Other ratios

C:N (or carbohydrate:protein) ratios are important with respect to the relative requirements of plants and microbes. Straw has a C:N value of approximately 80:1, whereas after ploughing under to form a humus-rich soil, the value narrows to about 12:1. Albrecht found that the humus fraction of the experimental Sanborn Field, cultivated over 50 years, had a C:N ratio of about from 2:1 to 3.4:1, where the lower ratio is similar to that of the microbes themselves. Therefore, if microbes feed on straw that has been incorporated into the soil, they will require an additional source of nitrogen, and happen to be more successful at competing with plants for the same nutrient. In Missouri clay, Albrecht found 1.5% C and 0.15% N, which represents a favourable ratio of 10:1, and is an average value for well-weathered soils (Walters, 1989).

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