Crop Rotation

One of the basics of organic vegetable production is the rotation of crops, i.e. the growing of a succession of different crops in the same bed over the course of a few years. This doesn't mean that one year we can only grow brassicas - each bed is at a particular stage in the rotation, allowing many crops to be grown simultaneously in any number of beds.
Why? The predominant reason is the management of pests and diseases (soil-borne pathogens). Because pesticides cannot be used in organic farming (and arguably should not be used full-stop!), crop rotation is one of the main ways of controlling pests. Each crop family has its particular nemesis - club-root for brassicas, nematodes for solonaceae, and scleretonia for alliums, for example - so by rotating crops we repress the pathogens by removing their food source, thus keeping diseases at minimal, and hopefully manageable, levels. Crop rotation also allows better management of weeds, fertility, and soil structure, all of which are affected differently by different crops.
How? Various rotations can be practised, such as a rotation based on rooting depth for example, but we choose to rotate our crops according to crop-family, based on each family's disease potential and preferred soil fertility level (this is the most common system within organic production). We follow a 4-year rotation, though recommended time-spans vary from 3 to 6 years. This entails keeping records of what has been grown where in previous years, so we know what to plant next.
Year 1: - The solanaceae family - potato, tomato, capsicum, and aubergine. - By far the largest area is dedicated to potatoes. - The large leaves of potato plants suppress weeds. - Solonaceae demand very high soil-fertility.
Year 2: - The brassica family - cabbage, cauliflower, broccoli, and brussels sprouts. - Brassicas require high soil-fertility, but lower than solonaceae.
Year 3: - The legume family - peas and beans. - Legumes are nitrogen-fixing, so increase soil nitrogen levels and therefore fertility. - Legumes require lower soil fertility than brassicas.
Year 4: - The allium family - onions, garlics, and leeks. - Alliums require the least soil fertility of all the crops.
The drawback of a rotation like this is that, if followed strictly, in any year one quarter of your land is dedicated to each of the four crop-families. We therefore build some flexibility into the system, whilst never straying from the 4-year rotation, which basically means slotting additional crops into stages of the rotation as and when beds become available. These additional crops are less problematic where pests and diseases are concerned, and include (but not exclusively):- - beans, sown outside the legume stage, often planted to grow up the stems of maize, or as a second crop after the early potatoes have been harvested - beans can suffer from root-aphid (careful rotation is needed to avoid the build-up of this soil-borne pathogen); - maize; - leaf-beet (swiss chard); - beetroot, though not as successor or precursor to leaf-beet as both crops are members of the beet family; - lettuce, which can also suffer from root-aphid; - cucurbits (cucumbers, pumpkins, melons etc..); - carrots, which can be affected by carrot root-fly, an air-borne pest; - parsnips. These crops can either be substituted for one stage of the rotation (for example, instead of planting 4 beds of brassicas, plant 3 of brassicas, and in the fourth bed plant maize and beans), or planted as a late crop once the early crop has been harvested, the early crop having been within the rotation (for example, in the allium stage, harvest the over-wintered leeks in spring, then plant beetroots for harvesting later in the season). We also have perennial beds, such as artichokes, raspberries, asparagus, herbs, blackberries etc.. which do not form part of the crop rotation.
Information sheet created by Hotel Posada del Valle. (