Crop planning and crop rotation

The organization of crop rotation, i.e., spatial and temporal change of crops is an inevitable measure in the production of arable and horticultural crops. It has a great importance in organic production since it is a fundamental measure for pest regulation. It is an ancient human experience that long-term cultivation of the same crop accumulates diseases, pests and weeds in the soil, and thus this was the reason for the crop rotation introduction.

Consecutive cultivation of the same culture affects the structure of microorganisms’ population in the soil, i.e., it causes a decrease in the number of useful microorganisms and fauna, and the spread of pathogens in the soil. Although soil diseases are slowly transmitted and are initially limited to smaller areas and a smaller number of infected plants, by growing the same or related crops on the same land, the number of pathogens and infected plants will increase from year to year. A particular problem is the accumulation of parasitic nematodes and virus-vector nematodes in the soil. Some crops, such as potatoes, are particularly susceptible to nematodes, while the nematodes are virus vectors in others, such as grapevine. The most successful way to control nematodes is to change crops, grow resistant varieties and destroy their host weeds.

In continual cultivation, weed companions are widespread. Thus, it is required to alternately shift monocotyledons with dicotyledons, narrow spacing crops with wider spacing ones, sowing of broadleaf species after narrow leaf ones, etc.

When compiling the crop rotation, it is necessary to know the characteristics of each individual species, their tolerance to repeated cultivation as well as their interrelationships. It is mandatory to alternate non-related species with diverse growing requirements and characteristics, such as cereals, vegetables and root species, and to avoid the cultivation of related (potato/tomato, celery/carrot) species one after another. Cereals can be grown more often in crop rotation because they are not conducive to the development of diseases in the soil, while the crops that are susceptible to soil diseases should be planted in crop rotation rarely or always on a new surface. By alternating species that a particular pest feeds on with those that a pest does not eat is a long-term strategy to reduce their population.

A well-designed crop rotation will reduce the accumulation of weed seeds in the soil but will also reduce the appearance of new seeds. It is recommended to alternately grow fast developing species that provide high planting density with species that can be dug for a long time. If the population of perennial weeds grows despite all the measures taken, crop rotation is one of the few opportunities to reduce them.

Simultaneous cultivation of two or more crops on the same lot (consociation) has many positive crop rotation characteristics since it provides optimal use of available space in the field and helps with pest prevention. It can be organized in different ways, from sowing two or more species together randomly on the same surface, through sowing intercrops of one species in the interrow spacing of another, to alternating several rows of one species with several rows of another one. The growth of plants in consociation stimulates a rich and diverse life in the soil and thus helps to control both harmful organisms in the soil and weeds. The different species in the field provide a fast-growing and well-covering vegetation layer that prevents weed development. If another crop is grown in addition to a crop with a large space between plants, the vegetation layer on the soil will develop faster and less effort will be needed to regulate the weeds. For example, if tall crops that ripen earlier are grown with those that remain low to the ground and ripen later, the growth of the second crop will be slower at first, but after the end of a high crop growing season, the second crop will start growing more intensively and thus prevent weed growth.

The second crop can be used as the vegetation around the field to serve as a barrier to fungal spores, pests and virus vectors. Furthermore, some species may attract natural enemies or act as repellents for pests of the species with which they are grown in consociation.