Short Communications

A comparison of several nitrogen- availability indices on four Natal maize-producing soils

Published in: South African Journal of Plant and Soil
Volume 2, issue 3, 1985 , pages: 164–166
DOI: 10.1080/02571862.1985.10634160
Author(s): B.L. Schroeder, Republic of South Africa, M., P.W. Farina, Republic of South Africa, M.V. FeyDepartment of Soil Science and Agrometeorology, Republic of South Africa

Abstract

Four methods used in obtaining nitrogen-availability indices were compared using soil and plant samples taken from maize trials conducted on four widely differing Natal soils. NO3 N was determined after extraction of the soil with NH4HCO3, Ca(OH)2 and KCl, using a specific ion electrode, phenoldisulphonic acid and brucine respectively. In addition, NO3 -N and NH4 + -N were determined after steam distillation of KCl extracts. The measurements so obtained were correlated with the rates of nitrogen application and leaf-N content at flowering. The four NO3 -N determinations were all closely correlated with each other and with the level of N applied. The overall correlation across soils between N applied and increase in NO3 -N exceeded 0,85. Inclusion of NH4 + - N did not materially improve the relationship between soil test and N application rate. NO3 -N was also well correlated with leaf-N content. The levels of NO3 -N measured in the absence of fertilizer N relate well to previously measured N responses on these soils.

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