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Sweet-corn
	Genetic background Normal sweet corn Extra sweet varieties Sweet-gene-hybrids Cultivation Fertilization and water supply Plant stand Side shoots Weed control/pests and diseases Extension of the harvest period Early cultivation Harvest Cooling Preparation and marketing


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Cultivation

Place and climate

In its origin, corn is a plant of warmer regions with large sunshine periods (C4-plant), which demands a good and regular supply of water and nutrients.

As is the case with field corn, where the growing of earlier and adapted hybrids led to a rapid development of its cultivation, today sweet corn varieties with good properties for the cultivation in Central and Northern Europe are also available. One may say that in all regions where field corn is cultivated, it is also possible to cultivate sweet corn. However, in colder regions, measures such as later sowing and early covering are necessary to meet the higher demands on soil temperature. The requirement of a higher soil temperature can be explained by the fact that these hybrids store smaller quantities of starch as reserve material in the nutritive tissue of their grains. This reduces the germination and vigour of young plants. For this reason, a soil temperature of aprox. 12 -13° is necessary for the development of the young plants, whereas field corn requires only 10°.

Sweet corn seeds (type normal sweet su1) are largely shrunken and usually have a smaller 1000 seed count weight than field corn (aprox. 125 - 250 g/ 1,000 grains). Due to the reduced storage of starch, the grains of extra sweet varieties (sh2 - su1) are even more shrunken. This is the consequence of the much slower transformation of sugar into starch. So the great advantage in comparison with field corn has been achieved by making concessions in this respect.

Consequently, sweet corn has higher demands on soil temperature and structure than field corn. When it is sown early, a higher safety margin has to be calculated when determining the seed quantity. The following table shows the relation between germination period, germination temperature and vigour.

	Soil temperature and germination period

soil temperature	10	15	20	25	40
days before germination	22	12	7	3-4	0
vigour*	15	74	82	84	0

Observation:	min. germination temperature 10° max. germination temperature 40°
* our own observations on commercial seeds with germination x

According to these figures, sweet corn should be sown when the soil temperature is between 12 and 13°.

Before sowing, one should make sure that the seed bed is sufficiently loose and moist, but not wet. To prevent losses of vigour caused by low soil temperature, it is generally recommended to start sowing after the first decade of May.

Commercial seeds of our varieties are coated against field born diseases (fungicides). Of course, untreated seeds for biological cultivation are also available.

Required seed quantity
The required seed quantity for direct sowing ranges from 14 to 20 kg/ ha, depending on 1000 seed count weight, germination and variety. The following calculation shows how the seed quantity can be determined:

Example

	desired number of plants/ m2 x 1000 seed count weight
	Kg/ha=	expected field emergence %
recommended variety:	7 plants/m²
1000 seed count weight (g)	158
indicated germination:	90 %
expected field emergence	80 %
	7x158 = 80	13,82 kg/ha

The element of uncertainity in the foregoing example is the expected field emergence. If values for the vigour are not available, the indicated germination should principally be reduced by 10% for calculation purposes. For early sowing, or if the soil is cold and wet, this percentage must be increased to 15%. According to our experience, a cold test as is usual for field corn can also be realized for sweet corn in order to determine the best sowing time. However, this test should be realized on the basis of 12° instead of 10°.