*2.1. Experimental Design*

Between 2016–2018, experiment was conducted each year at the Gorzy ´n Experimental and Educational Station, Pozna ´n University of Life Sciences (N—52.56692, E—015.90933, 69 m AMSL) to assess plant reactions and soil microbiological changes after the application of selected biostimulators and foliar fertilizers during the cultivation of pea ('Tarchalska' variety). The experiment was a randomised block design with four replications and 36 plots (plot size 14 m × 1.5 m (21 m2)).

The research factor was the use of biostimulators or foliar fertilizers with 9 levels:


Each biostimulator and fertilizer was applied in a timely manner, according to the manufacturer's recommendations (Table 1).


BBCH—A uniform decimal code for growth stages of crops and weeds, IDHA—chelating agent.

A chlorophyll fluorescence meter (OS5p, Opti-Sciences, Inc., Hudson, NY, USA) with a photosynthetic active radiation (PAR) clip was used to measure the following parameters: F0—minimum fluorescence, Fm—maximum fluorescence, Fv—variable fluorescence and Y—quantum yield of photosynthetic energy, which are necessary to calculate the maximum photochemical efficiency of photosystem II (Fv/Fm), according to the formula (Fv/Fm = Fm − F0/Fm). Settings for the fluorometer protocols were selected according to Sulewska et al. [16] as follows: modulation source: red; modulation intensity: 25; detector gain: 08; saturation flash intensity: 30; flash count: 001; flash rate: 255 (s). A chlorophyll meter CCM-200 was used to determine the Chlorophyll Content Index (CCI). Leaf Area Index (LAI) was determined with a SunScan Canopy Analysis System type SSI (Delta-T Devices, Cambridge, UK). The agrotechnical and cultivation treatments were carried out in accordance with the principles of good agricultural and experimental practice for this species [17]. Agrotechnical treatments and the dates of their implementation in the individual years of the study are presented in Table 2.


**Table 2.** Type and date of agrotechnical treatments carried out in the study.

CS—capsule suspension, SL—soluble concentrate, EC—emulsifiable concentrate, SC—concentrate in the form of a concentrated suspension.

We used the white-flowered pea variety 'Tarchalska' from Danko (Poland). According to the FAO/WRB classification, the soil at the study site was classified as a typical luvisol soil formed from light loamy sands, deposited in a shallow layer on light loam (*Haplic Luvisols*) [18]. Potassium, manganese, copper and iron contents were average; phosphorus, magnesium, boron and zinc contents were high; and molybdenum content was very low (Table 3). Soil pH was 6.5, which indicates that the soil was slightly acidic, and humus content was also low.
