Tillage
Soil cultivation or tillage in its various forms has long been the mainstay of weed control and is the most effective way to reduce the weed seed bank. Seeds are encouraged to germinate and then the soil is cultivated mechanically to kill off the plants. The mouldboard plough is the traditional implement for burying weeds and crop residues as ground preparation for establishing a new crop. One piece of research showed that the annual loss of seeds from a natural soil weed seedbank (with no addition of fresh seed) was 22% with no cultivation. When the soil was cultivated twice a year the annual loss was 30%, and when cultivated four times it was 36%. However, it is not just the cultivations associated with the post-harvest incorporation of crop and weed residue that have weed control benefits. The method, depth, timing and frequency of cultivation may influence the composition, density and long-term persistence of the weed population.
Tillage is often divided into three types: primary, secondary and tertiary. However there are many operations that do not easily fall into these categories or span them all. We have provided an outline of the main tillage types below (see our topic sheet as well).
Primary tillage: is the principal cultivation operation before crop establishment. The main choice is between plough or non-plough systems (reduced or minimal cultivation, conservation tillage, no-till, direct-drilling etc. (see below)). A range of machinery is available for primary tillage and some combinations can even work a stubble down to a seedbed in a single pass. Ploughing is seen as a method by which weed seeds can be buried below the depth from which they are capable of germinating, and it is sometimes said that ploughing can be used to bury a weed problem. This is particularly useful for small-seeded or annual grass weeds, which are often short-lived and may survive being buried. But this short-term solution to poor weed control in a previous crop often leads to long term problems due to the persistence of the buried weed seeds in the soil seedbank as viable seeds may be brought to the surface by ploughing in subsequent years and will germinate if conditions are suitable.
Reduced tillage: the concept of direct drilling crops without resorting to ploughing became popular after the development of the non-residual herbicides but recently, there has been renewed interest, primarily out of concern for soil conservation. Under reduced tillage there is better control of soil erosion, conservation of soil moisture and more efficient use of fossil fuel. However wind disseminated and perennial weed species can increase and volunteer weeds are also likely to be a problem. However, not all soils are suitable for reduced tillage and less nitrogen may be made available to crops where cultivation is reduced to a minimum
For more information on reduced tillage please go to our page on reduced tillage or see our factsheet.
Many organic farmers find it impossible to dispense with the plough routinely. Each method of cultivation has its advantages and disadvantages and the principle should be to use as many different types of cultivation as possible over the rotation which prevents any one type of weed getting the upper hand. Finer seedbeds produce more weed seedlings but a smooth surface makes direct weed control easier. Larger clods of soil produce fewer weed seedlings but the rough surface gives emerged weeds protection against direct weeding operations.For more information follow the link for a discussion on ploughing and reduced tillage.
Secondary tillage is used to prepare seedbeds and leave a level surface for drilling. Typically it involves disking or harrowing to a depth of 10 cm. Rotovators and power harrows are also used and are able to prepare seedbeds even when ploughing has not been carried out. Implements are available that can combine shallow seedbed preparations with some deeper cultivations in a single pass. Others can loosen the soil below the surface while leaving the preceding crop debris on the soil surface.
Stale or false seedbed: is a seedbed prepared several days, weeks or even months before planting or transplanting a crop. The technique is recognised as a strategy suitable for organic farming and has been widely used for many years. The stale seedbed is based on the principle of flushing out weed seeds ready to germinate prior to the planting of the crop, depleting the seedbank in the surface layer of soil and reducing subsequent weed seedling emergence. The soil is cultivated about four weeks before drilling to stimulate germination and encourage the first, and usually biggest, flush of weeds. If irrigation is available it could be used to help
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Some mentions of deep ploughing, feel high quality shallow (4-6inches) more suitable to control weeds and preserve topsoil and soil life. Use subsoiler if compacted.
I spent heavily on dock spraying prior to conversion. It made them grow very well!!! Re-inforced my disillusion with synthetic farming.
Feel most effective weed control to be livestock and good fencing!
I'm interested in bi-cropping cereals/clover and grazing cereals, if you have any information please.
- Nick Adams 5---0-2006