EFFECTS OF WATER SUPPLY

6.4.1. Effects of irrigation on drug yield

It can be established that the goal of irrigation is assuring a production of optimal yield and drug quality taking into consideration the aspects of profitability and sustainability.

Cultivation of some species is not realizable without irrigation which means that irrigation is a fundamental condition for them. The high importance of irrigation is supported by the fact, that in Israel, on the territory of the Negev desert 1000 hectares of high intensity horticultural crops, - among other those of medicinal plants - have been established and operate prosperously.

The yield of Mediterranean species may be increased even under their indigenous conditions reducing the retarding effects of drought and high temperatures. In Bari (South-Italy) the production of glycorice (Glycyrrhiza glabra) roots could be elevated from 14.6 tonnes to 20 tonnes by irrigation. This plant should be irrigated eight times in Tadzhikistan to assure optimal yields.

It may be an even bigger challenge if the cultivation of moisture/water demanding species is established in permanently arid or semi-arid regions. An example for this is calamus (Acorus calamus) which needs thick and rich soil layer, continuous water saturation.

Diverse response reaction on the water shortage of species characterised by variable water requirement is reflected in the behaviour of basil and savory. According to the experimental results, the biomass of basil dropped to two-third if water capacity of the soil decreased from 70% to 30%. At the same time the production of savory suffered only a 20% loss (Table 6.4).

Table 6.4. Production of basil and savory under different water regimes of the soil

Species Fresh mass (g) Essential oil content (ml/ 100g d.w.)

WC 70% WC 50% WC 30% WC 70% WC 50% WC 30%

Satureja hortensis 17,80 15,60 13,40 2,01 2,04 2,27

Ocimum basilicum 29,17 24,04 20,75 0,46 0,44 0,48

An optimal water supply is frequently a prerequisite of introduction of intensive agrotechnical methods aiming the increase of yields. Irrigation enables for example the very intensive cultivation system of poppy in Australia. It has been established that under the arid, warm climatic conditions at least 300 mm irrigation water is necessary for appropriate yields. Without this water amount the fertilizers can not be utilised either. Growth of plants is retarded, may stop, accumulation of alkaloids decreases by about 10%, capsule yield is minimised and ontogenesis shortened.

In Hungary it is well known that some spice species (e.g. marjoram, lovage) can be sown to direct place and a uniform juvenile development, necessary density of the stand can only be assured by proper water supply.

In lack of regular watering small seeds are not able to germinate, the stand will be very thin. In consequence of this, the danger of weed cover increases and most likely the field must be ploughed out.

Utilization of nutrients by the plants needs a proper moisture content of the soil, too. Own studies proved, that spearmint can take up and optimally utilize 200 kg/ha K2O in average years but it is able to utilize a higher dosage up to even 300 kg/ha if there is more precipitation during the vegetation year.

Unfortunately, abundant water supply contributes in a plant stand not only to optimal development of the cultivated crop but improves the life circumstances of many weed species, too. Therefore, irrigated cultures necessitate a well established and careful weed control system including proper crop rotation, mechanical and chemical herbicide technologies.

Water demand of medicinal plants depends also on the fact which organs provide the medicinally used drug. Most demanding are the ones giving leaf drugs (folium) like peppermint, lemon balm, plantain. In their fields it may cause a severe problem if the useful water capacity of the soil drops below 50% for a longer period (1-2 weeks). In case of species giving shoot drug (herba) the stem parts are less sensitive for drought conditions but a permanent soil water capacity value below 25% may cause severe harm. Somewhat higher soil water capacity is necessary for species providing root drug (radix). Here, a WC less than 30% may result in development of thinner, less valuable roots and deeper growth of the root system which would make the harvest more difficult. A moderate water demand is characteristic for the species giving flower drugs (flows) or even more for those which supply fruit and seed drugs (fructus and semen). For them, precipitation during flowering or ripening period might have negative effects. However, if soil WC drops below 20% even these crops require irrigation in order of proper biomass production.

6.4.2. Effect of irrigation on the content of active principles

There is much less information about the second most important point which is the effect of water on the accumulation of biologically active molecules in the drugs.

According to the experiences it seems, that the chemical properties of a given effective compound are not the only influencing factors of the response to water supply. It is also very important in which species we examine this response. The level of water supply will namely provoke a diverse reaction e.g. concerning the essential oil content of the hydrophyte Mentha or the xerophyte Lavandula species, respectively.

It has been demonstrated formerly, that an abundant precipitation would lead to a decreased alkaloid content of the Solanaceae species. Further research cleared however, that this decrease might be in connection

also with the lack of enough light like in nature, where rainy weather comes together with clouds and decrease of sunny hours. Accumulation of tropane alkaloids hyoscyamine and scopolamine in nightshade (Atropa belladonna) which prefers humid habitats, has been however higher under stress conditions (drought). Based on detailed investigations, it seems to be most likely, that in majority of species the water supply has less influence on the formation and accumulation of alkaloid type compounds. At the same time irrigation may still be very useful when increasing the biomass production and at the same time the total production of active compounds.

Similarly, it has been shown in case of hairy foxglow (Digitalis lanata) that irrigation enhances primarily the drug yield which contributes to the elevation of yield of glycosides, however the concentration of these glycosides remains practically unaffected.

In cycle of essential oil containing species the picture is rather complex. Among the species regularly cultivated in our region, the demand of peppermint (Mentha piperita) seems to be the best known. It has already been established in the 1960s that irrigation would modify the content of essential oil depending on the phenological stage. A regular water supply in this crop is a prerequisite not only for the desired drug yield but also for the essential oil level characteristic of the variety. Our own results show that a proper watering could contribute not only to the growth of overground organs but accelerate the development of the stolons, too (Table 6.5.).

Table 6.5. Effect of water supply on the yield and content of active ingredients of peppermint (Zámboriné és Tétényi, 1986)

(plus natural precipitation) 1360 360 2,46 51,7

Completed the natural

precipitation to 20 mm/week 1190 410 2,62 52,8

Without irrigation

(natural precipitation) 920 320 2,02 51,2

Regular irrigation might be especially important on arid, high temperature areas. The cultivation of M.

piperita var. citrate can be carried out in India only by regular water supply. Based on research data by this way the production both of the drug and the essential oil content can be increased by 60-80%. Irrigation however, does not influence the essential oil content of chamomile (Matricaria chamomilla) which is a species adapted to less humid circumstances. Moreover, it seems that too much water should lead to damage. It can be concluded that the reaction of essential oil containing plants is much dependent on species and ecotype (intraspeciefic unit of a species which has common genetic background for adaptation to a certain environment).

Penka (Checz author) published the following groups concerning the water response of these taxa.

Irrigation results in an increase of essential oil content (concentration):

- caraway (Carum carvi) - fennel (Foeniculum vulgare) - angelica (Angelica archangelica)

Essential oil content (concentration) does not change as consequence of irrigation:

- anis (Pimpinella anisum) - lemon balm (Melissa officinalis)

Irrigation results in a decrease of essential oil content (concentration):

- parsley (Petroselinum crispum) - lavender (Lavandula spp.)

During a long term experiment in cultivation of hyssop of Mediterranean origin, measurements revealed a significant, negative correlation (r=0.93) between the amount of precipitation in flowering period and the content of essential oil in the flowers (Figure 6.4.).

Figure 6.4. Connection between essential oil content of hyssop and the amount of precipitation during the flowering period

In case of another perennial spice plant, of estragon, irrigation in the optimal periods during the plant development enhanced both shoot biomass and its essential oil content (Table 6.2.). According to the studies on Taxus brevifolia it has been shown that the trees produced higher amounts of taxanes (terpene-alkaloid compounds) and abscisic acid among arid growing conditions than other ones under irrigated conditions.

In Mediterranean areas the accumulation level of both diterpenic compounds of rosemary (Rosmarinus officinalis) carnosil and carnosol decreases significantly due to the lack of precipitation and the effect of bright sunshine. Most likely, this decrease occurs in consequence of the enzymatic changes as result of the stressed environment. Similarly, in stress conditions connected to low supply of water the content of diosgenine (steroid-saponin compound) decreases in fenugreek (Trigonella foenum-graecum).

No uniform pattern could be established for the fatty acids and fatty oils, either. Water regime near the optimum level proved to accelerate the biomass of the species but had less effect on the accumulation of fatty oils. It was demonstrated in Iran by investigations on oil flax (Linum usitatissimum): an irrigation dosage of 60 mm significantly increased the height and number of branches and that of fruits but did not influenced the quality and composition of fatty oil of the seeds.

On agricultural fields of Central-Asia even safflower should be irrigated because of the uneven distribution of natural precipitation (Figure 6.5).

Accumulation of phenolic compounds is strongly influenced by the weather. Investigating chamomile population in Hungary for several years showed, that varying weather conditions generated larger differences in the flavonoid content of the flowers than geographical and edafic differences among growing areas did.

As summary we could establish that the type and size of response of the plant on drought stress depends both on the species itself and also on the chemical features of the active compound.

Figure 6.5. Effect of drought stress on the composition of fatty acids in safflower

6.4.3. Other effects of irrigation

Quality of the drug is usually determined not only by the content of active ingredients but also by outside characteristics (e.g. surface, colour) and pollution by organic or inorganic materials. Water supply might have a great influence also on these features, too. Pollution by organic materials may be increased by the fact that water induce kicking up of soil particles for the ground on the surface of the leaves. This may be a severe problem especially in species of lower growth which provide shoot or leaf drug (herba, folium) like marjoram, savory, lemon balm or mint species.

Due to the irrigation, the proportion of different plant organs in the total biomass might change considerably. In medicinal plant production, a change between the proportions of vegetative and reproductive organs (leaves/flowers, fruits) has a big importance. In crops cultivated for their flowers or seeds like chamomile, marigold, borago, mustard, etc. presence and high proportion of leaves or/and stems is unambiguously a drawback.

An abundant supply of water might result in exuberant growth of plant, in a thick plant stand which further on decreases the size and mass of the leaves. An increased mass proportion of the stems in the plant material raises the transport costs and reduces the content of effective materials.

Not only morphological features (well identifiable by sight) can be modified as consequence of regular water supply but also inside composition, tissue structures, anatomical features. In researches connected with valerian are described a modification of palisade parenchym ((a coloumn like tissue usually below the surface epidermis of a leaf with numerous chloroplasts and intercellular ducts) and a connected attenuating of the leaf width as consequence of irrigation technology. The acclimation potential of the plant is shown by the fact that at the same time the diameter of the transfer elements, the area of cross section of the main vessel were also modified.

It is a known fact, not only characteristic of the medicinal plants that irrigation –especially in a tight plant stand- may contribute to the spreading of diseases, fungi and bacteria. It is obviously in connection with the differences in precipitation, that fungi like Sclerotinia, Septoria and some others mean a continuous danger in caraway production in The Netherlands, while there are practically unknown in Hungary. Similarly, in rainy weather the plant protection procedures against Peronospora and Helminthosporium fungi must not be left out while in dry years such interventions may not be necessary at all.