ISSN:0038-075X    

出版商:OVID    

年代:1983

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1983

数据来源: OVID

摘要:

This paper deals with the genesis, characteristics, and development of genetic horizons of paddy soil in China. On the basis of the pedogenic characteristics of this soil, an idea of its classification is given.

ISSN:0038-075X    

出版商:OVID    

年代:1983

数据来源: OVID

摘要:

Xizang plateau has been lifted since the end of the Tertiary period—the current height of the surface of the plateau ranges from 4500 to 5000 meters—and it is continuously lifting. Due to the arid and cold climate, the processes of chemical weathering and soil formation are weak. The soils of the region are light in texture; their clay minerals are mainly hydromica and chlorite. The synthesis of biomass and the decomposition of organic materials are very slow, and fulvic acid is generally predominant in the humus of soil. Because of the lift of the land surface, the soils originally formed in a low altitude were lifted to a high altitude. Therefore, some micromorphological and mineralogical features of paleosol, including ferric oxide impregnation matrix, fragments of ferruginated mineral grains, and illuviation argillans, gibbsites, and kaolinites, which are inconformable to the current soil formation process, are usually found in the soil profiles.

ISSN:0038-075X    

出版商:OVID    

年代:1983

数据来源: OVID

摘要:

This paper gives an account of the clay mineral composition of several major soil types in China and discusses its relationship with the hydrothermal condition, topography, and parent materials. Various soils formed on analogous igneous rocks are conspicuously characterized by horizontal or vertical zonality in clay mineral composition. To a certain extent, the clay mineral composition of the soils developed on Pleistocene deposits differs from that of the soil developed on igneous rocks, and the soils derived from sedimentary rocks have more significant inheritance of soil minerals from their parent materials. Hydromica and chlorite are known as the common components in soils of less weathering, whereas smectite occurs in great abundance in chestnut soil, chernozem, podzolic soil, and clayey alluvial soils. The amount of vermiculite increases with the increase of leaching intensity until reaching its peak in mountain yellow earths, but in the upper horizons of strongly acid soils, cheluviation of aluminum always leads to the transformation of vermiculite into chlorite. Kaolinite and gibbsite are distributed extensively in subtropic and tropic soils; their content is closely related to temperature, rainfall, and parent materials. As a rule, soils derived from basic rocks tend to contain much more gibbsite and iron oxides. As a result of the uplift of earth crust, polygenetic mineralogical profiles may be regarded as the important characteristics of the soils on the Qinghai-Xizang Plateau.

ISSN:0038-075X    

出版商:OVID    

年代:1983

数据来源: OVID

摘要:

Ferrous iron may be distinguished as water-soluble, exchangeable, complexed, and precipitated. pH plays an important role in determining the relative proportions among the various forms. The water-soluble iron exists in the form of chelates carrying a negative or positive charge or ions. The stability constants of ferrous chelates as well as manganese chelates are of the order of 2.5 to 5.5. pH is determinative with respect to the concentration of both molecular H2S and ionic S2-. There is a close relationship between Eh and the amount of reducing substances in the soil.

ISSN:0038-075X    

出版商:OVID    

年代:1983

数据来源: OVID

摘要:

Nitrification and denitrification occur in both “oxidation” and “reduction” layers of the plow horizon of paddy soil during the growth period of rice. The nitrite bacteria obtained from paddy soil oxidize ammonium nitrogen to nitrite nitrogen under anaerobic cultural conditions. It is a facultative anaerobic ecotype of nitrite bacteria and is closely associated with denitrifying bacteria. The close association of nitrifying and denitrifying bacteria provides a free route of conversion of ammonium nitrogen to gaseous nitrogen through nitrite (and nitrate) at the same locus in the soil.

ISSN:0038-075X    

出版商:OVID    

年代:1983

数据来源: OVID

摘要:

This paper offers a brief discussion of the factors that should be considered in improving the efficiency of nitrogen of chemical fertilizer and organic manure in rice production in China. The factors discussed include: (1) nitrogen supply from soil throughout the growing period of rice, (2) nitrogen recovery by rice plant from chemical fertilizer and organic manure, (3) the nitrogen mineralization pattern of soil organic matter and organic manure, and (4) the nitrogen uptake pattern of rice plant from native soil ammonium-N and chemical fertilizer-N. It is suggested that, for the moderate-yield level, the former two factors are of primary importance, and for the high-yield level, in addition to those two factors, the latter two also play an important role.

ISSN:0038-075X    

出版商:OVID    

年代:1983

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1983

数据来源: OVID

摘要:

Well irrigation and drainage, adopted for the improvement of salt-affected soils in China, has been beneficial in recent years. In regions where the groundwater is fresh or contains few minerals, well irrigation can simultaneously lower the groundwater level, leach the salts downward from the soil, alleviate the harmful effects of flooding, and promote the salt-leaching effect by natural precipitation. In regions where the ground-water is highly mineralized, extraction and drainage of the highly mineralized ground-water by well can control the groundwater level and replenish the groundwater layer by irrigation with fresh water diverted from rivers, so as to accelerate salt-leaching from soil and prevent secondary salinization of soil. But well drainage cannot replace ditch drainage. Generally, a combination of well drainage and ditch drainage should be adopted to improve salt-affected soils. The distribution of wells is discussed, as is their construction appropriate to the local economic and natural conditions of salt-affected soil regions of China. According to the soil and hydrogeological conditions of the salt-affected soil regions in China, there are three patterns of well application for the improvement of salt-affected soils: (1) a combination of well irrigation and well drainage in regions where the groundwater is fresh or contains only small amounts of minerals; (2) a combination of deep and shallow wells in regions that have mineralized ground-water, and (3) shallow well drainage in regions of highly mineralized groundwater.

ISSN:0038-075X    

出版商:OVID    

年代:1983

数据来源: OVID