نوع مقاله : مقاله پژوهشی
نویسندگان
1 گروه علوم و مهندسی خاک، دانشکده کشاورزی، دانشگاه تهران، کرج، ایران، رایانامه
2 گروه علوم و مهندسی خاک، دانشکده کشاورزی، دانشگاه تهران، کرج، ایران
3 دانش آموخته دکتری گروه علوم و مهندسی خاک، دانشکده مهندسی و فناوری کشاورزی دانشگاه تهران
4 موسسه تحقیقات خاک و آب، سازمان تحقیقات، آموزش و ترویج کشاورزی، کرج، ایران، کرج، ایران
چکیده
کلیدواژهها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
One of the limiting factors in crop yield in calcareous soils of arid and semi-arid regions is the deficiency of micronutrients in these soils. This study was conducted to examine the effects of various commercial humic acids (HAs) and fulvic acids (FAs) on the release of manganese (Mn) in 15 calcareous soils. The results indicated that the application of all five different HAs used in this study had no significant effect (P<0.05) on the release of Mn, but the effects of FAs varied in different soils, the majority of them resulted in a significant increase (P<0.05) in Mn release. In 20% of the soils, either three or all five FAs, and in 26.7 % of the soils, either two or four of the FAs resulted in a significant increase in Mn release. In one soil, none of the FAs were effective in increasing Mn release. Two FA samples, FA1 and FA5, were much more efficient in releasing Mn, indicating that the effectiveness or ability of the marketed or commercial FAs to release Mn, on an equal weight basis, is not the same and varies greatly among them. The difference was, to some extent, due to the ability of these humic substances to form strong (multidentate) complexes with Mn or act as a chelating agent. The results also indicated that effectiveness was dependent on soil characteristics, which were related to the binding strength of Mn with surface functional groups of soils and the solubility of Mn minerals in the soil.
کلیدواژهها [English]
Effect of Different Kinds of Humic and Fulvic Acids on the Release of Manganese from Calcareous Soils
EXTENDED ABSTRACT
One of the limiting factors in crop yield in calcareous soils of arid and semi-arid regions is the deficiency of micronutrients, including manganese (Mn), in most of these soils. In arid and semi-arid regions, the micronutrient deficiency is intensified due to the deficiency of soil organic matter, and high and pH levels. Soil organic matter can play a key role in controlling the mobility of metals. Humic substances are part of soil organic matter. Today, many organic humic products are available worldwide for agricultural use. The reason for the widespread use of humic substances in commercial fertilizers is their ability to increase the availability of nutrients, especially micronutrients and phosphorus.
This study was conducted to examine the effects of ten commercially available, purified humic and fulvic acids with different structures on Mn release in 15 calcareous soils with various physico-chemical properties.
In this study, five humic acids and five fulvic acids with different structures were selected. Then FTIR infrared spectroscopy and CHNOS elemental analysis of the humic and fulvic acids were performed. A total of 15 soil samples were selected, which differed not only in their physical and chemical properties, but also in their available Mn content. To treat the soils with humic substances, one mL of 1% humic acid or fulvic acid solution was added to each soil sample and then the moisture content of all soil samples was adjusted to 40% of the saturation percentage by adding distilled water. Untreated soils were also included in the experiment as controls. The samples were then incubated at a constant temperature of 20 ºC for two weeks. At the end of the incubation period, the Mn content of the soil samples was extracted using 1 M sodium acetate solution buffered at pH=8.2. Manganese concentration in soil extracts was determined by flame atomic absorption spectrometry (Perkin Elmer 1100).
The results indicated that the application of all five different HAs used in this study had no significant effect (P<0.05) on the release of Mn, but the effects of FAs varied in different soils, the majority of them resulted in a significant increase (P<0.05) in Mn release. In 20% of the soils, either three or all five FAs, and in 26.7 % of the soils, either two or four of the FAs resulted in a significant increase in Mn release. In one soil, none of the FAs were effective in increasing Mn release. Two FA samples, FA1 and FA5, were much more efficient in releasing Mn, indicating that the effectiveness or ability of the marketed or commercial FAs to release Mn, on an equal weight basis, is not the same and varies greatly among them. The difference was, to some extent, due to the ability of these humic substances to form strong (multidentate) complexes with Mn or act as a chelating agent. The results also indicated that effectiveness was dependent on soil characteristics, which were related to the binding strength of Mn with surface functional groups of soils and the solubility of Mn minerals in the soil.
The study results demonstrated that the effectiveness of humic substances on the release of Mn in calcareous soils depends on factors such as the type of humic substances (humic acid or fulvic acid), the source (different structural and chemical properties) and the type of soil.