Establishment And Application Of Index Systems Of Soil Series Classification For Major Soil Orders In Hubei Province

Hubei province, located in the central region of China, is a transition zone. Its terrain transits from the second terrace to the third, and the topography in the west is higher than the east. The climate is warm temperate zone to subtropical zone. Because Hubei province is located in the middle and lower reaches of the Yangtze River, this area has advantageous conditions for agricultural production and a long history of farming. Therefore, it is necessary to establish the index systems of soil classification for major soil orders in Hubei Province and do a good job of soil basic classification. According to field investigation on soils in Hubei province and lab analysis of four main soil orders, the soil family identification indexes that adapted to this region are confirmed, referred to the control section of basic categories of classification units and family differentiae. According to the quantitative requirements of Chinese soil taxonomy and combined with particular case of the soils in Hubei province, we systematacially analyse the principles and methods of soil series index. We reformulate these characteristic horizons, like ferrimanganic mottling layer, ferrimanganic deposited layer, structural layer(B), fragmental layer etc. Based on soil families we have confirmed, different index systems of soil series classification for four soil orders in Hubei province have been established, by using coefficient of variation and correlation analysis.(1) Index system of soil series classification for stagnic anthrosols:For morphological characteristics, we use gley horizon and ferrimanganic mottling layer as the soil classification indexes. For different soils, there are significant differences if the diversity among thickness of gley horizon reaches2times or more than30cm, and vice versa. Taking50cm and100cm as the boundary, we divide ferrimanganic mottling layer into three levels on the basis of its upper-boundary. For physical and chemical properties, we regard organic matter content of topsoil and ironization as the soil classification indexes. We divide organic matter content of topsoil into three levels by20g/kg and40g/kg, which represent lower, medium and higher soil fertility respectively. Using40percent and60percent as the bounds, we divide ironization into three levels, which represent the free degree of iron.(2) Index system of soil series classification for Argosols:For morphological characteristics, we take argic horizon, ferrimanganic deposited layer and clay coating as the soil classification indexes. For different soils, there are significant differences if the diversity among thickness of argic horizon and ferrimanganic deposited layer reaches2 times or more than30cm, and vice versa. We divide argic horizon into two levels by60cm, and divide ferrimanganic deposited layer into three levels by50cm and100cm. To15%as the boundary, we divide clay coating into bit and mass. For physical and chemical properties, we take argillic value and CEC as the soil classification index. To1.50and1.80as the boundary, we divide argillic value into three levels. We divide CEC into three levels by10cmol/kg and20cmol/kg, which represents the capacity of nutrient preserving of soils.(3) Index system of soil series classification for cambosols:For morphological characteristics, we regard sand layer, clip sand layer and structural layer(B) as the soil classification indexes. We can judge different soil series by the existence of sand layer. For different soils, there are significant differences if the diversity among thickness of clip sand layer and structural layer(B) reach2times or more than30cm, and vice versa compared to the thickness. And we divide structural layer(B) into three levels by50cm and100cm. For physical and chemical properties, we regard organic matter content of topsoil and texture of plough layer as the soil classification indexes. To20g/kg and40g/kg as the boundary, we divide organic matter content of topsoil into three levels, which represent lower, medium and higher soil fertility respectively. And we divide texture of plough layer into sandy, clayey and loamy.(4) Index system of soil series classification for Primosols:For morphological characteristics, we take thickness of soil, fragmental layer as the soil classification indexes. Thickness of soil which is thinner than50cm is shallow soil, and others are ordinary soils. For different soils, gravel layer is divided into two levels by25cm. For physical and chemical properties, we take texture of plough layer as the soil classification index, including sandy, clayey and loamy.These soils can be divided into different soil series if they have one or more different indexes from others, which have been established above. Making use of these index systems of soil series classification and the classification demands of higher taxon in Chinese Soil Taxonomy,49soil profiles have been divided into4soil orders,7suborders,10soil groups,11subgroups,17soil families and45soil series, and soil series retrieval is established as well. According to the application in Hubei province, the index systems of soil series can well divide these soils into different soil series, which have significant differences in morphological, physical and chemical properties. And the division process is simple and convenient. The feasibility of these index systems of soil series classification we have established have been further validated.