[Effects of long-term fertilization on reddish paddy soil quality and its evaluation in a typical double-rice cropping region of China].

In order to quantify the effects of 27 years application of chemical fertilizers, pig manure, and rice straw on the reddish paddy soil quality in double rice cropping region, the indices of soil bulk density, porosity, maximum water holding capacity, normalized mean weight diameter, pH, cation exchange capacity, available nutrients, organic matter, microbial biomass C, enzyme activities, and rice yield were selected as the evaluation indicators, and classified into four functional groups, i. e., resistance to physical degradation, plant nutrients supply and storage, resistance to biochemical degradation, and sustaining of crop productivity. The soil quality index (SQI) was calculated based on the four functional groups. The results showed that the SQI ranged from 0.544 in treatment CK to 0.729 in treatment NPK plus rice straw. Treatments PK, NP, and NK induced soil degradation, compared to treatment NPK. The deficiencies of soil P and K were the main limiting factors for the double rice productivity in reddish paddy soil area. Even though 30 t x hm(-2) x a(-1) of pig manure and 4.2 t x hm(-2) x a(-1) of rice straw were applied, the soil P and K were still not adequate for the requirement of rice growth. There was no obvious effect of long-term application of lime on the reddish paddy soil quality. The combined application of NPK with organic manure was an important and effective measure in improving soil quality in double rice cropping regions of Southern China.

[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.