*2.6. Analytical Determinations*

Selenium, iron, manganese and aluminum concentrations were determined by using an atomic absorption spectrophotometry, Varian—spectraAA-300system. For the determination of Se at low concentrations, a Varian model VGA77 hydride generator was used. Available phosphorus concentrations were determined by a Shimadzu UV-1700 spectrophotometer. Every 10 samples a control sample was analyzed, and at the end of the measurements procedure 30% of the samples were reanalyzed to test reproducibility.

## *2.7. Statistics*

Correlation and *t*-test analysis (*p* < 0.05) were performed using STATISTICA 10 software (StatSoft Inc., Tulsa, 74104 OK, USA).

#### **3. Results**

### *3.1. Soil Properties*

The physicochemical properties of the studied soils and the total Se concentrations are summarized in Table 1. Most of the soils are characterized as medium to fine textured with low organic carbon content, as expected for Mediterranean agricultural soils, and with very low total Se concentrations, less than 0.28 mg kg<sup>−</sup>1, pointing to Se deficiency [33]. Ammonium oxalate and dithionite extractable Fe, Al and Mn are expressed as % oxides content (g 100 g−<sup>1</sup> soil) and presented as Feo, Alo, Mno and Fed, Ald and Mnd, respectively. Metal oxide concentrations greatly varied, ranging between 0.08 and 0.40% and 0.72 and 6.32% for Feo and Fed, between 0.55 and 1.03% and 0.06 and 0.26% for Alo and Ald and between 0.01 and 0.10% and 0.02 and 0.15% for Mno and Mnd. The pH range of both alkaline and acid soils was very narrow—7.4 to 7.8 for alkaline soils and 5.5 to 6.0 for acid soils. Electrical conductivity values in the alkaline soils were significantly higher than in the acid soils (*p* < 0.001, *n* = 4), but were not restrictive for the growth of crops. Most soils were marginally to moderately supplied with available phosphorus.


**Table 1.** Soil physicochemical characteristics.
