[Physical properties of paddy soils with different productivity in double-rice cropping region of Hunan Province].

A total of 24 paddy soil samples with different productivity were collected from eight main rice production counties in east, central, and northwest Hunan Province, with the parameters of soil physical properties and clay mineral composition, including bulk density, particle density, porosity, field water-holding capacity, water-stable aggregates, mean weight diameter, normalized mean weight diameter, aggregate destruction rate, organic carbon, organic cementing materials, inorganic cementing materials, and clay minerals determined. The results showed that highly productive (>14,000 kg x hm(-2)) paddy soil possessed bulk density below 1.2 g x cm3, soil particle density about 2.0 g x cm3, and 5-0.5 mm water-stable macroaggregates about 20%. Most of the test parameters had no significant differences between highly productive and medium productive (10,000-13,500 kg x hm(-2)) paddy soils, but significant differences between highly productive and lowly productive (<10,000 kg x hm(-2)) paddy soils, suggesting that under good management, medium productive paddy soils could be upgraded to highly productive paddy soils. At present, the physical properties of lowly productive paddy soils were poor, which need to be improved to raise productivity.