THE ROLE OF CROP ROTATION AND PRE-CROP (HELLA SIMKO) 1. The definition of crop rotation and its elements

During agricultural production instead of monoculture cultivation (only one species is grown after itself for a long period at the same habitat without changing) (which depletes the nutrients and water resources of the soil one-sidedly and in the long run it impoverishes the soil making the soil less fertile at the end) it is worth applying crop rotation, alternation of crops because this way not only the yield can be increased but the quality as well, accordingly an environmentally friendly and sustainable agricultural production can be maintained. The more unfavourable the environmental conditions are, the more important it is to apply crop rotation.

Crop rotation means the efficient utilization system of the habitat by cultivated plant species; or rather it is a methodical plant-growing system, in which species follow each other in a pre-planned order both in space and time. Species showing reduced yield-capacity after having been cultivated after themselves, can be cultivated successfully only in crop rotation. When planning crop rotation there are four elements to be ascertained:

-Plant combination: that is to say, what kind of plant species are going to be cultivated at the (to some extent) uniform area of a given farm. While considering the range of species, the aim must be to involve more and more species into crop rotation in order to make the diversity-level higher. Of course this must be adjusted to the market demands.

-The ratio of species in crop rotation: Means defining the area-percentage of each species in their sector taken from the total area. In this case there are many factors to be taken into account, primarily the economic situation of the farm (profitableness, possibility of sales and of establishing power agriculture and manual labour supply etc.).

-Order of species: how the species follow each other (consecutively) on a given sector in the course of time. By configuring the order of plant species, the green crop effect of the different species is determinant.

During cultivation, each species is a green crop of the subsequent species (coming next in the crop rotation).

-Circulation (rotation): Means defining a time period, which tells us how much time has to pass until the species in question can be replanted to the same sector. The time interval, during which all of the species of the crop rotation progress the whole area and at the end return their initiative sector, is called the crop rotation interval.

3.2.2. Classification and types of crop rotations

Crop rotations, in which the composition and ratio of the cultivated species are particularly determined, the order of the species is worked out both in space and time, are called classical or coherent crop rotation . Crop rotations, in which we can not name concrete species but single out plant groups or families which possess the same agricultural conditions (for example: vexillars, intertilled crops demanding organic manure, industrial crops, Apiaceae species, etc.), are called frame crop rotation.

Crop rotations can be grouped according to the type of sectors. The sector (of a crop rotation) is the basic unit of the crop rotation area, on which a given portion of the species is cultivated. On the basis of the latter mentioned fact we can differentiate between simple-sectored crop rotations (where the sector of crop rotation is occupied by one species) and divided-sectored crop rotations (where at least one sector is planted with two or more species). Sectors within the crop rotation can be of different area.

Crop rotations can be divided on the basis of the crop rotation interval as well. There are short (lasting to 2-3 years), middle-long (lasting to 4-10 years) and long (lasting more than 10 years) crop rotation intervals. In the short crop rotation the species reach their original sector soon, so the isolation against pathogens can not be developed in due time. While establishing long crop rotations the organizational processes split into smaller acts and then transparency becomes deteriorated. Therefore in general, farms are aimed at organizing middle-long crop rotations.

If we are interested in involving perennial species into cultivation and crop rotation, which phenomenon is very frequent at cultivation of medicinal plants, the sector occupied by the perennial plant (e.g. lavender) is left out from the rotation during its cultivation and hence its sector is called sector out of rotation. After perennial plants become superannuated, they are grubbed out and then their sector reconnects into the rotation area.

Instead the area of the newly planted perennial plant becomes the sector out of rotation. On the basis of the latter mentioned facts, we can differentiate between crop rotations with and without out of rotation sectors.

Furthermore crop rotations can be irrigated or non-irrigated ones, agronomic (industrial, above 30 ha) or intertilled/horticultural scaled (2-30 ha). Crop rotations consisting of only medicinal plants are very rare; the medicinal plants are planted together with spiciferous plants at agronomic-scaled cultivations and primarily with vegetables at smaller farms.

3.2.3. The objectives of crop rotation and the aspects of its planning 3.2.3.1. Maintenance and development of soil fertility

The amount of organic matter given to the soil by cultivated plants is very varying. Some species leave less root and stubble behind, while others leave more amount of organic matter, which is replaced into the soil by tillage. There are differences according to the speed of root-decay of the species. Some species possess roots which decay faster; while others have roots which rot more slowly (the decaying root ensures the distribution of humus the most perfectly in the soil). It has been observed that the amount of the organic matter left behind in the soil is in positive correlation with the amount of crops gathered. By means of changing of species rooting to different soil levels, the water management of the soil can also be improved.

When planning crop rotation one must pay attention to applying species possessing different root-types, considering the amount, the type, the soil-netting ability of the root and even how deep it can get into the soil.

After species possessing slow-decaying roots it is suggested to plant species sown in spring. Species which root deeply in soil are: liquorice, hyssop, valerian, medicinal pumpkin, Malvaceae spp., sage etc.; species which root shallow in the soil are: tagetes, chamomile, marjoram and mint species.

The nutrition demand and the ability of nutrient intake of the different species are varying as well. Some species are able to intake huge amount of nutrients from the soil (e.g. angelica, peppermint, lemon balm, hop, lovage, medicinal pumpkin, sage and tarragon) and there are the vexillars which can countervail the nutrient deficiency of the soil. By applying vexillars the soil nitrogen-content can be regenerated, hence less ameliorator is needed during cultivation. That is why it is advisable to plant species possessing high nitrogen demand after vexillars in the crop rotation. Furthermore after species of soil-depleting type, the sowing of species with high nutrient demand should be avoided, and it is worth cultivating species with increased organic matter consumption (intertilled crops) after plants which contributed to the organic matter of the soil (perennials).

After species requiring farm-manure and being cultivated usually at the beginning of the crop rotation, the remainder plants follow according to their demand for farm-manure. Species requiring farm-manure are:

lemon balm, purple coneflower, rue, medicinal pumpkin, tarragon, rosemary; and species non-demanding for farm-manure are: woundwort, tagetes, ox-tongue, white mustard, marigold, poppy etc.

3.2.3.2. Maintenance and improvement of soil water management

The effect of plant species on the soil water management is important primarily in non-irrigated cultivations, while this effect is less determining under terms of irrigation. When planning the crop rotation we must make sure that after a water demanding species, a xerotherm species follows. Species of high water demand type are: angelica, common basil, peppermint, purple coneflower, lovage, valerian, marjoram and species of low water demand type are: Satureja, absinth, common thyme, lavender, sage, hairy mullein, rosemary, etc.

3.2.3.3. Maintenance and development of soil construction

If the cultivated species possesses wide leaves, their huge amount of green yield provides shade for the soil, and it can moderate the unfavourable effects of the weather on the soil. It also lowers the impact power of raindrops and the soil drying effect of the sun and wind. It can hinder nutrients from being washed quickly into the subsoil and it helps preserving water content of the soil. Furthermore it is beneficial for the looseness and aeration of the soil and for the biological activity of the soil. Green crops overshadowing the soil create good conditions after being gathered for the tilling and they benefit the initial growth of the following plant.

Good shading plants are: densely sown species cultivated in single-crop system (for example: Apiaceae spp., lady‟s thistle, mustard species) and species possessing huge leaves (for example: ox-tongue, hairy mullein).

Species with less shading ability are: intertilled crops (for example: basil, common thyme, marjoram) where the spacings are free. When planning the crop rotation it is worth alternating good shadowing species with intertilled species.

3.2.3.4. Protection against erosion and deflation

40 % of the Hungarian plough-lands can be found on slopes, where one must calculate upon regular damages caused by erosion. Appropriately established crop rotations can do a lot for the protection of the most valuable upper layer of the soil, full of nutrients. The best form of protection is the coverage of the soil by plants. It is important that plants should protect the soil at critical period of time as well (for example: in the rainy days of autumn, winter and early spring). Hence soil coverage must be ensured before sowing plants in spring at areas exposed to erosion.

The protection effect of the vegetation is appropriate if the stand density is balanced, the rate of shadowing is good and the vegetation period is long enough. Densely sown plants ensure higher protection level than intertilled crops, that is why it is forbidden to cultivate intertilled crops on slopes having more than 12%

inclination.

At areas exposed to erosion we may involve a new accession before the sowing of the following plant in crop rotation, on the stubble of plants gathered in summer (to obtain green manure), in order to increase the soil preventing effect of the cultivation. For this purpose such plants are suitable which develop strong roots, grow fast and have cheap sowing-seed (for example: fiddleneck, white mustard, fodder radish, summer rape).

3.2.3.5. Protection against replant problem

The sensitivity of plants concerning their cultivation after themselves is called soil sickness or replant problem in practice. There are many reasons for the existence of replant problem, for example the accumulation of toxic compounds in the soil, microbiological damage, deficiency of microelements, destruction of soil construction, nematode infection in the soil etc. Its effect is a remarkable yield-reduction.

With the help of crop rotation the replant problem can be avoided, if we pay attention at the planning stage to plant a given species, which can not be cultivated after itself, to the same sector only after certain years.

Otherwise the growing of the plant is endangered. The necessary waiting time has been calculated for several medicinal plants, it is 2-3 years for Satureja spp., 4 years for common thyme and caraway, 4-6 years for flax, 3-5 years for poppy and 2-3 years for carthamus etc. If literature doesn‟t supply us with data relating to waiting time, it is advisable to calculate with 3-4 years. Chamomile can be cultivated in monoculture as well.

3.2.3.6. Protection against weeds

Crop rotation is the cheapest and one of the most effective ways of cleaning weeds. With help of crop rotation the frequency of clearings and the amount of herbicides used can be significantly reduced. Its effect is based on the fact that there are two types of cultivated plants: „anti-weed” plants and „weed-growing” plants. The characteristic feature of a good weed-suppressing plant is, that under their cultivation we carry out intensive and careful clearing (for example: intertilled crops), and these plants hinder the growth of weeds by their fast initial

growing rate and by their huge amount of green mass (for example: ox-tongue, Jerusalem artichoke, lady‟s thistle). Plants of weed-growing type are not able to act this way, they even have low initial growing rate and poor foliage hence weeds can grow fast between them and can easily propagate. Weed-growing species are for example: woundwort, fox-glove, flax, marigold and marjoram. When planning crop rotation one must be pay attention to the alternation of weed-growing and weed-suppressing plants. Slowly growing species (coriander, fox-glove, marjoram) must follow weed-suppressing plants.

The clearing can be supported by the appropriate timing of the different cultivation time of plants and of the interval between the two consecutive plants. If we plant chamomile as green crop, and after it comes a plant sown in spring, the summer weeds can be cleaned up to a great extent during stubble-ploughing and nursing. If valerian was cultivated on the area the previous year (which is gathered at the end of October), and after it we sow plants in late spring (for example: medicinal pumpkin), then we have the opportunity to clean up weeds piercing out in early spring.

3.2.3.7. Preventive protection against pathogens and pests

When compiling the plant order it is an important principle that host-plants of the same pests and pathogens must approach each other neither in time nor in space (for example members of Apiaceae, Solanaceae, Brassicaceae families, or after the perennial vexillars the poppy, as they have common pathogens:

Fusarium spp.). Plants can be planted after themselves or after other host-plants until pathogens and pests lose their vitality and reproductivity (isolation in time). While placing the plants we must pay attention that host-plants of given pests and pathogens mustn‟t be planted even on the neighbouring sector in following years (spatial isolation).

The transmission of pathogens and diseases from one plant to another can be moderated if host-plants are alternated with non-host-plants, this way the food-chain of pests and pathogens is cut.

3.2.3.8. The importance of timing in soil preparations

When establishing crop rotation it is important to have enough time for soil-preparation after the green crop had been gathered and before the following plant is sown. Hence plants sown in autumn are planned to be planted after species gathered earlier. If plants gathered early follow plants sown in spring, the long period between the two accessions can be used for cultivation of green manures (cover crops), primarily under habitat conditions of higher precipitation levels.

By observing the mentioned principles of plant alternation, not only a balanced and higher yield can be obtained but significant cost-saving can be counted on, as the beneficial effects of plant alternation can be substituted only by expensive agrotechnical and nursing operations. Along with the economical and effective cultivation, the unnecessary pollution of the environment is hindered as well, so we can establish an environmentally friendly, sustainable farming (production).

3.3. APPLIED TILLAGE METHODS AND THEIR MACHINES IN MEDICINAL PLANT CULTIVATION (LASZLO