| Because of increasingly serious landform fragmentation, soil degradation, water loss and soil erosion and other conditions in the Loess Plateau, our country has carried out a large-scale comprehensive management in the Loess Plateau, and the role of plantation solving the existing environmental issues is highlighted in the process. The loess plateau terrain fragmented, soil degradation, soil erosion in the increasingly serious, for this country on the loess plateau area in aggressively comprehensive management, in the process of solving environmental problems existing plantation role highlight The loess plateau terrain fragmented, soil degradation, soil erosion in the increasingly serious, for this country on the loess plateau area in aggressively comprehensive management, in the process of solving environmental problems existing plantation role highlight The loess plateau terrain fragmented, soil degradation, soil erosion in the increasingly serious, for this country on the loess plateau area in aggressively comprehensive management, in the process of solving environmental problems existing plantation role highlight Loess plateau area Loess plateau area. Robinia pseudoacacia occupies an extremely important position in the plantation planted in the Loess Plateau. Populus tomentosa plantation in the Loess Plateau is not as widespread as Robinia pseudoacacia, but by vitue of its advantages its fast growth, short maturation and high yield, Populus tomentosa has gained more and more favor of plantation in the Loess Plateau. China is the largest plantation country in the world, but the long-term extensive operation of plantation has made the soil productivity of plantation decline, and the plantation is in the face of obvious health problems. With the Robinia pseudoacacia and Populus tomentosa plantation as the research object, this study made use of isometric collection of soil samples to collecte soil samples, depth of each soil samples dug 10cm, 60cm depth samples, a total of 324 samples for soil analysis and to measure the contnet of soil organic carbon, total nitrogen, total phosphorus, total potassium, available nitrogen, available phosphorus, and available potassium respectively, to calculate the detemination indicator in different levels and different locations, to explore the spatial distribution rule of soil nutrients in plantation, to compare and evaluate the effect of different plantations on soil nutrients, in the hope of providing a theoretical basis for carrying out a scientific and effective luxuriant plantation management, preventing the soil capability dcline of plantation and restoring its specific eclogical system fucntion.Study came to the following conlusions:1. Distribution characteristics of distribution ruke of soil nutrient content in the horizontal direction were different becauce of different species, different distances from the bupretis of the Robinia pseudoacacia exerted an obvious effect on potassium content(P <0.05), but that of the the Populus tomentosa exerted an significant effect on organic carbon and total nitrogen content(P <0.05). But organic carbon and total nitrogen content of the two forest types all showed maximum soil content at 70cm from the buprestis, and minimum total phosphorus content at 30cm, but a larger overall effect on available nitrogen; the Robinia pseudoacacia forest consumed much more available phosphorus at 30cm from the buprestis, with the largest content of available potassium, but the Populus tomentosa forest was just the opposite. So, the impact on organic carbon and total nitrogen content of Robinia pseudoacacia forest and Populus tomentosa had the greatest effect at 70cm, and for other nutrients content, the closer to the forest growingpoint, the more intense the impact, and the impact strengh on soil nutrient content was always small at 110cm long distance from the growingpoint.2. At every distance from the buoprestis, soil organic carbon, total nitrogen, total phosphorus, available nitrogen, and available potassium content of the Robinia pseudoacacia forest were greater than that of Populus tomentosa forest, and the impact of Robinia pseudoacacia forest and Populus tomentosa forest on above-mentationed soil nutrient conent had the maximum difference at 30cm, with the most obvious difference on the surface, there was a greater impact difference on total K and available phosphorus content between the two forest types at 70cm, which was inconsisitent or opposite to the mode of action in the horizontal distance, and had a stronger capacity to recombine the distribution of nutrient content .3. The study on Robinia pseudoacacia and Populus tomentosa yongplantation showed that compared the wasteland with that of no afforestation, there was no significant difference between wasteland and Robinia pseudoacacia forests in soil organic carbon and total K content (P> 0.05), but there was significant difference in soil total nitrogen, available nitrogen, available phosphorus and available k content (P <0.05). There was no significant difference between wasteland and Populus tomentosa forests in soil organic carbon, total nitrogen, total phosphorus, total potassium and available nitrogen (P>0.05), but there was significant difference in available phosphorus and potassium content (P <0.05). Compared the wasteland with that of no afforestation , the soil organic carbon and available phosphorus of two types of forest all reduced than that of no afforestation, and soil total nitrogen, phosphorus and potassium content were all increased, soil available nitrogen and available potassium of the Robinia pseudoacacia forest were increased, but those of Populus tomentosa forest were reduced. Content distribution of various soil nutrient in vertical section had distinct levels, and the regression of soil depth and soil nutrients were all fitted the cubic curves, except the total potassium and available phosphorus content, which were the lowest at the surface (0～10cm), and increased gradually downwards, other elements all shown that the content was decreased gradually downwards from the surface. Soil nutrient content of the study area was in the "extremely low" level. According to the degradation index of soil quality, the Robinia pseudoacacia forest showed a trend to improve soil quality, but Populus tomentosa forest showed a slight degradation trend.4. Forest growingpoint at different horizontal distances had a minor impact on the soil bulk specific weight , but a greater impact on the water content, with such a rule—the more closed to the buprestis, the more greater the water content.The comparison of soil bulk specific weight and water content between Robinia pseudoacacia froest and Populus tomentosa froest which had the same distence from the buprestis showed that the differences of soil bulk specific weight and water content were significant at every horizontal distance(P<0.05), the average soil specific weight of the Robinia pseudoacacia forest was greater than that of Populus tomentosa forest, with the maximum difference at 30cm, and the average soil water content of the Robinia pseudoacacia forest was less than that of Populus tomentosa forest ,with the maximum difference at 70cm. The construction of two species of plantations all reduced the soil bulk specific weight, and the Robinia pseudoacacia had an obvious effect than that of Populus tomentosa; contrast to the wasteland, the water content of Robinia pseudoacacia lowered , and water content of Populus tomentosa increased, subsurface of Robinia pseudoacacia consumed much more soil moisture, and 0-30cm of Populus tomentosa forest had a well water retaining capacity. |
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