Does long-term inorganic and organic fertilization affect soil structural and mechanical physical quality of paddy soil?

Few studies deal with the impacts of long-term fertilization on soil mechanical physical properties. A long-term fertilization experiment initiated in 1996 was performed in the paddy soil (Endoaqualf) of China. The treatments included: control (CK), chemical fertilizers (NPK), rice straw (RS), pig manure (PM), rice straw plus chemical fertilizers (RS+NPK) and pig manure plus chemical fertilizers (PM+NPK). The PM, PM+NPK, RS and RS+NPK treatments significantly (p< 0.05) increased the percentage of > 2 mm macroaggregate compared with the CK treatment, while application of chemical fertilizers alone had no significant effect on the formation of macroaggregate. Application of organic fertilizers significantly increased soil liquid limit (LL), plastic index (PI), and deformation relative to CK, while decreased soil plastic limit (PL), COLE, TS and cohesion. In contrast, the application of chemical fertilizers significantly increased the PL, COLE, TS, cohesion and internal friction angle, while decreased the LL and PI compared with the PM treatment. The application of different types of organic fertilizers could also affect the soil mechanical properties differently. The study suggested that soil management practices in paddy soil should preferably include integrated use of chemical fertilizer and manure or straw to maintain better physical environment of the soil.