Effect of salinity on growth, water use and nutrient use in radish (Raphanus sativus L.)

Radish (Raphanus sativus L.) plants were grown at five soil salinity levels (1, 2, 4, 9 and 13 dS m(-1)) to analyse the effects on growth, dry matter partitioning, leaf expansion and water and nutrient use. Salinity was varied by proportionally changing the concentration of all macro nutrients. When the electrical conductivity (EC) of the soil solution increased from 1 to 13 dS m(-1), the influx concentration of the nutrients absorbed by the plants (the ratio between the uptakes of nutrients and water) increased only from 1.6 to 3.5 dS m(-1). The total nutrient uptake showed an optimum at an EC of the soil solution of about 4 dS m(-1). The data suggest that at low salinity level (less than or equal to 2 dS m(-1)) the nutrient uptake was limited by availability while at high salinity (> 4 dS m(-1)) it was limited by the growth of the plant. Total water use by the plants decreased and water use efficiency increased at high salinity. Plant growth was optimal at 2-4 dS m(-1). At salinities higher than 4 dS m(-1) total plant dry weight decreased 2.8% per dS m(-1). About 80% of the growth reduction at high salinity could be attributed to reduction of leaf area expansion and hence to reduction of light interception. The remaining 20% of the salinity effect on growth was most likely explained by a decrease in stomatal conductance. The small leaf area at high salinity was related to a reduced specific leaf area and increased tuber/shoot weight ratio. The latter could be attributed to tuber formation starting at a smaller plant size at high salinity.