Sulfur in Ghanain soils

Abstract

Sulfur availability in twenty selected surface soils (0–22 cm), which varied in both physical and chemical properties and sampled under cultivated and uncultivated management in the various ecological zones of Ghana, was studied. Texture varied from coarse sand to clay, with 16–85% sand and 10–51% clay. Organic C varied from 0.45 to 2.24% and total N from 0.034 to 0.215%; soil pH (0.01M CaCl2) from 3.69 to 7.43 and total S from 44 to 273 ppm. Inorganic sulfate formed 2.3 to 14.8% of the total S, HI-reducible S 4.4 to 28.2, C-bonded S 4.4 to 28.2 and unidentified organic S 12.7 to 63.2%. Sulfur availability was assessed by chemical extraction methods and electroultrafiltration technique as follows: (i) extraction with Ca(H2PO4)2·H2O solution containing 500 ppm P, (ii) extraction with 0.1M LiCl and (iii) electroultrafiltration (EUF) at 80°C, 400 V for 10 min and also on seven of the soils the standard EUF fractionation procedure of Nemeth. Ca(H2PO4)2-extractable S was not significantly correlated with LiCl-extractable S nor with any of the EUF values. LiCl-extractable S was not significantly correlated with sulfate extractable by and EUF−1+2+3 fractions (r=0.911**). Dry matter yield of oat seedlings and EUF−1+2+3 fractions (r=0.911**). Dry matter yield of oat seedlings was not correlated with any of the availability indexes. Total S uptake was significantly correlated with LiCl-extractable S (r=0.629** without S and 0.729** with S applied) and with EUF-80°C, 400 V/10 min (r=0.561**), EUF-1 (r=0.953***) and EUF-2 (r=0.912**). On all the soils, more S was taken up by oat plants than could be accounted for by the inorganic S and S mineralized from organic S during an incubation period of 4 weeks.