soil amendments, fertilizers, mulches, and cover crops ...ccag-eh.ucanr.edu/files/271979.pdf ·...

Soil Amendments, Fertilizers, Mulches, and Cover Crops: Think Outside the Bag

Santa Clara Master Gardener Talk October 19, 2017

Chuck Ingels

Farm & Horticulture Advisor

UCCE Capitol Corridor MCP, Sacramento County

http://ccag-eh.ucanr.edu

http://ccag-eh.ucanr.edu/



Topics to be Covered

• Soil organic matter and soil structure

• Fertilizers

– Synthetic vs. Natural

– Effects on Soil Microbes

– N Mineralization and Availability

– Fertilizing Specific Plant Types

• Soil Nutrient Analysis

• Mulches

• Cover Crops

Soil Structure

Structure - the arrangement of soil particles into aggregates

Good structure: holds water (micropore space) and has air space (macropore space)

Poor structure: lacks adequate macropore space

A Key Goal = Good Soil Tilth

Soil Organic Matter

• Serves as energy source (food) for microorganisms, which promote stable aggregation of the soil particles

• Essential nutrients are obtained by plants as organic matter decomposes

• Enhanced by OM additions but destroyed by cultivation

How Organic Matter Additions Improve the Soil

• Increased biological activity

• Increased soil aggregation

• Decomposition releases nutrients

• Increased pore structure

– Improved water retention (sandy soil) and infiltration (clay soil)

• Bacteria, polysaccharides, etc. – micro-aggregate formation

• Fungal hyphae – enmeshing micro-aggregates into macro-aggregates

Soil Aggregation

© 2012 Nature Education

http://www.nature.com/scitable

http://www.microped.uni-bremen.de/SEM_index.htm

Fungal hyphae growing through the soil, can stabilize micro-aggregates



• Fertilizers






• Mulches

• Cover Crops

Synthetic Fertilizers

• Commonly derived from petroleum

• A typical 40-pound bag of lawn fertilizer contains the fossil-fuel equivalent of 2.5 gallons of gasoline (Univ. of Vermont)

• Prolonged use of ammonia-based fertilizers can greatly reduce soil pH

Making of Synthetic N Fertilizers

• Natural gas = 98% methane (CH4)

• Chemical reactions hydrogen gas (H2)

• Air = 78% N2

• Haber-Bosch Process:

– High pressure & heat Makes ammonia (NH3)

– N2 + 3 H2 → 2 NH3

Conversions of Ammonia to Various N Fertilizers

Slow-Release N Fertilizers

• Synthetic

– UF (urea formaldehyde), MU (methylene urea), IBDU (isobutylidenediurea) (uncoated polymers)

– Polymer-coated (e.g., Osmocote)

– Longer lasting, not readily leached

– Label says “Slow Release Nitrogen”

• Water-Insoluble Nitrogen (W.I.N.)

• Natural (e.g., compost, feather meal)

Polymer-Coated Fertilizer

• % nitrogen (N)

• Phosphorus (P)

% phosphoric acid P2O5

• Potassium (K)

% potash K2O

‘Complete’ Fertilizers

Fertilizer Blends

• “Complete” fertilizer = Contains N, P, & K

• “Balanced” fertilizer = Equal amounts of N-P-K

• Examples: 16-16-16 (multi-purpose), 12-4-8 (fruit tree & vine), 5-10-10 (tomato & veg.), 4-8-5 (camellia/azalea), 25-6-4 (lawns)

• Blends are not standardized!

Examples of Fertilizer Blend Ratios

Ratios

1-1-1: (e.g., 16-16-16): General purpose

2-1-1: Orn. & fruit trees, estab. lawns, leafy veggies

1-2-2: New lawns

1-2-1: Vegetables, seedlings, flowers, bulbs

0-1-1: Woody plants in fall

Example of Fertilizer Label

Calculating Fertilizer Amounts

Divide the amount of N needed by the %N

Ammon. sulfate (21-0-0)

1 lb. N/1,000 sq. ft. ÷ 0.21 = 4.8 lbs.

Multi-purpose (16-16-16)

0.5 lb. N/tree ÷ 0.16 = 3.1 lbs.

Fruit tree fert. (12-4-8)

0.75 lb. N/1,000 sq. ft. ÷ 0.12 = 6.3 lbs.

Soil Builders vs Organic Fertilizers

• <2% nitrogen

• Can apply at higher rates

to build SOM

• C/N ratio: 15-30:1

• >2% nitrogen

• Applied at rates

estimated to meet crop

nutrient needs

• Dry organic fertilizers:

C/N ratio: 5:1 or less

Manures Characteristics and Uses

• Poultry, dairy, feedlot, steer, rabbit, sheep/goat

• May contain salts and weed seeds

• N content varies greatly

– Poultry may have >3%N (ammonia smell)

– Aged feedlot manure may have <1% N

N Content of Raw Manures

(Bary et al., 2000)

Compost Characteristics and Uses

• Contains most nutrients required by plants

• May contain weeds & plant pathogens

• N content usually about 1-2%, very slow release

• Considered a soil amendment, not fertilizer

“Finished” Compost

• Has undergone thermophilic heating process with turning and water

• Temperature low, no ammonia smell

• Contains diverse microbial populations

• Contains most nutrients required by plants

• N content usually 1-2%, very slow release

• Adding an organic soil amendment builds organic matter, fertilizers generally don’t

Earthworm Castings vs. Compost

• Both improve soil structure & nutrient retention

• Earthworm castings likely better:

– Greater microbial activity

– Formation of more humic acids (humification)

– Improved soil aggregation

• Earthworm castings more expensive

• Using compost and some EW castings ideal

• By-product of animal slaughter

– Blood meal (13-0-0)

– Bone meal (2-13-0)

– Feather meal (13-0-0)

– Fish products (4 to 11% N)

Selected Animal-Based Natural Fertilizers

• Manures

– Bat guano

(Up to 10% N, 12% P)

– Livestock manures

Selected Plant-Based Natural Fertilizers

• Alfalfa meal (about 2-1-2)

• Cottonseed meal (6-2-2)

• Soybean meal (7-2-1)

Mined Natural Fertilizers

• Rock phosphate

• Potassium

– Muriate of potash

– Sulfate of potash

– Greensand

Mining of Rock Phosphate

• Source : Natural deposits in N. America, China, Morocco, & former Soviet Union

• N. America – Florida, Idaho/Mont./Utah/

Wyoming, N. Carolina, Tennessee

Rock Phosphate

• Hard-rock phosphate

– 20% P and 48% Ca – can raise pH

– Breaks down very very slowly

• Soft-rock phosphate

– 16% P and 19% Ca, many micronutrients

– Form that plants can use more easily

– Breaks down very slowly

Mining of Potassium Fertilizers

• World reserves deposited when water from ancient inland oceans evaporated

– K salts crystallized into beds of potash ore

– Covered by thousands of feet of soil

• Most deposits chloride (KCl), some sulfate (K2SO4)

• From Canada (#1), Russia, Belarus, US (#7)

– New Mexico, Utah, Canada

Potash

• Historically used for bleaching textiles, making glass, making soap (lye)

• Originally, came from extraction of K2CO3 by leaching ashes and evaporating the solution in iron pots, leaving a white residue ("pot ash“)

• Now potash is the common term used for the fertilizer forms of potassium

• Standard measurement is potassium oxide (K2O)

Potash Banding

K attaches to soil particles

K concentrated, so extra K leaches down

Broadcasting K (or P) has little effect – nutrients are locked up in top 1-2” of soil

Must be banded or incorporated

Synthetic Fertilizers

• No C-H linkage, so not used as energy source by soil microbes

• Nutrients in synthetic fertilizers are attached directly together with ionic bonding, which separates or dissociates readily in water

• Because of the lack of carbon, fertilizers “feed the plant but not the soil”

Natural Fertilizers

• Carbon-hydrogen linkage in natural fertilizers slows the release of the nutrient ions

• Carbon forms covalent bonds with carbon and other elements – allows the formation of complex chemicals and structures

• Slow release, low leaching and burning potential

• “Feed the plant and feed the soil”

Synthetic vs. Natural Fertilization

• Plants take up nutrients from natural and synthetic sources (no preference)

• Natural fertilizers feed soil microbes and require them for breakdown

• Microbes (and roots) release compounds like organic acids, enzymes, and chelates convert nutrients from organic form into a plant-available (soluble) form

• Derived from non-renew-

able source (fossil fuels)

• Requires large amounts of energy to produce

• Evidence shows they do not harm soil microbes

• Usually less expensive

• Consider using only when necessary for deficiency

Synthetic Fertilizers Natural Fertilizers

• Derived from renewable source (often waste)

• Lower analysis; requires more energy to transport

• Enhance microbes and need them for breakdown

• Usually more expensive

• Consider using when possible

Synthetic vs. Natural Fertilization

Advantages of Synthetic Fertilizers

• Nutrients available to plants immediately

• Produce exact ratio of nutrients desired

• Ratios and chemical sources easy to understand

• Inexpensive

Disadvantages of Synthetic Fertilizers

• Made from nonrenewable sources (fossil fuels)

• May not promote soil health

– No decaying matter for improving soil structure

– Most do not replace micronutrients

• Nutrients readily available chance of overfert.

• Tend to leach faster than natural

• Long-term overuse can change soil pH, harm soil microbes, increase pests

Advantages of Natural Fertilizers

• May also improve soil structure

• Most are slow-release; not easy to overfertilize

• Renewable and biodegradable

• Can make your own from waste (compost, worm castings) or obtain locally (manure)

Disadvantages of Natural Fertilizers

• May not release nutrients as they are needed

• Nutrient content of manure & compost often unknown

• % nutrients usually lower than chemical fertilizers

• Tend to be bulkier, requiring more fossil fuels and producing more GHG; more expensive

Product Weight Analysis Price $/Lb. of N

SYNTHETIC

Azalea/Camellia 5 lbs. 10-10-6 $7.50 $16

Rose “ 10-12-6 $7.50 $16

All-Purpose “ 16-16-16 $7.50 $10

Citrus “ 14-4-8 $7.50 $11

“NATURAL” BRAND

Azalea/Camellia 4 lbs. 5-5-3 $7.50 $39

Rose “ 5-6-3 $7.50 $39

All-Purpose “ 5-5-5 $7.50 $39

Citrus “ 7-3-3 $7.50 $28

Nutrient Costs of Selected Fertilizers Local Sacramento Nursery, Sept. 2017

Product Weight Analysis $/Lb. N

LOCAL NURSERY

Alfalfa meal 3 lbs. 2-0-3 $108

Blood meal 3.5 lbs. 13-0-0 $20

Cottonseed meal 3.5 lbs. 6-2-1 $31

Bat guano 1.5 lbs. 9-2-1 $70

FARM SUPPLY CO.

Alfalfa meal 40 lbs. 3-0-2 $27

Blood meal 50 lbs. 14-0-0 $9

Cottonseed meal 50 lbs. 5-2-1 $20

Bat guano 25 lbs. 9-3-1 $22

Nutrient Costs of Selected Fertilizers Local Nursery vs. Farm Supply Co.

Pelleted chicken manure

Org. soybean meal

Pelleted feather meal

http://lghttp.17653.nexcesscdn.net/808B16/cdn_images/media/catalog/product/cache/1/thumbnail/9df78eab33525d08d6e5fb8d27136e95/f/9/f940-a.jpg

Product Weight Analysis $/Lb. N

Nutri-Rich 50 lbs. 4-3-2 $7.50

Feather meal 50 lbs. 13-0-0 $6.15

Org. soybean meal 50 lbs. 7-2-1 $26.70

Modesto Milling:

Org. soybean meal 50 lbs. 7-2-1 $11.2

Nutrient Costs of Selected Fertilizers Farm Supply Co.



• Fertilizers






• Mulches

• Cover Crops

Approximate Numbers of Microbes in Soil

Microbial Group No./Gram of soil

Bacteria 100,000,000 to 1 billion

Fungi 100,000 – 1,000,000

Algae and Cyanobacteria 1,000 – 1,000,000

Protozoa 1,000 – 100,00

Sylvia, Fuhrmann, Hartel and Zuberer, 1998.

Soil Microorganisms

• The majority of the living part of soil organic matter

• Store and release nutrients from organic matter

• Produce gummy substances (polysaccharides, mucilages, etc.) that help create soil aggregates

• Increase with incorporation of org. amendments

Ways to Promote Soil Microorganisms

• Reduce tillage

• Grow cover crops

• Add soil amendments, especially compost or worm castings

• Use organic fertilizers, reduce synthetic fertilizers?

Long-Term Effects of Mineral Fertilizers on Soil Microorganisms

(Daniel Geisseler and Kate M. Scow, 2014)

• Analysis of 107 studies from 64 long-term trials

• Use of mineral fertilizers led to:

– Increased microbial biomass over unfertilized treatments by 15% (greater crop growth)

– Increased soil organic matter content, which likely increased microbial biomass

• Ammonium concentrations were likely far below levels toxic to microorganisms

• In general, fungi were found to benefit from mineral N fertilization

• Using N fertilizers doesn’t appear to have direct negative effects on soil microbial biomass in ag.

Long-Term Effects of Mineral Fertilizers on Soil Microorganisms

(Daniel Geisseler and Kate M. Scow, 2014)



• Fertilizers






• Mulches

• Cover Crops

0 10

Min

era

l N

itro

gen

lb

s N

/A/D

ay

WEEKS

Crop Demand

Fertilizer

Mineralization

2.0

3.0

4.0

5.0

Soil organic matter

mineralization

1.0

Cover Crop

Mineralization

Timing of N Mineralization

N in Composts & Manures

Material Total N C/N Ratio

Pelletized poultry manure 4.7 4.5

Aged poultry manure 3.1 9.1

Poultry compost 3.8 5.7

Aged feedlot manure 2.0 12.4

Feedlot manure compost 2.2 11.4

Yard waste compost 1.6 14.4

Yard waste compost 1.0 12.0 Hartz et al, 2000

OSU Organic Fertilizer

Calculator

N. Andrews et al.

Fertilizer

Total % N

% PAN, 28 days

% PAN, season

Alfalfa meal (2.5-0.5-2) 2.5 11 26

Bat guano—high N (10-3-1) 10.0 60 75

Blood meal (12.5-1.5-0.6) 12.5 60 75

Bone meal (3-15-0) 3.0 17 32 Comp. manure (1.5-0.5-0.5) 1.5 5 10 Cottonseed meal (6-0.4-1.5) 6.0 60 75

Feather meal (12-0-0) 12.0 60 75

Fish meal (10-6-2) 10.0 60 75

Nutri-Rich (4-3-3) 4.0 36 51

Soy meal (6.5-1.5-2.4) 6.5 60 75

Plant Available Nitrogen Organic Fertilizer Calculator (Oregon Tilth, OSU)

Mineralization and Immobilization

N Mineralization Compost and Manures

• Nitrogen release from compost and

manures was measured as:

Material Mean N

recovery

(%)

High N

recovery

(%)

Manure 11 27

Composted Manure 6 15

Composted Yard

Waste 2 6

Source: Richard Smith

Plant Available N from Manures, Compost Decay Series

• UC research, 1970s

• Average plant-available N over 3 years (years 1, 2, and 3):

– Chicken (90%, 10%, 5%)

– Dairy (75%, 15%, 10%)

– Feedlot (35%, 15%, 10%)

– Compost (~10% in year 1)



• Fertilizers






• Mulches

• Cover Crops

• Garden soils rarely contain all nutrients in optimal amounts

• Equally rare for garden soil to be deficient in several nutrients

• When appropriate, add only N or the nutrients that are deficient

Should I Fertilize?

FERTILIZING

“Adding fertilizer, soil amendments, or root stimulants to the planting hole or backfill soil is not recommended. Most nursery-grown trees

are well fertilized during production and seldom respond to fertilizing at planting except in the

most infertile soils.”

• Trees adapted to low soil N levels!

• Routine N-P-K fertilization unjustified unless deficiency exists

• High N wasteful, polluting, and may increase insect & disease problems

• Trees in turf likely do not require fertilization

• Use slow release fertilizers if necessary

Landscape Tree Fertilization Points to Remember

Nutrient Deficiencies are Rare in Woody Ornamentals

• N – Sandy, overwatered, or sub soils

• P – Deficient in foothills

• Ca – Acidic or sandy soils

• Fe, Mn, Zn, B – High-pH or waterlogged soils

N Fertilization for Fruit & Nut Trees The Home Orchard, UC Pub. 3485

• Total lbs. of N/year to correct a deficiency: – Large fruit tree: 1 lb. – Small fruit tree: 0.5 lb. – Large nut tree: 2 lbs. – Small nut tree: 1 lb.

• Deciduous trees: Late spring and summer

• Citrus: Jan. or Feb. just before bloom, then in May and perhaps in June

Vegetable Fertilization Veg. Gardening Basics, UC Pub. 8059

• Preplant: N-P or N-P-K

– Use 1/3 lb. N per 100 sq. ft.

• Side dressing when plants 3-4” high

– 0.4 lb. N per 100 sq. ft.

– Banded application

Lawn Fertilization Practical Lawn Fertilization, UC Pub. 8065

• Cool-season grass: 4 lbs. actual N/1,000 sq. ft./year

• Low N-using species (buffalo, Zoysia): 2 lbs. N/year

• Slightly less where grasscycling is used

• Split applications: Up to 1 lb. N/application

• Organic and slow-release fertilizers:

– Can use higher rate & fewer applications

Conclusions about Fertilizers

• N is the nutrient most often deficient; complete fertilizers (with P and K) are generally not necessary

• P and K are mined, so there is a limited supply

• Do not fertilize trees or shrubs at planting

• After planting, consider only fertilizing trees and shrubs when deficiencies occur

• Periodically amend soils with compost, and mulch around plants when possible



• Fertilizers






• Mulches

• Cover Crops

• Doesn’t always tell what plants take up

• Good for baseline info and detecting deficiencies and changes

• Use soil sampler

• Soil & plant testing labs

– cesonoma.ucanr.edu

(Viticulture Pubs.)

Soil Nutrient Analysis

• Sample in rooting zone (0-12”, maybe 12-24”)

• Mix multiple cores in bucket for each “sample”

• Use 1 pint per sample, place in bag, send to lab

– See http://cagardenweb.ucdavis.edu

• Additional samples from distinct areas

• Include: Total N, NO3-N, P, K, Ca, Mg, soil texture, pH, OM, CEC, salts(?)

Soil Nutrient Analysis Methods

Selected Home Soil Testing Kits

“Rapitest” (Luster Leaf)

“Soil Master” (Mosser Lee)

“Professional” (Luster Leaf)

pH Test Winners



• Fertilizers






• Mulches

• Cover Crops

Mulches Serve Many Purposes and Add Beauty

Mulch reduces evaporation from soil, but not transpiration

Mulch vs. Compost

• Mulch = Organic or inorganic material spread on the soil surface

• Compost = Mass of rotted organic matter made from decomposed plant material and/or manure

– Thermophilic decomposition (heat)

– Finished compost is not hot

– Usually incorporated into the soil

Potential Benefits of Mulch

• Insulates roots from temp. extremes

• Increases:

Root growth Microbial biomass

Water penetration

• Protects trees from mechanical injury

• Improves plant establishment

• Reduces Weeds and erosion

Environ. stresses

Soil moisture loss

Potential Problems with Mulch • May prolong saturation in heavy soils

– Favors root and crown rot

• Can’t see soil moisture

• May host plant diseases, insects, and nuisance fungi

• Some wood chips poor quality

• Time consuming to spread

Mulch Basics (Wood Chips)

• Remove weeds, water before applying

• Replace grass with mulch under trees

• Keep mulch 6-12 in. away from the base of trees & shrubs

• Application rate: Generally 2-4 in. deep

– Fine = <2 in. Coarse = 4-6 in.

• Keep mulch on top of soil to prevent N tie-up

More Mulch Basics

• Durability of wood chips increases with underlying fabric or plastic

• Mulch has little or no effect on termites

• Softwood mulches (pine, cypress, etc.) last longest

– Less microbial feeding

Do Wood Chips Affect Soil Nutrients? • Tie-up of N?

– N immobilization from high C:N mulch

– Generally N tie-up at interface only

– But since soil is mixed by fungal hyphae, earthworms, may be tie-up

– Better tree growth w/ N fert. or compost

– Avoid mulch in planting holes

• Soil pH – little effect (pine needles acidic)

N K OM (%)

Bare soil 9.5 94 3.2

Cocoa shells 18.1 627 3.2

Wood chips 8.3 165 3.3

Compost 16.7 251 3.4

Horse manure 19.6 445 3.3

Mulch Nutrient Release Study (Arbor. J., v. 24, 2000 – U.K.)

• Left on bare soil 12 mo., then raked off

• Available Nutrients in Top 4” of Soil (mg/L):

Ventura Avocado Mulch Trial Faber, Downer, & Menge WAC (2003)

• Mulch layer kept 6 in. deep

• Soil nutrient levels after 4 yrs.:

N P K Zn

(%) (ppm)

Mulch 1.6 a 17 a 285 a 7.3 a

No mulch 1.2 b 12 b 218 b 6.7 b

Mulch Reduces Weeds if Deep Enough

Bermudagrass

Bindweed

Mulch Doesn’t Control Perennials!

Some Weeds Blend in With Mulch

Spotted spurge

Mulching and Weed Control

• Thickness to mulch depends on mulch type

• Various studies:

– 3-in. layer: 85% weed control over 3-yrs.

– 4-in. mulch gave better control than 3-in.

– Phenols & tannins in coniferous bark improved weed control

Allelopathy

• Suppression of growth of a plant by a toxin released from a nearby plant

• Black walnut and some others, not Eucalyptus

• Only relates to annual seedlings, not mature plants

• Composting materials or irrigating reduces effect

Sheet Mulching

• Layering mulch to suppress weeds

– Knock down or mow existing weeds

– Add compost, weed barrier, mulch, water

• Biodegradable – plant right into it

Sheet Mulching Albany, CA

Can Mulches Spread Diseases? Some Potential Problems

• Pine pitch canker

• Sudden oak death

• Dutch elm disease

• Don’t transport these wood chips

• Compost first

• Keep mulch 6 in. away from trunks

• Oak root fungus?

• Verticillium wilt?

• Fire blight?

Heating Mulch to Kill Pathogens

• Several studies have shown:

– Temps. in large piles easily reach 120 to 150F

– 3 days exposure enough to kill all pathogens of woody plants

– Piles should be turned two to three times to expose all portions to high temps.

Nuisance Fungi that Grow on Wood Chips

Dog Vomit Fungus (Slime Mold)

Dyemaker's puffball

Stinkhorn

Other Mulch Fungi

Bird’s nest fungus

Mushrooms

Rock Mulches

• Long-lasting, may look good

• Absorb and reflect heat

– ↑ ET; Heat roots?

• Rocks eventually mix with soil

– Difficult to remove later

• Do not improve soil quality

• Weeds eventually come through

Can Be Aesthetically Pleasing

…Or Not

Synthetic Mulches Polypropylene and Polyester

• Better weed control than chips alone

• Slower breakdown of wood chips

• Allow water & air movement

• Do not improve soil quality

• Most are effective 3-5 yrs. (under chips)

• Most are not recyclable (landfill!)

Weed Control After 4 Years (UCD)

1 pre-emerg.

applic.

1 wood chip

applic.

Wood chips

+ woven

polyprop.

Plastic or Fabric Underneath?

Synthetic mulches will usually become

exposed and shred, especially on slopes

Don’t Do It!

Mulch Affects the Soil Surface

Well aerated surface

and short-lived roots

under mulch better

water penetration

Crusting can

occur w/o mulch

Problems with Wood Chip Quality

Mower

blight

Avoid

weedeating

by trunk

Avoid turf or

weeds by trunk

Expanding Drip Line Mulch Hides Soil and Drip

Mulch alone won’t keep soil in place on steep slopes

Mulch Doesn’t Solve Soil Problems!

Uncompact

soil

Add

compost

Mulch

Mulch – Conclusions • Avoid mulch in planting holes

• Control perennial weeds first

• Caution on clay soils; away from trunks

• Little or no N tie-up; add N or compost

• Little or no disease transmission

• Root growth improved

• Fabric reduces weeds but it shreds

• Benefits outweigh disadvantages



• Fertilizers






• Mulches

• Cover Crops

Lowest energy use

On-site production of N

May still need additional N

Add organic matter

Improve soil tilth, water penetration

Cover Crops Benefits

Atmosphere = 78% N; only legumes can use

Rhizobium bacteria in roots use N in soil air

Store N in nodules on roots

Resemble root-knot nematodes

Most N translocated to foliage

Contribute up to 2-3 lbs. N/1,000 sq. ft.

Cover Crops Nitrogen Fixation of Legumes

Nodules Created by Rhizobium Bacteria

Berseem clover

Seed can be difficult to find

Cannot grow winter crop in that space

Requires chopping and rototilling in spring

Cover Crops Potential Problems

Winter:

Bell beans, vetch, and field peas

With or without oats or barley

Clovers (crimson, rose, sub)

Summer:

Cowpeas, buckwheat,

sudan grass

Cover Crops Species

• Grass alone requires N

• Avoid N fertilizers on legumes

– High soil N - legumes fix little N

• Max. N contribution is at early flowering (incorporate in March)

• >80% of N is in above-ground parts; <20% in roots

Cover Crops Nutrition

Cover Crop, Tomatoes

N Release from Cover Crop Residue

N Release %N Examples

Will Tie up N 0.5 Cereal Straw

Will Tie up N 1.0 Cereal Straw

Will Tie up N 1.5 Cereal at heading

May Tie up N* 2.0 Cereal pre heading

May Tie up N* 2.5 Mustards at heading & immature cereal

Will Release N 3.0 Mustards, legumes and juvenile cereal

Will Release N 3.5 Legumes and immature mustards

Will Release N 4.0 Legumes

N Release Pattern from Cover Crops

0

2

4

6

8

10

12

14

16

18

0 11 25 39 53 67

Days After Incorporation of Cover Crop

To

tal M

ine

ral N

itro

ge

n (

pp

m)

Legume Mix

Mustard

Oats

Questions? http://ccag-eh.ucanr.edu




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