The majority of soil breaking actions are carried out to produce a seedbed and establish a crop, although activities such as subsoiling, soil aeration and mole ploughing are carried out as remedial actions primarily for compacted soils. Weed suppression with hoes and other mechanical weeding machinery also break the soil. As we learn more about the impacts of breaking and turning over the soil, the need for such cultivations are increasingly being questioned.
More and more farmers are seeking ways of minimising their cultivations to limit this damage. Whilst groups of farmers are actively investigating methods to reduce reliance on the plough, to date most organic farms use it to control weeds, and incorporate organic matter from one crop, in preparation for the next. Despite the disruption caused by ploughing, organically farmed soils have an average of 21% more soil organic matter (SOM), so if you get the machinery and timing right, appropriate cultivation can be an important part of building healthy soils.
The damage to soils from machinery will depend on the time of year, depth of cultivation and frequency of such actions, as well as the soil type itself. Such actions turn the structure of the soil and all the SOM producing flora and fauna upside down. Repeated use of machinery can reduce SOM, as soil microorganisms become more compromised and less able to re-establish their ecosystem.
Weed control by ‘out competing’ or avoiding weed seed germination should be the first port of call. Undersowing crops or bi-cropping offers effective ways to reduce weed seed germination, alongside the use of cover crops prior to crop establishment. One way to think about weed control is that if we need to use a mechanical weeder, it should be because all other techniques to prevent weed seed germination have failed.
Mechanical weed control can be highly damaging to soil microorganisms, particularly fungi. Ideally you want to limit cultivations as much as possible by optimising timing and making sure that the technique used is as benign as possible. Weed control techniques like flaming, hand pulling (on bed weeders) and brush weeding, tend to be less disturbing than tractor pulled hoe or mechanical cultivators.
Subsoiling is the chief cultivation method to address deep compaction. Other techniques include mole ploughing and soil aeration. These are used to remedy problems caused by previous cultivations, machinery use on land at times of year when the soils were incapable of carrying such a load, or where livestock poaching has occurred causing soil pans.
Such cultivations can improve soil drainage, root penetration and, in some cases, increase water availability. Deep rooting green manures, such as lucerne and chicory, can also help to break up soil structure. All cultivations will cause disturbance to soil life and should only be used where there is clear evidence of compaction.
When using any technique designed to alleviate compaction, timing of operations is key to avoid smearing and further damage to soils. As well as damage to soil structure, incorrect timing of cultivations can lead to nitrogen leaching. In organic rotations, autumn incorporation of grass clover leys is the riskiest time for nitrate leaching as drainage rates may be high and crop growth slow. So, where possible, incorporate leys for spring cropping and consider fields adjacent to watercourses as your priority.
Arable and Soils Advisor
Jerry has experience in arable and mixed farming having run the family farm in Devon for 25 years. The farm was initially a dairy farm, before converting to organic and being run as a beef, sheep and arable unit. Alongside farming he converted a range of farm buildings into a holiday cottage complex, was chairman of a local farmer owned co-op grain store and became involved in the national grain supply chain. Jerry can often be found wherever the Exeter chiefs Rugby team are playing!
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