Nitrogen and sulfur mineralization of several Manitoba soils and N:S ratios in rape and barley
Hamm, Jacob Wallace
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A field experiment, conducted in the summer of 1967, disclosed that total N:S ratios of plants in the early stages of growth can be used to evaluate their sulfur status. The critical ratios above which rape and barley are sulfur deficient were suggested to be 12:1 and 16:1, respectively. The critical sulfur concentration in rape at the flowering stage was proposed to be 0.25% total sulfur. The water soluble SO4 fraction of soils was further evaluated as an index of plant available sulfur. A critical level of 10 lb/Ac to the 24 inch depth at seeding was suggested for cereals. The corresponding value for rape was thought to be in the range of 20 to 25 lb/Ac. The relative rates of nitrogen and sulfur mineralization in soils were studies under field and laboratory conditions. The mean ratio of NO3-N:SO4-S release in soils cropped to rate and barley at two sites was found to be 4.3:1. This ratio was somewhat narrower than observed in the laboratory experiment. The ratios of release in soils of the Chernozemic and Podzolic Orders after incubation for 12 weeks at 18'C and near field capacity moisture content were 11.9:1 and 28.4:1 respectively. Nitrogen was found to be released faster than sulfur. The amounts of NO3-N and SO4-S released on incubation were correlated to the organic matter content of the soils.