Cucumber

Cucumber

Physiological Aspects of the Cucumber crop (Cucumis Sativus)

The length of each phenologic condition in cucumber crop is very variable, depending on the type (Caipira, Aodai, Japanese, or for Preserves) and on the cultivation and conduction method (open field or greenhouse, wiring or creeping cultivation). Contrary to the majority of annual crops, in this crop phenologic stages overlap. Vegetal development, blooming, growth, and fruit ripening occur simultaneously after blooming starts. Senescence occurs while the crop is still in the production stage, and the cycle end is defined by the reduction of the production instead the termination of the production.

Main Nutrients
In general, nutrient absorption by crops is proportional to the amount of nutrients available in the root area. For each nutrient, there is a higher demand period when absorption is significantly higher that during other cycle periods. For fruit vegetables, the group to which cucumber belongs, the highest demand period generally matches the start of fruit formation, remains high during the entire production period, and decreases when the plant enters the senescence stage.

Cucumber absorbs and uses large amounts of nutrients, but it is very sensitive to excess of nutrients or sudden variation of it in soil solution, and its roots are quite sensitive to those variations (PAPADOPOULOS, 1994). The amount of each nutrient absorbed during the cycle depends on the variety and the plant conduction and cultivation system.

The same as with every fruit vegetable, the main absorbed nutrient is not nitrogen, but potassium. It is important to note that nitric/ammoniac nitrogen balance is very important for nitrogen optimal utilization and maximum absorption.

For the Aodai variety, nitrogen need is small at the beginning of the cycle, and it increases on the 36th day after the emergence (figure 1), as shown in the dry matter accumulation curve (figure 2). This behavior is also noted in the rest of macro and micro nutrients (figure 1).

A - B
C

Phosphorous

Phosphorous absorption quickly increases with production start. Approximately 80% of phosphorous is absorbed between the 48th and 72nd day after emergence, a period in which the largest part of fruit production concentrates, accumulating around 50% of the absorbed phosphorous.

Potassium

Potassium is absorbed in largest quantities. Approximately 90% of potassium is absorbed during the last 36 days of the crop cycle. Potassium plays an important role in fruit quality by increasing the amount of soluble solids and, therefore, fruit palatability, in addition to being an important enzyme activator and acting in the plants perspiration process by controlling stoma opening and closing. The noblest and more efficient potassium absorption source is SQM potassium nitrate (Ultrasol® K). This fertilizer is characterized by its synergy in 100% nitric nitrogen absorption, together with potassium, with 1/3 N/K ratio, respectively, an ideal ratio for fruit active growth. In a development condition close to harvest, when nitrogen is not needed, potassium sulphate (Ultrasol® SOP) is an ideal source of potassium, with a high potassium and sulphur content, which activates numerous enzyme functions that help increasing fruit ripening and weight together with potassium.

Calcium

Calcium is a very important nutrient for production. Lack of this element produces fruit with Stem-end rot. Lack of calcium is also related to the root system malformation and plant growth reduction. The amount of calcium absorbed during the cultivation cycle and absorption start-up is similar to that of nitrogen. Contrary to other nutrients, Ca transportation in the plant occurs mainly through the xylem vessels, and transportation rate is controlled water movement in the plant perspiration process (MOLTAY et al., 1999). Under air high relative humidity conditions, the perspiration rate reduction may result in calcium deficiency, even when the soil contains enough amounts of the element (BAKKER; SONNEVELD, 1988). This way, closing of side curtains in protected crops in cold weather regions, spite of increasing temperature, could lead to Ca deficiency and increase in plant perspiration. High doses of N and K promote plant growth and Ca absorption (MOLTAY, 1999).

In this case, the noblest and fast-absorption source is Ultrasol® Calcium, to be provided during the blooming, rooting, and small fruit stages, when calcium is absorbed and displaced towards fruit, ensuring firmer fruit with less diseases and low physiologic disorders related to calcium.

Magnesium and Sulphur

Magnesium and sulphur are absorbed in relatively low amounts compared to other nutrients, but they are indispensable for a good crop development. Mg is part of the chlorophyll molecule, responsible for photosynthesis, while S is a component of the plant different organic compounds. Providing large amounts of K and Ca in order to guarantee high production and fruit quality in an excessive nutrition may cause Mg deficiency in the plant, as a result of the antagonistic effect between the said elements and Mg. S deficiency is not common in cucumber crops, as nutrient used generally contain enough quantity of this nutrient, as in the case of ammonium sulphate, magnesium sulphate, and potassium sulphate.

Nutrient

LNMP(1)

Papadopoulas (1994)

Vetanovetz (1996)

Macronutrient

 

(dag kg-1)

 

N

4,5-6-0

3,0-6,0

2,5-4,5

P

0,3-1,2

0,3-1,3

0,4-0,8

K

3,5-50

3,5-5.0

6,0-10,0

Ca

1,5-3,5

0,5-5,0

6,0-10,0

Mg

0,3-1,0

0,35-0,70

0,5-1,5

S

0,4-0,7

-

-

Boro

90 gr/ha

0,08

 

Micronutrient

-

(mg kg-1)

 

B

25-60

30-120

40-120

Cu

7-20

8-20

7-10

Fe

50-300

100-300

100-420

Mn

50-300

50-250

100-300

Zn

25-100

40-100

90-150

Table. An optimal level of nutrient concentration in cucumber leaves dry matter.

In general, micronutrient extraction by gourd plants responds to the following model:

Fresh wt

kg/t

Water

960

Nitrogen

1.43

Phosphorus

0.38

Potassium

1.7

Sulphur

0.16

Calcium

0.25

Magnesium

0.15

Micronutrients in Cucumber
Micronutrient availability is essential for plant correct growth and development and for high production. When there is a deficiency of one or several minor elements, these become a limiting factor for growth and production, although other nutrients amount may be appropriate.

During the last years, use of micronutrients in nutrition programs has increased, mainly due to:

• Continuous removal of minor elements by crops which, in some cases, has reduced their concentration in the soil to levels below those necessary for normal growth.
• Intensive crops, with a higher use of nutrients in order to increase yields, have increased the use of minor elements which are not returned to the soil at harvest.
• Excessive soil acidity that reduces some micronutrients availability.
• Use of high-purity nutrients has eliminated minor elements contribution which, in small quantities, were present in lower quality products used in the past.
• Better knowledge on vegetal nutrition, which has contributed to deficiency diagnosis in minor elements and not considered before.

Which is micronutrients’ function in crops

Micronutrients role is very complex and it is associated to essential processes where they work together with other nutrients. The following is a general presentation of the six micronutrients main functions:

• Zinc: It participates in the forming of hormones that affect plant growth and the forming of proteins. If the amount of zinc in a plant is not correct, nitrogen and phosphorus are not well used. Zinc contributes to better size fruit.
• Boron: It is related to sugar transportation in the plant. It affects photosynthesis, use of nitrogen, and synthesis of proteins. It participates in the blooming process and forming of the plant root system, and regulates its water contents.
• Iron: It is necessary to the forming of chlorophyll and it is an important part of some proteins and enzymes. It is a catalyst in oxidation and plant reduction processes.
• Copper: It is a breathing catalyst and forms enzymes. It participates in carbohydrate and protein metabolism and in protein synthesis.
• Manganese: It influences nitrogen use by the plant and acts on nitrate reduction. It is important in carbon dioxide assimilation (photosynthesis) and the forming of carotene, riboflavin, and ascorbic acid.
• Molybdenum: It is important in protein synthesis and nitrogen symbiotic fixation of nitrogen. It has also been associated to iron absorption and translation mechanisms.
Phenological stages
Germination

Germination occurs from 3 to 4 days after sowing, in temperatures of 25° C to 30° C (WIWN, 1997), and transplanting occurs between 8 and 10 days after sowing for tray-produced moulting. In direct sowing, germination occurs from 5 to 10 days after sowing. Optimal soil temperature for germination is from 16° C to 35° C (LORENZ; MAYNARD, 1988). Cucumber is one of the vegetables that requires the shortest time for molting, compared to other vegetables such as lettuce, tomato, and pepper, whose molting is transplanted from 22 to 28 days after sowing. In the case of grafted cucumber, molting time is considerably longer (30 to 40 days), as the grafting and bonding processes require certain time.

Vegetative Development

Cucumber plant growth is quite fast during almost the entire crop cycle, and becomes slower only during the final stages, when the plant starts the senescence process. The figure shows the Hokushin crop growth curve, grafting in Excite Ikki type pumpkin, conducted in a protected environment for the winter-spring period by Blanco, (researched in Brasil (1999)). It was possible to verify that growth pace kept practically continuous up to approximately 80 days after transplanting, but growth was drastically reduced after that period. The foliar area index (AIF) also showed a permanent growth up to the 63rd day after transplanting; however, measurements carried out at the end of the crop cycle showed a slight AIF decrease due to leaves senescence and reduction of the crop growth pace.

Altura de las plantas e índice de área foliar de plantas de pepino, cv. Hokushin, injertadas sobre zapallo híbrido Excite Ikki, en ambiente protegido, en diferentes épocas después del trasplante de las mudas al campo.


Plant height and foliar area index in cucumber plants, cv. Hokushin, grafted in hybrid Excite Ikki pumpkin in a protected environment in different seasons after transplanting moulting to the field.

Blooming


Cucumber is considered a neutral plant compared to the photoperiod, which means that it starts blooming independently from the day length. However, short photoperiods, low light intensity, and low temperatures increase the proportion of female flowers (FILGUEIRA, 1981). Nitsch et al. (1952) verified that an extended photoperiod (16 hours) severely reduced the number of female flowers and, under high temperature conditions (30 °C), they did not get to form at all. Cantliffe (1981) studied the effects of environmental factors (light intensity, photoperiod, and air temperature) on the alteration of the flower sexual expression in different crops and hybrids of cucumber for preserves. When environmental factors were analyzed independently, it was verified that the increase in light intensity resulted in the increase of female flowers. High temperatures (above 26° C) favored the forming of male flowers, while the photoperiod did not affect the plants sexual expression. However, when interaction between environmental factors was studied, high temperatures generally involved a reduction in female flowers, mainly in environments of low light intensity.

Insects play an important role in cucumber production, as they act as pollinating agents, responsible for the female flower fertilization and, therefore, for the forming of fruits, considering that cucumber pollen grains are not transported by the wind. This was a great difficulty that the first producers of cucumber faced in a protected environment, as insect population in these environments is quite reduced compared to the outdoors environment. Currently, hybrids cultivated under protected conditions present parthenocarpy, which means that fruits develop even without the pollination of the female flower which represented an increased productivity under those conditions.

Flowering occurs between 15 and 25 days after transplanting to the field, but in the case of grafted cucumber, flowers may appear quite early (between 7 and 10 days) because, as a result of the grafting process, there is a delay in moulting which, when transplanted to the field, is already in a more advance physiologic development with regards to the non-grafted moulting.

Production and Harvest

Harvest starts approximately 33 to 44 days after transplanting (in a protected environment) or 40 to 70 days after sowing (open field) (BLANCO et al., 2002; CAÑIZARES; GOTO; 2002; FILGUEIRA, 1981; RESENDE et al., 2001; SOLIS, 1982; SONNENBERG, 1980), and it may vary according to the crop environmental conditions or the hybrid used.

In traditional crops in open field, caipira, Aodai, and preserves cucumber are generally cultivated, whose cultivation cycle lasts from 90 to 120 days. Harvest is not based on the fruits ripeness, but on their size. For Aodai and Japanese cucumber, harvest is when fruit is 20 to 25 cm long. In the case of the caipira group, harvest occurs when fruit is 10 to 15 cm; in the case of preserves cucumber, when it is 5 to 16 cm long (SONNENBERG, 1980). For cultivation in a protected environment, where generally the Japanese-type cucumber is cultivated, the crop cycle goes from 60 to 90 days for non-grafted cucumber and from 100 to 140 days for grafted cucumber.
Phenological Stages


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