Managing clubroot disease (caused byPlasmodiophora brassicaeWor.) by exploiting the interactions between calcium cyanamide fertilizer and soil microorganisms

Abstract

SUMMARYCalcium cyanamide is a nitrogenous fertilizer used predominantly for over a century in field and glasshouse vegetable and salad production. The current review draws together, for the first time, knowledge concerning the biological properties of the compound that benefit crop production by encouraging sustainable soil health and quality. This is achieved through the increase of microorganisms antagonistic to plant pathogens. The review also reports on the natural occurence and degradation of cyanamide. The literature survey provides a perspective of research from the early 1900s to current studies. This identifies that nitrogen is released steadily into the rhizosphere from this fertilizer. Calcium is also readily available for plant roots and promotes the alkaline soil conditions beneficial to benign microorganisms. Consequently, soil suppressiveness towards organisms such asPlasmodiophora brassicae, the cause of clubroot disease in brassicas, develops. The effects of calcium and accompanying changes in soil pH values are discussed in relation to the life-cycle stages ofP. brassicaeand the development of clubroot disease. Formulations of calcium cyanamide contain the dimeric form, dicyandiamide. This compound slows soil nitrification and subsequent nitrate leaching into ground waters, reducing potential pollution. Calcium cyanamide is normally used for growing specialized fresh produce and is not available in quantities comparable with ammoniacal fertilizers. It is contended, however, that it has properties deserving wider assessment because of their implications for sustainable cropping.