Cover Crops: A California Perspective 

Z. Kabir, Ph.D.Conservation Agronomist

California Nutrient Management TeamUSDA‐NRCS

Adapted from NASA

Sacramento Valley

Central Valley, Fresno

Practices That Accelerate Soil Erosion

Rain Drops & Soil Erosion

When Raindrops Impact Bare Soil 

Raindrop splash pattern from a slope landscape, (Envr. Soil Physics, Hillel, 2005)

Dislodging soil particles and splashing them 3 to 7 ft away

Soil Erosion

Sheet: is the uniform removal of a thin film of soil from the land

surface

O’Geen, UC Davis

When sheet flows begin to concentrate on the surface, rill

erosion occurs

Gully: as duration and/or intensity of rain increases and runoff volumes accelerate - create

incised channels

Splash Sheet Rill Gully Channel erosion

Planting Cover Crops

Winter Runoff, University of California, Davis

Cover Crop

Fallow

Kabir & Horwath, unpublished

0

10

20

30

40

50

60

0

20

40

60

80

100

1-17

1-24

1-25

1-31 2-5

2-11

2-13

2-14

2-26 3-9

Prec

ipita

tion

(mm

)

Perc

ent o

f Rai

nfal

l (%

)

CONVENTIONALLOW INPUTORGANICPrecipitation

Runoff as Percentage of Rainfall, UC Davis 

CC

Grower‐Collaborator Field Site

Winter Fallow (NCC)  Winter Cover Crop (CC) 

Discharge  Hydrograph Comparing Growers’ Fields

Early Storm Season (December 29th, 2003)

Late Storm Season (February 25th, 2004)

0.00

0.01

0.02

0.03

0.04

012345

3AM25 Wed Feb 2004

6AM 9AM 12PM 3PM 6PM 9PM 26 Thu 3AM 6AM 9AM 12PM 3PM

25-26 February 2004

m3smm

2/25/2004 2:00:00 AM - 2/26/2004 4:00:00 PM

Cover Cropped (133.723 m3) Non Cover Cropped (912.445 m3) Precip (52.7 mm)

0.00

0.01

0.02

0.03

0.04

012345

6AM29 Mon Dec 2003

9AM 12PM 3PM 6PM

29 December 2003

m3smm

12/29/2003 3:00:00 AM - 12/29/2003 9:00:00 PM

Cover Cropped (58.015 m3) Non Cover Cropped (246.951 m3) Precip (49.7 mm)

Precip.FallowCover Cropsmm3

/ s

mm

Storm event 1 Storm event 2

Kabir & Horwath

Grower FieldTotal Winter Discharge Comparisons, UC Davis

16.3%

0.52 m/s

0.9%Rainfall Discharged as Runoff

Average Peak Runoff Velocity

Fallow (NCC) Cover Crops

0.24 m/s

Above and Below Ground

B. Pleasant, 2009Mother Earth News 

Cover Crops Roots attract Microbes 

Bacteria and fungi are like little fertilizer bags

Exudates: carbohydrates and proteins secreted by roots; attract bacteria, fungi, nematodes, protozoa

Nematodes and protozoa eat exudates and excrete fertilizer

The world above the ground surface and the world below are very tightly linked.

D. Read

Glomalin: Soil Protein

S. Wright, USDA‐ARS

0 10 20 30 40 50 6010

20

30

40

50

60

FallowRyeOatsRye + Oats

Hyphal length = 19.06 + 0.74 (%WSA)

Mycorrhizal hyphal length (m g‐1)

Soil Aggregate Stability

Kabir and Koide, 2002

Corn Early Tassels in Cover Crop Plots

Fallow plots

CC plots

Kabir & Koide, 2000

CC plots

Ear Production of Sweet Corn in Different Cover Crops

Total ears Marketable ears0.0

0.2

0.4

0.6

0.8

1.0

1.2Fallow Oats Rye Oats & Rye 

b

a a a

c

bab

a

Cover Crops in Between the Rows

Smith & Kahn

Cover Crops in Vineyard

Chuck Ingels, UCCE

Flowering Cover Crops

Cover Crops in Walnut Orchard 

Cover Crops in Walnut Orchard

Cover Crops in Almond Orchard

Almond Picked Up from the Orchard Floor

Cover Crops Mowed to Ground Level

Cover Crops may Serve as Sources of Inoculum for Diseases in Cash Crops

Sclerotinia on vetchVetch

Rust on Cover Crop may Carry Over to Corn

Identify What we Want the Cover Crop to Do?

B. Pleasant, 2009Mother Earth News 

• Improve Nutrient availability• Improve soil properties• Reduce soil erosion & improvewater quality

• Suppress weeds, pests and diseases• Provide beneficial habitat• Provide surface mulch  

How to Choose a Cover Crop?

B. Pleasant, 2009Mother Earth News 

Once we Identify Cover Crop/s We Need

Identify a Planting Windows where the Cover Crop can Fit into Our Crop Rotation

Thank You

Any questions?