A SIMPLE AVAILABLE SOIL NITROGEN INDEX

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Abstract
Summary: Available soil‐N values in commonly cultivated East African soils were determined in the laboratory by several methods, and correlated with one another.Mineralizable‐N was correlated more with total‐N than with organic‐C. The values of mineralizable‐N (Δ mineral‐N) obtained on aerobic incubation were correlated with crop yield and nitrogen uptake in greenhouse experiments. The yield of dry matter and N uptake by the tomato crop in the absence of applied nitrogen were significantly correlated with Δ mineral‐N in the soils; the degree of correlation decreased with increasing rates of fertilizer‐N applied and Δ mineral‐N and dry‐matter yield were not correlated at the largest rate used. N uptake by the crop was significantly correlated with Δ mineral‐N at all rates of applied nitrogen.The Δ mineral‐N value determined on soil samples conditioned by 6 weeks incubation followed by 3 weeks air drying was considered to provide a good index to available nitrogen.