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Protected Cropping: Using Green Manures

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

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Protected Cropping: Using Green Manures

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  1. Protected Cropping:Using Green Manures

  2. 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

  3. Content overview • Costing Green Manures • Comparison of N sources • Additional benefits • 3 examples

  4. 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?

  5. 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

  6. Cost per m2 – based on 160m2

  7. 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.

  8. Comparison of N sources For 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)

  9. 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?

  10. 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.

  11. 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.

  12. 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 >

  13. 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

  14. 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

  15. Phacelia • Fast growing • Shades out weeds • Flowers attract beneficial insects • Soft tissue = rapid breakdown • Cut before seed set • 3g / m2

  16. Quick Mix – 4 Weeks

  17. 26th Aug – 22nd Sep

  18. 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

  19. Sweet Clover • Fast growing N-Fixer • Relatively quick to germinate • Extensive root system • Rapidly nodulates when inoculant is used – advised! • Tall growing, competative

  20. 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

  21. Sweet and Crimson Clover

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

  23. Clover – 7 weeks

  24. 10 weeks

  25. 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.

  26. Tares / Vetch • Excellent late or Winter sown • The best option for N-fixing before Summer crops • Deep rooting • Dense foliage

  27. Vetch and Rye – 10th Jan

  28. 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.

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