Application of nitrogen (N) fertilizer is one of the most important measures that increase grain yield and improve grain quality in winter wheat (Triticum aestivum L.) production, so there is a huge number of investigation experiments in this field on the different nitrogen fertilizer applying regimes. However, currently, still there exists a serious problem of low nitrogen use efficiency, especially under winter wheat high yield condition: unsuitable nitrogen fertilizer often leads to lower income benefit and the larger accumulation of nitrate in soil, bringing potential risk to environment. A lot of previous studies are mostly involved in the effects of nitrogen fertilizer rate and ratio of base and topdressing on wheat grain yield. Now in wheat production, a shortage still is the effects of nitrogen fertilizer applying regimes on wheat grain yield, N utilization, N balance and residual soil NO-3-N under high yield field. In order to explore the optional regime of nitrogen fertilizer application suitable for environment and economy, a field experiment on the different rate and ratio of base and topdressing of nitrogen fertilizer at the different growth period of winter wheat was conducted.
The field experiment was conducted from the fall of 2003 to the summer of 2004 in Zhongcun village, Longkou city, Shandong province, China. The brown soil nutrient components were: organic matter at 13.1g•kg^－1, and available nitrogen (N), phosphorus (P) and potassium (K) at 87.5 mg•kg^－1, 10.49 mg•kg^－1 and 84 mg•kg^－1, respectively. Winter wheat Variety: Jimai 20, typical strong gluten cultivar currently used locally was selected for this experiment.
The field experiment of three replicates for each treatment was randomly arranged in a split-plot design. The major plot was nitrogen fertilizer rate as urea at the three level of 0 kg N per hm2 (CK), 168 kg N per hm² (A), and 240 kg N per hm² (B); sub-plot was ratio of base and topdressing nitrogen fertilizer at the different development period of wheat, which are 1/2∶1/2 (A1 and B1), 1/3∶2/3 (A2 and B2) and 0∶1 (A3 and B3). Treatment B1 is a regime applied now in local region. Basal N fertilizer, total P2O5 (135 kg•hm^－2) and K2O (105 kg•hm^－2) was applied before sowing; topdressing N fertilizer was at jointing stage. Each plot size was 3 by 8 m. At the three-leaf stage of seeding, plants each plot were thinned to a density of 150 plants per m2. The date of sowing wheat seeds was October 4, 2003 and harvested date was June 15, 2004. Totally, 3 times irrigation (before winter stage, jointing stage and 28d after flowering were taken through wheat life.
Two soil sites were sampled randomly each plot in 20cm increments to a depth of 200cm at five growth stages ［sowing, before winter, jointing (before fertilization), flowering and maturity］ with a soil auger and the sample was obtained after mixing and frozen immediately. The procedure for treating sample was: (1) sifting after mixing the defrosted sample with a 2mm-sieve; (2) 5g each sample was weighted and was extracted in 0.05L of 0.01mol/L CaCl2 on a horizontal shaker for 0.5 hour; (3) Nmin were determined using an auto analyzer (AA3) after filtering. Soil water content each sample was measured as well.
Plant samples taken at jointing and maturity stage were oven dried at 70 degree up to a constant weight. The nitrogen content in plant tissue and grain were determined by the standard macro-Kjeldahl digestion method.
It was showed that the amount of N accumulation in plant have no significant difference between treatments with applying nitrogen fertilizer. Grain yield and grain protein content were all elevated remarkably by applying nitrogen fertilizer compared with those of treatment CK; there was no significant difference of grain yield and grain protein content between treatment A2 and treatment B2 and B3. However, compared with those of treatment B2 and B3, treatment A2 increased nitrogen using efficiency and reduced residual soil NO－3-N and N losses. On the condition of the same rate of nitrogen fertilizer, increasing topdressing nitrogen rate clearly elevate grain yield, grain protein content and nitrogen using efficiency markedly. The results indicated that residual soil NO-3-N amount in treatment A1 and B1 accumulated higher than those in treatment CK at 80～100cm and 100～160cm soil layers at jointing stage, but that of treatment A2 have no significant difference compared with that of treatment CK at 0～200cm soil layers. At maturity stage, in treatments B2, B3 and A3 more residual soil NO^-₃-N were detected than those in treatment CK in 120～180cm soil layers, which could not be absorbed by roots of wheat, and lead to be eluviated easily. But soil NO-3-N accumulation amount in treatment A2 have no significant difference compared with that of treatment CK at 100～200cm soil layers. In conclusion, treatment A2, whose nitrogen fertilizer rate is 168 kg•hm^－2 and the ratio of base and topdressing is 1/3∶2/3, had higher grain yield and grain protein content, and heightened N using efficiency and minimized the risk of NO^-₃-N leaching, which will be one of the most appropriate nitrogen fertilizer applying regimes in wheat production in local region, China.