RESUMEN
The study on the size distribution of water-stable aggregates (WSAs) in calcic kastanozem of Loess Plateau after 27 years fertilization showed that compared with those of natural soil, the contents of > 0.25 mm WSAs in 0-10 cm and 10-20 cm layers of cultivated soil decreased by 21.35% and 38.82%, respectively, and those of > or = 0.5 mm WSAs also had a decreasing trend, with the greatest decrement of > 5 mm and 5-2 mm WSAs. On the contrary, the contents of 0.5-0.25 mm WSAs in the two soil layers increased by 104.75% and 23.13%, respectively. All sizes WSAs had higher contents in 0-10 cm than in 10-20 cm soil layer. Fertilization had remarkable effects on the formation of WSAs. Under the applications of organic manure and its combination with chemical fertilizers, the content of 5-2 mm WSAs increased most, followed by that of > 5 mm WSAs. After applying organic manure, organic manure plus chemical fertilizers, and straws, the contents of larger sizes WSAs increased significantly, being beneficial to the improvement of soil structure. In all fertilization treatments, the mean mass diameter (MMD) of WSAs was larger in 0-10 cm than in 10-20 cm soil layer. Compared with non-fertilization, long-term fertilization increased the MMD of WSAs, and organic manure was superior to chemical fertilizers. The MMD of WSAs was positively correlated with the amount of > 0.25 mm WSAs.