Paddy Soils

Paddy soils are managed for the purpose of growing rice. Rice is grown in flooded soils, poorly drained soils, and well-drained soils. In this section, we primarily discuss the flooded paddy soils (lowland) used for rice production. Management practices imposed on paddy soils include 

Alternate flooding/draining during growing season Draining after a rice harvest 

Leaving fallow for 4-6 months during a nongrowing season Developing hard pan or plow pan 

Continuous puddling of soil in the surface 15-20 cm soil layers creates a hard pan below the plow layer, which is highly compacted and has very low permeability. The hard pan development does not occur in recently developed paddy soils, but in soils that have been under cultivation for several years. 

In paddy soils, oxygen is introduced through the floodwater and consumed at the soil-water interface, and to some extent oxygen is also introduced through the plants into the root zone. Manganous manganese and ferrous iron formed in the anaerobic zone of surface layer diffuses in two directions (1) to the surface layer, where it is oxidized and (2) to the subsurface layer, where it is oxidized. 

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Koyama, T. (1963). Gaseous metabolism in lake sediments and paddy soils and the production of atmospheric methane and hydrogen, /. Geophys. Res. 68, 3971-3973. 

Dannenberg S, Conrad R. Effect of rice plants on methane production and rhizo-spheric metabolism in paddy soil. Biogeochemistry. 1999 45 53-71. 

Aulakh MS, Wassmann R, Bueno C, Rennenberg H. Impact of root exudates of different cultivars and plant development stages of rice (Oryza satiza L.) on methane production in a paddy soil. Plant Soil 2001 230 77-86. 

Ponnamperuma FN. Some aspects of the physical chemistry of paddy soils. In Institute of Soil Science, Academia Sinica, editor. Proceedings of Symposium on Paddy Soils. Beijing, Science Press 1981. pp. 59-94. 

Holzapfel-Pschorn A, Conrad R, Seiler W. Effects of vegetation on the emission of methane from submerged paddy soil. Plant Soil. 1986 92 223-233. 

Furukawa Y, Inubushi K. Effect of application of iron materials on methane and nitrous oxide emissions from two types of paddy soils. Soil Sd. Plant Nutr. 2004 50 917-924. 

Huang Y, Sass RL, Fisher FM. Methane emission from Texas rice paddy soils. 2. Seasonal contribution of rice biomass production to CH4 emission. Global Change Biol. 1997 3 491-500. 

Gong WQ, Li LQ, Pan GX (2006) Cd uptake and accumulation in grains by hybrid rice in two paddy soils interactive effect of soil type and cultivars. Huan Jing Ke Xue 8 1647-1653... 

China Plain contain 0.1-4.5 mg/kg, and average total Mo contents are in the range of 0.48-2.4 mg/kg. In soils of the North West region, total Mo is 0.4-3.1 mg/kg with an average of 0.985 mg/kg. Soils in Tibetan areas contain 0.1-5.5 mg/kg and have average total Mo between 0.9-1.1 mg/kg. Calcareous paddy soils vary in total Mo concentrations from 0.26-1.21 mg/kg with an average of 0.57 mg/kg. 

The bioavailability of trace elements in soil-water-plant ecosystems of arid zones is largely determined by their partitioning between solution and solid-phase components. The redistribution and transformation of trace elements among solid-phase components under various biogeochemical conditions strongly adjust their lability and bioavailability. Soluble, exchangeable and organically bound forms are bioavailable to plants. The carbonate bound fraction represents a reservoir of potentially bio-available trace elements to plants. In paddy soils, the amorphous Fe/Al oxide fraction contributes to trace element availability as well. 

Soils in the North China Plain and Loess Plateau regions contained 0.04-3.01 mg/kg DTPA-extractable Zn with an average of 0.44 mg/kg. The concentrations of DTPA-extractable Zn in northern China are presented in Table 7.7. In the loessial soils of the Loess Plateau, 64% of the soil samples had less than 0.5 mg/kg of bioavailable Zn. The bioavailable Zn in the arid soils of North China varied from 0.08-11.84 mg/kg with an average of 1 mg/kg, with 41% of the soil samples having < 0.5 mg/kg of bioavailable Zn. The average amount of bioavailable Zn in calcareous soils was 0.35 mg/kg (trace - 1.12 mg/kg). The North China Plain and Loess Plateau are major Zn-deficient regions in China. Calcareous paddy soils frequently displayed Zn deficiency in rice. Zinc fertilizers have been applied to rice, maize, sorghum, wheat, cotton and fruit trees where bioavailable Zn was less than 0.5 mg/kg. 

Loessial soils in the Loess Plateau contained 0.01-4.20 mg/kg DTPA-extractable Cu with an average of 0.93 mg/kg (Table 7.7). Bioavailable Cu in the North China Plain varied from 0.07-9.95 mg/kg. In the North West region, soils contained 0.06-19.20 mg/kg DTPA-extractable Cu. The average bioavailable Cu was 1.83 mg/kg in the calcareous paddy soils with a range of trace to 6.85 mg/kg. Copper deficiency was not often observed in the arid and semi-arid soils of China. 

A common critical limit for Zn deficiency in soils has been 0.5 mg/kg DTPA-extractable Zn for different crops (maize, wheat, and rice) (Sillanpaa, 1982). DTPA-extractable Zn concentration of 0.5-1.0 mg/kg has been marginal for sensitive crops (Sillanpaa, 1982). Brown isohumic calcareous soils of New South Wales in Australia with 35-60 mg/kg of total Zn showed Zn deficiency due to the low bioavailability of Zn. Zinc deficiency has been reported to occur in wheat on solidized solonetz and solodic soils and other calcareous soils of South Australia. Zinc application at the rate of 0.6-28 kg/ha to cereals, pastures, and maize of Australia has been reported (Reuter, 1975). Zn deficiency occurs in Turkey, India, Iraq, Mexico, and Pakistan (Table 7.8). Zinc deficiency is frequently observed in rice on calcareous paddy soils. 

Zhong WFI, Cai ZC (2007) Long-term effects of inorganic fertilizers on microbial biomass and community functional diversity in a paddy soil derived from quaternary red clay. Appl Soil Ecol 36 84-91... 

Li ZJ, Xu JM, Tang C, Wu JJ, Akmal M, Wang HZ (2006) Application of 16S rDNA-PCR amplification and DGGE fingerprinting for detection of shift in microbial community diversity in Cu-, Zn-, and Cd- contaminated paddy soils. Chemosphere 62 1374-1380... 

In soils, PCP persisted for 15 to more than 60 days, depending on soil conditions and application rate. At initial concentrations of 100 mg PCP/kg soil, the Tb 1/2 was 10 to 40 days at 30°C under flooded conditions. However, in aerobic soils there was virtually no degradation after 2 months (Kaufman 1978). In rice paddy soils, initial concentrations of 4 mg PCP/kg fell to 2 mg/kg in 7 days (Bevenue and Beckman 1967). Pentachlorophenol was still measurable after 12 months in warm, moist soils (Cote 1972 USEPA 1980). In estuarine sediments, degradation was most rapid under conditions of increased oxygen and a pH of 8.0 (DeLaune et al. 1983). 

Class 4 is found in Paddy soil zones sporadically distributed throughout China and in the Purplish soil zone in the Sichuan River Basin. 

Minami K. 1982. Volatilization of sulfur from paddy soils. Jpn Agric Res Q 15 167-171. 

Minami K, Fukushi S. 1981. Volatilization of carbonyl sulfide from paddy soils treated with sulfur-containing substances. Soil Sci Plant Nutr 27 339-345. 

Garg AK, Sethi GR. 1980. Persistence of insecticide residues in paddy soil. Ind J Plant Protect... 

Chin KJ, Conrad R. 1995. Intermediary metabolism in methanogenic paddy soil and the influence of temperature. FEMS Microbiol Ecol 18 85-102. 

Conrad R, Bak F, Seitz HJ, et al. 1989. Hydrogen turnover by psychrotrophic homoacetogenic and mesophilic methanogenic bacteria in anoxic paddy soil and lake sediment. FEMS Microbiol Ecol 62 285-94. 

Achtnich C, Schuhmann A, Wind T, Conrad R. 1995. Role of interspecies H2 transfer to sulfate and ferric iron-reducing bacteria in acetate consumption in anoxic paddy soil. FEMS Microbiology Ecology 16 61-69. 

Greenland DJ. 1981. Recent progress in smdies of soil structure, and its relation to properties and management of paddy soils. In Proceedings of Symposium on Paddy Soil. Berlin Springer-Verlag, 42-58. 

Jeffrey JWO. 1961. Defining the state of reduction of a paddy soil. Journal of Soil Science 12 172-179. 

Kern JS, Gong ZT, Zhang GL, Zhuo HZ, Luo GB. 1997. Spatial analysis of methane emissions from paddy soils in China and the potential for emission reduction. Nutrient Cycling in Agroecosystems 49 181-195. 

Krylova NI, Conrad R. 1998. Thermodynamics of propionate degradation in methanogenic paddy soil. FEMS Microbiology Ecology 26 281-288. 

Kyuma K. 2003. Paddy Soil Science. Kyoto Kyoto University Press. 

Shioiri M. 1943. The Chemistry of Paddy Soils. Tokyo Japanese Agricultural Society (Dainihan-Nokai). 

Takai Y. 1952. Microbiological studies on paddy soils. Journal of the Science of Soil and Manure Japan 23 37-41. 

Yagi K, Tsuruta H, Minami K, Chairog P, Cholitkul W. 1994. Methane emission from Japanese and Thai paddy soils. In Minami K, Mosier AR, Sass RL, eds. CH4 andN20 Global Emissions and Controls from Rice Fields and Other Agricultural and Industrial Sources. Tsukuba National Institute for Agroenvironmental Sciences, 41-53. 

Yao H, Conrad R. 1999. Thermodynamics of methane production in different rice paddy soils from China, the Philippines and Italy. Soil Biology and Biochemistry 31 463-473. 

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