Saturday, 15 July 2006

Water-Stable Aggregates of Back Soil under Long-Term Application of Chemical Fertilizers and Recycled Organic Manures.

Xiaozeng Han1, Shouyu Wang1, and Baoshan Xing2. (1) Northeast Institute of Geography and Agro-ecology, Chinese Academy of Sciences, Haping Road 138, Harbin, China, (2) Dept of Plant, Soil, and Insect Sciences, Univ of Massachusetts, Stockbridge Hall, Amherst, MA 01003

Soil water-stable aggregates have direct influence on the soil quality and crop growth. In this research, the effect of organic matter input on particulate organic matter and water-stable aggregates in black soils was examined using a long term experiment at Hailun Agricultural Ecology Experimental Station (China), Chinese Academy of Sciences. There were 8 fertilization treatments with 3 replications, and crop rotation was wheat, corn and soybean. The 8 treatments were: I. control (no fertilizer); II. recycled organic matter (ROM); III. N (N only for wheat and corn, but no for soybean, the N fertilizer was urea); IV. N+ ROM; V. NP (N and P 18.6; VI. NP+ ROM; VII. NPK (K fertilizer was potassium sulfate); VIII. NPK+ ROM. Compared to the soil samples prior to the long term experiment, content of water-stable aggregates (>0.25mm) decreased in the 4 treatments of control, ROM, N, and NP, but increased in the treatments of NP+ROM, NPK, NPK+ROM. The water-stable aggregates (>0.5mm) increased with depth, but the water-stable aggregates(<0.5mm) decreased.The content of Particulate Organic Carbon (POC) varied with different aggregate size. The ratio of POC to total organic carbon in the aggregates of 3-5 mm was the highest, 32-54%; the ratio of 0.25 to 3 mm was 8.5-26%; that of <0.25mm aggregates was the lowest, 8.5-13%. Different soil management practices strongly affected the content of POC in the water-stable aggregates. For the water-stable aggregates of 0.25 to 5 mm, POC decreased in the 4 treatments of control, ROM, N, NP, but increased in the 3 treatments of NP+ROM, NPK, NPK+ROM. For the water-stable aggregates of <0.25mm, POC did not changed much, except for NPK+ROM. Overall, nutrient management had great influence on the soil water-stable aggregates and their POC contents. Selection of appropriate management systems can increase the content of water-stable aggregates and their POC, thus improving soil quality and preventing soil erosion.

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