Andy Dibben is a triallist in the field lab testing strip till in a living mulch. In this article, he outlines the challenges and benefits of this approach, his technique, and what he's learnt so far.
Farm – Abbey Home Farm.
Grower – Andy Dibben.
Scale – 15 acres of horticultural crops,
Crops – 90 different kinds of fruit and veg.
System – Organic cover crop based system, Field scale, market garden and protected cropping.
Route to market – Farm shop and Café.
Introduction
We have been producing Organic vegetable crops at Abbey Home Farm for over 25 years, the system was established by grower Keith Denning under the guidance of Iain Tollhurst (Tolly). Not surprisingly due to Tolly’s influence the system established was originally based around and continues to rely on building and maintaining soil health with extensive and intricate use of green manures. Outdoors rotations all start with with 2 or 3 years of mixed species green manures to build fertility for the following years of cash crop production. During the cash crop stages of the rotation green manures are still extensively used for protecting soils and recycling nutrients, both by undersowing vegetable crops and sowing over winter green manures after crops.
Strip tillage - the concept
As our knowledge on soil health and botany develops, it becomes clearer and clearer that few if any plants prefer growing in isolation as a monocrop. All life interacts with each other and if managed correctly allows for a beneficial symbiosis to occur. From this starting point I have become increasingly interested in the trials happening around the world into strip tillage, especially those that involve strip tilling an established green manure and then drilling seed or planting young plants in tilled strips between the green manure. The potential of this technique is not to be understated. Currently whole fields are often ploughed or sprayed off with herbicides to prepare a field before planting. Both these techniques can lead to problems. If the strip tilling technique can be refined, it would lead to half the field being cultivated, leading to much better soil health, less erosion, boosting biodiversity, reducing labour time, diesel costs, and emissions associated with tillage.
For many years I have been a keen user and promoter of green manures for many reasons, however it has always bothered me that I often cultivate a green manure to then establish a cash crop and then undersow again with another green manure. The concept of having a green manure that stays down for a full rotation and has cash crops accurately planted into permanent tilled strips is a very attractive one, it even potentially offers the opportunity to cash crop the system every year with no need to rest fields for fertility building phases. Something we do a lot of at the moment. In order to investigate the potential of strip tilling we have been trialling the system on a small scale on the farm over the last 3 years.
Trialling the concept
We have started trialling the technique on a small scale, although the most meaningful potential of this approach I believe would be realised on field scale Organic systems that still rely on ploughing, this would require investment in expensive purpose designed strip tillage machinery. As a relatively small farm with limited budgets, we need to solidly prove the concept works to deliver at least the same commercial results we are achieving at the moment with a plough. Therefore we are experimenting with the technique in our market garden. We have focused the trials on courgettes and legumes. So far with mixed results.
Technique
Green manures for strip tilling are established the year before cash crops, we have been trialling two different species mixes for strip tilling into. The first mix is white clover and yellow trefoil, which is the mix we often use to under sow crops. The second mix we have been trialling and slowly modifying is a much more diverse mix including a variety of clovers, herbs, flowers and grasses. The thinking behind this is that if we can make it work it has potential longevity to stay in for a whole 5 year rotation more effectively that just white clover and trefoil that probably wouldn’t last as a dense sward for 5 years.
Once established we now initially prepare strips in the autumn before cropping the following year, we have used different techniques for initial strip preparation, which technique we use has often depended on what the weather allows. Either we use our 80cm power harrow running on a BCS two wheeled tractor, we remove the outside pair of tines from each side of the power harrow, reducing the width of the tilled strip to 40 cm, we have also fitted baffles under the hood to prevent soil spilling outside the strip. In wet years we have also prepared the strips with narrow sheets of synthetic mulch (Mypex) layed again in the Autumn. Depending on crop choice strips are spaced either 75cm apart centre to centre (Legumes) or 1.5m (courgettes). The long term plan would be having established strips at beginning of rotation, that they would be tilled 4 times a year, Early Spring, just before crop, just after crop and just before winter. Aiming to keep strips weed free and with plantable tilth. Crops are then planted and into these strips and weeded with hand tools, we envisage that on a field scale that weeding could be carried out with a modified steerage hoe fitted with discs to keep soil in the strips. The living mulch between the crops is managed currently with a pedestrian or ride on mower depending on strip spacing. On a field scale specialist tractor mounted inter row mowers would need to be designed.
Potential challenges
The interaction between cash crop and living mulch is the key area of focus here, if successfully managed this should realise the potential benefits of cropping multiple species in close proximity and unleashing the benefits of symbiotic relationships between root exudates, thriving soil health and cash crop growth, however if not managed correctly this will lead to the living mulch outcompeting the cash crop.
Above ground – the interaction between cash crop and living mulch is defined by a process called ‘Shade avoidance response’ (SAR), this is response is triggered when the cash crops senses competition from nearby plants outcompeting it for light, if triggered the cash crop will alter it’s hormonal behaviour, putting more effort into vertical growth and less energy into root development, this will result in leggy weaker crops and impact yield significantly. This challenge is managed by active mowing of the living mulch during establishment allowing cash crop to become dominant species in the area and continuing to grow steadily and in same way they would in bare ground.
Under ground – Competition between the roots of cash crop and living mulch for water and nutrients is a more complex area of the system, this can be managed through intelligent species selection for the living the mulch and potentially using machinery to keep the roots of living mulch from invading the strips where cash crop is planted, especially during early stages of cash crop establishment. This the part of the system where we are experiencing the most problems currently. We initially used cocksfoot in our more diverse mix, but this resulted in far too much underground competition, we have now switched Cocksfoot for Sheep’s fescue which is far less dominant. However we are still experiencing excessive competition from living mulch, it would appear the key area of competition is for nitrogen, especially early in cash crops growth.
Results so far
After two years of trialling this system, both years trialling the two different living mulch mixes against a control plot where we are cultivating whole area. We have had mixed results and definitely not mastered the approach yet.
Courgettes – We have not yet achieved successful commercial performance in a living mulch with this crop, the first year the courgettes in both living mulch plots failed to reach harvest and suffered significant early problems in establishing, plants were small and weak and looked to be struggling to source enough nitrogen. In the second year Courgettes in the white clover and yellow trefoil plot were significantly slower and smaller than the control plot, however they did reach harvest point although yields were not acceptable for a commercial operation. The courgettes in the diverse living mulch again failed to reach harvest, small and lacking vigour they too were definitely struggling to access enough nitrogen early in there establishment.
Legumes – We have had more success with legumes in this system, Broad Beans, French climbing beans, Runner Beans and Californian wonder bush beans, have all successfully produced acceptable commercial yield of beans. However they have been slower to do this than a conventionally prepared tillage system. We put the better results from the legume crops down to the fact that legumes produce 80% of their required nitrogen themselves, there slower start we put down to the time for the symbiotic relationship with bacteria to get going in their roots.
Conclusion
So far the potential promise of this technique has definitely not been realised, however having seen effective use of this technique in chemical agriculture, we are determined to keep investigating and improving. Our focus next year will be to problem solve early nitrogen availability for the cash crop. We hope to do this by applying a larger amount of compost to the strips at planting to offset nitrogen robbery by the living mulch. We are also interested in experimenting with the width of the tilled strip and using discs to keep living mulch roots away from cash crop during establishment. Perhaps also look at trialling other crops, other members of the trial group have had better results with brassicas, although again crops have been slower to establish and reach harvest point. Perhaps courgettes that we had picked because they are such a strong vigorous crop, might actually be suffering exactly for this reason, their vigour being there downfall in an environment where they are struggling to access adequate nitrogen. Lots more work to be done to make system work, but if successful the rewards are potentially so big that it warrants continued trialling and refining.
Andy Dibben – Head Grower, Abbey Home Farm.