(A) Fertility cycle

Knotty kale is a biennial plant, under suitable climatic conditions, it forms leaf balls in the first year, completing the nutritive growth. After the winter low-temperature vernalization, to the following spring under long sunshine flowering and fruiting, to complete the growth and development process from sowing to harvesting seeds (Figure 10-13), this process can be divided into the nutritional growth period and reproductive growth period.

Figure 10-13 Diagram of the growth cycle of kale

1. Overwintering of seedlings 2. Overwintering of seedlings (bud differentiation at low temperatures) 3. Uncooked shoots (high temperatures and long sunlight) 4. Shoots in the bulb 5. Nodulation of side shoots (low temperature overwintering) 6. Flowering (high temperatures and long sunlight) (cited in Seizo Iwamae, 1976)

1. Nutritional growth period

(1) Germination The germination period is from the time of sowing to the time when the first pair of basal true leaves unfold and form a cross shape perpendicular to the cotyledons. The length of the germination period varies from season to season, 8 to 10 d in summer and fall, and 15 to 20 d in winter and spring.

(2) Seedling period From the unfolding of the first true leaves to the formation of the first leaf ring to reach the group planting is the seedling period. Generally, early-maturing varieties grow 5 leaves, medium-late maturing varieties grow 8 leaves, summer and fall season requires 25-30d, winter and spring season 40-60d.

(3) rosette stage From the second leaf ring to the formation of the third leaf ring, the beginning of the ball is the rosette stage. The number of days required varies according to varieties, early-maturing varieties generally need 25d, medium-late maturing varieties need 35-40d.

(4) balling period from the heart leaves began to wrap the heart of the leaf to the leaf ball-shaped into the balling period. According to the different varieties, early varieties need 25 ~ 30d, medium and late varieties need 35 ~ 45d.

2. Reproductive growth period

(1) Shooting period from the planting of seed plants to the flower stalks for the Shooting period, the north of the about 20 ~ 25d.

(2) Flowering from the beginning of the flower to the end of the flower for the blooming period. According to the different varieties, the length of the flowering period varies, usually 25 to 50d.

(3) podding from the flower to the yellow ripe fruit pods, about 40 to 50d.

(2) the requirements of the environmental conditions

1.Temperature

Knotting kale like mild and cool climate, but have a certain degree of tolerance for cold and high temperatures. It is generally best grown at 15 to 25℃. There are also some differences in the temperature requirements in various growth periods. Such as seeds can germinate slowly at 2 to 3 ℃, but the germination temperature is 18 to 20 ℃, rosette leaves can be grown at 7 to 25 ℃, 5 to 10 ℃ low temperature, the leaf ball can still grow slowly, the balling period to 15 to 20 ℃ for the appropriate.

Seedling cold tolerance with the increase in seedling age and improve, just out of the ground seedlings weak cold resistance, with 6 to 8 leaves of robust seedlings can withstand a longer period of -1 ~ -2 ℃ and short-term -3 ~ -5 ℃ low temperature, the low-temperature exercise of the seedlings can withstand a very short period of -8 ℃ or even -12 ℃ of cold. Mature leaf ball cold tolerance varies according to varieties, early maturing varieties can tolerate short-term -3 ~ -5 ℃ low temperature, medium-late maturing varieties can tolerate short-term -5 ~ -8 ℃ low temperature. Drawing flowering period, cold resistance is very weak, 10 ℃ below the low temperature affects the normal pollination and fruiting, flower shoots meet -1 ~ -3 ℃ low temperature that is subject to frost damage.

The adaptability to high temperatures varies in different growth periods, in the seedling and rosette leaf formation period, the high temperature of 25 to 30 ℃ has a strong adaptability. Entering the period of nodulation, a mild and cool climate is required. High temperature will hinder the process of nodulation, such as high temperature plus drought, it will cause the outer leaves to scorch the edges, the leaf ball loose, yield decline, quality deterioration, or even make the leaf ball loose. If the flowering is met with high temperature above 30℃ for several consecutive days, it will adversely affect the flowering, pollination and fruiting.

2. Moisture

Knotting kale root distribution is shallow, and the outer leaves are large, water evaporation. Therefore, it is required to grow under moist cultivation conditions, generally growing well under 80% to 90% air humidity and 70% to 80% soil humidity. Among them, especially the soil moisture requirements are strict, such as dry air and insufficient soil moisture, will result in slow growth and delayed bunting. Knotting kale is also intolerant of waterlogging, if there is too much rain, poor soil drainage, often make the root system soaked and impregnated and browning death.

3. Light

Knotting kale likes light, before passing through the vernalization stage, sufficient sunlight is conducive to growth, a wide range of adaptability to light intensity, light saturation point of 1441.0 μmol/(m2s), light compensation point of 47.0 μmol/(m2s). Therefore, it can grow normally both in the south where there are many cloudy and rainy days and weak light and in the north where there is strong light. At the appropriate temperature, long sunshine has a promotion effect on the seed plants pumping and flowering after completing vernalization.

4. Soil and Nutrition

Kale is well adapted to soil, from sandy loam to clay loam. It grows well in neutral to slightly acidic (pH 5.5 to 5.6) soils. However, it does not perform well in overly acidic soils and is susceptible to diseases such as Rhizoctonia. Kale can tolerate a certain degree of salinity and alkalinity, according to the Shanxi Academy of Agricultural Sciences survey, in the salt content of 0.75% to 1.2% of saline soil can also be normal growth and balling. Kale is a fertilizer-loving, fertilizer-tolerant crops, seedling and rosette need more nitrogen, phosphorus, potassium, followed. The amount of phosphorus and potassium required increases relatively after the start of balling. Nitrogen demand peaked at the rosette stage, and phosphorus demand peaked at the nodule stage. Knotting kale throughout the growth period to absorb nitrogen, phosphorus, potassium ratio of 3: 1: 4. In addition to nitrogen, phosphorus, potassium, but also need other inorganic elements, calcium deficiency or can not absorb calcium, especially in the growing point near the leaves will cause leaf edge wilting or leaf ball dry heart disease. The need for magnesium, boron, manganese, molybdenum, iron and other trace elements is not much, but once the lack of will also cause a variety of adverse reactions.