| 其他摘要 | Heavy metals are one of major pollutants which are released to the environment during the process of production and life of human. The application of fertilizers and pesticides, sewage irrigation and sludge treatment and so on can increase the artificial input of the heavy metals to the agro-ecosystem. The migration of heavy metals in the soil is one of the most important contents of the research on material circulating in pedosphere. This article has studied the changes of soil heavy metal content in agriculture and orchard ecosystem as well as their forms and law of migration .On the one hand, it can enrich the theory of heavy metal migration and transformation in ecosystems, on the other hand, It is of great theoretical and practical application value in preventing soil pollution on Loess Plateau and realizing a sustainable development of regional economic and ecological. The main conclusions are as follows:1 Relationship between trace element fertilizer and crop yields, soil microelements and heavy metals1.1 Applying trace element fertilizer for many years, the average yield of wheat increased more than 6%, Effect of trace element fertilizer on yield have great differences depending on the annual precipitation. In a average year, the yield increase probability is bigger than 54%, Applying Cu fertilizer, the yield increased by 13.1%, Applying B、Zn、Mn fertilizer, it increased more than 6.3%; In a drought year, yield increase probability is 83.3% when the Cu and B fertilizer supplied, and the yield increased 11.8% and 10.8% separately; Applying Zn fertilizer, it increased 5.5%. In a wet year, Applying Mn fertilizer, the yield increased 10.5%, Applying Zn fertilizer, it increased 9.3%, the increase probability is 80%.1.2 Applying trace element fertilizer for a long time, the corresponding microelements can increase in topsoil, when applied copper fertilizer total-Cu increased by 75.2%, in which available Cu increased 5.75 times. When applied Zn fertilizer, the content of available Zn increased 3.58 times. When applied Mn fertilizer, Available Mn of soil increased 40.1mg/kg. Profile distribution of different microelements is different, Available Cu decreased in the 20-60cm soil layers, and slightly increased in the 60-100cm soil layers; Below 100 cm it reduced gradually. Available Zn in the 0-60cm has a significant difference and it decreased rapidly with the deepening of the soil. Available Mn accumulated in the 80-cm soil layers.1.3 Applying trace element fertilizer for a long time, the soil As content reduced in the soil. The soil Hg content varied depending on fertilization and soil layers. Applying Cu fertilizer, the soil Hg content in 0-5cm layer was 0.064mg/kg,which decreased by 19.0%; in 5-10cm layer it was 0.606mg/kg,which increased 1.9 times; in 10-20cm layer it was 0.369mg/kg, which increased 3.9 times; Mn fertilizer can increase soil Hg content in 0-5 cm layer, it decreased significantly in 5-10 cm and 10-20 cm soil layers; when B、Zn and K fertilizer supplied, the soil Hg content reduced. Applying Zn、Mn、Cu fertilizer, the Cd content of the soil increased 3.4%～12.1%, Applying B fertilizer, it decreased 11.8%. Applying B、Mn、Cu fertilizer, the soil Pb content decreased 8.6%～28.9%. The Cr content of the soil varies due to the trace fertilizer.2. Research on the soil heavy metals in agro-ecosystem2.1 When wheat applied one chemical fertilizer or several fertilizer combined, soil Hg content increased 6.1%~181.8% in 0-5 cm layer; When applying P fertilizer or fertilizer combined, soil Hg increased in 5-10 cm layer; the changes of soil Hg content in 10-20cm are the same as those in 5-10 cm. Soil As content in 0-5 cm layer increased by 5.9% when applying NP only. When applying single N or P fertilizer or combined manure, soil As increased in 5-10cm layer. When applying N、P、M、NP、NPM fertilizer, soil As content in 10-20cm layer increased. It decreased when applying NM、PM fertilizer. In the control which has no fertilizer supplied, soil Hg content reduced 36.5% and 26.0% obviously contrast to the fallow.2.2 when NPM and NP fertilizer applied in corn continuously, soil Hg contents in 0-5 cm increased 82.7% and 48.1% and it increased 18.6% and 74.4% in 5-10cm layer; Soil Hg content in 10-20cm layer decreased by 20% when applied NPM fertilizer in corn field, and it increased 48.0% when applying NP fertilizer in wheat-corn rotations. Soil As content increased in 0-5cm layer as NPM applied, and it decreased in 5-10cm and 10-20cm layers; Applied NP in the system of wheat-corn rotations, soil As content decreased 47.3%、40.5% and 43.3% obviously in 0-5cm、5-10cm and10-20cm layers separately.2.3 Cultivated with pea and alfalfa, soil As content increased significantly, when applied NPM in the system of alfalfa continuously, soil As increased 29.0%、31.3% and 26.5% obviously in 0-5cm、5-10cm and10-20cm layers separately, followed by wheat or corn systems. In different crop systems, As content increased 1.5%～41.7% in 0-5cm layer, and its Hg content increased 15.4%～82.7% . In 5-10cm layer soil Hg increased by 4.7%～107.0%; and in 10- 20cm layer, soil Hg content decreased 52.0% and 20.0% in alfalfa and corn systems separately, and it decreased 78.0% and 22.0% in wheat and pea systems separately. Soil Hg varied distinctly in different soil layers. Soil Cd content increased 26.4% and 8.6% separately in pea and alfalfa system. The soil Cr content were 70.93 mg / kg, 70.92mg/kg, 77.30mg/kg and 77.87 mg / kg when Alfalfa, peas, corn, wheat cultivated.3. Research on soil heavy metals in Orchard ecosystem3.1 Soil Cu content increased with the apple tree age, in 0-60cm layers soil Cu content increased more than 7%; Deep soil Cu content is a high than topsoil in 6 a orchard, but it is higher in topsoil when the was more than 6 years old. Re-Cu are about 80% of the total Cu, which accumulated more than 50 kg/hm2 in the soil and have a low validity. The amount of potential useful Cu cumulated 30-40 kg/hm2 in 0-60cm layer, and the Ex-Cu cumulated about 10 kg/hm2.Soil Zn content is different in Orchard with different ages. Topsoil Zn content is 114.89 mg/kg in a 26 year orchard, increased 2.43 times than that in a 6 year old orchard soil. Ox- Zn is more than 56% of it, Re-Zn is about 35%. The cumulative amount of Zn is 166.9 ~ 468.1 kg/hm2 in 0－40cm layer, most of which is useless or potential used; Available Zn accumulated 4.7～14.6kg/hm2.3.2 Soil Cr content increased linearly with ages. The Cr content in 36a orchard increased 17% compared to that in 6a. In topsoil the cumulative amount of Cr reached to 100 ~ 150kg/hm2. Ex- Cr and Ox-Cr are 22～25%. Ex-Cr reached to 1/4, increased 58.9% compared to that in 6a orchard. Potential used Cr increased 51.9% compared to that in 6a orchard. In 20-40cm layer, soil Cr content increased linearly in a rate of 0.797 mg / kg.a. In 40-60cm layer, the cumulative amount of Cr is 110～135kg/km2. Potential used Cr is 52 ~ 60%, when the orchard was more than 15 years, Potential used Cr increased more than 15%, in 36 years orchard it increased 41.9% compared to 6 years orchard. Planting apple trees for a long time can change the content and composition of Ex-Cr and potential used Cr.3.3 The Cd content of orchard soil:0-20cm > 20－40cm > 40－60cm, and it decreased after the first increase With the age increasing. Re-Cd is about 70% in 6a, 15a and 36a Orchard. In topsoil of 26a orchard, Re-Cd is 39.7%, Ox-Cd is 26.9%, Ex-Cd is 23.8%; in 20-40cm layer, Re-Cd is 51.7%, Ox-Cd is 25.8% ,and is Ex-Cd is 3.5%～16.8%; in 40－60cm layer, more than 65% Cd exist in the soil as the form of Re-Cd, Ox-Cd is 16～22%,and Ex-Cd is less than 7%; Soil Pb content in orchard eco-system changed with ages according to parabolarule. Soil Hg and As are also changing with the increasing ages, 15 yaer is the turning point of Hg and As content changes in the soil orchard eco-system, the changes of Hg and As in the orchard soil showed different trends before and after 15 years. |
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