Abstract The effects of a compost (produced from by-products of the olive oil industry) and a poultry manure on mineral ion solubility and exchangeability in a highly saline agricultural soil (electrical conductivity for a 1:5 soil:water extract = 1.85 dS m −1) from Murcia (SE Spain) were studied. The organic amendments did not change significantly the soil electrical conductivity or the soluble Na +, Ca 2+ or Mg 2+. Only soluble K + increased, due to the K + supplied by the amendments. The cation exchange capacity increased in treated soils, the exchange complex being mainly saturated with Ca 2+, Mg 2+ and K +. However, Na + was not retained in the exchange sites, and the sodium absorption ratio remained low. The compost and manure increased markedly the shoot growth of the salt-tolerant Beta maritima L. (sea beet) and Beta vulgaris L. (sugar beet). For B. maritima, this seemed to be related to decreases in the shoot concentrations of Na + and Cl − and increases in K + and H 2 PO 4 - . In the case of B. vulgaris, increases in shoot H 2 PO 4 - and B and, for manure-treated soil, a decrease in shoot Na + may have been involved. Cultivation of tomato ( Lycopersicon esculentum Mill. cv. Moneymaker) in the soil used previously for B. vulgaris indicated that the effects of the manure on tissue cation concentrations were longer-lasting than those of the compost.