Caraway as a plant of high soil requirements grows and yields best on deep and warm soils, rich in humus and nutrients. The most suitable are fen soils, loess, chernozem, limestone soils and deep but not too heavy clays ().
The best forecrops for caraway are considered root and vegetable plants previously supplied with a full rate of farmyard manure (20–40t/ha). Suitable are also clover, lucerne and other mixed papilionaceous crops. Besides, plants ploughed-in for green manure could also be recommended.
In contrast, cereals are considered the least suitable forecrops for caraway. On the other hand caraway itself performs well as a forecrop for cereals, by leaving a field almost weed-free, and above all, due to its early harvesting there is enough time to conduct all pre-sowing agricultural practices, so essential for cereals ().
Caraway is highly sensitive to soil water, considering the level of that underground and soil-bound. Too high water table and stagnant water in particular are dangerous especially in spring and may cause mass wilting of the plants. A relatively high, stable soil moisture is necessary for the adequate development of caraway since it originates from wet meadows.
According to Buszczak () and Wêglarz (), soil moisture between 50–80% is optimum for caraway plants, ensuring their harmonious growth and the highest yield of the fruits. Under such conditions the plants use evidently less water to produce a particular weight of the fruits and the best weight ratio of fruits to straw is observed. At extreme levels of soil moisture there is more non-flowering plants in the second year, while those with already formed generative organs show a delayed flowering and more abundant umbel malformations (). Upon the experience and longtime observations by caraway growers in Poland this crop should be considered particularly sensitive to water deficiency during germination and emergence, being comparable to spring cereals.
Caraway grows well only on neutral or slightly alkaline soils (). Rumiñska and Kaczor () proved that an increased pH through adequate liming enhanced the yields of both fruits and essential oil. Calcium fertilizers are usually applied either before a forecrop or in late autumn preceding spring sowing.
Soil nutrients pertain to the factors highly essential for the process of caraway yielding, having both indirect and direct effect. The first is reflected in the influence of fertilizers on the size of plants at the end of the first year, that is a decisive factor for their potential vernalization and in consequence, flowering and yielding in the following season. Initially, Kramer () pointed that the increased rates of nitrogen in the first year of caraway cultivation brought about more flowering plants and a higher fruit yield next season. Such a relation was also evidently shown by Wêglarz (). In a pot experiment the plants poorly nourished in the first year were too small to form generative organs next spring. Instead, an increased NPK fertilization in the first year resulted in significantly larger plants, being subsequently able to flower and yield. The same author () tried to determine the relationship between the size of caraway roots and its productivity. Rootstocks classified into 3 grades: thick (root diameter 16–25mm, fresh weight 51–150g), medium (diameter 8–15mm, fresh weight 26–50g) and thin (diameter 2–7mm, fresh weight 4–25g) produced the plants which flowered in 100, 85 and 65% respectively.
Another interesting relationship appears from Figure “Effect of root size on the number of floral sprouts (%): 1—Thick roots; 2—Medium roots; 3—Thin roots”. During the 3 year research all the plants obtained from thick roots formed umbel shoots. At the same time flowering of the plants obtained from medium and thin roots in particular differed within the years, proving a considerable influence of climatic factors on development of caraway. Seed plants obtained from thick roots were bearing substantially more fully-formed seedstalks and showed a higher weight of both total and 1000 fruits. However, there were neither significant differences in germination capacity nor in essential oil content in the fruits.
Direct influence of soil nutrients on caraway yielding occurs in the second year of cultivation, however, it has never been subject of a detailed investigation. Both in researches and agricultural practice the effect of fertilization is regarded as whole for two growing seasons.
Nutrient intake by caraway plants is intensive estimated by Schröder () as 85kg N, 39kg P2O5 and 94kg K2O per ha, to yield 1.2 and 4.2 tons of fruits and straw respectively.
There is a positive response to both organic and mineral fertilization. The most intensive intake of nutrients is observed during summer and autumn in the first year and also in early spring of the following season (). Detailed study conducted by Kordana et al. () focused on the dynamics of nutrient intake and revealed that most nitrogen was absorbed by caraway plants at the rosette stage, i.e. July-September of the first year and during the formation of umbel shoots in the following season. Potassium intake was high in both years of cultivation, although it particularly enhanced in the second season while the plants were forming umbel shoots and during flowering. Maximum intake of calcium and phosphorus took place in September and October of the first year, then during fruit formation and ripening.
Most authors researching into caraway fertilization consider nitrogen the most essential nutrient that determines the level of fruit yield (). Fertilizer formulation and its quantity considerably depend, as in most crops, on the type and soil fertility as well as on forecrop, weather conditions etc.
Experiments conducted during 1950s in the former Soviet Union () showed a very strong positive relationship between a direct fertilization with farmyard manure and caraway fruit yield. Moreover Aflatuni et al. () found that composted manure increased essential oil content in the fruits. Caraway crops in Poland are often provided with farmyard manure (20–40 t/ha) which is usually applied prior to forecrop. However, the main source of nutrients are mineral fertilizers, supplied in both years of cultivation. In northern and central Poland, where the plantation of this plant is most concentrated and cultivated on fen and chernozem soils, pure crop is usually provided with the following rates of fertilizers: 60–80kg N, 70–80kg P2O5, 100–120kg K2O and 20–30kg MgO, applied both in the first and second growing season. In the case of mixed cultivation, in spring of the first year a cover crop is supplied with its full rate of fertilizers. At that time caraway is provided only with half of recommended amount of nutrients while the other half is given after a cover plant is harvested. Fertilization applied in the second year follows the recommendations for a pure crop (). The above rates of fertilizers correspond with those suggested by Nordestgaard ().
Timing of mineral fertilization seems to be particularly important. Full rates of PK compounds together with half amount of N-fertilizers are applied prior to sowing in late autumn or early spring. The other half of nitrogen is provided after caraway emergence. Some growers supply nitrogen compounds in three rates, especially in a mixed crop, giving the final portion after cover plant harvest. In the second year of cultivation the entire PK fertilization and half of N-compounds are applied in early spring as soon as possible. The remaining part of nitrogen should be supplemented 2–3 weeks later.
N-fertilization, as mentioned before, is highly effective but, if incorrectly performed, it may cause considerable damage, especially if applied at excessive rates or too late. Such negative effects in the first year may bring an exuberant vegetative growth of caraway plants, that subsequently disturbs their harmonious entry into winter dormancy. In the second season, consequences can be more serious. At a long-lasting high soil moisture, due to heavy precipitation, caraway flowering is prolonged, that subsequently causes non-uniform ripening of umbels and fruit shattering. Excessive N-rates can also lead to substantial losses if during fruit ripening there are high temperatures and strong insolation, and in consequence— physiological drought. Under such circumstances, even immature green plants wilt in a very short time. A considerable part of fruits may not be properly formed, thus reducing fruit yield, seed germination and essential oil content. The latter was proved in a long-time observations by the author of the present paper. It seems particularly important, considering the observations of recent years which show a constant decline in essential oil content in fruits from caraway plantation.
At present in most European countries, multicomponent fertilizers of adequate composition for particular crops are in common use. For caraway, mixed formulations with a substantial content of magnesium are very suitable, particularly on light soils. Besides, Polish growers observed a positive effect of boron on both seed yield and essential oil content in the fruits.
Kordana and Zalêcki () examined a multicompound liquid formulation (Agrosol U) used for foliar feeding of caraway plants. At full mineral soil fertilization, there was an additional positive effect of such treatment at the rate of 6–8kg/ha, expressed by 20% rise yield, including an increase in both 1000 fruit weight and essential oil yield. These results show a high biological potential of caraway plants and should prompt further research to enhance productivity of this crop.
Selections from the book: “Caraway. The Genus Carum”. Edited by Éva Németh. Series: “Medicinal and Aromatic Plants — Industrial Profiles”. 1998.