Sulphur Status Of Some Kenya Soils And Its Availability To Plants

Abstract

The sulphur status of major agricultural soils of Kenya was estimated through laboratory determinations of total sulphur, organic sulphur and sulphate sulphur and through use of the Janssen double-pot technique. The soils used were four Ferralsols, three Nitosols, two Vertisols, two Arenosols, one Luvisol and one Andosol.

The total sulphur content was generally low (average

143 ppm S, range 12-406 ppm S) with more sulphur in the topsoils (0-30 cm) than in the subsoils (30-60 cm). The sulphate-sulphur content varied between 8.61 ppm S to 86.05 ppm S in the topsoils, while in the subsoils it varied be- tween 7.31 ppm S to 115.14 ppm S. In two soils (both Ni- tosols), there was evidence of sulphate sulphur accumula­ tion in the subsoil. The organic sulphur content of the soils varied between 5.25 ppm S to 320.11 ppm S in the top­ soils and 5.25 ppm to 324 ppm S in the subsoils. The Janssen double-pot experiment indicated a response

to sulphur and this response was best predicted by the sul­ phur Sufficiency Quotient or percentage dry matter yield. Although subsoil S was less than that in the topsoil, it was more available for plant uptake, indicating that &)rbed

S in the subsoil is subsequently available for plant uptake.

A sulphur fertilizer rate pot study indicated that for Ferralsols, Andosols, Arenosols and Luvisols, sulphur rates for maximum growth would be between 15 Kg S/ha and 30 Kg S/ha and about 15 Kg S/ha for Vertisols.