Abstract:

【Objective】 The purpose of this study was to indicate the effects of phosphate fertilizer applied to topsoil on the movement and residual effect of nitrate which was accumulated in deep soil profile in North China Plain. 【Method】 The injection technique of labeled NO3--N was adopted in a field micro-plot experiment. Three phosphate fertilizer treatments were desigred at each experimental site. The labeled NO3--N was injected in 110 cm soil profile. 【Result】 At this condition, the distribution of residual amount of 15N in each soil profile after wheat harvest was: P60＜P120＜P0. The labeled NO3--N moved at vertical distance. It moved 50 cm to the topper soil profile and 70 cm to the lower.The peak appeared in the depth of 120-140 cm where it was 30 cm below the labeled place. After maize harvest , most 15N was detected in 100-180 cm. The peak moved to 140-160 cm. Maize could absorb the residual 15N with the utilization ratio of nitrate 1.2%, 2.5%, and 2.2% for the treatments of P0, P60, and P120, respectively. The phosphate fertilizer which was applied to topsoil in wheat season made the roots of maize grow better with more root length density and dry root weight than without phosphate fertilizer. The phosphate fertilizer improved the proportion of root length density and dry root weight in 80-150 cm. More deep soil nitrate could be used by maize, so the utilization ratio of nitrate improved.【Conclusion】The residual effect of 15N was influenced by phosphate fertilizer which was applied to wheat. Phosphate fertilizer made the maize roots grow better in 80-150 cm soil profile. So the utilization ratio of nitrate was improved. The accumulation of 15N in soil profile was reduced.

Key words: 15N movement, maize, nitrate, residual effect, roots