Effects Of Long-term Fixed Experiment On The Chemical Characteristics Of Soil Zinc, Copper, Manganese, Iron In Dry Land

Based on an 18-year long-term fixed experiment conducted in dry land on LoessPlateau, we used sequential extraction technique to study the effects of different plantingsystems and different fertilization treatments on the availability and fractions distributionof Zn, Cu, Mn and Fe in soil. The soil chemical characteristics of Zn, Mn and Cu were alsostudied after 18 years application of Zn, Cu, and Mn fertilizers. Besides, the relationshipbetween availability of soil Zn, Cu, Mn, Fe and their fractions and some soil properties (pH,organic matter, available phosphorus and calcium carbonate contents) were discussed toinvestigate the effects of such factors on availability of soil Zn, Cu, Mn and Fe. What havebeen achieved in this study are as follows: 1. Long-term planting and fertilization reduced the values of pH and content ofcalcium carbonate, while increased soil organic matter and available phosphorus contents.The improvement of such properties accelerates transformation of soil Zn, Cu, Mn and Feto plant available forms. 2. Zinc, Cu and Fe are mainly existed in soil minerals and distributes little to otherfractions, but mineral bond and oxide bond Mn are the two major forms of Mn in soils, thepercentage of these two Mn fractions to total Mn ranges from 36.57% to 45.27% and from33.15% to 44.50%. 3. Long-term planting depleted soil available Zn and Cu and thus reduced the contentsof DTPA extractable Zn and Cu in soil. Copper fractions in surface soil were alsodecreased due to long-term planting, but Zn bond to oxide and organic matter wereincreased. We also found that long-term planting exerts no significant effects on Zn and Cufractions in subsoil. DTPA extractable, exchangeable bond and carbonate bond Mn were higher whileoxide bond and organic matter bond Mn were lower in mono alfalfa continuous plantingsystem than in fallow treatment. Long-term planting of wheat decreased soil carbonatebond, organic matter bond and mineral bond Mn, whereas rotation of crops and legume hasno influence on Mn fractions. After long-term planting of mono alfalfa and mono wheat, iron in surface soil movedfrom mineral bond to other forms and made the increment amount of such forms surpassedthe amount of plant absorbed, therefore, the contents of exchangeable, carbonate bond,oxide bond and organic matter bond Fe showed an increasing trend. But the organic matterbond Fe decreased in crops and legume rotation systems.4. Long-term application of manure fertilizer increased soil DTPA-Zn and Zn and Cufractions in soil. Besides, such increase varied with the difference of planting systems andsoil depth. DTPA-Mn was augmented in mono wheat and mono maize continuous plantingsystems and reduced in crop-legume rotation system after application of manure. Afterlong-term application of P fertilizer, soil carbonate bond Mn was higher in mono alfalfacontinuous planting and crop-legume rotation systems, but in the same systems, the oxidebond Mn and organic matter bond Mn were lower than that in CK treatment. Manurefertilizer exerts great function in reducing soil oxide bond Mn but increasing soil carbonatebond Mn and organic matter bond Mn in the three studied planting systems. Soil DTPA-Fe was increased in all the fertilization treatments. Although decreasedsoil carbonate bond, oxide bond and organic matter bond Fe in mono alfalfa continuousplanting and crop-legume rotation systems, P fertilizer increased soil exchangeable, oxidebond and organic matter bond Fe in mono wheat continuous planting system. Whileapplication of manure fertilizer presented a trend to reduce soil oxide bond Fe and increasesoil organic matter bond and mineral bond Fe content in three planting systems. 5. A significantly positive correlation exists between soil organic matter, available Pand DTPA extractable Zn, Mn and Fe contents, therefore, soil organic matter and availableP exert direct impact on the availability of Such elements in soils.