Rotation explained, with Brian Callaghan
Now Brian Callaghan’s new allotment has been cleared, he is marking out the rotation areas
With the main sowing and planting period rapidly approaching, it is time to begin marking out the rotations on my new allotment. It is timeconsuming and can be difficult. Why bother with this?
Different crops have different soil fertility requirements and grouping these plants together just makes it easier to provide the fertility they require in order to maximise growth. Cultivations, growing of green manures, applications of organic matter, and even watering, are all made simpler by the use of rotations.
Providing just enough food to meet the needs of the crops minimises wastes of time, energy and other resources and helps reduce pollution from run-off of excess fertiliser. Members of the legume family, for example, have the ability to ‘fix’ some of the nitrogen that is present in nearly 80% of the atmosphere and deposit it in nodules attached to their roots. This ‘free fertiliser’ is then made available to the growing plant and any under-sown lettuce etc, plus residues may also be left for the following crop. Brassicas, on the other hand, are hungry for nitrogen and usually follow the legumes in a rotation to mop up these residues.
Pest and disease control
The interdependent working of the natural world ensures that wherever a crop is grown for our needs, a food source, or habitat, is also provided for less-desirable organisms such as aphids, slugs, eelworms, onion rot, club root etc. While outbreaks of aphids and slugs can quickly be brought under control, diseases such as onion white rot and club root can remain active in the soil for decades. With the gradual withdrawal of chemical controls for these problems, even conventional growers are compelled to pay close attention to better husbandry in the form of rotations to help ensure these problems never develop to damaging levels.
Some crops have other effects on the soil that can be utilised to provide better growing conditions for the following crop. For example, the mechanical cultivations involved in potato production and the dense crop canopy it develops helps suppress weed development and leaves the soil in a cleaner condition than before it was cropped. It follows that crops which often struggle with weed problems, such as carrots, can often benefit if they are preceded in a rotation by ground-clearers such as potatoes.
Although it is possible, in principle, to achieve a perfect rotation, there is no need to be despondent if it does not run perfectly to plan. Poor seed germination, pest and disease attacks, weak growth etc all conspire to leave unplanned gaps which are often filled with very distant cousins of those that should be in that section of the rotation. Further, every year I struggle to construct a growing plan which can accommodate our household preference for far more potatoes than brassicas. Devising a growing plan which can accommodate the differing sized rotations leaves me with an annual puzzle I rarely solve. Do the best you can in the circumstances and leave perfection for the next world.
Potato foliage and cultivations help keep the soil clear of weeds
Time spent removing perennial weeds now is well spent
Initial cultivations on the four-year rotation plan Inset: Brian’s cultivations uncovered some Jerusalem artichokes