Cover Crop Contributions to Cover Crop Contributions to Nitrogen FertilityNitrogen Fertility

Richard SmithRichard SmithVegetable Crop and Weed Science Farm AdvisorVegetable Crop and Weed Science Farm AdvisorUniversity of California Cooperative Extension University of California Cooperative Extension Monterey CountyMonterey County

Cover Crops: BackgroundCover Crops: Background•• Cover crops are an important agricultural Cover crops are an important agricultural

production practiceproduction practice•• In modern agriculture their use is In modern agriculture their use is

common in permanent crops but is more common in permanent crops but is more problematic in annual cropsproblematic in annual crops

•• They are mostly grown in the winter, but They are mostly grown in the winter, but can can ““get in the wayget in the way”” of preparing the of preparing the ground for early spring planting if wet ground for early spring planting if wet weather prevents soil incorporationweather prevents soil incorporation

Cover Crops: BackgroundCover Crops: Background•• Cover crops can be a source of nitrogen Cover crops can be a source of nitrogen

for subsequent cash cropsfor subsequent cash crops•• However, regarding N availability, there However, regarding N availability, there

are important agronomic details that need are important agronomic details that need to be discussed to better understand the to be discussed to better understand the role that cover crops can play in providing role that cover crops can play in providing nitrogen to subsequent cropsnitrogen to subsequent crops

Legumes: Fix N from the air and provide a net input of N to the soil

Cereals, Mustards, Others: Scavenge & recycle residual N from soil

Sweet CloverSweet Clover

OatsOats

Legume have the ability to obtainthe N they need by N fixation

Low Nitrogen Scenario: Oat are N Stressed (yellowed)

Legumes can leak some of their nitrogento plants growing in their immediate vicinity

Compare the color of these two oat plants

Legume and cereal mixestake advantage of the N fixing ability of

legumes and the N scavenging ability of cereals

How Much N do Cover CropsHow Much N do Cover Crops Contain?Contain?

Nitrogen Content of Cover CropsNitrogen Content of Cover Crops Organic Farm in San Benito County Organic Farm in San Benito County –– moderate Nmoderate N

Six year AverageSix year Average

Cover CropCover Crop Lbs N/ALbs N/A

CerealsCereals 131.5131.5

LegumesLegumes 145.7*145.7*

Cereal/Legume MixCereal/Legume Mix 177.1177.1

* How much is net fixation is not known

Cover CropsCover CropsBiomass Biomass

T/AT/A% N% N

in Topsin Topslbs N/acrelbs N/acre

in Topsin Tops

White MustardWhite Mustard 2.52.5 3.93.9 194.8194.8Indian MustardIndian Mustard 2.22.2 4.54.5 199.7199.7Cereal Rye Cereal Rye 3.13.1 3.33.3 203.7203.7

Scavenging of Nitrogen by Cover CropsScavenging of Nitrogen by Cover CropsFollowing Conventional Lettuce Production Following Conventional Lettuce Production –– high Nhigh N

Chualar, 2003Chualar, 2003

What rate is the nitrogen contained What rate is the nitrogen contained in cover crops made available to in cover crops made available to

the subsequent cash crop?the subsequent cash crop?

•• The release of nitrogen by cover The release of nitrogen by cover crops is dependent on soil moisture crops is dependent on soil moisture and temperatureand temperature

•• The nitrogen concentration of the The nitrogen concentration of the cover crop is importantcover crop is important

N Release Pattern from Cover CropsN Release Pattern from Cover Crops

0

2

4

6

8

10

12

14

16

18

0 11 25 39 53 67Days After Incorporation of Cover Crop

Tota

l Min

eral

Nitr

ogen

(ppm

)

Legume MixMustardOats

Smith & Brennan, 2003Smith & Brennan, 2003

Percent of Cover Crop Nitrogen Percent of Cover Crop Nitrogen Mineralized at 8 WeeksMineralized at 8 Weeks

Various legume, and non-legume, cover crops, Hartz, unpublished

Perc

ent C

over

Cro

p N

Min

eral

ized

Nitrogen Content of Cover Crop - Percent

Nitrogen release from cover crop Nitrogen release from cover crop residue based on the N contentresidue based on the N content

Nitrogen ReleaseNitrogen ReleasePercent N Percent N

in Cover Cropin Cover CropExamples of Cover CropsExamples of Cover Crops

Will Tie up NWill Tie up N 0.50.5 Cereal StrawCereal Straw

Will Tie up NWill Tie up N 1.01.0 Cereal StrawCereal Straw

Will Tie up NWill Tie up N 1.51.5 Cereal at headingCereal at heading

May Tie up N*May Tie up N* 2.02.0 Cereal pre headingCereal pre heading

May Tie up N*May Tie up N* 2.52.5 Mustards at heading and Imm. cereal Mustards at heading and Imm. cereal

Will Release NWill Release N 3.03.0 Mustards, legumes and juvenile cerealMustards, legumes and juvenile cereal

Will Release NWill Release N 3.53.5 Legumes and immature mustardsLegumes and immature mustards

Will Release NWill Release N 4.04.0 LegumesLegumes

Cereal Residue Legume ResidueCereal Residue Legume ResidueHigh C:NHigh C:N Lower C:NLower C:N

Cover CropCover CropProteinsProteins

MicrobesMicrobesNeed carbon and nitrogen for Need carbon and nitrogen for

their growththeir growth

AvailableAvailableMineralMineral

NitrogenNitrogen(Nitrate & Ammonium)(Nitrate & Ammonium)

Rate of mineralization Rate of mineralization depends mostly on depends mostly on nitrogen concentration of nitrogen concentration of the tissuethe tissue

Nitrogen Release by Cover CropsNitrogen Release by Cover Crops

•• The amount of N provided by the cover The amount of N provided by the cover crop is importantcrop is important

•• The nitrogen demand by the cash crop is The nitrogen demand by the cash crop is also important to understandalso important to understand

Biomass Accumulation and Biomass Accumulation and Nitrogen Demand of LettuceNitrogen Demand of Lettuce

•• Rapid growth from 30 to 60 days following plantingRapid growth from 30 to 60 days following planting•• High Peak Demand for NHigh Peak Demand for N

4-5 lbs Nitrogen/Acre/dayPeak Uptake Demand

Field Trial on Nitrogen Release and Field Trial on Nitrogen Release and Crop ResponseCrop Response

•• A field study conducted by Rick Miller A field study conducted by Rick Miller (1987(1987--1988), conducted on the UCD farm, 1988), conducted on the UCD farm, illustrates an optimal situation of a cover illustrates an optimal situation of a cover crop providing adequate amounts of N in crop providing adequate amounts of N in synchrony with crop demandsynchrony with crop demand

Nitrogen Content of Cover Crop TopsNitrogen Content of Cover Crop Tops Two Year Average (1987/1988)Two Year Average (1987/1988)

Miller, 1989

Nitrogen Uptake in Grain lbs/ANitrogen Uptake in Grain lbs/A Two Year Average (1987/1988)Two Year Average (1987/1988)

Miller, 1989

Grain Yield lbs/AGrain Yield lbs/A Two Year Average (1987/1988)Two Year Average (1987/1988)

Miller, 1989

Conclusions of this StudyConclusions of this Study•• The release of N from the cover crop and The release of N from the cover crop and

the uptake demand of corn synchronized the uptake demand of corn synchronized wellwell

•• This is an example of optimal use of This is an example of optimal use of nitrogen from the cover crop by the nitrogen from the cover crop by the subsequent cash cropsubsequent cash crop

2006 & 2007 Cover Crop 2006 & 2007 Cover Crop & Fertilizer Trial & Fertilizer Trial -- SalinasSalinas

Year Biomass T/A

N in TopsPercent

N in Tops lbs/A

2006 3.21 3.1 194.52007 3.71 2.1 153.4

Smith and Muramoto, 2007

2006 Soil Mineral Nitrogen2006 Soil Mineral Nitrogen Cover Crop Incorporation to Planting BroccoliCover Crop Incorporation to Planting Broccoli

2007 Soil Mineral Nitrogen2007 Soil Mineral Nitrogen Cover Crop Incorporation to Planting BroccoliCover Crop Incorporation to Planting Broccoli

2006 Nitrogen in Broccoli Biomass lbs/A2006 Nitrogen in Broccoli Biomass lbs/AAt HarvestAt Harvest

2006 Nitrogen in Broccoli Biomass lbs/A2006 Nitrogen in Broccoli Biomass lbs/AAt HarvestAt Harvest

2007 Nitrogen in Broccoli Biomass lbs/A2007 Nitrogen in Broccoli Biomass lbs/AAt HarvestAt Harvest

Broccoli Yield 2006 Trial

Broccoli Yield 2007 Trial

Summary of Cover Crop and Nitrogen Fertility Trial

When the nitrogen concentration in the cover crop was >3%, the cover crop provided the equivalent of 63 lbs of fertilizer N to the broccoli

Cover crop N boosted the yield of broccoli at all fertilization rates

Summary of Cover Crop and Nitrogen Fertility Trial

When the nitrogen concentration in the cover crop was 2%, the cover crop tied up nitrogen and it took 225 lbs of fertilizer N to over come this effect

The nitrogen concentration in the cover crop greatly affected N release to the subsequent cash crop

Composition of Cover Crop MixesComposition of Cover Crop Mixes

•• Planting Date, weather conditions and soil Planting Date, weather conditions and soil fertility can affect the composition of fertility can affect the composition of cover crop mixes and can impact their cover crop mixes and can impact their nitrogen concentration at incorporationnitrogen concentration at incorporation

Comparison of Cover Crop Comparison of Cover Crop Composition on Two Soil TypesComposition on Two Soil Types

black = cereal; gray = legumeblack = cereal; gray = legumeHollister Year 2

0

10

20

30

40

50

60

70

80

90

100 < 1 < 1 < 1 < 1 < 1 < 1 < 1 < 1 < 1

84 64 32 19 81 63 254

83 63 158

15 35 68 81 18 37 75 96 17 37 85 92

H1 H2 H3 H4 H1 H2 H3 H4 H1 H2 H3 H41X 2X 3X

Seeding Rate

Abov

e G

roun

d D

ry M

atte

r (%

)

D

Brennan et al, in press

Salinas Year 2

0

10

20

30

40

50

60

70

80

90

100 18 10 < 1 9 4 < 1 4 1 < 1

59 77 84 63 65 80 83 62 73 79 72 51

23 13 16 37 25 16 17 38 23 20 28 49

H1 H2 H3 H4 H1 H2 H3 H4 H1 H2 H3 H41X 2X 3X

Seeding Rate

Abo

ve G

roun

d D

ry M

atte

r (%

)

B

Sandy loam, low fertility Clay loam, high soilSandy loam, low fertility Clay loam, high soil fertilityfertility

How Much Cover Crop N is Made How Much Cover Crop N is Made Available for Crop GrowthAvailable for Crop Growth

•• Cover crops can Cover crops can contain 100 contain 100 –– 200 200 lbs N but typically lbs N but typically less than half of less than half of this is made this is made available to the available to the subsequent cropsubsequent crop

Lettuce Soil Organic NLettuce Soil Organic NCropCrop

Jackson, 2000Jackson, 2000

Cover Crop in LettuceCover Crop in LettuceFour months after incorporationFour months after incorporation

Mineralization of Mineral Nitrogen Mineralization of Mineral Nitrogen from Cover Cropsfrom Cover Crops

•• Cover crops also play a larger role in soil Cover crops also play a larger role in soil building and provide a longbuilding and provide a long--term source term source of N that contributes to total soil nitrogen of N that contributes to total soil nitrogen content and that behaves the same as soil content and that behaves the same as soil organic matterorganic matter

Impacts of Organic Soil Building Impacts of Organic Soil Building on Nitrogen Storage in Soilon Nitrogen Storage in Soil

Soil TypeSoil Type ManagementManagement Total Soil N %Total Soil N %

Clay LoamClay Loam Organic Organic 0.170.17

Clay LoamClay Loam ConventionalConventional 0.140.14

LoamLoam Organic Organic 0.140.14

LoamLoam ConventionalConventional 0.110.11

Fine Sandy LoamFine Sandy Loam Organic Organic 0.120.12

Fine Sandy LoamFine Sandy Loam ConventionalConventional 0.060.06

Smith, 2003

Impacts of Organic Soil Building Impacts of Organic Soil Building on Nitrogen Storage in Soilon Nitrogen Storage in Soil

Soil TypeSoil Type ManagementManagement Total Soil N %Total Soil N %

Clay LoamClay Loam Organic Organic 0.170.17

Clay LoamClay Loam ConventionalConventional 0.140.14

LoamLoam Organic Organic 0.140.14

LoamLoam ConventionalConventional 0.110.11

Fine Sandy LoamFine Sandy Loam Organic Organic 0.120.12

Fine Sandy LoamFine Sandy Loam ConventionalConventional 0.060.06

Smith, 2003

Summary of Nitrogen Fertilization Summary of Nitrogen Fertilization of Organic Horticultural Cropsof Organic Horticultural Crops

•• Some crops may be able to achieve Some crops may be able to achieve economically acceptable yield from economically acceptable yield from nitrogen from cover crop decompositionnitrogen from cover crop decomposition

•• Many crops (e.g. lettuce) generally need Many crops (e.g. lettuce) generally need greater quantities of available mineral greater quantities of available mineral nitrogen to achieve economically viable nitrogen to achieve economically viable yieldsyields

Nitrogen Fertilization of Organic Nitrogen Fertilization of Organic Horticultural CropsHorticultural Crops

•• The key is for organic sources of N to The key is for organic sources of N to mineralize in sufficient quantities and mineralize in sufficient quantities and quick enough to meet crop demandquick enough to meet crop demand

•• Synchrony of supply and demandSynchrony of supply and demand

Effective Synchrony Between Effective Synchrony Between Mineralization from the Various Mineralization from the Various

Sources and Crop DemandSources and Crop Demand

Management of Cover Crops to Management of Cover Crops to Provide Nitrogen to Subsequent Provide Nitrogen to Subsequent

Cash CropsCash Crops

•• Cover crops should be incorporated in a Cover crops should be incorporated in a juvenile enough stage to prevent juvenile enough stage to prevent immobilization of N: immobilization of N:

•• Nitrogen content of the tops > 2.5%Nitrogen content of the tops > 2.5%–– Legumes at flowering or beforeLegumes at flowering or before–– Cereals well before headingCereals well before heading

Management of Cover Crops to Management of Cover Crops to Provide Nitrogen to Subsequent Provide Nitrogen to Subsequent

Cash CropsCash Crops

•• Allow sufficient time for the cover crops Allow sufficient time for the cover crops to decompose and release nitrate and to decompose and release nitrate and ammoniumammonium

•• Manage water carefully to not leach Manage water carefully to not leach available N below the root zoneavailable N below the root zone

Thank you for your attentionThank you for your attention