Effects of soil management practices on stability and distribution of aggregates in Lou soil

Soil aggregate is a main component of soil, and its size distribution has an important effect on soil function. This study investigated effects of soil management practices on distribution of dry aggregates and water-stable aggregates based on a 22-year long-term experiment on Lou soil in Guanzhong Plain, Shaanxi province, China. The soil management practices were cropland abandonment (Set aside), bare fallow without vegetation (Fallow) and a wheat-maize cropping system (Cropping). The Cropping was combined with the following nutrient management treatments: control (CK, no nutrient input), nitrogen only (N), nitrogen and potassium (NK), phosphorus and potassium (PK), NP, NPK and straw plus NPK (SNPK) and two levels of manure plus NPK (M1NPK and M2NPK). The soil management practices have significantly effects on the distribution of dry aggregates and water stable aggregates in the surface and subsurface soil layers (0-10 and 10-20 cm). Compared with the Cropping, the fallow treatment increases the proportion of dry microaggregates (0.25 mm), but has no significant effects on distribution of water-stable aggregates, and the Set aside treatment increases the proportion of macroaggregates (larger than 2 mm in size) and aggregate stability. The distributions of dry aggregates and water stable aggregates are significantly impacted by the fertilization in all soil depths under the Cropping. Generally, the proportions of aggregates in sizes 1 mm under the fertilization are lower than those of no fertilization, and the proportions of aggregates in sizes of 0.25-0.5 mm and 0.5-1 mm in the treatments which received both N and P are higher than that of the control. It is concluded that the abandonment of cropland after 22-year significantly improves aggregate stability, while the long-term fertilization practices significantly influence the distribution of soil aggregates and have not significant effects on the aggregate stability under the cropping system in Lou soil.