BASIC PRINCIPLES OF NUTRIENT SUPPLY IN INTEGRATED MEDICINAL PLANT PRODUCTION In medicinal plant production it is desirable –similarly to other branches of horticulture – to follow the

Figure 5.2. Loose bushes of lavender due to overdosage of nitrogen fertilizer

5.2. BASIC PRINCIPLES OF NUTRIENT SUPPLY IN INTEGRATED MEDICINAL PLANT PRODUCTION In medicinal plant production it is desirable –similarly to other branches of horticulture – to follow the principles of the integrated cultivation. A prerequisite is a minimal load to the environment and maintenance –or even improvement, if possible- of the soil fertility. During nutrient supply we have to focus on the product quality too, by this way promoting the health of the consumers, furthermore, the economically most advantageous solution should be chosen. Cultivation method should correspond to the geographical, natural circumstances of the area, fertilizers should be applied in optimal quantity and at suitable time according to the needs of the target crop. The GACP guideline (http://whqlibdoc.who.int/publications/2003/9241546271.pdf), puts down –among others- that all types of fertilizers should be applied sparingly, in harmony with the needs of the culture, avoiding the hazard of washing out the chemicals into the soil water. Each organic manure shall be composted appropriately. In enterprises where procedures of the up-to-date quality assurance management are applied, basic numbers and data on nutrient supply and fertilization are among the necessary documents. An example for this documentation is provided in the table constructed and required by the Hungarian Agricultural Ministry (Figure 6.9.).

It is known, that the connection between the supply of the plants by nutrients and –as result of it- the biomass production is not linear but moreover a function close to the optimum one (Figure 5.3.). By increasing dosages of mineral nutrients– after an initial so-called “dilution” phase- the biomass production is growing but by a decreasing speed. Near to an optimal supply the biomass production increases very slowly and after this phase, in the period of the overdosage the biomass starts to decrease showing signs of toxicity.

Figure 5.3. Connection between concentration of minerals in the plant and production of biomass

Basic principles of nutrient supply are of course valid also for the medicinal plant species and during their production we have to take them into consideration. According to the law of Justus Liebig http://en.wikipedia.org/wiki/Justus_von_Liebig described in 1840 (Figure 5.4.) the production of the plant is always determined by the factor which is in minimum level at the given time. This rule is valid for each environmental factor in a wider sense, too. In case of nutrients it means, that an optimal level of any mineral can not be used effectively by the organism if there is another one whose concentration is not enough for normal metabolism. It is useless for example to give the plant much potassium if there is a lack of iron in the soil. In the cultivation practice soil analysis may usually assure data about the absence or critical level of the target element.

Short of extreme values, in general, the demand of plant species may be much different. Therefore it is a big problem that we have very few exact data for medicinal and aromatic plants and we could only relay on values of related species or on local experiences.

Figure 5.4. Model of the Liebig-Law

Another general principle has been described as law of Mitscherlich http://en.wikipedia.org/wiki/Eilhard_Mitscherlich which used to be entitled as “Law of the decreasing yield growth”

(Figure 5.5.). According to this principle, the increasing dosages of fertilizers provide continuously smaller increase in yield even in case if any other agrotechnical factors are optimalized. With other words: the plant is less and less able to react on the continuously improving circumstances. In case of each variety (older or more

N

intensive ones) the maximum plant response and by this way the best effective dosage of fertilizers may be different and for each variety a different optimum amount should be declared.

Figure 5.5. Model of the Mitscherlich Law X axis: Dosage of nutrient, Y axis: Yield

Establishment of the optimal dosage of each element for the plant can be carried out by several means.

Chemical analysis of the harvested plant material supports data on the amount of nutrient which has been removed from the field. This amount is the Nutrient removal value (kg/ha). Calculating to unit yield, we get the value of the Specific Nutrient Content (kg/t). Unfortunately, unlike to cereals and other larger crops – in case of medicinal plant species there are few reliable data available. Most data exist on the species which are generally grown on large fields like cereals. Some experimental data have been summarized in Table 5.1. It shows that there are noticeable differences among species. Evaluating the levels of potassium we can see for example, that a relatively large amount of this element is removed from the soil by caraway, fennel, lemon balm while only low amount of that is taken away by horsetail or lovage. It can be observed, that species assuring fruit drugs seem to consume a higher level of phosphorous in the soil which is important to consider in agricultural practice.

Table 5.1a. Specific nutrient contents of some cultivated species of higher importance (kg/t fresh mass), (Hoppe, 2010)

Species Drug Nitrogen Phosphorous Potassium

Angelica Root 3,0 1,0 5,4

Basil Shots with leaves and flowers 3,3 0,4 0,9

Pfeffermint Shots with leaves 4,2 0,5 4,6

Lemon balm Shots with leaves 4,9 0,6 6,3

Fennel Fruit 27,8 5,5 12,6

Thyme Shots with leaves and flowers 4,4 0,5 6,4

Chamomile Flowers 4,2 0,9 4,5

Cone-flower Shots with leaves and flowers 4,4 0,6 6,9

Cone-flower Root 4,6 0,6 4,2

Caraway Fruit 26,5 5,0 12,9

Marygold Flowers 3,0 0,5 3,8

Lovage Root 2,1 0,7 2,0

Lovage Shots with leaves 3,7 0,5 1,1

Valerian Root 2,9 0,8 1,9

Marjoram Shots with leaves and flowers 4,8 0,6 4,9

Sage Shots with leaves 4,9 0,5 5,1

Isotopic experiment provides the possibility to follow the movement of minerals in the plant body, their incorporation, excretion. This may help in determining the optimal dosage and form of fertilizers. Nevertheless, this method requires a sophisticated laboratory background, therefore its application is less frequent at the present practice.

Experiments with direct nutrient supply are closest to the everyday agricultural practice, both pot experiments (Figure 5.6 ) or open field ones (Figure 5.7.). One variation of pot experiment is the situation when the plants are grown in special solution of a single or some of the minerals. Another possibility is to check the behaviour of the plants in solutions which are lacking of certain or of some of the essential elements. However, as the soil in vivo is always a complex system of many factors, these pot experiments have restricted relevance on the practical situations. Open field small pot experiments have the drawback that in this complex soil system the results caused by individual elements can hardly be followed and interpreted because of their interactions and changing weather conditions.

Figure 5.6. Pot experiment with peppermint and basil

Figure 5.7. Field experiment with spearmint

The necessary amount of a mineral in a given field can be determined by the following formula:

Nutrient need (kg/ha)= Need of the plant (a) + Correction due to soil (b) – Other corrections (c)

Need of the plant (a) can be calculated if the planned yield is multiplied by the specific nutrient content of the given species.

Correction factor due to soil (b) depends on the situation if the concentration of the target element in the soil is reaching the optimal value or not. If it is less, the correction factor is equal to the amount lacking to optimal refilling while if it is more than that, the surplus should be deduced from the plant need. The rate of optimal refilling is depending on the area, on the type of soil. These values are summarized in information tables. By soil analysis on our field we should establish whether the existing amounts are less or more than those of the optimal loading. Soil analysis should be carried out in specialized laboratories from 1-2 kg homogenous soil sample taken from the root sphere after harvesting the previous crop (Figure 5.8.).

Figure 5.8. Results of a soil analysis

Other corrections (c) are needed for example in case of large dosage of manure or in case of pulses (Fabaceae) plants whose roots are in symbiosis with nitrogen fixing bacteria, etc.

Practically, in case of an optimal loading of the soil with minerals, the necessary dosage is equal with the need of the plant, so we only have to refill the amount which has been removed from the soil by the harvested crop. It is however, necessary, that we do not forget the soil being a complex system where the effect of nutrients is influenced not only by the optimal loading but also by several other factors like interaction of the elements, physico-chemical parameters of the soil and its living, microbiological constituents.