On Planning And Engineering Design Of Citrus Orchard In Three Gorges Reservoir Area

The Three Gorges Reservoir area is one of the most optimum areas to plant citrus. Up till now, it has become the dominate industry to develop economy and make rich for farmers. However, during developing, there are still some problems to be faced, such as wide area planting with sporadic distribution; thin soil with many rocks; high concentration of CaCO3 with high pH values; severe soil erosion. All the problems block the development of citrus, and the main reason is that most of the farmers plant citrus by their own idea or the arrangement of government for pursuit of economies other than technical guidance of agronomy and horticulture and rational planning. Therefore, in order to improve the technology of citrus planting, water and soil conservation, reasonable soil fertility improvement and irrigation and drainage engineering measures could be taken, which makes it meaning for effectively controlling and reducing soil erosion. As it stays in the experience stage for modern soil engineering, it is necessary to strengthen the design and study of standardization and programming. In our study, the two area were taken as examples, aiming at the growth and soil characteristics, rock types and topographic conditions, soil physicochemical and engineering properties, and the relation between topographic conditions and arrangement of citrus were studied, programs of engineering and land production were proposed, to pave the way for planning and designing the citrus in different geomorphic types and soil conditions in the Three Gorges Reservoir.(1) It was based on topographic and grade conditions for citrus design in dry land. Four standards were divided in our study:0°-6°,6°-15°,15°-20°and＞25°.According to the grade distribution, designed areas were chosen:grade areas＜6°were not for bench terrace, yet dry land grade ranging from 6°to 25°were suiting for. The principle of "equal altitude but not aequilate, and paper with curved" were taken in dealing with field arrangement:the width was greater than 3m, and the altitude difference was less than 2m between adjacent dry lands. The arrangement of drainage channel should be depended on natural brooks and the discharge area. Main drainage channels should be constructed in field linking with the lord drain and pool zones, in order to gather and eliminate redundant surface water,soil water and underground water. The design of filed roads should be set in the base of the hills, went through the hills and be connected with each other.The design of citrus in dry land were mainly for improving the soil and filed. In the present study, rocks, grades, thickness and nutrients of soil were analyzed. The results showed that the average slope thickness of base, middle and top were 61cm,46 cm and 20 cm, respectively. Based on ArcGIS software to build up the DEM and rock distribution, for areas lying in the middle and top of the slope with effect soil thickness less than 80 cm, bombing were chosen to improve the soil. As the soil in target area lacked of N,P,K elements, sufficient minimal nutritions should be put into after bombing. The width after rebuilding was often between 3 to 12m, with wider accompanying by lower gradient, which could suit for citrus planting and maximumly limit the earth volume.(2) In paddy field, the design for citrus was firstly concerned about the soil characteristics, which could influence the root drainage. Based on current field, the planting area direction were accordance with isoheight lines. Directing at drainage, waterway were placed accordance with planting area, and dorsolateral and box grooves were constructed to eliminate ponding. Besides the current traffic structure, in areas with gentle slopes, arterial roads usually went through the middle of the citrus, with circuit brances crossed per 200-400m.30 soil profile were digged to investigate the soil gradients. The soil were thick, much more than 80 cm. But except the plough layer about 20 cm were loose, others were all compaction, which made it easier to form sump and led to lack of oxygen and root rot. Therefore, in designing the development of soil, growth condition of root should be concerned, and soil should be compacted more. Otherwise, as lack of N,P,K nutrition, additional minimal fertilizer should be added.In this study, growth characteristics of the citrus, soil characteristics, rock types and soil conditions were analyzed in the Three Gorges Reservoir, and physicochemical properties, engineering, and the relation between topographic conditions and citrus design were stuided, which provided evidences for design of citrus. However, there still are some limitations in project theory and distribution differences, and the universal laws were not summarized in different hill district for citrus planting in Chongqing. Since there were some trouble deciding the optimum terrace engineering, depending on the complex area conditions in the Three Gorges Reservoir, much more work need to be done.