THE EFFECTS OF SOIL SODICITY ON EMERGENCE, GROWTH, DEVELOPMENT AND YIELD OF OILSEED RAPE (BRASSICA-NAPUS)

The effects of exchangeable sodium on emergence, growth, development a nd yield composition of oilseed rape were investigated at Buenos Aires , Argentina in 1992. A pot experiment was performed using five exchang eable sodium levels, expressed as Sodium Adsorption Ratio (SAR: 12, 20 , 27, 34 and 44). Soil with nine different exchangeable sodium content s (SAR from 0.5 to 50) and seven different particle size distributions (from sandy loam to clay) were used in a parallel trial to study the effect of soil crusting on oilseed rape emergence. Soil crusts were ma de using a rainfall simulator after seeds were sown. Both experiments showed that the direct effect of sodium on emergence occurred with SAR values higher than those which caused clay dispersion (SAR > 20). Oil seed rape seedlings could penetrate crusts having a resistance of < 23 0 kPa. At SAR values > 20, main stem growth and yield decreased signif icantly (P < 0.05). These reductions were counterbalanced by an increa se in the number of secondary stems. At SAR levels > 34, stem number, grain number per pod on the main stem, as well as pod number on both m ain stem and secondary stems, were reduced, leading to a marked reduct ion in total yield. The most important agronomic effect of soil sodium on oilseed rape would be at emergence stage, due to soil crusting.