CHARACTERISTICS AND POTENTIAL PRODUCTIVITY OF VERTISOLS RESOURCES IN CHINA
Zhang , Min Gong Zitong (Institute of Soil Sciences, The Chinese Academy of Sciences, Nanjing 210008)
Versitisols resources in China are extensively distributed from tropic, subtropic to temperate zones. It is estimated that the area of this soil resources is approximately occupied 1 percent of total land area of China. Because nearly most of the Vertisols areas have been cultivited into farmland, the area of this soil resources is about ten percent of the total arable land. Therefore, Vertisols are the very important agricultural siols in ChinaAlthough Vertisols are distributed in different bioclimatic zones, their gentic and fertility characteristics are quite similar. The common characteristics of the soils are. have the alternately seasonal dryness and wetness and all are in low and even landform with similar basic parent materials, and heavy soil texture. Owing to the high content of montmofillonite, the soil bodies intensely swell and shrink, which leads to extensive cracking upon drying and swelling-puddling when rewetted. "Soil pedoturbation", and "Self-mulching", are occured in the,, upper parts of the soils, and a large,number of 'slickensides and wedge-shaped structural units are commonly observed in the soils.As ancient agricultural soils, Vertisols have special fertility 'characterized by being easily waterlogged and dried and intensely swelling-shrinking which leads to poor perviousness, stiff and sticky soil structure. In addition, low content of active soil organic matter, deficiency of available nutruents also give the result of low agricultural productivity, so,Vertisols belong to low. productive agrotype soilsAlthough Vertisols are limited by many low productive factors, but these soil resources possess great potential productivity. Firstly, Vertisols have favo-rable physical conditions. l.Good heat regime and fairly high precipitation; 2. Even landform with very deep soil layers and being suitable for mechanized tillage and management; 3. Rich groundwater resources with good water's quality; 4. Convenient transportation in the Vertisol area and near social and economic base. Secondly, Vertisols itselves have some advantageous properties: 1.Relatively high content of organic matter; 2.High cation exchange capacity (CEC) and great nutrient-reserving capability; 3. High base-saturation percentage with neutral soil reaction and no threat of salinization; 4. Suitable, to plant a great variety of crops. Finally., because of present soil productivity level in considerabely low, Vertisols have great potential for increasing productivity. The improvement and utilization of Vertisol must be conformed to the char-acteristics of the soil resources. The most suitable way is to adopt comprehensive measures. To solve the problems of waterlogging and drying and reinforce the farmland capital construction. Experiments have shown that the most suitable way to improve the low productive soils is to apply chemical fertilizers with proper ratio of nitrogen and phosphorous as a leading step, then progressively extending the method of "Reture straw to the soil" and inter-cropping of cereals and green manure. Meanwhile, to increase the application of organic manure and using deep tiliage method to improve the soil fertility Besides, to adopt the disversified agriculture and combine agriculture, forestry and animal husbandry togather should be also emphasized in order to establish a good ecological agri-culture system.