Crop rotation

I try to avoid gardening publications which provide simplistic crop rotation schedules. Most of these apply somewhat narrowly to vegetable plots, and fail to address the entire garden as a complex biological entity. They also tend to be inflexible with regard to the seasonal preparation and selection of individual plant species. Most of my understanding of crop rotation is derived from a combination of agricultural textbooks and practical garden experience. Over the years, I’ve attempted to develop my own system of garden rotations. I have enjoyed reasonable success on several private estates in the northern hemisphere and am presently adapting my approach to suit smaller gardens in a considerably warmer climate. I will describe the basic principles and benefits of crop rotation. For specific enquiries on this topic, please contact me by using the comments section that appears below this article.

What is crop rotation?

Crop rotation is an agricultural system where related species are grown together in one area which is harvested then replanted with a different family of plants the following season. In its various forms, crop rotation has been practiced for thousands of years. Roman influences upon Britain and Continental Europe contributed to the basic three field rotation which became widespread during medieval times. Initially designed to provide spring and winter cereals, the rotation schedule was later modified to include pasture, and high value crops like sugar beet, potatoes, and hops. In many respects, crop rotation improved agricultural production to a level which enabled states to expand and develop their political and economic stability. The historical impact of crop rotation was determined by a series of biological factors which remain relevant to anyone interested in growing healthy plants without the widespread use of toxic chemical treatments.

It is widely understood that families of plants have varying nutrient requirements and these will place certain demands upon the soil. One of the aims of crop rotation is to avoid a situation whereby similar soil nutrients are required by one family of plants over consecutive growing seasons. This can be achieved by rotating distinct plant families in a logical sequence. For example, vegetable crops in the brassica family (cabbage, broccoli, kale) are heavy feeders which require plenty of nitrogen for rapid leaf growth. At the conclusion of their growing season it is beneficial to replant the area with legumes such as peas, beans, and lentils. Legumes have fewer nutrient demands and actually initiate an enzymatic process which fixes nitrogen, improving its availability for future crops. In addition to preserving the nutrient profile of extensively cultivated soils, crop rotation can offer protection against various toxins which are released by plants themselves. When allowed to concentrate in a soil, these toxins may restrict the normal activity of soil microbes. This will eventually create an unsatisfactory environment for the recycling and utilisation of organic materials.

Controlling insects and disease organisms

Most of my efforts in developing plant rotation schemes have been focused on the control of nuisance insects and disease organisms. In order to survive and thrive, a majority of plant destroying pests and disease pathogens must concentrate and establish themselves within a particular territory. Insects are usually attracted to suitable host plants by visual characteristics, smell, taste, and other chemical signals. When their favoured crops are rotated to different locations, the destructive organisms have their breeding cycles disrupted. With few exceptions, juvenile insects and larvae are particularly vulnerable to relocation of their normal food supplies. In attempting to overcome the barrier of distance, many will be taken by garden predators such as ants, spiders, lizards, and birds. To control plant pests, rotation schedules must be flexible enough to accommodate the seasonal shifts which can result in the early or late arrival of new generations.

There are plenty of gardening books suggesting that plants should be grouped according to their susceptibility to certain pest and disease conditions. In my experience, there is little to be gained from this approach. On many occasions I have discovered that susceptibility cannot be entirely inherent in the plants themselves. I have seen strawberry plants thrive in one garden location while alternately sited runners from identical stock were repeatedly destroyed by aphid. It appears that functional susceptibility is largely dependent upon the complex interactions between local garden conditions, pest populations, and natural plant resistance. The correct appraisal of local garden conditions should include aspects of seasonal climate, plant distribution, soil structure, composition, including the variety and concentration of microbial soil organisms. The majority of pest populations are more readily controlled by interventions which directly influence these factors.

Rather than focusing upon the particular susceptibilities of individual plant species, pest problems may be solved by a broader process of observation and analysis. The aphid infestation was eventually corrected by adapting the rotation schedule to avoid open sites. By rotating strawberries across locations with varied assortments of cover vegetation, we provided suitable accommodation for the aphid’s natural insect predators. Within several seasons, the aphid population was diminished to a harmless capacity.

The organic application of crop rotations can also be based on obtaining maximum efficiency and productivity with minimal risk to long term soil fertility and the environment. A carefully planned rotation schedule can also reduce some of the physical work associated with herb and vegetable gardening. Carrot and root crop seedlings require loose soil. Instead of digging the ground, the seedlings can be directly planted to a section which has already raised shallow root crops like lettuce followed by deep rooting plants like tomatoes.