Doubly labeled barley ( Hordeum vulgare L.) plants were grown in a closed chamber containing 13 C‐enriched CO 2 and 15 N‐enriched nutrient solution. Tops and roots were separated, ground, and added to Columbia fine sandy loam in fritted glass filter tubes. Soil samples were incubated with continuous flow aeration for 5 years. Evolved CO 2 was trapped for 22 weeks. Mineral nitrogen was leached from the samples at intervals throughout the 5‐year period. After 5 years, only 12% of the carbon from tops and 16% of that from roots remained in soil, compared with 38% of the nitrogen in tops and 57% of the root nitrogen. Average annual losses of carbon from soil organic matter were 6.1–6.8%; annual turnover of nitrogen varied from 6.3 to 7.4%. Availability ratios for nitrogen decreased as a function of time from about 2.5 initially to 1.2 at the end of the incubation period. Unaccounted‐for losses of nitrogen from barley tops and from soil organic matter were 15–17%, but only 2% from roots.
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Broadbent et al. (1974) studied this question.