Nutrient responses of medicinal plants

We can influence several plant characteristics by supply of different nutrients, minerals; this is of course valid both for medicinal plants and any other crop. Therefore it is highly important and at the same time very difficult to optimize and take each factor into consideration.

In the simplest case the farmers prefer a high biomass or drug yield. A well designed fertilization may result in a significant increase of these yields in most cases. As the example of the formerly less studied species, spearmint (Mentha spicata var. crispata) shows, that an additional application of potassium being in minimum in the soil was able to assure the growth of yields (Figure 5.11.). Besides an appropriate content of the soil with nitrogen and phosphorous, submission of 200 kg/ha potassium resulted in 25% excess yield of the shoot, however, higher ratios may have already a retarding effect. Data of the four year experiment also show that factors being in minimum quantity may have a big influence on the biomass under the given circumstances. In a year of high precipitation (2010) even the 300 kg/ha dosages could be well utilized by the plant.

1 2 3 4 5

Figure 5.11. Shoot yield of spearmint in different nutrient treatments: 1.untreated, 2. N+P, 3.N+P+K100kg/ha, 4. N+P+K200kg/ha, 5. N+P+K300kg/ha

This statement can be confirmed also by the following two examples. A caraway stand in soil poor of nitrogen was not able to utilize even the highest amounts of potassium (Figure 5.12.). In another soil of chernozem type rich in each elements any additional fertilization had a retarding effect on the yields. This was due to the excess quantities of nutrients (Figure 5.13.).

Figure 5.12. Yield of caraway in different fertilization treatments (Soroksár)

Figure 5.13. Yield of caraway in different fertilization treatments (Szarvas)

A similar experience has been described in two German habitats. While fertilizing a fennel (Foeniculum vulgare) plantation by different macroemelents resulted in improved yield in Aschersleben according to optimum function, the same treatments were not able to assure any surplus in the field of Weissenfels (Table 5.4.). This latter area has namely a much higher nutrient content of the soil, practically saturated by the target minerals.

These results also demonstrate the fact mentioned in Chapter 5.1. about the importance of correction factor according to the soil nutrient content during calculating the optimal dosages of fertilizers. In a soil appropriately supplied by the necessary elements, fertilization may retard plant growth, decrease the profitability of the production and cause an environmental load.

Table 5.4. Effect of increasing dosages of N, P and K fertilizers on the yields of fennel in two German habitats (through Müllenberg, 1966)

P 60 1,07 1,63

K 0 1,09 1,51

K 20 1,14 1,68

K 40 1,08 1,52

K 60 0,89 1,55

In case of medicinal plants the general law that the emergence of any nutrients should be influenced by the presence and rate of the other ones is also valid. Findings during the introduction experiments of nightshade (Atropa belladonna) would well demonstrate it. It has been proved that the effect of potassium (K) macroelement is strongly depending on the available concentrations of the microelement manganese (Mn) (Table 5.5.)

Table 5.5. Effect of potassium and manganese treatments on the height and herbage yield of nightshade (through Mohammad et al., 2011)

Rates of fertilizer Plant height (cm) Herbage yield (g/plant)

K0 Mn0 137 58

There are several plant characteristics influencing the harvestable yield indirectly and many of them may be affected by the nutrient supply. There are some useful examples even in case of medicinal plant species for this phenomenon.

Unit yield of while mustard is strongly influenced by the density of the plant stand, by the individual yield potential but also by the size of the developed seeds (defined usually as thousand seed mass). Although mustard does not have a specifically high demand for nutrients, an additional fertilization may manifest itself in increased seed size (unit mass). This reaction is however, characterised by an optimum function as observable in Figure 5.14.).

Figure 5.14. Thousand seed mass of white mustard (g) in different fertilization treatments: 1.Control, 2. N+P, 3.

N+P+K,50kg/ha, 4. N+P+K100 kg/ha, 5. N+P+K150kg/ha

Nutrients also frequently influence the dynamics of plant development, the ontogenesis. They have a role in transition processes from the vegetative to the generative phase, in development of flowers but also in fertilization and accelerating ripening, too. In caraway plots additional supply with potassium and magnesium resulted in an earlier and more uniform flower formation. This process leads to an earlier, uniform ripening, better harvesting and higher yields.

However, we must not forget the possible negative effects, either. The phenomenon that an overdosage of nitrogen may result in elevated height and weaker stems causing a lay down of the crop. This may happen in cycle of our species, too, like in case of poppy, fennel, mustard, etc. As a consequence of the better nutrient supply the herbage yield of spearmint was increased, as mentioned above (Figure 5.11.). At the same time however, a decrease in the size of the leaves could be observed (Figure 5.15.). The largest leaves were achieved by the smallest potassium dosages. A potassium rate above the 100 kg/ha dosage had a negative influence on leaf size, obviously as consequence of the higher yield. In a higher plant stand of longer stems, many leaves and high biomass, there is namely no place and reduced light for the individual leaves. As the leaf drug (folium) has frequently a priority on the market and a usually higher price than the shoot drug (herba), this phenomenon should be of importance for the practice.

Figure 5.15. Size of leaves of spearmint due to different nutrient supply Treatments: 1=0; 2=NP;

3=NPK100kg/ha; 4=NPK200kg/ha; 5=NPK300kg/ha)

A balanced nutrient supply and especially higher potassium fertilization may contribute to stress tolerance of different species like tolerance against drought, diseases. In lavender stand we also found an increased frost tolerance in plots supplied by different fertilizers. A treatment by complex nitrogen, phosphorous but especially by potassium fertilizer increased winter resistance of the plants. In this latest case the number of frost damaged plants was reduced by one third compared to the non-treated plots (Figure 5.16.). It seems, that in young stands of this species of Mediterranean origin, a proper and well designed, balanced nutrient supply may be of high importance, even if this species usually known as less nutrient demanding one. Increasing frost tolerance may have a big significance especially in loose, sandy soil.

Figure 5.16. French lavender damaged by winter frosts

In production of medicinal and aromatic plants we usually cultivate species and only in exceptional cases one is dealing with selected varieties. Therefore we have only a limited knowledge about the differences of genotypes, varieties of the same species concerning their nutrient requirements and responses. It is well known from the circle of field crops or vegetables that there are considerable differences between the fertilization technologies of intensive and extensive varieties. In case of medicinal plants there is hardly any information regarding this aspect, but obviously we have to take it into consideration. As example, let‟s mention here the findings with nettle (Urtica dioica) during the introduction experiments into the agriculture. Although nettle is usually considered to have high nitrogen preference, it was proven that there are some genotypes of lower nitrogen requirement, too (Figure 5.17.). Based on practical experiences we can state, those poppy varieties of longer vegetation period need more nutrients, especially nitrogen than varieties ripening earlier (even by 2-3 weeks). Nitrogen supply in spring might contribute also to a better start of growth and strengthening of the overwintered plantlets of winter poppy varieties.

Figure 5.17. Response of different nettle accessions to nitrogen treatment