Adsorção, cinética e disponibilidade de fósforo em latossolo amarelo e gleissolo háplico na Amazônia Central

Abstract

Understanding the behavior of phosphorus (P) in Amazonian soils has been the focus of many researchers in soil science in the region. Gathering complex factors involved in P sorption in these soils is essential to support future recommendations for phosphate fertilizers for different soils in Central Amazon. The objective of this thesis is to contribute with the knowledge of adsorption, availability and kinetics of adsorption of P in soils of the Amazon. Two soil profiles were selected: a hydromorphic soil (Haplic Gleysol Ta - GXv) and a non-hydromorphic soil (Dystrophic Yellow Oxisol - LAd) in the central region of the Amazon, in the state of Amazonas, Brazil. Soil samples were collected at five depths: 0-5 cm, 5-10 cm, 10-20 cm, 20-40 cm and 40-60 cm. Physical, chemical, mineralogical and morphological attributes of the soils were determined according to methodological procedures described by Embrapa (2017), as well as the adsorption and availability of P were evaluated through the following variables: P remaining, P available, maximum capacity adsorption of P, binding energy of P and the capacity factor of P. Langmuir adsorption isotherms were constructed and correlations were structured between the variables analyzed and the physical, chemical and mineralogical attributes of the soils. To determine isotherms and phosphorus adsorption kinetics, the different samples were stirred in 10 mmol L-1 CaCl2 solution containing 60 mg L-1 of P (KH2PO4) for the following stirring periods 0.25; 0.50; 1; 2; 4; 6; 12; 18; 24; 48; 72; 96; 120; 144; 168 and 192 hours. At the end of each stirring period, the concentration of P in the equilibrium solution was determined and general and linear equations of adsorption kinetics were used, as well as the adsorption time of specific percentages of P and the specific sorption speed of each phase. linear (I, II and III). The results show that silt contents are higher in GXv, while clay contents are higher in LAd. In both soils, the levels of organic matter decrease in depth. Attributes such as pH in H2O and KCl, zero charge point and ΔpH were similar between soils. Exchangeable Al3+, potential acidity, effective and potential CTC are higher in non-hydromorphic soil. In both soils, the bases reduce in subsurface (> 20 cm). The levels of goethite (Gt) and hematite (Hm) are high in depth in non-hydromorphic soil and decrease in hydromorphic soil. There were no differences between P-Disp between soils. The remaining phosphorus was similar among the soils on the surface, but higher in the GXv subsurface. The isotherm in the LAd showed greater affinity between the adsorbent (soil) and the adsorbed (P) and differed only in depth 40-60 cm from GXv. In LAd, the decrease in organic matter and the increase in oxides in depth may explain the adsorption of P. In GXv, the decrease in organic matter and the decrease in oxides, due to gleization, indicate the sorption behavior of P. To describe the adsorption kinetics, the Kue and Lotse (1974) equation proved to be effective in the adsorption process in Amazonian soils. The adsorption kinetics in LAd is similar between depths and less intense in depth 40-60 cm in GXv. About 80% of the P is adsorbed in 2.5 and 2.1 days, respectively on the surface (<20 cm) and on the subsurface (> 20 cm) of the LAd. In 3.2 and 3.5 days, P adsorption occurs, respectively on the surface (<20 cm) and subsurface (> 20 cm) of GXv. Three P adsorption phases were identified in the depths of Amazonian soils. Phase I (fast) occurs between 0-18 hours, phase II (intermediate) between 18-96 hours and phase III (slow) between 96-192 hours onwards. The adsorption phase I is respectively 35.2 and 238.6 times faster than phases II and III in the LAd. The adsorption phase I is respectively 25.5 and 198.8 times faster than phases II and III in GXv. The decrease in organic matter and the decrease in oxide hydroxides in depth seem to explain the relationship of P with the soil, respectively in the Yellow Latosol and Haplic Gleysol. Isotherms, adsorption capacity and sorption energy are influenced by organic matter and Fe reduction processes. The P adsorption time varies between the two soils and the five depths, indicating that different P managements can reduce the losses of this nutrient in the soil.