02428nam a2200217 a 450000100080000000500110000800800410001910000130006024500730007326001660014652017410031265000120205365000090206565300210207470000220209570000190211770000200213670000180215670000190217470000170219320695712021-11-11       2017    bl uuuu     u00u1 u    #d1 aVOLF, M.  aSilt as K source for crops in tropical soils.h[electronic resource]  aIn: FRONTIERS OF POTASSIUM SCIENCE CONFERENCE, 2017, Rome. Proceedings... Peachtree Corners: International Plant Nutrition Institute, 2017. Ref. P185-P193.c2017  aThe original soil exchangeable potassium (K) concentrations are at or above critical levels in many Brazilian Cerrado (savanna) soils. Hence, many cropped areas have been fertilized with low K rates, below crop requirements, but yields have not decreased as expected. In these areas, topsoil exchangeable K analyses have shown no decrease, or even some increase. The aim of this study was to evaluate exchangeable and non-exchangeable K forms in soils under different uses and managements in the Vale do Araguaia region of Mato Grosso state, Brazil. Soil samples were taken from 91 sites at depths of 0-20 cm and 20-40 cm, in areas under grain crops, pasture and native vegetation (Cerrado or forest). Silt content ranged from 12 to 175 g kg-1 and clay from 90 to 595 g kg-1, and the predominant clays were kaolinite, hematite, goethite and gibbsite. Under pasture, the soils had high levels of exchangeable K in the 0-20 cm layer and high levels of non-exchangeable K from 20 to 40 cm. This can be a result of the absorption of non-exchangeable K by grasses, the main cultivated species, by recycling K to the exchangeable fraction in the topsoil. There was a positive relationship between silt and non-exchangeable K contents. Ratios of exchangeable to non-exchangeable K were over 3 in soils with silt above 70 g kg-1, in which non-exchangeable K was over 100 mg dm-3. Cover crops growing in soils rich in silt take up non-exchangeable K and exchangeable K from deeper layers, which is recycled to the soil as exchangeable K upon plant residue mineralization, which may have been responsible for the maintenance or increase in exchangeable K levels in the 0-20 cm layer in areas where low K rates have been used for grain production.  aCerrado  aSolo  aVale do Araguaia1 aBENITES, V. de M.1 aROSOLEM, A. C.1 aCRUSCIOL, A. C.1 aMORAES, F. M.1 aMENEZES, F. J.1 aSILVA, C. A.