The process of carrot ontogeny is closely linked to the prevailing biotic and abiotic factors. Only when all the factors that determine the growth of carrots are at their optimum level can the yield of carrots be maximized in terms of potential and quality. Yields are mainly influenced by temperature, light, humidity, soil, and nutrients.
Carrots are not demanding of heat. Their seeds start to germinate at temperatures of 3-4°C. Short frosts of up to -3-5°C do not harm young plants. Once grown, carrots can withstand short frosts of – 6°C in autumn, but if these frosts last longer, the root heads split and the carrots do not survive the winter. The optimum temperature for carrot seed germination is 15-20°C. With sufficient humidity, the seeds will germinate in 10-12 days, whereas at 5-10°C it takes 25-30 days. When there is a lack of humidity, seeds take even longer to germinate.
During the growing season, the optimum temperature for carrots is 15-20°C, while the sum of positive temperatures above 10°C in Lithuania is 1500-2200°C. The more optimal the growing season, the higher and better the quality of the carrot crop.
When the average air temperature exceeds 25°C, especially when the daytime temperature is 30°C and above, carrot growth processes slow down considerably, transpiration increases, the leaves lose their turgor, and a large number of substandard rootlets are produced. High temperatures are particularly bad for plants when the soil is deficient in moisture. Carrots need more heat during the reproductive period than during the vegetative period. Temperatures of 8-15 °C should be kept to 8-15 °C to ensure that strong roots form, as warmer temperatures result in the rapid formation of the flower stems, the plants failing to produce strong roots and leaves, and the seeds being weak and poorly produced. For flowering and maturing seeds, a temperature of 18-25°C is optimal. Cooler weather delays flowering and seed maturation, many seeds do not mature at all, and germination vigor and germination are lower.
Carrots are long-lived plants. They grow best when the day is at least 12 hours long. Therefore, especially at the beginning of the growing season, the carrot crop should be at optimum density and should not be weedy. A dense crop lacks light, which results in poor root growth and poor leaf growth. yellowing and wilting. When there is a lack of light, the quality of the roots deteriorates due to the accumulation of carotene, sugars, and minerals. The more hours of sunshine during the period of intense root growth (August-September), the more carotene and sugars accumulate in the carrots, the redder and sweeter they become.
Carrots require different amounts of moisture at different stages of growth. The critical period is considered to be the germination stage. When there is a lack of moisture. 20-120 plants/m2 may germinate in the field, although their laboratory germination is good. Later on, the carrot roots penetrate deep into the soil and the fine roots reach the moisture from deeper layers. During the intensive growth of the roots, constant soil moisture is needed, as a lack of moisture results in a large number of small and deformed roots. If there is a prolonged drought during this period and a sudden heavy rainfall, many of the roots will break down. Carrots do not grow well when the water table is closed. This results in a large number of carrots that are branched, deformed, short and hairy. The optimum water table is 60-80 cm. Carrot seeds need the most moisture at the beginning of their growth to form strong roots. Relative humidity of 4060% is most favorable during flowering and seed maturation.
Carrots are best suited to sandy soils and drained peat bogs. The depth of the arable layer is 25-30 cm. Carrots do well on humusy, weed-free soils. The optimum acidity is pH 5,5-7,0. In heavy, rotten soils, the carrots do not germinate for a long time and there are many deformed, pointed, and split roots.
In terms of nutrient uptake, carrots are one of the first crops after cabbages. According to the literature, each tonne of carrots takes up 1,3 kg of phosphorus (P.0), 3,2 kg of nitrogen (N), 5,0 kg of potassium (K,O), and 4,0 kg of calcium (Ca) from the soil. Carrots absorb nutrients from the soil better than other plants but are affected by excessive salt concentrations. The nutrients they need most are in the second half of the growing season when root growth is intense. Carrots need boron, iron, sulfur, manganese and other trace elements. The balance of all nutrients must be correct throughout the growing period, as a deficiency of any one element slows down the growth of carrots. A lack of nitrogen results in poorer leaf growth, pale green leaves, and rapid yellowing. Excess nitrogen leads to severe foliage growth, poor winter hardiness, faster decay, and nitrate accumulation in the roots. Lack of phosphorus causes the leaves to turn reddish and the carrots to be unpalatable, as phosphorus has a positive effect on the accumulation of sugar. Potassium improves the consistency and retention of the roots and has a positive effect on seed maturation. When potassium is deficient, the food in the plants deteriorates and the leaves turn yellow and mottled.