| The experiment was done in"national monitoring base of soil fertility and fertilizer efficiency on loess soil"from 2007-2009, to study the effect of different nitrogen rate on crop yield, nitrogen utilization ratio, soil nutrient and soil nitrogen rinse under wheat/maize rotation pattern. With the combination of my experiment, we investigated into the fertilization status of households in wheat/maize rotation area within Guanzhong irrigation area, and the important results are listed below:1. Effect of nitrogen rate and straw cover on the yield and nitrogen utilization ratio of winter wheat and summer maizeThe experiment included different fertilizer treatments: Non-fertilizer (N1, 0 kg?hm-2?a-1), customized fertilization (N2, 471 kg?hm-2?a-1, nitrogen rate per year and the same below.), recommended fertilization (N3, 330 kg?hm-2?a-1), reduced N application (N4, 165 kg?hm-2?a-1), increased N application (N5, 495 kg?hm-2?a-1) and recommended fertilization plus straw mulching (N3+S) in wheat-corn rotation farmland. Results showed that in addition to the N4 treatment, the maize yield increased significantly under each fertilization treatment compared to the non-fertilization treatment in 2008. However, the differences between each fertilization treatment were not significant, with the yield under the straw cover treatment reaching the highest (4729 kg/hm2), and being higher than the yield under the non-fertilization treatment by 48.5%. The nitrogen utilization ratio under the N4 treatment achieved the highest, while the wheat yield under this treatment had no significant difference with the yield under the non-fertilization treatment. In 2009, the wheat yield under each fertilization treatment grew significantly compared to non-fertilization treatment, with the yield under the N3 treatment reaching the highest (6240 kg/hm2), being 44.4% higher than the non-fertilization treatment and 16.2% higher than N4 treatment. The fertilization ratio under N3 treatment achieved 53.6%, being higher than the N2,N4,N5 treatment obviously. In 2008, maize yield was the highest under the N3 treatment (8739 kg/hm2), 49.5% higher than the non-fertilization treatment. The nitrogen utilization ratio under the N4 treatment achieved the highest (27.4%), while the maize yield under this treatment had no significant difference with the yield under N1 treatment. In 2009, maize yield rose obviously under each fertilization treatment than the non-fertilization treatment, with the yield under N3+S treatment reaching the highest (being 77.6% higher than N1 treatment), and the nitrogen utilization ratio under this treatment being 35.2%. The yield under N2 treatment increased 77.4% than the non-fertilization treatment, but the nitrogen utilization ratio under this treatment was only 17.9%. Under the condition of my experiment, the reasonable fertilization rate was 150kg/hm2 for wheat and 180kg/hm2 for wheat. The effect of crop cover, however, needs to be explored further.2. Effect of N application rate and crop residue cover on nutrient accumulation of soil profileBy using in situ leaching device, we studied effects of accumulation of nitrate in the soil profile (0 to 100 cm depth). The results showed that after two years rotation of wheat and maize, accumulation of NO3- -N in 0-1m soil profile ranged between 39.1～345.4 kg/hm2 for different treatments, in the order of N2>N5>N3+S>N3>N4> N1. Among the treatments with fertilizers, the lowest accumulation (51.01 kg/hm2) was found in the treatment of N4; the highest (345.4 kg/hm2) was in N2 treatment, which is much higher than those in the treatments of N1 and N4. The straw mulch treatment did not affect distribution of NO3--N in the soil profile when annual N was 330 kg ? hm-2. No significant difference was found in NH4+-N concentration in the same layer of different treatments. NH4+-N accumulation of N5 treatment peaked at 7.49 kg/hm2 in the 60-80cm layer, which was 84.9%,48.9% and 59.0% higher than those in layers 0-20 cm,20-40 cm and 80-100 cm, respectively. N3+S treatment peaked at 8.62 kg/hm2 in the 60-80 cm layer, which was 60.8%,57.7% and 85.6% higher than those in layers 0-20 cm,20-40 cm and 80-100 cm, respectively. The distribution of available P in the soil profile was similar among the treatments, with the highest content in layer 0-20 cm. Then it decreased in the lower layers and became stable. The distribution of available P of N3 treatment peaked at 20.45 kg/hm2 in the 0-20 cm layer, which was respectively 106.7%and 65.5% higher than N1and N5. Total N, total P and organic matter content in plow layer didnot differ among the treatments. N3+S significantly increased available K content in plow layer, 26.4% higher than that in N1 treatment and 17.0% higher than N2. In conclusion, N3+S was the best management strategy, for which NO3--N accumulation was reduced and residue cover improved soil fertility in plow layer.3. The effect of N application rate and residue cover on N leaching from soil NO3--N increased as the increase of N application rate. Over fertilization and residue cover are likely to increase N leaching. In 2008, the treatment (N3+S) with recommended N rate and residue cover had largest leaching (22.32 kg ? hm-2) at 90cm depth, of which 16.44 kg ? hm-2 was caused by fertilization, and it was 158.9% higher than the plot without residue cover. In 2009, the treatment (N5) with recommended N rate and residue cover had largest leaching (3.33 kg ? hm-2) at 90cm depth. The annual total N of each fertilization treatment high than the non-fertilization treatment, with N2 treatment reaching the highest (being 152.3% higher than the N1 treatment, 3.74 kg/hm2), which was increased 20.5%with annual application rate of N decreased 4.65%. In conclusion, residue cover is likely to increase N leaching at flooding; whereas, it can mitigate leaching in natural rainfall conditions.4. The Fertilization status of Guanzhong irrigation field in Shaanxi provinceWe investigated the fertilization status in Yangling,Wugong and Fufeng in Guanzhong area in 2009. The average pure nitrogen rate in winter wheat and summer maize was 218.7 and 277.9 kg/hm2 respectively, and the average P2O5 rate in winter wheat and summer maize was 133.4 and 15.9 kg/hm2 respectively. The difference between each household was considerably large. According to the crop nutrient coefficient and the recommended reasonable fertilization ranger established by experts, the households using appropriate nitrogen rate for winter wheat only accounted for 19.8%, the households using lower nitrogen rate occupied 36.6%, and the households applying much higher nitrogen rate took account for 35.6%. For the households cultivating summer maize, the proportion of households applying appropriate nitrogen rate only accounted for 13%, and 76% households applied nitrogen exceeded the reasonable range. 50% households applied annual total P2O5 rate within the reasonable range, and 34% households applied lower. Farmers applied P fertilizer mainly focused in wheat season, and mostly input P fertilizer for once as basal fertilizer. Few farmers'top dressed P fertilizer. The local farmers'fertilization habit is unreasonable, and therefore the departments should cooperate with each other to help the farmers handle fertilization technology.
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