Phosphorus efficiency of cabbage (Brassica oleraceae L. var. capitata), carrot (Daucus carota L.), and potato (Solanum tuberosum L.)

Plant species and genotypes within the same species may differ in phosphorus efficiency. The objective of this research was to study phosphorus efficiency of cabbage (Brassica oleraceae L.), carrot (Daucus carota L.), and potato (Solanum tuberosum L.) and to quantify the contribution of morphological root characteristics to P uptake of the plant species. An experiment was conducted in a glasshouse with six P levels: 0, 12, 27, 73, 124 and 234 mg P kg(-1) soil, and with six replications. Cabbage attained 80% of its maximum yield already at the level of no P supply, whereas carrot and potato reached only 4 and 16% of their highest yields respectively at this level of P supply. This indicated that cabbage was P-efficient compared to carrot and potato. Root/shoot ratio (cm root g(-1) shoot d. m.) increased in the order of cabbage < carrot < potato, and was enhanced at lower P levels. Root hair length was not affected by P level, and averaged 0.22, 0.03 and 0.18 mm for cabbage, carrot, and potato, respectively. Predicting P uptake by a mechanistic simulation model revealed that root hairs contributed about 50% to the total P uptake of cabbage and potato, but only 0.3% to that of carrot. The relationship between the observed P uptake and the predicted P uptake of the plants revealed that model parameters explained nearly 4/5th of the total P uptake of carrot and potato, but only 2/5th of that of cabbage. This showed that the P uptake of cabbage was strongly under-predicted, whereas that of carrot and potato was predicted well. Therefore, it was hypothesised that cabbage may have the ability to mobilise and take up soil P additionally by other root mechanisms such as exudation of organic acids.