1. Introduction
Greece is a country in the Mediterranean basin with a rich and varied flora across its length and breadth. Such is the diversity that it comprises 6620 taxa, 5758 species, and 1970 subspecies, with 223 of these endemic taxa located on the southernmost island of Crete [
1,
2]. One of the most well-known medicinal plants native to Crete is
O. dictamnus, also known as Dittany. With 75% of its species found only in the Eastern regions, the genus Origanum is highly represented in the Mediterranean region [
3,
4]. However, thus far,
O. dictamnus has not received much attention from the scientific community, and unlike other Origanum species, not much research has been conducted on it.
Dittany is a perennial plant and member of the Lamiaceae family, recognized for its medicinal properties since ancient times. It grows wild at an elevation of 400–1700 m in phrygana, garigue, rocky areas, and openings in Pinus forests [
5]. Nevertheless, nowadays, Dittany can also be cultivated on farms for its pharmaceutical properties [
6]. People use the plant’s aerial parts as an additive in the food industry [
7] and drink its herbal infusion, referred to as “vrastari” in Crete. The word comes from the Greek verb “vrazo”, meaning ‘to boil’. This infusion is used to alleviate coughs, sore throats, stomach aches, and gastric diseases and to maintain good health [
8,
9,
10,
11].
The interest in aromatic herbs and medicinal plants is not, however, limited only to Greek culture. Over the last three decades, individuals have been concerned about the physical and chemical composition of the ingredients that are added to foods. In an effort to improve their overall health (both physically and mentally), customers have been increasingly selective about their food choices, leaning towards products derived from aromatic, medicinal plants (MAPs) with promising antioxidative, anti-inflammatory, and antimicrobial properties [
12]. As a result, it is estimated that 75% of people on the planet regularly use different aromatic medicinal plants to fulfill a range of medical and health needs [
13].
Different nutrient management and fertilization methods can have a beneficial or negative impact on plant development as well as the quality of the produced goods [
14]. Nitrogen and phosphorus fertilizer additions can greatly affect plant growth. Fundamental processes in plant physiology, such as photosynthesis and leaf development, are positively affected by nitrogen [
15,
16]. In contrast, plant cell function and division and the development of their morphological characteristics are regulated by phosphorus [
17]. However, prominent studies conclude that the food system is facing a crisis related to land usage, environmental degradation, and the sustainability of agriculture due to excessive fertilizer applications [
18,
19]. These have provoked numerous environmental and ecological problems, including soil acidification, soil quality degradation, nitrate pollution of surface and groundwater, air and soil contamination through nitrogen leaching, and water eutrophication [
20,
21,
22]. Research suggests that there is insufficient nitrogen loss from agriculture to the environment to ensure a “safe operating space for humanity” [
23]. If there are no major improvements made to the entire food production–consumption chain during the next few decades, factors such as the growing population and the intensified agriculture to cover the population’s food demands will increase nitrogen fertilizer applications and exacerbate the trespassing of the “safe operating space” [
23].
For this reason, farmers and regulatory agencies are proposing new agronomic management techniques and cutting-edge sustainable methods for the cultivation of MAPs that come at a low cost to the environment [
24,
25,
26,
27]. Emphasis is placed on the use of organic fertilizers, as they have been linked to increasing crop development and growth, preserving the quality of the soil and the soil’s ability to hold water.
They serve as a productive source of energy for soil microorganisms, enhancing the microbial activity in the soil, resulting in better nutrient cycling, increased levels of organic matter, and an overall proliferated soil ecology, leading to an improved soil structure [
28,
29,
30]. Organic fertilizers preserve the nutritional balance necessary for crop plants, allowing them to grow healthily by releasing nutrients into the soil solution gradually. Through this gradual release, they lessen potential environmental issues related to synthetic fertilization, such as run-offs, and, unlike synthetic fertilizers, they lessen the need for frequent applications to preserve soil fertility, resulting in higher yields and better quality produce [
31]. The use of organic fertilizers in aromatic–medicinal plants (MAPs) cultivation is mentioned in many studies in the literature [
16,
32,
33,
34,
35]. Furthermore, most of the studies related to Dittany cultivation refer to the effect of various factors on the essential oil of the plant. To our knowledge, no research has been reported on the influence of the cultivation of
O. dictamnus under organic fertilization circumstances. Thus, this should be mentioned as a research gap that should be studied.
In this framework, the objective of this research was to examine the impact of organic fertilizer at different rates on the agronomic characteristics and herbaceous plant diversity of Dittany in the Crete region.
2. Materials and Methods
2.1. Site Description
The experiments were conducted in Crete (Greece), on the campus of the Department of Rural Development and Food, which is located in Istron Kalou Xoriou in the municipality of Agios Nikolaos Lasithiou. The campus has an altitude of 50 m, a latitude of 35°07’28.3″ and a longitude of 25°44’07.8″ (
Figure 1).
2.2. Meteorological Data
The meteorological data were provided by the nearby meteorological station of the Institute of Environmental Research and Sustainable Development at the Hellenic National Observatory of Athens.
Average, maximum, and minimum air temperatures and total rainfall during the study period (May to September) are shown in
Figure 2 and
Figure 3. The average air temperature ranged from 16.6 °C in May to 32.2 °C in July. Regarding precipitation, a total of 60 mm fell during the duration of the experiment. The highest rainfall was observed in June, while the lowest occurred in August.
2.3. Soil and Plant Analysis
Before conducting the experiment, five different sub-samples (0–20 cm) from the studied soil were collected and mixed to form a composite soil sample. The soil sample was then transferred to the Soil Laboratory of Hellenic Republic, Ministry of Rural Development and Food in Heraklion (Greece) for subsequent analysis. The sample was air-dried and passed through a 2 mm sieve. The following physicochemical parameters were determined: pH (1:2.5 d. H
2O), electrical conductivity (1:5 d. H
2O), calcium carbonate (CaCO
3) using a calcimeter, the percentage (%) of sand, clay, and silt using the Bouyoukos method [
36], and organic matter using the Walkley–Black method [
37]. Furthermore, the Kjeldahl method was used for measuring the total nitrogen (N) content [
38], while the available soil phosphorus (P) was determined using the Olsen method [
39] and analyzed with ammonium vanadomolybdate/ascorbic blue. The phosphorus content was measured in a UV spectrophotometer at 882 nm. Exchangeable potassium (K) was determined using a 1:10 extraction with 1 M CH
3COONH
4 at pH 7 [
40] and analyzed using a flame photometer.
The physicochemical properties of the soil are presented in
Table 1. The soil used in the experiment was sandy loam in texture and alkaline, with a pH of 7.31 and a calcium carbonate (CaCO
3) content of 3.98%. Moreover, according to the soil analysis results, the soil had a 2.25 % content of organic matter.
2.4. Establishment of Field Experiment and Measurements
Two-month-old Dittany plants were obtained from a local nursery (named Anagnostakis Ioannis, Sitia Crete) and were immediately transplanted to the field on 2 May 2023. The experimental period lasted from May to September 2023. The distance between plants was 40 cm and between rows 60 cm. Each plot was 0.24 m2 in size. Fertilization was the primary component in the completely randomized blocks (CRB) experiment design. An organic fertilizer (named Prima Humica Ledra Fertilizers, Thessaloniki, Greece) was applied 10 days after the transplantation and immediately after the first harvest. The experiments included three nitrogen fertilization treatments: T0: 0 g/plot, T1: 300 g/plot, and T2: 600 g/plot of organic fertilizer. The organic fertilizer was composed of 68–78% organic matter, 5% total N, 3% P2O5, and 0.0% K2O. Each treatment consisted of 10 replicates. A total of 30 plants were transplanted in the field.
An automated drip irrigation system with 2 L/h adjustable drippers was used to water the crops. Watering was conducted once every three days.
Measurements were taken to determine each plot’s plant height. Two plant material cuttings were collected during the study period on 30 July 2023 and on 20 September 2023. The aboveground biomass was then collected and immediately weighed to record the fresh weight using a portable scale. Subsequently, the harvested plants of each plot were oven-dried at 40 °C until constant weight was achieved. Finally, the dry biomass was calculated.
Moreover, the Leaf Area Index (LAI) was calculated from 15 leaves that were harvested from the plant of each plot, and the measurement was conducted using an automatic LI-COR.
2.5. Herbaceous Plant Composition
Τhirty 0.24 m
2 sites were used for the herbaceous plant sample. The abundance and composition of herbaceous plant species in organic
O. dictamnus were noted in each plot [
41].
2.6. Statistical Analysis
The statistical data analysis was performed using the software package “STATGRAPHICS Centurion” software package (v.18.1.01, Statgraphics Technologies, Inc., The Plains, VA, USA), with the LSD test conducted at a significance level of 95% (p < 0.05).
The Shannon plant diversity index was calculated using the Species Diversity and Richness IV software [
30]. The Shannon index (SH) is a widely utilized index that considers both species abundance and species richness [
42,
43]. The SH was computed for every sample.
where,
s equals the number of species and
Pi is the relative cover of its species. The Shannon diversity index value ranges from 1.5 to 3.5 [
44,
45] (for a detailed description of this index, see Seaby and Henderson [
42]).
5. Conclusions
In this study, the cultivation of O. dictamnus was investigated under different organic fertilization schemes.
In general, T2 nitrogen fertilization (600 g per plot) resulted in higher values of plant height, fresh and dry weight, and LAI. This implies that the optimal dosage of an organic fertilizer for O. dictamnus cultivation corresponds to a quantity of 600 g/plot.
As for the plant diversity in Dittany cultivation, in this research it was noticed that within the O. dictamnus ecosystem, the Anthemis arvensis L. and Piptatherum miliaceum (L.) Coss species are promoted. Also, the highest herbaceous plant species richness and Shannon diversity index were detected using the T2 fertilizer scheme.
The data from this study can be used for the development of a healthier fertilization program under the framework of organic practices. Furthermore, the information in this research provides a base for sustainable and eco-friendly agricultural systems.