In many parts of Europe, including Switzerland, April and May is the season for this plant which produces flowers with an intense yellow color. The plant is known as canola, colza, rapeseed or in Latin – Brassica. It is a member of the Cruciferous (Brassicaceae) family, sometimes referred to as the mustard family. The name “cruciferous”comes from the shape of its flowers, which have four diagonally opposite petals in the form of a cross. In Europe, this plant is primarily cultivated to provide animal feed – cattle, due to its high lipid and medium protein content.  Commercial plantings of rapeseed are recorded in the Netherlands as early as the 16th century. At that time rapeseed oil was used primarily as an oil for lamps. Later it came to be used as a lubricant in steam engines. The farms here grow a variety of crop and will use the same field for something else later in the year. According to Wikipedia:

Some varieties of rapeseed (called 油菜,”oil vegetable” in Chinese; yau choy in Cantonese; cải dầu in Vietnamese; phak kat kan khao [ผักกาดก้านขาว] in Thai; and nanohana [菜の花]/nabana [菜花] in Japanese) are sold as greens, primarily in Asian groceries, including some in California, where it is known as yao choy or tender greens. They are eaten as sag (spinach) in Indian and Nepalese cuisine, usually stir-fried with salt, garlic and spices.

I can see the resemblance but am not sure if it tastes good or even edible. These pictures were taken just outside Yverdon-les-bains, a city half way on my commute to the office.  My train passes seas of bright yellow flowers during this time of year. This area constitutes obviously one of the flatter parts of Switzerland. It is on the western edge of the Swiss plateau at the foot of the Jura mountains. There were several stables and riding schools in the area. . The trees were still a bit naked at this time of year. The epiphytes growing on the trees were clearly visible (at first we thought they were bird’s nests). . The field was readied for planting another kind of crop. What kind of crop ? There is also a small airfield here. The fields of yellow flowers must be quite a sight from above. .