ENVIRONMENTAL IMPACT OF PHOSPHATE FERTILIZERS AND BY-PRODUCTS ON AGRICULTURAL SOILS - Fertilizers: Components, Uses in Agriculture and Environmental Impacts - page 48

different subsequent dates: T1=5, T2=12, T3=16 months for PG application and T1=4, T2=11
and T3=15 months for PF application after the initial application and sampling from the
reference plot R at T0. Samples were collected from the cored cylindrical soil blocks at 5 cm
intervals to a depth of 20 cm, then at 15 cm intervals to a final depth of 55 cm. Plant roots and
leaves were also collected simultaneously with soil samplings from each parcel.
Figure 2. Experimental plot and parcels distribution.
Analytical Methods
Soil samples were cleaned from roots and stones, oven-dried at 50 ºC, sieved to pass a 2
mm sieve and ground to a fine powder using an agate pestle and mortar. Whereas, vegetation
samples were washed in ultra-pure water, dried at 60 ºC, and ground to a fine powder using
an agate pestle and mortar. The following methods were applied on soil and vegetation
samples. Soil pH was determined in a ratio 1:5 soil:ionized water suspension according to
AFNOR X 31-103. Total organic carbon (TOC) in soil samples was determined using
elemental analyzer of type (Flash EA1112 NC). Cation exchange capacity (CEC) of the soil is
measured by displacing the exchangeable cations with a solution of cobalthexamine chloride.
The displaced cations (Ca 2+ , Mg 2+ , K + , and Na + ) are determined by the flame atomic
absorption spectroscopy and the summation is the cation exchange capacity.
Trace elements were measured using an Iris advantage ERS Inductively Coupled Plasma-
Optical Emission Spectrometer ICP-OES ―ThermoFischer‖ and trace elements by ICP-MS
X7 ―ThermoFisher‖, after melting the samples and phosphogypsum with lithium metaborate,