Calcium Cyanamide in Relation to Control of Clubroot of Cabbage'

In a previous publication ^ the writers reported comparative studies of the effect of calcium hydrate (Ca(0H)2), calcium carbonate (CaCOa), and certain other compounds, when applied to infested soil, upon infection of cabbage by the clubroot organism {Plasmodiophora brassicae Wor.). It was shown that, in well-watered soil in the greenhouse, infection was reduced perceptibly when the reaction of an acid soil was changed to about pH 7.0, and it was usually inhibited completely at pH 7.2 and above. In the field even heavier applications of Ca(0H)2 and CaCOs often failed to control the disease although the reaction of the soil was maintained at pH 7.0 or above. When soil was removed from such field plots, however, and tested by growing cabbage plants upon it in the greenhouse, inhibition of the disease was usually complete. The difference between field and greenhouse environments, therefore, appeared to influence the effectiveness of these materials upon clubroot development. The present paper is a report of a comparative study of Ca (011)2 and calcium cyanamide (CaCN2) upon clubroot infection. When applied to moist soils CaCN2 undergoes hydrolysis as a result of which Ca(011)2 and urea (CO(NH2)2) are formed. Before hydrolysis is complete, the cyanamide anion (CN2) may be toxic to higher plants. Cyanamide disappears from the sou solution more slowly in some soils than in others, and the factors which influence this change have been studied recently by Fink ^. In normal soils urea is ammonified rapidly and at this stage a marked increase in alkalinity or decrease in acidity results because two basic substances, Ca(0H)2 and (NIl4)2CO3, have been produced. When nitrification of the latter takes place, there should be no change in reaction because there is sufficient Ca in the CaCN2 to combine with the nitric acid formed. The extent of the influence of the addition of CaCN2 to a soil on the reaction of that soil will thus depend on soil conditions and the time that has clasped since the addition. In the case of very acid soils, a marked decrease in acidity should result for some time, because the soil acids will combine with the free lime and ammonia as soon as they are