Protected Cropping:Using Green Manures

Why?

• Compost / manure availability or quality may fall short.

• Improvement of wider soil health.

• We need to reduce reliance on imported nutrients while maintaining productivity and health

Content overview

• Costing Green Manures

• Comparison of N sources

• Additional benefits

• 3 examples

Economic viability

• The main reason for not using glasshouse green manures is the space and time occupied, can they be viable and how might we measure the benefits?

• When and how might a green manure be utilised with minimum impact and maximum benefit on production?

An attempt at figures

• Fixed cost (glasshouse) = £2.50/m2/y

• Cost of seed, labour, machinery to establish a Green Manure

Row and Hoe = 30p/m2

Broadcast = 10p/m2

• Cost of water (+/- 20p) = £1.20/m3

• Average turnover (wholesale value)

= £20/m2/y

Cost per m2 – based on 160m2

Space Labour, seed, tools

Water Total

Summer legume3 month

60 p 30 p 16 p £1.06

Quick non-leg’m2 month

40 p 10 p 9 p £0.59

Winter legume 5 month

100 p 30 p 6 p £1.36

Variability

The costs do not include potential lost production, this is seasonal and market dependant.

eg. At Hankham we crop less protected area in the Summer due to increased productivity and reduced box numbers.

This makes a summer green manure more viable and a winter one less so.

Comparison of N sourcesFor 6p / m2…

•Restricted pelleted fertiliser = to 90KgN/ha

(100g @ 9%N)

•Liquid fertiliser = to 18L N/ha

(30ml @ 6%N)

•Compost = to 200KgN/ha

(2 Kg @ 1%N – PAS100 green waste)

Interpretation• Can N % in compost, solid and liquid

fertilisers be compared? (C:N ratio is more relevant for compost)

If not what use are these figures?

• Can we determine how much N a green manure may contribute – research needed

• What about crop health and the wider system, can these be measured and at what value?

Never mind the b******Observed benefits of a green manure

Where correctly managed…

•Improved soil structure

•Improved crop health

•Increase in soil OM

•Provision for beneficial insects (nectar)

•Reduced inputs, the opportunity to apply inputs with discretion and an improved incorporation into plant/soil system.

3 tried and tested

• Quick Mix – 2-3 month non-leguminous mix, fast growing, weed suppressive and reasonably drought tolerant.

• Summer N-Fix – 3-4 month, 2 clovers, requires weed control and inoculant, good potential for N and OM

• Winter N-Fix – 5-6 month, requires weed control, good before hungry summer crops.

Quick Mix

Use: Buckwheat (4g/m2)

Ameranth (0.3g/m2)

Phacelia (1.2g/m2)•Sow anytime from April – Aug•Broadcast buckwheat separately.•Perhaps mix sand with small ameranth/phacelia seed to assist even sowing.•Can be incorporated from 6 weeks >

Buckwheat• Fast Growing• Shades out weeds• Attracts beneficial

insects• Phosphate accumulator• Will germinate well in

decomposing crop debris

• Slow to form viable seed• 12g / m2

Green Ameranth

• Fast growing• Drought resistant• Large woody plant if

allowed to mature = possible N lock-up

• Will not seed in long days

• Buy as ‘grain’• 0.5 – 1g / m2

Phacelia

• Fast growing• Shades out weeds• Flowers attract

beneficial insects• Soft tissue = rapid

breakdown• Cut before seed set• 3g / m2

Quick Mix – 4 Weeks

26th Aug – 22nd Sep

Summer N-Fix

• Sweet clover/crimson clover 50/50.

• Sown in 10” rows with earthway seeder radish/leek disc (= about 2g / m2 ).

• Use wheel hoe when clover is 3-4”.

• Flail mow and incorporate at 10 weeks, or cut to allow regrowth

• Can be undersown with Quick Mix when hoed to increase bulk

Sweet Clover

• Fast growing N-Fixer• Relatively quick to

germinate• Extensive root system• Rapidly nodulates

when inoculant is used – advised!

• Tall growing, competative

Crimson Clover

• Fast growing N-Fixer• Relatively quick to

germinate• Good amount of

foliage• Good short term N-fix

potential• Easy to destroy• Will regrow from cut

Sweet and Crimson Clover

Weed control with Glaser ‘Pico’ wheel hoe – 3½ weeks

Clover – 7 weeks

10 weeks

Winter N-Fix• Sow as for Summer N-Fix but use 1002-14

disk for beans/small peas

• Using 20% annual rye helps as a row marker and to fill out the tares

• Hoe just before tares start to ‘wander’

• Can be undersown with phacelia late Feb, to add volume.

• Good option to follow and/or precede Toms, cuc, peppers etc.

Tares / Vetch

• Excellent late or Winter sown

• The best option for N-fixing before Summer crops

• Deep rooting

• Dense foliage

Vetch and Rye – 10th Jan

Conclusion• Green manures are potentially an

expensive way to build fertility in protected systems

• With rotation planning and market consideration this cost can be reduced

• More research is needed to measure tangible benefits.

• Other strategies may further improve viability. Eg. Under-sowing, mobile structures, making compost from field green manure cuttings.