orchardmeasurements

Frostü Monitororchardtemperaturesfromsoilto

tree(topsoil,3feet,5feetheight)from

December-Marchü Orchardrelativehumidityü Covercropcanopytemperature

(IRthermometer)ü Monitorfrostdamagetotreeatblooming

<<

WaterUsageDr.JeffreyM itchell,UCDavisü Watermassbalancemodelforeachsite

ü Pressurebombing/Stemwaterpotentialoftreesü Covercropevapotranspirationü Neutronprobessetto7feetdepth

PollinationDr.NealW illiam s,UCDavisKim iora Ward,UCDavisProjectSpecialist

ü Averageflowerabundance(numberoffloralunits/metersquare)

ü Visitationü Spatio-temporalco-occurrenceofflowers

andanimals(phenology)

WeedsDr.BradHanson,UCDavisStevenHaring,Ph.D.Student

ü Weedpressure(squaretransects&numberofweeds)

ü Weedidentityineachmetersquaresectionduringcovercroppingandaftertermination

ü Totalweedbiomassü C:Ncontentofbiomass

ParasiticNematodeDr.AndreasWestphal,UCRiversideü Parasiticnematodehoststatusofdifferent

covercropspeciesandmixtures(greenhousestudy)

ü Root-lesionandroot-knotnematodemonitoring

ü StudyofCrotalariajuncea ,nematode

suppressingcovercrop

Roots&SoilHealthDr.Amé lie Gaudin,UCDavisCynthiaCrézé ,Ph.D.Student

ü Biologicalanalysis:microbialfunctionalgroupsü Chemicalanalysis:C:Ncyclingisotopestudy,organicmatter

content(%OM),rootexudationcharacterizationü Physicalanalysis:aggregatestability,infiltrationrate,water

holdingcapacity

ü Rootfunctionaltraitassessment

SoilFoodWebDr.Am andaHodson,UCDavisü Foodwebanalysis(enrichmentindex

andstructureindex)ü Nematodecount,IDandgroup(i.e.

entomopathogenic nematodes)ü Fungalfeeders

Yieldsü Almondyieldproductivityand

quality

ü Leafnutrient&saltcontentü CovercroptotalbiomassandC:N

ratio

Pestsü Insectpestpressure

ü NavelOrangeworm (NOW)monitoring

2017California-Alm ondCoverCropsurveyThisanonymoussurveycollectsdataoncovercropuseinalmondorchardsandidentifiesthemostimportantbenefitsandconcernsofgrowerstoshaperesearch.Weinviteyoutotakethissurvey!

https://ucdavis.co1.qualtrics.com/jfe/form/SV_3UepPhXFE82QvS5

How does cover croppingimpact soil and surface

temperatures and frost

risk at blooming?

How does termination date affectecosystem services in orchard

systems? (i.e. water usage, soil

inorganic N dynamics, C returns...)

What is the effect of covercropping compared to rippingon soil compaction and

resulting water infiltration andsoil water retention?

Almond production in California is faced with multiple challenges associated with uncertainties ofirrigation water supply, N and groundwater regulations, pollinator health and an urgent need toreduce its environmental footprint. Based on the BIOS project (Bugg et al., 1994) and farmers’

experience, cover cropping is clearly compatible with almond production in California. However, it has

not been widely implemented due to concerns regarding water usage, and push towardsindustrialized models to enhance almond productivity. Based on a recent Almond Board of CaliforniaSustainability survey, only 5.6% of growers keep a winter soil cover (planted cover crop). Renewed

interest for soil health and ecological intensification is leading to a rising demand for soil-building

resources and information on benefits and constraints of implementing cover crops in our unique

Mediterranean climate. Literature suggests that cover crop trait selection could bring much-needed

services to orchards including C sequestration, nitrogen fixation by legumes and non-chemical weedsuppression. However, significant knowledge gaps remain to limit potential tradeoffs so as to make

this practice relevant to different production regions and to increase the adoption and benefits of

cover cropping at a larger scale. In particular, there is currently limited accurate data on water use

requirements of cover crops and on the potentially increased risks of frost damage in the spring

(Pritchard et al., 1989). Improved knowledge about opportunity costs involved with cover croppingcould help develop strategies to enhance the sustainability of almond production in California.

BR

AS

SIC

A

1)SoilM ix(5species/3families)at50lbs./acre

ü 10%Bracco W hiteM ustard

(Brassicah irtum )ü 10%DaikonRadish

(Raphanus sa tivu s)

ü 30%M ercedRyegrass

(Lo lium perenne )

ü 20%Berseem Clover(Trifo lium alexand rinum )

ü 30%Com m onVetch

(V ic ia sativa )

GR

ASS

LEG

UM

E

ReferencesBugg,R.L.Anderson,G.Eck,R.Hendricks,L.&Lashbrook,C.(1994)BiologicallyIntegratedOrchardSystems(BIOS)forAlmondsinMercedCounty.CommunityAlliancewithFamilyFarmersFoundation:Davis,CA,UnitedStates.

Pritchard,T.L.Sills,W.M.Asai,W.K.Hendricks,L.C.&Elmore,C.L.(1989)Orchardwateruseandsoilcharacteristics.Californ iaAgricultureJournal,23-25.

4treatm entsx5sitesRCBD,replicated

BR

ASS

ICA

Coefficient gradient

Final stage:

Overall performance

Ecosystem services

• Per cover crop combinations

• Based on coefficient

gradients of ecosystem

services

Site-SpecificStudies

DevelopingCoverCropSystemsforAlmondOrchardsCynthia M.Crézé1,JeffreyMitchell1,AndreasWestphal2,DanielleLightle3,DavidDoll3,MohammadYaghmour3,

Mae Culumber3,NealWilliams4 ,AmandaHodson4,BradHanson1,andAmélie C.M.Gaudin11Department ofPlant Sciences,University ofCalifornia– Davis

2DepartmentofNematology,University ofCalifornia– Riverside3 University ofCaliforniaAgriculture andNaturalResources – CooperativeExtension

4 Department ofEntomology andNematology,University ofCalifornia– Davis

Developfeasibleandpracticalwintercovercropsystem sforalm ondgrowers,whichm axim izeagronom ic

benefitsandreduceoperationalconcerns.Objective

Introduction ExperimentalSites

Wegis &YoungMohammadYaghmour,UCCE,KernCounty

BosqueVerdeDanielleLightle,UCCE,G lennCounty

ValleyPrideFarmingMaeCulumber,UCCEFresnoCounty

KearneyExperimentalStationFresnoCounty

CastleFarmDavidDoll,UCCE,MercedCounty

Temp/FROSTMONITORINGSoil,surfaceandtree

TERMINATIONDATESBeforeb loomorsummer

NEMATODESUPRESSIONInfectedorchard

COMPACTIONComparetoripping

Compaction Term inationdateFrost

ExperimentalDesign

2)PollinatorM ix(5species/1family)at8lbs./acre

ü 15%Bracco W hiteM ustard

(Brassicah irtum )ü 20%DaikonRadish

(Raphanus sativus)

ü 15%Nem fix Yellow M ustard

(Brassicajuncea )

ü 15%Com m onYellow M ustard(Brassicah irtum )

ü 35%Canola(Brassicanapus)

Comparedto3)PerennialResidentVegetation4)Baresoil– conventionalherbicidecontrol

Acknowledgem entsFinancial support for this research is provided by The Almond Board of California (Modesto, CA).

The authors would like to thank Steve Gruenwald, Herb Kalar, Jeff Bergeron and Greg Wegis for

providing the sites to conduct this research. The authors would also like to acknowledge CindyMontes, Cameron Zuber and members of the Gaudin Lab for their help in orchard operations.

Orchardmeasurements

Frostü Monitororchardtemperaturesfromsoilto

tree(topsoil,3feet,5feetheight)from

December-Marchü Orchardrelativehumidityü Covercropcanopytemperature

(IRthermometer)ü Monitorfrostdamagetotreeatblooming

<<

WaterUsageDr.JeffreyM itchell,UCDavisü Watermassbalancemodelforeachsite

ü Pressurebombing/Stemwaterpotentialoftreesü Covercropevapotranspirationü Neutronprobessetto7feetdepth

PollinationDr.NealW illiam s,UCDavisKim iora Ward,UCDavisProjectSpecialist

ü Averageflowerabundance(numberoffloralunits/metersquare)

ü Visitationü Spatio-temporalco-occurrenceofflowers

andanimals(phenology)

WeedsDr.BradHanson,UCDavisStevenHaring,Ph.D.Student

ü Weedpressure(squaretransects&numberofweeds)

ü Weedidentityineachmetersquaresectionduringcovercroppingandaftertermination

ü Totalweedbiomassü C:Ncontentofbiomass

ParasiticNematodeDr.AndreasWestphal,UCRiversideü Parasiticnematodehoststatusofdifferent

covercropspeciesandmixtures(greenhousestudy)

ü Root-lesionandroot-knotnematodemonitoring

ü StudyofCrotalariajuncea ,nematode

suppressingcovercrop

Roots&SoilHealthDr.Amé lie Gaudin,UCDavisCynthiaCrézé ,Ph.D.Student

ü Biologicalanalysis:microbialfunctionalgroupsü Chemicalanalysis:C:Ncyclingisotopestudy,organicmatter

content(%OM),rootexudationcharacterizationü Physicalanalysis:aggregatestability,infiltrationrate,water

holdingcapacity

ü Rootfunctionaltraitassessment

SoilFoodWebDr.Am andaHodson,UCDavisü Foodwebanalysis(enrichmentindex

andstructureindex)ü Nematodecount,IDandgroup(i.e.

entomopathogenic nematodes)ü Fungalfeeders

Yieldsü Almondyieldproductivityand

quality

ü Leafnutrient&saltcontentü CovercroptotalbiomassandC:N

ratio

Pestsü Insectpestpressure

ü NavelOrangeworm (NOW)

monitoring

2017California-Alm ondCoverCropsurveyThisanonymoussurveycollectsdataoncovercropuseinalmondorchardsandidentifiesthemostimportantbenefitsandconcernsofgrowerstoshaperesearch.Weinviteyoutotakethissurvey!

https://ucdavis.co1.qualtrics.com/jfe/form/SV_3UepPhXFE82QvS5

How does cover croppingimpact soil and surface

temperatures and frost

risk at blooming?

How does termination date affectecosystem services in orchard

systems? (i.e. water usage, soil

inorganic N dynamics, C returns...)

What is the effect of covercropping compared to rippingon soil compaction and

resulting water infiltration andsoil water retention?

Almond production in California is faced with multiple challenges associated with uncertainties ofirrigation water supply, N and groundwater regulations, pollinator health and an urgent need toreduce its environmental footprint. Based on the BIOS project (Bugg et al., 1994) and farmers’

experience, cover cropping is clearly compatible with almond production in California. However, it has

not been widely implemented due to concerns regarding water usage, and push towardsindustrialized models to enhance almond productivity. Based on a recent Almond Board of CaliforniaSustainability survey, only 5.6% of growers keep a winter soil cover (planted cover crop). Renewed

interest for soil health and ecological intensification is leading to a rising demand for soil-building

resources and information on benefits and constraints of implementing cover crops in our unique

Mediterranean climate. Literature suggests that cover crop trait selection could bring much-needed

services to orchards including C sequestration, nitrogen fixation by legumes and non-chemical weedsuppression. However, significant knowledge gaps remain to limit potential tradeoffs so as to make

this practice relevant to different production regions and to increase the adoption and benefits of

cover cropping at a larger scale. In particular, there is currently limited accurate data on water use

requirements of cover crops and on the potentially increased risks of frost damage in the spring

(Pritchard et al., 1989). Improved knowledge about opportunity costs involved with cover croppingcould help develop strategies to enhance the sustainability of almond production in California.

BR

AS

SIC

A

1)SoilM ix(5species/3families)at50lbs./acre

ü 10%Bracco W hiteM ustard

(Brassicah irtum )ü 10%DaikonRadish

(Raphanus sa tivu s)ü 30%M ercedRyegrass

(Lo lium perenne )ü 20%Berseem Clover

(Trifo lium alexand rinum )

ü 30%Com m onVetch

(V ic ia sativa )

GR

ASS

LEG

UM

E

ReferencesBugg,R.L.Anderson,G.Eck,R.Hendricks,L.&Lashbrook,C.(1994)BiologicallyIntegratedOrchardSystems(BIOS)forAlmondsinMercedCounty.CommunityAlliancewithFamilyFarmersFoundation:Davis,CA,UnitedStates.

Pritchard,T.L.Sills,W.M.Asai,W.K.Hendricks,L.C.&Elmore,C.L.(1989)Orchardwateruseandsoilcharacteristics.Californ iaAgricultureJournal,23-25.

4treatm entsx5sitesRCBD,replicated

BR

ASS

ICA

Interdisciplinary evaluation of the impacts

Alyssa DeVincentis, PhD student Dr. Sam Sandoval

• Weed control • NOW pressure and

control • Soil health• Pests and beneficial

nematodes• Water footprint • Pollinators • Yields

3rd year

A feasible, flexible rainfed practice

6-10” stripsNo till drill/seederEnd of Oct-NovLittle to no irrigationmicro sprinklers

Termination end March/AprilMulch after mowingHerbicide

Clean soils at harvest No need for conditioner

Can we keep good harvest conditions ?

• It is possible!

• Species choice:• balanced C/N ratio• Legumes are faster in

decomposing

• Termination: promptly postbloom using mowing and/orherbicide is effective

• There will be newopportunities with off groundharvests

No negative impacts on yieldsTrends toward yields increase in very compacted

orchardsUp to ~+ 225 lbs/acre (year 2)

Enhance water use efficiency

Sustain pollinators

and pollination

Improve soil health

Decrease pest

pressures

Yields &

Inputs

Common production constraints/needs in Almond systems

Cover crop and water use efficiency

J.Mitchell

Capture and conservation of winter rainfall

Pictures: D.DollMerced, February 2017

Across the road

In season capture of irrigation water

Water infiltration -2 years of Cover Crops-

• Infiltration: Improved infiltration during the cover crop

• Higher capacity for winter rainfall to penetrate the soil • Reduced risks of runoff

• Water conservation

• Conditions tend to revert back to original infiltration rates post-cover crops

• Less pooling of irrigation water

• Long term improvements

C.Creze, A Gaudin

0.0000 0.0005 0.0010 0.0015

Soil Mix (n=3)

Bare (n=3)

Kern

Infiltration (cm/s)

Tre

atm

en

t

Soil Mix (n=3)

Bare (n=3)

0.0000 0.0005 0.0010 0.0015

Soil Mix (n=3)

Bare (n=3)

Merced

Infiltration (cm/s)

Tre

atm

en

t

Soil Mix (n=3)

Bare (n=3)

0.0000 0.0005 0.0010 0.0015

Soil Mix (n=3)

Res. veg. (n=3)

Corning

Infiltration (cm/s)

• Water is used to create biomass that provides other benefits

• Function of establishment, growth and species• Seed ahead of the first rain

C.Creze, Jeff Mitchell, Alyssa DeVincentis, Samuel Sandoval

Water usage: Keeping irrigation water use low

• Direct competition for water is low • No significant differences in soil moisture or

tree water status in the spring • Very close ET values for winter cover crop

and bare soils • Water retention and use efficiency ?

Picture: Rich Collins

Frost potential ?

Tradeoff: Cover crops can reduce soil-to-tree heat transfer and therefore, increase damage during sensitive frost nights

Cover crops help buffer temperatures

• Topsoil temperatures were cooler under cover crops

• We observed no ambient air temperature differences at 3 and 5 feet:

C.Creze, Dani Lightle2017

→ Cover cropped orchards may not experience higher frost risks but could keep soils cooler. →Mowing and irrigating for frost control can be done anytime→ Consider a low-growing cover such as sub-clover for instance

Enhance water use efficiency

Sustain pollinators

and pollination

Improve soil health

Decrease pest

pressures

Yields &

Inputs

Common production constraints/needs in Almond systems

Managing competition for weed control

• We measured weed suppression when the cover crop emerges early and is really abundant.

• Suppress growth

• Weed germination and emergence are not affected

• Decrease weed diversity

• Summer weeds?

→ Early seeding of a mixture ahead of winter rain is critical

S.Haring, B.Hanson

MowingHerbicide

Dry conditions

NOW pressure: Sanitation effectiveness?

• Trafficability can be improved in the winter to facilitate sanitation

• NOW mortality may increase on mummies in cover crops

• At the same time, cover crops could interfere with sanitation efficacy

• More difficult to blow/sweep nuts from rows with a dense stand of cover crop (??)

→ Shaking and sanitation is still necessary and feasible

→ Sanitation before planting the cover crop is an option → Combine cover crop mowing with flail-mowing of the mummies

H.Wilson

Pests nematodes

• Some cover crop species might • Host and increase nematode population densities• limit reproduction of pests nematodes

• Greenhouse and field tests of cover crop species

• Most plant lines allowed limited reproduction RLN,, except lupine

• Radish and Sunn hemp seems to be the poorest hosts • Cover crops that suppress RLN do not necessarily suppress

RRN• Large variability between species ie: clover types (Rose

Clover)

Andreas Westphal

→ Cover crop roots need to grow in the area of the tree roots, extended growth periods

Root ring nematode

Root lesion nematode

37 Brassica lines 9 legumes

Enhance water use efficiency

Sustain pollinators

and pollination

Improve soil health

Decrease pest

pressures

Yields &

Inputs

Common production constraints/needs in Almond systems

Feeding pollinators

• Provision of forage resources to bees during and after almond bloom

• Brassicas are especially visited.

Neal Williams, Elina Lastro Niño

3

2

1

0

Brassica

Raphanus

Sinapis

Vetch

Pollinatormix

Soil mix

Ho

ney

be

e v

isit

s (p

er

flo

we

r/m

in)

Honeybee Use of Planted Species

• Achieving blooming synchrony is not

trivial – early planting, mowing

strategy (sanitation..)

• Little to none competition for

pollination with Almond while having

the potential to provide useful

habitat to improve bee health

Enhance water use efficiency

Sustain pollinators

and pollination

Improve soil health

Decrease pest

pressures

Yields &

Inputs

Common production constraints/needs in Almond systems

Orchard soil health

• Significant decrease in sodicity under all the

vegetative covers compared to bare soils

• Improvements in soil aggregation with

vegetative covers

• Water infiltration

• Dust

• Soil biology responds rather quickly, site/mix

dependent

• ++ Microbial biomass

• Shifts in soil food web

• Enrichment in bacterial feeding nematodes

• High sodicity, poor

aggregation and high

compaction are limiting • higher soil health

conditions

• C storage

C.Creze, A Hudson

Economic feasibility

Costs Benefits

Seed Increased Yield

Planting (labor) Soil erosion control

Termination (labor) Nutrient cycling

Depreciation of machinery

Weed control

Opportunity cost of time spent learning to

grow cover crops

Increased soil organic matter

Reduced surface water runoff

Soil-carbon storage

Discounted beehives

Alyssa DeVincentis, Samuel Sandoval

Conclusions

Cover crops are a medium/long term investmentso are trees….

• Different species or classes of cover crops can target different management goals

• Mixtures: many goals, higher chance of good stand

• Despite identical seeding rates and mix composition, cover crop composition and biomass will likely be different every year and in your different blocks Katherine Jarvis-Shean, UCCE Orchard Advisor

http://www.sacvalleyorchards.com

-0.5 0.0 0.5

MBC

PoxC

% Change

Corning Merced Arvin

-0.5 0.0 0.5 1.0

Infiltration

Bulk density

Agg. Stability

% Change

Corning Merced Arvin

Corning, Tehama County

Merced,Merced County

Arvin,Kern County

1) Soil Mix (5 species/3 families) at 50 lbs./acre

ü 10% Bracco White Mustard

(Brassica hirtum)ü 10% Daikon Radish

(Raphanus sativus)

ü 30% Merced Ryegrass (Lolium perenne)

ü 20% Berseem Clover (Trifolium alexandrinum)

ü 30% Common Vetch

(Vicia sativa)

GR

ASS

LEG

UM

EB

RA

SSIC

A

Cultivating cover crop multifunctionality for soil health

in California’s almond orchardsCynthia Crézé1, Amanda Hodson2, Jeffrey Mitchell1, Andreas Westphal3, Danielle Lightle4,

Mohammad Yaghmour4, David Doll4, Cameron Zuber4, Sequoia Williams1 & Amélie Gaudin1

1Departm ent of P lant Sciences, University of California – Davis2Departm ent of Entom ology and Nem atology, University of California – Davis

3Department of Nem atology, University of California – Riverside 4University of California Agriculture and Natural Resources – Cooperative Extension

Introduction

Conclusions and Future Research

Cover Crop Species Composition

In light of climate change challenges facing California agriculture (Pathak etal., 2018), there is an increased need for both mitigating and adaptivestrategies to secure food production. Although cover cropping has beendemonstrated to provide multiple ecosystem services, including carbonsequestration, its capacity to support climate change adaptation is lessevident. Furthermore, less certain is its adaptability and potential inMediterranean climates, as the majority of research stems from theMidwest. Although short-term studies conducted in the 1990s showed that

cover cropping is compatible with California almond production, this practicewas never widely implemented in these systems due to concerns overoperational constraints and resource competition. Based on a recentAlmond Board of California Sustainability Survey, only 6% of almondproducers currently use seeded cover crops. This project addresses theincreasing demand for data on the impacts of cover crops on soil health andresource conservation, to support the development of climate-smart soilmanagement strategies specific to Mediterranean climates.

We thank Project APIS and Kamprath Seeds for providing the seeds for this study. Financialsupport for this research is provided by the Almond Board of California, the WesternSustainable Agriculture Research and Education graduate fellowship (WSARE), the CDFAHealthy Soils program and Annie’s Sustainable Agriculture scholarships. The authors would alsolike to acknowledge the help of UCCE Centers (Glenn, Merced and Kern counties). We alsoacknowledge the help of the Gaudin and Hodson labs for the support in conducting field workand sample analyses.

Baseline – Legacy effects of past practices

Baseline soil analyses indicated consistent trends of

resource localization at the center of the orchard middles,away from the tree berms. This must be taken intoconsideration when designing cover crop systems to

enhance tree nutrition.

Acknowledgements

• With identical seeding, the species-composition varied widely by location, which likely implies differences in functionality and plant-soil feedback potential.

• Cover crop production was positively related to precipitation with highest

production in the Northern-most site in Tehama county.

Soil Health Shifts

Bio

log

ica

l

Research Question

Methods

Ch

em

ica

l

Ph

ysi

cal

• Chemical analyses revealed loose trends with higher NO3- after both mixes (P=0.26) and higher SO43- in the

soil mix (P=0.184) at the Kern county site, higher K+ in the pollinator mix at two sites (P=0.10, P=0.12).

Soil MixSoil MixSoil Mix

Pollinator MixPollinator MixPollinator Mix

We established three randomized complete block design (RCBD) trials withfour replications (3 tree rows x 4 treatments x 4 blocks). A total of threesites have been chosen in three ecoregions of California: Tehama county inthe Sacramento Valley, Merced county in the North San Joaquin Valley,and Kern county, in the South San Joaquin Valley. Cover crop mixes weredrill-seeded following almond harvest in October to November 2017 andterminated in early April (∼ 6 month cover). Soil samples were taken priorto cover crop seeding and ∼ 6 month post cover crop termination.

NSSP>0.05

NSSP>0.05

NSS

P>0.05

NSSP>0.05

Research efforts are being continued to provide a second season of data to solidify the findingsand to elucidate long-term impacts of cover cropping for almond orchards. This project isintegrated within a larger system-wide evaluation of multiple co-benefits of cover cropping onecosystem services (pollinator habitat, weed management and water dynamics) to provide acomprehensive opportunity cost assessment and to support the adoption of sustainable soil

management practices in light of other benefits and tradeoffs.

*

P=0.04

Past practices: • Bare tree berms using chemical control and blowers.• Prunings and mummies are piled and flail-mowed in 3-6 feet wide

middles.• Micro-sprinkler irrigation: ~ 6 feet wide radius in 21 feet wide middles

Two cover crop mixes:

Can cover crop management enable climate change adaptation by

supporting soil health and reducing resource vulnerability, throughthe provision of multiple ecosystem services: augmented soilbiological activity, increased retention of mineralized nutrients, andthe joint improvement of water infiltration and retention capacity?

-0.5 0.0 0.5

MBC

PoxC

% Change

Corning Merced Arvin

-0.5 0.0 0.5 1.0 1.5

Total C

Olsen P

SO43-

K+

NO3-

pH

CEC

% Change

Corning Merced Arvin

-0.5 0.0 0.5 1.0 1.5

Total C

Olsen P

SO43-

K+

NO3-

pH

CEC

% Change

Corning Merced Arvin

-0.5 0.0 0.5 1.0

Infiltration

Bulk density

Agg. Stability

% Change

Corning Merced Arvin

2) Pollinator Mix (5 species/1 family) at 8 lbs./acre

ü 15% Bracco White Mustard (Brassica hirtum)

ü 20% Daikon Radish (Raphanus sativus)

ü 15% Nemfix Yellow Mustard

(Brassica juncea)ü 15% Common Yellow

Mustard (Brassica hirtum)ü 35% Canola

(Brassica napus)

BR

AS

SI

CA

M : center of the orchard alleyways

T : within the micro-sprinkler wetting zone, ∼5-6 feet from the Nonpareil tree row

• Physical analyses indicated improved aggregate stability trends at all sites and for both mixes, with a

significant difference for the pollinator mix (P=0.04)

at the Kern county site.

• Biological analyses indicated no statistically significant changes

∼ 6 month after cover crop

termination.

Tehama

Merced

Kern

Tehama

Merced

Kern

Tehama

Merced

Kern

Soil Mix composition

Pollinator Mix composition

Olsen P

CEC

SO4 2-

K+

Mg2+

pH

NO3-

Total C%

0 100 200 300

0

200

400

600

800

Cumulative seasonal precipitation (mm)

Bio

mass p

rod

ucti

on

(g

/m2)

Soil Mix

Pollinator Mix

Resident Vegetation

y = 2.7x - 114.0

R2 = 0.92

y = 3.2 x - 156.8

R2 = 0.89

y = 1.0 x - 47.9

R2 = 0.48

Reference: Pathak, T.B., Maskey, M.L., Dahlberg, J.A., Kearns, F., Bali, K.M., & Zaccaria, D. 2018. Climate changetrends and impacts on California agriculture: a detailed review. Agronomy 8, 25.

=Species selection Environment Managementx x

Soil Mix Pollinator Mix

Treat it as a winter rainfed crop

Cover cropping in orchard can take many forms

• Orchards age and spacing• Region

• Precipitations • Soil type• Temperatures …

• Objectives• Experience and advise

Thank you for your attention

Alyssa DeVincentis, PhD student Dr. Sam Sandoval

Growers and managersBosque Verde, Sandridge, Wegis&Young, Castle Farm

QUESTIONS ?

Amélie Gaudin

Assistant Professor of Agroecology,

Department of Plant Sciences, UC Davis

https://gaudin.ucdavis.eduagaudin@ucdavis.edu

Preliminary results

Soil health and yields: Cover crop species respond differently to different plant-parasitic nematodes