An introduction to cover cropping. Tim Martyn

Transcription

1 An introduction to cover cropping Tim Martyn

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8 Freshwater only 35 g P per litre ` OR 35 millionths of a gram

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13 160m 3 ha 10m 3 ha 433m 3 ha 381m 3 ha SS 213kg ha 9kg ha 719kg ha 1551kg ha PP 859g ha 37g ha 3029g ha 5762g ha

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19 Catch and Cover Crops An extra crop between two of the main crops in a rotation Soil protection (min- or no-till drills) Fertility building Supplementary stock feed Replacement of main crops that have failed Livestock for grazing or folding Sow early for improved establishment/effect

20 Pros Building soil organic matter (SOM) green manure, particularly on sandy soils Reducing suspended solids in runoff retaining soil Nitrate scavenging early est. best Improving soil structure Aeration/Drainage SOM & soil structure increases water retention Weed suppression

21 Cons Reliability of establishment early establishment best Appropriate soil conditions for establishment not usually suited to heavy or dry land Depletion of soil water in spring Clean land to minimise weed control problems Fertilise - Uptake of soil plant available nutrient Possible delays in seedbed preparation

22 Carbon:Nitrogen Ratio Bacterial biomass has a C:N ratio of 6:1 Well decomposed humus between 10 and 12:1 Other organic remains have much more C Breakdown of material having wide C:N ratio, such as cereal straw (140:1), is slow unless N is readily available Soil bacteria uses plant available N (mineral or inorganic N) in the decomposition process N used (immobilised) becomes organic N, mostly unavailable to the plant. However, it can be made plant available at a later date by a process called mineralisation.

23 Pests and Diseases Must not harbour pests or diseases of any main crop in the rotation, e.g. rape is highly susceptible to clubroot Do not use brassica cover crops in rotation with beet Rye, IRG or Westerwold preferred in rotations including cauliflower, swedes or OSR Green bridge if grasses present aphids and cereal fungal diseases Slugs

24 Source: Nickersons

25 Cover Crop Seed Costs Crop /kg Seed rate, kg/ha Seed cost, /ha Forage rape (treated) Mustard Phacelia Westerwolds Red clover Forage rye Buckwheat

26 Summary Remove compaction avoid soil destabilisation Early establishment following harvest when soil temp. higher, prior to winter, to maximise root and canopy growth Good seed to soil contact imperative together with minimal soil movement Avoid smearing if slot seeding waterlogged slot Care required with drill selection

27 Cover and Catch Crops

28 Crop Options IRG or rape on a scarified corn stubble following harvest, ploughed in, grazed or sprayed off then strip-tillage Rye/IRG/Westerwolds RG establish best when sown in early autumn White or Ethiopian mustard between harvest and drilling Oilseed radish Legumes and Phacelia Mixtures/undersowing consider following crops

29 Further options Buckwheat - Fast establishing producing a thick bushy plant which sheds seed in the Autumn. Allelopathic effects? Phacelia an extremely fast growing crop. It s dense growth habit smothers out most weed competition. Care must be taken to destroy the crop as Phacelia easily reseeds itself. Hybrid Forage Brassicas a Forage Rape x Kale cross that is quicker growing than Kale and more winter hardy than Forage Rape. Forage Brassicas are ideal for late sowings. Yellow Sweet Clover - a biennial plant which can last for several years due to it s ability to regenerate itself through shedding seed. Yellow sweet Clover has a sweet smell and produces large amounts of nectar making it highly attractive to insects which in turn attract birds. Best sown with an annual companion crop to produce a cover in first year. Texsel Greens an easy to establish, quick growing crop which is frost hardy and ideal for suppressing any weeds

30 Nitrogen Fixing and Accumulating

31 Yield t dm / ha Legume % N in plant kg / ha N fixed kg / ha White clover/grass Red clover/grass Lucerne/grass Beans % Vetches %

32 Nitrogen Scavenging & Accumulating

33 Nitrogen Scavenging Work by IGER found growth over-winter of rye to be generally better than Westerwolds or IRG Consequentially higher herbage N recovery Rye has greater frost tolerance (leaf proteins) Rye can be established later in autumn but early drilling gives better establishment (regional) Establishes better in free-draining (aerobic) soils Faster earlier est. means higher LAI

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35 Nematode Reduction Nematode reduction oilseed radish and mustards Harvest date and the time available to sow the cover crop Weather most cover crops are best sown in July and August and will need moisture to germinate Soil type (determine the sowing rate) Ability to mow and incorporate the cover crop in late autumn

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37 Biofumigation Plant breakdown releases chemical substances known as Isothiocyanates (ITC): Ethiopian and white mustards, oilseed radish Prussic acid production : Sudan grass Used to control, Fusarium, Pythium, Rhizoctonia fungal diseases and soil borne insects. Likely to reduce beneficial mycorrhizal soil fungi Works well on light textured, low organic matter soils.

38 Benefits of Biofumigation Crops Natural Control of soil borne pests but also beneficial ones too Traps and re-cycles nitrogen via the plant Improves soil structure by increasing organic matter Improved soil water retention Reduces soil erosion

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44 Yield of grain (t/ha, 15% moisture) of wheat grown with and without N, either conventionally or in a clover understorey Treatment Bi-cropped, no input Bi-cropped, low input Conventional, moderate input Conventional, high input Source: Burke et al

45 Bi-cropping - Pros Permanent understorey of a companion crop, i.e. white clover. Crop drilled using a Hunter stripseeder (strip-till drill) White clover may help to interrupt spread of splash borne fungal disease spores Non-inversion of soil promotes beneficial invertebrates and mycorrhizal fungi Uniform green canopy may reduce aphid alighting (

46 Bi-cropping - Cons Competition for moisture, sunlight and nutrient by companion crop Restricts choice of herbicide a.i. Can harbour pests (slugs, etc) but also provides cover for beneficial predators (ground beetles) balance required

47 Summary Soil protection conservation tillage Nitrogen fixer or scavenger Pest reduction Consider following crop when selecting CC Bi-cropping Environmental benefits beyond reducing DWPA wildlife