Abstract:

【Objective】 The purpose of this study was to indicate the effects of phosphorus application on utilization ratio of nitrate accumulated in deep soil profile by wheat in north China. 【Method】 Field micro-plot experiments and the injection technique of labeled NO3--N were adopted. 【Result】The results showed that, 15N which was injected in 100-120 cm soil profile and diffused in the near layers could be absorbed by wheat with the utilization ratio of nitrate 6.8%, 16.4%, 11.2% in three P levels of P0, P60, P120. The phosphorus applied in the topsoil made the roots grow better with more root length density and dry root weight in it than without phosphorus, by which more deep soil nitrate could be assimilated by wheat and then improved the utilization ratio of nitrate by wheat. 【Conclusion】 Phosphorus application promoted the growth of roots in the deep layers which accelerated the absorption of nitrate accumulated in deep soil profile by wheat, while too much phosphorus fertilizer inhibited the growth of roots of wheat.

Key words: 15N, phosphorus, wheat, nitrate, utilization ratio of nitrate, roots