Abstract: Soil samples, collected from the 25-year long-term fertilizer experiment carried out on the manual loessial soil situated sub-humid farmland ecological system, were used to study the distribution of soil organic matters, total nitrogen, nitrate nitrogen, and ammonium nitrogen in different grades of soil aggregates in order to study the effects of long-term application of organic manures in combination with chemical fertilizers. Result showed that the percentage of mass of the soil macro-aggregates with long-term application of fertilizers, whose sizes are between 5-2 mm, is increased compared with that of the samples with no fertilizer. It is easier to form lager size soil macro-aggregates because of the long-term application of organic manures in combination with chemical fertilizers. As the results show that the contents of organic matters, total nitrogen and nitrate nitrogen are all higher after those treatments with different combinations of fertilizers, while there is a little effect on the contents of ammonium nitrogen after the same treatments. The contents of organic matters, total nitrogen in the grades of soil macro-aggregates from the plough layers of those treated farmland exhibit significant difference. Moreover, the contents of organic matters and total nitrogen in the soil macro-aggregates with the size of 1-0.25 mm is the highest in all types of treated soil samples. The contents of nitrate nitrogen in soil macro-aggregates increase with the increasing of soil macro-aggregate size except those of soil samples with the application of chemical fertilizer and lower amount of straw. The results of correlation analysis reveal that there exists a significant positive correlation between the percentage of mass of soil macro-aggregates with the size of 5-2 mm and the contents of organic matters and total nitrogen and the nitrate nitrogen in the soil samples. However, the correlation between the percentage of mass of soil macro-aggregates with the size of 1-0.25 mm and the contents of total nitrogen and nitrate nitrogen is significantly negative. From the study it is also showed that the highest contributing rates of macro-aggregates fractions in soil fertility is from the soil macro-aggregates fraction with the size of 1-0.25 mm in most of the cases.

Key words: Long-term fertilizer experiment, Organic matters, Soil macro-aggregates, Nitrogen, Cinnamon soil