[Effects of organic manure application on dry land soil organic matter and water stable aggregates]

A four-year (2007-2010) field experiment was conducted to study the effects of applying different amounts (7500, 15000, and 22500 kg x hm(-2)) of organic manure on the organic matter content, aggregate particle size distribution, and aggregate stability in different soil layers in a continuously cropped maize field on the Weibei Dry Land, Shaanxi Province of Northwest China. In 0-20 cm soil layer, the organic matter content in treatment 22500 kg x hm(-2) of organic manure was 4.1%-4.6% higher than that in treatment 7500 kg x hm(-2) of organic manure (P < 0.05), and the organic matter content in treatments 15000 and 22500 kg x hm(-2) of organic manure was 4.6%-11.2% higher than that in CK (chemical fertilization) (P < 0.05). In the fourth year (2010) of applying 7500 kg x hm(-2) of organic manure, the organic matter content in 0-20 cm soil layer was 4.7%-6.3% higher than that of CK (P < 0.05). In 0-30 cm soil layer, all treatments with organic manure application had an increased amount of soil water stable aggregates (> 5 mm), and the amount of the aggregates increased significantly with the increasing application rate of organic manure. Applying organic manure increased the amount of soil water stable aggregates (> 0.25 mm), aggregate mean mass diameter, and aggregate stability in 0-30 cm soil layer, as compared with CK, and these three indices increased significantly with increasing organic manure application rate.