Zinc and phosphorus responses in transplanted oilseed rape (Brassica napus)

Raising seedlings in a nursery and then transplanting them into the mainfield is a common practice for intensive cropping systems but the special nutrient requirements of the transplanted field crop have seldom been considered, In the present study, the sensitivity of oilseed rape seedlings to post-transplanting zinc (Zn) and phosphorus (P) deficiency was examined in seven field experiments in Hubei province, central China. Oilseed rape was sown in nurseries in late September according to standard farming practice for transplanting at the 4-6 leaf stage into mainfields treated with seven Zn levels from 0-45 or 0-60 kg ZnSO4, ha(-1) in late October to mid-November. Increase of soil Zn supply resulted in the increase of shoot dry matter of plants at the rosette stage by up to 100%, at the green bud stage by up to 50%, and seed yield by up to 18%. That Zn fertilizers stimulated seed yield even on soils with 0.84 mg Zn kg(-1) suggests that Zn uptake by oilseed rape was inefficient. That oilseed rape plants from the rosette stage through the green bud stage contained more than adequate Zn in their young leaves for growth suggests that the plants were free of Zn deficiency for all but a short period after transplanting. The strong relative responses of oilseed rape to Zn at the rosette stage, and the weakening of the response with time suggests that oilseed rape experienced a temporary Zn deficiency after transplanting which limited final seed yield. The significance of these results for the nutrition of transplanted crops is discussed.