توصيفگر ها :
رهاسازي پتاسيم , كاني هاي رسي , فلوگوپيت , پاليگورسكيت , اسمكتيت , كائولينيت , ريزوسفر
چكيده انگليسي :
Soils of arid and semiarid regions contain considerable amount of micaceous minerals which, as 2:1 potassium (K) bearing minerals, play an important role in plant nutrition. Other silicate minerals, known as 2:1 minerals such as palygorskite and smectite, also exist in these soils with various quantities which have a great potential to absorb and fix K. The presence of a high quantity of 2:1 clay minerals in rhizosphere can influence the release of K from micaceous minerals, something that has not been well investigated yet. The objectives of this study were (i) to investigate the impact of 2:1 clay minerals including palygorskite and smectite, as compared to that of kaolinite as a 1:1 clay mineral, on K release from phlogopite in the root zone, (ii) to understand the effect of the quantity of associated clays (palygorskite, smectite, and kaolinite) on K release and its uptake by the plant, and (iii) to examine the role of the plant type on the rate of K release from phlogopite in the presence of other clay minerals. This research was carried out under greenhouse conditions, with barley and alfalfa as the test plants, using a completely randomized design with factorial arrangement and four replications. Factors included the type of associated clay mineral (palygorskite, smectite, and kaolinite), and their quantity (control, 1, 1.5, and 2 %). Palygorskite dominated sediment and smectite dominated soil were taken from Ramsheh and Kuhrang, respectively, while Georgia kaolinite was obtained from Clay Minerals Society (CMS) repository, USA. Carbonate free clay fraction of these samples was separated, checked by X-ray diffraction, and used in the experiment. Clay samples were mixed with phlogopite and quartz sand and used as the growing medium in 700 g pots for either barley or alfalfa. Plants were supplied with either K-free Stigner nutrient solution or distilled water during the 4-month growing period. At the end of the experiment, available K in the root zone, K concentration of both shoot and root, plant biomass and K uptake in both shoot and root were determined. Based on the results obtained, the addition of smectite dominated clay to the growth medium of both barley and alfalfa caused a significant increase in available K, likely indicating that smectite, as a 2:1 clay mineral, played a pivotal role in K release from phlogopite as a micaceous mineral. The concentration of K in the barley shoot decreased as the quantity of added clay increased. This could be attributed to the competition of clay particles with the roots to access the K in the interlayers of phlogopite. However, the concentration of K in the alfalfa shoot was not negatively affected by the presence of clays. The addition of smectite to the growth medium of both barley and alfalfa could increase the root K concentration as compared to the control. This treatment did not influence the root and shoot dry biomass in barley, but increased alfalfa root and shoot dry biomass. In addition, the K uptake decreased in the barley shoot and increased in its root, whereas the K uptake increased in both shoot and root of barley. The application of palygorskite dominated clay to the growth medium of barley and alfalfa resulted in an increase in available K as compared to the control. This probably indicates that palygoskite as a 2:1 clay also plays an effective role, similar to smectite, on K release from phlogopite. As the amount of palygorskite in the growth medium of barley increased, the level of K concentration in shoot also increased, but the root K concentration was not significantly affected. Root and shoot dry biomass as well as their K uptake in barley also increased as compared to those in control. Using palygoskite dominated clay in the growth medium of alfalfa could increase the root and shoot K concentration, dry biomass, as well as the K uptake in both root and shoot as compared to the control.
