Pyrethrum (Tanacetum cinerariaefolium Trev.) contains environmentally-safe insecticidal ether compounds pyrethrin I and II. It grows as a wild species in southern Montenegro on lithosol, calcomelanosol, terra rossa and deposol soils. All of these soils are characterized by neutral or alkaline chemical reaction, different organic matter and total nitrogen contents, rather low content of available phosphorus, and medium or high content of potassium. Contents of the available microelements Zn and Fe were found to be high, with medium or high contents of Cu and Mn. However, the amount of humus, available potassium and microelements was not found to be high due to shallow solum and extremely rocky surface.

Key words: pyrethrum, soil, chemical properties.

Pyrethrum (Tanacetum cinerariaefolium Trev.) is a perennial herbaceous plant of the Asteraceae family containing insecticidal ether compounds (pyrethrin I and II) in its aboveground parts, particularly the ovary. Naturally-occurring pyrethrins are environmentally safe, which is why they have been given priority over similar synthetic products.

Pyrethrum is an endemic plant species populating coastal areas of eastern Adriatic, and our research aimed to expand the currently limited insight (Stepanović, 1983; Šilić, 1984) into soil properties in habitats of wild pyrethrum in Montenegro. Pyrethrum was imported in Europe and other continents in the past century and has been cultivated ever since. In Yugoslavia, it is grown experimentally and its production currently receives much attention.

Our field research included pedological profiling at defined locations (a total of 32), morphological description of characteristic profiles and sampling for further laboratory work (JDPZ, 1967). In laboratory proceedings, the following methods were applied (JDPZ, 1966): Potentiometric method for soil reaction (pH in H₂O and KCl); Kappen method for soil hydrolythic acidity; Kappen method for total adsorbed basic cations; Tjurin method, modified by Simakov, for total carbon; Kjeldahl method for total soil nitrogen; Egner-Riehm Al method for available phosphorus in soil; Schachtshabel method for available potassium in soil; nuclear absorption spectrophotometry method for contents of available micro-elements (Zn, Mn, Cu and Fe). Statistic data processing involved the method of correlation analysis (Stanković et al., 1989).

Naturally-occurring pyrethrum is mostly found in south Mediterranean and sub-Mediterranean regions of Montenegro, namely the Morača river canyon, the area surrounding Lake Skadar, the Crnojević river banks, Mt. Orjen overlooking Cetinje, Buljarica area, cape Trsteno overlooking the bay of Jaz and southern slopes of Mt. Orjen. The regional relief is karst, with an inclination of >40^o and over 50% rocky surface. These features make the principle limiting factor for agricultural production, so that all investigated locations were uncultivated areas. The main substrate includes Mesozoic karst rocks. The climate is Mediterranean and sub-Mediterranean characterized by dry and warm summers, and humid and mild winters. Irregularity of precipitation over the year and water deficit over the vegetation period, especially in June and July, is the chief climatic feature.

We differentiated four types of soil on location: lithosol, calcomelanosol, terra rossa and deposol developed upon the remains of a former quarry. As the soils belong to different classes and stages of development, they show considerable mutual difference. On the other hand, similar properties of the basic substrate, climate and other pedogenetic factors have resulted in a number of similar physical and chemical characteristics.

Figure 1. Soil pH in water (minimum, medium and maximum) in different layers of deposol, (A) lithosol horizon, A calcomelanosol horizon, and A and (B)rz terra rossa horizon.

Soil chemical reaction was established to be neutral or alkaline (Fig.1), with medium acid to neutral reaction found only in the cambic horizons of terra rossa. Neutral and alkaline profiles contained carbonic skeletal soils mixed with fine earth in profile, found also on the surface as rocky mulch, while acid reaction was found only in the cambic horizons of terra rossa at 20 cm depth, which are non-skeletal and fit into large pockets among karst rocks. Pyrethrum root is unable to penetrate into such (B)rz horizons of terra rossa owing to their texture. Exchange acidity was also found only in the non-skeletal cambic horizons of terra rossa.

Figure 2. Organic matter content (minimum, medium and maximum values in %) in deposol layers, (A) lithosol horizon, A calcomelanosol horizon, and A and (B)rz terra rossa horizon.

Figure 3. Content of total nitrogen (minimum, medium and maximum values in %) in deposol layers, (A) lithosol horizon, A calcomelanosol horizon, and A and (B)rz terra rossa horizon.

The analysis of adsorption complex indicates high values of exchangeable cation capacity (32.72-90.82 m.ekv.) and total adsorbed basic cations (21.87-88.0 m.ekv.). The unsaturated levels of the adsorption complex with basic cations range between 1.54 and 11.39 m.ekv., so that saturation level is 65.75 in the cambic horizon of terra rossa, and 97.82 m.ekv. in calcomelanosol.

Great importance is currently attributed to NPK fertilization of cultivated pyrethrum fields in Kenya, Australia, Japan and some other leading countries in pyrethrum production (Casida and Quistad, 1995; Salardini et al., 1994a, 1994b). Research is currently directed toward establishing optimum rates and times of application (fertilization and top dressing) aimed at securing maximum yield of pyrethrum flowers and maximum pyrethrin concentration. In Montenegro, wild pyrethrum grows on soils characterized by highly different availability of basic nutrient elements in soil.

Pyrethrum habitats differ considerably regarding organic matter content, from as much as 28.1% of organogenic calcomelanosol to barely 0.36% in the skeletal layers of deposol (Fig.2). Total nitrogen varies as well, from the maximum of 0.75% in best calcomelanosol to barely 0.06% in lithosol, or mere traces in deposols (Fig.3). However, due to unfavourable xerothermic hydrothermal conditions in soil, especially over the vegetation period, the process of nitrogen mineralization is slowed down, resulting in reduced availability of nitrogen to plants even in profiles well-supplied with total nitrogen.

Available phosphorus was mostly found in traces alone, while the content of available potassium (Fig.4) varied over a wide range, providing medium or good supply of the nutrient (3.4-48.7 mg/100g of soil).

Figure 4. Content of available K₂O (minimum, medium and maximum values in mg/100g of soil) in deposol layers,
(A) lithosol horizon, A calcomelanosol horizon, and A and (B)rz terra rossa horizon.

Content analysis for some crucially important available microelements (Fig.5) showed that some soils populated by pyrethrum are well supplied with available Zn and Fe, and medium or well supplied with available Cu and Mn (Žeželj and Panmeleeva, 1972). However, nutient supplies per hecatar are considerably limited in all types of soil owing to shallow solum, and considerable participation of skeletal soil and surface rocks.

Figure 5. Average content of available microelements: Cu, Zn, Fe and Mn (in mg/kg of soil) in deposol layers, (A) lithosol horizon, A calcomelanosol horizon, and A and (B)rz terra rossa horizon.

CONCLUSION

All habitats of naturally-occurring pyrethrum have neutral or alkaline chemical reaction, mostly high values of exchangeable base capacity and total adsorbed basic cations, as well as a high level of basic saturation of the adsorption complex. Soils differed greatly regarding organic matter content and total nitrogen, from humus lacking deposol layers with low nitrogen supply to humus-rich organogenic calcomelanosol. Expressed in mg/100 g and mg/kg of soil, available phosphorus was found mostly in traces, while available potassium and microelements (Zn, Mn, Cu, Fe) were found to be medium or well supplied. However, humus supplies measured in t/ha, and available potassium and microelements in kg/ha were not high in pyrethrum habitats due to shallow solum and considerably rocky character of the surface.

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