**5. Growth conditions and agronomic management**

Oilseed rape seeds start to germinate at 2–3°C. However, the most favourable germination temperature is 12–16°C. Their seeds germinate at this temperature and normal soil moisture in 5–7 days. However, their germination may take up to 20–30 days in a dry period. The temperature over the growing season has a significant relationship with yield. The optimum temperature for oilseed rape growth is 20–21°C. Temperature higher than 30°C is harmful for pollination and shortens the pod and seed development phase, thus reducing yield and quality. Moreover, high temperature during winter hastens plant growth, shortens the growing season, and reduces yield potential [18, 25].

Winter oilseed rape withstands up to −3°C cold in autumn. And with a rosette containing 5–7 leaves, and a snow cover thicker than 6 cm, it withstands up to

−25°C frosts in winter. However, under snowless and frost conditions, or when the seedlings overwinter with only 3–4 leaves, the plants die at −12°C cold. Low temperatures mainly damage the root collars and terminal buds of winter oilseed rape. Also, winter oilseed rape is sensitive to spring temperature fluctuations, as the plant consumes many nutrients during the winter and is, therefore, most vulnerable at that time [25–27].

High yields of oilseed rape are obtained when the plants are optimally developed before flowering. For optimal growth, oilseed rape should be planted in a welldrained and finely tilted area with a pH ranging from 5.5 to 8.5 and with moderate soil salinity for optimal growth where *Brassica* crops have not been planted for at least 3 years. What is more, the level of the primary nutrients (nitrogen, phosphorus, potassium, and sulphur) should also be maintained. The requirement of nitrogen ranges from 45 to 70 kg per acre. The recommended rates of phosphorus range from 0 to 30 kg per acre, depending on the current levels in the soil. And the recommended rates of potassium range from 0 to 65 kg per acre according to present soil fertility levels.

Several types of tillage systems are currently used in oilseed rape cultivation. The conventional tillage system is the most commonly used type of tillage system. Parallelly, few alternative tillage systems are used, e.g., the reduced tillage. Nevertheless, it has no significant effect on the oilseed rape yield it is confirmed as the valuable alternative to conventional tillage due to lower fuel and labour consumption and sustainability. To ensure successful reduced tillage practice special conditions must be met. These are the diverse crop rotation, the use of combine with straw chopper and chaff spreader qualities [28–30].

Weed control is the other challenging task for oilseed rape growers. One of the important parts of weed control is the establishment of weed-free fields. Thus, grass and broad-leaved weeds should be targeted, and the oilseed rape seeds should be sown as soon as possible: for winter type – immediately after the harvest and for the spring type – as soon as soil moisture is sufficient for entry of machinery. Nevertheless, the use of herbicides is very effective weed control method, due to their presence in drinking water, health damaging properties and increasing herbicide resistance in certain weed species, the restrictions on herbicide use are getting tougher.

The type of tillage method also has an impact on weed potential. A higher risk of grass weeds and germination of cereal crop grain shed from previous harvest may be present when the soil is prepared by reduced tillage method, because seeds of some weed species after ploughed down in previous rotation may be ploughed back up to the soil surface. Thus, bearing in mind that some weed species have a durable seedbank, and can reappear in ploughed soil, then 1 year at depth ploughing may be a good strategy for their control. The other tool for oilseed rape weed control is the use of various types of herbicides. E.g., non-selective herbicides are often used for weeding control in inter-row gaps, and the application of the residual herbicides is beneficial due to the season-long weed control. However, despite the success of herbicide applications there are few disadvantages of their use: herbicides are harmful for health and are being found in drinking water, herbicide effectiveness of certain herbicides has declined due to the increasing herbicide resistance in some weeds. The occurrence of these shortcomings resulted in introduction of legislation changes [31–33].

The maintenance of the optimal density of the crop is also essential. For oil production, oilseed rape is seeded directly into soil, aiming to achieve a density of 25–40 plants/m2 . Too dense crop leads to the formation of weak plants. Biometric analysis of *Oilseed Rape: Biology, Use, Current Cultivation Issues and Agronomic Management DOI: http://dx.doi.org/10.5772/intechopen.109180*

the crops showed that weaker oilseed rape plants remain in the shooting stage. Thus, most of these plants are overshadowed by stronger and faster-growing oilseed rape plants and eventually die [3, 34].

The other mean factor for oilseed rape yield is the distribution of rainfall. The rainfall is undesirable after maturity. However, a long rainy season with sufficient rain and lower temperature during earlier developmental stages is very favourable [3, 10]. The sufficient humidity level in the soil is dramatically important for high oilseed rape yielding, especially during the stages of flowering, yield formation and ripening. Therefore, under conditions of water scarcity, irrigation needs to be applied to avoid the loss of yield. Studies have also showed that irrigation at the beginning of flowering improves nitrogen assimilation and oil content [35, 36].

A complex of actions and measures is taken to increase the yield of plants. One such action is the use of growth regulators. Aiming to improve oilseed rape yield (to stimulate growth and flowering, inhibit plant elongation and the opening of productive elements, protect against diseases and pests, enhance the quality of harvest and quantitative indicators, product nutrition, restore damaged plants and increase resistance to adverse environmental conditions, such as drought, flooding, cold etc.) a list of growth regulators (growth hormones, osmoregulators, retardants, fungicides, etc.) has been tested and used till now. Scientific studies show that the effect of exogenous compounds can cause physiological changes in the plant cell and change the defence response to biotic and abiotic environmental factors [3, 25, 37, 38].
