cover crops (functionnal mixtures) in ogh

COST Action FA 1105: Training School - 15-19 Sept 2014 - CIHEAM – IAMB

Soil fertility, Suppressiveness & Water management for organic agriculture: constraints and opportunities for greenhouse horticultural production

COST FA 1105: Biogreenhouse Towards a sustainable and productive EU organic greenhouse horticulture

Cover crops (functionnal mixtures) in OGH

Hélène VEDIE




Soil Fertility Management in GH Greenhouse : intensive system, 2 crops/year

- Problems of soil structure (intensive traffic, inter-rows…)

- Increased Soil Organic Matter (SOM) mineralization (soil tillage,

climate, solarization…)

- High nutrient demand

- Weed species selection (chickweed, purslane, amaranth…)

- Sanitary problems with poor crop diversification Solanaceae – Cucurbitaceae – Asteraceae




Why growing cover crops in OGH ?

One solution to some of the problems in greenhouses : crop rotation, soil structure, SOM improvement (low ressources of animal manure or

compost), crop nutrition, weed management, sanitary problems…

- Both can be viewed as a type of crop rotation (diff. families)

- Many similar functions – many similar species - Main difference : a cover crop will protect the soil between 2

crops, & possibly during the crops (living/dead mulch)

a green manure is a « soil building crop » to produce OM for incorporation into the soil between 2 crops

Cover crops and green manures




1. GENERAL BENEFITS OF COVER CROPS




Cover crop… to enhance Crop rotation




Soil structure improvement During cover crop cultivation

Surface protection

Roots work

They improve soil porosity

They maintain soil aggregates

They produce exsudates




Soil structure improvement After cover crop incorporation

Earthworms stimulation : +++ porosity

Microbial biomass activity : +++ soil aggregates, stability

Soil structure stability

Weeks Months Years

Green manure

Straw

Compost




SOM and nutrition improvement - By bringing +/- large amounts of organic matter, will have +/-

effects on SOM (with indirect effects on soil structure) and biological activity

a question of amounts a question of quality (C/N) - C/N < 25 : mineralization – N release C/N > 25 : immobilization – +++ SOM - Strategy ? : terminate the GM early to increase N availability… but overall biomass and OM production are reduced




SOM and nutrition improvement

C/N around 12 (from 10 for pea to 18 for italian RG + vetch)

0123456789

Dry biomass (t/ha)- autumn 2013 - 3,5 months

Fabaceae Poaceae + fabaceae

Faba bean + lentil

Rye + pea





C/N around 35 (from 28 for millet to 57 for sorghum)

0

2

4

6

8

10

12

14

16

18

20

Millet (+pois) Sorgho Lablab Moha (+trèfle) Sarrasin (+vesce) Niébé

Dry biomass (t/ha)- summer 2013 - 53 days

Poaceae

Fabaceae

Fabaceae Polygonaceae

(+fab)

Temp. : 25,4 °C

Vigna sinensis





0,0

2,0

4,0

6,0

8,0

10,0

12,0

Dry biomass (t/ha)- summer 2014 - 48 days

Polygonaceae + Fabaceae Poaceae + Fabaceae

Temp. : 23,9 °C

Buckwheat + brassica juncea + Vigna sinensis




SOM and nutrition improvement Cover crops trap +/- important amounts of soil nutrients

100 -200 N / 30 P2O5 / 150-300 K2O Differences with families/species ; soil contents…

and will release these nutrients in a more readily available form

Cover crops can explore different ressources Dif. Plant rooting patterns extraction in different soil layers

ex.: root density/ symbiotic association with mycorrhizae for immobile P

Root activity effect on nutrient availability: insoluble nutrients are released by

the action of organic acids, chelates…produced by the roots

- mustard, buckwheat / P

- brassica sp. / K et S

Legumes capacity to fix N2 from the atmosphere (nodules)




SOM and nutrition improvement Nutrients release will depend on the mineralization rate of

the cover…. : - Soil temperature - Soil humidity - Faster decomposition if the cover is chooped and turned under - P and K have a very good availability

- C:N ratio for N availability

Sometimes contradictory results on a green manure effect on subsequent crop nutrition… but globally positive effects on the long term




SOM and nutrition improvement 2t/ha Dry Biomass

N mineralized

(% N org)

Soil temperature and humidity !!!

Modelisation according Justes et al., 2008




Weed control weed growing is limited by :

- Direct competition (light, water, nutrients…)

- Allelopathy : biochemicals produced by plants (buckwheat, rye)

fast growing cover crops have general suppressive effect Buckwheat, Italian ryegrass, Brassica sp., sorghum sp., millet, …

… some have more specific effects (Pousset, 2000)

-Rye against couch grass (Elytrigia repens L.) -Rapeseed against brassica weeds

-High nitrogen consummers (brassica sp.) against nitrophilous weed species (chickweed [stellaria media], nettel [Urtica sp.]




Suppressive effects on pathogens

Many beneficial effects of cover crops on plants pathogens have been attributed to their direct and indirect effects on the physical and chemical properties of the soil as well as to promoting the activities of beneficial microorganisms (Abawi, 2000)

Soil-inhabiting organisms can affect plants pathogenic organisms by competition (nutrients, space, water…) and direct predation or parasitism

Toxic compounds produced during growth (root exudates) or during decomposition can inhibit some soil-borne pathogens




Suppressive effects on pathogens Some examples to control root-knot nematodes (Meloidogyne sp.)

Crotalaria retusa Crotalaria grantiana

Crotalaria sp. (Fabaceae)

Non-host plants

Ovicidal effect of root exudates

Nematostatic effect of plant extracts

Tagetes sp. (Asteraceae)

Nematicidal effect of root exudates

Trap plants : no reproduction

Tagetes patula

Tagetes minuta




Suppressive effects on pathogens Toxic compounds released by some plants (biofumigation)

Brassica sp. contain GLS (brassica juncea, forage radish…)

Sorghum sp. contain dhurrin (sorghum-

sudangrass hybrids)

Alliaceae sp. contain thiosulfinates (allium,

onion…)

Breakdown in the soil

isothiocyanates Hydrogen cyanide

Dimethyl Disulfide (DMDS)

Many litterature with results on soil-borne diseases (verticillium, sclerotinia, fusarium..)and nematodes Not always very clear effects in the fields…




Suppressive effects on pathogens Some risks too !!!

Family/specie Risks

Brassica sp. Hosts for various fungi: clubroot

(plasmodiophora brassicae) sclerotinia (autumn),

rhizoctonia (summer) and many pests: flea

beetle (delia radicum) diamondback moth

(plutella xylostella) cabbage worms (pieridaea sp.),

slugs, …)

Phacelia Host for Y potato virus and pests

(aphids, white flies, thrips)

Trèfle, vesce Slerotinia, slugs…




A good cover crop …

Will allow soil fertility (physical, chemical, biological properties) enhancement, weed suppression, and, to some extent, will have some suppressive effects on pathogens….

First… : a good cover

crop has to grow under greenhouse !




2. CULTIVATING COVER CROPS UNDER GREENHOUSE




When growing cover crops in OGH ?

Cash crop

Inter cropping

Cover crop

Solarization

Autumn Winter Spring Summer Greenhouse occupation




How to choose ?

CHOICE

Cultivation conditions (crop

rotation, sanitary problems…)

Inter cropping Period

Seeds (availability,

price)

Inter cropping duration

Main goal of the cover crop ?




Growing cover crops in summer Poaceae

SORGHUM/SUDANGRASS -50 kg/ha or less -Cycle : short to long (cuttings)

PEARL MILLET (Pennisetum glaucum)

-30 kg/ha or less -Cycle : short to long (cuttings)

Panicum germanicum -30 kg/ha or less -Cycle : up to 50 d -Less weed suppression

Fast growth – high biomass - Weed suppression – High temperatures




Growing cover crops in summer Brassicaceae

FODDER RADISH (Raphanus sativus)

-20 kg/ha -Cycle : short (30 d)

TURNIP RAPE (Brassica rapa oleifera)

-10/15 kg/ha -Cycle : medium (40 d)

MUSTARDS (Sinapis alba, brassica juncea)

-10/15 kg/ha -Cycle : short (30-40 d)

Fast growth – high biomass - Weed suppression – Diseases (rhizoctonia) and pests (flea beetle,

diamondback moth) risks




Growing cover crops in summer Polygonaceae

BUCKWHEAT (Fagopyrum esculentum)

-40/60 kg/ha -Cycle : short (30-40 d)

Fast growth – Soil structure - Weed suppression – high T°C CMV risk




Growing cover crops in summer Fabaceae

FIELD PEA (Pisum sativum arvense)

-150-200 kg/ha -Cycle : 40-50 d

COWPEA (Vigna sinensis)

-80 kg/ha -Cycle : 40-50 d

Tonga bean, hyacinth bean

(Dolichos lablab, Lablab purpureus)

-80 kg/ha -Cycle : 40-50 d)

Fast growth – High temperature – N2 fixation Medium weed suppression : to be mixed with other plants (stake)




Growing cover crops in autumn/spring

Basically, most of the cover crops used in open field can be used in the mild seasons under greenhouse : the references are numerous, and adapted to all the geographical areas




Poaceae: Italian ryegrass, rye,

oat, barley, wheat…

Brassicaceae: mustards,

radish, turnip…

Fabaceae: common vetch,

hairy vetch, field pea, crimson clover (t.i), beersem clover (t.a), lentil, horse bean…

Growing cover crops in autumn/spring

! Sclerotinia, slugs risk

! Sclerotinia, slugs risk

! Sclerotinia on rye in 2013




3. CULTIVATING COVER CROPS FUNCTIONNAL MIXTURES ?




COVER CROPS MIXTURES : WHY ?

The potential to fulfill all the cover crops benefits may be increased by using mixed rather than single species cover crops. Mixtures may also increase cover crop survival (soil, weather, pests conditions…)

Research on mixed species cover crops is in its infancy : many of the potential benefits are hypothesized rather than known.




COVER CROPS MIXTURES : HOW ?

Susan Tallman, USDA, W Sare

To reduce nitrogen imputs To add soil carbon and promote aggregation

To minimize compaction and move nutrients upwards

To provide ground cover to reduce weed establishment and evaporation




COVER CROPS MIXTURES : HOW ? Interest to mix species from different functionnal groups : - Improve overall performance due to their seedling

vigor, rooting behavior and environmental tolerances - Complementary development ex : erect cereal as a

stake for viney legumes (vetch, pea, cowpea…) - Complementary N content (C/N ratio) to manage N

release - Interest to mix erect plants for biomass with smaller,

shade tolerant, to compete with weeds




COVER CROPS MIXTURES : HOW ? And difficulties : - Good seed rates to allow each specie to grow

Brassica have to be sown with very low rates in the mixes - Seeds with different sizes require different depth of planting : difficult in

1 pass - The more species in the seed mix, the potentially more expensive…

17 species ?

More research is needed




4. GREEN MANURE versus COVER CROP ?




The cover crop can be used as a “dead mulch”

Some conditions : - Sufficient biomass (10 t/ha ?) - Growth stage of the CC / species choice to avoid regrowth (no herbicides !!!)

- Specific machinery

Many questions : - Subsequent crop nutrition ? - Pests and diseases development on decaying CC ?

As for the green manure, it will be implemented between 2 crops




The cover crop can be used as a “dead mulch”

Some publications

Much more research is needed, no references under greenhouse




A cover crop can be used as a “living mulch”

Cover crop sown before plantation : - Very high competition with the cash crop - Even with legumes CC (clover)

Undersowing : - Popularised by Iain Tolhurst and Eliot

Coleman - First results show no competition with

the crop ? - Not suitable for too dense foliage crops

(leafy winter vegetable) or sensitive to root competition (onion, radish…)

- One solution to implement a cover crop in greenhouses with longer cash crops ?

The cover crop is implemented during the cash crop

Cover crop between the cash crop raws




Thank you for your attention

Cover crops in OGH

cover crops (functionnal mixtures) in ogh

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