Abstract: A long term pot experiment shows that the composition of various particle sizes of micro-aggregates in albic soils could be altered through adding organic materials. The content of＜1μm and 1～2μm micro-aggregates was decreased, while that of 2～5μm and 5～10μm micro-aggregates increased. The contents of organic C and total N were markedly increased in all sizes micro-aggregates after organic materials amendment, which mainly distributed in small sizes of micro-aggregates. The P content was higher in small sizes of micro-aggregates, while the 10～50μm micro-aggregates had the least P content. There was a significant positive relationship between total P and Olsen P in ＜1, 1～2 and 5～10μm micro-aggregates. The effect of cow manure was better than that of wheat straw.

Key words: Organic materials, Micro-aggregate, Nutrients