Zhang, Wei Li, Kolbe, H., Zhang, Ren Lian, Zhang, Ding Xiang, Bai, Zhan Guo, Zhang, Jing, and Shi, Hua Ding
The reviewing soil surveys and soil investigations in different countries shows that in order to understand the soil resources and soil quality, the soil surveys and investigations carried out by different countries since the end of the 19th century can be divided into four categories, namely: survey for soil classification, investigation and evaluation of farmland fertility, testing of soil chemical properties for fertilizer recommendation and soil investigations related to environmental issues. Among the four categories, soil classification is the earliest and the most widely implemented survey works carried out in the world. Main purpose of the classification survey is to clarify the differences in soil types and their spatial distributions caused by various soil formation processes. Since soil formation processes under natural conditions can reach tens of thousands of years, the main outputs of the classification survey—the soil maps and the records of soil profiles, expressing the physicochemical properties of various soil types, have a long timeliness and are widely used in various research areas. After the completion of nation-wide soil classification surveys in the last century in developed countries, the updated survey was not conducted in these countries. In the second national soil survey in China, large-scale soil maps covering the whole country were completed by relatively higher profile sampling density. The physicochemical properties of 100 000 soil profiles, representing different soil types, were also recorded. Both the map scale and the richness of soil profile data from the survey surpassed the outputs from classification surveys in many developed country. Soil classification data obtained from this survey are valid for a long time to different disciplines and sectors. In order to meet needs for easy-to-understand farmland fertility grades by land management sectors and farmers, investigation and evaluation of farmland fertility have been carried out in Central European countries, where per capita arable land resources have been in shortage. Through high-density profile samplings, soil fertility evaluation for each farmland plot with an independent cadastral code was carried out. An officially certified fertility grades in percentile index and the records of soil profiles were established and archived for each plot. The investigation results have been widely used in farmland management, taxation, agricultural subsidies, farmland leasing, trading, lending, insurance and other sectors, and have become the indispensable and centennial basic information for farmland quality. China's per capita arable land is much less than that of Central European countries, but so far there has been still in shortage of soil fertility data for farmland management. For preservation of arable land resources with high fertility and ensure food safety, it is essential and also urgent to establish precise and reliable fertility archives for each farmland plot in China. Also more efficient investigation and evaluation approaches, which are compatible with China's economic and social condition should be developed. The review of testing soil chemical properties to make fertilizer recommendation shows that such testing has been incorporated into the technical supporting system for best farming management practices in the developed countries. To improve farmers' fertilization techniques, it is more important to establish an efficient technical supporting system and maintain its running, in comparison to nation-wide soil nutrient census of farmland. In the past, there was continuous weakening of applied researches and extension works for fertilization technological chain from basic research to farmers' application. Due to inadequate research works, the technical indexes for fertilization, that should be differentiated to and compatible with the various regional soil and climate conditions and hence easy to be followed by farmers of different regions, have not been issued yet in China. Also the intelligent tools that can reach and provide targeted guidance to farmers were not available. Unbalanced and excessive fertilization was common in vegetable, fruit and other cash crop growing area, which accounted for 23.6% of the total cropping area in China. This resulted in reduction of crop yield and quality as well as benefit of farmers and also leaded to agricultural non-point source pollution. Making up for the shortcomings in the technical supporting system has become the key to improve both crop yield and soil fertility. Since the end of the last century, soil investigations related with environment issues have been carried out in different countries. Main purposes of these investigations are to clarify the status of environmental pollution and changing, to develop control strategy and to check effects of countermeasures. With the quick progresses of GIS-, GPD-, RS- and big data techniques, the traditional mapping approaches have be replaced by digital soil mapping techniques. An exact defining of investigation objectives and a comprehensive reviewing of relevant research progress as well as available auxiliary data are essential for drafting sampling design and achieving investigation tasks finally.