| This experiment was carried out during the winter wheat and summer maize growing season from October 2012 to October 2014, which was located at the experimental farm of Shandong Agricultural University in Tai’an, Shandong Province. In the experiment, the wheat variety Jimai 22 and maize variety Zhengdan 958 were selected as the experimental materials. During the winter wheat growing season, the nitrogen treatments N0, N0+120, N60+120, N120+120, N180+120, N120+0, N120+60, N120+180 were set up to study the effects of nitrogen managements on N2O flux. The nitrogen application rate during the maize growing was the same to examine the effect of nitrogen managements of wheat on grain yield of maize. The results are as follows:1 Effects of nitrogen treatments on N2O emissionN2O emissions reached the peak two days after the nitrogen fertilizer was applied. The rates of N2O emission in N treatments were higher than that of the control. The rates of N2O emission increased as the N fertilizer rate increased. The result showed that fertilization could significantly promote the N2O emission from soil. The N2O emission flux decreased rapidly and gradually leveled off. The flux of N2O increased gradually after topdressing, the emission peak reached after sixth days after topdressing. The rates of N2O emission in N treatments were higher than that of the control. In the case of the same nitrogen content, the N2O emission flux was different because of the different nitrogen application. The rates of N2O emission increased as the N fertilizer rate increased. Compared with the N2O emission of basal fertilization, the N2O emission of topdressing produced lower N2O than the corresponding treatments. Thereafter, the N2O emission flux decreased gradually, but there was a certain rebound after anthesis. The emission flux in N0 and N120+0 only slightly fluctuated during the whole observation period, which was lower than other treatments. Thus, nitrogen fertilizer is one of the important driving factors of N2O emission.2 Relationships between soil mineral N content and N2O emissionNitrate nitrogen content at the 0-20 cm soil layer increased gradually and nitrate nitrogen content increases as the N fertilizer rate increased. The content of nitrate nitrogen in the soil surface reached the maximum after fertilization, and then began to decline. Different to the content of nitrate nitrogen, the content of ammonium nitrogen reached the maximum in 2 to 3 days after fertilization. The content of ammonium nitrogen increased as the N fertilizer rate increased, and then the content of ammonium nitrogen decreased rapidly. There was a significant positive correlation between the content of ammonium nitrogen in soil surface and N2O emission flux, but no significant correlation was observed between nitrate nitrogen content and N2O emission flux. The nitrification of ammonium nitrogen was the main source of soil N2O emission in winter wheat in autumn and winter.Except N0 and N120+0, the content of nitrate nitrogen at the 0-20 cm soil layer increased gradually, and the content of nitrate increased as the N fertilizer rate increased. As for the same topdressing N rate, the content of nitrate nitrogen increased as the basal N fertilizer rate increased. As for the same total N rate, the nitrate nitrogen content of a higher basal N ratio in the surface soil was higher. But later the nitrate nitrogen content of a higher basal N ratio in the surface soil was lower. Compared with changes of soil nitrate nitrogen content after basal fertilization, nitrate nitrogen content increased more slowly. Except N0 and N120+0, the content of ammonium nitrogen in soil surface increased rapidly after urea application, and the content of ammonium nitrogen increased as the topdressing N fertilizer rate increased. As for the same topdressing N rate, the content of ammonium nitrogen increased as the basal N fertilizer ratio increased. Compared with the content of ammonium nitrogen after basal N fertilizer application, the maximum value was reached in the 7 days after fertilization, and then decreased slowly. There was a very significant positive correlation between the content of nitrate nitrogen and ammonium nitrogen in soil and the emission flux of N2O in soil. The results showed that the soil N2O emission showed an increasing trend with the increase of the content of nitrate and ammonium nitrogen in the soil surface.3 Relationships between soil N2O emission and N fertilizer application rateAfter the basal nitrogen fertilization, the total amount of N2O emission increased rapidly, and then increased slowly. The total amount of N2O emission was higher than that of control, and the total amount of N2O emission increased with the increase of nitrogen application rate. After the application of nitrogen fertilizer, the total amount of N2O emission increased at the same rate. The total amount of N2O emission in N treatments were higher than that of control, and the total amount of N2O emission increased with the increase of nitrogen application rate. In the case of the same total amount of nitrogen application, the total amount of N2O emission was at the same level. The total nitrogen rate was positively related to the total amount of N2O emission, and increased as the nitrogen application rate increased.4 Effects of nitrogen managements on grain yieldDuring the wheat seasons, No significant difference in spikes m-2 was observed between years. Despite no significant difference in kernels spike-1 was observed from N2 to N5, it is obvious that kernels m-2 increased as the N fertilizer rates increased from N1 to N5. Thousand kernels weight（TKW） in 2013–2014 averaged 41.70 g, which was 5% greater than that in 2012–2013（39.84 g）. Over two years, compared with N3, average grain yield for N1 and N2 decreased significantly by 21% and 6%, respectively. Average grain yield for N5 increased significantly by 11% compared with N3. Average AGDM increased significantly by 21% as the N fertilizer rates increased from N1 to N4. The highest AGDM was obtained in N5. Significant increase in AGDM was observed between N4 and N5 in 2013–2014, but not observed in 2012–2013. Compared with 2012–2013（0.47）, a 6% increase in average HI（0.50） was observed in 2013–2014. No significant difference in HI was observed as the N fertilizer rates increased from N2 to N5.During the maize seasons, average ears m-2 over two years ranged from 6.44 with N1 to 6.91 for N5, respectively. Average kernels ear-1 increased significantly by 10% as the N fertilizer rates increased from N1 to N4 and by 10% from N4 to N5. Over two years, average TKW ranged from 303.0 g with N1 to 337.8 g for N5, respectively. The highest TKW was obtained in N5. Over two years, average grain yield increased significantly by 15% as the N fertilizer rates increased from N1 to N3 and by 25% from N3 to N5, respectively. The highest grain yield was obtained in N5. There was significant difference in grain yield as the N fertilizer rates increased from N1 to N5 in 2013–2014. Average AGDM ranged from 16.3 t ha-1 with N1 to 21.4 t ha-1 for N5, respectively. AGDM increased significantly by 21% as the N fertilizer rates increased from N3 to N5. No significant increase in HI was observed as the N fertilizer rates increased from N3 to N5. Due to similar AGDM and HI, no significant difference in grain yield for N5 was observed over two years.5 Effects of nitrogen managements on nitrogen uptake and useNo significant increase in grain N concentration was observed as the N fertilizer rates increased from N2 to N5. Average straw N concentration increased significantly by 24% as the N fertilizer rates increased from N1 to N4. N uptake by grain ranged from 137.1 with N1 to 212.6 kg N ha-1 for N5 and from 40.2 to 61.1 kg N ha-1 by straw, respectively. The greatest N uptake by grain was achieved in N5. No significant increase in N uptake by grain was observed between N3 and N4 in 2012–2013. There was significant difference between the remaining N treatments. N uptake by straw increased significantly by 50% as the N fertilizer rates increased from N1 to N4. No further increase in N uptake by straw was observed between N4 and N5. The highest NHI was observed in N3. NHI decreased significantly as the N fertilizer rates increased from N3 to N4. PFPN decreased significantly as the N fertilizer rates increased from N2 to N5 in both years. The highest IEN was obtained in N1. No significant difference in IEN was observed as the N fertilizer rates increased from N3 to N5.Average N concentration for grain and straw increased significantly by 6%（1.29% for N1 and 1.36% for N5） and by 9%（0.86% for N1 and 0.94% for N5） as the N fertilizer rates increased from N1 to N5. No further increase in N concentration for grain and straw was observed as the N fertilizer rates increased from N3 to N5. Average N uptake by grain and straw increased significantly by 51% and by 30% as the N fertilizer rates increased from N1 to N5. The highest N uptake by grain and straw were observed in N5. As the N fertilizer rates increased from N1 to N5, NHI ranged from 0.60 with N1 to 0.64 for N5, respectively. Average PFPN ranged from 45.1 kg kg-1 with N2 to 64.9 kg kg-1 for N5. No significant difference in IEN was observed, except N2 and N5 in 2013–2014. |
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