Effect of cultivars and nature-based solutions for the reduction of phosphate fertilizer usage on oilseed rape

Oilseed rape (Brassica napus L.) is the most important temperate oil crop globally. Maintenance of soil phosphate (Pi) availability, through the application of Pi fertilizers and manures, is needed to maintain seed yield of oilseed rape. Over-application of the Pi fertilizers results in Pi accumulation in agricultural soils and adjacent ecosys-tems, where it can drive eutrophication in freshwater and coastal systems. In this study, two years of field ex-periments were conducted to explore the optimal Pi fertilizer application rate for four oilseed rape cultivars and the potential of nature-based solutions including Pi solubilizing bacteria (PSB) and rooting agent (RA) to reduce Pi fertilizer application rates for oilseed rape. The seed yields of cultivars Shengguang 168 (SG168) and Huayouza 9 (HYZ9) were significantly higher than those of cultivars Zhongyouza 19 (ZYZ19) and Zhongshuang 11 (ZS11) across all Pi application rates. In comparison with Farmers' fertilizer practice (P26.2, 26.2 kg P ha-1), Pi fertilizers could be reduced by more than 25% for the four cultivars, and be reduced by as much as 50% for SG168. The shoot dry weight and seed yield of ZS11 with the addition of RA at P21.0 (21.0 kg P ha-1) in Expt. 2-1 and P15.7 (15.7 kg P ha-1) in Expt. 2-2 showed no significant difference to that of P26.2 at the ripening stage, but were significantly higher than that of P21.0 and that of P15.7, respectively. At P0 (0 kg P ha-1), addition of PSB significantly increased the shoot dry weight and seed yield of ZS11 at the ripening stage. However, at P21.0 in Expt. 2-1 or at P15.7 in Expt. 2-2, addition of PSB had no effect on shoot dry weight and seed yield of ZS11. These results highlighted the feasibility and potential to reduce the application rate and improve the use efficiency of Pi fertilizers in oilseed rape using nature-based solutions.