Effects of Hemp Retting Water on the Composition of Soil Bacterial Community and on Wheat Yield

BACKGROUND. The effect of hemp retting water on test plots has been evaluated by molecular and agronomic analyses. The purpose was to consider the possibility of an ecologically compatible disposal of these effluents in agricultural ecosystems, in the event of a revival of industrial hemp cultivation. METHODS. Plots of wheat received 3 doses (0, 80 and 160 m 3 ha -1 ) of retting water in 2000. During the cultivation cycle, soil samples from the 0-20 cm layer were collected and analysed molecularly (DNA extraction, DGGE analysis and specific hybridisation of the eubacterial community and autotrophic oxidising ammonia bacteria). The agronomic analyses examined the biometric and production characteristics at harvesting: plant density and height, number of kernels per spike, seed weight and grain production. RESULTS. Molecular analysis indicates that a modification in the microflora occurred as soon as the water was spread. This change disappeared during the growing cycle and the DGGE profiles of the different trials were identical in May and July. The biometric and production data do not indicate any effect of the water on the plants’ phenotypic and production characteristics. CONCLUSIONS. The water from hemp retting, at the doses tested, seemed to have no negative effects on the telluric microflora nor on the morpho-biometric and production characteristics of the wheat plants. It instead tended to improve crop yield, although not significantly.