Abstract

Sunflower and canola (rapeseed) are the important edible oilseed crops in Turkey and the world. Both crops have strong demand as a healthy vegetable oil due to their low level of saturated fats, making them popular as cooking vegetable oil and for use in processed foods.

More than 75 % oil type sunflower and canola crops are grown in Trakya and Marmara region of Turkey. Especially, canola is rapidly gaining acreage as a rotation alternative with small grains and other crops in last ten years in Trakya region.

Profitable sunflower and canola production relies heavily on adequate plant nutrition, which in turn is affected by management of soil fertility. In addition, the nutritional level of the plant will affect the crop response to stress factors such as disease and adverse weather conditions. Balanced, effective fertilizer management not only contributes to profitable sunflower and canola yield but also helps to maintain the productivity of the soil resource.

In case of potassium (K) deficiency in soil reduces overall sunflower and canola growth. Since K is mobile within the plant, deficiencies are first visible in older leaves. The edges and areas between veins of older leaves tend to turn pale green or yellow, followed by withering. The yellowing can occur first in middle leaves before older ones if observed at bolting to flowering stages. In severe cases, plant leaves die but remain attached to the stem. Small white spots can develop on leaves. Plants are usually prone to wilting during midday.

Very sandy soils are the most likely soil types to have very low K soil test values. Other factors that increase the likelihood of K deficiency are free lime in the rooting zone, acid soil, poor drainage, cool temperatures, soil compaction, shallow root zone, and sodium toxicity. Researches show that salinity affects plants more detrimental in the soil deficient in potassium, but it less affect the plants grown in the soil containing optimum and high potassium.

The major function of K in plants is in water relations. Potassium helps to maintain a favorable water status in plants in several different ways. Potassium cations dissolved in cell sap perform major potassium cations also maintain the water relations in plants through their crucial role in regulating water loss by transpiration from pores in the leaves. Therefore, potassium deficient plants often have higher transpiration rates and display wilting.

Potassium should be applied if recommended by soil test. Researches suggest that a 2500 kg per hectare sunflower or canola crops would take up about 100 kgs/ha of potassium. Due to plants sensitivity to seed-placed K fertilizer, a band placement away from the seed row is more advisable. Sideband placement is an efficient method and the separation between fertilizer and seed reduces the risk of germination damage.

Key Words: Sunflower (Helianthus annuus L.), canola (Brassica napus ssp. oleifera L.), potassium, fertilization.