Odlingens och lagringens inverkan på utsädes grobarhet

Abstract: At seed-growing the aim is to produce a commodity with high germination capacity, good soundness and purity, and also slight admixture of seeds from other species. The capacity of germination and the vigour of the seeds may become impaired in consequence of mechanical damage, infection of diseases, growth of mould, attacks of vermin, high drying temperature, secret germination, sprouting in the ears etc. The germ belongs to the outer and most unprotected parts of the seed, and consequently this is much exposed. Even quite sound seeds can instantaneously have low capability of germination. It can be due to the fact that the seeds are in rest of germination, i.e. they absorb water without germinating, or that they are unable to take up water (a condition called hard seeds). All plant species have a more or less pronounced rest of germination. During damp harvest weather, seeds with optimal rest of germination escape secret germination and sprouting in the ears, but later at germination test or sowing, they are tended to germinate. At germination analysis, there are methods to break the rest of germination, partly by chemical treatment but also by influence from the surroundings as for example temperature regulation. Hard seeds occur in legumes for ley and in some other leguminous plants as for instance lupin and field beans. The hardness may be short, but often it lasts in several years. In order to attain a high capacity of germination in the finished product an even ripeness is required, for which the conditions are best in even plant stands with optimal compactness. The mother seed should be of good vigour, the conditions of germination proper, the growing of side-shoots reduced etc. At seed breeding, threshing is ought to be performed during the later parts of the harvesting ripeness, because the germination capacity is rising during the advancing of ripening, provided that no sprouting in the ears is initiating. This doesn't concern peas, which are particularly crack-willing at low water content. Regarding peas and oil plants the sensitivity to mechanical effects is continuously increasing with lowering water content of the seeds. Generally grain however have a minimum of sensitivity at a water content of 17-20 %. At lower water content, there is a risk of cracks or other defects in the germ of the hard and dry seed. At higher water content the seed is so soft that it easily is split at rough treatment for example in the thresher. Ley plants are more tended to shed seeds and have more pronounced disposition towards sprouting in the ears than the contemporary assortment of cereals. As for pasture grass, the risk of shedding seeds can be reduced by a sufficiently early windrowing or by a well-balanced supplying of nitrogen. The velocity of circumference of the threshing cylinder is determining the emergence of damage on the seeds, while the concave clearance to a greater extent regulates the threshing and wearing. High number of revolutions on the cylinder easily cause cracks, which are impairing the germination viability. These cracks can induce increased breathing, sensitivity to drying and disinfection and also constitute an entrance-gate for pathogens. The pods of the oil plants are very easy to thresh and the threshing shouldn't be harder than that the unripe seeds stay in their pods and are separated from the seed goods. Clover seed demands comparatively hard threshing with concave cover plates, at the same time as too high number of revolutions risk occasioning damage of germination on the superficial germ. If the plants are quite dry and the weather is sunny the clover hulling is making easier. To grass seed, which generally is easily threshing the cylinder-speed should be the lowest possible to avoid damage of germination. At threshing of timothy, there is a risk that the seeds will be hulled. At combine harvesting of peas, you must notice that the pegs of the reel easily can harm the inside of the pods at incautiously handling. In general, at threshing and internal transport, the seeds are exposed to the most mechanical strain. During the drying the sensitivity to mechanical damage of the goods have increased. 6 In order to prevent increasing heat production and growth of mould with deteriorated germinating as a consequence, a moist crop product requires an immediate after-treatment. The moister the seed is the more sensitive to high drying temperature it is. At specific initial water content, it's the temperature in the seed which is determining the reduction in capability of germination. The highest permitted temperature in the drying-air is individual for different drying plants, but as a rule it is a little higher than the critical temperature of the seed. Carefully performed drying and cooling reduce the risk of attacks of the heat-depending noxious insects, which often search for the nutritious germ. At heavy drying oil-seeds become more brittle and sensitive to mechanical influence during the later handling. In opposite of peas, for oil-seed the drying itself doesn't seem to initiate emergence of cracks. Owing to large volume, weak permeability of the shells and the great tendency to emergence of cracks, peas are a kind of seed which is much difficult to dry. Drying with supplemental heating may be an advisable method, considering the apparent risk of cracks. Peas can also be dried in hot air, but this high temperature-drying must be done with especial carefulness. At drying, the risk of emergence of cracks is enhanced with increasing water content, drying temperature and drying time. After harvest moist leyseed demands to be prompt blown through with large air quantities. When the water content have gone down below 20 % the final drying with slightly heated air can begin. Drying to level of solid storing must be finished before growth of mould is initiated, for which reason the humidity of the drying air isn't allowed to be too high, the drying temperature not too low and the height of storage must be limited. Furthermore the air quantity must be large, whereas the air speed and the distance between the side canals should be restricted.