Comparing Canola and wheat seedling use of different sources of phosphorus

A glasshouse study, using soil collected from two sites, was undertaken to compare how 30-day-old seedlings of canola (Brassica napus) and wheat (Triticum aestivum) utilized phosphorus (P) from freshly-applied (current) triple superphosphate (TSP), and TSP and rock phosphate [North Carolina and Queensland (Duchess) apatites] (RP) applied in field experiments 11 years previously (previous P). The P was applied to the soil surface and incorporated into the top 10 cm of soil with a rotary hoe. After application of the current P in the field, samples of the <2-mm fraction of the top 10 cm of soil were collected for the glasshouse study. Both canola and wheat produced poor yields without P but responded strongly to applied P. Regardless of the source of P (current and previous TSP, previous RP), canola required less P than wheat to produce the same percentage of the maximum yield of dried tops. For each amount of applied P, the concentration of P in dried tops was from about 30 to 120% higher for canola than wheat, indicating that canola roots were better able than wheat roots at accessing P from the soil, regardless of the source of P.