The Effects of Several Agricultural Treatments on the Nitrogen Status of a Red Earth in Uganda

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Simpson,J. R.
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The rapid seasonal fluctuations in topsoil nitrate status, which characterize soils under cultivation in large areas of Uganda, have been described by ap Griffith (1951), Mills (1953) and Simpson (1960). Nitrate which has accumulated during a drier period is rapidly lost from the topsoil by leaching, by microbial reactions and by plant uptake during subsequent wet periods. Continued cultivation and cropping thus leads to a rapid decline in the available-nitrogen status of the topsoil and consequent severe fall in crop yields. Such effects may occur at Kawanda after four to six years of cropping during which two crops, usually a cereal crop plus a pulse or cotton crop, are taken each year. The later crops in the sequence thus show pronounced nitrogen deficiencies and sometimes phosphorus deficiencies while the topsoil may develop an acid reaction of pH 5.0 or less. At this stage, responses to cations, especially magnesium, have been obtained.
East African Agricultural And Forestry Journal, 26, p. 158-163