Lactuca sativa growth in compacted and non-compacted semi-arid alkaline soil under phosphate fertilizer treatment and cadmium contamination

•The effect of coupled interactions between soil compaction, superphosphate and cadmium on lettuce growth are investigated.•Cadmium mobility in soil and its accumulation and translocation in lettuce are also examined.•Compaction lead to an increase in root and shoot dry matter and leaf area and a decrease of chlorophyll content and NRA.•Cd uptake in plants increased when Cd was present in the soil.•Accumulation of Cd is less in plants cultivated in Cd-P treated soil than in plants cultivated in Cd contaminated soil.

Soil compaction is known to drastically modify soil properties and hence to affect both plant growth and metal distribution in the soil. Phosphate amendment is generally used to improve plant production but unfortunately it also gives rise to higher metal contamination in soils and plants. In this work, we aimed to study the effects of soil density, phosphate fertilization and cadmium contamination on the growth of Lactuca sativa. In particular, the migration of cadmium in the soil columns, its accumulation and translocation in lettuce were also examined. Lactuca sativa was selected as a model plant because it is widely cultivated in alkaline clay soils of eastern Mediterranean countries. Two levels of soil compaction (1.2 and 1.4 g cm−3), two rates of P amendment (0 and 109 mg P kg−1), and two levels of Cd contamination (0 and 84 mg Cd kg−1) were used in 24 model columns with a factorial randomized block experimental design. Soil compaction increased considerably both leaf area and dry weight of roots and shoots, whereas both chlorophyll content and NRA decreased. For the two soil bulk densities, the phosphate fertilizer improved lettuce growth characterized by plant height, dry matter, leaf number and NRA, whereas Cd contamination altered those parameters and increased the chlorophyll content. In soils contaminated with cadmium, the combination of compaction and phosphate fertilization resulted in a significant decrease in Cd migration along the soil columns. Cd uptake by plants increased in Cd treated soils; its accumulation was found to be more important than in plants grown in P-Cd treated soil where Cd uptake was clearly reduced in shoots and roots.