Abstract:The problems of practice and theory in the work of soil and water conservation were profoundly analysed on thebasis of the author's scientific research practice, actual investigative information and experience more than half a cen-tury. Then,opinions about some important problems in the present work of soil and water conservation were ad-vanced. It includes four parts. 1) a non-unified strategic arrangement and a unclear surmount objective for the con-trol work of soil erosion; 2) unagreement between the guiding thought of scientific researches and the practice condi-tions; 3) the thought and ways for concluding experience to be improved scientifically; 4) some suggestions about landmanagement in the Loess Plateau and the middle and upper reaches of the Yangtze.

Abstract:The present situation and harms of soil and water loss in China were discussed in this paper. Meanwhile, the natural and man-made factors to cause soil and water loss were analysed., In addition, the achievements and benefitsachieved after the build-up of new China in the work of soil and water conservation were evaluated. At last, the author put forward some suggestions about how to take laws for control soil and water loss and how to make a goodwork in soil and water conservation.

Abstract:The conditions of small watershed control and agriculture in American were investigated by the authors in Oct,1991. Based on the investigation, the characteristics of small watershed control and agriculal production betweenAmerican-China were compared and analysed. It was concluded that the plans, aims, ways and medels for regionexploitation are all different obviovsly because of their different situations. For these, we Chinese should studyourself's experience and Walk ourself's directions of scientific research and control.

Abstract:The semi-arid zone of the middle reaches of the Yellow River formed in some geological times,then,its naturaland environmental features appeared in the same time as follows: 1) the concentrated and fluctuated rainfall; 2)the sur-face material with loose structure; and 3.) the simple vegetation type and lower vegetative coverness. The characteristicsof erosion and Sediment-producing which were caused by the reoded environment are shown as; 1) the types of ero-sion and sediment are plentiful; 2)sediment layers are diverse; 3) the production of ediment is also characterized bythe natures of concentration and fluctuation. Finally,the authors put forward that it is difficult to change the fedturesof the semi-arid ecolongical environment,But,by means of the regulations of man-land relationship and landuse struc-ture and industrial structure,the people may control the deterioration of the eroded environment.

Abstract:The water-reserving benefits of man-made forest and natural secondary forest in the upper reaches of Miyunreservoir were systematically studied through determining the physical properties and infiltration of the soil, moistureholding capacity of forest litter and through observing the surface runoff produced by simulated rainfall. The resultsshow that each species of these trees has distinct benefits of water-reserving. The water-reserving benefits of naturalsecondary forest are higher than that of man-made forest. Using curve-fitting techniques,the relationship between thevelocity and time of soil infiltration and between the time and amount of that were given respectively. The runoff coef-ficient model of forest soil under simulated rainfall was developed with step by step regression.

Abstract:The influences of piled soil under artificial and mechanical silt-eliminating on soil erosion factorssuch as infiltrative ratio of soil, runoff,anti-erosibility and anti-scourability were mainly studied. Itwas pointed that the piled soil under artificial silt - eliminating has a higher soil inflitration, littlerunoff, greater ability of anti-erosibility and anti- scourability and little erosion intensity,But, thesecharactreistics of the piled soil under mechanical silt-eliminating are completely contrary to that onesunder artificial silt-eliminatipg.At last, the advantages and disadvantages and land use of the two dif-ferent ways were discussed.

Abstract:Using the two-dimensional order clustering algorithm which had been revised by the author,and combining principal components analysis and resources indices analysis of agriculture in different counties and cities,Yanan prefecture is divided into four agricultural regions. The situation in northeastern region is the worst,and its developing strategies are to control soil erosion and to create satisfactory cycles for ecological system. The situation in northwestern region is also worse, and the developing strategies are to control soil erosion，to exploit underground water and to use the cultivars of crop and grass that perform well in cold climates. The situation in southwestern region is moderate,the potential for developing the southeastern region is the largest,its developing strategies are to increase stock raising,to exploit natural resources on the mountains,to enlarge the scale of crop production and to construct the base for agriculture, forestry and stock raising. These results provide a scientific basis for the developing planning of agriculture in this area. At the same time,the computer software of two-dimensional order clustering algorithm was given in order to provide a effect tool for the application and studies.

Abstract:The development strategies and application methods of soil and water conservation program inNingan county of Heilongjiang province were made based on the system dynamic model. The modelconsists of such as six sub-systems as that of crop planting, forestry, animal husbandry, fishing, popu-lation and soil and water conservation, which include 279 active equations and 229 parameters. Themulti-objective evaluation on the simulating results of three development strategise were carried outapplying eco-economical methods,in order to provide scientifical basis for the development strategiesof ecological agriculture and the planning of soil and water conservation in the county.

Abstract:The geographical condition of Guyuan prefecture of Ningxia was briefed in this paper.Its hydrological properties were analysed in order to provide a lot of basic data for the works of scientific research and control of soil and water conservation in soil and water loss area of South Ningxia.

Abstract:The occurrence and development of soil and water loss in Lianhe river watershed were analysedbased on a lot of hydrological and environmental monitoring data in this paper. It was concluded that:1 )water Contamination in Lianhe river watershed is mainly caused by face cource contamination; 2)the soil and water loss in Lianhe river presents the developal trend. All these results are mainly causedby human beings. In accordance with those results and combining the actual conditions of Chendemountain areas, the control measures for soil and water loss were discussed.