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/m 2 /y Cost of seed, labour, machinery to establish a Green Manure Row and Hoe= 30p/m 2 Broadcast= 10p/m 2 Cost of water (+/- 20p) = £1.20/m 3 Average turnover (wholesale value) = £20/m 2 /y

Cost per m 2 – based on 160m 2 SpaceLabour, seed, tools WaterTotal Summer legume 3 month 60 p30 p16 p£1.06 Quick non-leg’m 2 month 40 p10 p9 p£0.59 Winter legume 5 month 100 p30 p6 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 sources For 6p / m 2 … Restricted pelleted fertiliser = to 90KgN/ha 9%N) Liquid fertiliser = to 18L N/ha 6%N) Compost = to 200KgN/ha (2 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/m 2 ) Ameranth (0.3g/m 2 ) Phacelia (1.2g/m 2 ) 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 / m 2

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 / m 2

Phacelia Fast growing Shades out weeds Flowers attract beneficial insects Soft tissue = rapid breakdown Cut before seed set 3g / m 2

Quick Mix – 4 Weeks

26 th Aug – 22 nd Sep

Summer N-Fix Sweet clover/crimson clover 50/50. Sown in 10” rows with earthway seeder radish/leek disc (= about 2g / m 2 ). 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 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 – 10 th 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.