POTASSIUM RESERVES IN THE CLAY FRACTION OF A TROPICAL SOIL FERTILIZED FOR THREE DECADES

Author(s)

Firmano, Ruan F. ^[1] ; Melo, Vander Freitas ^[2] ; Montes, Celia Regina ^[3] ; de Oliveira Junior, Adilson ^[4] ; de Castro, Cesar ^[4] ; Ferracciu Alleoni, Lus Reynaldo ^[1]

Affiliation

^[1] Univ Sao Paulo, Luiz de Queiroz Coll Agr ESALQ, Dept Soil Sci, Ave Padua Dias 11, BR-13418260 Piracicaba, SP - Brazil

^[2] Univ Fed Parana, Dept Soils & Agr Engn, UFPR, Rua Funcionarios 1540, BR-80035050 Curitiba, Parana - Brazil

^[3] Univ Sao Paulo, Ctr Nucl Energy Agr CENA, Av Centenario 303, BR-13418900 Piracicaba, SP - Brazil

^[4] Brazilian Agr Res Corp, Natl Soybean Ctr, Rodovia Carlos Joao Strass Orlando Amaral Access, BR-86001970 Londrina, Parana - Brazil

• Document type: Journal article
• Source: CLAYS AND CLAY MINERALS; v. 68, n. 3 JUL 2020.
• Web of Science Citations: 1

Abstract

Highly weathered soils of the humid tropics generally provide a poor mineral reserve of potassium (K), but evidence has been found which indicates that even in such soils non-exchangeable forms of K can be made plant available and this warrants further investigation. The objective of this study was, therefore, to determine the extent to which K can be released from poorly available reserves over a long period of time. The focus was on an Oxisol in southern Brazil cultivated for 32 years with a rotation of soybeans (Glycine maxL.), maize (Zea maysL.), wheat (Triticum aestivumL.), and oats (Avena strigosaL.) with and without K fertilization. Mineral sources of K were identified by X-ray diffraction and by sequential chemical extraction from the clay fraction. The amounts of K-bearing mineral species and the amounts of total and plant-available K were quantified, then the effects of the long-term K-fertilization regime on these values were evaluated. The clay fraction was dominated by hematite, gibbsite, and phyllosilicates such as kaolinite. These minerals were unaffected by the K deprivation in the cropping systems, but in the clay fraction the absence of K fertilization for 32 years reduced the structural order of the 2:1 phyllosilicates associated with K reserves. This effect was most prominent in the root zone of the soil. Deprivation of K for more than three decades decreased the crystallinity of 2:1 phyllosilicates, which could be better evaluated from XRD patterns after the removal of kaolinite and Fe (oxyhydr)oxides. The K-free cultivation reduced the amounts of total soil K by increasing the depletion of K from pools that typically are poorly accessible to plants. (AU)

• FAPESP's process: 15/18952-3 - Residual effect of potassium fertilization on the forms of the nutrient in the soil
• Grantee: Ruan Francisco Firmano
• Support Opportunities: Scholarships in Brazil - Master
• FAPESP's process: 15/19121-8 - Multi-User Equipment approved in grant 2015/05942-0: micro X-Ray Fluorescence system
• Grantee: Hudson Wallace Pereira de Carvalho
• Support Opportunities: Multi-user Equipment Program