Effects of nitrogen fertilizer application rate on soil microflora and sunflower yield in saline-Alkali soil

In order to form a solid basis for an effective fertilization mode in saline-Alkali soils , a field experiment was conducted to determine the effects of different levels of nitrogen on soil microoganisms and sunflower yield in Hetao Irrigation District in Inner Mongolia. Six treatments were designed including five nitrogen fertilizer levels , viz. , 75 kg-hm-2(N1) , 150 kg-hm-2(N2) , 225 kg-hm-2(N3) , 300 kg-hm-2(N4) , 375 kg-hm-2(N5) and a control ( CK) . The results indicated that: (1) Applying nitrogen fertilizer could significantly increase the number of microorganisms and the diversity of flora in the root zone. The order of soil microorganisms at 0 ∼ 20 cm soil depth arranged was N4 > N3 > N5 > N2 > N1 > CK. (2) Applying nitrogen fertilizer could promote the growing and development of sunflower as well as yield. The growth vigor and dry matter of sunflower increased gradually and yield varied parabolically with nitrogen application rates. Therefore , the yield of five nitrogen fertilizer levels treatments were higher than CK by 0.06% , 36.27% , 61.95% , 105.36% and 85.03% , respectively. (3) Appropriate nitrogen application rate could reduce soil salinity of 0 ∼ 40 cm depth. After harvest , the order of salt accumulation arranged was N2 > CK > N5 > N3 > N1 > N4. (4) There is a significant positive correlation between the numbers of soil microorganisms , advantage bacteria flora and nitrogen application , root dry matter. However , there is a significant negative correlation between the numbers of soil microorganisms, advantage bacteria flora and soil salt content, salt accumulation. In summary, the appropriate nitrogen application rate is 300 kghm-2 for sunflower on the moderate saline-Alkali soils in Hetao Irrigation District in Inner Mongolia.