7.   PLANT PRODUCTION

7.1. Crop rotation

Crop rotation and succession of plants are very important for preserving soil fertility, plant protection, rational fertilization, enhancing productivity of cultivated plants and improving the quality of harvested crops. In case of proper plant succession the productivity of all crops will improve and damages caused by diseases (stripe disease of barley, etc.), pests (potato cyst nematode, etc.) and weeds (wild oats, etc.) as well as their spreading will be avoided.

Crop rotation and plant succession as methods for restoring soil fertility have been used in Estonia already since the 18th century. Leguminous plants and crops grown for green manure as well as letting land lie fallow help to decrease significantly the degree of environmental pollution with dangerous chemicals. For restoring and increasing soil fertility and for decreasing erosion, it is recommended to grow biennial tame hay (mix of clover and timothy) on fields and alfalfa, red or white clover as well as galega on permanent grasslands and to do it with regular intervals. Fallow without vegetation cover are used only in cases when it is inevitable to control weeds, pests or diseases. In Table 3 forecrops the best suited for different cultivated crops are described.

Table 3. Plants which can be used as forecrops for various field crops.* 

* If it is not possible to sow after a forecrop of the best quality, the forecrops of medium quality ought to be preferred and these of inferior quality avoided.

The succession of plants must be planned so that part of the fields would be covered with vegetation before snowfalls. Annual and perennial grass is the best suited for this purpose. If part of the fields has some vegetation on them also in winter, it will decrease soil erosion and leaching of nutrients.

In a nitrate sensitive area it is especially important to see that nutrients will not leach into surface or ground water. The extent of leaching out plant nutrients is smaller in fields, which have a plant cover in winter.

The Water Act provides that in a nitrate sensitive area during the period from November 1^st until March 1^st, at least 50% of arable land used by an agricultural producer must be covered with vegetation.

7.2. Green manure

Monoculture cultivation causes plant nutrient losses. Green manure helps to improve the characteristics of soil. Green manure crops protect the surface, improve the soil characteristics, prevent soil erosion, hinder spreading of weeds, and fix in soil the nutrients, which have not been absorbed and make succession of plants more effective.

Leguminous plants - clover, sweet clover, vetch and lupine - are the most appropriate crops for green manure. Oats, rye grass, spring turnip rape and rye can also be used for this purpose. Green manure used in late summer or utilised as litter serves to fix nutrients, which have not been absorbed by the plants, preventing outwashing of these substances from the upper layers of soil. Green manure is appropriate forecrops for winter and spring cereals, for root crops and also for fruit trees and berry bushes. If a field were situated in such a place to which it is difficult and inconvenient to transport manure, it would be advisable to consider growing green manure on this field. When we use green manure, we must take into account that their effects will last for a long time, especially if leguminous plants have been grown there. Thus, the norm of nitrogen ought to be reduced by 50 kg per ha in the first year and by 25 kg per ha in the second year.

7.3. Tillage

In plant production it is advisable to use such agrotechniques, which make it possible to reduce the number of cultivation operations. The aim of soil tillage is to create the conditions necessary for achieving high harvests, at the same time improving the soil characteristics. Annual intensive tillage may reduce the content of humus and worsen the structure of soil by compacting layers under the ploughing horizon. Compacted soil, in its turn, prevents the growth of plant roots, the biological processes come to a halt, the permeability of water drops and the yields decline. Restoring the structure of compacted soil, however, is a long-term and expensive process.

If the soil were of the type, which compacts easily, regular deep tillage would be a beneficial method. Another method would be to avoid growing such plants, which are harvested in late autumn. If soil tillage is started too early in spring, when there is still too much humidity in the soil, the result will be compacting of ploughing horizon. Crop cultivation operations must be started when the conditions on the particular field are suitable. Reducing soil tillage to a minimum and using wider or additional tires for machines helps to minimize the pressure and prevents compacting of the ploughing horizon. It would be useful to diminish the number of times when the machines go to the fields. It is possible when we use combined equipment. If soil tillage is reduced to a minimum the content of humus in the upper layers of soil will increase, the soil structure will improve, the activity of earthworms and micro-organisms in the soil will be more intensive, compacting of lower bed will be diminished, the expenditures on crop farming will be reduced and working hours shortened. From the point of view of protecting the soil and water environment, it would be expedient to use the method of direct sowing, provided that there are the special drills needed for this. Direct sowing gives especially good results for winter crops.

Choosing the right way of driving reduces compacting of the soil

Figure 3. Such a way of driving (on the left) reduces the area of compacted soil significantly.

In certain cases a method of soil tillage with no ploughing is used, i.e. tillage is carried out without turning the soil, provided that there are no perennial weeds on this field, and the acidity and content of phosphates of the soils are appropriate.

By using the technology the plant residues remain in the upper layer of soil, activities of earthworms and micro-organisms, become more intensive and the danger of crust be formed on the soil surface diminishes. Stubble and plant residues, mixed with the upper layer of soil fix nitrogen and that reduces the danger of water pollution. This method requires the use of cultivators, rotary hoes, disc arrows and other special machines in autumn. However, if this method is used for several years in succession, it may cause accumulation of plant residues, worsening of the conditions of pre-sowing tillage and sowing, increase the spreading of crop diseases and danger that plant nutrients will be washed out from the upper layer of soil

Autumn ploughing must be carried out as late as possible on the soils with fine granulometric composition, especially if organic manure is applied during this procedure, otherwise autumn rains will wash the nutrients out. In crop management (inter-row cultivation, fertilizing, plant protection, etc.), it is advisable to construct special roads for the equipment. On the whole soil tillage has to adapt to the changes in climatic and environmental conditions.

When a piece of land has been left uncultivated for some time, there is a possibility that it overgrows with weeds. To avoid it, perennial crops (alfalfa, galega, perennial grasses etc.) must be grown on such a piece of land. Spreading of weeds, especially those with pappus, e.g. corn thistle, field sow thistle and similar weeds is dangerous as from this uncultivated area the weeds will spread also to adjacent areas.

7.4. Erosion

Sometimes cultivated land suffers from soil erosion. Erosion means wearing away and transport of particles of the upper layer of soil by running water or wind. Erosion can be reduced by suitable soil tillage methods and plant succession, and also by growing particular crops.

In Estonia natural erosion, not caused by the activities of man, is insignificant. Water erosion can be observed only in some regions in the hillocks of southern Estonia. Wind erosion prevails in western Estonia and on the islands. On the slopes erosion may be caused by soil tillage, which makes the soil particles move and which may be followed by water erosion. Soil material or plant nutrients, which have been transported due to erosion, may cause pollution of water bodies:

It is recommended to use areas with significant inclinations (over 20^O) where a danger of water-erosion exists, as woodlands or grasslands and keep them always covered with vegetation. When soils are influenced by erosion it not only causes the outwash of upper layers of soil, but also leaching of plant nutrients. In these areas fertilization is permitted only immediately before sowing or simultaneously with it.

Establishing buffer strips on the slopes of hills and on the shores of water bodies helps to reduce erosion. Windbreaks must be planted at an angle of 90^O to prevailing winds and the interval between them should be 50 - 100 m. Mechanical erosion can be reduced by diminishing the number of soil tillage operations, limiting the speed of tillage equipment and selecting the roads more rationally. If possible, soil tillage ought to be carried out across the inclination of the slope and in level areas the displacement of soil towards the central part of the field ought to be avoided.

7.5. Soil acidity

The appropriate soil reaction is one of the prerequisites of crop cultivation and effective use of mineral fertilizers. Most of crops prefer weakly acid or neutral reaction (PH_KCI = 5,6 - 7,2). Table 4 shows the appropriate soil reaction for field crops.

Different field crops require different soil reaction and in the course of planning crop rotation also the degree of acidity of particular fields has to be taken into account. Acidity influences plants through nutrient mobility and through the activity of microorganisms. In acid soils the activity of soil organisms is lower and so is the degree of absorption of most important elements of plant nutrients. The mobility of most of the microelements, including heavy metals, however, is higher. Accumulation of heavy metals into crops can be avoided by soil liming.

Figure 4. Mobility of nitrogen in the soil

Figure 4 characterizes the mobility of nitrogen in the soil.

Liming must be carried out only on soils which really need it and using norms which are determined on the basis of the maps of lime requirement or on the basis of on the spot measurements of pH.

Because of economic considerations it is recommended to give the field half of the required amount of lime. The maximum amount of lime, which can be given at a time, is 5 - 6 t/ha. If some fields require more lime, it ought to be carried out in two stages (the first stage before ploughing and the other before pre-sowing soil tillage). This guarantees that lime and soil will be mixed more evenly throughout the entire ploughing horizon.

Soil liming, if carried out properly, will improve the conditions of crop nutrition. When using Estonian lime fertilizers, more complex fertilizers (which contain not only calcium but also other plant nutrient elements like K, Mg, S, P etc) ought to be preferred. Also powdery lime fertilizers (clinker dust and oil-shale ash) and those made of dolomite (limestone meal rich in magnesium) are to be recommended. As acidity of soils will be restored after some time, field liming ought to be repeated every 4...7 years.

7.6. Fertilization of pants

Nowadays, fertilizers should be used in a manner, which makes it possible not only to increase the yields and improve the quality, but also to improve soil fertility without polluting the environment.

It is important to increase the yields not by increasing the amount of fertilizers, but first of all by utilizing them more effectively. Fertilizers cannot compensate for the shortages in other methods of soil tillage.

Soil is the source of most of the nutrients, which plants need. In Estonian soils nitrogen, phosphorus, potassium, magnesium and sulphur and some microelements are the main nutrients, which influence plant growth and the volume of crop harvest. Although the content of these important nutrients is rather big (the ploughing horizon of mineral soils contains 0,1 ... 0,2% N; 0,04 ... 0,07% P and 1,2 ... 3,0% K), the bulk of plant nutrients exists in the form of compounds which do not dissolve easily and which are not easily assimilated by plants.

In Estonian climatic conditions cereals can absorb 0,5 - 1,5% (20 - 45 kg/ha) of total nitrogen per year. For root crops this amount is 1- 2% (40 - 80 kg/ha) per year.

The degree to which phosphorus and potassium are absorbed by plants can be characterized using the content of lactate dissolvable compounds in these substances. There is always some lactate dissolvable phosphorus and potassium in the soil of arable land (usually 2 - 120 mg/kg), but plants are unable to utilize these nutrients to the full extent.

During one year plants grown in crop rotation system can utilize on average 9 - 13% (5 - 7 kg/ha) of the phosphorus reserves and 20 - 23% (30 - 40 kg/ha) of the potassium reserves in soil.

As the bulk of crops are removed from the fields in the form of harvest, a great amount of nutrients are also removed. Table 5 shows how big is the average amount of plant nutrients removed from field in the course of harvesting (amount of the removed nutrient in kilograms per 100 kilograms of the main product). Table 6 gives recommendations for fertilization of different crops on the basis of these data.

We can see that the proportions of N, P and K removed in the course of harvest are different for each separate group (cereals, root crops, field grasses) of field crops. These proportions are 1: 0.17-0.22 : 0.58-0,83 for cereals; 1 : 0.13-0.22 : 1.10-2.10 for root crops and 1: 0.11-0.15 : 0.83-1.58 for field grasses. This means that if compared with root crops and field grasses, cereals need proportionally more phosphate fertilizers and less potassium fertilizers.

The amount of nutrients given to soil with fertilizers must be equal to that removed by crops. From the point of view of production requirements and environmental protection it is important to estimate the need for nutrients and draw up fertilization plans on the basis of these estimates, so that significant amounts of nutrients will not remain in soil after harvesting, to be leached out easily in common climatic and other conditions.

The Water Act provides that in case of crop rotation the permissible average annual amount of nitrogen per hectare of arable land applied in the form of manure, must not exceed 170 kg and in the form of mineral fertilizers and such amount of nitrogen, which is necessary for the growth of field crops.

In the nitrate sensitive zone it is allowed, on the basis of the protection rules, to restrict the average annual amount of nitrogen when applied in the form of mineral fertilizers up to 120 kg per hectare of arable land.

In nitrate sensitive zones on limestone and karst areas with unprotected groundwater, and where the thickness of the surface layer is up to 2 m, it is allowed, on the basis of the protection rules, to restrict the average annual amount of nitrogen applied in mineral fertilizers up to 80 kg per hectare of arable land. (The Water Act)

One of the objectives, which must be set when applying fertilizers, is to maintain the balance of nutrients in the soil, taking into account the yield, crop rotation, characteristics of the soil and other conditions of plant growth. Plants can assimilate only a certain part of the nutrients from fertilizers, the rest will be fixed in the soil or lost (through evaporation or leaching). As most of nitrogen fertilizers are easily soluble, plants will assimilate quite a big amount of them. During the first year plants assimilate 40 - 50% of all nitrogen, which was applied with mineral fertilizers and during whole period of crop rotation the degree of assimilation will be 50 - 60%. If the best methods of soil tillage are used (e.g. spot fertilization) and the weather is favorable, even a larger part of nitrogen will be absorbed. In case of crop failure, whether because of unfavorable climatic conditions or because of shortages in some other factor of growth, part of nitrogen will not be absorbed by the end of the vegetation period. There is a possibility that it will leach out. To prevent this, it is recommended to plough chopped straw under in autumn. This will help to decrease groundwater pollution. Nitrate nitrogen, which has not been absorbed by plants, will not remain in the soil, but will evaporate into the air or leach into the water.

Table 5. Average amount of plant nutrients removed from the field in the course of harvesting the most important crops.

Table 6. Fertilization of field crops. Appropriate soil reaction.

*- When the nitrogen amount is so great, it should be given in parts and stem stabilizer should be used.

**-If the amount of nutrients in soil is so small, it is not suitable for growing high quality wheat.

***-NPK norms per hectare should be increased by 20, 3 and 10 kg per each additional 1,000 kg of the harvest correspondingly.

****- N fertilizer is not applied for galega during the period when a new field is established and during the growth period.

Figure 5. Volatilization of ammonia, compacting of the soil and yield losses due to damaging the plants when driving in the fields are closely connected with the time of spreading manure. If manure rich in ammonia is spread in autumn, ammoniacal nitrogen could turn into nitrate nitrogen and there is a danger that this will be leached or denitrified in autumn or early spring.

On an average the field crops are able to absorb 17 - 20% of phosphorus from superphosphate and 47 - 55% potassium from potash fertilizers during the first year of applying these fertilizers. During the whole period of crop rotation plants absorb about 40% of all phosphorus from superphosphate and 60 - 80% of potassium from potash fertilizers.

The average amount of phosphorus per hectare of arable land is up to 30 kg, as applied in the form of mineral fertilizers. (The Water Act)

The mobility of phosphorus taken into the soil with fertilizers is low and it does not leach easily. The losses of phosphorus because of leaching do not exceed 0.5%, the average level of these losses in Estonia being 0.1% of the amount acquired from fertilizers. Perennial crops may receive at once a supply of phosphorus for 3 years, but it is prohibited to form such reserves on sandy and alluvial soils and also on soils where the danger of erosion exists.

Potassium is also not very mobile, but its mobility is higher than that of phosphorus. The losses of potassium because of leaching are significant only on sandy (up to 10%) and peat soils (up to 5%). On loamy and sandy clay soils the losses are negligible (less than 1%).

Part of nutrients will be lost because of leaching. The extent of this process depends on the relief, vegetation, and thickness of snow cover and intensity of precipitation. To avoid overgrowing of water bodies, it is especially important to prevent leaching of different forms of phosphorus into these water bodies.

7.7. Manure as fertilizer 

 Organic fertilizers are not only a good source of plant nutrients, but they also help to increase the content of humus in soil, improve the soil characteristics and support the life processes of micro-organisms. It should be recommended that all the fields receive organic fertilizers on a regular basis. On using organic fertilizers, especially manure, their long-term effects are taken into account as well as the more slow dissolution of nutrients contained in them compared to mineral fertilizers. When planning the use of organic fertilizers, we also have to take into account the residual effects of the organic fertilizers applied in previous years.

Manure is the most important type of organic fertilizer and its quality depends on the type and age of the animals, the method of keeping these animals, the fodder used, the type and quantity of litter used the technology of storage of manure, etc. That is why before applying manure and other types of organic fertilizers, their nutrient content should be determined. Table 7 gives the approximate allowed amounts of solid manure and urine per year and the quantity of N, P and K in these amounts of manure per year.

If the amounts of solid manure used for fertilizing are rather moderate, mineral nitrogen fertilizers must be added. Experiments have shown that simultaneous use of both mineral fertilizers and farmyard manure is the most effective method for increasing soil fertility.

The permitted average amount of nitrogen per hectare of arable land applied by manure is up to 170 kg per year. (The Water Act)

  The amount of nitrogen transferred into soil from 1 tonne of solid manure in the first year of application is approximately 1.0 - 1.25 kg, in the second year 0.5 kg and 0.25 kg in the third year. 

Figure 6. A trailing hose for spreading slurry and dung water - an example of new technology, which helps to reduce the losses of ammonia.

Table 7. Approximate amounts of solid manure and urine per year, as well as the quantity of N, P, and K contained in these amounts

*per animal place a year

It is recommended to apply solid manure only to the main crops of crop rotation, i.e. to winter cereals, root crops, and cereals with under sowing and to grasslands in the period of their foundation. If manure is used periodically, i.e. it is applied with intervals of several years, the recommended amount of solid manure of bovine animals is 40 - 60 m³/ha, the amount of solid pig manure 20 - 30 m³/ha and the amount of poultry manure containing litter 10 - 15 m³/ha.

Silage effluent has to be diluted before spreading in the proportion 1:1. The rate of application of this mixture per hectare shall be up to 30 tones. (Regulation of the Government of the Republic "Water Protection Requirements for the Storage of Fertilizers and Manure and the Silage Storage Sites, and Requirements for the Use and Storage of Mineral Fertilizers, Manure and Silage Effluent").

When sewage sludge, sludge mixture and sludge compost are used as fertilizer, in addition to the main analysis also the content of additional substances (heavy metals) must be determined and the use of these fertilizers on the lands where vegetables or berries are grown must be avoided.

The fields where sewage sludge, sludge mixture or sludge compost have been spread, must not be used for growing vegetables either for human food or animal fodder during one year. Grasslands where sewage sludge, sludge mixture or sludge compost have been spread, must not be used for grazing or making fodder during two months (Regulation of the Minister of Environment "Requirements for the Use of Sewage Sludge in Agriculture, Green Building and Recultivation Works.")

Slurry and urine can also be used for fertilizing plants during their period of growth. It is possible to diminish the evaporation of ammonia by incorporating into soil urine and slurry as quickly as possible or by using appropriate spreading technology e.g. the trailing hose system.

It is not recommended to spread slurry and urine during the period from 1 September to 31 October. During this period they should be spread only on growing crops or before autumn sowing.

When selecting the amount of slurry and urine the main consideration should be that this amount must under no circumstances surpass the needs of the particular field crop. 1m³ of slurry or urine contains approximately 2 ... 4 kg of nitrogen. The average amounts of slurry and semi-solid manure and the quantity of nitrogen nutrients in these amounts are shown in Table 8.

Table 8. The average amounts of semi-solid manure and urine per year, as well as the quantity of nitrogen nutrients contained in these amounts

*per animal place a year

7.8. The appropriate time and methods of using fertilizers 

The time and method of using fertilizers shall determine the depth of application of fertilizer, the fixation of nutrients in the soil, the extent to which the nutrients are absorbed by plants and the amount of losses of fertilizers from the soil.

Fertilization should be carried out in time. Especially when using mineral fertilizers, the deadline for applying nitrogen fertilizers ought to be observed very carefully. As nitrates are not fixed in soil, the saltpeter fertilizers are very mobile. Spring is the best time for incorporating saltpeter fertilizers into soil while in summer it is recommended to apply them on surface. Also the ammonium fertilizers should be applied in spring. Winter cereals, which already have received organic fertilizers, shall not be given nitrogen fertilizers in autumn. These will be applied as dressing in spring when the content of humidity in soil has fallen and the vegetation period has begun. Mineral nitrogen fertilizers should be applied to field crops sown in spring simultaneously with pre-sowing soil tillage, in the form of spot-fertilization during the sowing or as top dressing to growing crops.

In autumn after 1 September it is recommended to apply mineral nitrogen fertilizers only to the winter cereals. The norm is up to 30 kg N/ha, if used simultaneously with pre-sowing soil tillage or up to 10 kg N/ha, if used simultaneously with ploughing in the straw.

If, however, the nitrogen fertilizer norm exceeds this rate and is more than 100 kg N/ha and the cereals may lodge, the fertilizers will be applied in two parts. The first portion (2/3 of total amount) will be applied to spring cereals before or during sowing, to winter cereals in spring as top dressing. The second portion (1/3 of total amount) will be applied during stem growth or when the crops are coming into ear. This method reduces the danger of lodging and increases the content of protein in the grain.

Phosphate and potassium fertilizers should be applied in autumn but it is possible to apply them also before soil tillage in spring.

The amount of nutrients leached or washed out by surface waters depends also on the method of application of the mineral fertilizers. When the method of spot-fertilization is used, the amount of nutrient losses is smaller if compared to scattering them on soil surface. To guarantee the efficiency and precision of fertilization, the fertilizer spreaders must be in order and properly regulated.

To achieve the best results from the point of view of plant nutrition and water protection, the spreading of manure should be carried out in spring before ploughing. Slurry should be spread after the crops have been sown, but before they have come up, when the plants are already able to absorb the nutrients. Spreading manure before autumn ploughing is justified only for solid manure. In autumn manure should be spread as late as possible, but before the soil is still frozen.

Manure, silage effluent and mineral fertilizers must not be spread on snow or on frozen soil and mineral fertilizers must not be sown from aeroplanes (Governmental Regulation "Requirements for Storage of Manure and Silage, Water Protection Requirements for Silage Storage Sites and Requirements for the Use and Storage of Mineral Fertilizers, Manure and Silage Effluent").

Land is considered to be covered with snow, if for more than 24 hours it has been covered with a layer of snow with the thickness of more than 10 cm. Land is considered to be frozen, if for more than 24 hours a layer of soil with thickness of 5 cm has been frozen. When soil is frozen the life activities of plants have come to a halt and nutrients are not being absorbed. When the snow melts or the weather gets warmer, the nutrients will flow straight into the surface water or groundwater.

Manure, silage effluent and mineral fertilizers must not be spread in the sanitary protection zone of water intake, in the water protection zone of a water body and on periodically flooded land. (Governmental Regulation "Requirements for Storage of Manure and Silage, Water Protection Requirements for Silage Storage Sites and Requirements for the Use and Storage of Mineral Fertilizers, Manure and Silage Effluent").

Manure shall be spread with a spreader which is in good order and suitable for the particular type of manure. After it has been spread, manure must be taken into the soil as quickly as possible. In the case of top dressing of the growing plants the trailing hose or spot-fertilization equipment should be used.

Mineral fertilizers, which are applied as main fertilizer are often spread on the field with a fertilizer spreader and taken into soil in the course of the following soil tillage. Vertical distribution of fertilizers scattered to soil depends on the tillage equipment. During harrowing, cultivating and disking the fertilizers are mixed with the upper layer of soil only. Mineral fertilizers taken into the soil in the course of ploughing go into deeper layers. The efficiency of mineral fertilizers scattered on the soil surface is limited, if compared with that of fertilizers taken into the soil. Phosphate and potassium fertilizers are more efficient, if applied before ploughing. Also when spot-fertilization is used, the fertilizers can reach the necessary depth. Spot-fertilization increases the yield volume by 10 ... 20% for spring cereals and approximately by 5 - 10% for potato.

When the spot-fertilization method is used, the plant nutrients are more easily absorbed by the plants due to the favorable location of these nutrients. This makes it possible to reduce the fertilization rate by 15 - 20%. Spot fertilization diminishes significantly the danger of groundwater pollution.

To take into account all the essential factors of fertilization, a fertilization plan is drawn up. This plan must contain the following data: the crops cultivated in a particular farm, the location of different field crops, types of forecrops, fertilization of forecrops, planned yield volumes, the nutrient level in soil, the types and amounts of fertilizers used, rate of application of fertilizers, calculated amounts of fertilizers, the terms and methods of fertilization for each separate field.

The Water Act provides that agricultural producer must keep a field book where he records the data about the area of arable land, the characteristics of the soil, volume of harvested crops, types and amounts of fertilizers used and the dates when they were used. The structure of the book and the procedure for keeping it shall be established by Regulations of the Minister of Agriculture.

Regular fertilization guarantees high quality yields, preservation and increase of soil fertility, reduces the danger of water pollution and maintains healthy environment in the areas surrounding the fields.

7.9. Plant protection

Pests and plant diseases diminish the volume of harvested crops and worsen its quality. However, using plant protection products must not become an object in itself, a means of correcting mistakes and shortages in soil tillage. Incompetent and indifferent use of plant protection products in great quantities (exceeding the norms) will cause not only the production of products polluted with toxic residues, but also an increase of environmental pollution load, which may lead to polluting the groundwater, soil and air. The residues of plant protection products, which have been transferred to food products from animals and plants, can damage human health. It is recommendable to use such plant growing methods and technologies, which make it possible to diminish the use of chemical plant protection products or to avoid it completely.

In modern agriculture an integral plant protection system is preferred, because it spares the environment, is economically viable and guarantees ecologically clean production.

The integral system of preventing plant diseases and pests contains the following elements:

Plant protection products should be used in such periods when insects (bees, etc.) useful to plants, are protected from them. To preserve the number of these useful insects, it is advisable to have special protection belts around fields or to leave some areas or belts in the fields untreated.

Chemical plant protection products must be used only when there is a real need for them and all the instructions must be observed strictly. This means thorough examination of the conditions of each plot of land, careful consideration, of the preventive measures, precise estimation of the development phases of plants, following the weather forecasts and taking preventive measures in time.

Plant protection products are marketed either freely or on the basis of a plant protection certificate. The plant protection certificate certifies that this person has undergone training in plant protection and may market, purchase or use all types of plant protection products. (Plant Protection Act, RT I 2000, 29, 169).

Plant protection products, which are meant for a professional user may be purchased and used only by persons who have undergone the corresponding training and have the plant protection certificate to prove it.

The active substances contained in a plant protection product must have the quality declared by the producer. The plant protection product must not contain prohibited substances. (Plant Protection Act)

In Estonia, it is permitted to use only these plant protection products, which have been registered and the effects and characteristics of which are known. Using an unregistered or unknown plant protection product or commissioning a person without the plant protection certificate to carry out plant protection operations is very risky. Incompetent use of plant protection products or use of some plant protection product which, contains prohibited substances may ruin the quality of the whole crop and cause irreversible damage to the environment.

The Plant Protection Inspectorate, whose local agencies are in every county center, gives information concerning the plant protection products and obtaining the plant protection certificate.

Plant protection products, which are not so dangerous and are included in a separate list, may be purchased and used also by persons not having the plant, protection certificate. However, on using plant protection products health and environmental protection requirements must be observed. Plant protection products should be purchased always in the right amount and utilized completely so that there will be no leftovers. It is advisable to prefer preparations which are less toxic, may be applied in smaller amounts and which decompose quickly in natural environment, so that their effect on various useful organisms is less toxic and more of repellent nature and does not endanger aquatic organisms.

The Shore and Bank Protection Act and the Water Act set restrictions to the use of plant protection products on shores and banks and in the vicinity of springs and sinkholes (see also the restrictions on fertilization and the restrictions concerning nitrate sensitive zones).

Establishing corresponding restrictions may prohibit the use of chemical fertilizers and plant protection products on flooded areas of shores and banks. Liquidation of outbreak sites of plant diseases and pests on the shores and banks using toxic chemicals will be carried out on the basis of a single permit issued by the Minister of Environment or an official authorized by the Minister (Shore and Bank Protection Act)

It is prohibited to use plant protection products around springs and sinkholes in the radius of 10 meters from the water line or edge of the sinkhole. In a nitrate sensitive zone the radius must be up to 50 meters, while the scope of restrictions shall be established by the protection rules. (Water Act)

The regional environmental authorities or local Plant Protection Inspectorate agencies will give information about these restrictions. In the areas where the danger of chemical pollution to the environment is especially great (karst regions, water bodies situated in the vicinity, etc.) it would be reasonable to give up growing such crops, which absolutely need plant protection products to thrive.

Alternative plant protection methods should be considered. In horticulture and to the lesser extent in other areas of plant production and vegetable growing, it is possible to use biological preventive methods, covering the passages between plants with a cover material, use mulch, surface tissue, etc. To preserve the useful insects it is recommended to leave natural areas around fields, i.e. areas that are not treated with chemical substances.

It is essential to have plant protection equipment properly installed and regulated. Only sprayers which are in order and which have been tested may be used. The necessary precautionary measures to be taken are as follows:

The user of plant protection products must keep records of the used products. (Plant Protection Act). It is also necessary to keep a field book where the data about the use of plant protection products are recorded separately for each field. The following data must be recorded in the field book:

While the plant protection products and their used packages are stored in a warehouse, the valid safety regulations and conditions established for warehouses or storages must be observed.