Abstract:

【Objective】 The purpose of this experiment was to study the effects of topsoil water and nitrogen control on utilization ratio of nitrate accumulated in deep soil by wheat in North China. 【Method】 Two N levels including 0, 150 kgN?hm-2 and two irrigation methods were designed. There were four treatments: N0W1, N0W2, N150W1, and N150W2. Field micro-plot experiments and the injection technique of labeled NO3--N were adopted. 【Result】 Results showed that 15N which was injected into 110 cm soil layers could be absorbed by wheat with the nitrogen uptake of 336.7,900.3,497.4 and 657.1 mg?m-2 and nitrate utilization ratio of 8.4%, 22.4%, 12.4%, 16.3% in four treatments of N0W1, N0W2, N150W1, N150W2. The root length density of 80-150 cm layer was 12.8, 10.9, 10.6, and 9.7 cm?cm-3 and accounted for 24.4%, 32.3%, 26.4%, and 28.2% of that of 0-150 cm layer in four treatments of N0W1, N0W2, N150W1, N150W2. Less nitrogen and intensifying irrigation made the roots in subsoil grow better, by which more deep soil nitrate could be assimilated by wheat and then the utilization ratio of nitrate by wheat be improved. 【Conclusion】 Less nitrogen and reasonable water stress promoted the distribution of roots to subsoil layers and thus accelerated the absorption of nitrate accumulated in deep soil by wheat.

Key words: 15N, wheat, nitrate, water and nitrogen control, utilization ratio of nitrate, roots