Phosphate sorption indices as affected by the calcareousness of soils

An experiment was carried out to study the effects of calcareousness on phosphate sorption indices of soils using three representative calcareous soils, namely Sara (Aquic Eutrochrept), Gopalpur (Aquic Eutrochrept), and Ishurdi (Aeric Haplaquept) series of Bangladesh. Three non-calcareous soils, namely Belabo (Typic dystrudepts), Sonatala (Aeric Endoaquepts) and Ghatail (Aeric Haplaquept) series were also selected for comparison purposes. Phosphate sorption indices of soils were calculated using Langmuir and Freundlich isotherms. Isotherms were constructed taking one gram of air-dried sieved (< 2 mm) soil into a 50 ml centrifuge tube, and subsequently adding seven initial P concentrations, namely 0, 1, 10, 25, 50, 100 and 150 μg/ml to each centrifuge tube employing a soil/solution ratio of 1 : 20 (w/v). According to the Langmuir equation, the amount of phosphate sorbed followed the order: Sonatala > Ghatail > Sara = Gopalpur > Ishurdi > Belabo. The abundance of amorphous iron rather than the calcareousness was putatively responsible for the high phosphate sorption capacity of soils. Maximum phosphorus buffering capacity (MPBC) of the calcareous soils ranged from 33.4 - 62.8 l/kg. Langmuir and Freundlich equations produced different values for soil P requirements (SPR) at 0.2 and 1.0 mg P/l. Calcareous soils would require 27 - 44 mg P/kg soil to attain 0.2 mg P/l soil solution, which is deemed sufficient for crop growth. The soils would require 32 - 58 mg P/kg soil to reach 1.0 mg P/l soil solution, which is regarded to be safe for soils in terms of susceptibility to P losses. The calculated Langmuir constant b values were higher than the threshold value of 0.07 l/mg for two of the calcareous soils. Therefore, even though the non-calcareous soils sorbed more phosphate, higher bonding energy of P sorption for calcareous soils makes them less vulnerable to loss via surface runoff. Dhaka Univ. J. Biol. Sci. 28(1): 93-110, 2019 (January)

Phosphorus sorption characteristics of some representative soils of south India

Studies were conducted to investigate P sorption characteristics of representative soils from ten locations of alfisol and ultisol of India using Langmuir and Freundlich equations. The P sorption maxima (b) of soils derived from Langmuir equation in alfisol varied from 520.6 to 574.7 ?g g-1 and ultisol varied from 561.6 to 678.1 ?g g-1. The maximum phosphorus buffering capacity (MPBC) in alfisol ranged from 80.7 to 180.2 ml ?g-1 and ultisol ranged from 162.1 to 284.4 ml ?g-1. Phosphorus sorption maxima was significantly correlated with clay (r2=0.70), Al (r2= 0.73) and Fe (r2=0.81) forms, MPBC (r2=0.67) and Freundlich constants (r2=0.82). The standard P requirement (SPR) to maintain 0.2 mg l-1 P in soil solution for alfisol ranged from 15.62 to 27.62 mg kg-1 and ultisol from 41.98 to 46.35 mg kg-1. The SPR (0.2 mg l-1) was significantly correlated with binding strength coefficient (r2= 0.97) and binding strength coefficient supporting the fact that energy coefficient of a soil is an important index for planning P management strategies. Among the two soil orders in order to maintain optimum P concentration in soil solution for crop growth, ultisol will be required to supply with more P fertilizer as compared to alfisol.SAARC J. Agri., 13(1): 14-26 (2015)

Evaluating of phosphorus quantity/intensity parameters in soil with different systems of organic fertilizing

One of the refinement methods for estimating the parameters of phosphorus dynamics in soil is the construction of sorption isotherms in dependence on changes of exchangeable sorbed phosphorus in soil (&Delta;Q) and changes of phosphorus amount in soil solution (&Delta;I). Regression analysis allows to calculate equilibrium concentration (<I>c</I>_equ) and phosphorus buffering capacity (BC). The mentioned analyses were realised on soils from the long-term field experiments of the Czech University of Life Sciences (CULS) in Prague and Crop Research Institute (CRI) in Ruzyně, Czech Republic. The influence of different organic fertilisers compared to the control (not amended) treatment was tested. For the evaluating of parameters, the root and logarithmic functions were used. The lowest <I>c</I>_equ of the logarithmic function was always found on not amended treatment. Low amounts were found in the treatments amended with barley straw as well. The highest amounts were found in soil after potatoes cropping fertilised with farmyard manure (FYM). In the FYM variant fertilised with 70 kg P/ha, the <I>c</I>_equ value reached 0.45 mg P/l. Both treatments fertilised with sewage sludge (720 kg P/ha and 240 kg P/ha) showed similar values of about 0.25 mg P/l. A different trend was found for the phosphorus buffering capacity (BC); this was the highest at the control treatment and at the treatment fertilised with straw. The lowest BC was observed in both soils after potatoes fertilised with FYM, where it reached 61 mg P/kg and 65 mg P/kg, respectively. Similar trends were found when evaluating root function.