THE K NA AND CA/NA RATIOS AND RAPESEED YIELD, UNDER SOIL-SALINITY OR SODICITY/

Rapeseed (Brassica napus) is a crop relatively tolerant to salt and so dium. Our objective was to study the interactions between Na, K and Ca and their relationship with its yield under the isolated effects of s oil salinity or sodicity. Two experiments were carried out using pots filled with the Ah horizon of a Typic Natraquoll. There were three sal inity levels (2.3 dS m(-1); 6.0 dS m(-1) and 10.0 dS m(-1)) and three sodicity levels, expressed as sodium adsorption ratios (SAR: 12; 27 an d 44). The soil was kept near field capacity. As soil salinity increas ed, the K/Na and Ca/Na ratios in the tissues decreased markedly but yi elds and aerial biomass production were not affected. As soil SAR valu e increased, the K/Na and Ca/Na ratios in plants and K-Na and Ca-Na se lectivities decreased. Plants could not maintain their Ca concentratio n in soil with a high SAR. The grain yield and biomass production dimi nished significantly in the highest SAR treatment. Our results are con sistent with those showing detrimental osmotic effects of salts in Bra ssica napus. Conversely, under sodicity, the K/Na and Ca/Na ratios in plant tissues decreased considerably, in accordance with grain and bio mass production. These results show that the effects of sodicity are d ifferent from those of salinity.